Hot-work tool steel (H12)

SAVE OFFLINE

Tool Steels / 597

H12 Chemical

Composition. AISI: Nominal. 0.35 C. I .SO I\‘. S.00 Cr. (T20812): Composition: 0.30 to 0.40 C. 0.20 I.50 hlo. 0.10 V. AlSI/UNS to 0.50 hln. 0.80 to I .?O Si. 0.30 Ni max. 4.75 to 5.50 Cr. I .?S to I.75 hlo. I .OO to I .70 W. 0.50 I’ ma\ Similar Steels (U.S. and/or Foreign). ASThl A68 I I H- I?); FED QQ-T-570 (H-l?): SAE 51.37 (HI?). 5438 (HI?). 5167 (HI?): tGsr.) DIN 1.2606; (Fr.) AFNOR A3S-590 3432 Z 35 CWDV S: (Ital.) LrNl X 35 CrhloWOS KU: (Jap.) JIS G-UO-1 SKD 62: tl1.K.) B.S. 4659 BHI? Characteristics. A popular grade hn\ing \eq high toughness. H:I> e,xcellent resistance to heat checkmp and can be irater cooled tn SW ice. Cnn be c~burired or nitrided to tnc‘rease surfrlcc hardness with some loss in resistance to heat checking. A specinl die catinp Fade is nvailahls. Is suitahle for extrusion dies. die castin@ dies. mandrels. hot shexs. and hot forging dies and punches. Hx high reststunce to softstung at ele\ ared tempemture. Httrdnes\ does not \ urj up IO -125 “C (800 “FI snd tools can \\ ithbtand \+orbin& temperatures up IO S-W ‘C ( IO00 “F). Does not e\hihit notable second+ hardening etkct during tempering hecause of low carhon content. Httrdnsss begins to drop off rnpidlj when tsmperinp nhove 595 “‘C t II00 “F). Is deep hardening and has lo\\ distortion in hentinp treating. Hns medium \ieii~ resist;lnce. medium to high muchinabilit! nnd medium reststilnce to dscxburizution

preheating. die blochs or other 1001s for open furnace treatment should be placed in TVfurnace at :l temperrlture that does not exceed 260 “C (500 “F). Lf’ork packed in containers ma> be safely placed in a furnace at 370 IO S-10 “C 1700 to 1000 “‘F). Once the \rorkpteces (or container) have attained tempcrnturs. heat slow I) to 815 “C ( IS00 “F). ;Lt ;1 rate not to exceed I IO “C (200 “F) per h. Hold for I h per inch of thickness (or per inch of container thickness if packed). If douhls preheat facilities are available. such us salt bathb. thermal bhock can be reduced hq preheating at 540 to 650 “C t 1000 to I?00 “F‘, nnd then preheating at 8-15 to 870 “C (IS55 to I600 “F, Austenitizr ;I[ 99S to 1025 “C ( I825 to I875 “F) for IS to 10 min. Cke shorter time for small secttons and longer ttme for large sections. Quench in air. If air blnst cooled. nir should be dry and hlasted uniformI> on the surface to he hxdensd. To minimize scale. tools can be flash quenched in oil to cool the surface to below scaling temperature [approximntel> S-IO “C ( IOOW’F~]. hut this tncrtxses distortion. The safer procedure IS to quench from the nustenitiztng temperahtre into il salt bath held at 595 to 650 “‘C I I IO5 to I?00 “FL and hold in the quench until the workpiece renches the temperuture of the hnth. Then withdraw the uorkpiece and ttllo~ it to cool in uir. Quench hwdness. S? to 55 HRC

Stabilizing.

Optionnl.

For intricnte shapes. stress relisle temper at IS0 Rsfri_gsrate at -100 to -195 “C i-150 IO -320 ‘-FL Temper immediateI> ufter part reaches room temperature

to 160 “C (300 IO 320 “FI hrietl!.

Forging.

Heat ,lo\r I!. Preheat ilt 70.5 to 8 IS “C t I300 to I SO0 “FL w-t for_gin@ ut 1065 to I I SO “C ( I YSO to 7_IO0 “FL Do not forge after tempemture of forging stock drops belo\v YOU “C I 1650 “FI. Cool slog I!

Recommended Normalizing.

Heat Treating

Tempering.

Practice

Do not norm~~lire

Annealing. Surfrrce protrxtion ayinst decurhurization b! use of pa&. controlled atmosphere. or vacuum is required. Heat to 845 to 900 “C t I SSS to 16%) “FL Use lower limit for wtnll sections nnd upper limit for Iw~s sections. Hcnt 41~~ I> llnd uniformI>. e>psciallj for hludened tools. Holding time \xics from nhout I h for light sections and small furnace charge, to about -I h for hew> sections and ltuye charg.es. For puck annealing, hold I h per Inch of cross section. Cool ~IOU I! In tumnce to S-IO “C ( 1000 “F) ;1t 3 rate not to exceed 30 “C 155 -Ft per h. nftsr which il faster cooling mte I\ ill not affect final hardness. Typical nnneulcd hardness. 19’ to 235 HB Stress Relieving.

Optional. Hent IO 650 to 675 “C I 1200 to 124s “F) and hold for I h per mch of cross section rnunimum of I hr. Cool in air

Temper tmmediatel!~aftsr tool reaches about SO “C ( I?0 “FI ut S-IO to 6%) ‘C I 1000 to 1700 ‘.Ft. Forced-comection air tempering furnaces hsut tools ttt il moderately \afe rttte. Salt baths ttre ncceptahle for mall parts hut mu! cttuse lxgs or mtncnte shaped dies to crxk due to thermal utilizing salt. puck. controlled atmosphere.

H12: Hardness vs Austenitizing temper, 2 h

or carhurizxion or wx~um. For

and Tempering Conditions.

l l

Processing

Sequence

Rough mnchine Stress relis\ 5 toptionnl) Finish machine Preheat Xustsnitize Quench Stabilize (optional) Temper Finn1 grind to size

(a) H12. oil quenched.

Single

temper,

2 h. (b) H12, air quenched.

Single

598 / Heat Treaters

Guide

H12: Isothermal Transformation Diagram. Annealed H12 tool steel: 0.32 C, 0.35 Mn. 0.95 Si, 4.86 Cr, 1.45 MO, 1.29 W. Austenitized at 1010 “C (1850 “F). Critical points: AC,, 835 “C (1535 “F)

H12: Hardness vs Austenitizing and Tempering Temperature. H12 air cooled from 995 “C (1825 “F), 980 “C (1795 “F), 970 “C (1775 “F), and tempered. sal-Cyclops

Source: Univer-

H12: Tempering Temperature vs Hardness and Dimensional Change. H12: hardness and dimensional change at 2 austenitizing temperatures

Tool Steels / 599

H12: Jominy End-Quench Hardenability. H12 tool steel: 0.35 C, 0.92 Si, 4.76 Cr, 1.49 MO, 1.42 W. Source: Teledyne VASCO

H12: Isothermal

Transformation

Saville

H12: Typical Elevated-Temperature

Tensile Strength. Source: Carpenter Technology Corporation

Diagram. Source: Jessop-

600 / Heat Treaters

Guide

H12: Isothermal Transformation Diagram. Composition: 0.32 C, 0.35 Mn, 0.95 Si, 4.86 Cr, 1.45 MO, 1.29 W. Austenitized at 1010 “C (1850 “F)