再热蒸汽热段管道弯头软化原因分析

Analysis of Softening Reason of Reheating Steam Pipe Elbow

某电厂再热蒸汽热段管道弯头在热推制后出现硬度偏低、组织异常的现象,为了分析该弯头组织性能劣化的原因,进行了模拟折弯试验及弯后热处理试验。结果表明:在热变形过程中弯头组织发生动态再结晶,马氏体向铁素体+碳化物转变,导致硬度下降,再结晶后继续变形使铁素体沿变形方向被拉长;在成型结束后没有通过正火+高温回火处理来消除这种不正常的形变组织,是该弯头软化的主要原因。

The hardness of the reheating steam pipe elbow of a power plant reduced and its microstructure was abnormal. In order to analyze the causes of the material deterioration,simulative bending test and heat treatment test were carried out. The results show that in the thermal deformation process,the dynamic re-crystallization occurred in elbow structure,and martensite transformed to ferrite and carbide,resulting in the hardness decrease. After re-crystallization the ferrite was stretched along the direction of deformation with transforming. After forming, normalized and tempering treatment was not carried out to eliminate the abnormal deformation structure,which was the main reason for elbow softening.