Method for producing ultra-low carbon steel through RH oxygen blowing decarburization

Abstract

The invention provides an RH oxygen blowing decarburization refining method. The method comprises the following steps that firstly, molten steel is smelted through a converter and then discharged to a steel ladle; and then the steel ladle obtained in the previous step is subjected to RH refining under the vacuum condition and under the action of lifting gas, oxygen is blown into the steel ladle in a steel ladle bottom blowing mode, argon is blown into the steel ladle at the bottom after oxygen blowing is finished, bottom blowing is stopped after decarburization is finished, and then molten steel obtained after RH refining is obtained after the alloying step. According to the method, bottom blowing oxygen is adopted for forced decarburization, the carbon content in molten steel is reduced, the oxygen utilization rate is remarkably increased, and the problem of vacuum degree fluctuation caused by oxygen lance oxygen blowing decarburization is solved. The oxygen utilization rate of RH oxygen blowing decarburization can be increased, molten steel decarburization is promoted, and the problem of vacuum degree fluctuation caused by oxygen lance oxygen blowing decarburization is solved. After the method is implemented, obvious economic benefits are created, and the method can be popularized and applied in the same industry in China.

Description

Technical Field

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

[0002] With the continuous development of the automobile industry, the demand for ultra-low carbon automobile sheet steel is increasing, and users have put forward higher and higher requirements for ultra-low carbon automobile sheet steel. RH vacuum refining is a key link in reducing the carbon content in the production of ultra-low carbon steel. Since the decarburization reaction is a high-temperature and low-pressure reaction, the degree of the decarburization reaction directly affects the decarburization rate and becomes a process-limiting link affecting the RH cycle. The argon-driven RH vacuum device is a key equipment for ultra-low carbon steel refining. The circulation of molten steel under high vacuum can effectively decarburize, degas and remove inclusions.

[0003] At present, domestic steel mills mainly determine natural decarburization or oxygen-blowing forced decarburization based on the RH inlet carbon content. Some companies use the addition of decarburizers for decarburization. Oxygen-blowing forced decarburization mainly involves blowing oxygen from the lower oxygen lance. The oxygen yield of this method is unstable, and the decarburizer can easily cause a large temperature drop in the molten steel. In addition, the powder spraying device is easily blocked in direct contact with the molten steel, which affects decarburization. For example, a method for smelting and producing ultra-low carbon steel disclosed in patent 202311663969.2 adopts the process flow of converter low-temperature oxygen steel tapping → RH-OB decarburization → RH deoxidation alloying. This patent blows oxygen OB according to the oxygen content of the molten steel, and uses OB to increase the oxygen content in the molten steel for decarburization. This method has a low oxygen yield and is unstable. For example, a molten steel refining method for RH rapid decarburization disclosed in patent 202110571343.3. The process flow includes converter blowing and RH decarburization. This patent requires adding a decarburization accelerator containing limestone and hematite from a high-level silo, combined with bottom blowing of argon, to improve the kinetic conditions of the molten steel reaction and promote the decarburization reaction. However, adding limestone and hematite to the high-level silo will cause the molten steel to splash into the vacuum chamber, causing the vacuum chamber to stick to the steel. Furthermore, adding cold materials will lower the temperature of the molten steel, requiring the previous process to increase the temperature, increasing costs. Another example is a method for oxygen decarburization in a refining RH furnace disclosed in 202211078391.X. During the oxygen decarburization process, the oxygen lance height H changes with time according to the following formula: H = Hinitial (1-0.5t / ttotal); where H: oxygen lance height, m; Hinitial: initial oxygen lance height at the start of oxygen blowing, m; t: oxygen blowing duration, s; ttotal: total oxygen blowing time, s; during the oxygen decarburization process, the real-time oxygen flow rate FO2 = 20W×(C / O)1 / 2×[0.75+(t / ttotal)2-t / ttotal]|sin(πt / 180)|. However, this patent is a variable lance position and variable flow oxygen decarburization process, which requires dynamic adjustment of the oxygen lance height and oxygen flow rate, and has high operability requirements.

[0004] Therefore, how to find a more suitable RH oxygen blowing decarburization method for producing ultra-low carbon steel and solve the above-mentioned technical problems existing in the existing process has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for RH oxygen blowing decarburization refining, in particular, a method for producing ultra-low carbon steel by RH oxygen blowing decarburization. The present invention reduces the carbon content in the molten steel by bottom blowing oxygen for forced decarburization when producing ultra-low carbon steel, significantly improves the utilization rate of oxygen, and improves the problem of vacuum fluctuation caused by oxygen lance oxygen blowing decarburization. Moreover, the production method has simple process, good controllability, strong operability, and is more suitable for industrial promotion and application.

[0006] The present invention provides a RH oxygen blowing decarburization refining method, comprising the following steps:

[0007] 1) The molten steel is smelted in a converter and then discharged into a ladle;

[0008] 2) The ladle obtained in the above steps is subjected to RH refining under vacuum conditions and the action of lifting gas, and oxygen is blown into the ladle by bottom blowing of the ladle. After the oxygen blowing is completed, argon is blown into the bottom of the ladle. After the decarburization is completed, the bottom blowing is turned off, and then after the alloying step, RH refined molten steel is obtained.

[0009] Preferably, the outlet temperature of the converter after smelting is 1650-1670°C.

[0010] Preferably, the final carbon mass content of the converter smelting is 0.04% to 0.06%.

[0011] Preferably, the vacuum pressure is less than or equal to 300 Pa.

[0012] Preferably, the temperature of the RH refining is 1610-1630°C.

[0013] Preferably, the oxygen amount of the oxygen blowing is 20 to 150 m 3 .

[0014] Preferably, the flow rate of the oxygen blowing is 150-300 NL / min;

[0015] The oxygen blowing time is less than or equal to 4 minutes.

[0016] Preferably, the flow rate of the bottom blowing argon gas is 80 to 150 NL / min.

[0017] Preferably, during the RH refining and decarburization process, the flow rate of the lifting gas is 1400 to 3000 NL / min.

[0018] Preferably, the total decarburization time is 15 to 20 minutes;

[0019] After the decarburization is completed, the carbon content is less than or equal to 15 ppm.

[0020] The present invention provides a method for RH oxygen blowing decarburization refining, comprising the following steps: first, molten steel is discharged from a converter to a ladle after smelting; then the ladle obtained in the above steps is subjected to RH refining under vacuum conditions and the action of a lifting gas, oxygen is blown into the ladle by a ladle bottom blowing method, argon is blown into the ladle bottom after the oxygen blowing is completed, the bottom blowing is closed after the decarburization is completed, and then after an alloying step, RH refined molten steel is obtained. Compared with the prior art, the present invention creatively designs a method for RH oxygen blowing decarburization refining using bottom blowing oxygen for forced decarburization, which is a method for producing ultra-low carbon steel by RH oxygen blowing decarburization. When producing ultra-low carbon steel, the present invention uses bottom blowing oxygen for forced decarburization, reduces the carbon content in the molten steel, significantly improves the utilization rate of oxygen, and improves the problem of vacuum fluctuation caused by oxygen lance oxygen blowing decarburization. The present invention can improve the oxygen utilization rate of RH oxygen blowing decarburization, promote the decarburization of molten steel, and improve the problem of vacuum fluctuation caused by oxygen lance oxygen blowing decarburization. The invention creates significant economic benefits after implementation, and the invention can be promoted and applied in the same industry in China.

[0021] The method for producing ultra-low carbon steel by RH oxygen decarburization proposed by the present invention is to change oxygen lance oxygen decarburization to bottom oxygen decarburization, thereby increasing the contact area between oxygen and molten steel, increasing the carbon-oxygen reaction rate, thereby reducing the carbon content of the molten steel, and increasing the oxygen yield of oxygen decarburization at a low cost. By adopting the method provided by the present invention, since the bottom oxygen directly contacts and reacts with the molten steel, the oxygen utilization rate is improved compared with the oxygen utilization rate of top lance oxygen blowing. Moreover, the generated CO is conducive to the circulation of molten steel, accelerates the RH decarburization rate, and is conducive to the production of ultra-low carbon steel. Moreover, the process technology can increase the carbon content of the converter end point, which is conducive to the improvement of the alloy yield of the converter end point.

[0022] The actual production application results show that the invention can greatly improve the oxygen utilization rate of RH vacuum oxygen decarburization and reduce the carbon content in molten steel. After being implemented in Panzhihua Iron and Steel, the invention has created significant economic benefits, and is expected to generate more than 4.5 million yuan per year. DETAILED DESCRIPTION

[0023] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention rather than limiting the patent claims of the present invention.

[0024] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0025] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial purity or conventional purity in the field of ultra-low carbon steel production.

[0026] The brands and abbreviations of all raw materials of the present invention are conventional brands and abbreviations in the art. Each brand and abbreviation is clear and definite in the field of its related use. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the brands, abbreviations and corresponding uses.

[0027] The present invention provides a RH oxygen blowing decarburization refining method, comprising the following steps:

[0028] 1) The molten steel is smelted in a converter and then discharged into a ladle;

[0029] 2) The ladle obtained in the above steps is subjected to RH refining under vacuum conditions and the action of lifting gas, and oxygen is blown into the ladle by bottom blowing of the ladle. After the oxygen blowing is completed, argon is blown into the bottom of the ladle. After the decarburization is completed, the bottom blowing is turned off, and then after the alloying step, RH refined molten steel is obtained.

[0030] The present invention firstly smelts molten steel in a converter and then discharges the molten steel into a ladle.

[0031] In the present invention, the temperature of the converter after smelting is preferably 1650-1670°C, more preferably 1654-1666°C, and more preferably 1658-1662°C.

[0032] In the present invention, the final carbon mass content of the converter smelting is preferably 0.04% to 0.06%, more preferably 0.044% to 0.056%, and more preferably 0.048% to 0.052%.

[0033] The present invention then performs RH refining on the ladle obtained in the above steps under vacuum conditions and the action of lifting gas, adopts the ladle bottom blowing method to blow oxygen into the ladle, and after the oxygen blowing is completed, argon is blown into the bottom of the ladle instead, and after the decarburization is completed, the bottom blowing is turned off, and then after the alloying step, RH refined molten steel is obtained.

[0034] In the present invention, the vacuum pressure is preferably less than or equal to 300 Pa, more preferably less than or equal to 250 Pa, and more preferably less than or equal to 200 Pa.

[0035] In the present invention, the temperature of the RH refining is preferably 1610-1630°C, more preferably 1614-1626°C, and more preferably 1618-1622°C.

[0036] In the present invention, the oxygen amount of the oxygen blowing is preferably 20 to 150 m 3, more preferably 50 to 120 m 3 , more preferably 80 to 90 m 3 .

[0037] In the present invention, the flow rate of the oxygen blowing is preferably 150 to 300 NL / min, more preferably 180 to 270 NL / min, and more preferably 210 to 240 NL / min.

[0038] In the present invention, the oxygen blowing time is preferably less than or equal to 4 minutes, more preferably less than or equal to 3.5 minutes, and more preferably less than or equal to 3 minutes.

[0039] In the present invention, the flow rate of the bottom-blown argon gas is preferably 80 to 150 NL / min, more preferably 95 to 135 NL / min, and even more preferably 110 to 120 NL / min.

[0040] In the present invention, during the RH refining and decarburization process, the flow rate of the lifting gas is preferably 1400 to 3000 NL / min, more preferably 1700 to 2700 NL / min, and more preferably 2000 to 2400 NL / min.

[0041] In the present invention, the total decarburization time is preferably 15 to 20 minutes, more preferably 16 to 19 minutes, and more preferably 17 to 18 minutes.

[0042] In the present invention, the carbon content after decarburization is preferably less than or equal to 15 ppm, more preferably less than or equal to 14 ppm, and more preferably less than or equal to 13 ppm.

[0043] The present invention is to complete and refine the overall technical solution, better ensure the stability and efficiency of RH oxygen blowing decarburization to produce ultra-low carbon steel, and further improve the decarburization effect of RH oxygen blowing decarburization refining. The above-mentioned method for producing ultra-low carbon steel by RH oxygen blowing decarburization can specifically include the following steps:

[0044] A method for producing ultra-low carbon steel by RH oxygen blowing decarburization comprises the following steps:

[0045] (1) After the molten steel is smelted in a converter, the converter terminal temperature is controlled at 1650-1670°C, and the converter terminal carbon content is controlled at 0.04-0.06%;

[0046] (2) After the ladle is transported to the RH station, the amount of oxygen required for oxygen decarburization is calculated based on the carbon-oxygen balance model;

[0047] (3) Start vacuuming for decarburization operation. When the vacuum drops to 300Pa, start bottom blowing of the ladle at the riser position. According to the calculation results, oxygen is blown at the bottom, and the flow rate is controlled at 150-300NL / min. The oxygen blowing time is controlled within 4min. After the oxygen blowing is completed, the bottom blowing gas is replaced with argon, and the flow rate is controlled at 80-150NL / min.

[0048] (4) After decarburization is completed, turn off the bottom blowing and perform normal alloying operation.

[0049] (5) Among them, the RH decarburization time is controlled at 15 to 20 minutes, and the carbon content at the end of decarburization is ≤15ppm.

[0050] (6) The RH decarburization process increases the gas flow rate to control between 1400 and 3000 NL / min.

[0051] (7) Always keep the bottom air holes unobstructed to prevent blockage that may prevent gas from blowing in and affect decarbonization and stirring.

[0052] The present invention blows oxygen from the bottom air port to react with carbon in the molten steel, effectively increasing the carbon-oxygen reaction time. The small bubbles generated by the reaction can also promote the circulation of the molten steel, thereby avoiding the problem of low and unstable oxygen recovery rate during top gun oxygen decarburization and improving the problem of vacuum fluctuation caused by oxygen decarburization with the oxygen gun.

[0053] The above content of the present invention provides a method for producing ultra-low carbon steel by RH oxygen decarburization. When producing ultra-low carbon steel, the present invention adopts bottom blowing oxygen to force decarburization, reduce the carbon content in the molten steel, significantly improve the utilization rate of oxygen, and improve the problem of vacuum fluctuation caused by oxygen lance oxygen decarburization. The present invention can improve the oxygen utilization rate of RH oxygen decarburization, promote the decarburization of molten steel, and improve the problem of vacuum fluctuation caused by oxygen lance oxygen decarburization. The invention creates obvious economic benefits after implementation, and the invention can be promoted and applied in the same industry in China.

[0054] The method for producing ultra-low carbon steel by RH oxygen decarburization proposed by the present invention is to change oxygen lance oxygen decarburization to bottom oxygen decarburization, thereby increasing the contact area between oxygen and molten steel, increasing the carbon-oxygen reaction rate, thereby reducing the carbon content of the molten steel, and increasing the oxygen yield of oxygen decarburization at a low cost. By adopting the method provided by the present invention, since the bottom oxygen directly contacts and reacts with the molten steel, the oxygen utilization rate is improved compared with the oxygen utilization rate of top lance oxygen blowing. Moreover, the generated CO is conducive to the circulation of molten steel, accelerates the RH decarburization rate, and is conducive to the production of ultra-low carbon steel. Moreover, the process technology can increase the carbon content of the converter end point, which is conducive to the improvement of the alloy yield of the converter end point.

[0055] The actual production application results show that the invention can greatly improve the oxygen utilization rate of RH vacuum oxygen decarburization and reduce the carbon content in molten steel. After being implemented in Panzhihua Iron and Steel, the invention has created significant economic benefits, and is expected to generate more than 4.5 million yuan per year.

[0056] In order to further illustrate the present invention, a RH oxygen blowing decarburization refining method provided by the present invention is described in detail below in combination with examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

[0057] Example 1

[0058] For 120t ladle, when producing ultra-low carbon steel.

[0059] (1) After the molten steel is smelted in the converter, temperature measurement and sampling are carried out when it leaves the station to analyze the temperature and carbon composition of the molten steel to ensure that the temperature is controlled at 1660±5℃ and the carbon content at the converter end point is controlled at 0.04-0.06%;

[0060] (2) After reaching the RH refining process, the amount of oxygen required for oxygen decarburization is calculated according to the carbon-oxygen balance model. Assuming the RH inlet carbon content is 0.05%, the oxygen blowing amount can be determined to be 104m 3 ;

[0061] (3) Start vacuuming for decarburization operation. When the vacuum drops to 300Pa, start bottom blowing of the ladle at the riser position. According to the calculation results, oxygen is blown at the bottom, and the flow rate is controlled at 150NL / min. The oxygen blowing time is controlled within 3min. After the oxygen blowing is completed, the bottom blowing gas is replaced with argon, and the flow rate is controlled at 80NL / min;

[0062] (4) Alloying according to the composition of the incoming molten steel;

[0063] (5) Among them, the RH decarburization time is not less than 15 minutes, and the carbon content at the end of decarburization is 12ppm.

[0064] Example 2

[0065] For 200t ladle, when producing ultra-low carbon steel.

[0066] (1) After the molten steel is smelted in the converter, temperature measurement and sampling are carried out when it leaves the station to analyze the temperature and carbon composition of the molten steel to ensure that the temperature is controlled at 1660±5℃ and the carbon content at the converter end point is controlled at 0.04-0.06%;

[0067] (2) After reaching the RH refining process, the amount of oxygen required for oxygen decarburization is calculated according to the carbon-oxygen balance model. Based on the RH inlet carbon content of 0.04%, the oxygen blowing amount can be determined to be 78m 3 ;

[0068] (3) Start vacuuming for decarburization operation. When the vacuum drops to 300Pa, start the bottom blowing of the ladle at the riser position. According to the calculation results, blow oxygen at the bottom, control the flow rate at 200NL / min, and control the oxygen blowing time within 4min. After the oxygen blowing is completed, replace the bottom blowing gas with argon, and control the flow rate at 150NL / min;

[0069] (4) Alloying according to the composition of the incoming molten steel;

[0070] (5) Among them, the RH decarburization time is not less than 16 minutes, and the carbon content at the end of decarburization is 14 ppm.

[0071] According to the present invention, since the bottom-blown oxygen directly contacts and reacts with the molten steel, the oxygen utilization rate is improved compared with the oxygen utilization rate of the top-gun-blown oxygen. Moreover, the generated CO is beneficial to the circulation of the molten steel, accelerates the RH decarburization rate, and is beneficial to the production of ultra-low carbon steel. Moreover, the process technology can increase the carbon content of the converter end point, which is beneficial to the improvement of the alloy yield of the converter end point.

[0072] The above is a detailed introduction to a method for producing ultra-low carbon steel by RH oxygen decarburization provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A RH oxygen blowing decarburization refining method, characterized in that: The following steps are involved: 1) The molten steel is smelted in a converter and then discharged into a ladle; 2) The ladle obtained in the above steps is subjected to RH refining under vacuum conditions and the action of lifting gas, and oxygen is blown into the ladle by bottom blowing of the ladle. After the oxygen blowing is completed, argon is blown into the bottom of the ladle. After the decarburization is completed, the bottom blowing is turned off, and then after the alloying step, RH refined molten steel is obtained.

2. The method according to claim 1, characterized in that The temperature of the converter after smelting is 1650-1670°C.

3. The method according to claim 1, characterized in that The final carbon content of the converter smelting is 0.04% to 0.06%.

4. The method according to claim 1, characterized in that: The vacuum pressure is less than or equal to 300 Pa.

5. The method according to claim 1, characterized in that The temperature of the RH refining is 1610-1630°C.

6. The method according to claim 1, characterized in that The oxygen blowing amount is 20-150m 3 .

7. The method according to claim 1, characterized in that The flow rate of the oxygen blowing is 150-300 NL / min; The oxygen blowing time is less than or equal to 4 minutes.

8. The method according to claim 1, characterized in that The flow rate of the bottom blowing argon gas is 80-150 NL / min.

9. The method according to claim 1, characterized in that: During the RH refining and decarburization process, the flow rate of the lifting gas is 1400-3000 NL / min.

10. The method according to claim 1, characterized in that The total decarburization time is 15 to 20 minutes; After the decarburization is completed, the carbon content is less than or equal to 15 ppm.