PREPARATION METHOD OF STEEL FOR X80 ELBOW PIPE AND PIPE FITTING

摘要

Disclosed is preparation method of steel for X80 elbow pipe and pipe fittings. The steel comprises the following elements in mass percentage: 0.1-0.25 % of C, 1.3-2 % of Mn, 0.3-0.5% of Si,=0.010 % of P,= 0.005 % of S, 0.01-0.05 % of Al, 0.002-0.005 % of Ca,= 0.0008 % of N and the balance Fe. Carbon equivalent of the steel is 0.40-0.58%. The method involves smelting by blowing oxygen, spheroidizing, refining, degassing in vacuum furnace, blank making, rough rolling, fine rolling, steel plate making, shaping, hidden arc welding, producing elbow pipe by induction heating or producing pipe by thermal-mechanical forming, quenching, tempering and hydro-cooling. The elbow pipe and pipe fittings have yield strength of 555-705 MPa, tensile strength of 625-825 MPa, yield ratio of no more than 0.93, rate of elongation of no less than 25 %, the Charpy impact toughness of 60-300 J at -35~-50°C.