High-sulfur steel and process for producing the same

Abstract

The application discloses high-sulfur steel, including components and mass percentage: C: 0.67%-0.73%, Si: 0.15%-0.25%, Mn: 0.45%-0.65%, P: ≤0.045%, S: 0.060%-0.070%, Cr: 0.10%-0.20%, Mo: ≤0.06%, Ni: ≤0.20%, V: 0.03%-0.04%, Al: ≤0.03%, N: 0.012%-0.016%, the balance is Fe and impurities.The application provides a preparation process of high-sulfur steel, including the following steps: step S1, converter process; step S2, refining process; step S3, VD process; step S4, continuous casting process.The beneficial effect is that the Al content in the steel is controlled at a relatively high level to offset the secondary oxidation caused by the addition of quartz sand at the end of the refining, that is, the low oxygen state in the steel is ensured by Al.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically, to a high-sulfur steel and its preparation process. Background Technology

[0002] The high-S steel C70S6 used in the connecting rod of passenger car engine requires a high S content within a very narrow range, making it difficult to control. To achieve a relatively stable S content control level, the slag basicity needs to be controlled to a relatively low level. However, low slag basicity makes it difficult to raise the LF temperature. Excessively low basicity results in a thin slag layer, which in turn leads to poor protection of the molten steel by the top slag, as well as a series of contradictions such as reduced protection for deoxidation and molten steel.

[0003] Therefore, there is a lack of a process that can achieve precise control over the composition of high-S steel.

[0004] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a high-sulfur steel and its preparation process to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high-sulfur steel comprises the following components and mass percentages: C: 0.67%-0.73%, Si: 0.15%-0.25%, Mn: 0.45%-0.65%, P: ≤0.045%, S: 0.060%-0.070%, Cr: 0.10%-0.20%, Mo: ≤0.06%, Ni: ≤0.20%, V: 0.03%-0.04%, Al: ≤0.03%, N: 0.012%-0.016%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the optimal composition and mass percentages are: C: 0.69%-0.72%, Si: 0.16%-0.24%, Mn: 0.55%-0.60%, P: ≤0.020%, S: 0.060%-0.070%, Cr: 0.10%-0.15%, Mo: ≤0.03%, Ni: 0.05%-0.07%, V: 0.03%-0.04%, Al: ≤0.008%, N: 0.012%-0.016%, with the balance being Fe and unavoidable impurities.

[0009] According to another aspect of this application, a process for preparing high-sulfur steel is provided, comprising the following steps:

[0010] Step S1, converter process;

[0011] Step S2, refining process;

[0012] Step S3, VD process;

[0013] Step S4: Continuous casting process.

[0014] Furthermore, step S1 specifically includes the following procedures:

[0015] S11, converter smelting deoxidation and alloying;

[0016] S12, deoxidation and alloying are carried out during steel tapping.

[0017] In step S11, the steel composition control requirements are: C: 0.06%-0.18%, P≤0.012%, and tapping temperature≥1600℃.

[0018] Step S12 specifically includes the following steps:

[0019] S121: After 1 / 3 of the steel has been tapped, add 10-50 kg of carbon raiser, 0.5-1 kg / t of aluminum ingot for pre-deoxidation, and add high-purity ferrosilicon, high-carbon ferrochrome, and medium-carbon ferromanganese for alloying.

[0020] S122: After 2 / 3 of the steel has been tapped, 10-11 kg / t of cleaning agent and 3-4 kg / t of lime slag-forming material are added at once to form the top slag of the ladle.

[0021] Furthermore, step S2 specifically includes the following steps:

[0022] S21. After the ladle top slag obtained in step S122 is brought into the station, the refining slag is adjusted according to the C content at the converter endpoint and the slag discharge situation.

[0023] S22. After heating for 5 minutes and stabilizing the submerged arc, calcium carbide and silicon carbide are used for slag surface mixing and deoxidation.

[0024] S23. Control the dust removal opening to maintain a slightly positive pressure atmosphere inside the furnace;

[0025] S24. After the first heating, control Al to the target value of 0.020%. Add 2.3 kg / t of quartz sand 5 minutes before the end of refining to make the target binary basicity 2.5-2.85.

[0026] S25. Before hoisting the ladle, feed 0.6-1 m / t of pure calcium wire at a speed of 120 m / min. After feeding the wire, take a long-handled sample and leave the station to test the N and S content in the steel. The target temperature for leaving the station is 1625-1660℃.

[0027] The adjustment relationship between the C content at the converter endpoint and the refining slag in step S21 is as follows:

[0028] When the endpoint C ≤ 0.06%, the amount of lime added is 1-2 kg / t;

[0029] When the endpoint C is 0.06%-0.12%, the amount of lime added is 0.5-1 kg / t;

[0030] When endpoint C > 0.12%, the amount of lime added is 0;

[0031] For each furnace start-up and converter slag discharge, an additional 1-2 kg of lime may be added.

[0032] Meanwhile, in step S22, the calcium carbide + silicon carbide mixture ratio is 1:2, and it is spread evenly on the slag surface in small batches, with the amount controlled to be no less than 2Kg / t.

[0033] Furthermore, step S3 specifically includes the following steps:

[0034] After S31 and VD are introduced into the station and the shell breaking is completed, sulfur is fed into the line at a speed of 80m / min for 3m / t, with a target S content of 0.070%.

[0035] S32. Vacuuming operation, target vacuum ≤67Pa, holding time ≥10min;

[0036] S33. After the bottom blowing of nitrogen into the ladle is completed, nitrogen is added again by bottom blowing of nitrogen into the ladle at a rate of 100-110 Nl / t. The lid is then raised to switch to soft blowing of argon gas at a flow rate of 10-30 Nl / min. After soft blowing, a sulfur sample is taken for carbon and sulfur testing, and a nitrogen sample is taken for nitrogen content testing. Based on the sulfur composition, sulfur wire is fed into the molten steel to adjust the sulfur composition to 0.070%. Based on the nitrogen content test results, manganese nitride iron wire is fed into the steel to adjust the nitrogen content to 0.140%-0.160%.

[0037] S34, soft blowing, soft blowing time ≥20min, 0.4m / t of pure calcium line is fed into the boiler 5min before the water leaves the station for calcium treatment, and no feeding is done in other furnaces, the outlet temperature is 1515℃-1550℃, of which the superheat target is 20-35℃.

[0038] Furthermore, step S4 specifically includes the following steps:

[0039] S41. For continuous casting, an integral stopper rod tundish is used. Before pouring, the impact zone of the tundish and the spaces between each flow are purged with argon gas.

[0040] S42. Then start the ladle slide to start pouring, with a target superheat of 30-40℃ at startup and continuous pouring at 20-35℃. The pouring speed is controlled at 0.95m / min, the crystallizer water flow rate is 1900L / min, and the crystallizer electromagnetic stirring parameters are 400A current and 2Hz frequency. The end electromagnetic stirring parameters are 500A current and 10Hz frequency. The pouring process is protected throughout.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) By adding initial slag-forming material, the high basicity control target in the early stage of refining is achieved, which is conducive to refining deoxidation and heating and submerging arc, and solves the problems of refining deoxidation and heating; by changing slag in the later stage of refining, the basicity of slag is reduced, which meets the requirements of low basicity and stable sulfur control in the VD process; by controlling Al in the early stage of refining, the Al content in steel is controlled at a relatively high level to offset the secondary oxidation brought about by the addition of quartz sand after the end of refining, that is, Al is used to ensure the low oxygen state in steel.

[0043] (2) The light calcium treatment operation after refining can modify the oxidizing properties produced by the silicon-aluminum reaction after slag transformation. On the other hand, the residual calcium in the steel after breaking the vacuum can spheroidize the inclusions in the steel, which is beneficial to reducing the sulfide grade. The secondary sulfur control scheme of feeding S sulfur line before vacuum can greatly reduce the pressure of large feed amount, inaccurate sampling and low error rate caused by feeding S once after vacuum. It can effectively ensure the accurate control of S content in high S steel. The operation scheme of bottom blowing nitrogen + nitriding line fine adjustment can achieve nitrogen content control at low cost. The full protection casting of continuous casting is conducive to the stable control of S content. Detailed Implementation

[0044] The invention will now be further described in conjunction with specific embodiments:

[0045] According to an embodiment of the present invention, a high-sulfur steel comprises the following components and mass percentages: C: 0.67%-0.73%, Si: 0.15%-0.25%, Mn: 0.45%-0.65%, P: ≤0.045%, S: 0.060%-0.070%, Cr: 0.10%-0.20%, Mo: ≤0.06%, Ni: ≤0.20%, V: 0.03%-0.04%, Al: ≤0.03%, N: 0.012%-0.016%, with the balance being Fe and unavoidable impurities.

[0046] According to the above-described components of the present invention, a process for preparing high-sulfur steel is also provided, specifically comprising the following steps:

[0047] Step S1, converter process;

[0048] S11, Converter smelting deoxidation and alloying: Steel composition control requirements: C: 0.06%-0.18%, P≤0.012%, steel tapping temperature≥1600℃;

[0049] S12. Deoxidation and alloying are carried out during steel tapping. The order and weight of alloy addition are as follows: 10-50 kg of carbon raiser (added when the final C ≥ 0.08%) is added after 1 / 3 of the steel is tapped, 0.5-1 kg / t of aluminum ingot is added for pre-deoxidation, and high-purity ferrosilicon, high-carbon ferrochrome, and medium-carbon ferromanganese are added for alloying; 10-11 kg / t of purification accelerator and 3-4 kg / t of lime slag-forming material are added all at once after 2 / 3 of the steel is tapped to form ladle top slag (refining primary slag).

[0050] Step S2, refining process;

[0051] S21. After the slag enters the refining station, adjustments are made to the refining slag based on the final carbon content and slag discharge condition at the converter endpoint, ensuring good slag fluidity and meeting the control target of binary basicity R: 5-6.

[0052]

[0053] S22. After heating for 5 minutes and stabilizing the submerged arc, calcium carbide and silicon carbide are mixed on the slag surface for deoxidation. The mixing ratio is 1:2. The mixture is spread evenly on the slag surface in small batches, with the dosage controlled to be no less than 2 kg / t.

[0054] S23. Control the dust removal opening to maintain a slightly positive pressure atmosphere inside the furnace.

[0055] S24. After the first heating, control Al to the target value of 0.020% according to the sample. Add 2.3 kg / t of quartz sand 5 minutes before the end of refining, and add 2.7 kg / t of sand when starting the furnace to achieve the target binary alkalinity of 2.5-2.85.

[0056] S25. Before hoisting, feed pure calcium wire at a speed of 120m / min at 0.6-1m / t. After feeding, take a long-handled sample and remove it from the station to test the N and S content in the steel. The target temperature for leaving the station is 1625-1660℃ (adjusted according to the actual temperature drop).

[0057] Step S3, VD process;

[0058] After S31 and VD are introduced into the station and the shell breaking is completed, sulfur is fed into the line at a speed of 80m / min for 3m / t, with a target S content of 0.070%.

[0059] S32. Vacuuming operation, target vacuum ≤67Pa, holding time ≥10min;

[0060] S33. After the holding period, nitrogen is added by bottom blowing nitrogen into the ladle at a rate of 100-110 Nl / t. The ladle is then covered and switched to argon soft blowing (flow rate approximately 10-30 Nl / min). After soft blowing, a sulfur sample is taken for testing (carbon and sulfur detection), and a nitrogen sample is taken for nitrogen content detection. Based on the sulfur composition, sulfur wire is fed into the molten steel to adjust the sulfur content to 0.070% (approximately 0.06 m / t increases sulfur by 0.001%). Based on the nitrogen content detection results, manganese nitride or ferrochrome nitride wire is fed into the steel to adjust the nitrogen content to 0.140%-0.160%.

[0061] S34. Soft blowing time ≥ 20 min. 5 min before the start-up water exits the station, feed 0.4 m / t of pure calcium line for calcium treatment. Do not feed calcium line in other furnaces. Exit temperature 1515℃-1550℃ (target superheat 20-35℃, exit temperature can be adjusted according to casting conditions).

[0062] Step S4: Continuous casting process.

[0063] S41. For continuous casting using an integral stopper rod tundish, the impact zone of the tundish and the spaces between each flow path are purged with argon gas before casting begins.

[0064] S42. Then start the ladle slide to start pouring, with a target superheat of 30-40℃ at startup and continuous pouring at 20-35℃. The pouring speed is controlled at 0.95m / min, the crystallizer water flow rate is 1900L / min, and the crystallizer electromagnetic stirring parameters are 400A current and 2Hz frequency. The end electromagnetic stirring parameters are 500A current and 10Hz frequency. The pouring process is protected throughout.

[0065] Among them, the remaining casting volume of the ladle is ≥2.5t, the remaining casting volume of the intermediate ladle is ≥3.5t, and the slow cooling time of the billet in the pit is ≥36h.

[0066] Example 1:

[0067] According to an embodiment of the present invention, a high-sulfur steel comprises the following components and mass percentages: C: 0.67%, Si: 0.15%, Mn: 0.45%, P: 0.035%, S: 0.060%, Cr: 0.10%, Mo: 0.04%, Ni: 0.10%, V: 0.03%, Al: 0.01%, N: 0.012%, with the balance being Fe and unavoidable impurities.

[0068] Example 2

[0069] According to an embodiment of the present invention, a high-sulfur steel comprises the following components and mass percentages: C: 0.70%, Si: 0.20%, Mn: 0.50%, P: 0.040%, S: 0.065%, Cr: 0.15%, Mo: 0.05%, Ni: 0.15%, V: 0.035%, Al: 0.02%, N: 0.014%, with the balance being Fe and unavoidable impurities.

[0070] Example 3

[0071] According to an embodiment of the present invention, a high-sulfur steel comprises the following components and mass percentages: C: 0.73%, Si: 0.25%, Mn: 0.65%, P: 0.045%, S: 0.070%, Cr: 0.20%, Mo: 0.06%, Ni: 0.20%, V: 0.04%, Al: 0.03%, N: 0.016%, with the balance being Fe and unavoidable impurities.

[0072] Furthermore, the slag composition control range before and after the addition of quartz sand is shown in the table below:

[0073]

[0074] As shown in the table above, this application employs a combination of high basicity in the early refining stage with aluminum control and slag transformation in the later refining stage to resolve the contradiction between refining basicity and deoxidation. Combined with a secondary sulfur control scheme in a VD furnace, it solves the problem of precise sulfur composition control. Furthermore, a light calcium treatment operation after refining effectively spheroidizes sulfide inclusions in the steel, reducing their inclusion rating to meet product characteristic requirements. Simultaneously, by using bottom-blown nitrogen enhancement technology, production costs are controlled at a low level, enabling the development and application of the process for high-sulfur steel grade C70S6. Currently, our company has achieved precise cost control for this steel grade and has achieved 10 consecutive castings in a single ladle.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing high-sulfur steel, characterized in that, The high-sulfur steel comprises the following components and mass percentages: C: 0.67%-0.73%, Si: 0.15%-0.25%, Mn: 0.45%-0.65%, P: ≤0.045%, S: 0.060%-0.070%, Cr: 0.10%-0.20%, Mo: ≤0.06%, Ni: ≤0.20%, V: 0.03%-0.04%, Al: ≤0.03%, N: 0.012%-0.016%, with the balance being Fe and unavoidable impurities; the preparation process includes the following steps: Step S1, converter process, to obtain ladle top slag; Step S2, refining process; Step S3, VD process; Step S4, continuous casting process; Step S2 specifically includes the following steps: S21. After the ladle top slag obtained in step S1 is brought into the station, the refining slag is adjusted according to the C content at the converter endpoint and the slag discharge situation. S22. After heating for 5 minutes and stabilizing the submerged arc, calcium carbide and silicon carbide are used for slag surface mixing and deoxidation. S23. Control the dust removal opening to maintain a slightly positive pressure atmosphere inside the furnace; S24. After the first heating, control Al to the target value of 0.020%. Add 2.3 kg / t of quartz sand 5 minutes before the end of refining to make the target binary basicity 2.5-2.

85. S25. Before hoisting, feed pure calcium wire at a speed of 120m / min at 0.6-1m / t. After feeding, take a long-handled sample and leave the station to test the N and S content in the steel. The target temperature for leaving the station is 1625-1660℃. The adjustment relationship between the converter endpoint C content and the refining slag in step S21 is as follows: When the endpoint C ≤ 0.06%, the amount of lime added is 1-2 kg / t; When the endpoint C is greater than 0.06% and less than or equal to 0.12%, the amount of lime added is 0.5-1 kg / t; When endpoint C > 0.12%, the amount of lime added is 0; For each furnace start-up and converter slag discharge, an additional 1-2 kg of lime shall be added. Meanwhile, in step S22, the calcium carbide + silicon carbide mixture is mixed in a 1:2 ratio and is applied evenly to the slag surface in small batches, with the dosage controlled to be no less than 2 kg / t. Step S3 specifically includes the following steps: After S31 and VD are introduced into the station and the shell breaking is completed, sulfur is fed in at a rate of 80 m / min for 3 m / t, with a target sulfur content of 0.070%. S32. Vacuuming operation, target vacuum ≤67Pa, holding time ≥10min; S33. After bottom blowing nitrogen into the ladle and maintaining the nitrogen level, continue bottom blowing nitrogen into the ladle at a rate of 100-110 Nl / t. Then, switch to argon soft blowing with a flow rate of 10-30 Nl / min. After soft blowing, take a sulfur sample for carbon and sulfur testing, and a nitrogen sample for nitrogen content testing. Based on the sulfur composition, feed sulfur wire to adjust the sulfur composition of the molten steel to 0.070%. Based on the nitrogen content test results, feed manganese nitride iron wire to adjust the nitrogen content in the steel to 0.0140%-0.0160%. S34. Soft blowing, soft blowing time ≥20min. 5min before the furnace leaves the station, feed 0.4m / t of pure calcium line for calcium treatment. Do not feed for other furnaces. The outlet temperature is 1515℃-1550℃, of which the superheat target is 20-35℃.

2. The preparation process of high-sulfur steel according to claim 1, characterized in that, Step S4 specifically includes the following steps: S41. For continuous casting, an integral stopper rod tundish is used. Before pouring, the impact zone of the tundish and the spaces between each flow are purged with argon gas. S42. Then start the ladle slide to start pouring, with a target superheat of 30-40℃ at startup and continuous pouring at 20-35℃. The pouring speed is controlled at 0.95m / min, the crystallizer water flow rate is 1900L / min, and the crystallizer electromagnetic stirring parameters are 400A current and 2Hz frequency. The end electromagnetic stirring parameters are 500A current and 10Hz frequency. The pouring process is protected throughout.

3. The preparation process of high-sulfur steel according to claim 1, characterized in that, Step S1 specifically includes the following procedures: S11, converter smelting deoxidation and alloying; S12, Deoxidation and alloying are performed during steel tapping; The steel composition control requirements in step S11 are: C: 0.06%-0.18%, P≤0.012%, and tapping temperature≥1600℃; Step S12 specifically includes the following steps: S121: After 1 / 3 of the steel has been tapped, add 10-50 kg of carbon raiser, 0.5-1 kg / t of aluminum ingot for pre-deoxidation, and add high-purity ferrosilicon, high-carbon ferrochrome, and medium-carbon ferromanganese for alloying. S122: After 2 / 3 of the steel has been tapped, 10-11 kg / t of cleaning agent and 3-4 kg / t of lime slag-forming material are added at once to form the top slag of the ladle.

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