【作者】 王晓燕；

【导师】 苏宏华；

【作者基本信息】 南京航空航天大学 ， 材料学， 2008， 硕士

【摘要】 表面磨削淬火技术是利用磨削热将工件表层瞬间加热到奥氏体相变温度以上,以大于马氏体相变开始的临界淬火冷却速度急速冷却,使工件表层发生马氏体相变,达到淬硬目的。它把磨削加工与表面淬火结合起来集成于一体——利用磨削热直接对工件表面进行表面淬火,使工件达到或超过感应表面淬火工艺下的性能指标,节能、高效、环保,非常有前景。本文以汽车曲轴用钢F48MnV为研究对象,根据磨削淬火技术工艺已有的研究成果制定了磨削试验方案,开展了以下试验工作:热膨胀仪测定F48MnV的奥氏体转变温度,普通淬火试验,F48MnV-镍铬热电偶的标定,磨削力与工件表面磨削温度的测量、金相实验、扫描电镜实验、透射电镜实验等研究工作。从工件表面磨削温度的特征和固体相变原理上,深入地研究了磨削淬火工艺中的相变强化机理。研究结果表明,表面磨削强化工艺可获得HK700以上的高硬度淬硬层,最大淬硬层深达1.2mm以上。磨削热能量密度很高约106～108 W/cm2,工件表面升温和降温速率极快在～104℃/s量级。奥氏体区间非常窄,仅为零点几秒,奥氏体转变不完全,有部分铁素体未溶解,马氏体相变开始温度降低。磨削淬火形成的马氏体组织非常细小,光学显微镜下其金相组织为隐针马氏体,沿晶界等缺陷密度高的位置有自回火现象,呈时效强化。表层组织因受切向磨削力作用而拉长变形;淬硬层内由于马氏体相变为体积增大的相变,使得与基体交界处晶粒亦受拉应力作用有伸长变形。经透射电镜观察,磨削淬火马氏体内为大量孪晶亚结构,孪晶亚结构中有高密度的位错,且马氏体组织细小,呈现板条马氏体向片状马氏体转变趋势。更多还原

【Abstract】 Grinding-quenching is a new technology which is utilized grinding heat to quench the workpiece surface and introduce martensite to strengthen the surface layer. Through the process, the surface layer can achieve excellent properties in the hardness and wear resistance. It integrates surface heat treatment and grinding into one production line, which can decrease manufacturing cost, improve machining efficiency, and reduce production time.The grinding-quenching mechanism was studied by deeply analyzing the surface temperature changing rates and solid phase transformation on the basis of experiments. Several trails were done, mainly including mensurating the point of austenite transformation of F48MnV steel, conventional quenching experiment, marking F48MnV-NiCr half artificial thermocouple, measuring grinding force and temperature of the workpiece surface, taking topical micrographs, SEM and TEM micrographs etc.It was found that the micro-hardness of the grind-hardening layer was HK700 over, which was greatly higher than the conventional martensite, and the deepest layer could reach 1.2mm. The density of grinding heat was about～2.6×105W/cm2 and the heating and cooling rate arrived at the level of 104℃/s. The austenite existed only for ~10-1s, which brought into the austenite transformation was incomplete and partial ferrite wasn’t dissolved and Ms temperature played down. The optical micrograph of the grinding martensite (GM) was almost featureless and there were autokinetic temper phenomena along the area of high densities dislocations. By TEM, the GM consisted of mass twined-substructures including intensive dislocations and its grain size was smaller. In addition, the shape of the GM tended to transform from lath martensite to twins.更多还原