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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