Study On Strength And Toughness Improvement Treatment And Thermal Simulation Technology Of 550MPa Grade Low Temperature Bend Steel

Cu precipitation strengthening steel is a kind of low carbon low alloy steel with excellent welding performance and toughness matching.It is mainly used in shipbuilding and offshore oil production platforms.The main reinforcing method of this steel is precipitation strengthening of ?-Cu during aging..At present,most of the steel used for bend pipe/pipe fittings in low-temperature environments is X80 steel,and facilities such as heat traces or thermal insulation layers are often used.The cost of construction and maintenance is relatively high.Cu precipitation-reinforced steel is now used as bend steel.Its pre-rolling,heat treatment and later induction heating optimum process.In this paper,three kinds of test steels were prepared through different rolling and heat treatment processes in the earlier stage.Online quenching and tempering,off-line quenching and tempering,and off-line quenching and tempering of different thicknesses of steel were investigated.The effect of the tempering temperature was 650? and the time was 2 hours.Over-aging was used to increase the toughness by losing part of its strength.Then the three kinds of test steels after the tempering are used as the bend steel,and the actual bending pipe manufacturing process is simulated at different thermal simulation temperatures.Finally,a tempering treatment is performed at 650° C.to study the bending pipe during the entire experiment.The microstructure and properties of the steel used for pipe fittings were changed to determine the best rolling process for the steel plate and the best thermal simulation temperature in the elbow pipe production.The off-line quenching and tempering steel strength is slightly lower than on-line quenching and tempering steel,but the yield strength also reaches 590 MPa,and the low temperature toughness of-40? reaches more than 250 J.When the off-quenched steel is properly increased in the rolling process,the strength and low-temperature toughness of the tempered steel are improved.In the simulated bending pipe manufacturing stage,when the thermal simulation temperature is 1010?,the off-quenched quenched steel with a large reduction during rolling is the best in toughness,and the low-temperature toughness of-45? reaches more than 400 J.