Hot ductility behavior of a high alloy steel

Abstract

Hot ductility behaviour is studied in a cast steel at the intermediate temperature range. A low carbon cast steel is heated to 1,673K (1,400 degrees C) and cooled to 673-873K at the heating and cooling rate of 10K/s. Tensile test is performed at the target temperature. Ductility decreases abruptly, shows the lowest at 823K (550 degrees C), and then recovers gradually as the tensile testing temperature decreases. Fracture surface shows the intergranular fracture with small craters at 823K. Further study on the fracture behaviour reveals that the upper bainite structure existing the cementite at the prior austenite grain boundary is crucial for the embrittlement. Segregated phosphorus triggers the initial micro-crack generation at the grain boundary cementite/matrix interface. Detailed embrittlement mechanism and the fabrication way for sound cast iron are discussed.