Microstructure and properties of X80 pipeline steel after delay accelerated cooling

The relationship between microstructure and properties for X80 pipeline steel after delay accelerated cooling( DAC) was investigated through the experimental techniques such as thermal simulation,mechanical property test and microscopic analysis method.The results show that( B + F) dual-phase microstructure in the steel can be obtained by DAC. With the increasing of starting cooling temperature,the content of bainite increases and the content of ferrite decreases,leading to the increase of yield strength and the reduce of plasticity of the steel. When starting cooling temperature is 530 ℃,lower yield ratio,higher uniform elongation and strain hardening exponent of the steel can be achieved,which accord with the technical requirements of high deformation pipeline steel. Bainite with fine lath and ferrite with high dislocation density in the steel can be acquired through DAC,which endow the steel with higher strengthtoughness and good deformability.