Development Of 9% Nickel Steel For Liquefied Natural Gas Storage Tank In Baosteel Heavy Plate

The 9%Ni steel for building LNG storage tanks used to be imported for a long time,and A handful of qualified steel mills in China have encountered many problems such as unstable performance,poor surface quality and excessive remanent magnetism in batch production.Therefore,Baosteel Group has proposed the development plan of Ni cryogenic steel used for LNG storage tanks to meet the needs of national energy development.n this paper,a series of work is carried out with the aim of developing 9%Ni steel,which is intended to provide technical support for domestic production of high quality 9%Ni steel.In this paper,a series of work is carried out with the aim of developing 9%Ni steel,which is intended to provide technical support for domestic production of high quality 9%Ni steel.According to the results of laboratory research,the production technology of 9%Ni steel was carried out on the steel plate production line of baosteel.The control methods of remanence and surface micro crack of 9%Ni steel in batch industrial production were explored.In this paper,the following conclusions are obtained:(1)Based the work mentioned above,a set of 9%Ni steel production technology,including composition,steelmaking,continuous casting,reheating,rolling,heat treatment,etc.,has been developed in Baosteel heavy plate production line.(2)Under given condition of heat treatment,ultra-low carbon is benefit for improving low temperature impact toughness of 9%Ni steel;By alloying of Mo,yield strength of 9%Ni steel can be effectively increased without affecting the low-temperature impact toughness.(3)Double quenching plus tempering process can significantly increase low-temperature impact performance of 9%Ni steel.Judging from the optical microstructure of 9%Ni steel,martensite and a small amount of bainite are present after single quenching,while the martensite decomposes complete to tempered sorbite with relatively large grains after high temperature tempering,which is adverse to the low temperature impact toughness.Instead,the microstructure is ferrite matrix formed on the tiny island of martensite after double quenching,and precipitates distributed evenly after tempering.(4)Strain aging significantly reduces the low temperature impact toughness of 9%Ni steel,so in the practical application large amount of cold deformation should be avoided,especially the heat treatment after cold deformation.(5)Mechanical properties of steel has no obvious deterioration after SR processing between 560? and 600?.Steel plate can meet the conventional welding in engineering and has good welding cold crack sensitivity,good welding mechanical properties.(6)By improving the equipment,technological process and use specific demagnetization method,remanent magnetism of 9%Ni steel can be controlled within 2.5 mT,meetting the engineering requirements.By adjusting the continuous casting process,powder type,Al content,slab subcutaneous crack can be controlled at 5.5 mm or less.