CPM® REX® M4HC(HS)*
(AISI M4)
CPM REX M4HC(HS) is a high-vanadium special purpose high speed steel exhibiting better wear resistance and toughness than M2 and M3 in cold work punches, die inserts and cutting applications involving high speed and light cuts. The high carbon (HC) modification to standard M4 is designed to provide optimum hardening response in large cross-section tools or in vacuum or atmosphere heat treating. The high sulfur (HS) modification is standard for large diameter bars providing enhanced machinability and grindabiltiy.
Typical Chemistry
Carbon 1.40%
Manganese 0.30% (0.70%)*
Silicon 0.55%
Chromium 4.00%
Vanadium 4.00%
Tungsten 5.50%
Molybdenum 5.25%
Sulfur 0.06% (0.22%)*
Typical Applications
Broaches Milling Cutters
Gear Hobs Rolls
Shaper Cutters Punches
Shaving Cutters Dies
*The addition of .20/.25 S 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 225/255

Machinability in the annealed condition is approximately 45% of W1 Tool Steel (1%C), with about 30% additional improvement with the high sulfur modification.

Thermal Treatments

Critical Temperature: 1545F (840C)

Forging: 2000-2100F(1095-1150C). 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 BHN225/255.

Stress Relieving (After machining): 1100-1300F(595-740C), hold 2hrs. 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 at1850-1900F(1010-1040C) suggested for high temperature hardening in vacuum.

High Heat: 1875-2200F(1025-1205C). 2150-2200F(1175-1205C) recommended for cutting tools. 1875-2125F(1025-1160C) recommended for cold work applications.
Quench: Salt, oil or atmosphere quench to 1000-1100F(540-595C), equalize, then air cool to below 150F(66C) 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. Double tempering required and triple tempering recommended when hardening from 2100F(1150C) or higher. Air cool to room temperature between tempers.

Stress-relieving (Hardened parts): Temper 30F(15C) below original tempering temperature.

Toughness
C-Notch Charpy impact and Bend Fracture strengths related to hardening and tempering temperatures follow:
Hardening
Tempering
Hardness
Charpy C-Notch
Bend Fracture
Temperature
Temperature
Impact Value
Strength
°F
°C
°F
°C
HRC
Ft-lb
(Joules)
(ksi)
(MPa)
2200
1205
1025
550
65.5
20
27
738
5088
2125
1165
1050
565
63.5
28
38
744
5129
Hardening Data
Tempering
HEAT TREAT RESPONSE ±1 HRC (NOTE A)
Temperature
1875F
1975F
2050F
2100F
2150F
2200F
°C
°F
(1025C)
(1080C)
(1120C)
(1150C)
(1175C)
(1205C)
As Quenced
59.5
62.5
64.5
65
65
63.5
540
1000
58.5
61
62.5
63.5
65
66
OPTIMUM FOR MAXIMUM TOUGHNESS AND EFFECTIVE STRESS-RELIEVING.
550
1025
58
60.5
62
63
64.5
65.5
565
1050
57.5
59.5
61
62
63.5
64.5
595
1100
54
56
58.5
60
61.5
62.5
620
1150
50
53
55
56
58
59
650
1200
44
48
51
52
54
55
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)
45
30
20
15
10
5
MINIMUM NUMBER
OF TEMPERS (2 HRS)
2
2
2
3
3
3
Size Change During Hardening
Hardening
Temp.
Tempering
Temp.
HRC
Longitudinal
Size Change
%
°F
°C
°F
°C
2200
1205
1025
550
65.5
+.15
Surface Treatments
CPM REX M4HC(HS) 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 ...................................................................31 psi x 106 (214 GPa)
Specific gravity ............................................................................................................7.97
Density .......................................................................................0.288 lb/in3 (7972 kg/m3)
Coefficient of Thermal Expansion
Temperature
Range
Coefficient of Thermal
Expansion
°F
°C
in/in/°Fx10-6
mm/mm/°Cx10-6
100- 500
40-260
6.40
11.5
100- 800
40-425
6.58
11.8
100-1100
40-540
6.72
12.1

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