摘要为了进一步提高304奥氏体不锈钢的抗腐蚀性能，可以采用晶界工程中的形变热处理办法。本文通过不同的等径角挤压技术（ECAP）引入应变和后续热处理来改变不锈钢的组织结构和晶界特征分布，以探究不同的ECAP技术及后续热处理对不锈钢组织和性能的影响。利用OM、EIS、EBSD等技术研究奥氏体不锈钢在形变热处理前后组织特征和抗腐蚀性能的变化，并对产生这些变化的原因进行分析，得到以下结论：67817

（1）ECAP工艺可以细化奥氏体不锈钢晶粒，显著提升奥氏体不锈钢的硬度；但由于位错缺陷增多以及晶粒的细化所导致的晶界腐蚀通道的增加，从而降低了耐腐蚀性能。

（2）在相同ECAP挤压次数下，随着退火时间的延长，材料抗腐蚀性能先升高后下降；在相同退火时间内，随着挤压次数的增加，材料腐蚀性能也是先增加后下降。

（3）在退火温度为1150℃的情况下，测试了经ECAP1、2、4道次和退火时间1min、2min、5min的试样的耐腐蚀性能，电化学测试结果显示ECAP 1道次后退火处理1min试样抗腐蚀效果最好。该试样的EBSD测试结果显示其内部产生较多的低CSL特殊晶界和退火孪晶，有效地打断大角度晶界网络连通性，成功实现了GBCD（Grain boundary character distribution）的优化，说明ECAP工艺和后续退火处理手段可以优化304奥氏体不锈钢的GBCD和提高材料抗腐蚀性能。

毕业论文关键词：304奥氏体不锈钢，等径角挤压技术，晶界特征分布，退火处理，晶间腐蚀

毕业设计说明书（论文）外文摘要

Title      The research of grain boundary engineering of 304 austenitic stainless steel by ECAP                          

Abstract

In order to further improve the corrosion resistance of 304 austenitic stainless steel,we can use the approach of the grain boundary engineering based on thermomechanical processing. In this paper, microstructure and grain boundary character distribution (GBCD) are modified through different equal channel angular pressing (ECAP) and followed by different annealing treatment, to explore how different ECAP technology and heat treatment effecting on microstructure and properties of stainless steel. OM(Optical Microscope), EIS( Electrochemical Impedance Spectroscopy ) , EBSD (Electron Back Scatter Diffraction) were used to investigate the organizational characteristics and corrosion resistance change in the stainless steel after thermomechanical treatment, and analyze the causes of these changes,the main results are as follows:

(1)Austenitic stainless steel grain can be refined by ECAP process, the hardness of stainless steel is improved significantly; however, due to increasing in dislocation defects, the process reduces the corrosion resistance.

(2)Under the same number of ECAP extrusion, as the annealing time is lengthening,material corrosion resistance increased and then decreased;Annealing at the same time,and with the increasing in the number of ECAP, material corrosion resistance firstly increased and then decreased.

(3)Under the annealing temperature of 1150℃,corrosion resistance of the sampleare, cased by ECAP1, 2, 4pass, and the annealing time 1min, 2min, 5min, are tested. The electrochemical test results show that the corrosion resistance of the sample of ECAP 1 pass and annealing for 1min is the best. The result of EBSD testing the sample show that its internal produced more low-CSL special boundaries and annealing twins, effectively interrupting the connectivity of high angle grain boundary network, successfully achieving GBCD optimization, and it showd that the means of ECAP and subsequent annealing can effectively achieve GBCD optimization and improve the corrosion resistance of the material.