采用高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等分析手段研究了一种多相强化型马氏体时效不锈钢时效过程中的元素偏聚特征及其与材料力学和耐蚀性能的关系. 结果表明, 马氏体时效不锈钢在时效过程中析出3种强化相: 富Mo的R′相、Ni3Ti金属间化合物η相和富Cr的α′相. 其中R′相与η相一起形成核壳状结构, α′相则单独弥散分布于基体中. 时效时间延长至40 h后, 主要强化相η相的成分、数量密度和等效半径基本稳定, 同时马氏体时效不锈钢的强度不再发生明显的变化, 这种优异的抗过时效能力是由于核壳状结构的形成. 腐蚀实验结果表明, 由于富Cr的α′相的析出, 导致贫Cr区的形成, 进而降低了马氏体时效不锈钢的耐蚀性能.
Maraging stainless steels are the most widely used high strength stainless steels because of their excellent combination of high strength, superior corrosion resistance and good weldability. The typical heat treatment of maraging stainless steel consists of solution treatment and the following aging treatment. Aging treatment is the important process since it affects the steel's final properties and then determines its application prospect. Thus, understanding well the segregation behavior of alloying elements during the aging treatment plays a key role in developing the new maraging stainless steel with superior properties. In this work, segregation of alloying elements as well as its effect on mechanical properties and corrosion resistance of a multi-phase strengthened maraging stainless steel was studied by HRTEM and APT analyses. It was found that three precipitating species including Mo-rich R′ phase, η phase and Cr-rich α′ phase were identified in the steel. A unique core-shell structure with membrane-like R′ phase formed on the surface of η phase was identified however α′ phase distributed in the matrix separately. The core-shell structure enabled the maraging stainless steel a superior over-aging resistance and since aging time has reached 40 h, the characteristics of precipitations change little even aging time prolongs to 100 h. The corrosion test results indicated that the occurrence of α′ phase resulted in the formation of Cr-depleted zone and deteriorated the corrosion resistance seriously. In conclusion, the segregation behavior of alloying elements in maraging stainless steel has a significant effect on both mechanical property and corrosion resistance although some underlying mechanisms still haven't been understood well.
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