Experimental Study Of Production Technology For 690MPa Ocean Engineering Steel

In recent years, with the rapid development of ocean engineering and shipbuilding, special steel demand rises quickly and higher performance has been put forward. In this paper, as the background of developing a kind of low-cost and reduced 690 MPa ocean engineering steel, the main characteristics of the steel and heat treatment process are carried out by the laboratory study, and basic date have been acquired for industrial trial-production.After vacuum smelting and billet rolling sufficiently, samples are manufactured according to requirements of high temperature thermoplastic experiment. The results show: test steel phase transition point Ac1, Ac3, Bs and Bf are 712℃, 827℃, 515℃and 348 ℃; The first brittle interval is 1150~1300 ℃, the third brittle interval is625~800℃, the best thermoplastic interval is 800~1130℃. In the procedure of casting,straightening and rolling, these results could be a reference for making temperature parameter.Observation show that grain size of hot rolled steel in 1/2 point is 7 grade and 1/4point is 7.5 grade, including ferrite, bainite and pearlite.The quenching and tempering treatment uses different process paths and combinations. The results show that the way of 920℃ quenching, 640℃ tempering,quenching time 180 min, tempering time 350 min is an optimum heat treatment process.The microstructure after quenching consists of martensite, lath bainite and several retained austenite. The microstructure after tempering consists of tempered sorbite and morphology of fracture is ductile fracture. The yield strength, tensile strength,elongation and impact energy of 1/2 place are 686 MPa, 769 MPa, 19%, and 146 J..Guided by the above experimental results, adoptingin the production process of920℃ quenching, the quenching time 160 min, 640℃ tempering and the tempering time 350 min. The trial production performance meets the requirements, so this steel can be carried out for industrial production.