【作者】 王伟；

【导师】 侯振波；

【作者基本信息】 中国石油大学 ， 材料科学与工程， 2011， 硕士

【摘要】 35CrMo和40Cr等中碳低合金钢是制造各种机械主要结构件(如轴承零件、齿轮等)的重要钢材,也因其优异的综合性能备受青睐。然而在实际的应用中由于严酷的工矿环境其摩擦磨损现象日益严重,由此造成的经济损失和材料部件的浪费也越来越引起人们的关注。本文采用TJU-UMSNT-I型超声表面纳米加工处理装置对35CrMo和40Cr两种调质低合金钢进行加工处理,并对超声加工处理前后的材料进行550℃下的2小时和10小时的气体渗氮处理。采用透射电子显微镜对超声表面加工后的试样进行微观结构分析表明,经超声表面滚压加工处理后,在35CrMo和40Cr两种调质钢的表层形成了100μm左右的等轴纳米结构层,最表层的纳米晶粒大约为25nm,呈弥散分布,与心部未发生变化的晶粒相比,晶粒细化了约120倍。用金相显微镜对35CrMo和40Cr超声表面加工和超声表面加工前后渗氮试样进行微观组织观察,超声表面滚压加工在材料表面分别形成了约140μm和150μm左右的流变层;超声表面滚压加工前气体渗氮35CrMo和40Cr渗氮扩散层的厚度按渗氮时间的延长分别为:100μm、130μm和150μm、200μm,超声表面滚压加工后气体渗氮渗氮扩散层的厚度分别为:200μm、450μm和175μm、450μm。由此可知,表面纳米化预处理后的渗氮效果明显好于未表面纳米化预处理的试样,且渗氮时间越长,效果越明显。采用显微硬度计测试与分析超声表面加工和超声表面纳米化渗氮复合处理试样的显微硬度沿试样表面到心部的变化,结果表明,经超声表面滚压加工处理后材料的表面显微硬度HV分别为:695和706,与心部相比提高约2.6倍和2.5倍;超声表面纳米化前后气体渗氮处理,两种材料的表面显微硬度值与心部相比得到很大程度的提高,显微硬度值随距表面距离的增大而减小,且表面纳米化渗氮复合处理的渗氮时间越长,硬度梯度区域越大。不同处理后的试样经摩擦磨损试验后,通过磨损前后失重量变化、稳定摩擦阶段平均摩擦系数的测定等评价材料的耐磨性,采用扫描电子显微镜和体式显微镜对不同处理试样磨损后的形貌进行观察与分析可知,经超声表面纳米化加工和渗氮处理后,两种材料在稳定摩擦阶段的平均摩擦系数均比未处理试样的低,且平均磨损量均大幅度下降,说明两种处理方法均能明显改善材料的耐磨性,且表面纳米化处理试样的耐磨性效果更为明显;按照“调质-渗氮(2h和10h)-超声表面纳米化-表面纳米化气体渗氮(2h和10h)复合处理”,磨损方式由粘着磨损为主导的磨损机制向磨粒磨损为主导的磨损机制转变。因此,超声表面纳米化处理能显著提高低合金钢耐摩擦磨损性能,且其是一种提高其他表面强化处理方法强化效果的有效途径。更多还原

【Abstract】 35CrMo and 40Cr low-alloy steels are the main steels to create a variety of all kinds ofmechanical parts (such as bearing parts,and gear, etc.), and receive much concern because oftheir excellent comprehensive properties. However in the practical application, thephenomenon of their friction and wear becomes serious under the harsh mining environment,and the results of economic losses and waste of materials arouse people’s more and moreattention.In this paper, the samples of 35CrMo tempered steel and 40Cr tempered steel wereprocessed by TJU-UMSNT-I ultrasonic surface nanocrystallization device, and nitrided at 550℃for 2 and 10 hours before and after surface nanocrystallization.Then observe microstructure on the treated sample by Transmission Electron Microscope,and the result showed that Equiaxed crystal nanostructured surface layers about 100μm werefabricated on 35CrMo and 40Cr tempered steel by ultrasonic processing, with grain size of25nm at the top surface and random distribution of their orientation, at the same time, thegrain was highly refined.Examine and analyse the nitriding layers on the specimens before and afternano-treatment by metalloscope and hardness tester. And the results showed that about 140μmand 150μm flow layers were formed on two kinds of material by ultrasonic processing, andwith nitriding time different nitrided diffusion layers(35CrMo:100μm,130μm,200μm,450μmand 40Cr :150μm,200μm,175μm,450μm) were formed on the samples before and after surfacenoncrystalline processing. So, the effects of nano-nitriding samples were obviously better thannitriding with nitriding time.The surface hardness of 35CrMo tempered steel about 695HV and 40Cr tempered steelabout 706HV highly increased after ultrasonic surface processing and gas nitriding before and after surface nanocrystalline, compared with the center of the samples increased about 2.6times and 2.5 times. Hardness fell as the distance to the surface increases, and the range ofhardness region was prolonged with nitriding time after surface nanocrystalline.In the last, evaluate the abrasive resistance through measuring lost weights and averagefriction coefficient about materials after different processing, and analyze abrasion degree onthe samples treated through the different processing by Scanning Electron Microscope andasana microscope. Lost weights and average friction coefficient about materials by ultrasonicprocessing and gas nitriding treatment were obviously lower than unprocessed specimens, andsurface resistance to abrasion was enhanced．And the anti-wear performance of the samplesby ultrasonic processing were better. And wear mechanism changes from adhesive wear toabrasive wear.So Ultrasonic surface nanocrystallization treatment can significantly improve frictionand wear properties of low-alloy steel, and it is an effective way to improve other surfacehardening methods.更多还原