接触应力对FCB车轮钢组织演变与性能的影响

Effect of Contact Stress on the Evolution and Properties of FCB Wheel Steel

利用双盘滚动摩擦磨损试验机进行了贝氏体车轮钢的滚动磨损试验,采用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)分析不同接触应力条件下贝氏体车轮钢次表层微观组织演变.结果表明:在滚动磨损条件下,磨损机制由黏着磨损转变为疲劳磨损,增大接触应力对黏着磨损阶段的磨损量影响不大,但会显著增加疲劳磨损阶段的磨损量;贝氏体车轮钢在塑性变形的过程中,贝氏体铁素板条中位错逐渐增值、先累积形成小角度晶界,而后形成大角度晶界,使贝氏体铁素体发生细化;接触应力的大小影响表层组织的演变,当接触应力增至1150 MPa时,晶粒细化为超细等轴晶,继续增加接触应力,组织变化并不明显.接触应力大小会影响贝氏体车轮钢的表面硬度.接触应力增加使贝氏体车轮钢的表面硬度增高,硬化层深度增大.

The rolling wear test of bainitic wheel steel was carried out using a double-disc rolling friction and wear tester,and the microstructure evolution of the sub-surface layer of bainitic wheel steel under different contact stress conditions was analyzed by scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD).The results showed that under the conditions of rolling wear,the wear mechanism transited from adhesive wear to fatigue wear.Increasing contact stress had little effect on the amount of wear in the adhesive wear stage,while it significantly increased the amount of wear in the fatigue wear stage of bainitic wheel steel.In the process of plastic deformation,the dislocations in the bainitic ferrite lath gradually increased and firstly accumulated to form small-angle grain boundaries,and then formed large-angle grain boundaries.Consequently,bainitic ferrite was refined;the magnitude of contact stress affected the evolution of the surface structure.When the contact stress increased to 1150 MPa,the grains were refined into ultra-fine equiaxed crystals.As the contact stress further increased,and the structure change was not obvious.The contact stress affected the surface hardness of the bainitic wheel steel.The increase in contact stress increased the surface hardness of the bainitic wheel steel and the depth of the hardened layer increased.