REX® M4
(AISI M4)
REX M4 is a special purpose high speed steel designed to give high wear resistance in tools. Its high vanadium and carbon content provide for superior resistance to cratering and wear in cold work punches, die inserts, and cutting applications involving high speed and light cuts. It is designed to give maximum performance working with abrasive materials, exhibiting better wear resistance than M2 or M3.
Typical Chemistry
Carbon 1.30%
Manganese 0.30%
Silicon 0.30%
Chromium 4.00%
Vanadium 4.00%
Tungsten 5.50%
Molybdenum 4.50%
Sulfur 0.03% max.
Typical Applications
Broach Inserts Spade Drills
End Mills Punches
Form Tools Dies
Taps Rolls
Annealed Hardness: BHN 225/255

Machinability in the annealed condition is approximately 20% of W1 Tool Steel (1%C).

Thermal Treatments

Critical Temperature: 1545F (840C)

Forging: 2000F-2100F(1095-1150C) Do not forge below 1700F(930C). Slow cool.

Annealing: 1600F(870C), hold 2 hours, slow cool 30F (15C)/hour maximum to 1000F(540C), then air or furnace cool. Hardness BHN 225/255.

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. Second preheat stage at 1850-1900F(1010-1040C) suggested for high temperature hardening in vacuum.

High heat: 1875-2225F(1025-1218C). 2150-2200F(1175-1205C) recommended for cutting tools. 1875-2125(1025-1160C) recommended for cold work applications.
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. 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.
Hardening Data
Tempering
HEAT TREAT RESPONSE ±1 HRC (NOTE A)
Temperature
1875F
1975F
2050F
2100F
2150F
2200F
°C
°F
(1025C)
(1080C)
(1120)C
(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
+.2
Surface Treatments
CPM REX M4 can be nitrided, steam tempered or titanium-nitride coated if desired. If the CVD TiN treatment is used, care is required in vacuum hardening.

Toughness
Lowering the hardening temperature (underhardening) reduces the grain size and increases toughness.
Hardening
Temperature
Tempering
Temperature
Hardness
HRC
Charpy C-Notch
Impact Value
°F
°C
°F
°C
ft-lb
(J)
2200
1205
1025
550
65
8.5
11
2125
1165
1050
565
64
11
15
Physical Properties
Modulus of Elasticity ...................................................................31 psi x 106 (214 GPa)
Specific gravity ............................................................................................................7.97
Density .......................................................................................0.288 lb/in3 (7970 kg/m3)
Coefficient of Thermal Expansion
Temperature
Range
Coefficient of Thermal
Expansion
°F
°C
in/in/°Fx10-6
mm/mm/°Cx10-6
100-500
38-260
6.40
11.5
100-800
38-427
6.58
11.8
100-1000
38-593
6.72
12.1
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