Refining method for reducing total oxygen content of high-carbon chromium bearing steel casting blank

Abstract

The invention discloses a refining method for reducing the total oxygen content of a high-carbon chromium bearing steel casting blank. The refining method comprises the steps of LF refining and RH refining. The LF refining step comprises the following steps: in the LF furnace refining process, after alloying and completely melting the alloy, sampling and detecting the S content SLF in the molten steel; in the RH refining step, alloy is finely adjusted after deep vacuum treatment is carried out, sampling is carried out to detect the S content SRH in molten steel, and the deep vacuum circulation time T of an RH furnace is calculated according to the following formula: T = T1 + (SRH-SLF) * 5E5; wherein T is deep vacuum circulation time, min, of the RH furnace; t1 is the deep vacuum basic circulation time of the RH furnace and is 18-22 minutes; sRH is S content SRH,% in molten steel after alloy fine adjustment in the RH furnace; the SLF is the content of S in the molten steel after the LF furnace is powered on for the second time. According to the method, the RH refining vacuum circulation time can be dynamically adjusted to accurately control the oxygen content in the molten steel, and the inclusions in the molten steel can be effectively controlled.

Description

Technical Field

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

[0002] As a representative steel type of contemporary clean steel, GCr15 high carbon chromium bearing steel is mainly used in aircraft engine bearings, large thin plate rolling mill equipment bearings, wind power equipment bearings, etc., and occupies an important position in steel production. With the development of society, the quality requirements for high carbon chromium bearing steel are getting higher and higher. The quality of bearing steel is mainly measured from three aspects: steel cleanliness, performance uniformity, and surface quality. Non-metallic inclusions in steel seriously reduce the fatigue life of bearing steel and affect the quality of steel. The key to steel cleanliness control technology is to reduce oxygen in steel and reduce the size of inclusions. Therefore, reducing the oxygen content in molten steel and improving the cleanliness of molten steel will greatly improve the fatigue life of bearing steel.

[0003] GB / T 18254-2016 standard focuses on purity and uniformity of organization, and divides high-quality steel, advanced high-quality steel and special high-quality steel into three quality grades, TO≤12ppm in high-quality bearing steel, TO≤9ppm in advanced high-quality bearing steel, and TO≤6ppm in special high-quality bearing steel. Current research shows that when the oxygen content (mass fraction) in steel is controlled below 6ppm, Al2O3 inclusions are no longer a limiting factor in reducing the fatigue performance of the material.

[0004] In the prior art, the conventional process route is to reduce the oxygen content in the molten steel after vacuum treatment in the RH refining furnace. However, since the oxygen content of the molten steel entering the RH refining furnace cannot be determined, the oxygen content in the molten steel can be reduced by only extending the RH furnace treatment time, which increases production costs and is not economical or practical. Therefore, how to reduce the oxygen content in the molten steel after LF furnace treatment becomes a limiting link. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a refining method for reducing the total oxygen content of high carbon chromium bearing steel ingots.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: it includes LF refining and RH refining steps; The LF refining step: During the LF furnace refining process, after the alloy is completely melted, the S content in the molten steel is tested by sampling. LF ; The RH refining step: fine-tune the alloy after entering deep vacuum treatment, and take samples to test the S content in the molten steel. RH , calculate the RH furnace deep vacuum cycle time T according to the following formula (Ⅰ); T = T1 + (S RH -SLF )×5E5 (Ⅰ) Wherein, T is the deep vacuum cycle time of RH furnace, min; T1 is the deep vacuum basic cycle time of RH furnace, which is 18-22 min; S RH After fine-tuning the alloy for RH furnace, the S content in molten steel is S RH ,%;S LF It is the S content in molten steel after the LF furnace is powered on for the second time.

[0007] Furthermore, in the LF refining step, the target composition requirements of the refined slag are: T.Fe≤0.5%, CaO 50-60%, SiO26-12%, Al2O328-33%, MgO 5-8%, R≥5; the target oxygen content in the molten steel is ≤20ppm.

[0008] Furthermore, in the LF refining step, the LF furnace refining cycle is ≤50min, and the number of power transmissions is ≤3 times.

[0009] Further, in the RH refining step, the alloy is fine-tuned and circulated for 3 to 5 minutes before sampling and testing the S content in the molten steel. RH .

[0010] The beneficial effects of the above technical solution are as follows: the present invention determines the deep vacuum cycle time of the RH furnace according to the reduction value of the S content in the molten steel from the late stage of LF refining to the early stage of RH refining, thereby dynamically adjusting the RH refining vacuum cycle time to accurately control the oxygen content in the molten steel, and can effectively control the inclusions in the molten steel; the present invention has a simple process, strong operability, and significant effect, and can achieve the effect of stably controlling the oxygen content of the ingot to ≤6ppm, which can effectively ensure the stable production of bearing steel.

[0011] When a small square billet continuous casting machine is used to produce high carbon chromium bearing steel, the total oxygen value of the billet can be stably controlled below 6ppm, and the qualified proportion can reach above 99.9%, thereby effectively improving product quality and ensuring that the production process is stable and controlled; the production operation is simple, the impact on production is small, the production cost is reduced, and the efficiency of the enterprise is improved, and the invention has excellent promotion and application value in the industry.

[0012] The present invention further controls the LF furnace cycle, the number of power transmissions, the refined slag composition, and the reduction value of the S content in the molten steel in the later stage of the LF furnace, thereby being able to more accurately control the O content in the molten steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0014] Figure 1 It is a schematic diagram of the change of sulfur content in the LF refining and RH refining steps of an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The refining method for reducing the total oxygen content of high carbon chromium bearing steel ingot is particularly suitable for the production of high carbon chromium bearing steel GCr15. The composition requirements of GCr15 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≤0.010wt%, O≤0.006wt%, Ti≤0.0015wt%, Ca≤0.00010wt%, and the balance is Fe and unavoidable impurities.

[0016] The refining method for reducing the total oxygen content of high carbon chromium bearing steel ingots comprises LF refining and RH refining steps, and the processes of each step are as follows: (1) LF refining: During the LF furnace refining process, after alloying and complete melting of the alloy, samples are taken to test the S content in the molten steel. LF ; In the early stage of rapid heating and slagging of the LF furnace, lime and slagging agent are added to make slag. In the middle and late stages of the LF, Al powder and silicon carbide are added to the top slag in batches to reduce the oxidizability of the slag; the refining cycle of the LF furnace is ≤50min; the number of power transmissions is ≤3 times, and it is best to use a three-time power transmission process. The process control when using the three-time power transmission process is as follows: the first power transmission time is based on the station temperature, and the power transmission temperature is 15 to 20min, and the bottom blowing is controlled with a small amount of gas to achieve rapid heating in the early stage of LF to make desulfurized slag; sampling and testing after atmospheric desulfurization, and silicon carbide is added to reduce the oxidizability of the slag; the S content is adjusted according to the test results. If S≤0.010wt%, alloy is added at one time for alloying; if S>0.010wt%, the slag is adjusted according to the dipping of refined slag, and atmospheric desulfurization is performed until S≤0.010wt%.

[0017] The second power supply time is 5 to 8 minutes, the bottom blowing is controlled with a small amount of gas, the temperature is roughly adjusted and the alloy is melted, and the slag sample is sampled and dipped for component detection. The test result is the S content S LF ; The refined slag meets the target composition requirements, the target slag composition requirements are: T.Fe≤0.5%, CaO 50~60%, SiO26~12%, Al2O328~33%, MgO 5~8%, R≥5; the target oxygen content in molten steel is ≤20ppm.

[0018] According to actual production conditions, the third power supply time is 3 to 5 minutes, and the temperature stage is precisely controlled for sampling, testing, and exit.

[0019] (2) RH refining: Before RH refining, pre-evacuation is performed to accelerate the vacuum pressure drop rate in the early stage and quickly reach deep vacuum treatment; vacuum is evacuated to a vacuum degree of ≤35Pa before entering deep vacuum treatment, and then the alloy is fine-tuned according to the composition of the molten steel out of the LF station. The alloy is added at one time when the deep vacuum treatment lasts for 2 minutes. After 3 to 5 minutes of circulation, samples are taken to detect the S content in the molten steel. RH ; (3) According to the formula 3[S]+3CaO+2[Al]=3CaS+Al2O3, the increase in oxygen content in the molten steel can be determined. According to the formula, the S content in the molten steel decreases by 0.001wt%, and the O content in the molten steel increases by 5ppm. The S decrease in the process from the LF furnace to the RH furnace increases the O content in the molten steel by 1ppm, and the deep vacuum cycle time of the RH furnace increases by 1min. Therefore, the deep vacuum cycle time T of the RH furnace is calculated according to the following formula (I); T = T1 + (S RH -S LF )×5E5 (Ⅰ) Wherein, T is the deep vacuum cycle time of RH furnace, min; T1 is the deep vacuum basic cycle time of RH furnace, which is 18-22 min; S RH After fine-tuning the alloy for RH furnace, the S content in molten steel is S RH ,%;S LF is the sulfur content in molten steel after the LF furnace is powered on for the second time; 5E5 is scientific notation, 5×10 5 .

[0020] By performing deep vacuum treatment according to the RH furnace deep vacuum cycle time T obtained by formula (I), the oxygen content in molten steel can be effectively controlled, the number of inclusions can be reduced, the cleanliness of molten steel can be improved, and the fatigue life of high carbon chromium bearing steel can be greatly improved.

[0021] Example 1-7: The refining method for reducing the total oxygen content of high carbon chromium bearing steel ingot is specifically described as follows.

[0022] (1) LF refining: The LF refining furnace is a double-station electrode rotating furnace. The power supply is three times. LF refining is carried out according to the above process. After each power supply, the molten steel is sampled. The sulfur content of the sample taken after the first power supply is S LF1 , the sulfur content of the sample taken after the second power supply is S LF2 , the sulfur content of the sample taken after the third power supply is S LF3 , where S LF2 This is S in formula (I) LF ; The composition results of LF slag samples are shown in Table 1; The sulfur content of molten steel samples after each power supply is shown in Table 2; Table 1: LF slag sample composition results

[0023] (2) RH refining: The RH refining furnace is a double-station furnace; the sulfur content S of the molten steel sample after fine-tuning the alloy RH See Table 2; the sulfur content changes in the LF refining and RH refining steps are as follows Figure 1 As shown in the figure, LF2 and LF3 are the sulfur contents S sampled after the second power supply in the LF refining step. LF2 and the sulfur content S sampled after the third power supply LF3 RH process is the sulfur content S of the molten steel sampled after the RH refining step fine-tuning the alloy RH The oxygen increment of molten steel after the second power supply of LF to the fine adjustment of alloy at RH, and the vacuum cycle time of RH are shown in Table 3; Table 2: Sulfur content of molten steel samples (wt%)

[0024] Table 3: Molten steel oxygen increment and RH deep vacuum cycle time

[0025] In Table 3, DS1 is the reduction value of the sulfur content of the sample taken after the third power supply in the LF refining step compared with the sulfur content of the sample taken after the second power supply, DS1=S LF3 -S LF2 DS2 is the reduction value of the sulfur content of the molten steel sampled after fine-tuning the alloy in the RH refining step compared to the sulfur content of the sampled sulfur content after the third power supply in the LF refining step, DS2=S RH -S LF3 ; In formula (I), S RH -S LF =DS1+DS2. T1 is the deep vacuum cycle time added by the RH furnace, T1=(S RH -S LF )×5E5.

[0026] (3) The total oxygen content of the steel billets obtained in each embodiment is shown in Table 4; Table 4: Total oxygen content of steel billet

[0027] It can be seen from Table 4 that this method effectively controls the oxygen content in molten steel and improves the cleanliness of molten steel.

Claims

1. A refining method for reducing the total oxygen content of high carbon chromium bearing steel ingot, characterized in that: It includes LF refining and RH refining steps; The LF refining step: During the LF furnace refining process, after the alloy is completely melted, the S content in the molten steel is tested by sampling. LF ; The RH refining step: fine-tune the alloy after entering deep vacuum treatment, and take samples to test the S content in the molten steel. RH , calculate the RH furnace deep vacuum cycle time T according to the following formula (Ⅰ); T=T1+(S RH -S LF )×5E5 (Ⅰ) Wherein, T is the deep vacuum cycle time of RH furnace, min; T1 is the deep vacuum basic cycle time of RH furnace, which is 18-22 min; S RH After fine-tuning the alloy for RH furnace, the S content in molten steel is S RH ,%;S LF It is the S content in molten steel after the LF furnace is powered on for the second time.

2. A refining method for reducing the total oxygen content of high carbon chromium bearing steel ingot according to claim 1, characterized in that: In the LF refining step, the target composition requirements of the refined slag are: T.Fe≤0.5%, CaO 50-60%, SiO2 6-12%, Al2O3 28-33%, MgO 5-8%, R≥5; the target oxygen content in the molten steel is ≤20ppm.

3. A refining method for reducing the total oxygen content of high carbon chromium bearing steel ingot according to claim 1, characterized in that: In the LF refining step, the LF furnace refining cycle is ≤50min, and the number of power transmissions is ≤3 times.

4. A refining method for reducing the total oxygen content of high carbon chromium bearing steel ingot according to claim 1, 2 or 3, characterized in that: RH refining step, fine-tune the alloy and circulate for 3 to 5 minutes before sampling and testing the S content in the molten steel RH .

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