CPM® REX® M35HCHS*
(AISI M35)
CPM REX M35HCHS is a 5% cobalt modification of M2 high speed steel used almost exclusively for hobs and other gear cutting tools where higher red hardness is required. Made by the Crucible Particle Metallurgy process, CPM REX M35HCHS has excellent machinability and grindability characteristics.
Typical Chemistry
Carbon 0.98%
Manganese 0.70%
Silicon 0.40%
Chromium 4.05%
Vanadium 2.00%
Tungsten 6.00%
Molybdenum 5.00%
Cobalt 5.00%
Sulfur 0.22%
Typical Applications
Gear Hobs Milling Cutters
Shaving Cutters Shaper Cutters
* The addition of .20/.25 S 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 225/255

Annealed Hardness (Mill Process): BHN 277/302
Standard Full Anneal: BHN 225/255

Machinability in the annealed condition is approximately 50% of W1 Tool Steel (1%C).

Thermal Treatments

Critical Temperature: 1520F(827C)

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

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

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. A second preheat is suggested for vacuum or atmosphere hardening.

High heat: 2150-2240F(1175-1225C). Standard recommendation to achieve Rc 65-66 is to use 2225(1215C).
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 strongly recommended.

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
2150F
2175F
2200F
2225F
2240F
°C
°F
(1175C)
(1190C)
(1205C)
(1215C)
(1225C)
As Quenced
66
66
65
65
65
540
1000
64
64.5
6 5
63.5
66
OPTIMUM FOR MAXIMUM TOUGHNESS AND EFFECTIVE STRESS-RELIEVING.
550
1025
63
64
64.5
65
65.5
565
1050
62.5
63.5
64
64.5
65
595
1100
61
62
63
63.5
64
620
1150
57
59
61
61.5
62
650
1200
52
54
56
57.5
58
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
5
5
3
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
2225
1215
1025
550
65
+.15
Surface Treatments
CPM REX M35HCHS 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 (214 GPa)
Specific gravity ............................................................................................................8.11
Density .......................................................................................0.293 lb/in3 (8105 kg/m3)
Thermal Expansion
Temperature
Range
Coefficient of Thermal
Expansion
°F
°C
in/in/°Fx10-6
mm/mm/°Cx10-6
70-750
20-400
6.3
11.4
70-1100
20-595
6.4
11.5
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