应变诱发马氏体相变对304奥氏体不锈钢非线性超声响应的影响

发布时间：2018-01-20 05:58

本文关键词： 304奥氏体不锈钢应变诱发马氏体相变非线性超声技术　出处：《华东理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：奥氏体应变强化技术广泛应用于核电站、化工厂等处压力容器的制造,利用这一手段可以有效提高材料强度,从而实现安全生产、节约原料、降低能耗等目的。而304奥氏体不锈钢又是工业领域应用较广的材料,其应变强化是通过位错强化及应变诱发马氏体相变(DIMT)等微观结构强化共同实现的。因此,了解形变过程中材料微观结构变化情况对于了解材料机械性能十分关键,而针对微观结构变化的检测手段也就显得尤为重要。近年来的研究表明,非线性超声波检测技术能够表征材料变化,且作为一种无损检测技术值得研究与探讨。本文为了探究非线性超声波对应变过程中不同微观结构材料的响应情况,设计-70℃、25℃、300℃三种温度下的单向中断拉伸实验,得到含有不同马氏体相变量的试样,并对其进行各项超声波检测。实验结果表明,超声非线性参数在三种温度下均随形变量的增大而增大,且温度越低,非线性参数的增长率越高。通过透射电镜、电子背散射衍射等微观分析方法,对304奥氏体不锈钢形变过程中微观结构演化情况进行了细致分析,包括位错增长、位错胞的形成、层错和孪晶的产生、剪切带的发展以及马氏体相变的形核与生长过程。观察后可以确认,低温下试样中应变诱发马氏体相变过程的加快是导致非线性参数的增长率增加的重要原因。通过对α’-马氏体含量的检测,发现α’-马氏体的含量随形变量的增大而增加。通过拟合得到了α’-马氏体与非线性参数间的幂函数关系式,了解了马氏体相对超声非线性检测的影响。
[Abstract]:Strain strengthening technology is widely used in nuclear power plants, chemical plants and other manufacturing pressure container, use this method can effectively improve the strength of the material, so as to realize safe production, save raw materials, reduce energy consumption. And 304 austenitic stainless steel is widely used in industrial field materials, the strain hardening by dislocation and strain induced martensite (DIMT) microstructure strengthening achieve together. Therefore, understanding the microstructure during deformation of the material changes to understand the mechanical properties of materials is the key, and the detection means for the microstructure change is particularly important. Recent studies show that the nonlinear ultrasonic detection technique can characterize changes and, as a kind of nondestructive testing technology is researched and discussed. In order to explore different nonlinear ultrasonic strain in the process of micro structure of materials The response of the material, the design of -70 C, 25 C, 300 C three one-way interrupt tensile test temperature, containing samples with different martensite phase variables, and the detection of the ultrasonic. The experimental results show that the nonlinear ultrasonic parameters at three different temperatures increased with increasing deformation increases, and the lower the temperature, the higher the growth rate of nonlinear parameters. Through transmission electron microscopy, electron backscatter diffraction analysis method, the microstructure evolution of 304 austenitic stainless steel in deformation is analyzed in detail, including dislocation growth, the formation of dislocation cell, stacking faults and twins, as well as the development of martensitic shear zone phase nucleation and growth process. After the observation can be confirmed, speeding up the transformation process of strain induced martensite under low temperature in the sample is an important cause of nonlinear parameters increase the growth rate. The alpha '- martensite It is found that the content of alpha - martensite increases with the increase of the shape variables. The power function relation between the alpha - martensite and the nonlinear parameters is obtained through fitting, and the influence of martensite on ultrasonic nonlinearity is also known.

【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG142.71

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