复合等温淬火对GCr15Si1Mo钢贝氏体转变及磨损性能影响

Effect of Compound Isothermal Quenching on Bainite Transformation and Wear Properties of GCr15Si1Mo Steel

纳米贝氏体轴承钢具有优异的综合性能,然而长时间的等温转变周期是限制其广泛应用的主要难题.为了加速GCr15Si1Mo轴承钢纳米贝氏体转变,本文中以常规一步(190℃)等温淬火工艺作为对比,设计了1种复合三步(157℃+190℃+250℃)等温淬火工艺,并对试验钢进行了不同工艺下的热处理.使用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、透射电子显微镜(TEM)和洛氏硬度仪等对GCr15Si1Mo轴承钢微观组织和力学性能进行了表征,利用UMT摩擦磨损试验机和三维形貌轮廓仪对试验钢的摩擦磨损性能进行了测试,并分析了其磨损机制.结果表明:复合等温淬火工艺从纳米贝氏体的孕育期和转变期两阶段对其转变进行加速,当转变相当含量贝氏体(53%~55%)时其相转变时间较常规等温淬火工艺缩短了5 h,明显提高了贝氏体转变效率;与常规等温淬火工艺相比较,复合等温淬火工艺材料微观组织中的残余奥氏体含量明显降低,且块状残余奥氏体大量转变为薄膜状残余奥氏体,材料的冲击韧性明显提高,但随复合等温淬火时间的延长,材料的冲击韧性出现了先升高后降低的趋势;当复合等温淬火工艺参数为157℃×5 min+190℃×2.0 h+250℃×1.0 h时,材料的强韧性匹配和耐磨性最佳,且其耐磨性明显也优于常规等温淬火工艺下材料的耐磨性.磨损机制结果表明:复合等温淬火和常规等温淬火处理后试验钢的磨损机制均以磨粒磨损为主,但复合等温淬火工艺下材料的磨粒磨损程度有所减轻并伴随轻微的黏着磨损和疲劳磨损.

Nano-bainite bearing steel has excellent comprehensive properties,but the long isothermal transition period is the main problem that limits its wide application.In order to accelerate the nano-bainite transformation of GCr15Si1Mo bearing steel,a compound three-step(157℃+190℃+250℃)isothermal quenching process was designed in this paper as a comparison with the conventional one-step(190℃)isothermal quenching process,and the test steels were heat-treated under different processes.The microstructure and mechanical properties of GCr15Si1Mo bearing steel were characterized by scanning electron microscope(SEM),X-ray diffractometer(XRD),transmission electron microscope(TEM)and Rockwell hardness tester.The tribological properties and wear mechanism of the test steel were investigated by using UMT friction,wear testing machine and 3D topography profilometer.The results showed that the compound isothermal quenching process accelerated the transformation of nano-bainite from the two stages of gestation and transformation.Compared with the conventional isothermal quenching process,the phase transition time of the compound isothermal quenching process decreased by 5 h when they both transformed the equivalent content of bainite(about 53%~55%).Therefore it could significantly improve the transformation efficiency of nano-bainite.In the compound isothermal quenching process,the residual austenite content in the microstructure was obviously reduced,and the block residual austenite was largely transformed into thin film residual austenite,thus the impact toughness of the material which was treated by using the compound isothermal quenching was obviously improved.With prolonging the compound isothermal quenching time,the impact toughness of the material firstly increased and then decreased.When the compound isothermal quenching process parameter was 157℃×5 min+190℃×2.0 h+250℃×1.0 h,the strength and toughness matching and wear resistance of the material were the best,and the wear resistance of the material was better than that of the conventional isothermal quenching process.The results indicated that the dominant wear mechanism of the test steel was abrasive wear after the compound isothermal quenching and the conventional isothermal quenching,but the degree of abrasive wear of the material under the compound isothermal quenching process was reduced and accompanied by slight adhesive wear and fatigue wear.