The Effect of Heating Rate and Temperature on Microstructure and R-Value of Type 430 Ferritic Stainless Steel

Abstract

Typical applications of ferritic stainless steels require good formability of a steel that is highly dependent on the processing route. In this study, the effects of heating rate and peak temperature on the texture and formability of a 78% cold-rolled unstabilized 17%Cr (AISI 430) ferritic stainless steel were studied. The cold-rolled sheet pieces were heated in a Gleeble 3800 simulator at the heating rates of 25 °C/s and 500 °C/s up to various peak temperatures below 950 °C for 10 s holding before the final cooling at 35 °C/s to room temperature. Microstructures were characterized and the texture of the annealed samples determined by the electron backscatter diffraction method. The R-value in various directions was determined by tensile straining to 15%. It was established that the high heating rate of 500 °C/s tends to promote the nucleation of grains with the {111}<uvw> orientations during the early state of the recrystallization. The higher heating rate led to a slightly finer grain size and to a marginal improvement in the intensity of the gamma-fibre texture. A coarser grain size would be beneficial for the formability, but the grain growth was suppressed due to low peak temperatures and a short soaking time. Anyhow, the fast annealing resulted in an enhanced R-value in the transverse to rolling direction. The results indicate that even a short annealing cycle is plausible for producing ferritic stainless steels with the formability properties comparable to those of commercial counterparts.