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°C to 700°C 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°C to the melting points, the ductility region III is about 950°C~700°C 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°C~ 950°C 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.