Steel for heat treatment
What is thermal treatment?
Heat improvement is a combination of two heat treatment operations on steel, namely hardening and high or medium tempering. The measure of heat improvement is the ratio of yield strength to tensile strength (Re/Rm). Thanks to such treatment, the steel retains good strength properties and at the same time very good plastic properties.
Tempered steel is a very good material for the manufacture of such products as springs, springs, dies and other machine parts that are required to have high yield strength.
A very large proportion of structural components and machine parts are subjected to complex mechanical loads, so they should be made of steels with high strength and ductility properties and resistant to fracture under dynamic loads. The answer to such a demand is structural steels for quenching and tempering with an average carbon content of 0.25-0.5% and other alloying elements affecting the final value of mechanical properties.
Most of the steels for thermal improvement, are low-alloy steels with a total alloying additive concentration of 3 to 5%. Manganese introduced into the steel increases hardenability , but slightly reduces ductility. It can be replaced by silicon, which increases the elastic limit. Chromium improves strength and ductility properties. Nickel lowers the transition temperature to the brittle state and increases ductility.
Steels for tempering:
- Manganese steels (e.g. 30G2, 45G2): shafts, axles, bolts.
- Manganese-silicon steels (e.g., 35SG): wear-resistant parts.
- Chromium steels (e.g. 30H, 38HA, 40H, 40HA): heavily loaded shafts, connecting rods, axles, gears, bolts and other machine parts with small cross sections.
- Steels with molybdenum addition : aircraft engine crankshafts, drive shafts.
- Chromium-nickel-molybdenum-vanadium steels (e.g., 45HNMF, 30HN2MFA) and chromium-nickel-tungsten steels (e.g., 25H2N4WA): parts with large cross sections, exposed to variable loads, i.e., gears, shafts, pins.
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