High Speed Tool M42

Chemical Composition

The chemical composition of M42 molybdenum high speed tool steel is outlined in the following table.

Elements Min Max
Carbon, C 0.70 0.85
Manganese, Mn 0.00 0.40
Silicon, Si 0.00 0.40
Molybdenum, Mo 0.00 0.00
Chromium,Cr 4.50 5.50
W 17.00 19.00
V 0.80 1.20
Co 4.50 5.50

Physical Properties

The table below shows the physical properties of M42 molybdenum high speed tool steel.

AProperties Metric Imperial
Density 7.81 g/cm3 0.282 lb/in3

Mechanical Properties

Properties Metric Imperial
Hardness, Rockwell C (oil quenched from 1204°C, 5 minutes) 64.3 64.3
Hardness, Rockwell C (oil quenched from 1177°C, 5 minutes) 65.5 65.5
Hardness, Rockwell C(oil quenched from 1163°C) 65.8 65.8
Izod impact unnotched (oil quenched at 1191°C; 510°C temper temperature) 13.6 J 10.0 ft- lb
Izod impact unnotched (oil quenched at 1191°C; 622°C temper temperature) 24.4 J 25.8
Machinability (1% carbon steel) 35.0 - 40.0% 35.0 - 40.0%
Poisson’s ratio 0.27-0.30 0.27-0.30
Elastic modulus 190-210 GPa 27557-30458 ksi

M42 tool steel can be drilled, turned, threaded, broached, milled and tapped when it is in its annealed condition and rated at 45% of 1% carbon steel.


M42 molybdenum high speed tool steel is preheated to 871°C (1599°F) in a slow manner and then soaked. This is followed by rapid heating to 1093°C (1999°F) and slow cooling. Temperatures below 982°C (1799°F) are not suitable for the forging process.


M42 tool steel is tempered for three times at 538-593°C (1000-1099°F) and then cooled completely between cycles to obtain good results. Tempering is performed in vacuum furnaces or in salt baths.


M42 tool steel is heated at 871°C (1599°F) and then cooled slowly in a furnace.


M42 tool steel is preheated to 871°C (1599°F), soaked and finally heated to 1204°C (2199°F)


A salt media is used for quenching M42 tool steel at 538°C (1000°F) and then the steel is air cooled.

Heat Treatment

Heat treatment temperatures, including rate of heating, cooling and soaking times will vary due to factors such as the shape and size of each M42 steel component. Other considerations during the heat treatment process include the type of furnace, quenching medium and work piece transfer facilities. Please consult your heat treatment provider for full guidance on heat treatment of high speed steels.

Stress Relieving

If tools produced from M42 high speed steel are heavily machined or ground it is recommended to stress relieve after machining and prior to hardening to minimise the possibility of distortion. To stress relieve heat the component to 600-650°C and soak well (approximately two hours) Cool slowly in the furnace. The M42 tools can be finish machined before heat treatment.


M42 is highly Cobalt alloyed. The composition of M42 makes for a good combination of toughness and hardness. By virtue of these well-balanced properties M42 has come into wide use for all cutting tools.