International Welding Engineer (IWE) Module 2: Materials ...mechshop.ir/wp-content/uploads/2016/08/heat-treatment-of-base-materials-and-welded...International Welding Engineer (IWE)

International Welding Engineer (IWE)

Module 2: Materials and Their Behavior During Welding

2.6 – Heat Treatment of Base Materials and Welded Joints

by:

Kamran Khodaparasti

International Welding Engineer | 2.6 - Heat Treatment of Base Materials and Welded Joints | Kamran Khodaparasti | Apr 2009 2

Objective: Understand in detail /name the metallurgical transformations of

materials during different heat treatments.

Scope: • Normalizing

• Hardening

• Quenching and tempering

• Solution annealing

• Homogenizing

• Stress relieving (PWHT)

• Recrystallization annealing

• Precipitation hardening

• Heat treatment procedures

• Heat treatment equipment

• Regulations (codes and technical reports)

• Temperature measurement and recording

2.6 Heat Treatment of Base Materials and Welded Joints

Expected Result

• Explain each of the major heat treatments and their objectives

• Explain the mechanism of structural changes which take place when a

material is heat treated

• Interpret the effects of temperature and time on transformations

including the effect of temperature change rate

• Explain code requirements for heat treatment and why they are

stipulated

• Predict the necessity to perform heat treatment after welding depending

on the type and thickness of steel, the application and the code.

• Deduce appropriate heat treatment equipment for a given application

• Detail appropriate temperature measurement and recording methods for

typical applications


Ask a favor

4 International Welding Engineer | 2.6 - Heat Treatment of Base Materials and Welded Joints | Kamran Khodaparasti | Apr 2009

Definition

• Defined as an operation involving the heating of solid metals to definite temperatures, followed by cooling at suitable rates

• Heat treatment is a very important process in the various fabrication operations

• Heat treatment is done in order to obtain certain physical properties, associated with changes in nature, form, size and distribution of the micro-constituents


1) Heating 2) Holding 3) Cooling

Temp

Time

1

2

3

Objectives

• To achieve one or more of the following:

▫ To relieve internal stresses set up during cold-working, casting, welding

and hot-working operations

▫ To improve machinability

▫ To change grain size

▫ To soften metals for further treatment as wire drawing and cold rolling

▫ To improve mechanical properties

▫ To modify the structure to increase wear, heat and corrosion resistance

▫ To modify magnetic and electrical properties

▫ To remove trapped gases

▫ To remove coring and segregation


The iron–iron carbide phase diagram


L + Fe3C

2.14 4.30

6.70

0.022

0.76

M

N

C

P E

O

G

F

H

Cementite Fe3C

Heat treatment processes

• Depending upon the composition of the parent material, welding process

employed and the associated welding conditions involved various heat

treatment and related processes may take place or may be made to take place

for achieving the desired end product. Some of the well known processes and

treatments amongst them include the following.


Annealing

• Welding may seriously affect the size and the conditions of the grains of which

the material is composed. Depending upon the welding process used, the

grains of the material may grow to large size or they may be distorted due to

the stresses set up during welding and subsequent cooling. Such stresses are

corrected by annealing and the grains refined, so that the material becomes

softer and more ductile, and free from residual stresses.

• For annealing or full annealing a steel weldment is heated to 30 to 50°C

above the upper transformation temperature (A3) which varies with the carbon

content of the steel. It is held at that temperature long enough for the carbon

to distribute itself evenly throughout the austenite. For most practical

purposes it is held at the annealing temperature for 2.5 minute per mm

thickness of material. The steel is then cooled slowly, preferably in a furnace or buried in hot ashes or lime so as to cool at a rate of 55°C/hr or below.

Microstructure of steel obtained with carbon content of 0.83% or less is

normally grains of pearlite and ferrite. A variant of full annealing called

isothermal anneal is sometimes employed.


Annealing

• Welding may seriously affect the size and the conditions of the grains of which

the material is composed. Depending upon the welding process used, the

grains of the material may grow to large size or they may be distorted due to

the stresses set up during welding and subsequent cooling. Such stresses are

corrected by annealing and the grains refined, so that the material becomes

softer and more ductile, and free from residual stresses.

• Anneal means ―to soften‖

• It is often used to soften steel for improved machinability; to improve or

restore ductility for subsequent forming operations; or to eliminate the residual stresses and microstructure effects of cold working

• Several types of annealing processes are used on carbon and low-alloy steel.

These are generally referred to as full annealing, process annealing,

spheroidizing annealing and stress relieving annealing.


Full annealing

• Full annealing is the process of slowly raising the temperature of a steel

weldment about 50 ºC above the Austenitic temperature line A3 or line Acm =

Austenite cementite region

• It is held at that temperature long enough for the carbon to distribute itself

evenly throughout the austenite. For most practical purposes it is held at the

annealing temperature of 1hr/inch thickness of material.

• Cooling is performed slowly at

prescribed rate in a furnace or

insulator or buried in hot ashes

so as to cool at a rate of

55°C/hr or below.

• Result is a Pearlite / Ferrite

structure and steel becomes

soft and ductile


Spheroidizing annealing (spheroidizing)

• Spheroidization annealing process used for high carbon steels (Carbon > 0.6%) that will be softer

• Heat the part to a temperature just below the Ferrite-Austenite line, line A1

or below the Austenite-Cementite line. Essentially below the 727 ºC line. Hold

the temperature for a prolonged time (a number of hours) followed by fairly

slow cooling. Or cycle multiple times between temperatures slightly above

and slightly below the 727 ºC line, say for example between 700 and 750, and

slow cool


Process annealing

• Process Annealing is used to treat work-hardened parts made out of low-

Carbon steels (< 0.25% Carbon). Allows the parts to be soft enough to undergo

further cold working without fracturing. Process annealing is done by raising

the temperature to just below the Ferrite-Austenite region, line A1on the

diagram. This temperature is about 727 ºC so heating it to about 700 ºC. This

is held long enough to allow recrystallization of the ferrite phase, and then

cooled in still air. Since the material stays in the same phase through out the

process, the only change that occurs is the size, shape and distribution of the

grain structure.


Stress relieving annealing (stress relief)(PWHT)

• Stress relieving is carried out after welding to remove or reduce welding

stresses. Total elimination of residual stresses after welding is possible only by

annealing. However, that leads to excessive softening and reduction in

strength therefore stress-relieving is adopted

• Parts are heated to temperatures of up to 600 - 650 ºC and held for an

extended time (about 1 hour or more) and then slowly cooled in still air


recovery and recrystallization(annealing treatment)

• A heat treatment used to negate the effects of cold work, i.e., to soften and

increase the ductility of a previously strain-hardened metal

• Parts are not as completely softened as they are in full annealing, but the

time required is considerably lessened.

• Is frequently used as an intermediate heat-treating step during the

manufacture of a part.

• A part that is stretched considerably during manufacture may be sent to the

annealing oven three or four times before all of the stretching is completed.


Forging Rolling

Alteration of grain structure as a result of plastic deformation


Recovery

• During recovery, some of the stored internal strain energy is relieved by virtue

of dislocation motion, as a result of enhanced atomic diffusion at the elevated

temperature.

• There is some reduction in the number of dislocations, and dislocation

configurations are produced having low strain energies.

• physical properties such as electrical and thermal conductivities and the like

are recovered to their precold-worked states.


Recrystalization

• After recovery is complete, the grains are still in a relatively high strain

energy state.

• Recrystallization is the formation of a new set of strain-free and equiaxed

grains that have low dislocation densities and are characteristic of the

precold-worked condition.

• The driving force to produce this new grain structure is the difference in

internal energy between the strained and unstrained material.


Photomicrographs showing several stages of the recrystallization

and grain growth of brass. (a) Cold-worked (33%CW) grain

structure. (b) Initial stage of recrystallization after heating 3 s

at 580 C ,the very small grains are those that have

recrystallized. (c) Partial replacement of cold-worked grains by

recrystallized ones (4 s at 580 C). (d) Complete recrystallization

(8 s at 580 C )

Cont’d

• During recrystallization, the mechanical properties that were changed as a

result of cold working are restored to their precold-worked values; that is, the

metal becomes softer, weaker, yet… more ductile.

• Recrystallization is a process the

extent of which depends on both

time and temperature.

• The degree (or fraction) of

recrystallization increases with time.


Recrystallization temperature

• Is the temperature at which recrystallization just reaches completion in 1 h.

• it is between one third and one half of the absolute melting temperature of a

metal (Kelvin) or alloy and depends on several factors, including the amount

of prior cold work and the purity of the alloy.

• Increasing the percentage of cold work enhances the rate of recrystallization,

with the result that the recrystallization temperature is lowered.

• Recrystallization proceeds more rapidly in pure metals than in alloys.


0.3Tm 0.7Tm

alloying

Normalizing

• This low carbon and low-alloy steel heat treatment is similar to the annealing

process, except that the steel is allowed to cool in air from temperatures

above the upper critical temperature.

• Normalizing is faster than full annealing and is often used in the welding

industry to refine any coarse grain structure, to reduce stress after welding or

to remove any hard zones in the HAZ. Because of fine-grained structure, the

normalized steel has good toughness properties.

• It leaves the steel harder and with higher tensile strength than after

annealing. Normalizing is often followed by tempering


Summary


Hardening (quenching)

• Hardening is a heat treatment with following cooling at a speed that leads to

increasing the hardness by the formation of martensite.When steels are

heated to produce austenite and then cooled rapidly (quenched), the

austenite transforms into martensite. It has high strength and resistance to

abrasion. Martensitic steels have poor impact strength and are difficult to

machine

• Two types of hardening are distinguished:

1. Normal hardening by the formation of martensite, mainly applied on steels

with medium carbon contents,

2. Case hardening applied on components require a high extent of surface

hardness with a tough core at the same time. Here, the surface layer is

ausenitized. After that it will be quenched. Heating will be carried out by:

• Metal bathes (dip hardening)

• Gas flame (flame hardening)

• High-frequent current (induction hardening)


Quench media

• The severity of quench media: water > oil > air

• When water is used as the quenching medium it is held at 25°C or below and is continuously agitated during the quenching operation to achieve more uniform and faster cooling action. A 5% sodium chloride brine solution provides a more satisfactory cooling medium for carbon steels; it gives faster and more uniform quenching action and is less affected by increase in temperature. A 3 to 5% sodium hydroxide quenching bath is also recommended for carbon steels; it provides even faster cooling rates than sodium chloride bath.

• Oil quenching is resorted to for thin sections of carbon steel and high alloy steels because of less danger of cracking and reduced distortion and quenching stresses. Oil cools steel much more slowly during the last cooling stage. This is desirable as it results in much less danger of severe internal stresses, warping and cracking.

• Air cooling is employed for some high alloy steels of the air hardening type.

• Patenting: Is a special quenching operation that uses molten lead baths for thin cross-sectional parts such as wire


Comparison


Non-uniform cooling rate during quenching

• During the quenching treatment, it is impossible to cool the specimen at a

uniform rate throughout the surface will always cool more rapidly than

interior regions.

• The austenite will transform over a range of temperatures, yielding a possible

variation of microstructure & properties with position within a specimen


Tempering

• Tempering is a secondary heat treatment performed on some normalized and

almost all hardened steel structures. The object of tempering is to remove

some of the brittleness by allowing certain solid-state transformations to

occur. It involves heating to a predetermined level, always below the lower

critical temperature, followed by a controlled rate of cooling. In most cases

tempering reduces the hardness of the steel, increases its toughness, and

eliminates residual stresses. The higher the tempering temperature used for a

given time, the more pronounced is the property change

• The objective of tempering is to reduce the brittleness in hardened steel and

to remove internal strains caused by sudden cooling in the quench.


Stages

• During the tempering process of a hardened steel different processes take place depending on the tempering stage:

• 1st tempering stage up to approx. 150°C - the C-atoms diffuse on interstitial places - the tetragonal distortion decreases depending on temperature and time - precipitation of submicroscopic iron-carbide crystals

• 2nd tempering stage approx. 150°C up to approx. 290°C - change of position of C-atoms in the lattice and transformation of Mtetra into Mcub - precipitation of finest iron carbides - (shearing of residual austenite into cubic martensite)

• 3rd tempering stage approx. 290°C up to approx. 400°C - precipitation of all of the carbon as carbides - the cubic martensite is more and more transformed into the cubic ferrite (free of

carbon)

• 4th tempering stage approx. 400°C up to approx. 723°C - acicular ferrite with embedded carbides - coagulation of the carbides


Embrittlement

• In particular with Cr-, Mn- and Cr-Ni building steels the toughness will be

decreased, if it is tempered at certain temperature ranges. This decrease is shown

in the reduction of the notched bar impact toughness. Due to the range of the loss of toughness of T = 300°C.....350°C this fact is called―300°C-embrittlement‖.

• The cause for the 300°C embrittlement has not been found yet.

• Some steels, in particular Mn-, Cr-, Cr-Mn

and Cr-Ni-steels show a decreased toughness

after slow cooling (e.g. in the furnace) during

tempering. At a fast cooling (air, water) there

will be no embrittlement. Since this embrittlement

takes place at an tempering temperature of

approx. 500°C it is called ―500°C-embrittlement‖.


300°C embrittlement in the tempering

scheme of SAE 4340 40NiCrMo6

Secondary hardness

• In alloy steels which contain certain carbide forming elements such as tungsten, molybdenum, vanadium, etc., tempering after hardening produces precipitated carbides in such finely dispersed form that the hardness is considerably greater than after the original hardening. At the same time, the breakdown of the martensite results in increased toughness. Thus, for example, high speed steel reaches its maximum hardness only after hardening and tempering to about 550°C, by what is known as Secondary Hardening Effect. Steels of this type are also, in consequence, resistant to softening at quite high temperatures and, therefore, are suitable for high temperature service applications.

• For such steels a double tempering treatment is usually adopted, the steel being air-cooled between the two operations. The advantage of double tempering accrues from the fact that, after hardening, the steels normally contain a certain amount of retained (i.e. untransformed) austenite, which transforms to martensite, wholly or in part, after the first tempering treatment. The second tempering treatment breaks down this newly formed martensite and brings about additional secondary hardening. Besides increasing the hardness, this practically eliminates the presence of untempered martensite.


Martempering (step hardening)

• Martempering is carried out by cooling the steel from the hardening

temperature through the pearlite range to a temperature at or a little above the Ms temperature (205-260°C), holding at this temperature until the

temperature of steel is uniform throughout and finally air cooling through the

martensite range.

• The aim of martempering is to avoid the risk of cracking due to the thermal

stresses set up during rapid cooling from high temperatures. This also makes it

possible to cool slowly through the martensite range, thus minimising the

additional stresses set up as a result of the volume change which accompanies

the transformation of austenite to martensite thereby constituting a risk of

cracking.


Austempering

• If steel from hardening temperature is supercooled quickly to about 290°C, austenite at this temperature transforms to a fine pearlitic or bainite structure of uniform hardness of about 56HRC. It requires the holding of austenite at 290°C for about one hour to complete this change. This method of tempering without the formation of martensite is called austempering i.e., the direct tempering of austenite.

• It is accepted that the hardness of 56HRC

obtained by austempering is much tougher

than the same steel treated to the same

hardness by the usual method of quench

hardening and tempering. Also, non formation

of martensite eliminates much of the danger of

cracking, and reduces the amount of distortion

or warping caused by rapid quenching to room

temperature required for the formation of

martensite in normal quench hardening process.

• Limitations for plain carbon steels:

- relatively thin sections (i.e. 3/8‖ max)


Case hardening

• If low-carbon steel is used and toughness is need in the workpiece, its surface cannot be significantly hardened. Therefore a process to add carbon or nitrogen to the surface is done.

▫ Done by carburizing, nitriding, carbonitriding or cyaniding

▫ These elements diffuses into the outer layers of the steel to increase hardness.

▫ The steel surface can then be hardened by QUENCHING.

▫ After processing the carbon concentration of mild steel can go from 0.1% to 1.2%

▫ Can take from 1 to 20 hrs to complete and can be at a thickness ranging from 0.1 to 0.25 inches depending on the process, desired case thickness, and the metal

• Carburizing(cementation)

• Nitriding

• Carbonitriding (carbon and nitrogen obtained from a special gas atmosphere)

• Cyaniding (carbon and nitrogen obtained from a bath of liquid cyanide

solution)


Surface hardening

• If steel is hardened all the way through the part, it will be brittle. In parts

that have wearing surfaces such as gear teeth, shafts, lathe beds, and cams,

only the surface of the part should be hardened so as to leave the inside soft

and ductile.

▫ Flame hardening is widely used in deep hardening for large substrates.

▫ Induction hardening is suitable for small parts in production lines.

These processes are applicable only to steels that have sufficient carbon and

alloy content to allow quench hardening.


Outline of heat treatment processes for surface hardening


Process Metals hardened Element added to

surface

Procedure General Characteristics Typical applications

Carburizing Low-carbon steel

(0.2% C), alloy

steels (0.08–0.2%

C)

C Heat steel at 870–950 °C (1600–1750

°F) in an atmosphere of carbonaceous

gases (gas carburizing) or carbon-

containing solids

(pack carburizing). Then quench.

A hard, high-carbon surface is

produced. Hardness 55 to 65

HRC. Case depth < 0.5–1.5 mm

( < 0.020 to 0.060 in.). Some

distortion of part during heat

treatment.

Gears, cams, shafts,

bearings, piston pins,

sprockets, clutch plates

Carbonitriding Low-carbon steel C and N Heat steel at 700–800 °C (1300–1600

°F) in an atmosphere of carbonaceous

gas and ammonia. Then quench in oil.

Surface hardness 55 to 62 HRC.

Case depth 0.07 to 0.5 mm

(0.003 to 0.020 in.). Less

distortion than in

carburizing.

Bolts, nuts, gears

Cyaniding Low-carbon steel

(0.2% C), alloy

steels (0.08–0.2%

C)

C and N Heat steel at 760–845 °C (1400–1550

°F) in a molten bath of solutions of

cyanide (e.g., 30% sodium cyanide) and

other salts.

Surface hardness up to 65 HRC.

Case depth 0.025 to 0.25 mm

(0.001 to 0.010 in.). Some

distortion.

Bolts, nuts, screws, small

gears

Nitriding Steels (1% Al,

1.5% Cr, 0.3%

Mo), alloy steels

(Cr, Mo), stainless

steels, high-speed

tool steels

N Heat steel at 500–600 °C (925–1100 °F)

in an atmosphere of ammonia gas or

mixtures of molten cyanide salts. No

further treatment.

Surface hardness up to 1100

HV. Case depth 0.1 to 0.6 mm

(0.005 to 0.030 in.) and 0.02 to

0.07 mm (0.001

to 0.003 in.) for high speed

steel.

Gears, shafts, sprockets,

valves, cutters, boring

bars, fuel-injection pump

parts

Boronizing Steels B Part is heated using boron-containing

gas or solid in contact with part.

Extremely hard and wear

resistant surface. Case depth

0.025– 0.075 mm (0.001–

0.003 in.).

Tool and die steels

Flame hardening Medium-carbon

steels, cast irons

None Surface is heated with an oxyacetylene

torch, then quenched with water spray or

other quenching methods.

Surface hardness 50 to 60 HRC.

Case depth 0.7 to 6 mm (0.030

to 0.25 in.). Little distortion.

Gear and sprocket teeth,

axles, crankshafts, piston

rods, lathe beds and

centers

Induction

hardening

Same as above None Metal part is placed in copper induction

coils and is heated by high frequency

current, then quenched.

Same as above Same as above

Hardenability

• Hardenability: The ease with which full hardness can be achieved throughout

the material.

• The Jominy end-quench test : to measure hardenability

• ASTM Standard A 255, ―Standard Test Method for End-Quench Test for

Hardenability of Steel.‖


Hardenability curves

• A steel that is highly hardenable will retain large hardness values for relatively

long distances; a low hardenable one will not.


Why hardness changes with distance?


Effect of carbon content on hardenability

• The hardenability increases with the carbon content.


Alloying elements and hardenability

• The alloying element content and carbon content change the shapes of the

hardenability curve

• The principal reason for using alloying elements in the standard grades of

steels is to increase hardenability.

▫ Different alloys, which have the same

amount of carbon content, will achieve

the same amount of maximum hardness;

however, the depth of full hardness will

vary with the different alloys.

• The reason to alloy steels is not to

increase their strength, but increase

their hardenability


(plain carbon steel)

(0.85 Cr)

(0.55 Ni, 0.50 Cr, & 0.20 Mo)

(1.0 Cr & 0.20 Mo)

(1.85 Ni, 0.80 Cr, & 0.25Mo)

Precipitation hardening(age hardening)

• Small inclusions or secondary phases strengthen material

• Lattice distortions around these secondary phases limit dislocation

motion

• The precipitates form when the solubility limit is exceeded

• Precipitation hardening is also called age hardening because it involves

the hardening of the material over a prolonged time.

• Examples of alloys that are hardened by precipitation treatments include

aluminum–copper, copper–beryllium, copper–tin, and magnesium–

aluminum; some ferrous alloys are also precipitation hardenable.


Cont’d

• Solution heat treatment:

at To, all the solute atoms A are dissolved to form a single-phase (α) solution.

• Rapid cooling

across the solvus line to exceed the solubility limit. This leads to a metastable

supersaturated solid solution at T1. Equilibrium structure is α+β, but limited

diffusion does not allow β to form.

• Precipitation heat treatment:

the supersaturated solution is heated to T2 where diffusion is appreciable – β

phase starts to form as finely dispersed particles: aging.


Precipitation hardening

• Precipitations result, if the solubility of one or more components in a solid solution is reduced depending on the temperature

• Second phase particle can limit the movement of dislocation

• In Al-4%Cu, by rapid cooling we have supersaturated solution that after specific time, particles of CuAl2 are achieved

• This is aging process, by heating the specimen at 100-150°C, the aging can be accelerated

43

In HSLA steel, V and Nb are used for

strengthening by precipitating

International Welding Engineer | 2.6 - Heat Treatment of Base Materials and Welded Joints | Kamran Khodaparasti | Apr 2009

Microstructure of Copper-Beryllium before and after

Precipitation Hardening


(a) Solution heat-treated (b) Precipitation hardened

(x 750)

Overaging in precipitation hardening

• If precipitation treatment is continued for too long, the local aggregation of

atoms results in the formation of separate particles with a crystal structure

differing from the matrix. The local strain in the crystals is thereby relieved

and the hardness of the alloy is decreased and it is said to be overaged. For a

given alloy, the higher the precipitation treatment temperature the sooner the

optimum

• conditions are reached.


Welding of age-hardened aluminium alloys

results in a softened zone alongside the

weld due to the overageing effect

Artificial aging and natural aging

• Artificial aging ▫ Aging at some temperature higher than room temperature

• Natural aging ▫ Some solution-treated and quenched alloys age at room temperature

▫ Natural aging requires long times — about 4 days— to reach maximum strength.

▫ The peak strength is higher than that obtained in artificial aging and there is no

overaging.

▫ Duralumin (AI+4%Cu) is a typical natural ageing alloy

▫ Amongst steels mild steel is the most susceptible to aging. If nitrogen is present in steel, iron nitride can be precipitated at temperatures below AI' Precipitation of iron nitrides (FeI6N2)at room temperature is known as Steel Ageing. Ageing can take place in a zone heated to temperatures around 200-300°C if free nitrogen is present in steel. New metallurgical procedures have helped in lowering the nitrogen content in steel, or binding it to a stable nitride phase (e.g. AIN), and consequently present-day steels are generally not susceptible to ageing.


Typical precipitation hardened alloys

• Al ▫ 2014 Forged Aircraft Fittings, Al Structures ▫ 2024 High strength forgings, Rivets ▫ 7075 Aircraft Structures, Olympic Bikes

• Cu

▫ Beryllium Bronze: Surgical Instruments, Non sparking tools, Gears

• Mg ▫ AM 100A Sand Castings ▫ AZ80A Extruded products

• Ni

▫ Rene' 41 High Temperature

▫ Inconel 700 up to 1800F

• Fe ▫ A-286 High Strength Stainless ▫ 17-10P


Tips

• Precipitation hardening in the first aerospace aluminum alloy: The Wright

Flyer Crankcase

• An aluminum copper alloy (with a Cu composition of 8 wt%) was used in the

engine that powered the historic first flight of the Wright brothers in 1903.


Tips(cont’d)

• Two different size of the precipitate particles (10-22 nm vs. 3 nm) were

observed using transmission electron microscopy.

▫ The original alloy had undergone precipitation hardening (10-22 nm) as a result of being held in the casting mold for a period of time and at a temperature that was sufficient to cause precipitation hardening.

▫ Since when the alloy was developed in 1903 until about 1993 (almost 90 years), the alloy had continued to age naturally (3 nm).

• Two types aging involved in the precipitation hardening for this case:

▫ Artificial aging from the original casting practice

▫ Natural aging over the last 90 years

• The use of a precipitation-hardened alloy in the first aerospace application

occurred 16 years before the theory of precipitation hardening was proposed


Summary


Heating equipment

• Gas torch with or without air


Heating equipment(cont’d)

• Furnaces


electric furnace

muffle furnace tube furnace

Salt bath furnace Oil/gas fired furnace

Heat treatment equipment

• Other equipment


crucible tongs

heat resistant gloves

eye protection devices

Heat treatment equipment(cont’d

• Temperature measuring devices


thermocouple

optical pyrometer

Seger cones

A pyramid with a triangular base and of a defined shape

and size; the "cone" is shaped from a carefully

proportioned and uniformly mixed batch of ceramic

materials so that when it is heated under stated

conditions, it will bend due to softening, the tip of the

cone becoming level with the base of a definitive

temperature. Pyrometric cones are made in series, the

temperature interval between the successive cones

usually being 20 degrees Celsius. The best known series

are Seger Cones (Germany), Orton Cones (USA) and

Staffordshire Cones (UK)'.

Seger cones was developed by the German ceramics

technologist Hermann Seger and first used to control

the firing of porcelain wares in Berlin, in 1886. Seger

cones are to this day made by a small number of

companies.

Tips

• Tempering temp colors


Documents

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