Effect of coiling temperature on microstructure and properties of X100 pipeline steel

Multiphase structure of bainite and M/A(martensite/austenite constituent) can be obtained through coiling continuous-HOP (Heating On-line Partitioning) technology, resulting in excellent deformability for X100 pipeline steel. The microstructure and properties of the steel at different coiling temperatures were investigated by means of mechanical properties test, microscopic analysis and X-ray diffraction method. The results show that with the increase of coiling temperature, the strength decreases and the ductility increases because of the widening of bainite laths, the decrease of bainite content and dislocation density. However, because of the formation of martensite, the precipitation of carbides and the decrease of retained austenite at high coiling temperatures, the strength increases and the ductility decreases. Low yield ratio, high uniform elongation and high strain hardening exponent can be achieved at appropriate coiling temperatures through coiling continuous-HOP technology, which endows the steel with good ductility and excellent deformability.