It has been found that the impact performance of water-hardened steel is better than that of annealed or normalized steel because the rapid cooling prevents the formation of cementite at the grain boundary and promotes the grain size of the ferrite.
Many steels are sold under hot rolling conditions, and rolling conditions have a large impact on impact properties. Lower finish rolling temperatures reduce the impact transition temperature, increase the cooling rate and promote the graining of the ferrite grains, thereby increasing the toughness of the steel. The thick plate is slower than the thin plate because of the cooling rate, and the ferrite grain is thicker than the thin plate. Therefore, the thick plate is more brittle than the thin plate under the same heat treatment conditions. Therefore, normalizing treatment is often used after hot rolling to improve the performance of the steel sheet.
Hot rolling can also produce anisotropic steel and various mixed structures, pearlite strips, and oriented ductile steel with the same grain boundary and rolling direction. The pearlite band and the elongated inclusions are coarsely dispersed into scales, which have a great influence on the notch toughness at the low temperature range of the Charpy transition temperature range.http://www.skivingtubelw.com/
