形变温度对含ZrC粒子的20Mn2钢晶粒细化的影响

Effects of Deforming Temperature on Grain-refining of 20Mn2 Steel Containing ZrC Particles

采用热模拟单向压缩试验,研究了含碳化锆粒子的20Mn2钢在不同温度(850～1150℃)和不同形变量(30%～80%)下的晶粒细化行为.组织分析表明,ZrC粒子起到形变核心和再结晶核心的作用,提高了奥氏体动态再结晶形核率,即使在1150℃和1050℃的高温形变状态下,晶粒也能细化至3～4μm;同时因为ZrC作为形变核心的作用,增大了奥氏体内的局域集中形变程度,使得形变诱导铁素体相变能够在较高的温度(950℃)下提前发生;并因为晶粒的细化提高了获得马氏体组织的临界冷却速度,使得各温度下的形变淬火态组织发生了由马氏体向贝氏体乃至形变诱导铁素体的演变过渡.硬度分析表明,晶粒细化及应变产生的硬化作用不仅足以抵消因马氏体或贝氏体的减少和消失带来的硬度降低,还能够进一步提高20Mn2钢的硬度值,并且晶粒细化产生的硬化幅度更大.应力应变分析表明,由于奥氏体再结晶引起了1150℃和1050℃下的形变应力下降,同时由于形变诱导铁素体相变及其再结晶降低了950℃及其以下各温度的形变应力.

The grain-refining behaviors of 20Mn2 steel containing ZrC particles compressed with various degree of deformation （30% -80%） at different temperature （850℃ - 1150℃） were investigated by thermal simulating test. Microstructure analyses indicate that the role of ZrC particles as deformation nucleus and recrystallization nucleus enhances the nucleation rate of dynamic recrystallization of austenite and leads to grain refined with size of 3 -μm even when deformed at high temperature such as 1150℃ and 1050℃ ,further more that the ZrC particles as deformation nucleus increases concentrated degree of the located deformation in austenite makes deformation-induced ferrite transformation take place in advance at a higher temperature（950℃ ）. Because a super-refined grain increases the critical cooling rate for obtaining martensite,the water-quenched microstructure deformed at the employed temperature developes from martensite to bainite and deformation-induced ferrite. Hardness analyses indicate that the hardening effect created by grain super-refining and strain is enough to offset the soft effect led by decrease in amount or even disappearance of martensite and bainite, also it can further increases the hardness of 20Mn2 steel to a higher value while the grain refining creates a bigger effect than the strain does. Analyses on the stress and strain in the deformation indicate that the austenite recrystallization causes a decrease in deformation resistance when deformed at 1150℃ and 1050℃, while deformation induced ferrite transformation plays the same role when deformed below 950℃.