CPM® REX® 20 (HS)*
(AISI M62)
CPM REX 20 is a cobalt-free super high speed steel made by the Crucible Particle Metallurgy Process. It has high carbon, tungsten and molybdenum for heat treat response and red hardness comparable to M42 without the cobalt. With 2% vanadium and a high carbide volume fraction, CPM Rex 20 has at least twice the wear resistance of M42. The best applications are where high red hardness, high abrasion resistance, and good toughness can be used to advantage.
Typical Chemistry
Carbon 1.30%
Manganese 0.35% (0.70%)
Silicon 0.25%
Chromium 3.75%
Vanadium 2.00%
Tungsten 6.25%
Molybdenum 10.50%
Cobalt None
Sulfur 0.06% (0.22%)
Typical Applications
End Mills Shaper Cutters
Form Tools Broaching Tools
Gear Hobs Spade Drills
Milling Cutters Special Taps, etc.
*HS The addition of .20/.25S in larger diameter rounds (e.g. 2-9/16" and over) provides a uniform dispersion of small sulfides throughout the structure, resulting in machinability and grindability benefits with no deleterious effect on toughness.
Annealed Hardness: BHN 262/285

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

Thermal Treatments

Critical Temperature: 1490F(810C)

Forging: 2000-2100F(1095-1150C). Do not forge below 1700F(925C). Slow cool after forging.

Annealing: 1600F(870C), hold 2 hours, slow cool maximum 30F(15C)/hour to 1000F(540C), then air or furnace cool. BHN 262-285.

Stress-relieving (After machining): 1100-1300F(595-740C), hold 2 hours and air or furnace cool.
Straightening: Best done warm 400-800F(200-430C).

Hardening: (Salt, vacuum or atmosphere)

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

High heat: 2100-2200F(1150-1205C). Standard recommendation to achieve HRC 66/68 is 2150-2175(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 the 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 25F(15C) below original tempering temperature or 1000F(540C) minimum.
Hardening Data
Tempering
HEAT TREAT RESPONSE ±1 HRC (NOTE A)
Temperature
2100F
2125F
2150F
2175F
2200F
°C
°F
(1150C)
(1165C)
(1175C)
(1190C)
(1205C)
As Quenced
66
66
65
64
63
540
1000
65.5
66
66.5
67
67.5
OPTIMUM FOR MAXIMUM TOUGHNESS AND EFFECTIVE STRESS-RELIEVING.
550
1025
65
66
66.5
67
67.5
565
1050
64
65
65.5
66.5
67
595
1100
61.5
62.5
63
64.5
65
620
1150
57
58
59
61
62
650
1200
52
53
54
56
57
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
MINIMUM NUMBER
OF TEMPERS (2 HRS)
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
67.5
+.22
Surface Treatments
CPM REX 20 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 ...................................................................34 psi x 106 (235 GPa)
Specific gravity ............................................................................................................8.17
Density .......................................................................................0.295 lb/in3 (8172 kg/m3)
Coefficient of Thermal Expansion
Temperature
Range
Coefficient of Thermal
Expansion
°F
°C
in/in/°Fx10-6
mm/mm/°Cx10-6
70-200
20-94
5.92
10.66
70-400 20-205 6.21 11.18
70-600 20-315 6.47 11.65
70-800 20-425 6.60 11.88
70-1000 20-540 6.80 12.24
70-1100
20-595
6.99
12.58
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