Abstract：The effect of welding heat input on the toughness distribution and microstructure characterization of weld heat-affected zone(WHAZ)in the inside welding seam of X80 grade welded pipe was investigated by means of thermal simulation technique,microscopic analysis method and mechanical property testing.The results show that medium welding heat input(17-35kJ/cm)can produce good toughness in the weld coarse grained heat-affected zone(WCGHAZ)of welding seam of X80 pipeline steel.The toughness of WCGHAZ is the best when welding heat input is 20kJ/cm.But the toughness of WCGHAZ would become worse when welding energy input is less than 17kJ/cm and more than 35kJ/cm.Therefore,welding heat input at range of 17-35kJ/cm can be used as the recommended welding parameter in the outer welding process of X80 welded pipe.
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