Analysis on high temperature mechanical properties of alloy spring steel billet

The high temperature mechanical properties of SUP9,50CrVA,60Si2Mn,which are typical spring steels,are investigated with the Gleeble-1500 thermal analogue machine.Hot ductility and strength curves of these steels are measured in the temperature range of 600 ℃ to 1 350 ℃.Fracture mechanisms of the steels are analyzed based on the observation of the fracture surface with the help of scanning electron microscope(SEM).The effects of the inclusions and composition on high temperature mechanical property are discussed.The results show that there are two low ductility zones,brittle zone Ⅰ(Tm-1 315 ℃,Tm-1 281 ℃,Tm-1 316 ℃) and brittle zone Ⅲ(600-930 ℃,650-956 ℃,600-980 ℃).Origin of the former is that liquid membrane formed in interdendritic regions caused by concentration of S,P and O elements.Origin of the latter is that the appearance of ferrite thin film between austenitic grain boundaries and the precipitation of AlN.