QPQ盐浴复合处理对50钢耐磨性的影响

Influence of Quench-Polish-Quench Salt Bath Composite Treatment on Microstructure and Wear Resistance of 50 Steel

目前，对50钢采用QPQ盐浴复合处理后的研究报道不多，对其在冲击载荷下的摩擦磨损研究更为鲜见。用QPQ技术于570℃下对50钢氮碳共渗2h，再于温度370℃下氧化20min，利用SEM、显微硬度仪、x射线衍射仪和摩擦磨损试验机分别对QPQ渗层的显微组织、显微硬度、化学成分和耐磨性进行了研究。结果表明：QPQ渗层表面平整，渗层由外到内依次为氧化膜、疏松层、化合物层和扩散层；QPQ处理后试样的表面硬度为520HV1N，在QPQ处理过程中，由于N元素的不断渗入，钢的表面形成Fe2～3N和Fe4N相；经QPQ处理的试样在干摩擦、油润滑和存在冲击载荷的情况下，摩擦系数和磨损量均分别有不同程度的减小，摩擦系数最高减少了33％，最小磨损量仅为调质态试样的7．7％。

Few reports are currently available about quench-polish-quench( denoted as QPQ) salt bath composite treatment of 50 steel,and less concerns the friction and wear behavior of 50 steel after QPQ salt bath composite treatment in the presence of impact load. Therefore,QPQ salt bath composite treatment of 50 steel,involving 2 h of nitro-carburizing at 570 ℃ and follow-up 20 min of oxidation at 370℃,was conducted. The microstructure and phase composition of as-obtained QPQ permeation layer were analyzed with a scanning electron microscope and an X-ray diffractometer. The hardness of the QPQ permeation layer was determined with a microhardness meter,and its friction and wear behavior was evaluated with a friction and wear tester. Results indicated that as-obtained QPQ permeation layer was flat and consisted of oxidation film,loose layer,compound layer and diffusion layer from the outside to the inside. Besides,50 steel after QPQ salt bath composite treatment had a surface hardness of 520 HV1 N; and Fe2 ~ 3N and Fe4N phases were formed on the surface of the steel owing to continuous infiltration of N during QPQ treatment. Moreover,under dry sliding condition,oil-lubricated condition,and impact loading condition,both the friction coefficient and wear mass loss of the steel after QPQ salt bath composite treatment were reduced to different extents. Particularly,the friction coefficient could be reduced by up to 33% as compared with that of the untreated steel,and the minimum wear mass loss of the QPQ permeation layer was only about 7. 7% of the wear mass loss of the steel matrix.