A method for smelting 9ni steel in an electric furnace

Abstract

The invention discloses a method for smelting 9 Ni steel by an electric furnace. The method comprises the following processes: an EAF furnace primary smelting process, a VD furnace vacuum residual-oxygen decarbonizing process, an LF furnace refining process and a VD furnace vacuum treatment process, wherein in the VD furnace vacuum residual-oxygen decarbonizing process, a steel ladle enters a VD furnace, vacuum is released when vacuum degree is lower than or equal to 200 Pa, and carbon in molten steel is decarbonized until C content is lower than or equal to 0.01%. The method adopts the EAF furnace primary smelting to control the temperature and components of tapped molten steel, then, enters the VD vacuum decarbonizing process, enters the LF furnace refining process to remove oxygen and regulate components, and finally controls a casting temperature through the VD furnace vacuum treatment process. The produced 9 Ni steel is qualified in components, and is less in impurities; a rolled-out steel plate has a thickness lower than or equal to 50 mm, has yield strength Rp0.2 greater than or equal to 515 MPa, has tensile strength Rm of 690-825 MPa, has lowest impact power greater than orequal to 21 J at a temperature of (-)196 DEG C, and has lateral expansion greater than or equal to 0.381 mm.

Description

technical field [0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for smelting 9Ni steel in an electric furnace. Background technique [0002] 9Ni steel has good strength and toughness at ultra-low temperature (below -196°C), and has good processing and welding properties. It is an ideal material for low-temperature high-alloy pressure vessels such as LNG storage tanks. The alloy content is high (Ni is about 9%), and the impact energy at -196°C is required to be ≥ 21J in the transverse direction. P and S in the steel are required to be as low as possible. The main elements are C: 0.05% ~ 0.07%, Si: 0.16% ~ 0.30%, Mn: 0.70%-0.80%, P≤0.007%, S≤0.003%, Ni: 9.1%-9.4%. The amount of alloy added is large, the control of C and P in electric furnace smelting is difficult, and the requirements for inclusions are strict. [0003] Due to the low carbon content of 9Ni steel, if the 9Ni steel is directly smelted after the electric ...

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Problems solved by technology

[0003] Due to the low carbon content of 9Ni steel, if the 9Ni steel is directly smelted after the electric furnace is tapped, the C of the molten steel needs to be less than 0.02%. At this time, the molten steel has been severely overoxidized, not only need to consume a large amount of deoxidizer, but the deoxidizer increases the pollution of the molten steel; LF The amount of alloy added to the refining furnace is large, the power transmission time is long, and the carbon shed from the electrode makes the C of the molten steel easily exceed the upper limit and be judged as waste