Abstract: By using in-situ dynamic microstructure observation with high temperature confocal laser scanning microscope (HT-CLSM), and through identification of martensite relief and bainite relief under the dynamic view field, the microstructure transformation law and phase transformation point determination method of Cu-bearing steel austenite during continuous cooling were studied. The results show that as the cooling rate increases from 5 ℃/s to 20 ℃/s, the microstructure of the specimen gradually changes from bainite to lath martensite. During the dynamic observation process of HT-CLSM, the bainite formation rate is slow, and the growth process is accompanied by the “interlocking” phenomenon, resulting in shallow relief. As the cooling rate increases, the martensite relief produced has an explosive and staged trend, mostly in bundles and parallel distribution, and the martensite relief is deeper. When the cooling rate reaches to 20 ℃/s, by using the formation of bundled martensite under dynamic observation as the criterion, the Ms point is measured as 447.6 ℃. The microstructure is lath martensite at room temperature, meanwhile the microhardness is as high as 301 HV10, which is similar to the measurement result of other methods.

Key words: high temperature confocal laser scanning microscope (HT-CLSM), Cu-bearing steel, continuous cooling, phase transition point