Characterization of the Solidification Structures Within the Dendritic Core of M2 High Speed Steel

JAMES McLAUGHLIN, R, WAYNE KRAFT, AND JOSEPH I. GOLDSTEIN

The phases which are present within the dendritic core region during the solidification of AISI type M2 high speed steel (6 W, 5 Mo, 4 Cr, 2 V) were studied and character ized by metallography and quantitative microprobe analysis. A series of samples were quenched from various temperatures during solidification, " f reez ing in" the different solidification phases. The f i rs t phase observed to solidify in M2 is ferr i te w/-nch contains very little carbon. As the solidification process continues, most of the liquid surrounding the ferr i te t ransforms to austenite by virtue of a peri tectic reaction which initiates at 1330~ (L + F - - A). The ferr i t ic cores also t ransform at around 1330~ into an austenite plus car- bide aggregate. By the time the ingot cools to 1255~ the carbides at the center of the dendrites dissolve completely, leaving an austenitic phase of uniform carbon and alloy content. At temperatures below the solidus, very fine carbides precipitate from the aus- tenite. No eutectoid decomposition by products such as those commonly observed in T1 tool steel were observed in these specimens nor in samples from a commercial ingot.

HIGH speed steels are character ized by their hard- ness and wear resistance at elevated temperatures. ~,2 The hot hardness quality of these steels is achieved by substantial amounts of carbides which are included in the microstructure . These carbides exhibit thermal stability which allows them to remain hard at tempera- tures where the surrounding matrix is relatively soft.

The s t ructures which form upon freezing of high speed steels are very important and dictate many of the propert ies found in the finished product. Several studies have been conducted that explore the solidifi- cation process in these highly alloyed steels.3-6 The most pertinent investigation, which studied the f reez- ing of type M2 high speed steel, was conducted by R. Barkalow. %8 Employing thermal analysis and extensive metatlography on unidirectionally solidified laboratory specimens, Barkalow e t a f determined the reactions which occur during solidification, For a 0.80 pct C M2 tool steel they are as follows:

I) Delta ferr i te s tar ts to crystal l ize f rom the liquid at 1430~ L --~ F.

2) At 1330~ austenite forms from the peritectic re- action, L + F ~ A.

3)* MC type carbides begin to precipitate f rom the austenite and M6C carbides by a eutectoid reaction.

*It should be noted here that the third solidafication reaction, L ~MC, was only inferred by Barkalow. More recent work by Snyder 9 confirmed his hypothesis.

liquid at about 1262~ L ~ M C . 4) The remaining liquid crystal l izes at around

1242~ by a eutectic reaction, L -* A + M C + M6C.

In this work it was shown that any delta ferr i te , which is not consumed by the peritectic reaction during the nonequilibrium unidirectional freezing process, decom- poses be low the s o l i d u s into a two phase aggregate of

JAMES McLAUGHLIN, formerly Graduate Assistant at Lehigh Uni- versity, is n o w with Standard Oil Co. of California, Richmond, CA, and R. WAYNE KRAFT and JOSEPH I. GOLDSTEIN are Professors, Department of Metallurgy and Materials Science, Lehigh University, Bethlehem, PA 180t 5.

Manuscript submitted February 25, t977.

Many investigations have been conducted that char- acterize the carbides which crystall ize last from the liquid and outline the dendritic s tructure of the as cast ingot. 1-~ However, little attention has been focused on the reactions occurr ing within the dendritic cores. The purpose of this research is to character ize the phases present and reactions occurr ing within the core region during the freezing process of the M2 grade of high speed tool steel. Since it has been commonly assumed that the eutectoid reaction which occurs in T1 tool steel also occurs in M2, particular attention is focused on the decomposition reactions because they are not well understood in M2.

EXPERIMENTAL TECHNIQUES

Interrupted Quenching

Samples were melted and slow cooled to various temperatures in a vert ical furnace under an argon at- mosphere. They were then quenched to observe the s tructures present at the temperature from which the quenching was done. Samples were cooled at 6~ s imilar to the cooling rate observed near the surface of commercial ly cast tool steel ingots. This technique allowed for the indirect observation of the phases which form during the freezing of M2. This freezing technique differs markedly from that used by Barka- low 7 where reheated unidirectionally solidified sam- ples were used for studying the solidification reac- tions.

A vertical high temperature molybdenum furnace was employed for the experiments. Samples of an- nealed M2 bar stock* were placed in 18 mm ID alumina

*The M2 bar stock was supplied by Universal Cyclops Steel Corporation. The heat analysis of the M2 was: 0.82 pct C, 6.11 pct W, 4.95 pct Mo, 4.18 pet Cr, t.88 pet V, 0.009 pct S, 0.020 pct P, 0,26 pet Mn, 0.31 pct $1, 0.20 pct Ni, 0.17 pct Co, 0.08 pct Cu, and 0.021 pct AL The ingot from which the bar stock was made was a round cornered square ingot 23 cm (9 in,) on a rode at the bottom, 32 cm (12~(, m.) on a side at the top, 76 cm (30 in.) long and weighed 420 kg (930 lb), In addmon to the bar stock, 1 cm (0.5 in.) slices cut from the bottom, center and top of the ingot were also supplied. These were cut in the billet an- nealed conditaon (which was sufficient to chromate ingot crackang and penmtted saw cutting) before the balance of the ingot was processed into the bar stock.

METALLURGICAL TRANSACTIONS A VOLUME 8A,NOVEMBER 1977-1787

crucibles that were supported by a tungsten basket as- sembly. The entire crucible and basket assembly was suspended in the furnace by a thin piece of nichrome wire. When the samples had cooled to the temperature of interest, the nichrome wire was melted locally by passing current through the wire. The sample was then quenched in a water bath placed below the sample.

The sample temperature was monitored by a P t -P t 10 pct Rh thermocouple placed 1/4 inch above the sam- ple, An adjustable-range and adjustable zero str ip chart recorder also was employed to record the cool- ing rate of the samples during freezing and prior to quenching. To minimize decarburization a protective atmosphere of high purity argon (99.998 pct) was passed through the furnace at a rate of 2200 cc /min and bubbled into oit,

Quantitative Microprobe Analysis

The compositional variations across a dendrite were measured with an electron microprobe. Analyses were performed at an operating voltage of 10 KV and a sample current of 0.05 VA. A 4 pan beam ras te r was used during the analysis to average secondary carbide precipitates in the matrix. Ten micron steps were taken between point counts to eliminate any chance of measuring overlapping carbon contamination layers .

Pure standards of tungsten, molybdenum, and vana- dium were used along with a homogenized alloy of 4.9 pct Cr balance Fe. A meteorite (Canyon Diablo), which contained large cementite (Fe3C) particles, was used as a carbon standard. The raw X- ray intensity ratios obtained during the analysis were converted into wt pct utilizing a standard computer program which correc ts the raw data for atomic number, fluorescence, and absorption effects. 12 Since carbon is heavily absorbed by the other elements in M2, the mass absorption coefficients were carefully chosen and independently entered into the correct ion pro- gram.*

*The mass absorption coefficients for CK,:, were chosen from the data of Henke and Eblsu 13

Absorber pip for CKa (cm2/g)

Fe I3,300 W 18,750 Mo 322420 Cr 10,590 V 8,840 C 2,373

Since the investigation of carbon content in M2 was critical, a statistical analysis was employed to under- stand the data and contamination effects. A statistical method outlined by Thiesen 14 was used to calculate the carbon detectability limit, This limit was determined as +0.031 wt pct at a 95 pct confidence limit for the operating conditions employed during the analysis.

PRESENTATION AND DISCUSSION OF RESULTS

Metatlography

Samples of M2 were melted at 1500~ cooled at a rate of 6~ to a preselected temperature and finally quenched in water as described previously. The temperatures selected for four of the samples are shown on Fig. 1 which is the pseudobinary phase diagram for M2 type tool steels developed by Barka- low, ~'8 The labels on the curves describe the reac- tions occurr ing at the time the samples were quenched.

L~ O

i 1400

~J

~D 1350 <

w 1 3 0 0 n

u.11250 F-

1200'

3,

.8o i:o ~.2 ~.4 ~.e % CARBON

Fig. 1--Plot of reaction temperature v s carbon content (Ref. 7 and 8) illustrating the phases present when the samples were quenched.

Carbon contamination, which occurs as a resul t of electron beam and diffusion pump oil interaction, con- tributed a significant amount to the carbon background (~50 pct). Two forms of contamination were observed. The f irs t form appeared as a continuous film which adhered instantaneously to tile sample as it was placed in the high vacuum sample chamber whereas the second form increased at a constant rate during the analysis. The second form of contamination was re- duced during the analysis by employing an air jet which floods the analysis area with a fine s t ream of dried air. Even though the air jet did not eliminate the contamination build up entirely, it reduced the rate of contamination considerably ("30 pct) and increased the peak to background ratio for carbon.

Fig . 2 - - S a m p l e q u e n c h e d f r o m 1400~ 1) f e r r i t e , R c = 22; 2) a u s t e n i t e , B c = 63. N i t a l e t c h p l u s KMnO 4 s t a i n . F i e l d of v iew, 230 • 175 ~ m .

t 7 8 8 - V O L U M E 8A, NOVEMBER t977 METALLURGICAL TRANSACTIONS A

Fig. 3--Sample quenched from 1300"C: 1) austenite + carbide; 2) austenite. Nital etch plus KMnO4 stain. Field of view, 230 • 175 #m.

Fig. 4--Sample quenched from 1272~ 1) au~ctenite + carbide; 2) austenite. Nital etch plus KMnO4 stain. Field of view, 230 x 175 ~m.

The four s a m p l e s a r e ident i f ied on F ig . 1 a s 2, 3, 4, and 5 and t y p i c a l m i c r o s t r u c t u r e s a r e i l l u s t r a t e d in F i g s . 2, 3, 4 and 5, r e s p e c t i v e l y . Two o ther s a m p l e s quenched f rom l l 00~ (F ig . 6) and 900~ (F ig . 7) a r e not shown on F ig . 1 s ince they we re comple t e ly so l id at the t ime of the quench.

F i g u r e 2 i l l u s t r a t e s the t yp i ca l m i c r o s t r u c t u r e for a s a m p l e which was me l t ed , s low cooled to 1400~ and quenched, Within the d e n d r i t i c c o r e r eg ion , t h e r e a r e two m a j o r m i c r o c o n s t i t u e n t s . At the cen t e r of the co re , t h e r e e x i s t s the high t e m p e r a t u r e de l t a f e r r i t e which is the f i r s t cons t i tuen t to f r e e z e f r o m the l iquid. It i s s u r r o u n d e d by an aus t en i t i c phase which f o r m e d f r o m the l iquid upon quenching.

In th i s d i s c u s s i o n and on the p h o t o m i c r o g r a p h s the aus t en i t e which e x i s t e d at the high t e m p e r a t u r e s is l abe l ed as such. Af t e r quenching to r o o m t e m p e r a - tu re the phase had a un i fo rm t ex tu re and g ra in bound- a r y s t r u c t u r e . I t was a l s o v e r y ha rd ind ica t ing i t may have t r a n s f o r m e d to m a r t e n s i t e . I t was not c o n s i d e r e d f e a s i b l e to p e r f o r m X~ray d i f f r ac t ion analysis on these s m a l l r e g i o n s . The phase does not a p p e a r m a r -

t e n s i t i c to the eye . F e r r i t e was s ign i f i can t ly s o f t e r than this p h a s e as d e t e r m i n e d by m i c r o h a r d n e s s t e s t - ing with a 100 g load. The Rockwel l h a r d n e s s r e a d i n g s r e p o r t e d h e r e i n we re conver t ed f r o m the m i c r o h a r d - ne s s r e a d i n g s and a r e used b e c a u s e they a r e m o r e f a m i l i a r .

The next two m i c r o g r a p h s (F ig s . 3 and 4) exhib i t a d a r k e tch ing cons t i tuen t s u r r o u n d e d by the l ight e t c h - ing aus ten i t e , which f o r m s f r o m the p e r i t e c t i c r e a c - t ion in i t i a t ing at 1330~ (L + F ~ A). The d a r k e t ch - ing cons t i tuen t at the cen t e r of the d e n d r i t e is aus t en i t e with a f ine d i s p e r s i o n of c a r b i d e s . T h e s e c a r b i d e s p r e c i p i t a t e b e c a u s e the a l loy r i c h aus t en i t e can no longe r a c c o m m o d a t e a l l the W and Mo lef t by the p r e - ex i s t i ng f e r r i t e .

F i g u r e s 3 and 4 sugges t that the p e r i t e c t i c r e a c t i o n i s d iv ided into two p a r t s . P a r t one of this r e a c t i o n o c c u r s at 1330~ when most of the l iquid s u r r o u n d i n g the d e l t a f e r r i t e t r a n s f o r m s into aus t en i t e . Th i s p a r t of the p e r i t e c t i c r e a c t i o n accounts for the t h e r m a l a r r e s t which is o b s e r v e d d u r i n g the f r e e z i n g p r o c e s s 7 '8 The second p a r t of the r e a c t i o n o c c u r s within the f e r - r i t i c c o r e s at the c e n t e r of the dendr i t e . As the ingot cools , the f e r r i t e t r a n s f o r m s into an aus t en i t e p lus c a r b i d e mic rocons t i t uen t . Since th is r e a c t i o n is diffu- s ion con t ro l l ed , the a l loy r i c h f e r r i t e f i r s t t r a n s f o r m s into a low ca rbon aus t en i t e p lus c a r b i d e a g g r e g a t e . The c a r b i d e s m u s t f o r m to a c c o m m o d a t e the add i - t iona l W and Mo which ex i s t ed in the high t e m p e r a - tu re f e r r i t e . The ca rbon n e c e s s a r y for the aus t en i t e and ca rb ide f o r m a t i o n is ob ta ined by d i f fus ion which o c c u r s at a c c e l e r a t e d r a t e s a t these e l e v a t e d t e m p e r a - t u r e s (1330~ to 1270~

As the so l i d i f i c a t i on p r o c e s s cont inues , the c a r b i d e s d i s s o l v e in the aus ten i t e . Eventua l ly the c a r b i d e phase at the c e n t e r of the dend r i t e comp le t e ly d i s a p p e a r s d u r - ing cool ing unt i l only aus t en i t e of un i fo rm a l loy and c a r b o n content e x i s t s in the c o r e r eg ion . Th i s i s d e m o n s t r a t e d in F ig . 5 whe re the only phase p r e s e n t in the co re r eg ion is the l ight e tch ing aus ten i t e . I t should be e m p h a s i z e d that th is p h o t o m i c r o g r a p h , l ike the o the r s , is t yp ica l of many which we re examined .

The next two p h o t o m i c r o g r a p h s , F i g s . 6 and 7, c h a r - a c t e r i z e the r e a c t i o n s o c c u r r i n g within the dend r i t i c

Fig. 5--Sample quenched from 1255~ 1) austenite, R c = 66. Nital etch plus KMnO4 stain. Field of view, 230 x 175 #zm.

METALLURGICAL TRANSACTIONS A VOLUME 8A, NOVEMBER 1977-1789

core below the solidus t empera tu re . It is evident from the two micrographs that as the samples a r e cooled below the sol idus, fine carb ides p rec ip i ta te f rom the austeni te throughout the dendr i tes and pa r t i cu la r ly at the high energy s i t es provided by the austeni t ic gra in boundar ies .

The cooling ra te p r io r to quenching used for these labora tory specimens (6~ was se lec ted to pro- duce a dendr i t ic a r m spacing s im i l a r to that found for specimens taken about 8 cm or 3 in. f rom the s u r - face of a commerc i a l ingot. The cooling his tory for both the labora tory and commerc i a l spec imens was therefore considered to be essen t ia l ly the same and as shown in F igs . 6, 7 and 8, the mic ros t ruc tu re s of the two a re a lso essen t ia l ly the same. All three pho- tomicrographs display the same va r i e ty of carb ides within the core region; that is, carbides which p r e - cipitate f rom the austenite along the austenite gra in boundaries mud within the grains.

The t rends during the sol idif icat ion p rocess of grade M2 high speed s tee l have t radi t ional ly been compared with the t rends which exis t for grade T1 4 The same genera l reac t ions which occur between the tiquidus and solidus for T 1 also have been observed for M2. However, a big difference between T1 and M2 that this work emphasizes is that in labora tory and commerc ia l ingots of M2 eutectoid decomposit ion by products a r e not observed. In the T1 s tee l , the core region is com- posed a lmost en t i re ly of eutectoid decomposit ion by products which appear cha rac t e r i s t i ca l ly as a heavy concentrat ion of carbides at the dendri te cen te rs , a,l~ In contras t the cores of the M2 grade exhibited only isolated a r eas of heavy carb ides . Instead fine carbides p rec ip i ta te throughout the austeni t ic cores and pa r t i - cular ly at the austenite grain boundaries as shown in F igs . 6, 7 and 8.

Quantitative Microprobe Analys is

The composit ions of the var ious phases which were frozen in during the in ter rupted quenching exper iments were measured with the e lec t ron microprobe . The r e - sul ts a r e given in Table I. The del ta f e r r i t e which is quenched f rom 1400~ (Fig. 2) exhibits, within the

s t a t i s t i ca l var ia t ion of the microprobe data, a zero carbon concentrat ion which is indicative of the C solute re jec t ion which occur red during sol idif icat ion. F igure 9(a) i l l u s t r a t e s the var ia t ion of C concentration f rom austeni te to f e r r i t e to austeni te a c r o s s the cen- t e r por t ion of the dendri te shown in Fig. 2. Since the remain ing major alloy elements (W, Mo, Cr and V) a r e a l l f e r r i t e s t ab i l i ze r s , no solute re jec t ion oc- cu r red and the al loy concentrat ion was observed to be essen t ia l ly constant a c r o s s the core region.

Table I a lso gives the composit ions of the consti tu- ents which form af ter an M2 sample is melted, slow cooled and quenched from 1300~ the s t ruc ture of Fig. 3. The dark etching constituent which is an aus- tenite plus carbide aggregate displays a s l ight ly lower carbon content and an increased alloy content com- pared to the surrounding austeni te which formed di- r ec t ly f rom the liquid at 1330~ The carbon variat ion is probably not significant in that the expected va r i a - tion in the measurement is • wt pct. As shown in the Table the austenite genera l ly contains a l e s s e r amount of the al loying e lements .

Fig. 7--Sample quenched from 900~ 1) austenite + carbide. Arrows illustrate carbides outlining grain boundaries. Nital etch. Field of view, 230 x 175 ~m.

Fig. 6--Sample quenched from 1000~ 1) austenite + carbide. Arrows illustrate carbides outlining grain boundaries. Nital etch. Field of view, 230 • 175 ~m.

Fig. 8--Commercial ingot 3 in. from the edge. Arrows illus- trate carbides outlining grain boundaries. Nital etch plus KMnO4 stain. Field of view, 230 x 175 /~m.

1790-VOLUME 8A, NOVEMBER 1977 METALLURGICAL TRANSACTIONS A

Table I. Compositional Characterization of Selected Solidification Phases in M2 High Speed Steel (Average Composition 0.82 C, 6.11 W, 4.95 Mo, 4.18 Cr, 1.88 V)

Element

Sample Quenched from 1400~ (Fig. 2)

1) Ferrite

Sample Quenched from 1300~ (Fig. 3)

Sample Quenched from 1255~ (Fzg. 5)

2) Austemte I) Austenite + Carbide 2) Austenite l) Austenite

C 0.0 0.70 0,49 0,53 0.62 W 5.4 5.4 6.74 5,62 5,8 Mo 3,7 3.7 4.12 3.67 3.9 Cr 3.8 3.8 3.57 3,67 4.0 V 1.5 1.5 1.98 1,53 1.4

,80

m .60 :3 /

0 .40

.20

0

(a) c

0 2o 4o 60 BO 'iO0 DISTANCE ( M I C R O N S )

.80,

.6O U.I

_J 0 . 4 0 o'1

. 20

0

(b)

C

0 2o 40 60 8o ,0o DISTANCE (MICRONS)

Fig. 9--(a) Carbon composition across dendrite in Fig. 2. (b) Carbon composition across dendrite in Fig. 5.

As the so l i d i f i c a t i on p r o c e s s cont inues , the amount of c a r b i d e s at the c e n t e r of the d e n d r i t e d e c r e a s e s unt i l only a un i fo rm aus t en i t i c co re r e m a i n s . The compos i t i on of the aus t en i t e phase which is quenched f r o m 1255~ F ig . 5, a p p e a r s in the l a s t column of Tab le I. A l l the a l l o y i n g e l e m e n t s and ca rbon were un i fo rm within v e r y n a r r o w l i m i t s a c r o s s the d e n d r i t i c co re . F i g u r e 9(b) i l l u s t r a t e s the ca rbon concen t r a t i on a c r o s s the d e n d r i t e in F ig . 5. T h e s e c h e m i c a l a n a l y s e s and m i c r o s t r u c t u r a l o b s e r v a t i o n s show that the p e r i - t e c t i c r e a c t i o n (L + F ~ A) which beg ins at 1330~ cont inues ove r a r a n g e of t e m p e r a t u r e s and is com-

METALLURGICAL TRANSACTIONS A

p le t ed a t 1255~ l eav ing only aus ten i t e in the co re r e - gion.

The m i c r o p r o b e a n a l y s i s of the aus t en i t e which was quenched f r o m 1255~ i l l u s t r a t e s a v e r y i m p o r t a n t fac t about the s o l i d i f i c a t i o n p r o c e s s of M2. Employ ing coo l - ing r a t e s which a r e s i m i l a r to the r a t e s found in c o m - m e r c i a l ingots , i t i s d i s c o v e r e d that the p e r i t e c t i c r e - ac t ion which begins at 1330~ consumes a l l the f e r - r i t e , The f e r r i t e f i r s t t r a n s f o r m s into an aus t en i t e p lus c a r b i d e a g g r e g a t e . As cool ing cont inues , the c a r - b i d e s s lowly d i s s o l v e , and a t 1255~ the c a r b i d e s a r e d i s s o l v e d c o m p l e t e l y l eav ing a un i fo rm aus t en i t i c phase . Since f e r r i t e is not r e t a i n e d du r ing cool ing, the eu tec to id de c ompos i t i on r e a c t i o n r e p o r t e d by B a r k a l o w 8 in u n i d i r e c t i o n a l l y so l i d i f i ed s p e c i m e n s , which o c c u r s a t t e m p e r a t u r e s be low the so l idus , can not p r o c e e d . Ins tead , c a r b i d e s p r e c i p i t a t e f r o m the aus t en i t e throughout the m a t r i x and p a r t i c u l a r l y a t high ene rgy s i t e s p r o v i d e d by the aus t en i t e g r a i n b o u n d a r i e s .

SUMMARY AND CONCLUSIONS

The phases which form during the solidification of type M2 high speed steel were studied and charac- terized. The first phase to crystallize was the low carbon ferrite, L ~ F. As the freezing process con- tinued, most of the liquid surrounding the ferrite crys- tallized as austenite at 1330~ due to the peritectic re- action, L + F ~ A. The ferrite which exists at the center of the dendrites transformed at around 1330~ into an austenite plus carbide aggregate. The carbides f o r m e d to a c c o m m o d a t e a l l the W and Mo lef t by the p r e e x i s t i n g f e r r i t e . As the f r e e z i n g p r o c e s s con- t inued, the c a r b i d e s at the c e n t e r of the d e n d r i t e s c o m p l e t e l y d i s s o l v e d r e s u l t i n g in a un i fo rm aus t en i t i c phase , As s a m p l e s a r e quenched f r o m t e m p e r a t u r e s below the so l idus , fine c a r b i d e s p r e c i p i t a t e throughout the aus t en i t e with h ighe r concen t r a t ions o b s e r v e d at high ene rgy s i t e s p rov ided by aus t en i t e g r a i n bound- a r i e s . The as cas t m i c r o s t r u c t u r e o b s e r v e d in the c o m m e r c i a l ingot s u g g e s t s that the l a b o r a t o r y and c o m m e r c i a l ingots e x p e r i e n c e the s a m e f r e e z i n g r e - ac t ions .

ACKNOWLEDGMENTS

The au tho r s a r e g ra t e fu l to the A m e r i c a n I ron and S tee l Ins t i tu te who suppo r t ed th is work in a s e r i e s of r e s e a r c h p r o j e c t s on the so l i d i f i ca t i on of M2 tool s t e e l . The au tho r s a l so a r e g ra te fu l to Mr . Douglas Bush who s ign i f i can t ly con t r ibu ted to the m i c r o p r o b e a n a l y s i s .

VOLUME 8A,NOVEMBER 1977-t791

R E F E R E N C E S

1. P. Payson: The Metallurgy of Tool Steels. Wiley, New York, 1931. 2. G. A. Roberts, J. C. Hamaker, Jr., and A. R. Johnson. ToolSteels, Third

Edition. American Society for Metals, Metals Park, 1962. 3. K. Kuo' J. Iron SteelInst., 1955, vol. 181, pp. 128-134. 4. G. Hoyle and E. Ineson: J. Iron Steellnst., 1959, vol. 193, pp. 254-269 5. H. Brandls andK. Wiebking DEW-TechnischeBerichte, 1971,vol. l l , pp.

139-146. 6 E. J. Galda and R. W. Kraft Met. Trans., 1974, vol. 5, pp. 1727-1733. 7. R. H. Barkalow, R. W. Kraft and J. I Goldstem: Met. Trans., 1972, vol. 3,

pp. 919-926.

8. R. H. Barkalow: Sohdification Structures and Phase Relationships in M2 High Speed Steel. Ph.D. Dissertation, Lehigh University, 1971.

9. James Snyder 1I M.S. Thesis, Letugh Unwersaty, 1973. 10. D. J. Blickwede and M. Cohen: Trans. TMS-AIME, 1949, vol. 185, pp.

578-584. 11. F. Kayser and M. Cohen: MetalProgress, June, 1952, pp. 79-85. 12. J. I. Goldstein and P. A Comella: Report No. X-642-69-115, Goddard Space

Flight Center, 1969. 13 B. L. Henke and E S. Eblsu: Advances in X-ray Analysis, vol. 17, p. 150,

Plenum Press, New York, 1974. 14. R. Theisen: QuantttativeElectronMwroprobeAnalysis Berlin, Heidelberg,

New York, 1965. 15. M. A. Grossman and E. C. Bain: High Speed Steel. Wiley, New York, 1931.

1792 -VOLUME 8A, NOVEMBER 1977 METALLURGICAL TRANSACTIONS A