The Evolution of M/A in ultra-low carbon bainite steel

The amount, size and structure of M/A in ultra low carbon bainitic steels, which are mainly affect by the transformation process, the cooling rate and the tempering treatments, have been investigated. The different cooling rate induce the variation of distribution of amount and size of M/A. There are bigger M/A mass with harder phase at low cooling rate while smaller M/A with less hard phase at high cooling rate. A series tempering tests have been carried out, which indicating that the tempering treatment has significant effect on the evolution of M/A.