Effects of Rolling Processes on Yield Ratio and Formability of Hot Rolled Gas Cylinder Steel

Deep drawing properties of hot rolled gas cylinder steel was investigated by using HP295 steel in terms of microstructure, texture, yield ratio, plastic strain ratio (r-value) and plastic anisotropy (Δr). The grains in the hot strip were largely equiaxed, and the texture was weak, containing α- and γ-fibre. Reheating temperature, finish rolling temperature and cooling rate after rolling influenced the ferrite-pearlite band formation significantly, and the yield ratio increased steeply with decreasing coiling temperature below 630 °C. The anisotropy is relatively high due to retained severe ferrite-pearlite band. A mechanism of the band formation due to manganese segregation is elaborated and confirmed validly, from which the measures to avoid the band formation are worked out. Rolling parameters have been optimized by the measures, and industrial production of the gas cylinder steel has been made possible with much improved r-and Δr-values, while meeting other specifications.