低碳钢奥氏体晶粒尺寸的控制

CONTROL OF AUSTENITE GRAIN SIZE IN A LOW CARBON STEEL

分别采用高温形变再结晶和低温变形后快速加热冷却等两种方法获得尺寸不同的低碳钢奥氏体晶粒组织通过控制形变温度、形变量、应变速率及变形道次等工艺参数，低碳钢奥氏体高温形变动态再结晶可使晶粒细化到 １５－２０ μｍ左右奥氏体动态再结晶晶粒尺寸取决于 Ｚｅｎｅｒ－Ｈｏｌｌｏｍｏｎ（Ｚ）参数，提高应变速率及降低形变温度都有利于 Ｚ参数增大，流变应力峰值较高，奥氏体动态再结晶晶粒减小．通过奥氏体化后淬火－６５０℃回火－室温变形一快速加热冷却工艺，得到奥氏体的平均晶粒尺寸可达１０μｍ以下奥氏体晶粒细化可归结为铁素体向奥氏体的转变与铁素体回复再结晶的相互竞争。

Two approaches, i.e., hot deformation induced recrystallization and quickly heating and cooling after cold deformation, were adopted to obtain different austenite grain sizes of a low carbon steel. The austenite grain sizes of 15-20 μm can be produced by dynamic recrystallization through optimizing processing condition of deformation temperature, reduction, strain rate and deformation pass number. The final dynamically recrystallized austenite grain size depends on Zener-Hollomon parameter, which is increased with increasing strain rate and decreasing deformation temperature. In contrast, the austenite grain size smaller than 10μm can be achieved by austenitization followed by tempering at 650℃, and then deformation at room temperature followed by repeatedly quick heating 'and cooling. The austenite grain refinement in this case can be attributed to the competition between transformation from ferrite to austenite and ferrite recovery and recrystallization.