Cobalt Steel

M42 cobalt steel

For over 65 years, Griggs Steel Company has been known for providing the highest quality steel to the cutting tool and forming tool industries.

Our inventory of high-speed steels covers a variety of grades, including M42 cobalt steel.

What Is Cobalt Steel?

Cobalt steel is a type of high-speed alloy steel used primarily for cutting tools. Introduced to manufacturers in 1900, high-speed steel, containing a mixture of tungsten, chromium, and trace amounts of carbon, enabled manufacturers to double or even triple their production.

High-speed cobalt steel, also known as HSCO, has a higher concentration of cobalt added to increase hardness and tolerance to heat. The amount of cobalt used determines the grade.

High-heat applications such as jet engines or gas turbines require cobalt steel, as it has high wear and corrosion resistance and will remain strong at temperatures over 1,200° F. The concentration of cobalt in these applications varies from 5-65%.

HSCO steel in concentrations of 2-12% is also used to cut other hard steels. Hard facing materials can contain up to 65% cobalt.

How Does M42 Steel Differ From Other High-Speed Steels?

M42 cobalt steel is a molybdenum series, also known as M series, high-speed steel alloy. M series high-speed tool steels contain 7% molybdenum, tungsten and vanadium, and more than 0.6% carbon. More than 95% of all high-speed steels manufactured in the United States are M series steels.
M42 steel has another 8-10% cobalt added to the alloy for increased heat resistance, also called red hardness.

The common chemical composition of M42 cobalt steel is 1.1% carbon, 8.25% cobalt, 9.5% molybdenum 3.9% chromium, 1.2% vanadium and 1.6% tungsten. It has a heat-treated hardness, measured on the Rockwell scale, of 68 to 70 HRC. When used for cutting, it provides additional benefits like a lower initial cost, higher cutting speeds, lower cycle times and high production capacity.

How Is M42 Steel Used?

M42 is a vital component for machining portable, space-age materials. It is used for machining pre-hardened high-strength steels, high-hardness alloys and nonferrous superalloys used in the aerospace, oil, and power generation industries.

Some common tools made of M42 steel include:

  • Bandsaw blades
  • Twist drills
  • Saws
  • End mills
  • Milling cutters
  • Taps
  • Reamers
  • Broaches
  • Knives
  • Thread rolling dies

Griggs Steel Color Code:Red

Physical Properties


0.282 lb/in3 (7806 kg/m3)

Specific Gravity


Modulus Of Elasticity

30 x 106 psi (207 GPa)


35-40% of a 1% carbon steel

High Speed Steel Properties Comparison

Griggs Steel chart

M42 Cobalt Steel Chemical Composition


M42 Cobalt Steel Heat Treating


M42 Cobalt Steel Thermal Treatments

Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1500-1600°F (816-871°C, and equalize.

Heat rapidly from the preheat.
Furnace: 2150-2175°F (1177-1191°C)
Salt: 2125-2150°F (1163-1177°C)
To maximize toughness, use the lowest temperature. To maximize hot hardness, use the highest temperature.

Pressurized gas, warm oil, or salt. For pressurized gas, a rapid quench rate to below 1000°F (538°C) is critical to obtain the desired properties. For oil, quench until black, about 900°F (482°C), then cool in still air to 150-125°F (66-51°C). For salt maintained at 1000-1100°F (538-593°C), equalize, then cool in still air to 150-125°F (66-51°C).

Temper immediately after quenching. Typical tempering range is 1025-1050°F (551-565°C). Hold at temperature for 2 hours, then air cool to ambient temperature. Triple tempering is required.

Annealing must be performed after hot working and before re-hardening
Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1575-1650°F (857-899°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 50°F per hour (28°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air.