高钢级X100管线钢的组织和析出相

Microstructure and precipitates of X100 pipeline steel

利用扫描电镜,透射电镜对X100管线钢的显微组织和析出相进行观察,结果表明:X100管线钢的显微组织为粒状贝氏体和贝氏体铁素体,粒状贝氏体分割了取向多元的贝氏体铁素体,细化了晶粒尺寸,提高了材料的强韧性。管线钢中析出相为单相析出和复合析出,存在于晶界上、板条间、基体内、位错线上及其周围。管线钢中存在两种典型的单相析出,一种为尺寸较大,形状规则的TiN析出,一种为尺寸细小,形状为圆形的NbC析出。复合析出为在高Ti/Nb比的碳氮化物上附着着低Ti/Nb比的碳氮化物或硫化亚铜析出,为应变诱导析出。在高温下形成的TiN析出可以阻止晶界迁移,抑制奥氏体晶粒长大,对强度影响不大。低温形成的NbC和复合析出为应变诱导析出,平均尺寸为26.5 nm,在析出强化中占主导地位。

Microstructure and precipitates of X100 pipeline steel were observed by means of SEM and TEM. The results show that the microstructure of X100 pipeline steel consists of granular bainite and bainite ferrite. Granular bainite divides the multi-orientation bainite ferrite, refines grain size and improves strength and toughness of the material. Single precipitates and complex precipitates are observed in the steel, which distribute at grain boundaries, lath boundaries, matrix, dislocations and around the dislocations. There are two kinds of single precipitates. One is TiN precipitates with larger size and regular shape, and the other is spherical NbC precipitates with small size. Complex precipitates consist of the carbonitride with low Ti/Nb ratio or Cu2S precipitate attached to the carbonitride of high Ti/Nb ratio, which are strain induced precipitates. TiN formed at high temperature can prevent grain boundary migration, inhibit the growth of austenite grains and have little effect on strength. NbC and complex precipitates formed at low temperature are the strain induced precipitate, which have the average size of 26.5 nm and significant effect on strength.