Relation between Hot Ductility and Grain Boundary Embrittlement of Low-Carbon Killed Steels

Abstract

The hot ductility of low-carbon killed steels has been studied by the hot tensile tests, microscopic observations and the fracture surface observations.
The ductility during cooling after solution treatment at 1350°C decreased remarkably in the temperature range between 700 and 800°C and the fracture surface showed the intergranular ductile fracture accompanied with AIN or MnS precipitates. This loss of ductility is related to the formation of the primary ferrite along the austenite grain bondaries and the precipitation of AIN or MnS particles at the grain boundaries, and becomes very large when it occursconcurrently. The intergranular ductile fracture can be induced by the micro-void coalescence nucleated at the grain boundary precipitates as the result of strain concentration at the film-likeprimary ferrite formed along the austenite grain boundaries.