Effect of cooling rate on the transformation characteristics and precipitation behaviour of carbides in AISI M42 high-speed steel

Abstract

ABSTRACT The influence of cooling rate during austenitising process on the transformation characteristics and precipitation behaviour of carbides in AISI M42 high-speed steel was investigated through thermodynamic calculation, dilatometry, microstructural analysis, and steel inclusion analysis system. Results show that under low cooling rate (<1 K s−1), the carbides in the steel are coarse, growing along the grain boundaries, and forming a network distribution. Under high cooling rate (≥1 K s−1), the morphology of carbides turns into block shape, and martensitic microstructure has been achieved. The volume fraction of the carbides decreases with the increase of cooling rate, meanwhile, the size distribution of the carbides is meliorated. However, when the cooling rate further increases from 5 to 20 K s−1, the precipitated carbides becomes non-uniform with the increasing cooling rate. Consequently, an appropriate cooling rate of heat treatment can be selected to optimise the distribution of carbides.