Ultra-low carbon steel RH refining method

Abstract

The invention discloses an ultra-low carbon steel RH (Ruhrstahl Heraeus) refining method, which is characterized in that CO is used as lifting gas at the last stage of RH decarburization, and an'inert gas-CO-inert gas' lifting gas mode is adopted; at the end of the RH decarburization last stage, inert gas is blown into the ascending pipe, CO gas is blown into the ascending pipe instead, the temperature of the vacuum tank is kept at 1000-1200 DEG C, and the vacuum degree is kept at 3-15 KPa; the CO lifting gas flow is set to be 900-1600 L / min, the CO lifting gas consumption is controlled to be 3600-16000 L, and the treatment time is 4-10 min; according to the process mode, the decarburization effect in the smelting process can be guaranteed, CO gas can be used for reacting part of oxygen (in the form of ferric oxide), the use amount of part of Al residual oxygen removal is reduced, the generation amount of Al2O3 inclusions is reduced, the cleanliness of molten steel is improved, the production cost is reduced, and economic benefits are remarkable.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for RH refining of ultra-low carbon steel. Background Art

[0002] With the continuous development of the automobile industry, the demand for ultra-low carbon automobile plate steel is increasing, and the market has put forward higher and higher requirements for ultra-low carbon steel. RH vacuum refining is one of the most important refining methods in molten steel processing. It has the functions of decarburization, dehydrogenation, denitrification, deoxidation, and removal of non-metallic inclusions. Decarburization is one of the most important metallurgical functions of RH. Since the decarburization reaction is a high-temperature, low-pressure reaction, its degree directly affects the decarburization rate, becoming a process-limiting link affecting the RH cycle. Under the action of the driving gas Ar, the molten steel is circulated and degassed in a vacuum chamber. [C] in the steel reacts with [O] or injected O2 to generate CO gas, which is removed. The residual oxygen after decarburization needs to be deoxidized with metallic aluminum. Under this process, the deoxidation products of metallic aluminum are mainly Al2O3 inclusions. Most of the deoxidation products Al2O3 can be fully floated, but some fine Al2O3 inclusions still remain in the steel, reducing the cleanliness of the molten steel. Such inclusions have a negative impact on the surface quality and mechanical properties of the steel. They can also cause production problems such as nozzle blockage and deterioration of the crystallizer flow field. Therefore, in the smelting of ultra-low carbon steel, how to reduce the number of Al2O3 inclusions and improve the cleanliness of molten steel has become a key problem for the further development of such products. Summary of the Invention

[0003] In order to solve the above-mentioned bottleneck problems existing in the prior art, the purpose of the present invention is to provide a smelting method for producing ultra-low carbon steel using CO as the lifting gas in the final stage of RH decarburization. The lifting gas adopts an "inert gas-CO-inert gas" mode. This process mode can not only ensure the decarburization effect of the smelting process, but also use CO gas to react with part of the oxygen (in the form of iron oxide), thereby reducing the use of some Al to remove residual oxygen, reducing the amount of Al2O3 inclusions generated, improving the cleanliness of the molten steel, and reducing production costs.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides a method for RH refining of ultra-low carbon steel, which comprises the following steps:

[0005] ①The ladle containing molten steel is placed in the RH working position and the vacuum tank is evacuated;

[0006] ② During the RH decarburization period, inert gas is blown into the riser: the lifting gas is inert gas, the inert lifting gas flow rate is set to 900-1600 L / min, the inert lifting gas dosage is 3600-16000 L, and the treatment time is 4-10 minutes;

[0007] ③ At the end of RH decarburization, the inert gas is blown into the riser, and CO gas is blown into the riser: the vacuum tank temperature is maintained at 1000℃~1200℃ and the vacuum degree is 3~15KPa; the CO lifting gas flow rate is set to 900~1600L / min, the CO lifting gas dosage is controlled to 3600~16000L, and the treatment time is controlled to 4~10min;

[0008] ④ At the end of the RH treatment (alloying period), the CO gas is blown into the riser, and inert gas is blown into the riser again: the vacuum tank temperature is maintained at 1000℃~1200℃, and the vacuum degree is 3~15KPa; the inert lifting gas flow rate is set to 900~1600L / min, the inert lifting gas dosage is controlled to 3600~16000L, and the treatment time is controlled to 4~10min;

[0009] ⑤ Finish blowing inert gas into the riser.

[0010] In the above technical solution, further, in step ①, the chemical composition of the molten steel is C < 0.05%, Si ≤ 0.03%, Mn: 0.05% ~ 0.20%, P ≤ 0.020%, S ≤ 0.015%, O: 400 ~ 800ppm, and the remainder is Fe and unavoidable impurities; the temperature T ≥ 1610 ° C.

[0011] Furthermore, in step ①, the temperature of the vacuum tank is controlled to be 1000° C. to 1200° C., and the vacuum degree is controlled to be 3 to 15 KPa.

[0012] Furthermore, in step ②, the C content is controlled to be 0.01% to 0.03%, the residual oxygen content is controlled to be 150 to 350 ppm, and the molten steel temperature is controlled to be 1595° C. to 1620° C.

[0013] Furthermore, in step ③, the C content is controlled to be 0.01% to 0.03%, the residual oxygen content is controlled to be 80 to 150 ppm, and the molten steel temperature is controlled to be 1585° C. to 1595° C.

[0014] Furthermore, in step ④, the C content is controlled to be 0.01% to 0.03%, and the molten steel temperature is controlled to be 1580°C to 1590°C.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] ① The process of the present invention can not only ensure the decarburization effect of the smelting process, but also use CO gas to react with part of the oxygen (in the form of iron oxide), thereby reducing the amount of residual oxygen used in partial Al removal, reducing the amount of Al2O3 inclusions generated, and improving the cleanliness of the molten steel.

[0017] ② The use of inert gas in this technical solution is significantly reduced, which reduces production costs. Although the use of CO is increased, the cost of CO is much lower than that of inert gas.

[0018] ③ The number of non-metallic inclusions in the finished ultra-low carbon steel product obtained by this method is reduced, and its product performance can meet the product requirements of ultra-low carbon automotive steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a process flow chart of an ultra-low carbon steel RH refining method of the present invention;

[0020] Figure 2 This is a comparison chart of the number of inclusions and the amount of residual oxygen removed Al used in the example and comparative example products. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific examples, but the present invention is not limited in any way. To avoid redundancy, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0022] A method for RH refining of ultra-low carbon steel, the process flow is as follows Figure 1 As shown, the method includes the following steps:

[0023] ①The ladle containing molten steel is placed in the RH working position and the vacuum tank is evacuated;

[0024] ② During the RH decarburization period, inert gas is blown into the riser: the lifting gas is inert gas, the inert lifting gas flow rate is set to 900-1600 L / min, the inert lifting gas dosage is 3600-16000 L, and the treatment time is 4-10 minutes;

[0025] ③ At the end of RH decarburization, the inert gas is blown into the riser, and CO gas is blown into the riser: the vacuum tank temperature is maintained at 1000℃~1200℃ and the vacuum degree is 3~15KPa; the CO lifting gas flow rate is set to 900~1600L / min, the CO lifting gas dosage is controlled to 3600~16000L, and the treatment time is controlled to 4~10min;

[0026] ④ At the end of the RH treatment (alloying period), the CO gas is blown into the riser, and inert gas is blown into the riser again: the vacuum tank temperature is maintained at 1000℃~1200℃, and the vacuum degree is 3~15KPa; the inert lifting gas flow rate is set to 900~1600L / min, the inert lifting gas dosage is controlled to 3600~16000L, and the treatment time is controlled to 4~10min;

[0027] ⑤ Finish blowing inert gas into the riser.

[0028] Any matters not described in the following embodiments are the same as those described in the above specific implementation methods.

[0029] Example 1

[0030] A method for RH refining of ultra-low carbon steel, comprising the following steps:

[0031] ① The ladle containing molten steel is placed in the RH working position, and the vacuum tank is evacuated. Step ① The chemical composition of the molten steel is, by mass, C: 0.029%, Si: 0.006%, Mn: 0.07%, P: 0.010%, S: 0.007%, O: 499 ppm, with the remainder being Fe and unavoidable impurities; the temperature is T: 1619°C. The temperature of the vacuum tank is controlled at 1037°C, and the vacuum is controlled at 3-15 kPa.

[0032] ② During the RH decarburization period, inert gas was blown into the riser: the temperature of the vacuum tank was controlled at 1028°C and the vacuum degree was controlled at 5.75 kPa; the lifting gas was an inert gas, the inert lifting gas flow rate was set at 1000 L / min, the inert lifting gas dosage was 5000 L, and the treatment time was 5 min; in step ②, the C content was controlled at 0.018%, the residual oxygen content was 241 ppm, and the molten steel temperature was 1603°C.

[0033] ③ At the end of the RH decarburization period, inert gas was blown into the riser, and CO gas was blown into the riser instead: the vacuum tank temperature was maintained at 1030°C and the vacuum degree was 5.55 kPa; the CO lifting gas flow rate was set to 1200 L / min, the CO lifting gas dosage was controlled to 4800 L, and the treatment time was controlled to 4 min; in step ③, the C content was controlled to 0.015%, the residual oxygen content was 124 ppm, and the molten steel temperature was 1591°C.

[0034] ④ At the end of the RH treatment (alloying period), the CO gas blowing into the riser is ended and inert gas is blown into the riser again: the vacuum tank temperature is maintained at 1032°C and the vacuum degree is 5.61 kPa; the inert lifting gas flow rate is set to 1400 L / min, the inert lifting gas dosage is controlled to 11200 L, and the treatment time is controlled to 8 min; in step ④, the C content is controlled to 0.016% and the molten steel temperature is controlled to 1586°C.

[0035] ⑤ Finish blowing inert gas into the riser.

[0036] The ultra-low carbon steel prepared in Example 1 was sampled (three groups of samples were taken in each example: a, b, and c) and tested. The test results are shown in Table 1, indicating that the mechanical properties of the finished product can meet the product requirements of ultra-low carbon automotive steel.

[0037] Example 2

[0038] A method for RH refining of ultra-low carbon steel, comprising the following steps:

[0039] ① The ladle containing molten steel is placed in the RH working position, and the vacuum tank is evacuated. Step ① The chemical composition of the molten steel is, by mass, C: 0.034%, Si: 0.005%, Mn: 0.08%, P: 0.011%, S: 0.006%, O: 605 ppm, with the remainder being Fe and unavoidable impurities; temperature T: 1612°C. The temperature of the vacuum tank is controlled at 1076°C, and the vacuum degree is controlled at 3-15 kPa.

[0040] ② During the RH decarburization period, an inert gas is blown into the riser: the temperature of the vacuum tank is controlled at 1071°C and the vacuum degree is controlled at 6.14 kPa; the lifting gas is an inert gas, the inert lifting gas flow rate is set to 1000 L / min, the inert lifting gas dosage is 6000 L, and the treatment time is 6 min; in step ②, the C content is controlled to 0.017%, the residual oxygen content is 303 ppm, and the molten steel temperature is 1601°C.

[0041] ③ At the end of the RH decarburization period, inert gas was blown into the riser, and CO gas was blown into the riser instead: the vacuum tank temperature was maintained at 1085°C and the vacuum degree was 5.91 kPa; the CO lifting gas flow rate was set to 1200 L / min, the CO lifting gas dosage was controlled to 4800 L, and the treatment time was controlled to 4 min; in step ③, the C content was controlled to 0.015%, the residual oxygen content was 145 ppm, and the molten steel temperature was 1590°C.

[0042] ④ At the end of the RH treatment (alloying period), the CO gas blowing into the riser is ended and inert gas is blown into the riser again: the vacuum tank temperature is maintained at 1075°C and the vacuum degree is 5.74 kPa; the inert lifting gas flow rate is set to 1400 L / min, the inert lifting gas dosage is controlled to 11200 L, and the treatment time is controlled to 8 min; in step ④, the C content is controlled to 0.015% and the molten steel temperature is controlled to 1587°C.

[0043] ⑤ Finish blowing inert gas into the riser.

[0044] The ultra-low carbon steel prepared in Example 2 was sampled (three groups of samples were taken in each example: a, b, and c) and tested. The test results are shown in Table 1, indicating that the mechanical properties of the finished products can meet the product requirements of ultra-low carbon automotive steel.

[0045] Example 3

[0046] A method for RH refining of ultra-low carbon steel, comprising the following steps:

[0047] ① The ladle containing molten steel is placed in the RH working position, and the vacuum tank is evacuated. Step ① The chemical composition of the molten steel is, by mass, C: 0.041%, Si: 0.007%, Mn: 0.09%, P: 0.015%, S: 0.010%, O: 566 ppm, with the remainder being Fe and unavoidable impurities; temperature T: 1618°C. The temperature of the vacuum tank is controlled at 1061°C, and the vacuum degree is controlled at 3-15 kPa.

[0048] ② During the RH decarburization period, an inert gas is blown into the riser: the temperature of the vacuum tank is controlled at 1054°C, and the vacuum degree is controlled at 5.34 kPa; the lifting gas is an inert gas, the inert lifting gas flow rate is set to 1000 L / min, the inert lifting gas dosage is 5000 L, and the treatment time is 5 min; in step ②, the C content is controlled to 0.020%, the residual oxygen content is 267 ppm, and the molten steel temperature is 1598°C.

[0049] ③ At the end of the RH decarburization period, inert gas was blown into the riser, and CO gas was blown into the riser instead: the vacuum tank temperature was maintained at 1071°C and the vacuum degree was 5.91 kPa; the CO lifting gas flow rate was set to 1200 L / min, the CO lifting gas dosage was controlled to 4800 L, and the treatment time was controlled to 4 min; in step ③, the C content was controlled to 0.013%, the residual oxygen content was 118 ppm, and the molten steel temperature was 1591°C.

[0050] ④ At the end of the RH treatment (alloying period), the CO gas blowing into the riser is ended, and inert gas is blown into the riser again: the vacuum tank temperature is maintained at 1068°C and the vacuum degree is 5.44 kPa; the inert lifting gas flow rate is set to 1400 L / min, the inert lifting gas dosage is controlled to 11200 L, and the treatment time is controlled to 8 min; in step ④, the C content is controlled to 0.012% and the molten steel temperature is controlled to 1582°C.

[0051] ⑤ Finish blowing inert gas into the riser.

[0052] The ultra-low carbon steel prepared in Example 3 was sampled (three groups of samples were taken in each example: a, b, and c) and tested. The test results are shown in Table 1, indicating that the mechanical properties of the finished product can meet the product requirements of ultra-low carbon automotive steel.

[0053] Table 1 Performance analysis results of ultra-low carbon steel samples prepared in Examples 1-3

[0054]

[0055] Comparative Example 1

[0056] Comparative Example 1 adopts the traditional ultra-low carbon steel RH refining method. The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not use CO as the lifting gas at the end of RH decarburization, and its lifting gas is inert gas; the rest of the process methods are the same.

[0057] The ultra-low carbon steels obtained in Comparative Example 1 and Examples 1-3 were sampled and analyzed, and the same metallographic viewing area (15±0.2) mm was counted. 2 The comparison results are as follows: Figure 2 As shown, it can be seen that the number of inclusions in the ultra-low carbon steel sample prepared in Example 1 is 262, the number of inclusions in the ultra-low carbon steel sample prepared in Example 2 is 224, the number of inclusions in the ultra-low carbon steel sample prepared in Example 3 is 248, and the number of inclusions in the ultra-low carbon steel sample prepared in Comparative Example 1 is 285, which indicates that the purity of the molten steel in this technical solution is greatly improved.

[0058] The amount of Al used in the ultra-low carbon steel RH refining process for removing residual oxygen in Comparative Example 1 and Examples 1-3 is compared. The comparison results are as follows: Figure 2 As shown, it can be seen that the amount of residual oxygen removed Al used in Example 1 is 51 kg / furnace, the amount of residual oxygen removed Al used in Example 2 is 45 kg / furnace, the amount of residual oxygen removed Al used in Example 3 is 49 kg / furnace, and the amount of residual oxygen removed Al used in Comparative Example 1 is 57 kg / furnace; this indicates that the amount of residual oxygen removed Al used in this technical solution is significantly reduced, and the economic benefits are significant.

[0059] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for RH refining of ultra-low carbon steel, characterized in that: The method comprises the following steps: ①The ladle containing molten steel is placed in the RH working position and the vacuum tank is evacuated; ② During the decarburization period, inert gas is blown into the riser: the lifting gas is inert gas, the inert lifting gas flow rate is set to 900-1600L / min, the inert lifting gas dosage is 3600-16000L, and the processing time is 4-10min; ③ At the end of RH decarburization, the inert gas is blown into the riser, and CO gas is blown into the riser: the vacuum tank temperature is maintained at 1000℃~1200℃ and the vacuum degree is 3~15KPa; the CO lifting gas flow rate is set to 900~1600L / min, the CO lifting gas dosage is controlled to 3600~16000L, and the treatment time is controlled to 4~10min; ④ At the end of the RH treatment, CO gas is blown into the riser, and inert gas is blown into the riser again: the vacuum tank temperature is maintained at 1000℃~1200℃ and the vacuum degree is 3~15KPa; the inert lifting gas flow rate is set to 900~1600L / min, the inert lifting gas dosage is controlled to 3600~16000L, and the treatment time is controlled to 4~10min; ⑤ Finish blowing inert gas into the riser.

2. The method according to claim 1, characterized in that Step ① The chemical composition of the molten steel is as follows by mass: C < 0.05%, Si ≤ 0.03%, Mn: 0.05% to 0.20%, P ≤ 0.020%, S ≤ 0.015%, O: 400 to 800 ppm, and the remainder is Fe and unavoidable impurities; the temperature T ≥ 1610°C.

3. The method according to claim 1, characterized in that In step ①, the temperature of the vacuum tank is controlled at 1000° C. to 1200° C., and the vacuum degree is controlled at 3 to 15 kPa.

4. The method according to claim 1, wherein In step ②, the carbon content is controlled to be 0.01% to 0.03%, the residual oxygen content is controlled to be 150 to 350 ppm, and the molten steel temperature is controlled to be 1595°C to 1620°C.

5. The method according to claim 1, wherein In step ③, the carbon content is controlled to be 0.01% to 0.03%, the residual oxygen content is controlled to be 80 to 150 ppm, and the molten steel temperature is controlled to be 1585°C to 1595°C.

6. The method according to claim 1, characterized in that In step ④, the C content is controlled to be 0.01% to 0.03% and the molten steel temperature is controlled to be 1580°C to 1590°C.

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