Effect of Austenite Pancaking on the Microstructure,Texture, and Bendability of an Ultrahigh-Strength Strip Steel

The effect of austenite pancaking in the non-recrystallization regime on microstructure and texture evolution and thereby on bendability was investigated in an ultrahigh-strength strip steel with a martensitic-bainitic microstructure. The results indicate that an increase in rolling reduction (R _tot) below the non-recrystallization temperature, which improves the strength and toughness properties, increases the intensities of the ~{554}〈225〉 _α and ~{112}〈110〉 _α texture components along the strip centerline and of the ~{112}〈111〉 _α component at the surface region. Even with the highest R _tot of 79 pct, the bendability along the rolling direction was good, but the preferred alignment of rod-shaped MA constituents along the rolling direction led to a dramatic decrease in the bendability transverse to the rolling direction, with severe cracking occurring even at small bending angles. The early cracking is attributed to localization of the strain in narrow shear bands. It is concluded that the R_tot value has to be limited to guarantee successful bendability.