In order to develop an arctic line-pipe X70 type HSLA steel strip possessing high toughness and good weldability, additions of several micro-alloying elements and applications of different post-rolling treatments were performed. The base steel composition was 0.05C-1.0Mn-0.3Si and the micro-alloying elements added were Nb, V, Mo, and Ni. The post-rolling treatments applied were water-spraying cooling followed by either furnace cooling or air cooling to room temperature after the final controlled rolling at 800℃. It was found that the steel composition of Fe-0.05C-1.0Mn-0.35Si-0.03Nb-0.05V-0.1Mo-0.1Ni exhibited optimum combination of high strength (Y.S. 75ksi) and excellent impact toughness (250 joules at -20℃) after the water-spraying to 600℃ followed by furnace cooling to room temperature. The post-rolling treatment applied was the condition simulating hot strip production. This paper highlights the effects of micro-alloying elements and post-rolling treatments on structure and mechanical properties in a low Carbon-Manganese steel.
