Patent ID: 7501030

Claim:
A coiled, hot-rolled steel strip having superior low temperature toughness and weldability for a high strength electric resistance welding pipe, comprising: on a mass percent basis, about 0.005 to about 0.04% of C; about 0.05 to about 0.3% of Si; about 0.5 to about 2.0% of Mn; about 0.001 to about 0.1% of Al; about 0.001 to about 0.1% of Nb; about 0.001 to about 0.1% of V; about 0.001 to about 0.1% of Ti; about 0.05 to about 0.5% of Mo; about 0.03% or less of P; about 0.005% or less of S; about 0.006% or less of N; at least one selected from the group consisting of about 0.5% or less of Cu and about 0.5% or less of Ni; and the balance being Fe and incidental impurities, wherein Pcm represented by the following equation (1) is 0.17 or less: Pcm =(% C)+(% Si)/30+((% Mn)+(% Cu))/20+(% Ni)/60+(% Mo)/7+(% V)/10 Equation (1), in which (% M) indicates the content of element M on a mass percent basis, and the hot-rolled steel strip is composed of bainitic ferrite as a primary phase at a content of about 95 percent by volume or more and having a yield strength of at least 560 MPa, and wherein the ratio in percent of the amount of precipitated Nb to the total amount of Nb is from 5 to about 80%.