The Effect of Microstructure on Properties of High Deformation Pipeline Steel X70

Abstract

A high deformation pipeline steel X70 with low yield ratio of 74% was achieved has been processed on an industrial scale. The impact toughness of the investigated steel is 388.3 J/cm2 at -20°C and the shear area is 97% in drop weight tear test at -15°C. The microstructure of the steel constisted of primarily acicular ferrite, polygonal ferrite and a small proportion of scattered martensite-austenite constituents. The high deformation pipeline steel had low yield ratio and good toughness, which was attributed to high Nb microalloying and rapid cooling in the TMCP process.