Different austenite grain size in nonuniformly deformed billets

Conclusions

• 1. Austenite grain growth kinetics in the range of deformation with a degree less or more than the critical (for steel 15Kh ε_cr=20%) differ markedly. In the case of considerable deformation grain growth commences at temperatures close to the Ac₃ point, but grains coarsen comparatively uniformly. For ε < ε_cr there is selective intense growth of individual grains even with temperatures above 900°C and prolonged soaking leading to formation of coarser grains and a more different grain structure than in severely worked steel.

• 2. Production processes of cold extrusion for articles subject to heat or chemical heat treatment should be developed so that the degree of deformation in a blank cross section is less than the critical amount.

• 3. In nonuniformly deformed blanks with deformation ε > ε_cr the most uniform and fine grain structure forms as a result of treatment by the following schedules:

  • a) quenching and normalizing with rapid heating to a temperature not above 900°C;

  • b) gas carburizing at t=950–1000°C;

  • c) carburizing in a solid carburizing agent with t=930–950°C.