Method for controlling content of Ti in molten bearing steel

Abstract

The invention discloses a method for controlling the content of Ti in molten bearing steel. According to the method for controlling the content of Ti in the molten steel, the production process comprises the steps of molten iron pretreatment, converter smelting, LF refining, RH vacuum degassing and continuous casting, steel remaining operation is adopted in the converter smelting process, tapping and roughing slag are reduced, and appropriate slag charge and alloy are adopted in the LF furnace refining process, so that the content of Ti entering the molten steel is reduced. Through production of a large amount of bearing steel, the average value of the titanium content in the steel can be 15.28 ppm, the maximum value of the Ti content is smaller than or equal to 25 ppm, and the requirement of customers for the high titanium content of the bearing steel is met.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a method for controlling the Ti content in molten bearing steel. Background Art

[0002] Non-metallic inclusions in bearing steel destroy the continuity and uniformity of the metal. Under the action of alternating stress, they are prone to cause stress concentration, become the source of fatigue cracks, and reduce the fatigue life of the steel. In particular, TiC and TiN inclusions formed by nitrogen, carbon and titanium content in steel are brittle and hard inclusions. Under the same size conditions, TiC and TiN inclusions are more harmful than oxide inclusions and are particularly harmful to the fatigue life of steel. For bearing steel produced in converters, the N2 content in the steel is generally controlled at around 40ppm. If it needs to be further reduced, it is difficult to control. Therefore, we usually need to strictly control the residual Ti content in the steel. When the residual Ti content in the steel exceeds 30ppm, it will have a significant impact on the fatigue life of the bearing steel.

[0003] The production process uses conventional slag, alloys and ladles, and the titanium content in the steel is controlled at around 35ppm, which can basically meet the national standard for bearing steel production, but cannot meet the production of bearing steel with high requirements for titanium content (Ti≤25ppm).

[0004] The existing technical solutions mainly have the following problems:

[0005] (1) The Ti content in the molten steel is high, but it cannot meet the high titanium content requirements (Ti≤25ppm) for bearing steel production.

[0006] (2) The Ti content in molten steel is unstable and fluctuates greatly (the Ti content in molten steel fluctuates between 0.0025% and 0.0040%), which is not conducive to the stable control of the quality of the steel billet. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for controlling the Ti content in molten bearing steel.

[0008] The present invention provides a method for controlling the Ti content in molten steel of bearing steel. The production process comprises: molten iron pretreatment → converter smelting → LF refining → RH vacuum degassing → continuous casting, wherein: in the converter smelting process, steel retention operation is adopted to reduce slag during steel tapping, and in the LF furnace refining process, suitable slag and alloy are adopted to reduce the Ti content entering the molten steel.

[0009] The present invention has the following beneficial effects:

[0010] The present invention provides a method for controlling the Ti content in molten steel of bearing steel. By optimizing the converter smelting process and the LF refining process, such as adopting the steel retention operation in the converter smelting process to reduce the slag during steel tapping, and adopting suitable slag and alloy in the LF furnace refining process, after a large amount of bearing steel is produced, the average titanium content in the steel can be 15.28ppm, and the maximum Ti content is ≤25ppm, thereby meeting the high requirements of customers for the titanium content of bearing steel. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0012] A method for controlling the Ti content in molten bearing steel provided by an embodiment of the present invention is described in detail below.

[0013] The embodiment of the present invention provides a method for controlling the Ti content in molten steel of bearing steel, and the production process includes: (molten iron pretreatment) → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting. It includes the following steps:

[0014] 1. Smelting technology:

[0015] ① The converter adopts steel retention operation to reduce slag during steel tapping. The amount of steel retained is controlled at 5-10kg / ton of molten steel. The TiO2 content in the converter slag is 0.7-0.9%. As the diffusion deoxidation process proceeds during the refining process, the TiO2 in the slag is gradually reduced and enters the steel, causing the titanium content in the steel to increase during the refining process.

[0016] ② Increase the tapping temperature of molten steel and strengthen the purge of ladle air bricks to improve the ladle bottom blowing effect and avoid poor ladle bottom blowing during the smelting process. In the refining process, the ladle bottom blowing is poor, and the slag and the carbon powder floating on the slag react chemically under the high temperature of electrode heating, reducing the oxides in the slag, resulting in an increase in the Al and Ti content in the steel.

[0017] ③ Increase the proportion of alumina in the refining slag. The activity ratio of alumina and titanium oxide in the slag = m. When m is constant, the titanium content in the steel increases with the increase of acid-soluble aluminum. When the acid-soluble aluminum is constant, the larger the m, the smaller the titanium content in the steel at equilibrium. Increasing the Al2O3 content in the slag can significantly inhibit the reduction of TiO2 in the slag. Controlling the mass percentage of Al2O3 in the refining slag to 20% to 30% has a better control effect on the reduction of titanium during LF refining.

[0018] 2. Selection of slag and alloy

[0019] ① Slag: Use a steelmaking tempering agent specially made for bearing steel, with the composition of SiO2: ≤6.0%, Al2O3: 33-36%, CaO: 47-53%, MnO: 3-8%, TiO2: ≤0.03%. The TiO2 content in the steelmaking tempering agent is relatively low, with an average content of 0.03%, while the average TiO2 content of the pre-melted synthetic slag used in other steel grades is 0.3%, which is 10 times higher than that of the steelmaking tempering agent.

[0020] ② Alloy: Use high-purity or high-quality alloys. The titanium content of high-purity or high-quality alloys is much lower than that of ordinary alloys. Therefore, ferrosilicon, high-carbon ferromanganese, high-carbon ferrochrome, and silicon-manganese are not allowed to be used in smelting low-Ti steel (≤25ppm). The following table compares the titanium content of high-purity or high-quality alloys and ordinary alloys.

[0021]

[0022]

[0023] 3 Requirements for the use of ladle

[0024] A large amount of residue is left in the ladle during its use. When producing bearing steel, the TiO2 in the residue in the ladle is reduced and enters the steel, causing an increase in the titanium content in the steel. The TiO2 content detected in the residual slag in the ladle after the argon station is high, averaging 1.0%, mainly due to the oxidation of the slag from the converter and the titanium content of ordinary alloys into the slag. The TiO2 content detected in the residue in the over-refined ladle is relatively low, averaging 0.4%, mainly due to the reduction of TiO2 in the slag during the refining process. Therefore, the ladle that was over-refined low-titanium steel last time is selected for smelting bearing steel. The present invention is further described below in conjunction with the embodiments.

[0025] Example 1

[0026] A method for controlling Ti content in molten steel, the production process includes: (molten iron pretreatment) → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting.

[0027] 1. Smelting technology:

[0028] ① The converter adopts steel retention operation to reduce slag during steel tapping. The amount of steel retained is controlled at 5kg / ton of molten steel.

[0029] ② Increase the tapping temperature of molten steel and strengthen the purge of ladle air bricks to improve the bottom blowing effect of the ladle and avoid poor bottom blowing of the ladle during the smelting process.

[0030] ③ Increasing the proportion of alumina in the refining slag, the activity ratio of alumina and titanium oxide in the slag = m, and controlling the refining slag w(Al2O3) = 25%, has a better control effect on the reduction of titanium in the LF refining process.

[0031] ④ Selection of slag and alloy

[0032] Slag: Use a steelmaking tempering agent specially used for bearing steel, with a composition of SiO2: 5.0%, Al2O3: 33%, CaO: 47%, MnO: 5%, and TiO2: 0.025%.

[0033] Alloy: High-purity ferrosilicon, low-carbon ferromanganese, low-carbon ferrochrome, high-purity or high-quality alloy of metallic manganese.

[0034] ⑤ Requirements for the use of ladle

[0035] The ladle that was used for the last over-refined low-titanium 40Cr steel was selected. A large amount of residue was left in the ladle during the use of the ladle. When producing bearing steel, the TiO2 in the residue in the ladle was reduced and entered the steel, causing the titanium content in the steel to increase. The TiO2 content of the residual slag in the ladle after the argon station was high, averaging 1.0%, mainly due to the oxidation of the slag from the converter and the titanium content of the common alloy into the slag. The TiO2 content in the residue in the over-refined ladle was low, averaging 0.4%, mainly due to the reduction of TiO2 in the slag during the refining process.

[0036] The bearing steel produced by adopting the above control points has a titanium content of 19ppm.

[0037] Example 2

[0038] A method for controlling Ti content in molten steel, the production process includes: (molten iron pretreatment) → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting.

[0039] 1. Smelting technology:

[0040] ① The converter adopts steel retention operation to reduce slag during steel tapping. The amount of steel retained is controlled at 10kg / ton of molten steel.

[0041] ② Increase the tapping temperature of molten steel and strengthen the purge of ladle air bricks to improve the bottom blowing effect of the ladle and avoid poor bottom blowing of the ladle during the smelting process.

[0042] ③ Increasing the proportion of alumina in the refining slag, the activity ratio of alumina and titanium oxide in the slag = m, and controlling the refining slag w(Al2O3) = 29%, has a better control effect on the reduction of titanium in the LF refining process.

[0043] ④ Selection of slag and alloy

[0044] Slag: Use a steelmaking tempering agent specially used for bearing steel, with a composition of SiO2: 5.0%, Al2O3: 33%, CaO: 49%, MnO: 7%, and TiO2: 0.020%.

[0045] Alloy: High-purity ferrosilicon, low-carbon ferromanganese, low-carbon ferrochrome, high-purity or high-quality alloy of metallic manganese.

[0046] ⑤ Requirements for the use of ladle

[0047] The ladle that was used for the last over-refined low-titanium 45 steel was selected. A large amount of residue was left in the ladle during use. When producing bearing steel, the TiO2 in the residue in the ladle was reduced and entered the steel, causing the titanium content in the steel to increase. The TiO2 content of the residual slag in the ladle after the argon station was high, averaging 1.0%, mainly due to the oxidation of the slag from the converter and the titanium content of the common alloy into the slag. The TiO2 content in the residue in the over-refined ladle was low, averaging 0.4%, mainly due to the reduction of TiO2 in the slag during the refining process.

[0048] The bearing steel produced by adopting the above control points has a titanium content of 12ppm.

[0049] Example 3

[0050] A method for controlling Ti content in molten steel, the production process includes: (molten iron pretreatment) → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting.

[0051] 1. Smelting technology:

[0052] ① The converter adopts steel retention operation to reduce slag during steel tapping. The steel retention amount is controlled at 8kg / ton of molten steel.

[0053] ② Increase the tapping temperature of molten steel and strengthen the purge of ladle air bricks to improve the bottom blowing effect of the ladle and avoid poor bottom blowing of the ladle during the smelting process.

[0054] ③ Increasing the proportion of alumina in the refining slag, the activity ratio of alumina and titanium oxide in the slag = m, and controlling the refining slag w(Al2O3) = 26%, has a better control effect on the reduction of titanium in the LF refining process.

[0055] ④ Selection of slag and alloy

[0056] Slag: Use a steelmaking tempering agent specially used for bearing steel, with a composition of SiO2: 6.0%, Al2O3: 35%, CaO: 47%, MnO: 5%, and TiO2: 0.025%.

[0057] Alloy: High-purity ferrosilicon, low-carbon ferromanganese, low-carbon ferrochrome, metallic manganese, high-purity or high-quality alloys.

[0058] ⑤ Requirements for the use of ladle

[0059] The ladle that was used for the last over-refined low-titanium 42CrMo steel was selected. A large amount of residue was left in the ladle during the use of the ladle. When producing bearing steel, the TiO2 in the residue in the ladle was reduced and entered the steel, causing the titanium content in the steel to increase. The TiO2 content of the residual slag in the ladle after the argon station was high, averaging 1.0%, mainly due to the oxidation of the slag from the converter and the titanium content of the common alloy into the slag. The TiO2 content in the residue in the over-refined ladle was low, averaging 0.4%, mainly due to the reduction of TiO2 in the slag during the refining process.

[0060] The bearing steel produced by adopting the above control points has a titanium content of 15ppm.

[0061] Comparative Example 1 (Original Scheme)

[0062] 1. Smelting technology:

[0063] ① The converter adopts conventional operation, and there is slag during steel tapping. The TiO2 content in the converter slag is 0.7-0.9%. As the diffusion deoxidation in the refining process proceeds, the TiO2 in the slag is gradually reduced and enters the steel, causing the titanium content in the steel to increase during the refining process.

[0064] ② The ladle air bricks were not purged in a standardized manner, and the ladle had poor bottom blowing during the smelting process. The slag and the carbon powder floating on the slag reacted chemically under the high temperature of the electrode heating, reducing the oxides in the slag, causing the Al and Ti contents in the steel to increase.

[0065] ③ The proportion of alumina in the refining slag is relatively low, at 15% to 20%. Increasing the Al2O3 content in the slag can significantly inhibit the reduction of TiO2 in the slag. On the contrary, when the Al2O3 content in the slag is low, it cannot inhibit the reduction of titanium during the LF refining process, resulting in the reduction of TiO2 in the slag, thereby increasing Ti in the molten steel.

[0066] ④ Selection of slag and alloy

[0067] The use of ordinary slag / alloys has a higher TiO2 content, which leads to a significant increase in Ti content in the molten steel of the bearing steel during the smelting process.

[0068] ⑤ Requirements for the use of ladle

[0069] The use and control requirements of steel are not clear. A large amount of residue is left in the ladle during use. When producing bearing steel, the TiO2 in the residue in the ladle is reduced and enters the steel, causing the titanium content in the steel to increase.

[0070] In this comparative example, Ti was significantly increased during the smelting process of molten steel, and as a result, the Ti content in the molten steel was 38 ppm.

[0071] Comparative Example 2

[0072] The steps are similar to those in Example 1, except that the converter is operated in a conventional manner and there is slag in the converter during steel tapping. The TiO2 content in the converter slag is 0.7-0.9%. As the diffusion deoxidation process proceeds during the refining process, the TiO2 in the slag is gradually reduced and enters the steel, causing the titanium content in the steel to increase during the refining process. As a result, the Ti content in the molten steel is 30 ppm.

[0073] Comparative Example 3

[0074] The steps are similar to those in Example 1, except that the ladle air bricks were not purged in a standardized manner, and the ladle had poor bottom blowing during the smelting process. The slag and the carbon powder floating on the slag reacted chemically under the high temperature of the electrode heating, reducing the oxides in the slag, causing the Al and Ti contents in the steel to increase. As a result, the Ti content in the molten steel was 28ppm.

[0075] Comparative Example 4

[0076] The steps are similar to those of Example 1, except that the proportion of alumina in the refining slag is relatively low, 15% to 20%. Increasing the Al2O3 content in the slag can significantly inhibit the reduction of TiO2 in the slag. On the contrary, when the Al2O3 content in the slag is relatively low, it cannot inhibit the reduction of titanium during the LF refining process, resulting in the reduction of TiO2 in the slag, thereby increasing Ti in the molten steel. As a result, the Ti content in the molten steel was 28ppm.

[0077] Comparative Example 5

[0078] The steps are similar to those in Example 1, except that ordinary slag / alloy is used. Since ordinary slag / alloy has high TiO2, the Ti content in the molten steel of the bearing steel increases significantly during the smelting process. As a result, the Ti content in the molten steel is 33 ppm.

[0079] Comparative Example 6

[0080] The steps are similar to those in Example 1, except that the use and control requirements of steel are not specified. A large amount of residue is left in the ladle during use. When producing bearing steel, TiO2 in the residue in the ladle is reduced and enters the steel, causing the titanium content in the steel to increase. As a result, the Ti content in the molten steel is 33ppm.

[0081] By analyzing the results of the embodiments of the present invention and the comparative examples, the following conclusions can be drawn:

[0082] (1) Through the optimization of smelting process technology. The converter adopts steel retention operation to reduce slag during tapping; the tapping temperature of molten steel is increased and the purge of ladle air bricks is strengthened to improve the bottom blowing effect of the ladle and avoid poor bottom blowing of the ladle during the smelting process; the proportion of alumina in the refining slag is increased. The reduction of TiO2 in the slag during the smelting process can be effectively controlled, thereby controlling the Ti increase in molten steel.

[0083] (2) Through the selection of slag and alloy, the use of special steelmaking tempering agent for bearing steel and the use of high-purity or high-quality alloy can effectively reduce the increase in titanium caused by slag and alloy.

[0084] (3) Standardize the use of ladle and effectively improve the problem of TiO2 increase caused by residual slag from the previous furnace.

[0085] Through the above scheme, the Ti content in the molten bearing steel is controlled within 0.0025%, the Ti content in the steel is actually controlled within the range of 0.0010-0.0025%, and the average titanium content in the steel is 15.28ppm (0.001528%).

[0086] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for controlling the Ti content in molten bearing steel, characterized in that: The production process includes: molten iron pretreatment → converter smelting → LF refining → RH vacuum degassing → continuous casting, among which: steel retention operation is adopted in the converter smelting process to reduce slag during steel tapping, and suitable slag and alloy are used in the LF furnace refining process to reduce the Ti content entering the molten steel.

2. The method according to claim 1, characterized in that During the steel retention operation, the amount of retained steel is controlled at 5-10kg / ton of molten steel.

3. The method according to claim 1, characterized in that The use of suitable slag in the LF furnace refining process includes: using special steelmaking tempering agent for bearing steel.

4. The method according to claim 3, characterized in that The steelmaking tempering agent comprises SiO2: ≤6.0%, Al2O3: 33-36%, CaO: 47-53%, MnO: 3-8%, and TiO2: ≤0.03%.

5. The method according to claim 1, characterized in that The use of suitable alloys in the LF furnace refining process includes: using high-purity or high-quality alloys as alloying raw materials.

6. The method according to claim 5, characterized in that Ferrosilicon, high carbon ferromanganese, high carbon ferrochrome and silicon manganese are not allowed to be used as gold alloying raw materials for smelting steel with Ti content ≤ 25ppm.

7. The method according to claim 1, characterized in that Also includes: Improve the tapping temperature of molten steel in the LF furnace refining process and strengthen the purge of ladle air bricks to improve the bottom blowing effect of the ladle and avoid poor bottom blowing of the ladle during the smelting process.

8. The method according to claim 7, characterized in that The mass percentage of Al2O3 in the refining slag is controlled to be 20% to 30% to inhibit the reduction of TiO2 in the refining slag.

9. The method according to claim 1, characterized in that: Also includes: For smelting bearing steel, the ladle used for the previous refining of low-titanium steel is selected.

10. The method according to claim 1, characterized in that The average titanium content in the produced bearing steel is 15.28ppm, and the maximum Ti content is ≤25ppm.

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