时效对18Cr2Ni4WA钢微观组织的影响

用透射电镜和Ｘ－射线能谱仪对经自然和人工时效的１８Ｃｒ２Ｎｉ４ＷＡ钢的微观组织、析出相及其分布进行了研究。结果表明，在应力作用下，组织的回复趋于不均，沿晶界析出的脱溶物增多。回复较充分的铁素体板条中析出粗大的（Ｆｅ、Ｃｒ）３Ｃ，局部均匀分布；回复不充分处，沿晶界还析出长杆状的（Ｆｅ、Ｃｒ）３Ｃ和更细小的杆状Ｗ２Ｃ。时效后组织中元素Ｃ、Ｃｒ和Ｗ趋于沿晶界偏聚，其中Ｗ几乎全部以碳化物的形式存在于晶界附近。析出相（Ｆｅ、Ｃｒ）３Ｃ的［００１］晶带轴与α铁素体的［１２１］晶带轴近似平行。晶界脆性相的增多是该材料的螺栓在服役期间变脆和在腐蚀环境下失效的内在原因。

Effect of Aging on the Microstructure of 18Cr2Ni4WA Steel

The microstructures, precipitated phases and their distribution of 18Cr2Ni4WA steel, which were naturally and manually aged, have been investigated by means of CM200 TEM and EDAX/DX 4 X ray spectrometer. The results show that the working stress tends to cause the inhomogeneous restoration of the structure and the increase of the precipitates along the grain boundaries. Directionally arranged (Fe、Cr) 3C precipitated in the well restored lath ferrite, whereas the long bar-shaped (Fe、Cr) 3C and even thiner and smaller W 2C precipitated in the insufficiently restored area.Elements C,Cr and W tend to aggregate along the grain boundaries, of which W almost all gathered near the grain boundaries in carbides. The zone axis of of the carbide (Fe、Cr) 3C is nearly parallel to that of of the ferrite.The increase in the brittle precipitated phases along the grain boundaries is the inherent reason for embrittlement and failure of the bolt made of the steel when used in corrosive environment.