Characteristics of Hot Ductility Behavior and Fracture Mechanisms in Nb-Microalloyed Steel

摘要

The hot ductility and fracture mechanisms of Nb microalloyed steel have been investigated using conventional tensile test. Tensile tests were carried out ranging from 1350℃ to 700℃ and at the strain rate of 1×10~(-3)s~(-1). The fracture appearances at different temperatures showed that there were two brittleness areas, the first ductility region is 1350℃ to the melting points, the ductility region Ⅲ is about 950℃～700℃ and the ductility region Ⅱ does not exist in Nb microalloyed steel. The fracture mechanisms were clarified based on the examination to the fracture surface using a scanning electronic microscope. The initiation of crack at 1325℃～950℃ is transgranular fracture, the ductility recovery can be associated of dynamic recrystallisation. The crack at the temperature range of ductility region Ⅲ is intergranular fracture and ferrite film were found.