Casting production goes through a very complicated process. As long as one of the processes or one of the processes is mistaken, it will cause casting defects. Of course, the same type of defects often have different reasons for formation due to differences in occasions and parts. As the saying goes, "three-point smelting, seven-point casting." The quality of molten steel is closely related to the quality of the casting. In this paper, we mainly discuss how to provide high quality molten steel for casting production through out-of-furnace refining technology.
1. Introduction to refining technology outside the furnace
The innovations in steelmaking technology in the 20th century were mainly pure oxygen top-blown converter steelmaking and continuous casting. Due to the adoption of these practical technologies, steelmaking productivity has increased rapidly. The refining technology outside the furnace is a connection process between the converter and the continuous casting steel. The practical application of this technology greatly improves and perfects the liquid steelmaking method invented by Henry Bessemer. To improve the quality and output of cast steel production, it is also inseparable from the development of metallurgical smelting technology. Furnace refining technology is one of the applicable technologies in the production of castings.
1.1 Functions of the refining technology outside the furnace 1 Dehydrogenation, 2 deoxidation, 3 decarburization, 4 desulfurization, 5 non-metallic inclusion morphology control, 6 component adjustment (addition of alloy), 7 steel liquid composition and temperature fine adjustment and homogenization, 8 denitrification, 9 dephosphorization. In response to the above functions, extra-furnace refining equipment such as the LF method, the VD method, the VOD method, the RH method, and the SKF' method are derived. However, for which refining equipment is used by each manufacturer, they will consider the smelting steel grade, production volume, rough/refining combination, etc., and select the most suitable refining method outside the furnace.
1.2 Introduction of electric furnace plus ladle refining furnace double process At present, electric arc furnace steelmaking is one of the most extensive steelmaking methods in the production of steel castings. This method uses the high temperature and heat generated by the arc to melt the solid charge to achieve the purpose of smelting. In the electric arc furnace steelmaking, in order to remove gases and inclusions in the molten steel, the molten steel is usually boiled by the decarburization reaction, and the molten steel is violently oxidized. In the next step, in order to remove residual oxygen in the molten steel, it is necessary to deoxidize the molten steel, thereby generating a large amount of inclusions, which is a contradiction that is difficult to solve in electric arc furnace steelmaking. In order to solve this problem, the metallurgical workers have worked hard for many years to find out the double process method. The two major phases of the original electric arc furnace steelmaking, the oxidation period and the reduction period, are respectively placed in the electric arc furnace and ladle refining, and are operated independently to achieve the purpose of improving the smelting quality of the molten steel and improving the productivity. The following is the process of the double process: electric furnace feeding - melting - oxidation - heating - tapping - LF furnace steel solution - refining reduction - fine tuning composition, temperature adjustment - tapping - feeding Wire - steel liquid temperature measurement - molten steel pouring.
1.3 Product quality of the double process method For the quality of several cast steel mills using the double process method: 1 gas content: [H] < 3.5ppm, [O] < 40ppm, [N] < 80ppm; 2 impurity content : [P] <0.015%, [s] <0.0l%, si, Mn can be controlled within 0.02%, Ni, Mo, Cu can be controlled within 0.01%.
1.4 Material properties yield strength increased by 7% to 11%; tensile strength increased by 3% to 6%, impact toughness increased by 20% to 45%; the area shrinkage and elongation did not change. The content of inclusions was significantly reduced, and the distribution pattern was mostly discontinuous.
2. Analysis of economic benefits of refining technology outside the furnace
After several steel foundries used ladle refining equipment, the consumption of raw materials per ton of steel decreased. Such as the electricity consumption per ton of steel, down about 35 kwh. However, after adding LF furnace equipment, it is necessary to increase the water circulation system, dust removal system and other investments, so that the cost of molten steel smelting increases. However, the chemical composition of the molten steel is controlled stably, the composition of the alloy is accurately controlled, and the composition of the molten steel is uniform. No segregation phenomenon, high control of gas and inclusions in molten steel, excellent mechanical properties, and greatly reduced casting reject rate. For the above reasons, the cost of molten steel is generally flat.
3. Advantages of using ladle refining furnace technology
1 After the ladle refining furnace technology, the harmful elements and harmful gases in the molten steel are reduced to a lower level, which makes it difficult to form non-metallic inclusions in the steel which seriously damage the casting material, thereby improving the low temperature performance of the casting. And the adaptability of the casting to the environment of use. 2 Stirring of argon accelerates the chemical reaction between steel/slag, which is beneficial to the desulfurization and deoxidation of molten steel, promotes the floating and removal of non-metallic impurities in molten steel, and improves the uniformity of temperature and composition of molten steel. 3 Combined with ordinary electric arc furnace, the production cycle is accelerated and the alloy recovery rate is improved. 4 equipment is simple and the investment is low.
4. The use of ladle refining furnace also needs to solve the following problems
1 The temperature of the molten steel drops. Since the ladle refining furnace is connected to the common electric arc furnace, when the molten steel of the ordinary electric arc furnace is oxidized and the steel is tapped to the refining furnace, the temperature of the molten steel is lowered, and the smaller the furnace, the larger the temperature drop. In this way, the refining furnace needs to be warmed up, which will increase the power consumption a little. 2 The molten steel is used to increase the gas content. After the molten steel is refined outside the furnace, the content of various gases in the molten steel is reduced. However, in the process of pouring steel liquid, it is easy to make the steel liquid inhale, resulting in a slight increase in the gas content of the molten steel. At present, there are solutions.
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1. Introduction to refining technology outside the furnace
The innovations in steelmaking technology in the 20th century were mainly pure oxygen top-blown converter steelmaking and continuous casting. Due to the adoption of these practical technologies, steelmaking productivity has increased rapidly. The refining technology outside the furnace is a connection process between the converter and the continuous casting steel. The practical application of this technology greatly improves and perfects the liquid steelmaking method invented by Henry Bessemer. To improve the quality and output of cast steel production, it is also inseparable from the development of metallurgical smelting technology. Furnace refining technology is one of the applicable technologies in the production of castings.
1.1 Functions of the refining technology outside the furnace 1 Dehydrogenation, 2 deoxidation, 3 decarburization, 4 desulfurization, 5 non-metallic inclusion morphology control, 6 component adjustment (addition of alloy), 7 steel liquid composition and temperature fine adjustment and homogenization, 8 denitrification, 9 dephosphorization. In response to the above functions, extra-furnace refining equipment such as the LF method, the VD method, the VOD method, the RH method, and the SKF' method are derived. However, for which refining equipment is used by each manufacturer, they will consider the smelting steel grade, production volume, rough/refining combination, etc., and select the most suitable refining method outside the furnace.
1.2 Introduction of electric furnace plus ladle refining furnace double process At present, electric arc furnace steelmaking is one of the most extensive steelmaking methods in the production of steel castings. This method uses the high temperature and heat generated by the arc to melt the solid charge to achieve the purpose of smelting. In the electric arc furnace steelmaking, in order to remove gases and inclusions in the molten steel, the molten steel is usually boiled by the decarburization reaction, and the molten steel is violently oxidized. In the next step, in order to remove residual oxygen in the molten steel, it is necessary to deoxidize the molten steel, thereby generating a large amount of inclusions, which is a contradiction that is difficult to solve in electric arc furnace steelmaking. In order to solve this problem, the metallurgical workers have worked hard for many years to find out the double process method. The two major phases of the original electric arc furnace steelmaking, the oxidation period and the reduction period, are respectively placed in the electric arc furnace and ladle refining, and are operated independently to achieve the purpose of improving the smelting quality of the molten steel and improving the productivity. The following is the process of the double process: electric furnace feeding - melting - oxidation - heating - tapping - LF furnace steel solution - refining reduction - fine tuning composition, temperature adjustment - tapping - feeding Wire - steel liquid temperature measurement - molten steel pouring.
1.3 Product quality of the double process method For the quality of several cast steel mills using the double process method: 1 gas content: [H] < 3.5ppm, [O] < 40ppm, [N] < 80ppm; 2 impurity content : [P] <0.015%, [s] <0.0l%, si, Mn can be controlled within 0.02%, Ni, Mo, Cu can be controlled within 0.01%.
1.4 Material properties yield strength increased by 7% to 11%; tensile strength increased by 3% to 6%, impact toughness increased by 20% to 45%; the area shrinkage and elongation did not change. The content of inclusions was significantly reduced, and the distribution pattern was mostly discontinuous.
2. Analysis of economic benefits of refining technology outside the furnace
After several steel foundries used ladle refining equipment, the consumption of raw materials per ton of steel decreased. Such as the electricity consumption per ton of steel, down about 35 kwh. However, after adding LF furnace equipment, it is necessary to increase the water circulation system, dust removal system and other investments, so that the cost of molten steel smelting increases. However, the chemical composition of the molten steel is controlled stably, the composition of the alloy is accurately controlled, and the composition of the molten steel is uniform. No segregation phenomenon, high control of gas and inclusions in molten steel, excellent mechanical properties, and greatly reduced casting reject rate. For the above reasons, the cost of molten steel is generally flat.
3. Advantages of using ladle refining furnace technology
1 After the ladle refining furnace technology, the harmful elements and harmful gases in the molten steel are reduced to a lower level, which makes it difficult to form non-metallic inclusions in the steel which seriously damage the casting material, thereby improving the low temperature performance of the casting. And the adaptability of the casting to the environment of use. 2 Stirring of argon accelerates the chemical reaction between steel/slag, which is beneficial to the desulfurization and deoxidation of molten steel, promotes the floating and removal of non-metallic impurities in molten steel, and improves the uniformity of temperature and composition of molten steel. 3 Combined with ordinary electric arc furnace, the production cycle is accelerated and the alloy recovery rate is improved. 4 equipment is simple and the investment is low.
4. The use of ladle refining furnace also needs to solve the following problems
1 The temperature of the molten steel drops. Since the ladle refining furnace is connected to the common electric arc furnace, when the molten steel of the ordinary electric arc furnace is oxidized and the steel is tapped to the refining furnace, the temperature of the molten steel is lowered, and the smaller the furnace, the larger the temperature drop. In this way, the refining furnace needs to be warmed up, which will increase the power consumption a little. 2 The molten steel is used to increase the gas content. After the molten steel is refined outside the furnace, the content of various gases in the molten steel is reduced. However, in the process of pouring steel liquid, it is easy to make the steel liquid inhale, resulting in a slight increase in the gas content of the molten steel. At present, there are solutions.
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In addition to tool bags, there are also Tool Belts that serve a similar purpose. Tool belts are worn around the waist and typically have several pockets and loops for holding tools, while tool bags with larger containers with compartments for organizing and storing tools.
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