Ausforming effects on anisotropy of mechanical properties in HSLA martensitic steel

Abstract

In order to clarify effects of prior pancaked austenitic structure on microstructure and mechanical properties of transformed martensite in ausformed steel, a super-thin pancaked austenite was processed by multi-pass rolling in a 0.03–2.6Mn-0.06Nb-0.01Ti (wt%) low alloy steel. The evolution of prior pancaked austenite grain during multi-pass rolling was studied using Ni-30Fe model alloy. Related with the structure and texture in the prior super-thin pancaked austenite in Ni-30Fe alloy, the texture and anisotropy of mechanical properties of transformed martensite in the studied ausformed steel were focused on. There were mainly three kinds of rolling texture components in the super-thin pancaked austenite: Goss {110}〈001〉, copper {112}〈111〉 and brass {110}〈112〉. They were further transformed into the weak {001}〈110〉 and strong {112}〈110〉, {111}〈112〉 texture components in the martensitic structure. The orientation relationship (OR) of lath martensite transformation from pancaked austenite in the ausformed steel deviated larger from the exact Kurdjumov-Sachs (K-S) OR than in the case of equiaxed austenite without deformation. The tensile and yield strengths of the ausformed martensitic steel first decreased and then increased as the angle between tension direction and rolling direction increased. The main reason for the anisotropy of strength was considered as the texture component {112}〈110〉 in martensite. However, the anisotropy of impact toughness was more complex and the main reasons for it are unknown.