组织状态对45CrNiMoVA钢超声滚压表面完整性的影响

Effect of Microstructure on Surface Integrity of 45CrNiMoVA Steel by Ultrasonic Surface Rolling Process

针对组织状态对超声滚压(USRP)表面完整性影响规律不明的问题,分别对铁素体+珠光体和回火马氏体两种组织状态下的45CrNiMoVA钢进行USRP试验,结合两种组织状态下材料动态力学性能的差异,对表面形貌及表面粗糙度、表层显微硬度、残余应力和表层微观组织进行对比分析。结果表明,较软组织状态下的材料在USRP作用下更容易实现表面光整效果,表层材料更容易发生塑性变形,导致形成更明显的表层硬化效果,但是难以形成更高幅值的残余压应力;USRP在45CrNiMoVA钢表层引入的残余压应力幅值与其组织强度大小成正比,回火马氏体组织状态下表层残余压应力易呈"勺形"分布,最大残余压应力出现在亚表面,达到-1 272 MPa,铁素体+珠光体组织状态下表层残余压应力易呈"梯度"分布,最大残余压应力出现在表面,达到-694 MPa;体心四方(BCT)晶体结构的组织在USRP作用下更容易发生晶粒细化,而体心立方(BCC)晶体结构的组织在USRP作用下以塑性变形为主。以上规律可用于指导不同组织状态下材料加工表面完整性的精准调控。

To solve the problem that the effect of microstructure on the surface integrity of ultrasonic surface rolling process(USRP) is unclear,USRP tests were carried out on 45CrNiMoVA steel with ferrite + pearlite and tempered martensite respectively.The surface morphology,surface roughness,surface microhardness,residual stress,and surface microstructure were analyzed.The results show that the material with a soft phase is easier to achieve surface finishing effect under USRP,and the surface material is more prone to plastic deformation,resulting in a more obvious surface hardening effect,but it is difficult to form higher amplitude residual compressive stress.The results show that the magnitude of residual compressive stress introduced by USRP on the surface of 45CrNiMoVA steel is proportional to its microstructure strength.The residual compressive stress on the surface of 45CrNiMoVA steel is easy to be "spoon-shaped"under tempered martensitic structure,and the maximum residual compressive stress appears on the subsurface,reaching -1 272 MPa.The residual compressive stress on the surface of 45CrNiMoVA steel is easy to be "gradient"under ferrite + pearlite structure,the maximum residual compressive stress is-694 MPa on the surface.The results show that the structure of BCT crystal is more prone to grain refinement under the action of USRP,while the structure of BCC crystal is mainly plastic deformation under the action of USRP.The above rules can be used to guide the accurate regulation of material processing surface integrity under different microstructure states.