热老化对阀体CF8M不锈钢显微结构及性能的影响

Effects of Thermal Aging on Microstructures and Mechanical Properties of CF8M Duplex Stainless Steels Used in Valve Body

在400℃下对阀体材料CF8M进行不同时长加速热老化试验,研究热老化对CF8M材料微观结构、拉伸性能及冲击性能的影响。结果表明:CF8M材料奥氏体基体在热老化初期存在大量位错缠结。然而随热老化时间的延长,基体中的位错缠结程度明显减轻,随后铁素体相内产生调幅分解;此外,CF8M材料在室温和350℃下抗拉强度均不断提高,而屈服强度前期略有升高、老化1000 h后则略有下降;而且在冲击温度较低时,同时,CF8M各老化状态下试样的冲击曲线下降段陡变;而在冲击温度较高时,CF8M各老化状态下试样的曲线面积(冲击功)随老化时间而缩小;另外,CF8M试样上平台值和下平台值随老化时间的增加而降低,韧脆转变温度随老化时间的增加而升高。

CF8M cast duplex stainless steels used in valve body were performed on a series of accelerated thermal aging test at 400℃ to investigate the effect of thermal aging on microstructures, tensile and impact properties of CF8M. The results indicate that CF8M austenite phases still consist of plenty of dislocation tangles at the initial stage, however, dislocation tangles decrease gradually with the thermal aging time increasing. Subsequently, spinodal decomposition is observed in ferrite phases. Moreover, the tensile strength of CF8M increases gradually with the thermal aging time increasing but the yield strength is improved slightly and then reduces after 1000 h thermal aging at room temperature and 350 ℃. Furthermore, the force-displacement curves decline sharply and then remain almost unchanged at low temperature while the curve areas （impact energy） of the specimens at each aging state decrease gradually with the thermal aging time increasing at high temperature. In addition, the lower and upper shelf energy of CF8M decrease gradually while the ductile-brittle transition temperature increases significantly with the thermal aging time increasing.