Dynamic continuous cooling transformation of supercooled austenite in spring steel 55SiCrA

The critical temperatures,such as Ac1,Ac3,Ar1,Ar3 and Ms of spring steel 55SiCrA were determined by dilatometric change combined with metallographic test and microhardness measurement on a Gleeble-1500 thermal mechanical simulator.By measuring the dilatometric curves of supercooled austenite continuous cooling transformation at different cooling rates,dynamic CCT diagram was obtained.The effects of different cooling rates on microstructure and pearlite lamellar specing were studied by FE-SEM.The results show that with the increasing of cooling rate,the pearlite lamellar spacing decreases and microhardness of pearlite increases.The optimum cooling rate of spring steel 55SiCrA wire is recommended in the range of 0.5 ℃/s to 1 ℃/s.