Smelting method for reducing total oxygen content in high-carbon chromium bearing steel

Abstract

The invention discloses a smelting method for reducing total oxygen content in high-carbon-chromium bearing steel, and belongs to the technical field of steel smelting. The method comprises the working procedures of converter, LF refining, RH refining and continuous casting. In the converter process, hydrogen-based reduced iron balls are added according to the final temperature and the C content to increase the C content of the steel slag interface molten steel side, meanwhile, bottom blowing is weakened, steel slag is prevented from oxygenating molten steel, and therefore the oxygen [O] content of the molten steel is reduced; in the converter tapping stage, alloy and slag are added according to the final temperature, it is ensured that a steel ladle is free of lumps and good in slagging, and the gold slag interface desulfurization reaction is promoted. Strong bottom blowing and high-alkalinity slag are adopted in the early stage of the LF refining procedure to promote desulfurization reaction, and weak bottom blowing and low-alkalinity slag are adopted in the later stage to inhibit desulfurization reaction. And in the RH refining process, the vacuum circulation time is reasonably controlled, and inclusions are removed. Protective pouring is adopted in the continuous casting process, and secondary oxidation is prevented. The total oxygen content in the produced bearing steel is 4-7 ppm, the total oxygen content of the bearing steel is reduced, and the quality of the bearing steel is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting method for reducing the total oxygen content in high-carbon chromium bearing steel. Background Art

[0002] At present, domestic advanced bearing steel enterprises such as Xingcheng Special Steel, Nangang, and Baosteel have high product quality and are in a leading position in the field of bearing steel metallurgical production in my country. However, there are large differences between China and foreign advanced enterprises in smelting process, controlled cooling process and parameter control, resulting in a large gap in cleanliness control of bearing steel in my country compared with countries such as Japan, Sweden, and Germany. Studies have shown that reasonable control of the number, type, size, and shape of bearing steel inclusions can significantly improve the fatigue life of bearing steel. The degree of influence of different inclusions on the fatigue life of bearing steel is from high to low: Al2O3-CaO balls, non-deformed inclusions such as Al2O3 and TiN, and sulfide inclusions. Since the inclusions of steel grades are mainly oxides, the total oxygen (TO) content in steel is often used as an important indicator to measure the quality of bearing steel. The oxygen content in steel is crucial to the life of the bearing, and the increase in oxygen content causes the fatigue life of the bearing to decrease.

[0003] In summary, the total oxygen content seriously restricts the further improvement of bearing steel quality. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a smelting method for reducing the total oxygen content in high carbon chromium bearing steel, which can effectively reduce the total oxygen content, reduce the number of steel inclusions, improve the cleanliness of molten steel, and achieve an increase in the fatigue life of the bearing steel.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0006] A smelting method for reducing the total oxygen content in high carbon chromium bearing steel includes converter, LF refining, RH refining and continuous casting processes;

[0007] (1) Converter process: The final converter molten steel temperature T is controlled at 1620±20°C, the C content is 0.06-0.120wt%, the bottom blowing flow rate is reduced after the oxygen supply is stopped at the final point, hydrogen-based reduced iron balls DRI are added to the converter from both sides of the silo, and oxygen blowing is stopped for 5-8 minutes before steel tapping begins; during the steel tapping process, the following are added to the ladle in sequence: recarburizer → aluminum particles → ferrosilicon → ferromanganese → remaining recarburizer → low-titanium ferrochrome → pre-melted slag; wherein, according to the final converter molten steel temperature T, the amount of low-titanium ferrochrome added to the ladle is controlled to be 50-70% of the total weight of low-titanium ferrochrome added during the smelting process; specifically:

[0008] When 1600≤T<1610℃, the amount of low-titanium ferrochromium added is 50-60% of the total added weight;

[0009] When 1610≤T<1620℃, the amount of low-titanium ferrochrome added is 55-65% of the total added weight;

[0010] When 1620≤T≤1640℃, the amount of low-titanium ferrochromium added is 60-70% of the total added weight;

[0011] (2) LF refining process: The total LF refining time is controlled at 40-50 min; the early stage of LF refining is controlled at 10-15 min, the basicity of the refining slag is controlled at 6-8, and the corresponding ladle bottom blowing flow rate is controlled at 0.09-0.14 m 3 / (t·min); LF refining mid-term is controlled at 10-15min, refining slag basicity is controlled at 6-8, and corresponding ladle bottom blowing flow is controlled at 0.07-0.10m 3 / (t·min); LF refining is controlled at 20-30min in the later stage, the basicity of the refining slag is adjusted to 4.5-6.5, and the corresponding ladle bottom blowing flow rate is controlled at 0.05-0.08m 3 / (t·min), the control standard is that the diameter of the exposed area of ​​the ladle liquid surface is 20-30mm;

[0012] (3) RH refining process: vacuum holding time is controlled at 30 to 40 minutes;

[0013] (4) Continuous casting process: The feeding port of the tundish is sealed with refractory wool, and protective slag and covering agent are added to the tundish to ensure that the steel liquid surface in the tundish is not exposed. Continuous casting uses argon blowing plug rods and submerged nozzles.

[0014] Furthermore, in the converter process, the bottom blowing flow rate is reduced to 0.35-0.45 m / s after the oxygen supply is stopped at the end. 3 / (t·min).

[0015] Furthermore, in the converter process, hydrogen-based reduced iron balls DRI are added twice, 500 kg is added for the first time after the oxygen supply is stopped at the end point; the amount added for the second time is determined based on the C content w(C) of the molten steel measured by TSO:

[0016] If 0.06≤w(C)<0.08wt%, add 800~1000kg of hydrogen-based reduced iron balls for the second time;

[0017] If 0.08≤w(C)<0.10wt%, add 500-800kg of hydrogen-based reduced iron balls for the second time;

[0018] If 0.10≤w(C)≤0.12wt%, no hydrogen-based reduced iron balls are added for the second time.

[0019] Furthermore, in the converter process, when between 1 / 5 and 1 / 3 of the steel is tapped, the following are added into the ladle in sequence: recarburizer → aluminum particles → ferrosilicon → ferromanganese → remaining recarburizer → low-titanium ferrochrome → pre-melted slag.

[0020] Furthermore, in the converter process, the composition of the ladle sample after steel production is calculated by mass percentage as follows: C: 0.90-0.95%, Si: 0.05-0.10%, Mn: 0.22-0.30%, P≤0.015%, S≤0.015%, Al: 0.050-0.070%, Cr: 0.65-0.85%.

[0021] Furthermore, in the LF refining process, low-titanium ferrochrome, silicon carbide, lime, fluorite and slag-forming agent are added in the early stage of refining to make slag.

[0022] Furthermore, in the RH refining process, the vacuum is reduced to below 100 Pa and maintained for 2 minutes before adding alloy at one time to adjust the composition; after the refining is completed, Als in the molten steel composition is ≥200ppm.

[0023] Furthermore, in the continuous casting process, the flow rate of argon blowing through the stopper rod is 0.4 to 0.7 L / min.

[0024] Furthermore, the total oxygen content of the high carbon chromium bearing steel obtained by the method is 4 to 7 ppm.

[0025] Furthermore, the composition requirements of the high carbon chromium bearing steel are: C: 0.95~1.05wt%, Si: 0.15~0.35wt%, Mn: 0.25~0.45wt%, Cr: 1.40~1.65wt%, P≤0.020wt%, S≤0.015wt%, O≤0.0012wt%, Ti≤0.0015wt%, Ca≤0.00010wt%.

[0026] The technical idea and implementation path of the present invention are as follows:

[0027] (1) In the converter process, hydrogen-based reduced iron balls (DRI) are added according to the terminal temperature and C content information to reduce the oxidizability of the converter slag interface and increase the C content on the interface molten steel side. At the same time, the converter bottom blowing is weakened to inhibit the slag from adding oxygen to the molten steel (reaction ①), thereby reducing the initial oxygen content in the molten steel and reducing the amount of deoxidizer added during the steel tapping process and the inclusions formed by its oxidation;

[0028] (2) According to the final temperature of the converter, the amount of low-titanium chromium-iron alloy added is reasonably adjusted to promote the melting of the ladle alloy and synthetic slag, promote the desulfurization reaction at the ladle gold-slag interface②, promote the desulfurization task to start and complete as early as possible, and at the same time promote the early generation and removal of the reaction product Al2O3;

[0029] (3) In the LF refining process, the early desulfurization is promoted by controlling the basicity of the refining slag and the bottom blowing of the ladle. After the desulfurization task is completed, the desulfurization reaction is suppressed by adjusting the basicity of the refining slag and the bottom blowing. At the same time, the LF refining time is controlled to 40-50min, shortening the duration of the desulfurization reaction and reducing the formation of Al2O3 and CaO-Al2O3 inclusions in the middle and late stages of LF;

[0030] (4) In the RH refining process, the vacuum treatment time is appropriately extended to increase the removal effect of oxide inclusions and [O] in the molten steel, thereby reducing the total oxygen content of the molten steel;

[0031] (5) Protective pouring is adopted during the continuous casting stage to prevent secondary oxidation and inhibit the increase of total oxygen content in the molten steel.

[0032] FeO=Fe+[O]①

[0033] 3S+3CaO+2Al→3CaS+Al2O3 ②

[0034] The beneficial effects of the above technical solution are as follows: (1) The present invention can effectively reduce the total oxygen content of high carbon chromium bearing steel and reduce oxide inclusions, which helps to improve the fatigue life of bearing steel. (2) Adding DRI at the end of the converter can reduce the total iron oxidation of the converter slag, improve the metal recovery rate, and reduce the initial oxygen content of the molten steel. (3) Optimizing the addition of low-titanium ferrochrome can effectively solve the problem of ladle agglomeration and promote ladle slag, which can improve the LF power transmission and heating efficiency and shorten the LF refining time.

[0035] The present invention can reduce the total oxygen content of the bearing steel and the inclusions, and the total oxygen content of the high-carbon chromium bearing steel ingot obtained by smelting is 4-7ppm. DETAILED DESCRIPTION

[0036] A smelting method for reducing the total oxygen content in high carbon chromium bearing steel is suitable for the production of high carbon chromium bearing steel GCr15, and its composition requirements are C: 0.95-1.05wt%, Si: 0.15-0.35wt%, Mn: 0.25-0.45wt%, Cr: 1.40-1.65wt%, P≤0.020wt%, S≤0.015wt%, O≤0.0012wt%, Ti≤0.0015wt%, and Ca≤0.00010wt%.

[0037] The equipment process parameters are as follows: the converter is a 130t top and bottom double-blown converter with a loading capacity of 150±5t and a molten steel volume of 140±5t; the LF refining furnace is a double-station electrode rotating furnace; the RH refining furnace is a double-station furnace; the small square billet continuous casting machine is an 8-machine 8-stream 200mm×200mm square billet continuous casting machine.

[0038] The smelting method for reducing the total oxygen content in high carbon chromium bearing steel comprises converter, LF refining, RH refining and continuous casting processes, and the steps of each process are as follows:

[0039] (1) Converter process: The converter terminal molten steel temperature T is controlled at 1620±20℃, the C content is 0.06-0.120wt%, and the bottom blowing flow rate is reduced to 0.35-0.45m after the oxygen supply is stopped at the terminal. 3 / (t·min), DRI is added to the converter in two portions from both sides of the silo, oxygen blowing is stopped for 5 to 8 minutes and steel tapping begins;

[0040] After the oxygen supply is stopped at the end point, 500 kg of DRI is added for the first time; after the TSO test result is obtained at the end point, the second batch of DRI is added immediately. The second amount of DRI added is determined based on the C content w(C) of the molten steel measured by TSO:

[0041] If 0.06≤w(C)<0.08wt%, add 800~1000kg of hydrogen-based reduced iron balls for the second time;

[0042] If 0.08≤w(C)<0.10wt%, add 500-800kg of hydrogen-based reduced iron balls for the second time;

[0043] If 0.10≤w(C)≤0.12wt%, hydrogen-based reduced iron balls are not added for the second time;

[0044] When the steel is between 1 / 5 and 1 / 3 tapped, add the following into the ladle in sequence: carburizer → aluminum particles → ferrosilicon → ferromanganese → remaining carburizer → low-titanium ferrochrome → pre-melted slag; wherein, the amount of low-titanium ferrochrome added into the ladle is controlled to be 50-70% of the total weight of low-titanium ferrochrome added during the smelting process according to the final molten steel temperature T of the converter; specifically:

[0045] When 1600≤T<1610℃, the amount of low-titanium ferrochromium added is 50-60% of the total added weight;

[0046] When 1610≤T<1620℃, the amount of low-titanium ferrochrome added is 55-65% of the total added weight;

[0047] When 1620≤T≤1640℃, the amount of low-titanium ferrochromium added is 60-70% of the total added weight;

[0048] The composition of the ladle sample after steel tapping is calculated by mass percentage as follows: C: 0.90-0.95%, Si: 0.05-0.10%, Mn: 0.22-0.30%, P≤0.015%, S≤0.015%, Al: 0.050-0.070%, Cr: 0.65-0.85%.

[0049] The particle size of the hydrogen-based reduced iron ball DRI is controlled at 7.0-10.0 mm. Calculated by mass percentage, its components include C: 2.5-3.5%, P: 0.010-0.015%, S: 0.02-0.030, and TFe: 85-95%.

[0050] The amount of pre-melted slag added is 3.5-5.5 kg / t steel, and its components, in terms of mass percentage, include CaO: 25-35%, SiO2: 4-10%, Al2O3: 30-45%, MgO: 5-10%, and Al: 3-8%.

[0051] (2) LF refining process: low titanium ferrochrome, silicon carbide, lime, fluorite and slag-forming agent are added in the early stage of refining to make slag; the total time of LF refining is controlled at 40-50 min; the early stage of LF refining is controlled at 10-15 min, the basicity of the refining slag is controlled at 6-8, and the corresponding ladle bottom blowing flow rate is controlled at 0.09-0.14 m 3 / (t·min); LF refining mid-term is controlled at 10-15min, refining slag basicity is controlled at 6-8, and corresponding ladle bottom blowing flow is controlled at 0.07-0.10m 3 / (t·min); LF refining is controlled at 20-30min in the later stage, the basicity of the refining slag is adjusted to 4.5-6.5, and the corresponding ladle bottom blowing flow rate is controlled at 0.05-0.08m 3 / (t·min), the control standard is that the diameter of the exposed area of ​​the ladle liquid surface is 20 to 30 mm.

[0052] (3) RH refining process: After the vacuum is reduced to below 100 Pa and maintained for 2 minutes, the alloy is added at one time to adjust the composition; the vacuum holding time is controlled to be 30 to 40 minutes; at the end of refining, Als in the molten steel composition is ≥ 200 ppm.

[0053] (4) Continuous casting process: The feeding port of the tundish is sealed with refractory wool, and protective slag and covering agent are added to the tundish to ensure that the steel liquid surface in the tundish is not exposed. Continuous casting adopts argon blowing stopper rod and submerged nozzle; the argon blowing flow rate of the stopper rod is 0.4~0.7L / min.

[0054] The total oxygen content of the high carbon chromium bearing steel obtained by the above method is 4 to 7 ppm.

[0055] The process parameters of the converter process of each embodiment are shown in Tables 1-3; the process parameters of the LF refining process are shown in Table 4; the process parameters of the RH refining and continuous casting processes of each embodiment and the total oxygen content detection data in the obtained high carbon chromium bearing steel are shown in Table 5.

[0056] Table 1. Process parameters of converter process in various embodiments

[0057]

[0058] Table 2. DRI and pre-melted slag components of various examples

[0059]

[0060]

[0061] Table 3. Composition of ladle samples after steel tapping in converter process of various embodiments (wt%)

[0062] Example C Si Mn P S Al Cr 1 0.91 0.06 0.25 0.09 0.012 0.05 0.66 2 0.92 0.07 0.28 0.08 0.012 0.06 0.84 3 0.92 0.05 0.27 0.12 0.009 0.05 0.74 4 0.93 0.08 0.30 0.14 0.008 0.05 0.75 5 0.91 0.08 0.27 0.12 0.012 0.07 0.80 6 0.95 0.07 0.22 0.11 0.013 0.06 0.72 7 0.93 0.10 0.25 0.09 0.013 0.06 0.82

[0063] Table 4. Process parameters of LF refining process in various embodiments

[0064]

[0065] Table 5. Process parameters of RH refining and continuous casting process and total oxygen content of bearing steel in various embodiments

[0066]

Claims

1. A smelting method for reducing the total oxygen content in high carbon chromium bearing steel, characterized in that: Including converter, LF refining, RH refining and continuous casting processes; (1) Converter process: The final converter molten steel temperature T is controlled at 1620±20℃, and the C content is 0.06-0.120wt%. After the oxygen supply is stopped at the final point, the bottom blowing flow rate is reduced, and hydrogen-based reduced iron balls DRI are added to the converter from both sides of the silo. The oxygen blowing is stopped for 5-8 minutes before steel tapping begins. During the steel tapping process, the following are added to the ladle in sequence: recarburizer → aluminum particles → ferrosilicon → ferromanganese → remaining recarburizer → low-titanium ferrochrome → pre-melted slag. Among them, the amount of low-titanium ferrochrome added to the ladle is controlled to be 50-70% of the total weight of low-titanium ferrochrome added during the smelting process based on the final converter molten steel temperature T; specifically: When 1600≤T<1610℃, the amount of low-titanium ferrochromium added is 50-60% of the total added weight; When 1610≤T<1620℃, the amount of low-titanium ferrochromium added is 55-65% of the total added weight; When 1620≤T≤1640℃, the amount of low-titanium ferrochrome added is 60-70% of the total added weight; (2) LF refining process: The total LF refining time is controlled within 40-50 min; the early stage of LF refining is controlled within 10-15 min, the basicity of the refining slag is controlled within 6-8, and the corresponding ladle bottom blowing flow rate is controlled within 0.09-0.14 m 3 / (t·min); LF refining mid-term is controlled at 10-15min, the basicity of refining slag is controlled at 6-8, and the corresponding ladle bottom blowing flow rate is controlled at 0.07-0.10m 3 / (t·min); LF refining is controlled at 20-30min in the later stage, the basicity of the refining slag is adjusted to 4.5-6.5, and the corresponding ladle bottom blowing flow rate is controlled at 0.05-0.08m 3 / (t·min), the control standard is that the diameter of the exposed area of ​​the ladle liquid surface is 20-30mm; (3) RH refining process: vacuum holding time is controlled at 30 to 40 minutes; (4) Continuous casting process: The feeding port of the tundish is sealed with refractory wool, and protective slag and covering agent are added to the tundish to ensure that the steel liquid surface of the tundish is not exposed. Continuous casting uses argon blowing plug rods and submerged nozzles.

2. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 1, characterized in that: In the converter process, after stopping the oxygen supply at the end, the bottom blowing flow rate is reduced to 0.35-0.45m 3 / (t·min).

3. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 2, characterized in that: In the converter process, hydrogen-based reduced iron balls DRI are added twice, 500 kg is added for the first time after oxygen supply is stopped at the end point; the amount added for the second time is determined based on the C content w(C) of the molten steel measured by TSO: If 0.06≤w(C)<0.08wt%, add 800~1000kg of hydrogen-based reduced iron balls for the second time; If 0.08≤w(C)<0.10wt%, add 500-800kg of hydrogen-based reduced iron balls for the second time; If 0.10≤w(C)≤0.12wt%, no hydrogen-based reduced iron balls are added for the second time.

4. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 3, characterized in that: In the converter process, when 1 / 5 to 1 / 3 of the steel is tapped, the following are added into the ladle in sequence: recarburizer → aluminum particles → ferrosilicon → ferromanganese → remaining recarburizer → low-titanium ferrochrome → pre-melted slag.

5. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 4, characterized in that: In the converter process, the composition of the ladle sample after steel is tapped is, in terms of mass percentage, C: 0.90-0.95%, Si: 0.05-0.10%, Mn: 0.22-0.30%, P≤0.015%, S≤0.015%, Al: 0.050-0.070%, and Cr: 0.65-0.85%.

6. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 5, characterized in that: In the LF refining process, low-titanium ferrochrome, silicon carbide, lime, fluorite and slag-forming agent are added in the early stage of refining to make slag.

7. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 6, characterized in that: In the RH refining process, the vacuum is reduced to below 100 Pa and maintained for 2 minutes, and then the alloy is added at one time to adjust the composition; after the refining is completed, Als in the molten steel composition is ≥200ppm.

8. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 7, characterized in that: In the continuous casting process, the flow rate of argon blowing by the stopper rod is 0.4-0.7 L / min.

9. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to any one of claims 1 to 8, characterized in that: The total oxygen content of the high carbon chromium bearing steel obtained by the method is 4-7 ppm.

10. The smelting method for reducing the total oxygen content in high carbon chromium bearing steel according to claim 9, characterized in that: The composition requirements of the high carbon chromium bearing steel are: C: 0.95~1.05wt%, Si: 0.15~0.35wt%, Mn: 0.25~0.45wt%, Cr: 1.40~1.65wt%, P≤0.020wt%, S≤0.015wt%, O≤0.0012wt%, Ti≤0.0015wt%, Ca≤0.00010wt%.

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