Refinement of grain boundary carbides in a Si–Cr spring steel by thermomechanical treatment

The microstructure and mechanical properties of conventionally heat treated or thermomechanically treated spring steel Fe–0.56C–1.50Si–0.67Cr–0.59Mn (mass%) are presented after tempering. At tempering temperatures between 623 and 673 K continuous cementite films form at the prior austenite grain boundaries when the austenite is quenched without any preceding deformation. Two austenite modifications, a recrystallized variant and an elongated pan-cake grain structure were produced by deformation prior to quenching. The first variant resulted in refined grain boundary carbides after tempering, while for the latter no grain boundary carbides were observed. Both modifications of austenite produced by thermomechanical treatment improve the ductility significantly.