| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric welded steel tube having excellent HIC resistance and low temperature toughness, and to provide manufacturing method thereof.SOLUTION: An electric welded steel is manufactured by conducting electric welding with adjusting an oxygen concentration in an atmosphere at electric welding such that a viscosity of oxide generated at electric welding is 2 poise or less, and/or time from melting initiation by heating to pressure-welding to 0.2 to 4 s, when a hot rolled steel strip containing, by mass%, C:0.03 to 0.59%, Si:0.10 to 0.50%, Mn:0.40 to 2.10%, Al:0.01 to 0.35% with a range of Mn/Si of 6.0 to 9.0 and having tensile strength TS: 434 MPa or more is roll-molded continuously to manufacture an open tube having an approximately circular cross section, and then an electric welding part is formed by performing electric welding by heating neighbor of butted parts of the open tube at the melting point or higher and pressure-rolling with a squeeze roll, and then applying a heat treatment with heating-cooling on-line to the electric welding part. |
