Study On The Heat Treatment Of Strengthening And Toughening Of High-strength Structure Steel For Ship

4NiCrMo steel and 8NiCrMo steel is low-alloy high-strength steel which for ship skull, this sort steel require not only high-strength but also good low-temperature flexibility and weldability, a sort material with strength and ductility. Traditionally, high-strength ship skull steel to Ni-Cr-Mo series is produced in the process of hardening and tempering, but the flow is that temper resistance is bad, yield ratio is too high and low-temperature flexibility is bad.Against above flaw, the article research heat treating regime of ship skull steel to Ni-Cr-Mo series, in order to improve strength and ductility, the feature is that proceeding secondary quenching in two-phase area after quenching, proceeding tempering subsequently. Research process effect on property, these process are QT, QQT, QQ'T and so on, and research effect rule of secondary quenching temperature and tempering temperature, observe microstructure of test steel in each heat treatment states carefully, discuss evolution rule of structure and which effect on property.Overall research demonstrate that fine structure of high strength ship skull steel make a change conspicuously, the final structure is a mixture structure of lath-like tempered martensite and ferrite, and inverse-transmission austenite precipitate along lath boundary also. The mixture structure decrease yield ratio and improve ductility. Another reason for improving ductility is precipitating of inverse-transmission austenite.In the basement of lab research result, make a test production of 4NiCrMo steel industrially by QQ'T process, the result demonstrate that each property cater to qualification, and with better abundance amount, yield ratio and transmission temperature of ductility to fragility decrease conspicuously, which hold better synthetical property.Through research work of the article, take the ship skull steel process which is secondary quenching in two-phase area and tempering, formulate the relation of structure and mechanical property, take a new routine for improve synthetic property of high strength steel of ship skull steel.