Method for controlling nitrogen content of steel grade in CV-LF-RH-CC process path

Abstract

The invention discloses a method for controlling the nitrogen content of a steel grade in a CV-LF-RH-CC process path, and relates to the technical field of ferrous metallurgy. The method aims at achieving stable control over the nitrogen content and alloy components of the steel grade in the CV-LF-RH-CC process path. According to the method, stable control over the nitrogen content and the alloy components is achieved by strictly controlling the converter bottom blowing process, the steel tapping alloying process, the slag variety and adding amount, LF temperature rising, slagging and alloying process bottom blowing, the RH refining vacuum degree and time, the wire feeding speed, the casting process and other processes. According to the method, through strict control over the converter blowing process, the deoxidation alloying process of the primary molten steel, the LF and RH duplex refining process and the like, all alloy elements can stably reach target values, and the nitrogen content is stably controlled to be 30 ppm or below.

Description

technical field [0001] The invention relates to the technical field of iron and steel metallurgy, in particular to a method for controlling the nitrogen content of steel grades in a CV-LF-RH-CC process path. Background technique [0002] Nitrogen has a great influence on the performance of steel, which is mainly reflected in the following aspects: 1) Nitrogen precipitates at the grain boundary, causing blue brittleness of steel; 2) The existence of nitrogen in steel reduces the impact toughness and welding performance of steel , the toughness of the thermal stress zone, which increases the brittleness of the steel; 3) Nitrogen combines with Ti or Al in the steel to form TiN or AlN, which weakens the grain boundary strength, changes the brittle zone of the steel, and easily causes cracks on the surface of the slab; 4) Continuous The nitrides precipitated in solid solution during casting have a more serious impact on the fatigue life of steel than the deoxidized products of th...

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Problems solved by technology

[0002] Nitrogen has a great influence on the performance of steel, which is mainly reflected in the following aspects: 1) Nitrogen precipitates at the grain boundary, causing blue brittleness of steel; 2) The existence of nitrogen in steel reduces the impact toughness and welding performance of steel , the toughness of the thermal stress zone, which increases the brittleness of the steel; 3) Nitrogen combines with Ti or Al in the steel to form TiN or AlN, which weakens the grain boundary strength, changes the brittle zone of the steel, and easily causes cracks on the surface of the slab; 4) Continuous The nitrides precipitated in solid solution during the casting process have a more serious impact on the fatigue life of the steel than the deoxidized products of the same size

[0003] Therefore, some high-grade steels have strict requirements on nitrogen content, and changes in nitrogen content will affect the structure and properties of HCM2S steel. When the nitrogen content in HCM2S steel is greater than 71×10 -6 Sometimes it will react with boron to form BN inclusions, which will reduce the amount of "effective boron" in the steel, reduce the hardenability of the steel, and finally affect the structure and performance of the steel, reduce the forming and cold bending properties of the steel, and reduce the toughness and plasticity of the steel

[0004] The stable control of nitrogen content is a difficult problem for steel types that have passed the LF refining process. The refining process is the most serious link in the production process of nitrogen increase. To achieve stable control of nitrogen content and ultra-low nitrogen content, strict control is required from all aspects , and there is no control method for steel types in the CV-LF-RH-CC process route on the market, it is difficult to stably control the nitrogen content and alloy composition

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