超低碳BH钢变形抗力和连续冷却转变热模拟

采用Gleeble-1500热模拟试验机,对两种超低碳烘烤硬化(BH)钢的变形抗力和动态连续冷却转变进行研究,观察了两种试验钢在不同变形和冷却工艺条件下的热变形和连续冷却转变组织。结果表明,在1100℃、应变速率1s-1时,两种试验钢均发生了动态再结晶,Ti+Nb超低碳BH钢的变形抗力比Ti+V超低碳BH钢高出约20MPa;在900℃、应变速率1s-1时,Ti+Nb超低碳BH钢发生了动态回复,Ti+V超低碳BH钢则未发生动态回复。两种试验钢在相同热变形条件下的组织形貌及晶粒尺寸差别较大。在不同连续冷却速度下,两种试验钢的金相组织均为多边形铁素体,铁素体晶粒均随着冷速的增加而细化。Ti+Nb超低碳BH钢铁素体晶粒较为细小,形状不规则,Ti+V超低碳BH钢铁素体晶粒则较为粗大,形状规则。

Research on hot deformation resistance and continuous cooling transformation of ultra-low carbon bake hardening steels

Research on hot deformation resistance and dynamic cooling transformation of two ultra-low carbon bake hardening steels were conducted by using the Gleeble-1500 thermal simulation testing machine.The optical microstructures of two test steels were also observed.It has been shown from the results that dynamic recrystallization occurs for the two test steels at 1100℃ with strain rate of 1s-1.The hot deformation resistance of Ti+Nb ultra-low carbon bake hardening steel is approximately 20MPa higher than that of Ti+V ultra-low carbon bake hardening steel at 1100℃ with strain rate of 1s-1.Dynamic recovery occurs for Ti+Nb ultra-low carbon bake hardening steel but not for Ti+V ultra-low carbon bake hardening steel at 900℃ with strain rate of 1s-1.The morphology of hot deformation microstructures and grain sizes of two test steels are different from each other distinctively.The optical microstructures of two test steels under various cooling rates are polygonal ferrites,and the ferrite grains become finer with increasing of cooling rates.The ferrite grains of Ti+Nb ultra-low carbon bake hardening steel are finer with irregular shape,while the ferrite grains of Ti+V ultra-low carbon bake hardening steel are much coarser with regular shape.