SWRCH35K钢连续冷却转变曲线的测定与分析

使用DIL805A热膨胀仪测定了SWRCH35K钢的热膨胀曲线。采用切线法结合微观组织及硬度，绘制了试验钢的连续冷却转变(CCT)曲线，分析了冷却速率对试验钢连续冷却过程组织演变的影响。结果表明，冷速在0.1～1℃/s范围时，试验钢的组织为多边形先共析铁素体和珠光体，随着冷速增加，组织细化，珠光体含量增加，硬度为148～165 HV;冷速为3℃/s时，开始出现少量魏氏组织及贝氏体，硬度增加至189 HV;冷速为5～50℃/s时，铁素体沿晶界呈网状，针状魏氏组织增加，组织为晶界铁素体、珠光体、魏氏组织和贝氏体，其中冷速为30～50℃/s时，铁素体含量大幅减少且尺寸明显减小，硬度为225～237 HV。珠光体在不同冷速下的形态不同，冷速较小时以片层及短棒状为主，还有少量球状，随着冷速增加，短棒状珠光体占比增加，片层及球状珠光体占比减小。

Determination and analysis of continuous cooling transformation curves of SWRCH35K steel

Thermal dilatometric curves of SWRCH35K steel were measured by DIL805A thermal dilatometer. The continuous cooling transformation (CCT) curves of the tested steel were drawn by the tangent method combined with the microstructure and hardness. The influence of the cooling rate on microstructure evolution of the tested steel during the continuous cooling process was analyzed. The results show that when the cooling rate is in the range of 0.1-1 ℃/s, the microstructure is polygonal proeutectoid ferrite and pearlite. With the increase of the cooling rate, the microstructure is refined, the content of pearlite increases, and the hardness is 148-165 HV. When the cooling rate is 3 ℃/s, a small amount of Widmanstátten structure and bainite begin to appear, and the hardness increases to 189 HV. When the cooling rate is in the range of 5-50 ℃/s, the ferrite appears as network along the grain boundary, and the acicular Widmanstátten structure increases, the microstructure is composed of ferrite at grain boundary, pearlite, Widmanstátten structure and bainite. When the cooling rate is 30-50 ℃/s, the ferrite content and size are greatly reduced, and the hardness is 225-237 HV. The morphology of pearlite changes differently under different cooling rates. When the cooling rate is small, the morphology of pearlite is mainly lamellar and short rod-shaped, and with a small amount of spherical. With the increase of cooling rate, the proportion of short rod-shaped pearlite increases, and the proportion of the lamellar and spherical pearlite decreases.