Effect of coiling temperature on residual stresses in hot-rolled X70 pipeline steel strips during laminar cooling

The thermal expansion coefficient,high-temperature yield strength and Young's modulus of hot-rolled X70 pipeline strips were tested with a thermal expansion instrument and a thermal simulation test machine Gleeble3500.The temperature field,bainitic volume fraction and residual stresses in the hot-rolled strips during laminar cooling were calculated with the finite element software Marc when the coiling temperature is 500,550 and 600℃,respectively.It is shown that stresses in the strip edge exceed the yield strength of the steel at the same temperature in the earlier water cooling stage,leading to edge waves;but in the end of water cooling,stresses in the strip edge exceed the yield strength again and generates plastic deformation,which causes center waves.Reducing the coiling temperature is in favor of completing bainite transformation and decreasing residual stresses in the hot rolled strips on the assumption that the properties of X70 pipeline steel are ensured.