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Weldability
42CrMo4 can be welded but should be preheated to 200°C–300°C to reduce the risk of cracking. Post-weld stress-relief annealing at 550°C–650°C is recommended to relieve residual stresses and preserve toughness.
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Machinability
In the soft-annealed condition 42CrMo4 machines well. In the hardened condition machining requires specially coated carbide tools. Use of cutting fluids is recommended to extend tool life, especially when machining hardened material. Tool wear is moderate in the soft-annealed state and substantially higher when machining hardened steel.
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Magnetic properties
As a steel material, 42CrMo4 is strongly magnetic.
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Forgeability
42CrMo4 forges very well. Recommended forging temperature range is 1100°C–1200°C. After forging, cool slowly in air; quenching in water can adversely affect mechanical properties. A subsequent normalization at approximately 850°C–900°C refines the grain structure and optimizes mechanical properties.
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Corrosion resistance
42CrMo4 has moderate corrosion resistance. Without surface protection the alloy is susceptible to rust. Galvanizing (coating with a zinc layer) improves corrosion resistance; paint or powder coatings also provide effective protection.
