CPM Rex 45 Steel

cobalt steelGriggs Steel Company is a provider of exceptional steel sourced from the world’s finest steel mills. Not only can we produce any size high-speed steel flat, but we can also provide a mill certificate of quality with each order.

What Is CPM Rex 45® Steel?

It is based upon the same chemical composition as M3-2 high-speed steel with the addition of cobalt. A high concentration of cobalt imparts superior hardness, even with high temperature usage. CPM Rex 45® steel is tougher than all the other super high-speed steels and has a longer cutting tool life than the M series steels. It is used for cutting tools where high hot hardness is required.

How Is CPM Rex 45® Steel Used?

CPM Rex 45® steel is an excellent material for machining nickel-base and titanium alloys, high-performance cutting tools and cold working tools such as:

  • Broaches
  • Drills
  • End Mills
  • Hobs
  • Shapers
  • Taps
  • Milling cutters
  • Shaper cutters
  • Form tools
  • Gear cutting tools

Parts made from CPM Rex 45® steel sometimes undergo surface treatments that impart additional qualities to the steel. The most common treatments are nitriding, CVD and PVD. Nitriding increases the fatigue strength and adds scuff and corrosion resistance by diffusing nitrogen and carbon into the surface of the metal. Chemical vapor deposition or CVD adds wear resistance. Physical vapor deposition or PVD is carried out in a vacuum chamber using an active gas, such as nitrogen, oxygen or methane to provide durability, corrosion and scratch resistance.

Griggs Steel Color Code:Brown

Physical Properties

Density0.287 lb/in3 (8256 kg/m3)Modulus Of Elasticity

34 x 106 psi (240 GPa)

High Speed Steel Properties Comparison


0.287 lb/in3 (8256 kg/m3)

Modulus Of Elasticity

34 x 106 psi (240 GPa)

High Speed Steel Properties Comparison

M2 steel

CPM REX 45® High Speed Steel Chemical Composition


CPM REX 45® High Speed Steel Heat Treating


CPM REX 45® High Speed Steel Thermal Treatments

840-930°F (450-500°C) and 1560-1650°F (850-900°C).

Heat rapidly from the preheat, typically by transferring to a second furnace.
1920-2160°F (1050-1180°C) according to the desired final hardness.

The tool should be protected against decarburization and oxidation during hardening.

Vacuum furnace with high speed gas at sufficient overpressure (2–5 bar).
Martempering bath or fluidized bed at approx. 1004°F (540°C).

Quenching should be continued until the temperature of the tool reaches approx. 120°F (50°C). The tool should then be tempered immediately.

In order to obtain a high toughness, the cooling speed in the core should be at least 20°F/sec. (10°C/sec.). This is valid for cooling from the austenitizing temperature down to approx. 1004°F (540°C). After temperature equalization between the surface and core, the cooling rate of approx. 10°F/sec. (5°C/sec.) can be used. The above cooling cycle results in less distortion and residual stresses.

Temper immediately after quenching.
For cold work applications tempering should always be carried out at 1040°F (560°C) irrespective of the austenitizing temperature. Temper three times for one hour at full temperature. The tool should be cooled to room temperature between the tempers. The retained austenite content will be less than 1% after this tempering cycle.

After hot working, annealing must be done before re-hardening.
Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1600°F (871°C), and hold at temperature for 1 hour per inch (25.4 mm) of thickness, 2 hours minimum. Then cool slowly with the furnace at a rate not exceeding 30°F per hour (17°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air.