高标轴承钢SUJ2的质量控制研究

发布时间：2019-03-24 17:42

【摘要】：随着轨道交通、隧道工程、风电和汽车等高端装备领域的高速发展,对轴承钢所用原材料质量提出了越来越高的要求,特别是轴承钢的冶金质量、碳化物的均匀性及表面脱碳深度等。本文针对国内某厂热轧高标轴承钢SUJ2存在网状碳化物及脱碳层深度超标等问题,通过对该钢的高温形变特征,高温氧化和脱碳特性,控轧控冷过程中网状碳化物特性的研究,分析造成该钢质量不稳定的内外部因素,为提高该钢的质量提供理论基础和实验依据。主要工作内容如下:对高标轴承钢SUJ2进行单道次压缩热模拟实验,研究了该钢在800~1050°C和0.01~10 s~(-1)条件下的热变形行为,建立了该钢高温热变形本构方程,基于DMM材料模型及Ziegle-Prasad失稳判据建立了热加工图,分析了工艺参数对SUJ2钢的热加工性能的影响。结果表明:该钢在低温高应变速率,高温高应变速率及高温低应变速率区间会发生失稳。利用热加工图确立该钢的最佳热加工区间为800~930°C,应变速率为0.01~0.3 s~(-1)及950~1050°C,应变速率为0.1~1 。通过高温加热炉对高标轴承钢SUJ2在1000~1220°C,不同氧流量(0.0 L/min、1.5 L/min、3 L/min)下的氧化和脱碳行为进行研究。结果表明:单位面积氧化增重量随着温度的升高和时间的延长而增加,脱碳层深度随着温度的升高先增加后降低。氧化层中相组成由内到外分别为Fe_(1-y)O、Fe_3O_4、Fe2O3,不同温度和不同氧流量下氧化层中三种物相的比例不同。随着脱碳层深度的增加,Fe_(1-y)O与Fe_3O_4的比值降低;随着脱碳层深度的降低,Fe_(1-y)O与Fe_3O_4的比值升高。氧流量1.5L/min条件下的脱碳层深度最低。采用热模拟机对高标轴承钢SUJ2进行连续冷却转变实验和轧后网状碳化物控制实验,研究了不同冷却速度(0~20°C/s)下的组织转变规律和轧后冷却速度(3~30°C/s)、终冷温度(750~550°C)及缓冷速度(1~5°C/s)对网状碳化物析出的影响。结果表明:随着冷却速度的增加,晶界处析出的碳化物由连续的网状转变为半连续状,抑制网状碳化物析出的临界冷却转变速度为8°C/s。在轧后控冷过程中,随着冷却速度增加,终冷温度降低及缓冷速度增加,可以抑制网状碳化物的形成,获得具有良好性能的热轧态索氏体组织。通过实验室开发的SUJ2钢组织性能预报系统对网状碳化物在轧制过程中的析出阶段和截面上的析出节点进行预报。对棒材而言,网状碳化物主要在截面的1/4和1/2处形成。对于不同规格的成品材而言,网状碳化物主要在精轧阶段及轧后上冷床过程中或在冷床上形成。
[Abstract]:With the rapid development of high-end equipment such as rail transit, tunnel engineering, wind power and automobile, the quality of raw materials used in bearing steel is required to be higher and higher, especially the metallurgical quality of bearing steel. The uniformity of carbides and the depth of surface decarbonization. In view of the problems of reticulated carbide and decarburized layer depth in SUJ2, a high standard bearing steel hot rolled in China, the characteristics of high temperature deformation, high temperature oxidation and decarbonization, and the characteristics of reticulated carbides in controlled rolling and controlled cooling process are studied by means of high temperature deformation characteristics, high temperature oxidation and decarbonization characteristics. The internal and external factors causing the instability of the steel quality are analyzed in order to provide theoretical basis and experimental basis for improving the quality of the steel. The main contents are as follows: the thermal deformation behavior of high standard bearing steel SUJ2 under 800 ~ 1050 掳C and 0.01 ~ (- 1) 10 s ~ (- 1) was studied by single pass compression thermal simulation experiment, and the constitutive equation of high temperature thermal deformation of the steel was established. Based on DMM material model and Ziegle-Prasad instability criterion, the hot-working diagram was established and the effect of process parameters on the hot-working properties of SUJ2 steel was analyzed. The results show that the steel will lose stability at high strain rate at low temperature, high strain rate at high temperature and low strain rate at high temperature. The optimum hot working interval of the steel is 800 ~ 930 掳C, the strain rate is 0.01 ~ 0.3 s ~ (- 1) and 950 ~ 1050 掳C, and the strain rate is 0.1 渭 1. The oxidation and decarbonization behavior of high standard bearing steel SUJ2 at 1000 ~ 1220 掳C with different oxygen flux (0.0L / min, 1.5L / min, 3 L/min) was studied by high temperature heating furnace. The results show that the increase of oxidation weight per unit area increases with the increase of temperature and time, and the depth of decarburization layer increases first and then decreases with the increase of temperature. The phases in the oxide layer are Fe_ (1) O, Fe _ 2O _ 3, Fe _ 2O _ 3 and Fe _ 2O _ 3 respectively from inside to outside. The ratios of the three phases in the oxide layer at different temperatures and different oxygen flow rates are different. With the increase of decarburization depth, the ratio of Fe_ (1) O to Fe_3O_4 decreases, and with the decrease of decarburization depth, the ratio of Fe_ (1) O to Fe_3O_4 increases. The depth of decarbonization layer is the lowest under the condition of oxygen flow rate 1.5L/min. The continuous cooling transformation experiment and reticulated carbide control experiment of high standard bearing steel SUJ2 were carried out by means of thermal simulator. The microstructure transformation rule and post rolling cooling rate (3 ~ 30 掳C / s),) at different cooling rates (0 ~ 20 掳C / s) were studied. The effects of final cooling temperature (750 ~ 550 掳C) and slow cooling rate (1 ~ 5 掳C / s) on the precipitation of reticulated carbides. The results show that with the increase of cooling rate, the precipitated carbides at the grain boundary change from continuous reticulated to semi-continuous, and the critical cooling rate to restrain the precipitation of reticulated carbides is 8 掳C. In the process of controlled cooling after rolling, with the increase of cooling rate, the final cooling temperature decreases and the slow cooling rate increases, the formation of reticulated carbides can be inhibited and the hot-rolled sorbite structure with good properties can be obtained. The microstructure and property prediction system of SUJ2 steel was developed in the laboratory to predict the precipitation stage of reticulated carbides in rolling process and the precipitated nodes on the cross section of the steel. For bars, the reticulated carbides are mainly formed at 1 / 4 and 1 / 2 of the cross-section. For different types of finished products, reticulated carbides are formed during finishing and post-rolling cooling beds or on cold beds.
【学位授予单位】：安徽工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1;TG335

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