REX® M42
High Speed Steel (AISI M42)
REX M42 is a super cobalt high speed steel which may be heat treated to HRC 68. This makes REX M42 outstanding for special purpose cutting tools, with requirements beyond the capability of general purpose high speed steels.
Typical Chemistry
Carbon 1.08%
Manganese 0.30%
Chromium 3.75%
Vanadium 1.15%
Silicon 0.30%
Tungsten 1.60%
Molybdenum 9.50%
Cobalt 8.00%
Sulfur 0.03% max.
Typical Applications
Broaches Gear Hobs
Drills Milling Cutters
End Mills Reamers
Form Tools Shaper Cutters
Annealed Hardness: BHN 235/255.

Machinability in the annealed condition is approximately 35% of W1 Tool Steel (1%C).

Thermal Treatments

Critical Temperature: 1560F(850C)

Forging: 2025-2075F(1105-1135C) Do not forge below 1700F(930C). Slow cool.

Annealing: 1600F(870C), hold 2 hours, slow cool 30F(15C)/hr max. to 1000F(540C), then air or furnace cool. Hardness BHN 235/255.

Stress-relieving (After machining): 1100-1300F(595-740C), hold 2 hrs., then air or furnace cool.

Straightening: Best done warm 400-800F(200-430C)

Hardening: (Salt, vacuum, or atmosphere).

Preheat: 1500-1550F(820-845C), equalize. A second preheat stage at 1850-1900F(1010-1040C) suggested for vacuum or atmosphere hardening.

High Heat: 2075-2175F(1135-1190C). Standard recommendation to achieve HRC 66/68 is to use 2150-2175F(1175-1190C).
Quench: Salt, oil or atmosphere quench to 1000-1100F(540-595C), equalize, then air cool to below 125F(50C) or hand warm. Vacuum or atmosphere quench rate through 1850-1300F(1010-705C) range is critical to achieve optimum heat treat response.

Temper: 1000F(540C) minimum recommended. Triple tempering required.

Stress-relieving (Hardened parts): Temper 30F(15C) below original tempering temperature or 1000F(540C) minimum.
Toughness
Lowering the hardening temperature (underhardening) reduces the grain size and increases toughness.
Hardening
Temperature
Tempering
Temperature
Hardness
HRC
Charpy C-Notch
Impact Value
Bend Fracture
Strength
°F
°C
°F
°C
ft-lb
(J)
(ksi)
(MPa)
2175
1190
1025
550
68
5
7
372
2565
2100
1150
1025
550
66
7
10
446
3075
Hardening Data
Tempering
HEAT TREAT RESPONSE ±1 HRC (NOTE A)
Temperature
2050F
2075F
2100F
2125F
2150F
2175F
°C
°F
(1120C)
(1135C)
(1150C)
(1165C)
(1175C)
(1190C)
As Quenced
66
66
66
66
65
63.5
540
1000
64.5
65
66
67
67.5
68
OPTIMUM FOR MAXIMUM TOUGHNESS AND EFFECTIVE STRESS-RELIEVING.
550
1025
63
64
65.5
66.5
67
67.5
565
1050
60
62
63.5
64.5
65
66
595
1100
54
57
59
60
61
63
620
1150
50
53
55
56
57
59
NOTE A:
RESULTS MAY VARY WITH HARDENING METHOD AND SECTION SIZE. SALT OR OIL QUENCHING WILL GIVE MAXIMUM RESPONSE. VACUUM OR ATMOSPHERE COOLING MAY RESULT IN UP TO 1-2 HRC POINTS LOWER.
MINIMUM TIME AT
AUST TEMP (MINS)
10
10
5
5
3
3
MINIMUM NUMBER
OF TEMPERS (2 HRS)
3
3
3
3
3
3
Size Change During Hardening
Hardening
Temp.
Tempering
Temp.
HRC
Longitudinal
Size Change
%
°F
°C
°F
°C
2175
1190
1025
550
67
+.25
Surface Treatments
REX M42 can be nitrided, steam tempered, or titanium-nitride coated if desired. If the CVD TiN treatment is used, care is required in vacuum hardening.
Physical Properties
Modulus of Elasticity ...................................................................30 psi x 106 (207 GPa)
Specific gravity ............................................................................................................7.81
Density .......................................................................................0.289 lb/in3 (8005 kg/m3)
Thermal Expansion
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