1- Heat Treatment

7/29/2019 1- Heat Treatment

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HEAT TREATMENT


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The Fe-C diagram in Fig. 1 is of experimental origin.

The knowledge of the thermodynamic principles and modern

thermodynamic data now permits very accurate calculations of

this diagram.

If alloying elements are added to the iron-carbon alloy (steel),

the position of the A1, A3, and Acm boundaries and the

eutectoid composition are changed

(1) all important alloying elements decrease the eutectoidcarbon content, (2) the austenite-stabilizing elements

manganese and nickel decrease A1

(3) the ferrite-stabilizing elements chromium, silicon,

molybdenum, and tungsten increase A1.


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Table 1 Important metallurgical phases and microconstituents

CharacteristicsCrystal structure of phases

Phase

(microc

onstitu

ent)

Relatively soft low-temperature phase; stable equilibrium phasebccFerrite (-iron)

Isomorphous with -iron; high-temperature phase; stable equilibrium phasebcc-ferrite (-

iron)

Relatively soft medium-temperature phase; stable equilibrium phasefccAustenite (-

iron)

Hard metastable phaseComplex orthorhombicCementite

(Fe3C)

Stable equilibrium phaseHexagonalGraphite

Metastable microconstituent; lamellar mixture of ferrite and cementitePearlite

Hard metastable phase; lath morphology when 1.0 wt% C and mixture of those in

between

bct (supersaturated solution

of carbon in ferrite)

Martensite

Hard metastable microconstituent; nonlamellar mixture of ferrite and cementite on an extremely fine scale; upper bainite

formed at higher temperatures has a feathery appearance; lower bainite formed at lower temperatures has an

acicular appearance. The hardness of bainite increases with decreasing temperature of formation.

. . .Bainite


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Accm. In hypereutectoid steel, the temperature at which the solution of cementite in austenite is

completed during heating.

Ac1. The temperature at which austenite begins to form during heating, with the c being derived fromthe French chauffant.

Ac3. The temperature at which transformation of ferrite to austenite is completed during heating.

Aecm, Ae1, Ae3. The temperatures of phase changes at equilibrium.

Arcm. In hypereutectoid steel, the temperature at which precipitation of cementite starts during

cooling, with the r being derived from the French refroidissant.

Ar1. The temperature at which transformation of austenite to ferrite or to ferrite plus cementite is

completed during cooling.

Ar3. The temperature at which austenite begins to transform to ferrite during cooling.

Ar4. The temperature at which delta ferrite transforms to austenite during cooling.

Ms(or Ar''). The temperature at which transformation of austenite to martensite starts duringcooling.

Mf. The temperature at which martensite formation finishes during cooling.


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One can conveniently describe what is happening during

transformation with transformation diagrams. Four differenttypes of such diagrams can be distinguished. These include:

Isothermal transformation diagrams describing the

formation of austenite, which will be referred to as

IT diagrams

Isothermal transformation (IT) diagrams, also referred to

as time-temperature-transformation (TTT)

diagrams, describing the decomposition of austenite

Continuous heating transformation (CHT) diagrams

Continuous cooling transformation (CCT) diagrams


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ITh Diagrams (Formation of Austenite).

During the formation of austenite from anoriginal microstructure of ferrite and pearlite or

tempered martensite, the volume (and hence the

length) decreases with the formation of the

dense austenite phase (see Fig. 3). From the

elongation curves, the start and finish times for

austenite formation, usually defined as 1% and

99% transformation, respectively, can bederived.


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Fig. 3 The procedure for determining isothermal heating (ITh)

diagrams. Line 1: Temperature versus time. Line 2: Elongation versus

time. S represents the start and F the finish of the transformation of theoriginal microstructure to austenite transformation, respectively.


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(Fig. 4). Below Ac1 no austenite can form, and between Ac1 and Ac3

the end product is a mixture of ferrite and austenite.


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Volume change, %(a)Transformation

4.64-2.21 (%C)Spheroidized pearlite-austenite

4.64-0.53 (%C)Austenite-martensite

4.64-1.43 (%C)Austenite-lower bainite

4.64-2.21 (%C)Austenite-upper bainite

Volume changes due to different transformations


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Hardenability Concepts The goal of heat treatment of

steel is very often to attain asatisfactory hardness. Theimportant microstructural

phase is then normallymartensite

The hardness of martensite isprimarily dependent on itscarbon content as is shown inFig

In practical heat treatment, itis important to achieve fullhardness to a certainminimum depth after cooling,that is, to obtain a fullymartensitic microstructure to acertain minimum depth, which

also represents a criticalcooling rate.

CCT diagrams constructedaccording to Atkins orThelning can serve thispurpose if one knows the

cooling rate at the minimumdepth

S f l h d i ll hi i th


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Successful hardening usually means achieving therequired microstructure, hardness, strength, ortoughness while minimizing residual stress, distortion,and the possibility of cracking.

The selection of a quenchant medium depends on thehardenability of the particular alloy, the section thicknessand shape involved, and the cooling rates needed toachieve the desired microstructure. The most commonquenchant media are either liquids or gases.

The liquid quenchants commonly used include:

Oil that may contain a variety of additives Water

Aqueous polymer solutions

Water that may contain salt or caustic additives

The most common gaseous quenchants are inert gasesincluding helium, argon, and nitrogen. These quenchantsare sometimes used after austenitizing in a vacuum.


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Jominy End-Quench Test.

The most commonly used experimental method forhardenability is the well-known Jominy test

For this test a round bar specimen that is 100 mm (4 in.)in length and 25 mm (1 in.) in diameter is used. The

specimen is heated to the austenitizing temperature ofthe steel with a holding time of 20 min. One end face ofthe specimen is quenched by spraying it with a jet ofwater. This causes the rate of cooling to decreaseprogressively from the quenched end along the length of

the bar. The hardness values are plotted on a diagram at

specified intervals from the quenched end.


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Fig. Calculated hardness (dashed line) and reported hardness (solid

line) from a Jominy test of AISI 4130 steel.


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Principles of Tempering of Steels

Martensite is a very hard phase in steel. It owe its high

hardness to a strong supersaturation of carbon in the iron

lattice and to a high density of crystal defects, especiallydislocations, and high- and low-angle boundaries. However,except at low carbon contents, martensitic steels haveinsufficient toughness for many applications.

Tempering of martensitic steels, by heating for a certain timeat temperatures below the A1, is therefore introduced to

exchange some of the strength for greater ductility throughreduction of the carbon super saturation initially present andreplacing it with more stable structures. Additionally, theretained austenite associated with martensite in steelscontaining more than about 0.7 wt% C can be decomposedduring the tempering process. In carbon steels containing

small percentages of the common alloying elements, onedistinguishes the following stages during tempering

In steels alloyed with chromium, molybdenum, vanadium, ortungsten, formation of alloy carbides occurs in the temperaturerange 500 to 700 C During stage 1, the hardness increases slightlywhile during stage 2, 3, and 4 the hardness decreases.


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TEMPERING OF STEEL

is a process in which previously hardened or normalized steel isusually heated to a temperature below the lower critical temperatureand cooled at a suitable rate, primarily to increase ductility andtoughness, but also to increase the grain size of the matrix. Steelsare tempered by reheating after hardening to obtain specific valuesof mechanical properties and also to relieve quenching stresses andto ensure dimensional stability.

Tempering usually follows quenching from above the upper critical

temperature; however, tempering is also used to relieve the stressesand reduce the hardness developed during welding and to relievestresses induced by forming and

machining.

Principal Variables

Variables associated with tempering that affect the microstructure

and the mechanical properties of a tempered steel include: Tempering temperature

Time at temperature

Cooling rate from the tempering temperature

Composition of the steel, including carbon content, alloy content,

and residual elements


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Fig. Tempering curves for some current steels. The steel 42CrMo4is equivalent to AISI 4142 and C45 to AISI 1045.


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Temper embrittlement The toughness of a steel increases with decreasing hardness.

However, when certain impurities such as arsenic, phosphorus,antimony, and tin are present, a toughness minimum "temperembrittlement" may occur in the temperature range 350 to 600C due to segregation of impurities to grain boundaries.

Temper embrittlement is a problem when parts are exposed totemperatures in the critical range for rather long times and is aconcern for parts exposed to these temperatures while inservice or when heat treating very massive parts which requirelong times to heat and cool.

It is not a concern, even for susceptible alloys, if small partsare exposed to these temperatures for an hour or so duringheat treatment, then used at ambient temperatures. Nuts andbolts, for example, made of various types of steels, are

tempered in this temperature range with no problems as longas they are used at lower temperatures. The time forembrittlement to occur at differing tempering temperaturesshows a C-shaped curve behavior

. Temper embrittlement can be removed by reheating the steelabove 600 C (1110 F) followed by rapid cooling, for example,

water quenching.


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Martensite embrittlement

Another type of embrittlement that affects high-strength alloysteels is tempered martensite embrittlement (also known as 350C, or 500 F, embrittlement), which occurs upon tempering inthe range of 205 to 370 C (400 to 700 F). It differs from temperembrittlement in the strength of the material and thetemperature exposure range. In temper embrittlement, the steel

is usually tempered at a relatively high temperature, producinglower strength and hardness, and embrittlement occurs uponslow cooling after tempering and during service attemperatures within the embrittlement range. In temperedmartensite embrittlement, the steel is tempered within theembrittlement range, and service exposure is usually at room

temperature. Therefore, temper embrittlement is often calledtwo-step temper embrittlement, while tempered martensiteembrittlement is often called one-step temper embrittlement


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MARTEMPERING

is a term used to describe an interrupted quench from theaustenitizing temperature of certain alloy, cast, tool, and stainless

steels. The purpose is to delay the cooling just above the martensitictransformation for a length of time to equalize the temperaturethroughout the piece. This will minimize the distortion, cracking, andresidual stress. The term martempering is somewhat misleading andis better described as marquenching. The microstructure aftermartempering is essentially primary martensitic that is untemperedand brittle.

Figure 1(a and b) shows the significant difference betweenconventional quenching and martempering. Martempering of steel(and of cast iron) consists of:

Quenching from the austenitizing temperature into a hot fluidmedium (hot oil, molten salt, molten metal, or a fluidized particlebed) at a temperature usually above the martensite range (Ms point)

Holding in the quenching medium until the temperature throughoutthe steel is substantially uniform

Cooling (usually in air) at a moderate rate to prevent largedifferences in temperature between the outside and the

center of the section


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Time temperature transformation diagrams with superimposed cooling

curves showing quenching and tempering.(a) Conventional process. (b) Martempering. (c) Modified martempering

The advantage of martempering lies in the reduced thermal gradientbetween surface and center as the part is quenched to

the isothermal temperature and then is air cooled to room temperature.


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Thermal Stresses during and Residual Stresses after

Heat Treatment

Heat treatment of steel, is usually accompanied by thelarge residual stresses, that is, stresses that existwithout any external load on the part considered.Causes for such stresses include:

1. Thermal expansion or contraction of a homogeneousmaterial in a temperature gradient field

2. Different thermal expansion coefficients of the variousphases in a multiphase material

3. Density changes due to phase transformations in themetal

4. Growth stresses of reaction products formed on thesurface or as precipitates, for example, external andinternal oxidation


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Cracking and Distortion due to Hardening.

Hardening is usually accompanied by distortion of a

workpiece. The degree of distortion depends on the

magnitude of the residual stresses.

Hardening procedures that minimize transient and residual

stresses are beneficial as well as the use of

fixtures (press hardening). Distortion can also occur during

tempering or annealing due to release of residual stresses or

phase transformations during tempering as describedpreviously

There is a risk for cracking of a workpiece if large tensile

stresses, transient or residual, are combined with the

presence of a brittle microstructure (particularly martensite).

Thermal stresses during cooling generally increase with thesize of a workpiece.


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Formation of residual stress on cooling considering thermal expansion and the austenite to

martensite transformation. The dashed line is the yield stress, s, at the surface.


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HARDENABILITY STEELS

H-steels, offer a wide range of mechanical properties thatdepend on the development of tempered martensite afterquenching and tempering. Typical room-temperatureproperties of quenched and tempered steels can vary as

follows: Hardness values of 130 to 700 HV (30 kgf load)

Tensile strengths of 400 to 2000 MPa (58 to 290 ksi)

Yield strengths of 300 to 1800 MPa (43 to 261 ksi)

Elongation of 8 to 28% in 50 mm (2 in.)


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Rockwell C hardness (HRC) with martensite contents of:Carbon, %

99.9%95%90%80%50%

433937.535310.18

464240.537.5340.23

4944.54340.536.50.28

5248.546.543.5390.33

54514946420.38

5753.55148440.43

6057545246.50.48


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Relationship between IT, CCT, and Jominy Curves

Relationship of CCT

(heavy lines) and IT

(light lines) diagrams of

eutectoid steel. Fourcooling rates from

different positions on a

Jominy end-quench

specimen are

superimposed on the

CCT diagram


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Comparison of IT

diagram for steel

with German

designation 42

CrMo 4 (0.38% C,

0.99% Cr, and

0.16% Mo)

determined by

dilatometry


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Stress-Relief Heat Treating of Steel

STRESS-RELIEF HEAT TREATINGis used torelieve stresses that remain locked in a structure as aconsequence of a manufacturing sequence.

This definition separates stress-relief heat treating from

post weld heat treating in that the goal of post weld heat

treating is to provide, in addition to the relief of residualstresses, some preferred metallurgical structure or

properties For example, most ferritic weldments are

given postweld heat treatment to improve the fracture

toughness of the heat-affected zones (HAZ). Moreover,austenitic and nonferrous alloys are commonly postweld

heat treated to improve resistance to environmental

damage.


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Stress-relief heat treating is the uniform heating of astructure, or portion, to a suitable temperature below thetransformation range (Ac1 for ferritic steels), holding atthis temperature for a predetermined period of time,followed by uniform cooling. Care must be taken toensure uniform cooling, particularly when a component iscomposed of variable section sizes. If the rate of coolingis not constant and uniform, new residual stresses canresult that are equal to or greater than those that the

heat-treating process was intended to relieve. Stress-relief heat treating can reduce distortion and high

stresses from welding that can affect serviceperformance. The presence of residual stresses can leadto stress-corrosion cracking (SCC) near welds and in

regions of a component that has been cold strainedduring processing.

Residual stresses in a ferritic steel cause significantreduction in resistance to brittle fracture


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Sources of Residual Stress Bending a bar during fabrication at a temperature where recovery

cannot occur (cold forming, for example) will result in one surface

location containing residual tensile stresses, whereas a location180 away will contain residual compressive

Quenchingof thick sections results in high residual compressivestresses on the surface of the material. These high compressivestresses are balanced by residual tensile stresses in the internalareas of the section

Grinding is another source of residual stresses; these can becompressive or tensile in nature, depending on the grindingoperation. Although these stresses tend to be shallow in depth, theycan cause warping of thin parts

Welding. The cause of residual stresses that has received the mostattention in the open literature is welding. The residual stressesassociated with the steep thermal gradient of welding can occur on amacroscale over relatively long distances (reaction stresses) or canbe highly localized (microscale) (Fig.). Welding usually results inlocalized residual stresses that approach levels equal to or greaterthan the yield strength of the material at room temperature.


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Examples of the causes of residual stresses:

(a) Thermal distortion in a structure due to heating by solar radiation.(b) Residual stresses due to welding. (c) Residual stresses due to grinding.


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Relationship between time and temperature in the relief of

residual stresses in steel.


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Typical stress-relief temperatures for low-alloy

ferritic steels are between 595 and 675 C (1100 and 1250 F).

For high-alloy steels, these temperatures may range from 900 to1065 C (1650 to 1950 F).

For high-alloy steels, such as the austenitic stainless steels,stress relieving is sometimes done at temperatures as low as400 C (750 F). However, at these temperatures, only modestdecreases in residual stress are achieved.

Residual stresses can be significantly reduced by stress-relief

heat treating those austenitic materials in the temperature rangefrom 480 to 925 C (900 to 1700 F). At the higher end of thisrange, nearly 85% of the residual stresses may be relieved.Stress-relief heat treating in this range, however, may result insensitizing susceptible material. This metallurgical effect canlead to

SCC in service. Frequently, solution-annealing temperatures ofabout 1065 C (1950 F) are used to achieve a reduction ofresidual stresses to acceptably low values.

NORMALIZING OF STEEL


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NORMALIZING OF STEEL

NORMALIZING OF STEEL is a heat-

treating process that is often

considered from both thermal and

microstructural standpoints.

Normalizing is an austenitizing heatingcycle followed by cooling in still or

slightly agitated air.

Typically, the work is heated to a

temperature about 55 C (100 F) above

the upper critical line of the iron-iron

carbide phase diagram, as shown inFig. that is, above Ac3 for

hypoeutectoid steels and above Acm

for hypereutectoid steels. To be

properly classed as a normalizing

treatment, the heating portion of the

process must produce a homogeneous

austenitic phase (face-centered cubic,

or fcc, crystal structure) prior to

cooling.

Typical normalizing temperatures for

many standard steels are given in

Table 1.

Table 1 Typical normalizing temperatures for standard carbon and alloy steels


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Grade Temperature(a) Grade Temperature(a) Grade Temperature(a) Grade Temperature(a)

C F C F C F C F

Plain carbon steels 1090 830 1525 3310 925 1700 4140 870 1600

1015 915 1675 1095 845 1550 4027 900 1650 4142 870 1600

1020 915 1675 1117 900 1650 4028 900 1650 4145 870 1600

1022 915 1675 1137 885 1625 4032 900 1650 4147 870 1600

1025 900 1650 1141 860 1575 4037 870 1600 4150 870 1600

1030 900 1650 1144 860 1575 4042 870 1600 4320 925 1700

1035 885 1625 Standard alloy steels 4047 870 1600 4337 870 1600

1040 860 1575 1330 900 1650 4063 870 1600 4340 870 1600

1045 860 1575 1335 870 1600 4118 925 1700 4520 925 1700

1050 860 1575 1340 870 1600 4130 900 1650 4620 925 1700

1060 830 1525 3135 870 1600 4135 870 1600 4621 925 1700

1080 830 1525 3140 870 1600 4137 870 1600 4718 925 1700

Grade Temperature(a) Grade Temperature(a) Grade Temperature(a) Grade Temperature(a)


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C F C F C F C F

4720 925 1700 5155 870 1600 8642 870 1600 9840 870 1600

4815 925 1700 5160 870 1600 8645 870 1600 9850 870 1600

4817 925 1700 6118 925 1700 8650 870 1600 50B40 870 1600

4820 925 1700 6120 925 1700 8655 870 1600 50B44 870 1600

5046 870 1600 6150 900 1650 8660 870 1600 50B46 870 1600

5120 925 1700 8617 925 1700 8720 925 1700 50B50 870 1600

5130 900 1650 8620 925 1700 8740 925 1700 60B60 870 1600

5132 900 1650 8622 925 1700 8742 870 1600 81B45 870 1600

5135 870 1600 8625 900 1650 8822 925 1700 86B45 870 1600

5140 870 1600 8627 900 1650 9255 900 1650 94B15 925 1700

5145 870 1600 8630 900 1650 9260 900 1650 94B17 925 1700

5147 870 1600 8637 870 1600 9262 900 1650 94B30 900 1650

5150 870 1600 8640 870 1600 9310 925 1700 94B40 900 1650


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Comparison of time-temperature cycles for normalizing and fullannealing. The slower cooling of annealing results in higher

temperature transformation to ferrite and pearlite and coarser

microstructures than does normalizing.


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Applications of Normalizing Based on Steel Classification

All of the standard low-carbon, medium-carbon,

and high-carbon wrought steels can benormalized, as well as many castings. Many

steel weldments are normalized to refine the

structure within the weld-affected area.

Austenitic steels, stainless steels, and maraging

steels either cannot be normalized or are not

usually normalized. Tool steels are generally

annealed by the steel supplier.

The purpose of normalizing varies considerably


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Normalization may increase or decrease thestrength and hardness of a given steel in a

given product form, depending on the thermaland mechanical history of the product.Actually, the functions of normalizing mayoverlap with or be confused with those of

annealing, hardening, and stress relieving. Improved machinability, grain refinement,

homogenization, and modification of residualstresses are among the reasons normalizing is

done.

The purpose of normalizing varies considerably


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Part Steel Heat treatment Properties after treatment Reason for normalizing

Cast 50 mm (2 in.) Ni-

Full annealed at 955 C

(1750 Tensile strength, 620 MPa (90 ksi); To meet mechanical-

valve body, 19 to 25 Cr- F), normalized at 870 C 0.2% yield strength, 415 MPa (60 property requirements

mm ( 3 4 to 1 in.)in

Mo (1600 F), tempered at 665

C (1225 F)

ksi); elongation in 50 mm, or 2 in.,

20%; reduction in area, 40%

section thickness

Forged flange 4137 Normalized at 870 C (1600 Hardness, 200 to 225 HB To refine grain size andF), tempered at 570 C

(1060

obtain required hardness

F)

Valve-bonnet forging 4140 Normalized at 870 C (1600 Hardness, 220 to 240 HB To obtain uniform

F) and tempered structure, improved

machinability, and

requiredhardness

Typical applications of normalizing and tempering of steel components

Annealing of Steel


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Annealing of Steel

ANNEALING is a generic term denoting a treatment that consists of

heating and holding at a suitable temperature followed by cooling at

an appropriate rate, primarily for the softening of metallic materials.

Generally, in plain carbon steels, annealing produces a ferrite-pearlite

microstructure. Steels may be annealed to facilitate cold working or

machining, to improve mechanical or electrical properties, or to

promote dimensional stability.

The following equations will give an approximate critical temperaturefor a hypoeutectoid steel

Ac1(C) = 723 - 20.7(% Mn) - 16.9(%Ni) + 9.1(%Si) - 16.9(%Cr)

Standard deviation = 11.5 CAc3(C) = 910 - 203 %C - 15.2(% Ni) + 44.7(% Si) + 104(% V) +

31.5(% Mo)

Standard deviation = 16.7 C


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Annealing Cycles

In practice, specific thermal cycles of an almost infinite

variety are used to achieve the various goals ofannealing. These cycles fall into several broad

categories that can be classified according to the

temperature to which the steel is heated and the method

of cooling used.

The maximum temperature may be below the lower

critical temperature, A1 (subcritical annealing);

above A1 but below the upper critical temperature, A3 in

hypoeutectoid steels,

or Acm in hypereutectoid steels (intercritical annealing);

or above A3 (full annealing).


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Subc ri t ical Anneal ing

Subcritical annealing does not involve formation of austenite. Theprior condition of the steel is modified by such thermally activatedprocesses as recovery, recrystallization, grain growth, andagglomeration of carbides.

In as-rolled or forged hypoeutectoid steels containing ferrite and

pearlite, subcritical annealing can adjust the hardness of bothconstituents, but excessively long times at temperature may berequired for substantial softening.

The subcritical treatment is most effective when applied to hardenedor cold-worked steels, which recrystallize readily to form new ferritegrains. The rate of softening increases rapidly as the annealing

temperature approaches A1. Cooling practice from the subcriticalannealing temperature has very little effect on the establishedmicrostructure and resultant properties.


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lntercr i t ical Anneal ing Austenite begins to form when the temperature of the steel

exceeds A1. The solubility of carbon increases abruptly(nearly1%) near the A1 temperature.

In hypoeutectoid steels, the equilibrium structure in theintercritical range between A1 and A3 consists of ferrite andaustenite, and above A3 the structure becomes completelyaustenitic.

In hypereutectoid steels, carbide and austenite coexist in theintercritical range between A1 and Acm; and the homogeneityof the austenite depends on time and temperature. The degreeof homogeneity in the structure at the austenitizingtemperature is an important consideration in the development

of annealed structures and properties. The more homogeneous structures developed at higheraustenitizing temperatures tend to promote lamellar carbidestructures on cooling, whereas lower austenitizingtemperatures in the intercritical range result in lesshomogeneous austenite, which promotes formation ofspheroidal carbides.


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A common annealing

practice is to heat

hypoeutectoid steels

above the upper critical

temperature (A3) toattain full

austenitization. The

process is called full

annealing.


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Recommended

temperatures and

cooling cycles for

full annealing

Recommended annealing temperatures for alloy steels (furnace cooling)


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Recommended annealing temperatures for alloy steels (furnace cooling)

Hardness (max), HBAnnealing temperatureAISI/SAE steel

C

1791550-1650845-9001330

1871550-1650845-9001335

1921550-1650845-9001340

. . .1550-1650845-9001345

1871500-1600815-8703140

1831500-1575815-8554037

1921500-1575815-8554042

2011450-1550790-8454047

2231450-1550790-8454063

1741450-1550790-8454130

. . .1450-1550790-8454135

1921450-1550790-8454137

1971450-1550790-8454140

2071450-1550790-8454145

. . .1450-1550790-8454147

2121450-1550790-8454150

. . .1450-155790-844161

AISI Temp Hardness


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. . .1450-155790-844337

2231450-155790-844340

HardnessTempAISI

1871500-1600815-87050B40

1971500-1600815-87050B44

1921500-1600815-8705046

1921500-1600815-87050B46

2011500-1600815-87050B50

2171500-1600815-87050B60

1701450-1550790-8455130

1701450-1550790-8455132

AISI Temp Hardness

AISI Temp Hardness


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1701450-1550790-8455132

1741500-1600815-8705135

1871500-1600815-8705140

1971500-1600815-8705145

1971500-1600815-8705147

2011500-1600815-8705150

2171500-1600815-8705155

2231500-1600815-8705160

2231500-1600815-87051B60

1971350-1450730-79050100

1971350 1450730 79051100


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1971350-1450730-79051100

2071350-1450730-79052100

2011550-1650845-9006150

1921550-1650845-90081B45

1741500-1600815-8708627

1791450-1550790-8458630

1921500-1600815-8708637

1971500 1600815 8708640


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1971500-1600815-8708640

2011500-1600815-8708642

2071500-1600815-8708645

2071500-1600815-87086B45

2121500-1600815-8708650

2231500-1600815-8708655

2291500-1600815-8708660

2021500-1600815-8708740

. . .1500-1600815-8708742

2291500-1600815-8709260

1741450-1550790-84594B30

1921450-1550790-84594B40


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As the hardness of steel increases during cold working,ductility decreases and additional cold reduction becomes sodifficult that the material must be annealed to restore itsductility. Such annealing between processing steps is referredto as in-process or simply process annealing. It may consist ofany appropriate treatment. In most instances, however, a

subcritical treatment is adequate and least costly, and the term"process annealing" without further qualification usually refersto an in-process subcritical anneal.

is often necessary to specify process annealing for parts thatare cold formed by stamping, heading, or extrusion. Hotworked high-carbon and alloy steels also are process annealedto prevent them from cracking and to soften them for shearing,turning, or straightening.

Process Annealing


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T f F


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Types of Furnaces

Types of Furnaces

Furnaces for annealing are of two basic types:1. Batch furnaces and

2. Continuous furnaces.

Batch-type furnaces are necessary for large parts suchas heavy forgings and often are preferred for small lots

of a given part or grade of steel and for the morecomplex alloy grades requiring long cycles. Specifictypes of batch furnaces include car-bottom, box, bell,and pit furnaces. Annealing in bell furnaces can producethe greatest degree of spheroidization (up to 100%).

However, the spheroidizing cycles in bell furnaces arelong and last from 24 to 48 h depending on the grade ofmaterial being annealed and the size of the load.


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Continuous furnaces such as roller-hearth,

rotary-hearth, and pusher types are ideal forisothermal annealing of large quantities of partsof the same grade of steel. These furnaces canbe designed with various individual zones,

allowing the work to be consecutively brought totemperature, held at temperature, and cooled atthe desired rate. Continuous furnaces

are not able to give complete spheroidization

and should not be used for products that requiresevere cold forming..


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A low-carbon sheet steel in the (a) as-cold-rolled unannealed condition,(b) partially recrystallized annealed condition, and (c) fully

recrystallized annealed condition. Marshall's etch. 1000


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(a) In the as-received hot-rolled condition, microstructure is blockypearlite. Hardness is 87 to 88HRB.

(b) In the partially spheroidized condition following annealing in a

continuous furnace. Hardness is 81 to 82 HRB.

(c) In the nearly fully spheroidized condition following annealing in a bell

furnace. Hardness is 77 to 78 HRB.

Documents

1- Heat Treatment