【作者】 魏莉；

【导师】 魏晓伟；

【作者基本信息】 西华大学 ， 材料加工工程， 2009， 硕士

【摘要】 本课题针对AISI 304奥氏体不锈钢进行辉光离子渗氮和离子氮碳共渗研究。目的在于提高奥氏体不锈钢硬度与耐磨性的同时,不显著减低其耐腐蚀性能。奥氏体不锈钢具有良好的耐腐蚀性能,广泛应用于化工、石油、食品和医疗器械等行业,但是其硬度低、耐磨性差。为了进一步扩大奥氏体不锈钢的应用范围,作者试图采用脉冲电流辉光离子渗氮的方法对其进行表面处理,提高其硬度及耐磨性。辉光离子氮化具有渗速快、工件变形小、节能等优点,广泛应用于各种金属材料,特别是不锈钢零部件,因为离子渗氮前不需要预先去钝化处理,离子氮化的阴极溅射效应,可以清除不锈钢表面的钝化膜。但是离子渗氮提高奥氏体不锈钢表面硬度和耐磨性的同时,使其耐腐蚀性能下降。本文研究了在氨气气氛中渗氮温度、时间、气压和电压,以及氨气与丙酮混合气氛中丙酮含量和共渗温度对渗层质量的影响,利用光学显微镜、扫描电子显微镜、X射线衍射仪、显微硬度计、电位仪等检测方法对渗层金相组织、渗层厚度、渗层相组成、表面显微硬度、极化曲线等进行研究,试验结果表明:离子渗氮与离子氮碳共渗渗层组织相似,均由扩散层构成,扩散层表面的白亮层不明显。渗氮温度对渗氮层和氮碳共渗层质量影响最大,随着处理温度增加,CrN的含量增加,渗层厚度增加,表面显微硬度先增加后减少,渗层硬度梯度逐渐平缓。渗氮时间主要影响渗层厚度,随着渗氮时间延长,渗层厚度显著增加。渗氮气压对渗层厚度和表面显微硬度影响较大,随着渗氮气压升高,渗层厚度增大,渗层表面显微硬度先增加后减小,渗层表面显微硬度梯度趋于平缓。渗氮电压影响渗层表面CrN含量和表面显微硬度,随着渗氮电压升高,渗层表面CrN含量减少,表面显微硬度增加。离子氮碳共渗气氛中丙酮含量影响渗层表面CrN的含量、渗层厚度、表面腐蚀速度及渗层硬度梯度,渗氮气氛中加入丙酮有利于降低CrN的含量,随着氮碳共渗气氛中丙酮含量的增加,渗层厚度先增加后减小。降低奥氏体不锈钢离子氮化过程中铬的沉积方法包括:降低渗氮温度,缩短渗氮时间,控制渗氮气压适中,控制渗氮电压偏高,渗氮气氛中添加丙酮。从综合的角度考虑,奥氏体不锈钢离子渗氮的工艺参数为:渗氮温度500℃、渗氮时间2h、气压350Pa、电压900V。离子氮碳共渗时,丙酮含量为2.5%。AISI304奥氏体不锈钢经上述工艺条件处理后,获得的渗层既具有高的硬度,又具有良好的耐腐蚀性。更多还原

【Abstract】 Glow discharge nitriding and nitrocarburising in AISI 304 austenitic stainless steel were approached in this paper. The aim of this paper was to improve the hardness and wear resistance of AISI 304 austenitic stainless steel and retain the corrosion resistance. The austenitic stainless steels are widely used in many fields such as chemical industry, oil industry, food processing and medical apparatus and instruments due to their well corrosion resistance, but they have low hardness and bad wear resistance. For further expanding the application of austenitic stainless steels, pulse current ionitriding was employed to improve their hardness and wear resistance. Because of the advantages of fast nitriding, small workpiece deformation and energy saving, ionitriding are widely used in different kinds of metal materials, especially the parts of stainless steel. The cathode sputtering effect of ionitriding can remove the passivating film on the surface of stainless steels, so it needn’t do previously depassivation processing before ionitriding. But ionitriding can improve the surface hardness and wear resistance of austenitic stainless steel as well as decrease its corrosion resistance.The effects of nitriding temperature, time, pressure, voltage in ammonia gas and content of acetone, nitrocarburising temperature in ammonia and acetone mixture on the quality of nitrided layers were studied in this paper. Some measurements were used such as an optical microscope, a scanning electron microscope, an X-ray diffractometer, a Vickers microhardness tester and an electrochemical testing technique to study the metallurgical structure, thickness, phase composition, surface microhardness and polarization curves of the nitrided layers. The results were shown:The nitrided layers after ionitriding and the nitrocarburized layers after ionitrocarburising were similar; they all exhibit a diffusion layer with an obscure "white" appearance on it. The most influence on the quality of nitrided layers and nitrocarburized layers is nitriding temperature. As treatment temperature increasing, the content of CrN and the thickness of nitrided layers increase; the surface microhardness of the nitrided layers increases at first and then decreases; and the microhardness gradients are gradually gentle. The nitriding time mainly affects the thickness of the nitrided layers. As the nitriding time extending, the thickness of the nitrided layers apparently increases. The nitriding pressure affects the thickness and the surface microhardness of the nitrided layers. As the nitriding pressure increasing, the thickness of the nitrided layers increases; the surface microhardness of the nitrided layer increases at first and then decreases; and the microhardness gradients are gradually gentle. The nitriding voltage affects the content of CrN and surface microhardness of the nitrided layers. As the nitriding voltage increasing, the content of CrN on the surface of the nitrided layers decreases; and the surface microhardness of the nitrided layers increases. The content of acetone in ammonia and acetone mixture during ionitrocarburising affects the content of CrN on the surface of the nitrocarburized layers, the thickness of the nitrocarburized layers, rate of corrosion on the surface of the nitrocarburized layers and the microhardness gradient. The addition of acetone in the nitriding gas helps to decrease the content of CrN. As the content of acetone in the nitrocarburising gas increasing, the thickness of the nitrocarburized layers increases at first and then decreases.The methods to decrease chromium precipitation in austenitic stainless steel during the ionitriding process include decreasing the nitriding temperature, shortening the nitriding time, making the nitriding pressure moderately, controling the nitriding voltage a bit higher and addition acetone in the nitriding gas. Comprehensive analysis, the processing parameters of austenitic stainless steel during ionitriding are nitriding at the temperature of 500℃, at the pressure of 350 Pa, with the voltage of 900 V for 2 h, and nitrocarburising with the content of acetone at 2.5 %. AISI 304 austenitic stainless steel treated in the condition of those processing parameters can obtain the nitrided layer with both high hardness and well corrosion resistance.更多还原