等温淬火温度对超细贝氏体钢组织及耐磨性的影响

Effect of austempering temperature on the microstructure and wear resistance of ultrafine bainitic steel

设计了一种0. 7C的低合金超细贝氏体钢,并通过膨胀仪、二体磨损实验、光学显微镜、扫描电镜、X射线衍射、激光扫描共聚焦显微镜及能谱仪,研究了不同等温淬火温度对超细贝氏体钢的贝氏体相变动力学、微观组织以及干滑动摩擦耐磨性的影响,揭示超细贝氏体钢在二体磨损条件下的耐磨性能和磨损机理.研究结果表明,不同等温温度下的超细贝氏体钢都由片层状贝氏体铁素体和薄膜状以及块状的残留奥氏体组成;随着等温温度的升高,超细贝氏体的相变速率提高,相变孕育期及相变完成时间缩短,但贝氏体铁素体板条厚度增加,残留奥氏体含量增加,硬度值有所降低;超细贝氏体钢磨损面形貌以平直的犁沟为主,主要的磨损机理为显微切削;不同等温温度下所获得的超细贝氏体的耐磨性能都优于回火马氏体,且随着等温温度的降低,耐磨性能提高.其中在250℃等温所获得的超细贝氏体钢具有最优的耐磨性能,其相对耐磨性为回火马氏体的1. 28倍.这主要与超细贝氏体钢中贝氏体铁素体板条的细化及磨损过程中残留奥氏体的形变诱导马氏体相变(TRIP)效应有关.

Ultrafine bainitic steels,which are derived from nanostructured carbide-free bainitic steels,exhibit a remarkable combination of ultra-high strength and toughness together with excellent wear resistance. Their excellent integrated mechanical properties has made ultrafine bainitic steels a popular choice for application as wear-resistant parts. In this study,a 0. 7-C low alloy ultrafine bainitic steel was designed,and the effects of different austempering temperatures on the bainitic transformation kinetics,microstructure,and dry sliding wear resistance of ultrafine bainitic steels were studied. Dilatometry,two-body abrasion testing,optical microscopy( OM),scanning electron microscopy( SEM),X-ray diffraction,laser-scanning confocal microscopy,and energy-dispersive spectrometry were used to study the abovementioned effects. Meanwhile,the wear performance and wear mechanism under two-body abrasion of ultrafine baintic steels with different austempering temperatures were also studied. The results demonstrate that the microstructures of ultrafine bainitic steel produced at different austempering temperatures comprise both lamellar bainitic ferrite and film-like and blocky retained austenite. With increasing austempering temperature,the transformation rate of bainite increases,and the incubation period and phasetransformation completion time of bainite significantly reduce; in addition,the bainitic ferrite plates are more coarsened,the volume fraction of retained austenite increases,and the hardness decreases. Moreover,when the ultrafine bainitic steel is subjected to the twobody abrasion test,the wear surface is mainly featured by furrows and grooves,and the predominant wear mechanism is micro-cutting.Furthermore,the wear resistance of ultrafine bainite post austempering at different temperatures is better than that of tempered martensite; this wear resistance increases with decreasing isothermal temperatures. Ultrafine baintic steel post austempering at 250 ℃ possesses the best wear resistance,and the relative wear resistance is 1. 28 times higher than that of tempered martensitic steel; this is attributed to the refined microstructure and the transformation induced plasticity( TRIP) effect of ultrafine bainitic steel.