heattreatment

Manufacturing Processes for Engineering Materials, 4th ed.Kalpakjian • SchmidPrentice Hall, 2003

Transformation of Carbon Alloys

FIGURE 5.36 (a) Austenite-to-pearlite transformation ofiron-carbon alloys as a functionof time and temperature. (b)Isothermal transformationdiagram obtained from atransformation temperature of675˚C (1247˚F). (c)Microstructures obtained for aeutectoid iron-carbon alloy as afunction of cooling rate. Source:ASM International, MaterialsPark, OH.

AME 50542: Manufacturing Processes for Engineering Materials (R.K. Roeder)

Heat Treatmentof Steel


Heat TreatmentProcesses

PROCESS METALSHARDENED

ELEMENTADDED TOSURFACE

PROCEDURE GENERALCHARACTERISTICS

TYPICALAPPLICATIONS

Carburizing Low-carbonsteel (0.2%C) , a l loysteels (0.08-0.2% C)

C Heat steel at 870-950 °C ( 1600-1750°F) in ana t m o s p h e r e ofcarbonaceousg a s s e s ( g a scarbur i z ing ) o rcarbon-containings o l i d s (packcarburizing). Thenquench.

A hard, high-carbon surface isproduced.Hardness 55 to 65HRC. Case depth< 0 . 5 - 1 . 5 m m(<0.020 to 0.060in.) Some distortionof part during heattreatment.

Gears, cams,shafts,bearings,p is ton rings,sprockets,clutch plates

Carbonitriding Low-carbonsteel

C and N Heat steel at 700-8 0 0 ° C ( 1 3 0 0 -1600°F) on ana t m o s p h e r e ofcarbonaceous gasand ammonia. Thenquench in oil

Surface hardness55 to 62 HRC.Case depth 0.07 to0.5 mm (0.003 to0.020 in.) Lessdistortion than incarburizing.

Bo l t s , nuts,gears.

Cyaniding Low-carbonsteel (0.2%C) , a l loysteels (0.08-0.2% C)

C and N Heat steel at 760-8 4 5 ° C ( 1 4 0 0 -1550°F) in a moltenbath of solutions ofcyanide (e.g., 30%sodium cyanide) andother salts.

Surface hardnessup to 65 HRC.Case depth 0.025to 0.25 mm (0.001to 0.010 in.) Somedistortion

Bo l t s , nuts,screws, smallgears.

Nitriding Steels (1%Al, 1.5% Cr,0.3% Mo),alloy steels(Cr, Mo),stainlesssteels, highspeed toolsteels

N Heat steel at 500-600°C (925-1100°F)in an atmosphere ofammonia gas ormixtures of moltencyanide salts. Nofurther treatment.

Surface hardnessup to 1100 HV.Case depth 0.1 to0.6 mm (0.005 to0.030 in.) and 0.02to 0.07 mm (0.001to 0.003 in.) forhigh speed steel

Gears, shafts,sprockets,valves, cutters,bor ing bars,fuel-injectionpump parts.

TABLE 5.7 Outlineof heat treatmentprocesses for surfacehardening.


Heat Treatment Processes (cont.)Boronizing Steels B Part is heated using

boron-containinggas or solid incontact with part

Extremely hard andwear res is tants u r f a c e . Casedepth 0.025-0.075mm ( 0.001-0.003in.)

Tool and diesteels

Flamehardening

Medium-carbonsteels, castirons

None Surface is heatedwith an oxyacetylenet o r c h , thenquenched with waterspray or otherquenching methods.

Surface hardness50 to 60 HRC,Case depth 0.7 to6 mm ( 0.030 to0.25 in.) Litt ledistortion.

G e a r a n dsprocket teeth,axles,crankshafts,p is ton rods,lathe beds andcenters

Inductionhardening

Medium-carbonsteels, castirons

None Metal part is placedin copper inductioncoils and is heatedby high-frequencyc u r r e n t , t h e nquenched.

Surface hardness50 to 60 HRC,Case depth 0.7 to6 mm ( 0.030 to0.25 in.) Litt ledistortion.

G e a r a n dsprocket teeth,axles,crankshafts,p is ton rods,lathe beds andcenters

Table 5.7 Outline of heat treatment processes for surface hardening (cont.).