Niobium-contg. constructional steel - with improved weldability, used for oil and gas pipelines

摘要

The constructional steel has the compsn. (by wt.) 0.005-0.04% C, 0.01-0.50% Si, 1.20-2.50% Mn, 0.01-0.07% Nb, 0.005-0.030% Ti, 0.005-0.06% Al, balance Fe, the (C% + 10N%) content being is not >0.10% and the Ti%/(C% + 10N%) content being 0.05-0.60. The content of martensite islands in the heat affected zone is limited to is not >15% of an area section. The steel may also contain one or more of =0.50% Cu, =1.50% Ni, =0.50% Cr, =0.60% Mo, =0.10% V, =0.003% B, =0.02% Ce and =0.003% Ca. The steel is useful for oil and natural gas pipelines use in cold regions. It has a yield strength of 40-70 kp/mm2, good heat-affected zone toughness and improved weld cracking resistance even when using high heat input welding techniques.