Microstructure evolution and toughness of X80 high strength pipeline steel joint by auxiliary heating and friction stir welding

Objective Using friction stir welding technology can complete the welding of steel materials with high quality, but the expensive stir tool is seriously worn, and auxiliary heating before welding is an effective way to reduce the wear of stir tool. Methods This paper uses the temperature control auxiliary heat pad to preheat the weld of X80 pipeline steel to 150 ℃ and 270 ℃, and then uses the friction stir welding technology to weld, and carries out a detailed study on the temperature change, microstructure characteristics and impact toughness of the auxiliary heat friction stir welding X80 pipeline steel. Results The results show that the microstructure of welded joints at room temperature and 150 ℃ is similar, mainly lath bainite and a small amount of granular bainite, and the impact toughness increases slightly. The microstructure of welded joints at 270 ℃ is mainly coarse granular bainite, and the impact toughness decreases. At a lower auxiliary heat temperature, the auxiliary heat softening material reduces the friction heat production of the main heat input stir tool of welding, and the impact of the increase of ambient temperature is small. The peak temperature decreases and then the grain is refined. At a higher auxiliary heating temperature, the influence of the increase of the ambient temperature is greater than that of the decrease of the heat generation of the stirring tool, so the peak temperature rises and the grain coarsens. Conclusion Therefore, good welding effect can be obtained by using a lower auxiliary heat temperature during welding.