Coarse-grained heat affected zone microstructure and toughness of copper-bearing age-hardening steels

Microstructure and toughness of copper-bearing age hardening steel was studied and SHCCT curve was also measured.The result showed that cooling rate have a great effect on microstructure of coarse-grained zone and the tougness.Microstructure of coarse-grained was changed from thick granular-bainite to thin lath bainite with the increase of cooling rate.It can obtain good NDT results under -50℃ when the cooling time from 800℃ to 500℃ is lower than 40s.On the contrary,the toughness of coarse-grain zone was decrease greatly because of the increase mount of M-A island which was considered to be the important reason leading to deteriorate of coarse-grain toughness.