Banded Structure Analysis of X70 Grade Steel with Dual Structures for Line Pipe（Part I）

Based on the results of the random test and the test with a first-lot factory certificate,discussed and analyzed are the banded structure features of X70 grade steel with the ferrite plus deficient pearlite and the acicular ferrite for the line pipe,the relations between the formation of the banded structure and the controlled rolling,the cold control process and the steel chemical composition,especially the Mo content,and also the influence of the banded structure extent on the base material Sharp impact toughness,the DWTT test SA values and the HIC resistance property of steel pipes.