Effects of strain and inter-pass time on the restoration behavior of 436 stainless steels

Abstract

Ferritic stainless steels (FSSs) are viable alternatives to nickel containing austenitic stainless steels. The AISI 436 FSS grade is fully ferritic at all temperature ranges, and therefore, grain refinement can only be achieved through controlling inclusions during solidification and/or recrystallization. In this work, the effects of strain and inter-pass time on the restoration behavior of 436 were systematically investigated using the Gleeble 1500 thermomechanical processing simulator. The aim of the study was to promote the accumulation of strain by delaying recrystallization during roughing rolling simulation to improve the driving force for recrystallization during finishing rolling simulation at lower temperature. Three roughing rolling schedules were designed, i.e., the first simulated the existing industry practice (Control), the second with increased inter-pass time (INT) and the last with both increased inter-pass time and strain per pass (INT + S). Roughing and finishing were each simulated in three-passes, amounting to a total of six-passes. The SEM-EBSD results revealed that the Control and INT schedules resulted in higher strain localization, particularly around particles. On the contrary, the increased inter-pass times and strains (INT + S) led to less strain accumulation. Annealing after roughing rolling simulation led to the nucleation of fine grains in the Control, which suggests that delaying finishing rolling would promote recrystallization and the breakdown of the cast structure.