Effects of final rolling temperature and coiling temperature on precipitates and microstructure of high-strength low-alloy pipeline steel

The strength-to-weight ratio is an important property of high-strength low-alloy(HSLA)steel in pipeline,whose precipitation strengthening can be improved.The final rolling temperature(FRT)and coiling temperature(CT)are the key process parameters in the control of precipitates and microstructure.Continuous cooling rate was fixed at 10℃/s,and the effects of deformation and coiling temperatures on precipitates and microstructure of Ti-Nb microalloyed HSLA steel were investigated through thermo-mechanical controlled processing on Gleeble 3500.The microstructure is mainly acicular ferrite with high density dislocation and several microns scale.The size and volume fraction of the precipitates were studied under transmission electron microscopy.The results showed that the diameter of the precipitates was in the range between 4 and 240 nm.The optimized combination of parameters is FRT of 820℃and CT of 550℃,and the volume fraction of precipitates obtained under this process is 0.59%.