1991 Volume 77 Issue 8 Pages 1312-1319
Effects of retained austenite on press-formabilities were investigated, using autempered 0.4C-Si-1.2Mn sheet steels with high tensile strength more than 100 kgf/mm2.
The results showed plausible relationships between formabilities and initial fraction of retained austenite (Vγ0). As Vγ0 increased, height of stretch forming increased linearly to the maximum at 0.2 Vγ0, and bendability as well as hole expandability of mechanically grinded hole were gradually improved to the best at 0.150.2 Vγ0. On the other hand, hole expandability of punched hole decreased slightly in less than 0.150.2 Vγ0 with Vγ0 increasing. More than 0.2 or 0.150.2 Vγ0, all of these formabilities decreased extraordinarily.
It was concluded that these effects of retained austenite on pressformabilities can be clearly understood in terms of Vγ0 and κ: a rate constant relating rate of deformation-induced transformation with uniaxial tensile strain, as a parameter showing stability of retained austenite in press-forming.
