热处理工艺对高碳贝氏体钢的组织与性能影响

Effect of heat treatment process on microstructure and properties of high carbon bainitic steel

以轴承用高碳贝氏体钢为研究对象,采用扫描电子显微镜、X射线衍射仪及硬度计等手段研究了不同奥氏体化温度对贝氏体钢组织形成及性能的影响,遴选出最优的奥氏体化工艺,同时对比了不同贝氏体等温转变后有无Ce元素添加的高碳贝氏体钢的力学性能。试验结果表明,950℃奥氏体化温度得到的组织中无明显的大颗粒未溶碳化物,组织尺寸和硬度性能居中,残余奥氏体中的碳含量最高,为最佳的奥氏体化温度。在同样的奥氏体化温度和贝氏体等温温度下,添加稀土元素有轻微的抑制晶粒长大作用,而对贝氏体束的尺寸、贝氏体转变完成率和钢的拉伸性能几乎没有影响,这与钢中固溶的稀土含量太少有关。随贝氏体等温温度从300℃降低到220℃,高碳贝氏体钢的硬度、抗拉强度、屈服强度均增大,但伸长率显著降低。这与组织中的贝氏体铁素体体积分数增加、贝氏体束尺寸细化以及残余奥氏体中的碳含量增加有关。300℃等温处理后的试样断口表面由细小的韧窝和解理平面构成,为准解理断裂模式;经过220℃等温处理的试样断口表面均为平坦的解理平面,为解理断裂。

The effect of different austenitizing temperatures on the structure and properties of high carbon bainitic steel for bearings were investigated by scanning electron microscope(SEM),X-ray diffractometer(XRD)and hardness tester.The optimal austenitizing process was selected,and the mechanical properties of high-carbon bainite steel with or without Ce addition after different bainite isothermal transformation processes were compared.The results show that there are no obvious large undissolved carbides at 950℃austenitizing.For this austenitizing temperature,the microstructure size and hardness performance are moderate and carbon content in retained austenite is the highest.It demonstrates that 950℃is the optimal austenitizing temperature.At the same temperature of austenitizing and bainite isothermal,the addition of rare earth elements can slightly inhibit the growth of grain size,whereas affects little on the size of bainite sheaves,accomplishment ratio of bainitic transformation and tensile properties of steel.It is due to the low content of rare earth elements in solid solution of steel.As the bainite isothermal temperature decreases from 300℃to 220℃,the hardness,tensile strength and yield strength of high-carbon bainite steel all increases,while the elongation decreases significantly.It is related to the increased volume fraction of bainitic ferrite,the refined bainite sheaves and increasing of carbon content in retained austenite.The fracture surface of sample after isothermal treatment at 300℃is composed of small dimples and cleavage planes,which is quasi-cleavage fracture mode.The fracture surface of sample treated at 220℃is covered by flat cleavage plane,which is cleavage fracture.