Stainless Steels & Nickel Alloys

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CASTI Handbook

Nickel AlloysStainless Steels &

1st Edition on CD-ROM

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CASTI HANDBOOK OF

STAINLESS STEELS & NICKEL ALLOYS

Stephen LambTechnical Editor

E xecut ive Edit or

J ohn E . B ringas , P .Eng.

CCASTI

C A S T I Publishing Inc.

10566 114 St reet

E dmonton, Alberta , T5H 3J 7, Ca na daTel: (780) 424-2552 F a x: (780) 421-1308

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ISBN 1-894038-34-7

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iii

CAST I H and book of St ain less St eels & N ickel Al loys

C A S T I PUBLICATIONS

C A ST I H A N D B O O K SE R I E S

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C A ST I G U I D E B O O K SE R I E S

Volum e 1 - CASTI G uide to ASM E S ect ion I I - Ma t eria ls In dex

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C A ST I S E L F-ST U D Y SE R I E S

Volum e 1 - CASTI S elf-S tu dy G uide t o Corrosion Cont rol

Fir st print ing, J uly 1999

Second printing, September 1999

Third printing*, November 1999

Fourt h prin t ing*, J un e 2000

IS B N 1-894038-34-7 Copyright 1999, 2000

* Includes addit iona l a ppendices

All r ights reserved. No part of this book covered by the copyright

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iv


FR O M TH EPU B L I S H E R

IM P O R T A N T NO T I C E

The mater ia l presented here in has been prepared for the general

information of the reader and should not be used or relied upon for

speci fic a ppl ica t ions w i thout f irs t securing competent technica l

a dvice. Nor should it be used a s a replacement for current complete

engineering codes a nd sta nda rds. In fact , i t is highly recommended

tha t the a ppropria te current engineering codes a nd s tanda rds bereview ed in deta il prior t o a ny decision ma king.

While th e ma terial in t his book w a s compiled wit h gr eat effort a nd is

believed t o be techn ica lly corr ect, th e a uth ors, C A S T I Publishing Inc.

a nd its sta ff do not represent or wa rra nt it s suita bility for an y genera l

or specific use a nd a ssume no liability or r esponsibility of a ny kind in

conn ection w ith t he inform a tion herein.

Nothing in this book shal l be cons t rued as a de fense agains t any

alleged infringement of letters of patents, copyright, or trademark, or

a s defense aga inst lia bility for such infringement.


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v


OU RMI S S I O N

Our miss ion a t C A S T I Publ ishing Inc . is to provide indust ry and

educa tiona l inst itut ions w ith pra ctica l t echn ica l books at low cost. To

do so, C A S T I publications focus only on timely topics needed to solve

current industry problems and are writ ten by respected experts in

their fields.

We w ould l ike to hear from you. Your comments a nd suggest ions

help us keep our commitment to the cont inuing quali ty of al l our

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C anad a

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vi


Chapter Author Peer Review

1 W. I . P ollock (C on su lt a n t) G . K obr in (C on su lt a n t)

F. G . Hodge

(Ha ynes Int erna t iona l)

2 M. B la ir

(S teel Found er's S ociet y)

R. Pa nkiw

(Duraloy Technologies Inc.)

C. S . Na lbone (Consulta nt)

J . L. G ossett (Fish er C ont rols)

A. P a ris, J . Echlin a nd

D. D riggers

(Duraloy Technologies Inc.)

3 A. S a ba t a (Armco, I nc.) J . Ziemia n ski (C on sult a nt )W. J . S chum a cher

(Armco, Inc.)

4 J . D . R edmon d, C . W. K ova ch

(Techn ica l Ma rket ing

Resources, I nc.)

J . Fr itz

(Allegheny Lud lum)

5 G . E . C oa t es

(Nickel D evelopment

Inst i tute)

C. Reid (Consulta nt )

6 I . A. Fr anson (C onsult a nt ) R. D avison

(Techn ica l Ma rket ing

Resources I nc.)

J . F. G rubb

(Allegheny L udlum )

D. E. Ba rdsley

(Beloit Piping)

7 J . R. Crum , E . H ibner

(S pecia lty Meta ls Corp.)

P . Crook

(Ha ynes Int erna t iona l)

D. R. Muna singhe


P . E lliott (Consulta nt)

N. C. Fa rr


8 D . J . Tilla ck (C on sult a n t) A. L esn ew ich (C on sult a n t)

S . D. Kiser

(INCO Welding Products)


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vii


PR E F A C E

It is our intent to preserve the technical experience and knowledge

gained over the past f i f ty years by material engineers in select ing

corr osion r esista nt a lloys for t he ha ndling of a w ide ra nge of corr osive

environments . This has become especia l ly impor t an t w i th the

cont inua l dow nsizing in industry toda y, consolida t ion of technica l

sta ff thr ough corpora te mergers, an d retirement of senior engineers.

Industry continues to optimize its processes, often demanding higher

temperat ures a nd pressures to y ield higher product ivity , which

requires th e use of more corr osion r esista nt engineerin g ma t eria ls.

Stainless s teels and nickel al loys provide solut ions to many of the

problems encountered in a ggressive environmenta l condit ions a nd

meet pa r t icular corros ive condit ions rela ted to s t ress corros ioncracking, reducing and oxidizing environments, halogenation, salts ,

hyd rogen sulfide, a nd high t empera tu res, to na me just a few.

Likew ise, this C A S T I Ha ndbook wa s w rit t en to provide the pra cticing

engineer, inspector, designer, or plant operator with guidelines and

up-to-dat e informa tion to help prevent or minimize mista kes tha t

ha ve been ma de in the pa st .

The information presented in this book was prepared by 30 authors

and peer reviewers, whos total combined work experience is more

t h a n 700 y ea r s. Th es e in div id ua ls a r e eit h er in volved w i th

manufac tur ing products , developing opera t ing processes , or ar e

practicing engineers and consultants working in industry today. Our

sincere th a nks, a pprecia tion a nd r ecognit ion is extended t o th em.

St ephen La mb (Consulta nt )

Techn ical E dit or


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ix


TA B L E O F CO N T E N T S

1. S ome H istorica l Notes 1Monel: Ni-C u Alloy 2

Ferr it ic (Fe-Cr) S t a inless S t eel 4

Aust enit ic (Fe-C r-Ni) S t a in less S t eel 5

Ha s telloys: Alloy B (Ni-Mo) and Al loy C (Ni-Cr-Mo) 7

Alloy 20 12

Alloy G 14

Alloy 825 15

AOD a nd New Refining Technology 15

D uplex S t a inless S t eels 16

6-Mo Alloys 20

Ferr it ic (Fe-C r-Mo) S t a inless S t eels 22

The Future? 24

2. C a st C orrosion a nd H ea t Resist a nt Alloys 31

Overview 31

Chemica l C omposit ions 33D escr ipt ion of Alloy D esign a t ion S yst em (AC I ) 39

Met a llurgy 41

Alloy Types 53

Ferr it ic S t a inless S t eels 53

Ma rt ensit ic S t a inless S t eels 55

Aust enit ic S t a inless S t eels 57

D uplex S t a inless S t eel 60

S upera ust en it ic S t a in less S t eel 62

Ca st H ea t Resista nt Alloys for th e

H ydroca rbon P rocessing Indust ry 69

3. Ma rt ensit ic a nd Ferrit ic St a inless S teels 85

Mar tensit ic S ta inless St eels 86

C hemica l C omposit ions 92

Mecha nica l P roper t ies 94

P recipit a t ion-H ardening S t a inless S t eels 106C hemica l C omposit ions 108

Fa br ica t ion 117



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3. Ma rt ensit ic a nd Ferrit ic St a inless St eels (Continued)

Ferr it ic S t a in less S t eels 131


Mecha nica l P roper t ies 135Applica t ions 139

4. Aust enit ic S t a inless S t eels 159

Int roduct ion 159

G enera l C ha ra ct er ist ics a nd Applica t ions 160


Mecha nica l a nd P hysica l P roper t ies 165

ASTM S pecifica t ions 167

C a st G ra des 171


AS ME Allow a ble S t resses 176

C orrosion P ropert ies 180

Fa br ica t ion 196

B a sis for Alloy S elect ion 200

D esign a nd Applica t ion 203

5. D uplex S t a inless S t eels 209Int roduct ion 209


H ist ory 214


Meta llurgy a s it Rela t es t o Fa brica tion 218

Int ermet a llic a nd Ot her P ha ses 219

Fa br ica t ion C ha ra ct er ist ics 221

Applica t ions 228

C orrosion P ropert ies 233

Acids 233

C a ust ic S olut ions 236

Loca lized C orrosion 237

6. Supera ust en it ic S t a in less S t eels 243

Int roduct ion 243

Alloy D evelopment 244S uper Aust enit ic Alloys 247



ASTM S pecifica t ions 250


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6. Superau stenit ic S ta inless St eels (Continued)

Corrosion P ropert ies 257

P it t ing a nd C revice C orrosion 258

S t ress C orrosion C ra cking 260

C orrosion in Acids 261

Fa br ica t ion C ha ra ct er ist ics 266

Applica t ions 269

7. Nickel-B a sed Alloys 287

Chemica l C omposit ions 291

America n S t a nda rds - Cross References 294

Applica t ions 297Wa ter, S ea wa ter a nd At mospheric 297

C hemica l P rocess I ndust ry 299

P ulp a nd P a per 302

Na t ura l G a s P roduct ion 303

P et roch em ica l a n d R efin er y P r ocessin g 312

G a s Turbines 314

Rocket s, Missiles, a nd S pa cecra ft 318

P ow er 319E lect r ica l Resist a nce Alloys 321

H ea ting/H ea t Trea ting E quipment 325

Aut omot ive 332

Corrosion Properties in Aqueous

a nd H igh Tempera t ure E nvironment s 334

8. Weld F a brica t ion of Nickel-C on ta in in g Ma t eria ls 353

Welding C ha ra cteristics of Aust enitic Sta inless S teels

a nd Nickel Alloys 354Welding Ma rt ensit ic S t a inless S t eels 359

Welding Ferrit ic S t a in less S teels 361

Welding Aust en it ic S t a inless S t eels 363

Welding D uplex S t a in less S teels 373

Welding P recipita t ion H a rdena ble Aust enitic

St a inless St eels 377

Welding Nickel Alloys 379

Weld ing P recipit a t i on Hard enab le N ick el Alloy s 382

S pecia lized Weldin g P r ocesses or P r ocedur es 385

Welding of C a st ings 392

Ma ximizing Weld C orr osion Resista nce Thr ough D esign 395


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Appendix 1 Abbrevia t ed Terms 399

Appendix 2 Tra de Na mes 401

Appendix 3 H a rdness C onversion Numbers 407

Appendix 4 U nit C onversions 417Appendix 5 P ipe D imensions 425

Appendix 6 S ta in less S teel Welding Filler Met a ls 431

Appendix 7 Nickel & Nickel Alloy Weld ing F i ller Meta l s 451

Subject Index 461

Alloy Index

AS TM S t a nda rds 479

Nickel Alloys 483

C a st S t a inless S t eels 491

Wrought S t a inless S t eels 493


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Chapter

1SOME HISTORICAL NOTES

Dr. Warren I. Pollock

Wilmington, Delaware

Historians studying the fa r reaching technologica l impacts of m eta llic

mate ria l s of const ruct ion can r igh t ly ca l l the 20t h century the

Corrosion-Resistant Al loy Ageor ma ybe more precisely th e Stainless

S t eel a n d N i ckel -B a sed A l l o y A g e . Although for thousands of years

precious meta ls, copper, lea d, t in, a nd zinc, a nd some a lloys ba sed onth ese element s, w ere know n for resista nce to var ious corr osive media ,

utiliza tion of th ese ma teria ls w a s mostly for coina ge, jewelry, cooking

and other so-called utilitarian necessit ies. As essential materials of

cons t ruct ion for rela t ively la rge sca le equipment , their use wa s

limited.

Ca rbon steel, iron ca stings, and w rought iron w ere the primar y meta ls

and a l loys that gave the indus t r ia l era o f the 19th centu ry its solid

foundation and remarkable success. During the 20t h century , i t w a s

the development a nd product ion of corrosion-resis ta nt iron- a nd

nickel-based a lloys th a t permitt ed th e n ew industria l complexes of

chemical, petrochemical, refining, pulp and paper, and other process

industries , a s w ell a s da iry , food, a nd pharma ceutica l companies , t o

des ign and fabr ica te cr i t ica l equipment , p ip ing , and s torage uni ts

ha ndling the w idest ra nge of ha zardous environments , of ten a t hightempera tur es a nd pressures. It is these importa nt opera ting fa cilit ies

so often t a ken for gra nted by th e general public tha t produce the

multitude of chemicals, plastics, drugs, foods, beverages, and many

oth er ty pes of products, even silicon chips, th a t a re a t th e very core of


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Chapter 1 Some Historical Notes 3


1906 Monel alloy 400 (Ni-Cu).

1914 Ferritic (Fe-Cr) and type 304(Fe-Cr-Ni) stainless steels.

1927-9 Commercial introduction ofaustenitic stainless steels.

1931 Hastelloy alloys B & C.

1930-40 Stabilized alloys using Ti/CbTypes 321 & 347.

1935 Cast alloy 20 development.

1940 Development of Nimonics in Europefor jet engines applications.Development of alloy 600 forhigh temperature applications.

1947 Wrought alloy 20 composition(later Carpenter alloy 20Cb-3).

1952 Incoloy alloy 825.

1953 Korean War (nickel shortage).

Development of alloy 800 (low cost alloy 600).

1960s Incoloy alloy 901, Inconel alloy 718.(High temp strength, age hardened alloys.)Introduction of early duplex alloys - 3RE60.

1966 C-276 patent & commercial introduction.

1970s Development of second generation duplexstainless steels.

1971 Introduction of 904L (4% Mo alloy).

1973 Development of E-BRITE.

1974 Alloy B-2 introduction.

1980s 6% Mo alloys - Nitrogen strengthening.

1985 Impact of Ni-Cr-Mo alloys (C-276; C-22; 625).Controlled expansion alloys - alloy 900 series.Introduction of mechanically alloyed materials.

1990s Proliferation of Ni-Cr-Mo-W alloysC-2000, alloy 59, alloy 686.Higher Cr bearing Ni-based alloys.

ALLOY

TECHNOLOGY

DRIVENElement addition impacts

Welding productdevelopment - Ni & Ni-Fefor welding cast iron

Complementary alloywelding productdevelopment

Melting technoloy

AOD : VODVIM : VARVIM : VARTriple melting

Electron beam melting

Air pollution controlAdvanced engines

Specialty chemicals

PRODUCTION

TECHNOLOGY

DRIVEN

APPLICATION

TECHNOLOGY

DRIVEN

Figur e 1.1 Alloy/Applica t ion His tory


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4 Some Historical Notes Cha pter 1


Needing plat e an d sheet to develop th e an ticipa ted siza ble ma rket for

the a lloy, Inco built a melting fa cility a nd rolling mill in H unt ington,

West Virginia, which went into operation in 1922. The site today is

t he head q uar t er s of I nco Alloy s I n t erna t iona l, ea r lier ca l ledH unt ingt on Alloys, now Special Meta ls Corpora tion.

In 1924, ba sed on th e w ork of Willia m A. Mudge a nd th e significa nt

d iscovery of P au l D . Mer ica tha t a luminum and t it an ium led to

precipi ta t ion ha rdening of n ickel-based a l loys , Inco int roduced

K-Monel conta ining a bout 3%a luminum a nd 0.5%t ita nium. Toda y s

UNS designation is N05500 (alloy 500).

Ferritic (Fe-Cr) Stainless Steel

The discovery of iron-chromium stainless steel is usually attributed to

t h e E n glish ma n H a r r y B r ea r ley . Wor kin g a t t h e B r ow n F ir t h

Resea rch La bora tories in Sheffield , En gla nd, a joint resea rch a nd

development labora tory of Thoma s F irth a nd Sons a nd J ohn B row na nd C o., Br ea rly beca me int erested in th e ma nufa ctur e of steels wit h

high chr omium cont ents . Try ing t o prevent erosion a nd fouling in r ifle

ba rr els, he concluded t ha t a steel w ith upwa rd of 10%chromium could

possibly be of a dva nta ge. The da t e of record is J un e 4, 1912.

The first commercial ca st w a s m a de in August of t he follow ing yea r.

P a r t o f t he he a t w as l a t e r f ab r i c a t e d in t o rustless table cut lery

blades. Its composition, 12.86%chromium and 0.24%carbon, a plain

chromium martensit ic steel, is the forerunner of type 420 stainless

steel (S 42000). B rea rley is credited w ith th e na me stainless, yet his

own account of the discovery in 1924 states Brearley first heard the

knives described a s s ta inless by Er nest St ua rt , a cut lery company

ma na ger, after Stua rt ha d at tempted to sta in th em with food acids.

The first commercial a pplica tion w a s knife ma king. D uring th e First

World Wa r t he sta inless steel wa s used in a ero-engine exha ust va lves.

Subsequently, there w a s a dema nd for a softer steel, an d th is wa s met

in 1920 by a steel containing 12-14% Cr and 0.1% C which became

know n as sta inless iron.


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Chapter 1 Some Historical Notes 5


In 1915, t he f irst s ta inless s teel ingot ca st in America w a s m a de a t

Firth S terling Ltd. in Pit t sburgh, Pennsylva nia . Br ea rley a pplied for a

U.S . patent the same year , and i t was granted in September 1916.

Curiously, no pat ent a pplica tion w a s made in G reat B rita in.

Not often mentioned is t ha t Elw ood Ha ynes, founder of the H a ynes

Stellit e Company , Kokomo, Ind iana , now Ha ynes In terna t iona l ,

previously C a bot Corpora tion, a lso discovered t ha t sta inlessness could

be impar ted to s teel by the add it ion of suf ficien t quant it ies of

chromium in a series of experiments made between November 1911

and Apr il 1912. Although Ha ynes U . S . s ta inless st eel pa t en t

a pplica t ion a ntedat ed by nearly a yea r the a pplica t ion submit ted by

B rear ley , i t w as denied . Ha ynes f iled for in ter ference, which he

eventua lly obta ined, a nd received a patent in April 1919. B y tha t

t ime, however, Ha ynes and B rearley ha d merged th eir interests. B oth

ass igned patents to an America n pa tent-holding company which

issued licenses to steel companies desiring to manufacture stainless

steel.

Austenitic (Fe-Cr-Ni) Stainless Steel

Mea nw hile in G erma ny, a ustenit ic iron-chromium-nickel s ta inless

steel was being developed. In October of 1912, German authorit ies

granted Fried. Krupp Werke (Friedrich A. Krupp Works) the first

patent for the ma nufacture of components in s ta inless chromium-

nickel steels.

A 1909 Krupp la bora tory r eport ment ions t ha t high-a lloy chrome a nd

chrome-nickel steels showed no signs of rust even after months of

exposure to humid laborat ory a i r. The d iscovery is a t t r ibuted to

Edua rd Maur er w ho not iced tha t some al loys tha t B enno Stra uss had

made were impervious to a t t ack a f ter months of exposure to ac id

fu mes in Mau rer s labora tory . Maurer had joined Kruppschen

Forschungsanstal t (Krupp Research Inst i tute) at Essen that year as

its first meta llurgist .


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In terestingly, w here Ni-C r-Mo a lloys a re toda y a ssocia ted mostly w ith

process industry equipment and piping systems handling very harsh

chemica ls , t he f irs t large-sca le use of a lloy C wa s for a mil it a ry

wartime use: 12-inch diameter reflectors for Navy searchlights whichw ere required by t he th ousa nds. The experience ga ined in ma king t his

product was invaluable later for the manufacture and fabricat ion of

pla te a nd sh eet for process needs.

The first a pplica tion of a lloy C in t he chemica l indust ry is report ed to

have been made by C. P . Di l lon a t the Texas Ci ty , Texas p lant o f

Union Carbide in about 1948. I t was for a bucket l iner in a newly

developed weak-acid isopropanol process.

Alloy 20

In the mid-1930s, a lloy 20, a Fe-Cr-Ni-Mo-Cu composition, w a s

invented. In 1934, Mars A. Fontana, af ter doctorate s tudies at the

U niversity of Michiga n (his P h.D . degree wa s a w a rded in 1935), joinedE. I . du Pont de Nemours Company a t i t s Experimenta l Sta t ion in

Wilming ton , Delaw are , and s t a r ted a comprehens ive research

program on materials of construction for sulfuric acid service. The

following year he found that an iron-based casting containing 20%Cr,

29% Ni, 2.25% Mo, a nd 3.25% Cu ha d superior resista nce. The

composition became known as alloy 20, named, i t i s sa id , for the

ca sting being the 20t h that Fontana made or perhaps tested. Another

explan a tion is the a lloy cont a ins 20%chromium.

Fonta na lef t DuP ont in 1945 to become professor of metal lurgica l

engineering a t The Ohio S ta te U niversity w here he esta blished one of

the first courses in corrosion in 1946. He continued to work on cast

corrosion resista nt a lloys, d eveloping w ith collea gues a lloy CD -4MCu

(J 93370), a duplex sta inless steel conta ining a bout 25% C r, 5%N i, 2%

Mo, an d 3%C u.

Based on Fontana s discovery, the DuPont Company began seeking

ca stings of a lloy 20 for severa l troublesome components, va lves in

particular. Suitable foundry practices needed to be developed and the


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Ferritic (Fe-Cr-Mo) Stainless Steels

In t he last th irty yea rs, th ere a lso ha s been considera ble development

of ferri t ic s ta inless s teels, in part icular Fe-Cr-Mo composit ions .Ferrit ics of more tha n nomina l 26% Cr a nd/or nomina l 2% Mo a re

commonly calledsuper ferr iticsorsuperferritics.

In the early 1970s, alloy E-BRITE (S44625), also called alloys 26-1

and XM-27, containing nominal 26% Cr and 1% Mo, was introduced

by Airco Vacuum Meta ls, th en a division of Airco ba sed in New J ersey.

This a l loy w a s developed prima rily a s a replacement for type 300

a ustenit ic s ta inless s teels in a pplica t ions requiring chloride s tress

corrosion cracking (Cl-SC C) resista nce.

Type 446 (S44600), the 26% ferritic stainless steel, has good Cl-SC C

cha ra ct eristics but poor t ough ness. Alloy 26-1 w a s a n effort to improve

the properties of type 446, 1% molybdenum being added for better

pitting resista nce.

The generally good toughness of alloy E-BRITE results from its extra-

low ca rbon a nd nitrogen interstit ial levels, less t ha n a bout 200 ppm,

a chieved by a new melting technology, electr on-bea m cont inuous-

hear t h ref ining in a high vacuum. However , even this high-tech

process did not give low enough concentrations of nitrogen to avoid

intergranular a t t a ck (IG A) of w eldments , a nd severa l yea rs la ter

columbium w a s a dded in concent ra tions from 13 to 29 times nit rogencontent wit h S44625 still reta ined a s the UN S designa tion.

In 1977, Allegheny Ludlum, now a n Allegheny Teledyne Compa ny,

a cquired the E-B RITE tra dema rk from Airco a nd s ta rted producing

a lloy 26% Cr -1%Mo a lloy by va cuum induction melting. This m elting

process required a dditions of sta bilizing element s to t ie up ca rbon a nd

nitrogen. A new grade was introduced, designated S44627, yet st il l

called alloys 26-1 and XM-27, having columbium addition of 0.05 to

0.20%, w ith ca rbon a nd nitrogen ma ximum content s of 0.10% a nd

0.015%, respectively. This w a s follow ed by a nother sta bilized gra de,

designa ted S44426 a nd ca l led a l loys 26-1S a nd XM-33, ha ving a


18/108


Chapter

2CAST CORROSION- AND

HEAT-RESISTANT ALLOYS

Malcom Blair

Steel FoundersSociety of America, Des Plaines, Illinois

Roman Pankiw

Duraloy Technologies, Inc., Scottdale, Pensylvania

Overview

The broad ca tegory of corrosion resistant al loysconsist s of h igh a lloy

steels and nickel-base alloys. Subcommittee A01.18 of the American

Society for Test ing a nd Mat erials (ASTM) ha s responsibili ty for

developing t he sta nda rds for th is broa d ca tegory, un like the w rought

products w here different subcomm itt ees develop sta nda rds for ferrous

and non-ferrous al loys . The primary al loying elements in the higha lloys a re chromium, nickel, iron, a nd ca rbon. The high a lloy gr oup is

usually divided into two broad groups: corrosion-resistant and heat-

resistant . The heat resistant grades are generally used in conditions

w here oxida tion a nd ca rburizat ion resista nce a re import a nt a s well a s

high tempera ture s trength. I n s teel ca st ings the difference betw een

corros ion-res is tant a nd heat -res is tant grades is ref lected in the

differences in t he ca rbon levels of t hese ty pes.

B eca use of th e domina nce of w rought product s, in t onn a ge terms, ca st

versions of wr ought gra des a re comm only a va ilable. Ta bles 2.1a, 2.1b,

and 2.1c l is t the var ious corros ion and heat res is tant cas t grades ,

in cludin g t heir AC I a n d U N S design a tion s a n d ch em ica l


19/108

Cha pter 2 Cast Corrosion

CAST I H and b

Ta ble 2.1a ACI Alloy Designa tions an d Ch emica l Composition Ra nges for Corrosio

CHEMICAL COMPOSITION OF CORROSION-RESISTANT CAST STAINLESS STEELSa

Grade UNS No. ASTM Specification %C %Mn %Si %Cr %Ni O

CA-15 J91540 A 217, A 487, A 743 0.15 1.00 1.50 11.5-14.0 1.0 0.50 Mo

CA-15M J91151 A 487, A743 0.15 1.00 0.65 11.5-14.0 1.0 0.15-1.00

CA-28MWV --- A 743 0.20-0.28 0.50-1.00 1.00 11.0-12.5 0.50-1.00 0.9-1.25 Mo

CA-40 J91153 A 743 0.20-0.40 1.00 1.50 11.5-14.0 1.0 0.5 Mo

CA-40F --- A 743 0.20-0.40 1.50 11.5-14.0 1.0 0.5 Mo, 0

CA-6N --- A 743 0.06 0.50 1.00 10.5-12.5 6.0-8.0

CA-6NM J91540 A352,A356,A487,A743 0.06 1.00 1.00 11.5-14.0 3.5-4.5 0.4-1.0 M

CB-6 J91804 A 743 0.06 1.00 15.5-17.5 3.5-5.5 0.5 Mo

CB-7Cu-1 J92180 A 747 0.07 0.70 1.00 15.50-17.70 3.60-4.60 2.50-3.200.05 N

CB-7Cu-2 J92110 A 747 0.07 0.70 1.00 14.0-15.50 4.50-5.50 2.50-3.200.05 N

CB-30 J91803 A 743 0.30 1.50 1.50 18.0-21.0 2.0 0.90-1.20

CC-50 J92615 A 743 0.50 1.00 1.50 26.0-30.0 4.0

CD-3MWCuN J93380 A 351, A 890 Gr 6A 0.03 1.00 1.00 24.0-26.0 6.5-8.5 3.0-4.0 M0.5-1.0 W

CD-4MCu J93370 A 351, A 744,A 890 Gr 1A

0.04 1.00 1.00 24.5-26.5 4.75-6.00 1.75-2.25

CE-8N J92805 --- 0.08 1.50 23.0-26.0 8.0-11.0 0.50, 0.2

CE-8MN J93345 A 890 Gr 2A 0.08 1.00 1.50 22.5-25.5 8.00-11.00 3.00-4.50

CE-30 J93423 A 743 0.30 1.50 2.00 26.0-30.0 8.0-11.0

CF-3 J92500 A 351, A 743, A 744 0.03 1.50 2.00 17.0-21.0 8.0-12.0

CF-3M J92800 A 351, A 743, A 744 0.03 1.50 1.50 17.0-21.0 9.0-13.0 2.0-3.0 MCF-3MN J92700 A 743 0.03 1.50 1.50 17.0-22.0 9.0-13.0 2.0-3.0 M

CF-8 J92600 A 351, A 743, A 744 0.08 1.50 2.00 18.0-21.0 8.0-11.0

CF-8C J92710 A 351, A 743, A 744 0.08 1.50 2.00 18.0-21.0 9.0-12.0 (8 x C) C


20/108

Chapter 2 Cast Corrosion- and Heat-Resistant Alloys 39


Description of Alloy Designation System (ACI)

Cast high al loy s teels and nickel-based al loys general ly use grade

designa tions t ha t a re different from th eir w rought count erpar ts . Thissystem can make recognition or identification of the cast grades more

difficult. Ca st st a inless steels a nd n ickel-ba se alloys a re split int o tw o

categoriescorrosion-resistant and heat-resistanta nd , a s ment ioned

earlier, the principal difference between these two types is reflected in

the ca rbon levels a nd how th e ca rbon level is referenced in t he a lloy

designa t ion. The system used is know n a s the ACI system a n d w a s

developed some years a go by the Alloy Ca st ing In st i tute w hich w a s

merged int o the S teel F ounders Society of America (SFSA). The ACI

system is, in principle, very simple a nd gives some indica tion of th e

principal alloying elements contained in the material . For example,

th e a lloy designa t ions for tw o comm on gra des, C F3M an d HK 40, ar e:

CF 3M C = corrosion resista nt

F = nickel cont ent

3 = 0.03%ma ximum car bon cont entM = molybdenum is a principa l alloying element

HK40 H = hea t res is t an t

K = nickel cont ent

40 = th e mid ra nge of the ca rbon cont ent

The ACI designa tions for a ll corr osion-resista nt sta inless steel gra des

a nd some nickel-ba se alloy gra des ha ve th e prefixC ,w hile a l l heat -

resista nt gra des ha ve th e prefixH .I mmediat ely follow ing th eC or

H designa tion is a series of numbers a nd lett ers.

The lett er aft er th eC (F in C F3M) indicat es the nickel cont ent, t he

let t er s in u se r ang ing from A t o Z, a l t hou gh each let t er of t he

a lpha bet is not used. I t is importa nt to note tha t t he let t er a f ter t he

C , in th is ca seF, is not a ssigned a par ticula r va lue, but is merelyan indicator of relat ive nickel content ; for example, the le t ter A

indicates that there is less nickel than an al loy with the le t ter F,

a nd t he let t er X indica tes tha t the gra de conta ins more nickel th a n

an a l loy wi th a le t t e r F. The relationship between the chromium


21/108



Ferrite in Welds

A method a lso exists for determining ferrite in w elds. It is import a nt

to recognize, a t th is sta ge, tha t th e level of ferrit e in a product is notonly a fun ction of th e composition, but is a lso a fun ction of th e cooling

ra te during solidifica t ion. Therefore , w here w elding is ca rried out

w ithout post w eld heat t reat ment , the a mount of ferri te w ill a lso be

a f fected by the very h igh cooling ra t es as socia t ed wi th the hea t

ext r act ion f rom t he pa r t being w e ld ed . Where pos t w eld hea t

trea tm ent is ca rried out, such a s solution a nnea ling, th e cooling r a te

during welding is not a significant factor, except in instances where

cracking of the weld could occur due to very high ferrite levels. The

method used for determining ferrite in welds is based on work done

by Schneider (2) a nd Scha effler.(3) Schn eider determin ed the chromium

and n ick el eq u iva len t s f or cooling r a t es w h ich a re t y pica l of

fa brica t ion condit ions to be:

Cre= %Cr + 2(%Si) + 1.5(%Mo) + 5(%V) + 5.5(%Al) + 1.5(%Nb) + 0.75(%W)

Nie= %Ni + %C o + 0.5(%Mn ) + 0.3(%Cu) + 25(%N) + 30(%C )

U sing th e Scha effler diagr a m (Figure 2.11), t he level of ferrite in th e

w eld ca n be determ ined.

Austenite

A + M

Martensite

F+M

M + F

A + M + F

A + F

Ferrite

100%Fer

rite

80%Fe

rrite40

%Fe

rrite20

%Fe

rrite10%Ferrit

e

5%Ferrit

e

NoFerrit

e

Chromium equivalent = % Cr + % Mo + 1.5 x % Si + 0.5 x % Nb

Nickelequivalent=

%

Ni+30x%

C+0.5x

Mn

0 4 8 12 16 20 24 28 32 36 40

28

24

20

16

12

8

4

0

Figure 2.11 Scha effler diagr a m showing th e a mount of ferrit e a nd

a ustenite in w eldment s a s a fun ction of Cr a nd Ni equiva lent s.(3)


22/108



Alloy Types

There a re tw o genera l ca tegories of ca st high a lloy steels: corr osion-

resista nt prefixed by t he lett er C in the ACI designa t ion a nd hea t-resistant high alloy steels prefixed by the letter H . The first part of

th is section on high a lloy gr a des w ill discuss t he propert ies of t he C

type ma teria ls, w hich include the nickel-base a l loys , The second

section will discuss theH series of ma teria ls.

Corrosion-Resistant Grades C

The corr osion-resist a nt C g rades a re produced in the fol low ing

broad types:

Ferrit ic

Martensit ic

Age ha rdena ble

Austenitic

DuplexSuperaustenitic

Nickel-ba se a lloys

Ferritic Stainless Steels

Ta ble 2.4 Chem ica l Composit ion (Weight %)

Grade UNS No. Ca Mna Sia Cr Nia

CB30 J91803 0.30 1.00 1.50 18-22 2.0

CC50 J92615 0.50 1.00 1.50 26-30 4.0

a . Single f igures denote ma ximum.

These ma t eria ls do not respond t o hea t t rea tm ent. Some improvement

in mecha nical properties of gra de C B 30 (J 91803) ca n be a chieved by

balancing the composition to produce some austenite, although the

str ength of gra de C C50 (J 92615) ca n be improved by solid solution

hardening.


23/108


Chapter

3MARTENSITIC AND FERRITIC

STAINLESS STEELS

A. Sabata and W.J. Schumacher

Armco Inc

Middletown, Ohio

Introduction

The yea rs bet w een 1910 a nd 1915 ma y be cons idered th e golden y ea r s

for inventions of stainless steels. The three basic classes of stainless

s teels were a l l developed in th is per iod and in three d if feren t

countries. The man commonly referred to as the inventor of stainless

steels is Harry Brearley , an Englishman who developed the 0.35%

carbon , 14% chromium a lloy which is known today as S42000

(ty pe 420). He w a s sea rching for a bett er a lloy for ma king gun ba rr els

at the t ime, and was trying unsuccessfully to etch a sample of thiscomposition for metallographic examination. Others had had similar

trouble but the spar k of genius in Mr. B rearley ena bled h im t o turn

th is an noya nce int o a d iscovery.

At the same t ime in America , Mr. Dants izen, working for General

Electric Compan y, w a s investiga ting similar a lloys primar ily for lead-

in wires in incandescent lamps. Certain properties of these alloys led

him to develop a lower carbon variation, similar to type 410 (S41000),

for u se a s t urbin e blades. The a pplica tion is st ill popular .

Concurrent ly in G ermany tw o men na med Ma urer a nd S t ra uss were

studying iron-nickel alloys for thermocouple protection tubes. They


24/108

Cha pter 3 Martensit

CAST I H and b

Ta ble 3.5 Mecha nical P ropert ies of Wrought Ma rt ensitic S ta inless S

Tensile Strength, min. Yield Strength, min.UNS No. (Type)

Product FormaASTM

Specification

Heat Treat

Conditionb ksi MPa ksi MPa

UNS S41000 (Type 410)

P, Sh, St A 240 --- 65 450 30 205

B, shapes A 276 A, HF 70 480 40 275

A 479 A 70 485 40 275

1 70 485 40 275

2 110 760 85 585

3 130 900 100 690

A, CF 70 480 40 275

T, HF 100 690 80 550

T, CF 100 690 80 550

T, HF or CF 120 830 90 620 UNS S41000 (Type 410)

B, W A 493 A 82 565 --- ---

LD 85 585 --- ---

W A 580 A 70 485 40 275

A, CF 70 485 40 275

IT, CF 100 690 80 550

HT, CF 120 825 90 620

UNS S41600 (Type 416)

W A 581 A 85-125 585-860 --- ---

T 115-145 790-1000 --- ---

HT 140-175 965-1210 --- ---

UNS S41000 (Type 410)

B, P, Sh, St A 582, A 895 A --- --- --- ---

T --- --- --- ---

H --- --- --- ---


25/108

106 Martensitic & Ferritic Stainless Steels Cha pter 3


Precipitation-Hardening Stainless Steel

Composit ions of most precipi ta t ion-ha rdening or age-ha rdening

sta inless s t eels a re carefully bala nced to produce ha rdening by tw oseparate mechanisms:

1. Tra n sf o rm a t i o n an a l lot ropic t rans format ion of aus ten ite to

ma rt ensite produced by t herma l a ustenite-conditioning tr ea tm ent

or by cold w orking .

2. Precipitationthe resulting structure is then given a simple, low-

tempera ture a g ing t rea tment tha t ha rdens by precip ita t ion of

in t erm et a l lic com pou nd s and sim ult aneou sly t em pers t he

martensite .

G rades tha t respond to th is pat t ern of ha rdness development are

classed a s ma rtensit ic or semi-a ustenit ic t ypes . A third ca tegory of

precipit a t ion-hardening s t a inless s teels does not t r ans form to

ma rt ensite. These a ustenitic types reta in th eir a ustenitic structure a t

r oom t em per a t u re follow in g s olu tion h ea t t r ea t m en t a n d a r eha rdened by a precipita t ion tr eat ment. The principa l a ustenitic alloy

in genera l use is S 66286 (A-286).

Some t rue ma rtensit ic types include S17400 (Armco 17-4 P H ),

S15500 (Armco 15-5 P H ), S 13800 (Arm co P H 13-8 Mo ), a nd S 45500

(Custom 455 ) . A martensit ic s tructure forms in these al loys upon

cooling from solut ion-treat ing or a nnealing tempera tures ra nging

from 1500 to 1900 F (816 to 1038 C), depend ing on the a l loy .

Subsequent a ging trea tm ents a t 900 to 1150 F (482 to 621 C ) develop

desired strength and toughness.

Semi-austenitic grades include: S17700 (Armco 17-7 PH ), S15700

(Armco P H 15-7 Mo ), S 35000 (AM350 ), a nd S 35500 (AM355 ).

These alloys a re principa lly sheet a nd strip m a teria ls . Compositions,

a re bala nced so th a t t he structure is au stenitic in th e solution-tr ea tedcondition (see Table 3.9). This ductile structure permits forming by

conventiona l techniques used for 18-8 s ta inless s teels. Follow ing

fabr ica t ion, the aus teni te is t rans formed to martens i te by thermal

t rea t m en t and su bs eq u en t cooling. M axim um st rengt h is t hen


26/108

Chapter 3 Martensitic & Ferritic Stainless Steels 151


Cold End

Figure 3.9b Schema tic of a t ypica l exha ust syst em

show ing t he cold end , I-pipe-mu ffler-t a il st ub.

The primary material requirements for an exhaust system include

oxid a t ion res is t ance, h ig h t em pera t u re st rengt h , f orm abilit y ,

w elda bility , a nd cond ensa t e corrosion r esista nce. The exha ust sy stem,

especial ly the hot end, is subject to high temperatures and enginevibrat ions . Ta ble 3.27a l is ts the var ious a l loys used in the exhaust

system with their nominal chemical compositions, while Table 3.27b

lists int erna tiona l cross-references of ferritic sta inless steels used for

this application.

Ta ble 3.27a Ferr itic Exha ust Ch emica l Compositions

Nominal Compositions (Weight %)

UNS No. Type/Alloy C Cr Ni Ti Cb Other

S40900 409 0.01 11.2 --- 0.20 --- ---

S40975 409Ni 0.01 11.0 0.85 0.20 --- 0.75 Mn

S43035(S43932)

439(439LT)

0.015 17.3 --- 0.300.28

---0.06

---

S44100 18CrCb 0.015 18 --- 0.25 0.55 ---

S44500 430M 0.015 19.2 --- --- 0.4 0.4 Cu

--- 436S 0.015 18.0 --- 0.35 --- 1.0 Mo

S44400 444 0.015 17.7 --- 0.25 0.15 2.0 Mo--- 18SR 0.015 17.3 --- 0.25 --- 1.7 Al

--- 11CrCb 0.010 11.3 --- 0.20 0.35 1.3 Si


27/108


Chapter

4AUSTENITIC STAINLESS STEELS

C.W. Kovach and J.D. Redmond

Technical Marketing Resources, Inc.

Pittsburgh, Pennsylvania

Introduction

The austenitic stainless steels possess an outstanding combination of

corros ion res is t ance, mechanica l proper t ies , and f abrica b ili t yproper t ies. F or t h is rea s on t hey a re u sed in a w ide va r iet y of

applicat ions ranging from consumer goods, where aesthet ics are of

pr imary impor t ance, t o applica t ions in many indus t r ia l , pow er ,

aerospace set t ings and in many kinds of equipment where service

performa nce is pa ra mount .

As a result of this great versatili ty , these steels are among the most

important commercial alloys. They are essential to the functioning of

m od ern s ociet y , and t hey const it u t e a m a jor pa r t of t he m et a l

producing a nd meta l w orking industries around th e world.

The ra t e of g rowth of aus ten it i c s t a in less s teel product ion and

consumption in recent year s ha s exceeded th a t of m ost oth er classes

of engin eerin g meta ls. This t r end is expect ed to cont inu e a s a result of

the increasing technica l complexity of our society , s trong ma rketdema nd in energy a nd environment a l segment s of th e w orld economy,

a nd a nt icipa ted improvements in cost r elat ive to oth er m a teria ls .


28/108

160 Austenitic Stainless Steels Cha pter 4


General Characteristics and Applications

The ba sic a ustenitic st a inless is U NS S30400 (type 304) sometimes

called 18-8 st a inless. I t is a n iron-ba sed a lloy conta ining nomina lly18% chr omium a nd 8.5% nickel, minor a mount s of ca rbon, nit rogen,

manga nese, a nd s il icon. This a l loy had i t s or igins in the second

deca de of th is century w hen it w as s imulta neously d iscovered in

England a nd G erma ny tha t an addi t ion of about 12% chromium to

iron would prevent the formation of rust that normally would develop

in moist a ir.

This effect, illustrated in Figure 4.1, was subsequently found to hold

in many environments and provides the bas is for the outs tanding

corrosion resista nce cha ra cteris t ic of a l l modern s ta inless s teels .

Shor t ly a f t er , i t wa s d iscovered tha t an add it ion of n ickel would

stabil ize the high temperature al lotrope of iron, austenite , at room

tempera tur e. Austenite, w ith a fa ce-cent ered cubic cryst a l st ructure,

provides highly desirable mechanical properties in terms of strength,

ductility , and toughness. Thus, through a fortuitous combination ofdiscovery a nd th ermodyna mics, th is fa mily of steels wa s born .

0.010

0.009

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

0

2 4 6 8 10 12 14 16 18 20

Corrosionrate,cm/y

Wt % chromium

ipy

0.003

0.002

0.001

0

Figu re 4.1 C orr osion ra t es of chromium -iron a lloys in

intermitt ent w a ter spra y, room tempera tur e.


29/108

Chapter 4 Austenitic Stainless Steels 183


chlor ide, the res is tance of a us teni t ic s ta inless s teels is s t rongly

dependent on water chloride content. With the exception of coastal

sites, th e chloride cont ent of most n a tu ra l w a t ers ra rely exceeds a bout

200 ppm w hich is a bout the service l imit of S30400 a t a mbienttempera tu re. Thus S30400 is suita ble for ma ny a pplica tions involving

n a t ur a l w a t er s(1). As t empera ture and other corros iv it y f actors

in cr ea s e, gr a d es con t a in in g in cr ea s ed lev els of ch r om iu m,

molybdenum, and nitrogen are required. The effect of temperature

a n d ch lor id e on gr a d e select ion f or w a t er h a n dlin g a n d h ea t

exchang er service is show n in F ig ure 4.2. Th is g rap h show s

a dva nt a ges ga ined by selecting S 31600 or S 31726 for severe chloride

service, but a lso illust ra tes tha t even th ese gra des ar e not suita ble for

bra ckish or seaw a t er service except in specia l circumst a nces. Some of

these exceptions include ca ses w here the s ta inless is ca thodica l ly

protected, as in fasteners used for steel piling, boat hardware that is

routinely clea ned, a nd evapora tors wh ere th e w a ter is deaera ted.

100

90

80

70

60

50

40

30

20

10

0

176

140

68

104Temperature(C)

Temperatu

re(F)

100 1,000 10,000 100,000

Chloride Ion Concentration (ppm)

Crevice corrosion

317LMN

316

T304

No crevice corrosion

Figure 4.2 E ffect of t empera tur e a nd chloride on th e initia tion

of crevice corr osion on aust enit ic a lloys in a era t ed

synt hetic sea sa lt solutions at pH 2.(2)


30/108



However, with proper attention the specifics of the application, even

S30400 can g ive good service in cer ta in circumstances . G eneral

considera tions involving th e ha ndling of ha logen sa lts include:

For a g iven sa l t concentra t ion, there is usual ly a cr i t ica l

tempera tur e below w hich loca lized corrosion w ill not occur.

This t empera tur e decrea ses wit h increa sing a cidity (pH ),

H igh oxygen increases th is critica l tempera tu re,

Depos it s or other crev ice formers a re very det r imenta l ,

especia lly in th e presence of oxygen,

Res is t ance to ha logen sa lt s increases s ign if ican t ly w i th

increas ing s t eel ch rom iu m and m oly bd enum con t en t .

Therefore, types S 31600 or S 31703 a re usua lly chosen for

a pplica tions involving these salt s.

Corrosion by Foods

The demonstr a ted h igh resista nce of t he a ustenitic sta inless st eels to

a cids a nd sa lts m a kes th em suita ble for food processing, cooking, a ndha ndling a pplica t ions . Corrosion ra tes a re so low tha t they a re of n o

consequence in these applica t ions . Many tes t s have a l so been

conducted sh ow ing t ha t t he int roduct ion of meta l species into food by

food processing in s ta inless s teels is neg ligible and of no hea lth

consequence.(7, 8, 9, 10) A fa ctor of ut most import a nce in food ha ndling

is the tendency of the surface contacting the food to harbor harmful

bacter ia . The a us teni t ic s ta inless s teels a re outs ta nding in the irabil i ty to resis t bacteria retent ion and to be cleaned and s teri l ized.

This a dva nta ge applies to phar ma ceutical a nd biotech a pplica tions a s

well.

High Temperature Corrosion

A fortuitous feat ure of t he meta l lurgy of chromium a nd iron is th a t

the 12% chromium required to confer passivi ty in ma ny a queous

en vir on m en t s a l so pr od uces a m a r ked im pr ovem en t in h igh

temperature oxidation resistance. This is not through a passivating

effect but rather because chromium stabilizes the high temperature

ch rom it e a n d ch rom ic oxides w h ich a r e pr ot ect ive a t h igh


31/108



WeightLoss,g/hr/m

2

40

30

20

10

0

Chromium, (wt %)

0 10 20 30

900 C

1000 C

1100 C

1200 C

Figu re 4.7 E ffect of a lloyed chr omium on oxida tion of steels

cont a ining 0.5%C , 220 hr .(11)

Hours of Cycles

WeightLoss,%

304

347

14 Ni-19 Cr

309

310

0 200 400 600 800 10000

10

20

30

40

50

60

70

Figu re 4.8 Sca ling resist a nce of some iron-chromium -nickel a lloys in

cycling-t empera t ur e cond itions a t 1800F (982C). Cycle consisted of

15 minut es in th e furn a ce a nd 5 minut es in a ir. Sh eet specimens

0.031 in . (0.737 mm ) thick w ere exposed on both sides.(12)


32/108

Chapter 4 Austenitic Stainless Steels 195


Ta ble 4.7. S uggest ed Ma ximum S ervice Tempera tu res in Air(13)

Intermittent Service Continuous Service

Grade

F

C

F

C201 1500 815 1550 845

202 1500 815 1550 845

301 1550 840 1650 900

302 1600 870 1700 925

304 1600 870 1700 925

308 1700 925 1800 980

309 1800 980 2000 1095

310 1900 1035 2100 1150316 1600 870 1700 925

317 1600 870 1700 925

321 1600 870 1700 925

347 1600 870 1700 925

The chemical composition of a high temperature atmosphere has a

st rong in flu ence on t he per form ance of s t a in less st eels. B es tperforma nce usua lly occurs in a dry a ir a tmosphere, regardless of

gra de. The presence of m oistur e, ty pica lly found in combust ion ga ses,

w ill often lea d t o prema tu re fa ilure of th e protective oxide an d require

a reduced operating temperature limit. If the atmosphere is oxidizing

a nd conta ins sulfur oxides , a l l of the a ustenit ic s ta inless s teels w ill

st il l perform fairly well . In a reducing environment, sulfidation can

lead to premature failure of the high nickel grades such as S31000.

Reducing a tm ospheres r ich in ca rbon produce ca rburiza tion in a ll of

these steels, but S31000 is reasonably resistant because of its high

nickel cont ent. H a logen cont a mina tes increa se corr osivity un der most

conditions, especially when conditions are reducing.


33/108


34/108

Cha pter 4

CAST I H and b

Ta ble 4.8 Typica l Applica t ions

UNS No. Grade Typical Applications

S20100 201 Hose clamps, cookware

S20200 202 Hose clamps, cookware

S20400 Nitronic 30 Bulk solids handling equipment, truck and car frames

S30100 301 Food equipment, hose clamps, wheel covers

S30200 302 Springs

S30430 302HQ Cold headed parts, fasteners

S30400 304 General purpose grade, kitchen equipment, architecture components, chemical ind

S30403 304L Welded applications of 304

S30451 304N Higher strength applications of 304

S30500 305 Deep drawn components

S31600 316 Chemical industry equipment, pharmaceutical production, coastal architectural app

S31603 316L Welded applications of 316

S31703 317L Paper mill equipment

S31726 317LMN Flue gas desulfurization scrubbers

S32100 321 Oil refinery, petrochemical equipment


35/108


Chapter

5DUPLEX STAINLESS STEELS

Gary Coates

Nickel Development Institute

Toronto, Ontario, Canada

Introduction

Duplex st a inless st eels (DS S) a re n ot new, ha ving been developed in

the 1930s (see Figure 5.1). They have received significant attention

for ind us t ria l ap plica t i ons in t he la s t t w o d ecad es, off er ing a

com bina t ion of h ig h s t rengt h and cor rosion resist ance, g ood

fabricabil i ty , and reasonable cost , which make them the most cost

effective ma t erials for ma ny a pplica tions.

The term duplex refers to the a l loy s tw o pha se micros t ructure,

conta ining both a ustenite a nd ferri te . An a l loy ca n be considered a

duplex a lloy if it nomina lly cont a ins a minimu m of 25-30% of a ny of

those tw o phases . (Some a ustenit ic s ta inless cast ings a nd a ustenit ic

w eld meta ls ma y conta in a s much a s 25% ferri te in their a ustenit ic

micros t ructure, and a re somet imes descr ibed as hav ing duplex

microstr uctures, but w ill not be a ddressed in th is cha pter.)

Most commercia l wr ought duplex s ta inless s teels ha ve 50-55%

aus ten ite and 45-50% ferr it e. This somewha t more complexmicros t ructure necessit a tes both cont rolled processing by the

ma nufacturer a nd extra considera t ion w hen fa brica t ing a nd w elding.

Ca re in select ion of q ua lif ied fabrica tors is a dvised, s imila r to w ha t

w ould be a dvised for t he higher a lloyed a ust enitic sta inless st eels.


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214 Duplex Stainless Steels Cha pter 5


History

I t is very instruct ive to examine the his tory of the development of

DS S, with th eir adva nta ges and th eir l imita t ions .(1)

The fir st record edintent iona l product ion a nd use of duplex s ta inless s teels w a s in the

early 1930s. The refining technology of the day resulted in relatively

high carbon levels (0.08%was considered low) in all stainless steels,

and the duplex grades w ere found to of fer superior in tergranular

corros ion res is tance compa red to the a us teni t ic grades. For th is

reason, duplex alloys were used, for example, in sulfite liquors (pulp

m ills) and in t he m anu fact u re of explosives u sing n it r ic a cid .

Improvement in r efining t echniques in th e electr ic a rc furna ce in t he

1960s ma de low ca rbon s ta inless s teels rela t ively inexpens ive.

Intergranular corrosion was no longer such an issue, with the result

th a t t he low car bon 300 series sta inless steels ca me to predomina te.

Duplex a l loys w ere a lso somewha t ea s ier to cas t , a nd the la rges t

usage in th eir early h istory w a s a s cast products . Addit iona lly , D SS

offered superior erosion corrosion a nd a brasive w ea r propert ies ,ma king them idea l for pump ca sings a nd impellers , a property w ell

used toda y for both cast a nd w rought DS S.

The early duplex grades (e.g. , AISI type 329) typically had higher

chromium contents tha n the s ta nda rd a ustenit ic gra des , result ing in

a higher general corrosion resistance in many environments. They

also of fered s ignif icant ly improved resista nce to chlor ide s t ress

corrosion cra cking (SC C), to w hich a ustenit ic s ta inless s teels a re

qu it e suscept ible.

S31500 (alloy 3RE60) was one of the first duplex grades developed

specif ica l ly w i th low carbon . I t wa s a imed a t applica t ions where

S30403 (type 304L) and S31603 (type 316L) suffered from chloride

SC C, a nd for the most part performed up to expecta t ions . H ow ever,

especially during welding of heavier sections, i t was possible to endup w ith too high a ferrit e cont ent in t he hea t a ffected zone (H AZ) of

the base meta l and a lso in the weld meta l i t se l f . This resul ted in

prema t ur e corr osion a nd /or m echa nica l failu res from low ductilit y. All


37/108

Cha pter

CAST I H and b

Ta ble 5.2 Mecha nica l P roperties of Some D uplex St a inless S teels (from AS TM

UNS No. Common Name

Yield Strength

ksi (MPa) min.

Tensile Strength

ksi (MPa) min. % Elongation

S32900 AISI 329 70 (485) 90 (620) 15

S31500a 3RE60 64 (440) 92 (630) 30

S32304 2304 58 (400) 87 (600) 25

S31803 2205 65 (450) 90 (620) 25

S32950 7-Mo Plus 70 (485) 100 (690) 15

S31200 44LN 65 (450) 100 (690) 25

S32550 Alloy 255 80 (550) 110 (760) 15

S32750 2507 80 (550) 116 (795) 15

S32760 Z-100 80 (550) 108 (750) 25

S31260 DP-3 70 (485) 100 (690) 20

a . U NS S31500 not in ASTM A 240/A 240M; mecha nica l va lues f rom AS TM A 790/A 790M.


38/108



Metallurgy as it Relates to Fabrication

Austenite/Ferrite Ratio and Welding

Although a full discussion of phase tra nsforma tions is outs ide the

scope of th is pra ct ica l ha ndbook, t here a re a few very s ignif ican t

points that should be unders tood when weld ing and heat t rea t ing

D S S .

B y h eat ing a D S S, e.g., S31803 (2205) w hich t ypica lly ha s a bout 55%

austeni te a nd 45% ferr i te a t room tempera ture, to jus t below the

melt ing poin t a t a round 2550F (1400C ), t he r esult in g

microstructure would be total ly ferri t ic . All of the austenite phase

would ha ve t ra ns formed into ferr i te. As the tempera ture is then

slow ly low ered, some of the ferri te t ra nsforms back to a ustenite, so

tha t w hen th e duplex a l loy is held a t 1830F (1000C) for sufficient

time, a norma l (55/45) structur e results a ga in. Very litt le ferrite-to-

a ust enite tr a nsforma tion ta kes place below 1830F (1000C ).

Figure 5.3 shows t he ferr ite/a ust enite ra t io for a D S S a s a function of

tempera tu re. If ra pidly cooled from th e nea r 100%ferrit e tempera tu re

range , there is insuff icient t ime for equil ibr ium condit ions to be

reached, and the ferrite is not allowed to transform completely. The

resul t i s a s t ructure wi th too high ferr i te, which results in poor

ductility and poor corrosion resistance.

How ever, by heat ing the ba se ma teria l back int o the 1830F (1000C )

temperature range or higher (annealing), and holding for sufficient

tim e, th e proper ferr it e/a ust enit e ra tio ca n be re-obt a ined.


39/108



occur at temperatures as low as 500-535F (260-280C ), depending on

the a l loy , so g rea t care shou ld be exercised when dea l ing wi th

a pplica t ion s in volvin g lon g t er m exposu re a t or a b ov e t h is

temperature.

The rate of embrit t lement at any temperature is also composit ion

specific. The highest temperature for alpha prime embrittlement for

S31803 (2205) is a bout 975F (525C ).

1100

sigma phase

phase

900

700

500

3000.02 0.05 0.1 0.2 0.5 1

Time (h)

2 5 10 20 50 100

C

Figur e 5.4 TTT curve for S 31803 (2205) sh owing

both sigma pha se a nd a lpha prime.(3)

In the tempera ture ra nge of 840-1470F (450-800C), chr omium

carbide precipitat ion may occur, as i t may in the austenit ic grades .

H ow ever, DS S a re less sensitive t o th is phenomenon a nd t his is ra rely

observed to be a problem, especially since a ll wr ought DS S today a re

low carbon g rades . C hromium nit r ides may a l so form a t a round

1650F (900C) in ni t rogen a l loyed DSS, but these are rare ly seen

except in sit ua tions w here th e ferrit e is too high or t he nitr ogen is too

high. These situa tions a rise occasiona lly a t w elds.


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Chapter 5 Duplex Stainless Steels 223


Figur e 5.5 Field inst a llat ion of a cont inuous digester

built of S31803 (2205) pla te, being pr epa red

for sta rt up a t a pulp mill.

To ma inta in th e proper pha se ba lan ce in w eld meta l, most but n ot a ll

duplex filler meta ls a re overa lloyed w ith nickel. Nickel, like nitr ogen,

promotes th e ferr ite-to-a ust enite tra nsforma tion. For w elding S 31803

(2205), th e sta nda rd filler meta l is AWS E2209 or AWS ER 2209,

w hich conta ins 3-4% more nickel tha n the base ma teria l . Nitrogen

levels in th e filler meta ls ar e a lso import a nt a nd should not be at th e


41/108

Cha pter 5 D

CASTI Handbook o

Ta ble 5.6a Ch emica l Pr ocess/P etrochemical In dust ry

Application Duplex Alloys Used

PVC stripper columns, reactors MD S

Alcohol production MD S

Production of organic acids and intermediates LD, MD, SD S

Formaldehyde evaporators, columns MD S

Brackish water heat exchangers LD, MD, SD S

Seawater heat exchangers SD 6

Production and storage of phosphoric acid (rakes, tanks, pipes, pumps, etc.) MD, SD S

Nitric acid equipment 23% Cr LD S

Piping e.g., carry hot fluids where exterior is possibly subject to SCC MD S

Air coolers MD C

Various heat exchangers, heating coils, condensers, etc. for process side conditions LD, MD, SD S

Ta ble 5.6b Offshore In dust ry

Application Duplex Alloys Used

Offshore platforms - pressure vessels, separators, risers, flow-lines, sub-seamanifolds and umbilicals, pumps, valves

MD, SD Slo

Offshore platforms - seawater systems SD Os

Gas processing plants, pipelines MD Slo

Explosion and blast walls LD S


42/108



Corrosion Properties

As a family of al loys , from low al loyed to very highly al loyed, DSS

show a very wide range of corrosion resistance. The emphasis in thissection w ill be on environments w here testing ha s shown th em to be

of s ignif ica nt in teres t , and there have been some a ppl ica t ions . I t

should be empha sized th a t t esting should be performed to ensur e th a t

any al loy is suitable in any part icular environment . I t appears that

compara ble a ustenit ic a l loys w ith nickel contents higher tha n their

DSS counterpa r ts a re usua l ly more forg iving to upset condit ions ,

where a mater ia l swi tches temporar i ly to an ac t ive f rom a pass ive

s t a te. In some environments , th is phenomenon i s par t icu lar ly

import a nt, e.g., sulfuric a cid. When using la bora tory tests to evalua te

suita bil ity for service, i t is w ise to electrochemica lly a ct ivat e the

meta l coupons dur ing testing t o monitor th eir a bility t o repa ssiva t e.

Acids

Sulfuric Acid

D SS ca n show excellent corr osion resista nce in w eak (


43/108



In middle (20-90%) concent ra tion sulfuric a cid solutions, genera lly

only th e copper a lloyed 25%C r SD S S (e.g., S32550 or S 32760) should

be considered. Where they remain passive, they can be very useful

m a t er ia l s. B u t t h e cor rosion r a t e ca n in cr ea s e by a n or der ofmagnitude or more with only a small change in condit ions , e .g . , a

tempera tur e increa se of 20F (6.7C). See Figure 5.10.(6)

400

350

Boiling Point Curve

Concentration, weight percent

50 mpy(1.3)

0-1 mpy

(0 - < 0.03)1 mpy

(< 0.03)

>50 mpy(>1.3)

Corrosion rates in parenthesis are in mm/year.

300

250

200

150

150

100

10 20 30 40 50 60 70 80 90 100

100

50

Temperature,F

Temperature,C

Figure 5.10 C orr osion resista nce of Ferra lium 255 (S32550)

in sulfu ric a cid iso-corr osion curve for 0.3 a nd 1.3mm /a .

In high (>90%) concentr a tion sulfuric a cid, th ere ha s been mixed

experience w ith the S31803 (2205). Ca ution is th erefore a dvised.

However, t he 25% Cr SD SS often give suita ble performa nce a nd a re

used w here high str ength a nd erosion resista nce is needed.

Phosphoric Acid

Wet process phosphoric a cid t ypica lly cont a ins sign ifica nt a mount s of

impurit ies, w ith th e chlorides a nd fluorides r endering t he w orkhorse

S31603 (t ype 316L) suscept ible t o corrosion. S 31803 (2205) ha s clea rly

superior corrosion resistance in these types of environments and is


44/108


Chapter

6SUPERAUSTENITIC

STAINLESS STEELS

Dr. I.A. Franson and Dr. J.F. Grubb

Allegheny Ludlum Corporation

Brackenridge, Pennsylvania

Introduction

The definition of superaustenitic stainless steelis not pr ecise. Over t he

past deca de or tw o this term ha s been used prima rily in reference to

the new aus tenit ic a l loys conta ining 6% molybdenum. How ever ,

num erous other new a ustenitic a lloys h a ve been developed w hich a lso

f it the superaustenitic descr ipt ion in tha t they a re more highly

a lloyed a nd offer significa ntly bett er resista nce to corrosion th a n th e

AIS I 300 series a ustenitic sta inless st eels. These newer a lloys cont a in

less nickel than the nickel-based alloys. Cost of the superaustenitica lloys, t herefore, is genera lly int ermedia te t o the 300 series a ustenitic

grades and the nickel-based alloys, while corrosion resistance, in some

cases, challenges that of higher nickel alloys.

The superaust enitic sta inless steels w ill include th ose commercial

Fe-Cr-Ni-Mo-N austenitic alloys which do not have AISI 300 series

des ignat ions , which ha ve i ron a s their la rges t cons t ituent , whichcontain less than 40%nickel, and which are used primarily for their

aqueous corrosion resistance. Even with this rather narrow definition,

there will be overlap. For instance, N08800 (alloy 800; Fe-21Cr-32Ni),

which fits the superaustenitic definition (except it has no molybdenum


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244 Superaustenitic Stainless Steels Cha pter 6


a ddition), is included in th e cha pter on nickel-ba sed a lloys beca use it

has been classified as part of this family of alloys. Other alloys which

may f it the superaus teni t ic a lloy composit ion ranges may a lso be

excluded beca use t hey a re principa lly used for high tempera turea pplica tions. In a ny ca se, only t hose supera ustenitic alloys w hich ha ve

U N S (U n i fied N um ber ing Sy st em ) d esig na t ions and w h ich a re

included in ASTM specifications are discussed.

In the early 1990s, the ASTM adopted a new definit ion of stainless

s teels, cons is tent wi th other interna t iona l s tanda rd specif ica t ion

orga nizat ions. Where previously a gra de ha d t o ha ve more tha n 50%

iron t o be a sta inless steel, the new d efinition requires tha t t he iron be

the la rgest element by w eight percent. A number of gra des, t ypica lly

designated N08XXX, and presently included in the B specifications,

would be S3XXXX stainless steels in the A specifications, if newly

intr oduced. These gra des a re grandfathered in the B specifications,

i.e. they will be retained in these specifications for an extended period

of t ime beca use of user dra w ings a nd qua lified procedures. H ow ever,

no new N08XXX grades will be accepted in the B specifications, andthe existing N08XXX gra des w ill be individually sponsored in th e A

specifica tions w hen th ere is producer/user int erest. E xistin g N 08XXX

gra des w ill reta in their U NS number to indica te their history.

Superaustenitic Alloy Development

Although many of the superaustenitic stainless steels are relatively

new, the earl iest developments date back more than 60 years . For

instance, the alloy now known as N08904 (904L) was developed in

France in the 1930s for use w i th sul fur ic ac id .(1) Hot w orkabili ty

problems with these early ful ly austenit ic al loys ini t ial ly inhibited

their commercialization. The discovery that rare earth additions were

effective in improving hot workability led to commercial production of

wrought N08020 (alloy 20) in 1951.(2) This a lloy a lso found primary

a pplica tion in th e ha ndling of sulfuric acid.

E x is ting su perau st en it ic a l loy s con t inued t o be im proved a s

experience with these materials was gained. N08020, for instance,


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Cha pter 6 Super

CASTI H andb

Ta ble 6.1 Ch emica l Compositions of Supera ustenit ic St a inless S teelsa (

UNS No. Alloy C Mn P S Si Cr Ni Mo N max.

S31050 310MoLN 0.030 2.00 0.030 0.010 0.50 24.0-26.0 21.0-23.0 2.0-3.0 0.10-0.16

S31254 254 SMO 0.020 1.00 0.030 0.010 0.80 19.5-20.5 17.5-18.5 6.0-6.5 0.18-0.22

S31266 B-66 0.030 2.00-4.00 0.035 0.020 1.00 23.0-25.0 21.0-24.0 5.0-7.0 0.35-0.60

S32050 SR50A 0.030 1.50 0.035 0.020 1.00 22.0-24.0 20.0-22.0 6.0-6.8 0.24-0.34

S32654 654 SMO 0.020 2.00-4.00 0.030 0.005 0.50 24.0-25.0 21.0-23.0 7.0-8.0 0.45-0.55

S34565 4565S 0.030 5.00-7.00 0.030 0.010 1.00 23.0-25.0 16.0-18.0 4.0-5.0 0.40-0.60

N08020 20Cb-3 0.07 2.00 0.045 0.035 1.00 19.0-21.0 32.0-38.0 2.0-3.0 ---

N08024 20 Mo-4 0.03 1.00 0.035 0.035 0.50 22.5-25.0 35.0-40.0 3.5-5.0 ---

N08026 20 Mo-6 0.03 1.00 0.03 0.03 0.50 22.0-26.0 33.0-37.2 5.0-6.7 0.10-0.16

N08028 Sanicro 28 0.030 2.50 0.030 0.030 1.00 26.0-28.0 30.0-34.0 3.0-4.0 ---

N08031 Nicrofer

3127hMo

0.015 2.0 0.020 0.010 0.3 26.0-28.0 30.0-32.0 6.0-7.0 0.15-0.25

N08320 20 modified 0.05 2.5 0.04 0.03 1.00 21.0-23.0 25.0-27.0 4.0-6.0 ---

N08366 AL-6X 0.035 2.00 0.040 0.030 1.00 20.0-22.0 23.5-25.5 6.0-7.0 ---

N08367 AL-6XN 0.030 2.00 0.040 0.030 1.00 20.0-22.0 23.5-25.5 6.0-7.0 0.18-0.25

N08700 JS700 0.04 2.00 0.040 0.030 1.00 19.0-23.0 24.0-26.0 4.3-5.0 ---

N08825 825 0.05 1.0 0.03 0.03 0.5 19.5-23.5 38.0-46.0 2.5-3.5 ---

N08904 904L 0.020 2.00 0.045 0.035 1.00 19.0-23.0 23.0-28.0 4.0-5.0 0.10

N08925 INCO 25-6Mo 0.020 1.00 0.045 0.030 0.50 19.0-21.0 24.0-26.0 6.0-7.0 0.10-0.20

N08926 INCO 25-6Mo,

1925hMo

0.020 2.00 0.030 0.010 0.50 19.0-21.0 24.0-26.0 6.0-7.0 0.15-0.25

N08932 URSB-8 0.020 2.00 0.025 0.010 0.40 24.0-26.0 24.0-26.0 4.5-6.5 0.15-0.25

a . Ma ximum unless otherw ise specified.


47/108

Chapter 6 Superaustenitic Stainless Steels 249


Specification

B a sic ASTM product form specifica tions covering the supera ustenitic

sta inless st eels a re listed in Table 6.2. As noted previously, ma ny of thea lloys a re covered in ASTM A specifica tions perta ining to sta inless

steels, while others are included in ASTM B specifications for nickel

alloys. Specifications other than those listed exist for some of the alloys.

These can be located by contact with producers of the individual alloys or

through search of the index of the va rious ASTM specificat ion volumes.

Mechanical Properties

Minimum mecha nica l propert ies for the var ious supera usteni t ic

a l loys , f rom the var ious applica ble ASTM pla te, sheet , a nd s t r ip

specifications, are given in Table 6.3.

Those alloys with no nitrogen additions exhibit properties similar to

those for 300 series a ustenitic sta inless steels. However, in genera l,

y ield and t ensile st rengt h va lu es a re h ig her t han for st and a rda ustenitic gra des ow ing to the higher a lloy cont ent a nd, pa rticularly,

th e presence of nit rogen in th e supera ustenit ic gra des.

Alloys w ith no nitrogen a ddition ty pica lly exhibit yield st rength s of 28

to 35 ksi (193 to 241 MP a ) a nd tensile strengt hs of 71 to 80 ksi (490 to

550 MP a ). Addition of 0.2% nitr ogen t ypica lly ra ises yield a nd tensile

st rengt hs t o 44 and 95 ksi (300 and 655 MP a ), r es pect ively ,

represent ing a 33% increase in yield strength a nd 24% increase in

tensile strengt h compa red t o th e nitr ogen-free a lloys. The a lloys w ith

0.5% nitrogen typica lly display 61 ksi (420 MP a ) yield strength a nd

110 ksi (760 MP a ) t ensile streng th , represent ing 85%increa se in yield

strength a nd 45% increase in tensile str ength compar ed to nitrogen-

free alloys. Nitrogen, thus, is a potent strengthener. Its influence is

significa nt ly stronger on yield strengt h th a n on tensile str ength .

In a ny event th e nitrogen-cont a ining supera ustenitic sta inless steels ar e

significa nt ly stronger t ha n t he conventiona l 300 series a ustenitic gra des

a nd , therefore, provide higher a llow a ble design stresses w hile exhibiting

excellent elonga t ion va lues typica l of a ust enitic sta inless steels.


48/108

Chapter 6 Superaustenitic Stainless Steels 269


N08020 and N08904 for which matching fil ler metals are available.

N orm a lly , m ore h ig hly a l loy ed n ickel-bas ed filler m et a l s a re

recommended. As-ca st supera ustenit ic w eld deposits of ma tching

composition a re h ighly segrega ted (cored) beca use of t heir high a lloycontent . Consequently the use of the more highly a l loyed (higher

molybdenum) nickel a lloy filler meta ls brings th e corrosion resista nce

of th e weld deposit up t o th e sam e level a s th e ba se meta l.

Aut ogenous w elds, if ma de, need to be given a full a nn eal t o elimina te

the ca s t s t ructure a nd d issolve second pha ses . Welding of these

superaustenitic alloys is discussed in more detail in Chapter 8: Weld

Fa brica tion of Nickel-Conta ining Ma teria ls.

Applications

The superaustenitic stainless steels are used to provide resistance to

corros ive env ironments tha t a re too severe for the 300 ser ies

a ustenitic sta inless steels. The superaust enitic a lloys a ll ha ve highernickel content w hich, together wi th their molybdenum content ,

provides much greater resistance to stress corrosion cracking (SCC) in

the presence of chlor ides tha n the 300 ser ies a lloys . P i t t ing an d

crev ice cor rosion res is tance, t oo, a re g enera l ly bet t er in t he

supera ustenitic a lloys beca use of high er chr omium, m olybdenum, a nd

nitrogen content, as reflected in PREN numbers. For these reasons,

th e supera ust enitic alloys ha ve been used w idely in pla ce of 300 series

a lloys in a broa d va riety of equipment w here pit t ing a nd/or crevice

corrosion or s tress corrosion cra cking w a s present or l ikely to be

present.

The a va ila bility of sta nda rd product forms such a s sheet, st rip, pla te,

tube, pipe, f it t ings, bar , b illet and ca s t ings, a nd the s imilar ity in

fabrica t ion requirements to s ta nda rd a ustenit ic al loys , ha ve a l low ed

th is subs t itu t ion to be ma de, in mos t cases , w i thou t too much

difficulty.

The h igher a lloy (chr omium, n ickel, molybdenu m, a nd copper) cont ent

of the supera ustenit ic a l loys a lso provides substa nt ia l ly improved


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tube-to-tubesheet joints, on ga sket surfa ces a nd on w eld sea ms of

nozzles of seawater cooled heat exchangers. (34)

Seawater

B et ter choices for sea wa ter service a re the 6Mo a nd more highly

al loyed superaus tenit ic a lloys wi th P REN values of 46 or higher

(Ta ble 6.5). These a lloys ha ve been used for over 20 yea rs in a w ide

variety of seawater applications, including nuclear and fossil power

plan t stea m surfa ce condenser tubing a nd t ubesheets, piping a nd hea t

excha ngers for nuclea r pow er pla nt service w a ter syst ems,(35) offshore

oil/ga s production pla tform piping syst ems, hea t excha ngers, ba llast

w a t er sy st em s, a n d fir e pr ot ect ion sy st em s.(36) The 6Mo-

superaustenitic stainless steels are also used in reverse-osmosis and

flash dis t i l lat ion desal inat ion plants ,(26,34) primarily in the form of

piping.

It ha s been suggested t ha t the 6Mo-superaust enitic a lloys be limited

to 95 F (35C) in continuously chlorinated seawater to avoid crevicecorrosion.(36) H igh er t em per a t ur e a pplica t ion s r eq uir e t he

superaustenitic alloys with PREN values of 60 or greater (Table 6.5).

S32654, for insta nce, ha s been show n t o resist corr osion in chlorina t ed

sea w a ter to 113F (45C ), w ith excursions t o 140F (60C ).(37)

Pulp and Paper

The 6Mo and oth er superaust enitic alloys w ith P RE N a bove 46 ha ve

found broad application in the pulp and paper industry. These alloys

ha ve been found suita ble for use in C- and D-sta ge blea ch w a shers ,

eff luent coolers , piping, paper ma chine hea dboxes, bla ck l iquor

recovery boilers , rehea ters, f il ter drums, a nd scrubbers a nd other

applications.(1,11,25) The superaustenit ic grades with PREN greater

th a n 60 (S32654 a nd S31266, Ta ble 6.5) a lso extend th e use of th ese

a lloys t o pulp mill blea ch pla nt environments th a t ma y be too severe

for the 6Mo al loys . These al loys demonstrate s imilar resis tance to

loca lized corros ion as high molybdenum nickel-based a lloys in

aggressive D-stage bleach plant environments,(17,37) a nd a re resis ta nt


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Sulfuric Acid

D a ta given in t he Corrosion P roperties section a nd Ta ble 6.7 illustra te

that the superaustenitic stainless steels offer excellent resistance tosulfur ic acid . Res is t ance wa s shown to increase wi th tot a l a l loy

content. N08031, with highest alloy content (27 chromium, 31 nickel,

6.5 molybdenum, 1.2 copper), provides exceptiona l resista nce a mong

th is group of a lloys.

Applica t ions for superaus ten it ic s t a inless s teels include acid

distribution systems,(17) a cid coolers , a nd piping (27) in production

pla nt s a nd a broa d ra nge of equipment ha ndling sulfuric a cid in other

process plants. For instance, N08031 is mentioned as having been

used for heat excha ngers a ssocia ted w ith sulfur ic ac id pickling

baths .(25) Where seaw at er cool ing is used for ac id coolers , the

supera ustenitic a lloys w ith sufficiently high P RE N n umber should be

considered.

F lu e g as d es ulfu riza t i on (F G D) s yst em s have consu med la rg equa nt ities of supera ustenitic a lloys. Ta ble 6.8 presents guidelines for

select ion of a l loys for FG D environments .(39) The severi ty of the

environment increases wi th decrease in pH and increase in the

a mount of ha lide ion present , as w ell as increa sing tempera tu re.

Ta ble 6.9 il lus t ra tes tha t 6Mo superaus teni t ic a l loys f il l the gap

between the S31726 (317LMN) austenitic stainless steel and nickel-

ba sed a lloys su ch a s N10276 or N06022. Alth ough not in cluded in t he

tests w hich formed th e ba ckground for Ta ble 6.8, N08031 or S32654

could be used under some of t he cond itions in

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Stainless Steels & Nickel Alloys