Thermochemical-thermal treatment of case hardening steels - with deep cooling between hardening and tempering

摘要

Thermochemical-thermal treatment of case hardening steels comprise the following steps. Case hardening or carbo-nitriding (1) takes place at 900 to 1950 deg.C. This is followed by quenching (2) down to a temp. below the Ar1 point at a rate chosen to avoid cementite precipitation at grain boundaries. The subsequent hardening process (3) involves heating at a rate from 20 to 80 deg.C/min and holding at 770 to 830 deg.C for 5 to 15 min. The treatment is concluded by tempering (5). Deep cooling (5) down to -70 to 120 deg.C is foreseen between the hardening (4) and tempering (6) processes. The structure in the boundary zone has finely dispersed inter-crystalline carbide precipitations, with an area greater than 8 per cent of the total and a grain size finer than 10 according to ASTM E112. USE/ADVANTAGE - For mfr. of components of internal combustion engines. Improves the wear resistance of severeley loaded components also under unfavourable lubricating conditions.