针状铁素体管线钢组织及强韧化机理研究

Research on microstructure and strength-toughening mechanism of acicular ferrite pipeline steel

采用TEM及原位TEM拉伸裂纹扩展观察等试验手段,研究了管线钢针状铁素体组织及各组织单元对位错运动及裂纹扩展的影响,分析讨论了针状铁素体的强韧化机理。结果表明,大角度晶界、M/A组元对位错的运动及裂纹扩展有显著影响,有效阻碍位错的运动和裂纹扩展,从而提高材料强韧性。小角度晶界对位错运动影响较小,对裂纹扩展几乎没有影响。针状铁素体组织中以块状转变机制形成的块状铁素体和非等轴铁素体使管线钢具有高的韧性,而低温转变的板条状贝氏体组织对强度贡献更大。

The microstructure of acicular ferrite pipeline steel and effects of the microstructural constituents of acicular ferrite （such as high-angle grain boundary, low-angle grain boundary, M/A island） on dislocation motion and crack propagation were investigated by transmission electron microscopy and in-situ tensile testing on a transmission electron microscope. The strength-toughening mechanism of acieular ferrite was discussed. The results indicate that the high-angle grain boundary and M/A island can effectively restrain dislocation motion and crack propagation, accordingly, improve the strength and toughness of the steel. The low-angle grain boundary exhibits an effect on dislocation motion, however, no significant effect on crack propagation is observed. The massive ferrite and non-equiaxial ferrite transformed by massive transformation mechanism in acicular ferrite microstructure make pipeline steel have high toughness. However, the lathy hainite structure transformed at lower temperature has great contribution to strength.