General Properties of Tool Steels

Reference table of the principal AISI tool steel grades, covering wear resistance, toughness, hot hardness, usual working hardness, depth of hardening, grain size and hardness after hardening. Ratings are relative comparisons on a 1 (low) to 9 (high) scale and are a practical starting point when selecting a grade for a given tooling application.

1–9 rating relative: 1 = low, 9 = high Depth of hardening: S = shallow, M = medium, D = deep · section sizes in the hardenability chart Grain size: Shepherd standard, at full hardness Core hardness: 25 mm (1 in.) diameter round

Grade	Wear^(b)	Toughness^(c)	Hot hardness	Working hardness, HRC	Depth^(d)	Grain size^(Shepherd)	Surface HRC	Core HRC
Molybdenum high-speed steels
M1	7	3	8	63–65	D	9½	64–66	64–66
M2	7	3	8	63–65	D	9½	64–66	64–66
M3, class 1	8	3	8	63–66	D	9½	64–66	64–66
M3, class 2	8	3	8	63–66	D	9½	64–66	64–66
M4	9	3	8	63–66	D	9½	65–67	65–67
M7	8	3	8	63–66	D	9½	64–66	64–66
M10	7	3	8	63–65	D	9½	64–66	64–66
M30	7	2	8	63–65	D	9½	64–66	64–66
M33	8	1	9	63–65	D	9½	64–66	64–66
M34	8	1	9	63–65	D	9½	64–66	64–66
M35	7	2	8	63–65	D	9½	64–66	64–66
M36	7	1	9	63–65	D	9½	64–66	64–66
M41	8	1	9	66–70	D	9½	63–65	63–65
M42	8	1	9	66–70	D	9½	63–65	63–65
M43	8	1	9	66–70	D	9½	63–65	63–65
M44	8	1	9	66–70	D	9½	63–65	63–65
M46	8	1	9	66–69	D	9½	63–65	63–65
M47	8	1	9	66–70	D	9½	63–65	63–65
Intermediate high-speed steels
M50	6	3	6	61–63	D	8½	63–65	63–65
M52	6	3	6	62–64	D	8½	63–65	63–65
Tungsten high-speed steels
T1	7	3	8	63–65	D	9½	64–66	64–66
T2	8	3	8	63–66	D	9½	65–67	65–67
T4	7	2	8	63–65	D	9½	63–66	63–66
T5	7	1	9	63–65	D	9½	64–66	64–66
T6	8	1	9	63–65	D	9½	64–66	64–66
T8	8	2	8	63–65	D	9½	64–66	64–66
T15	9	1	9	64–68	D	9½	65–68	65–68
Chromium hot-work steels
H10	3	9	6	39–56	D	8	52–59	52–59
H11	3	9	6	38–55	D	8	53–55	53–55
H12	3	9	6	38–55	D	8	53–55	53–55
H13	3	9	6	40–53	D	8	51–54	51–54
H14	4	6	7	40–54	D	8	53–57	53–56
H19	5	6	7	40–55	D	8½	48–57	48–57
Tungsten hot-work steels
H21	4	6	8	40–55	D	9	45–63	45–63
H22	5	5	8	36–54	D	9	48–56	48–56
H23	5	5	8	38–48	D	7	34–40	34–40
H24	5	5	8	40–55	D	9	52–56	52–56
H25	4	6	8	35–45	D	9	33–46	33–46
H26	6	4	8	50–58	D	9	51–59	51–59
Molybdenum hot-work steels
H42	6	4	7	45–62	D	8½	54–62	54–62
Air-hardening, medium-alloy, cold-work steels
A2	6	4	5	57–62	D	8½	63–65	63–65
A3	7	3	5	58–63	D	8½	63–65	63–65
A4	5	4	4	54–62	D	8½	61–63	61–63
A5	5	4	4	54–60	D	8½	60–62	60–62
A6	4	5	4	54–60	D	8½	60–62	60–62
A7	9	1	6	58–66	D	8½	64–66	64–66
A8	4	8	6	48–57	D	8	60–62	60–62
A9	4	8	6	40–56	D	8	55–57	55–57
A10	3	3	3	55–62	D	8	60–63	60–63
High-carbon, high-chromium, cold-work steels
D2	8	2	6	58–64	D	7½	61–64	61–64
D3	8	1	6	58–64	D	7½	64–66	64–66
D4	8	1	6	58–64	D	7½	64–66	64–66
D5	8	2	7	58–63	D	7½	61–64	61–64
D7	9	1	6	58–66	D	7½	64–68	64–68
Oil-hardening cold-work steels
O1	4	3	3	57–62	M	9	61–64	59–61
O2	4	3	3	57–62	M	9	61–64	59–61
O6	3	3	2	58–63	M	9	65–67	50–55
O7	5	3	3	58–64	M	9	61–64	59–61
Shock-resisting steels
S1	4	8	5	50–58	M	8	55–58	55–58
S2	2	8	2	50–60	M	8	61–63	56–60
S5	2	8	3	50–60	M	9	61–63	58–62
S6	2	8	3	50–56	M	8	56–58	56–58
S7	3	8	5	47–57	D	8	59–61	59–61
Low-alloy special-purpose steels
L2	1	7	2	45–62	M	8½	56–62	54–58
L6	3	6	2	45–62	M	8	58–63	58–62
Low-carbon mold steels
For hubbed and/or carburized cavities
P2 (e)	1(e)	9	2(e)	58–64 (e)	S	…	62–65 (a)	15–21
P3 (e)	1(e)	9	2(e)	58–64 (e)	S	…	62–64 (a)	15–21
P4 (e)	1(e)	9	4(e)	58–64 (e)	M	…	62–65 (a)	33–35
P5 (e)	1(e)	9	2(e)	50–64 (e)	S	…	62–65 (a)	20–25
P6 (e)	1(e)	9	3(e)	58–61 (e)	M	…	60–62 (a)	35–37
For machined cavities
P20 (e)	1(e)	8	2(e)	30–50	M	7½	52–54	45–50
P21	1	8	4	36–39 (e)	D	…	22–26	22–26
Water-hardening tool steels
W1	2–4	3–7	1	58–65	S	9	65–67	38–43
W2	2–4	3–7	1	58–65	S	9	65–67	38–43
W5	3–4	3–7	1	58–65	S	9	65–67	38–43

Notes & References

^(a) Rating range from 1 (low) to 9 (high).
^(b) Wear resistance increases with increasing carbon content.
^(c) Toughness decreases with increasing carbon content and depth of hardening.
^(d) S, shallow; M, medium; and D, deep.
^(e) After carburizing.

Toughness plotted against hot hardness and wear resistance for tool steels (ASM Handbook Fig. 6) — Toughness plotted against (a) hot hardness and (b) wear resistance for tool steels. Types underlined indicate shallow-hardened tool steels. The area between the dashed lines in (b) represents average values.

Elastic modulus of tool steels

For all practical purposes, the modulus of elasticity of all tool steels in all conditions is about 210 GPa (30 × 10⁶ psi) at room temperature. It decreases uniformly to about 185 GPa (27 × 10⁶ psi) at 260 °C (500 °F) and about 150 GPa (22 × 10⁶ psi) at 540 °C (1000 °F).

Wear resistance

Wear resistance increases with carbon content. At a given hardness, however, it may vary widely depending on the wear mechanism and heat treatment used. Steels with similar hardness can behave very differently under identical wear conditions. The grades that resist wear best are also the hardest to machine, and the machinability rating chart puts a number on that trade-off.

Toughness & testing

At maximum hardness, most tool steels are brittle, so tensile testing rarely gives reliable strength values. Compression, bending and torsion tests are more useful; torsion impact testing gives reproducible data on the effect of composition and heat treatment, particularly for drills and tools loaded in torsion. Where toughness and wear resistance pull in opposite directions, selection by application is the faster route to a grade.

Supply Scope & Technical Reference Note

Aobo Steel supplies tool steel in round bar and plate form, in annealed condition. Hardening, quenching and tempering are performed by the customer’s heat-treatment facility. The tool steel heat treatment guide covers austenitizing temperatures, soak times and tempering windows for these grades.

The property ratings and hardness data in this reference are relative comparisons compiled from ASM Handbook, Volume 1, Table 13. Actual performance depends on heat treatment, section size, tool geometry and service conditions. Always verify final properties and heat-treatment procedures with your heat-treatment facility.

Related reference pages

Tool steel composition chart · Tool steel hot hardness chart · Hardening and tempering temperatures · Machinability ratings · Selection by application · Grade comparison and equivalents · Hardness conversion calculator · Tool steel heat treatment guide · Tool steel thermal conductivity chart

Source: ASM Handbook, Volume 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys, Table 13 “General properties of tool steels” (data for grades marked “e” after carburizing). Reference data for comparison — verify final heat treatment with the grade supplier.