不同形变速率条件下低碳钢过冷奥氏体形变过程铁素体超细化

Formation of Ultra-fine Ferrite in Low Carbon Steel during Deformation at Different Strain Rates of Undercooled Austenite

研究了低碳钢过冷奥氏体在760℃,形变速率为l s-1和10 s-1变形时组织演变规律.结果表明,形变速率为1 s-1时真应力-应变曲线双峰特征为形变强化相变和铁索体动态再结晶的表征,相变形核集中在铁素体/奥氏体相界前沿奥氏体高畸变区,晶粒长大在时间和空间上受到限制,细化能力较高;形变速率提高到10 s-1时,相变动力学提前,曲线只表现为形变强化相变的单峰特征,相变形核除了在上述铁素体/奥氏体相界前沿奥氏体高畸变区,还分布到奥氏体晶内各处,晶粒间约束有所减小,尺寸稍大.通过形变强化相变和铁素体动态再结晶可以获得平均晶粒尺寸为(1.98±1.07)μm和(2.33±1.01)μm(10 s-1)左右的微细铁素体晶粒.

The microstructure evolution of undercooled austenite to ferrite in a low carbon steel during deformation at 760°C and strain rates of 1 s-1 and 10 s-1 was investigated. The results show that the true stress-strain curve at 1 s-1 demonstrates two peaks, indicating Deformation Enhanced Ferrite Transformation (DEFT) and ferrite dynamic recrystallization involved respectively. More pronounced ferrite refinement is achieved at 1 s-1 because of the restriction against grain growth both in the two aspects of time and space of the new ferrite grains nucleating repeatedly and rapidly chiefly at the front of the phase boundaries between ferrite and austenite. As the strain rate increasing to 10 s-1, the true stress-strain curve demonstrates only one peak indicating DEFT involved mainly because of the acceleration of transformation kinetics. In addition to the phase boundaries above-mentioned, ferrite nucleates in the intragranular of austenite, which weakens the restriction against grain growth somewhat and ferrite grain size become coarsening slightly. Based on the theory of DEFT and ferrite dynamic recrystallization, ultra-fine ferrite structure with grain sizes of about (1.98 ± 1.07) μm and (2.33 ± 1.01) μm was formed at strain rates of 1 s-1 and 10 s-1 respectively.