What Is M42 Tool Steel?
Introduction
Molybdenum high-speed steels and tungsten high-speed steels are two types of high-speed tool steels. Molybdenum high-speed steels, also known as group M steels, comprise less initial cost. Molybdenum steel types M1 to M10 have tungsten whereas cobalt is not found in type M6. Cobalt is totally absent in these types of molybdenum high-speed steels.
M42 tool steel, a type of molybdenum high speed tool steel, has good wear resistance and hot hardness along with high hardness values.
Chemical Composition
The chemical composition of M42 molybdenum high speed tool steel is outlined in the following table.
| Element | Content (%) |
| C | 1.05-1.15 |
| Mn | 0.15-0.40 |
| Si | 0.15-0.65 |
| Cr | 3.50-4.25 |
| Ni | 0.3 |
| Mo | 9.00-10.00 |
| W | 1.15-1.85 |
| V | 0.95-1.35 |
| Co | 7.75-8.75 |
| Cu | 0.25 |
| P | 0.03 |
| S | 0.03 |
Physical Properties
| Physical Properties | Metric | Imperial |
| Density | 7.81 g/cm3 | 0.282 lb/in3 |
Mechanical Properties
| Mechanical 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 | 24.4 J |
| 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 | 27557-30457 ksi |
Other Designations
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Equivalent materials to M42 molybdenum high speed tool steel are:
AFNOR 07-05-04-04-02
DIN 1.3246
ASTM A600
FED QQ-T-590
UNS T11342
DIN 1.3247
Fabrication and Heat Treatment
Machinability
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.
Forging
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.
Tempering
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.
Annealing
M42 tool steel is heated at 871°C (1599°F) and then cooled slowly in a furnace.
Hardening
M42 tool steel is preheated to 871°C (1599°F), soaked and finally heated to 1204°C (2199°F).
Quenching
A salt media is used for quenching M42 tool steel at 538°C (1000°F) and then the steel is air cooled.
Applications
M42 tool steel is mostly used for machine materials and super alloys that are difficult to machine. The machine materials include chasers, broaches, form and gear cutters, hobs, drills, milling cutters, end mills and taps.
