Influence of composition and microstructure on hot workability of austenitic stainless steels

Abstract

The behaviour of a steel during hot working is determined by composition, thermomechanical history, and processing parameters. An experimental assessment of hot ductility has been made using hot tensile tests to show the importance of compositional and microstructural variations in austenitic stainless steels. The effects of a substitutional solute (molybdenum), a precipitation-hardening solute (niobium), and delta ferrite formation are described. Low-ductility failures arising from intergranular cracking were most severe in coarse-grained material at low test temperatures. Crack growth was impeded by dynamic recrystallization, and ductility was much improved, the blunted cracks reorientating with increasing strain and growing in the same manner as voids nucleated at inclusions. Molybdenum and niobium strengthened the matrix and enhanced intergranular cracking. The significance of these findings in relation to hot-rolling schedules is considered, and the metallurgical desirability of using low soaking temperatures and high finishing temperatures in rolling austenitic stainless steels is emphasized.