贝氏体钢轨钢组织调控与性能优化

发布时间：2018-07-07 16:18

本文选题：贝氏体钢轨钢 + 强韧性　；参考：《北京交通大学》2017年博士论文

【摘要】：本文以20Mn2SiCrMo贝氏体钢轨钢为对象,进行了"成分-工艺-组织-性能"的系统研究,基于动态/静态CCT曲线和TTT曲线,结合模拟计算和实验检测,探究了成分、关键工艺参数与组织性能间的关系;针对贝氏体钢轨大生产时轧后空冷过程中出现的类等温平台现象,揭示了不同等温温度对相变、组织及性能的影响规律;研究了回火过程中残余奥氏体形态、含量及稳定性等对强韧性的影响规律;就深冷处理对贝氏体钢轨钢的影响进行了初步探索,并就调整后的贝氏体钢轨与珠光体钢轨的磨损与接触疲劳性能进行了对比研究,获得结果如下:1.元素Mn、Mo、Ni强化钢淬透性的作用明显,在现有贝氏体钢轨成分体系基础上,当Mn含量大于1.9wt.%左右时,能避免60kg/m重载钢轨轧后空冷过程中先共析铁素体的形成。模拟计算和试验检测吻合度较高,获得了—整套"模拟计算预测—实测—组织表征—关键部位仿真计算—反馈"的科学研究方案。2.在跟踪贝氏体钢轨实际生产时发现,轧后空冷到室温的过程中,在中温区某一温度附近钢轨将经历一定时长的类等温平台,该平台温度对钢轨的相变行为、显微组织及综合性能等有重要影响。随等温温度升高,粒状贝氏体含量逐步增加,板条贝氏体含量降低,马奥岛尺寸逐渐增大。通过调整等温平台温度可达到组织细化和性能优化的效果。当等温温度为325℃时,抗拉强度、断后伸长率及室温U型冲击韧性分别为1391 MPa、15%、142 J,比350℃等温时的冲击韧性高出约46%。以本研究结果为基础,后续通过进一步探究等温平台参数(温度、时间等)与相变行为的内在联系,从而可根据该等温平台的参数来感知钢中相变行为,并对钢轨的组织和性能进行预测与调控。3.回火处理后组织中残余奥氏体的含量、形态及稳定性对钢轨性能具有重要影响。随回火温度升高,马奥岛分解程度增加,残余奥氏体数量减少,钢轨钢韧性出现先升高后降低的趋势。回火处理可提高热轧态钢轨中残余奥氏体的稳定性,经280℃回火后,残余奥氏体的稳定性较高,可获得最佳的强韧性匹配。与钢轨轧态、250℃回火状态相比,280℃回火处理后贝氏体钢轨室温冲击韧性分别相应提高约90%和10%。4.深冷处理可作为贝氏体钢轨钢性能优化和延长钢轨服役寿命的一种潜在工艺。钢轨钢经深冷处理后,除残余奥氏体稳定性得到进一步提高外,其强度、延伸率及硬度等均获得不同程度提高。5.在滑动磨损和冲击磨损过程中,钢轨的相对耐磨性与实验所采用的载荷大小紧密相关。较大实验载荷下,贝氏体钢轨钢的耐磨性优于珠光体钢轨钢;较低实验载荷下,珠光体钢轨钢的耐磨性相对较好。在滚动接触疲劳过程中,珠光体组织比贝氏体组织更易形成表面硬化层,该硬化层与基体组织的界面是潜在的裂纹扩展路径。6.贝氏体钢轨服役过程中的失效分析表明,膜状马奥岛对于裂纹扩展具有抑制作用。
[Abstract]:In this paper, a systematic study of 20Mn2SiCrMo bainite rail steel was carried out. Based on the dynamic / static CCT curve and the TTT curve, the relationship between the components, the key process parameters and the microstructure and properties was investigated by the combination of the dynamic / static CCT curves and the TTT curves. The effect of different isothermal temperature on the phase transition, microstructure and properties of different isothermal temperatures is revealed, and the influence of the retained austenite shape, content and stability on the strength and toughness during the process of tempering is studied, and the influence of the cryogenic treatment on bainite rail steel is first explored, and the adjusted bainite rail and pearlite are made. The wear and contact fatigue performance of the body rail are compared. The results are as follows: 1. elements Mn, Mo and Ni strengthen the hardenability of steel obviously. On the basis of the existing bainite rail composition system, when the content of Mn is more than 1.9wt.%, the formation of the eutectoid ferrite in the cold process of heavy rail after 60kg/m heavy load can be avoided. A scientific research program of "simulated calculation, measurement, measurement, organization characterization, key position simulation calculation feedback" is obtained from the test test, and.2. is found in the actual production of bainite rail. It is found that in the process of air cooling to room temperature after rolling, the rail will undergo a certain length of class in the middle temperature zone near a temperature. Temperature platform, the temperature of the platform has an important influence on the phase transformation, microstructure and comprehensive properties of the rail. With the increase of temperature, the content of granular bainite increases gradually, the content of bainite decreases, and the size of Ma o Island increases gradually. The effect of microstructure refinement and performance optimization can be achieved by adjusting the temperature of the isothermal platform. At 325 C, the tensile strength, the elongation at the end and the U type impact toughness at room temperature are 1391 MPa, 15%, 142 J respectively, and the impact toughness is about 46%. higher than that of 350 C, based on the results of this study, and further explore the internal relations between the isothermal platform parameters (temperature, time, etc.) and the phase variation behavior, which can be based on the parameters of the isothermal platform. The phase transformation behavior in steel is perceived and the microstructure and properties of the rail are predicted and the content, morphology and stability of the retained austenite in the.3. tempering process have important influence on the rail performance. With the increase of tempering temperature, the decomposition degree of the Mao Island increases, the amount of the retained austenite decreases, and the toughness of the rail steel increases first. The tempering treatment can improve the stability of retained austenite in the hot rolled rail. After tempering at 280 C, the stability of the retained austenite is higher and the best strength and toughness can be obtained. Compared with the rail rolling state and the tempering state at 250 C, the impact toughness of the bainitic steel rail at 280 C after tempering is about 90% and 10%.4., respectively. Cryogenic treatment can be used as a potential process for optimizing the performance of bainite rail steel and prolonging the service life of rail. After cryogenic treatment of rail steel, the strength, elongation and hardness of the retained austenite are further improved, and the relative resistance of rail to.5. in the process of sliding wear and impact wear is improved in varying degrees. The wear resistance of the bainite rail steel is better than the pearlite rail steel under the larger experimental load. The wear resistance of the pearlite rail steel is better under the lower experimental load. In the rolling contact fatigue process, the pearlite structure is more prone to form the surface hardening layer than the bainite structure, and the hardened layer is more easily formed. The interface between the matrix and the matrix is the potential crack propagation path.6. bainite rail service failure analysis shows that the membrane like maro island has an inhibitory effect on the crack growth.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：U213.4

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