Heat treatments are commonly applied in the martensitic stainless steels to achieve high wear resistance and hardness; however, they can lead to a decrease in corrosion resistance due to the precipitation of chromium-rich carbides. The present work investigates the effect of austenitizing and tempering parameters on the microstructure, hardness, and passivation and reactivation currents of AISI 440C. A double-loop electrochemical potentiodynamic reactivation test is performed to evaluate the dissolution and precipitation of chromium-rich carbides. The volume fraction of phases after heat treatment is estimated by X-ray diffraction. Results show that an increase in the austenitizing temperature leads to an increase in the carbide dissolution, and also in the amount of retained austenite. As a consequence, low passivation and reactivation currents are obtained. When austenite is the main phase, the increase of austenitizing time contributed to an increase in the degree of sensitization due to austenite grain boundary carbon enrichment. However, the presence of austenite after tempering kept part of the carbon in a solid solution resulting in low passivation and reactivation currents.

中文翻译：

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热处理对高碳马氏体不锈钢贫铬区的影响

马氏体不锈钢通常采用热处理以达到高耐磨性和硬度；然而，由于富铬碳化物的沉淀，它们会导致耐腐蚀性能下降。目前的工作研究了奥氏体化和回火参数对 AISI 440C 的微观结构、硬度以及钝化和再活化电流的影响。进行双回路电化学动电位再活化试验以评估富铬碳化物的溶解和沉淀。热处理后相的体积分数通过 X 射线衍射估计。结果表明，奥氏体化温度的增加导致碳化物溶解的增加，以及残余奥氏体的量增加。作为结果，获得低钝化和再激活电流。当奥氏体为主相时，由于奥氏体晶界碳富集，奥氏体化时间的增加有助于敏化程度的增加。然而，回火后奥氏体的存在使部分碳保持在固溶体中，从而导致低钝化和再活化电流。