Effect by Titanium-nitrogen Ratio on Low Temperature Impact Toughness of High Strength Line Pipe

The low-temperature impact of high-grade pipeline steel linepipe with different titanium-nitrogen ratios are studied.The microstructure and -30℃ low-temperature impact fracture morphology are analyzed by optical microscope and scanning electron microscope,and the relationship between fracture and titanium-nitrogen ratio was studied.The results show that with the increase of Ti/N ratio,the low temperature impact uniformity of steel decreases.The main reason is that nitrogen and microalloying element titanium in steel are easy to form large size TiN inclusions,which is easy to cause stress concentration and significantly reduce the low temperature impact uniformity of steel. When the ratio of titanium to nitrogen in steel is less than 3.0,the low temperature impact performance of steel is the best,and so is the uniformity thereof.