Effect of Cold Deformation and Multiphase Treatment Conditions on Low‐Carbon, Low‐Silicon Multiphase Steel

Abstract

This paper presents multiphase (MP) treatments of a low‐C, low‐Si cold rolled steel. Despite the much lower content of Si compared to a typical TRIP steel, up to about 8 pct of retained austenite (γr) with 1.2 % carbon content can be obtained. Increasing prior cold deformation (i.e. decrease of parent austenite grain size) accelerates the transformation to bainite resulting in a decrease of the volume fraction of residual austenite (γr + martensite). Tensile strength of MP steel intercritically annealed at high temperature increases with higher cold reduction degree due to the smaller grain size of the present phases. On the contrary, the ductility and strength‐ductility balance deteriorate because the banded structure becomes more pronounced and the γr volume fraction diminishes. Decreasing intercritical annealing temperature results in an increasing γr fraction and a uniform distribution of second phases. Hence, the ductility and strength‐ductility balance are improved. Crystallographic preferred orientation is evident in the ferrite and martensite and its extent increases with higher cold deformation.

Austenite Decomposition and Precipitation Behavior of Plastically Deformed Low-Si Microalloyed Steel

“…Unfortunately, such a high amount of this element deteriorates the sheet wettability by liquid zinc during hot-dip galvanizing [15]. Therefore, industrial requirements prefer low-Si grades in TRIP-aided steels [16,17]. The decrease of the solid solution potential of silicon and a resulting decrease of the strength level (Al has a smaller solid solution strengthening effect) can be compensated by Nb, Ti, and/or V microalloyed additions [18][19][20][21][22].…”