Metallurgical process for reducing flaw detection of 20MnCrS5 gear steel

Abstract

The present application relates to alloy material technical field, specifically to a kind of metallurgical process for reducing 20MnCrS5 gear steel flaw detection defect.The present application uses converter-LF refining-RH refining-continuous casting production process, the content of Al, S, Ca, Mg in molten steel and the composition of slag in smelting process are strictly controlled, the number of Ca-Mg-Al-O inclusions with composition of 35%(CaO+MgO)-65%Al2O3 in molten steel is reduced, a large amount of composite inclusions with small size Al2O3 as core, containing small amount of Ca, Mg, and (Ca, Mn)S wrapped around in periphery are obtained in solidification process;The composite inclusions usually exist alone, without aggregation tendency, can effectively avoid the formation of large size aggregation type Ca-Mg-Al-O inclusions, thereby reducing ultrasonic flaw detection defect, and improving ultrasonic flaw detection qualified rate.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, specifically a metallurgical process for reducing defects in the flaw detection of 20MnCrS5 gear steel. Background Technology

[0002] 20MnCrS5 gear steel is a high-performance automotive gear steel. Its austenite grain size is primarily controlled by AlN particles, generally requiring an Al content of no less than 0.03 wt.%. Additionally, to ensure good machinability, an S content of no less than 0.015% is required. Due to its high Al and S content, it easily forms Al2O3 and CaS-like inclusions during smelting. This not only affects the castability of the molten steel but also tends to aggregate into large inclusions, which pose a significant hazard to automotive gear steel.

[0003] Ultrasonic testing is an important non-destructive testing method that can detect media that differ significantly from the matrix, such as cracks, pores, and large inclusions. It plays a crucial role in controlling the quality of gear steel during production. While there are various causes of defects during ultrasonic testing, in recent years, sporadic large inclusions have gradually become the main type of defect and are difficult to control effectively.

[0004] During the production of 20MnCrS5 gear steel, the inventors discovered a millimeter-sized, aggregated inclusion through ultrasonic flaw detection. The inclusion was over 1 mm in length and 100-500 μm in width (e.g., ...). Figure 1 As shown). Analysis revealed that the large inclusions were composed of numerous aggregated small-sized Ca-Mg-Al-O inclusions (as shown). Figure 2 As shown), its main components, expressed as mass fractions, are 35% (CaO+MgO)-65% Al2O3 (e.g. Figure 3 As shown in the image, some CaS may also be attached to the outer periphery. The occasional occurrence of such inclusions can cause significant fluctuations in the ultrasonic flaw detection pass rate, making it difficult to achieve a pass rate of over 90%.

[0005] Miao et al. reported in the paper: Agglomeration and Clustering of CaO-Al2O3-MgO Leading to Super Large-Size Line-Shape Inclusions in High Carbon Chromium Bearing Steel (Metallurgical and Materials Transactions B, 2022, 53(1):512-525.) that large-sized inclusions with similar characteristics were found in bearing steel by water immersion ultrasonic flaw detection. This indicates that such inclusions are formed by the aggregation of Ca-Mg-Al-O inclusions with a composition of 35% (CaO+MgO)-65% Al2O3 generated during the smelting process during solidification. Patent CN202211642781.5 proposes a metallurgical process to reduce such large inclusions. By finely controlling the smelting process and strictly controlling the formation of Ca-Al-O inclusions, a significant reduction in flaw detection defects is achieved. However, this process is mainly applicable to non-calcium-treated aluminum deoxidized steel that does not require S content, and is not applicable to 20MnCrS5 gear steel that requires S content. Furthermore, this process has high requirements for raw materials and operational details, making it difficult to implement. Summary of the Invention

[0006] The purpose of this invention is to provide a metallurgical process for reducing defects in the flaw detection of 20MnCrS5 gear steel, so as to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a metallurgical process for reducing defects in 20MnCrS5 gear steel, comprising the following steps: converter → LF refining → RH refining → continuous casting; the content of Al, S, Ca, and Mg in the molten steel and the composition of slag are strictly controlled during the smelting process to reduce the amount of Ca-Mg-Al-O inclusions with a composition of 35% (CaO+MgO)-65% Al2O3 in the molten steel. During the solidification process, a large number of composite inclusions with small-sized Al2O3 containing a small amount of Ca and Mg as the core and surrounded by (Ca,Mn)S are obtained. These composite inclusions usually exist alone and have no tendency to aggregate, which can effectively prevent Ca-Mg-Al-O from aggregating into large-sized inclusions, thereby reducing ultrasonic testing defects and improving the ultrasonic testing pass rate.

[0008] The formation of Ca-Mg-Al-O inclusions with a composition of 35% (CaO+MgO)-65% Al2O3 in molten steel originates from inclusions such as Al2O3 generated during the tapping process. If the inclusions in the molten steel are not effectively removed during the refining process, they will react with Mg to form MgO-Al2O3, and then react with Ca to gradually form 35% (CaO+MgO)-65% Al2O3 inclusions. These inclusions are mainly liquid at high temperatures and are difficult to float and remove. During solidification, they will transform into a solid phase and are prone to aggregation, thus forming large-sized inclusions.

[0009] Therefore, to reduce the amount of inclusions with a composition of 35% (CaO+MgO)-65% Al2O3, it is necessary to first minimize the Al2O3, MgO-Al2O3 and other inclusions generated in the molten steel during the smelting process. In addition, small-sized 35% (CaO+MgO)-65% Al2O3 inclusions in molten steel are usually difficult to completely remove. The literature: Characteristics of Sulfides in Commercial Ca-Treated Resulfurized Steel with Different Deoxidation Modes. (Metallurgical and Materials Transactions B, 2023, 54(6):3343-3360.) discloses that small-sized Al2O3 containing a small amount of Ca and Mg can serve as an efficient nucleation core for MnS, forming a composite inclusion with Al2O3 containing a small amount of Ca and Mg as the core and (Ca,Mn)S as the periphery during solidification. Therefore, by controlling the Ca, Al, and S content in the molten steel, small-sized 35%(CaO+MgO)-65%Al2O3 inclusions can be transformed into small-sized Al2O3 inclusions containing small amounts of Ca and Mg elements. The MnS precipitated during the solidification process can then be used to encapsulate these inclusions, thereby preventing the aggregation of 35%(CaO+MgO)-65%Al2O3 inclusions during solidification.

[0010] First, when tapping steel from the converter, the carbon content needs to be controlled to be no less than 0.08 wt.% and the tapping temperature to be no less than 1600℃. This ensures that the initial dissolved oxygen content in the molten steel is at a low level to reduce the amount of inclusions formed later. On the other hand, it ensures that the deoxidizers, alloys and slag materials added later can melt quickly.

[0011] During the tapping process, when 1 / 3 of the steel has been tapped, Al blocks are added for deoxidation at a rate of 1.1~1.5 kg / ton of steel. When 2 / 3 of the steel has been tapped, ferrochrome, ferromanganese, ferrosilicon, pre-melted slag, and lime are added sequentially to ensure that the molten steel is fully deoxidized and to reduce the formation of various types of inclusions due to alloy oxidation.

[0012] Furthermore, the Al content is controlled to be no less than 0.04 wt.% when the LF refining process arrives at the station and no less than 0.025 wt.% when it leaves the station. This ensures that the dissolved O content in the molten steel is extremely low, reducing the amount of inclusions generated in the subsequent smelting process. It also ensures that the inclusions generated in the steel are mainly high-melting-point Al2O3, which is conducive to flotation removal and absorption by the slag, thereby reducing the formation of 35% (CaO+MgO)-65% Al2O3 inclusions in the subsequent process.

[0013] In the LF refining process, low-pressure argon gas is used to promote the homogenization of the steel composition and the removal of inclusions by flotation. Alloys are added to ensure that the composition of elements such as C, Si, Mn, Cr, Ni, and Mo meets the requirements. The LF refining process adds as little Al as possible to reduce the amount of inclusions generated and to minimize interference with the slag's absorption of inclusions.

[0014] Furthermore, by adjusting the addition ratio of pre-melted slag and lime during the tapping process, the main component composition range of the LF refining slag delivered to the station is controlled as follows: ω(CaO) 53~58%, ω(SiO2) 5~8%, ω(Al2O3) 25~30%, ω(MgO) 3~7%, ω(FeO+MnO) ≤2%, and binary basicity 6~8. Silicon carbide is used for slag surface deoxidation during the LF refining process, with a total addition of 0.3~1.0 kg / ton of steel. After 20 minutes of refining, an appropriate amount of lime is added, at a rate of 0.5~1.5 kg / ton of steel, to maintain the slag composition within the above range. Through these operations, on the one hand, the slag is homogenized as early as possible, allowing for better absorption of Al2O3 inclusions in the molten steel; on the other hand, the steel slag composition reaches equilibrium as early as possible, reducing the amount of inclusions formed, thereby reducing the subsequent formation of 35% (CaO+MgO)-65% Al2O3 inclusions.

[0015] Furthermore, at the end of LF refining, the S content in the molten steel is controlled to be no higher than 0.005 wt.%. This allows the slag to introduce 0.0005~0.0010 wt.% Ca into the molten steel, which is beneficial for promoting the transformation of MgO-Al2O3 inclusions into CaO-Al2O3 inclusions, rather than forming 35%(CaO+MgO)-65%Al2O3 inclusions. When the Ca content is below 0.0005 wt.%, more 35%(CaO+MgO)-65%Al2O3 inclusions are easily formed. When the Ca content is above 0.001 wt.%, subsequent increases in S content are likely to form more CaS inclusions, reducing the castability of the molten steel.

[0016] Furthermore, the RH vacuum treatment time is controlled to be 25-45 min. 10 min before the end of the RH vacuum treatment, Al-iron is added from the vacuum chamber hopper to increase the Al content to 0.03-0.04 wt.%. Five min after adding Al-iron, S-iron is added from the vacuum chamber hopper to increase the S content to 0.02-0.03 wt.%. When the S content is below 0.02 wt.%, the supersaturation of MnS precipitation during solidification is insufficient, which is not conducive to the early precipitation of MnS to encapsulate oxide inclusions. When the S content is above 0.03 wt.%, it easily reacts with Ca to form more CaS-like inclusions, reducing the castability of the molten steel. Increasing the Al and S content in the molten steel can reduce the CaO content of CaO-Al2O3 inclusions. By increasing the Al and S content in the molten steel through the above operations, it can both promote the transformation of CaO-Al2O3 inclusions into Al2O3 inclusions containing a small amount of Ca and avoid the generation of new inclusions during the Al and S addition process.

[0017] At the end of RH refining, the Mg content is controlled to be no more than 0.0005 wt.%. Under normal smelting conditions, the molten steel will contain no more than 0.0005 wt.% Mg, which means that the small-sized Al2O3 in the molten steel contains a small amount of Mg. A Mg content greater than 0.0005 wt.% easily promotes the formation of more (CaO+MgO)-65% Al2O3 inclusions.

[0018] In summary, at the end of RH refining, the composition of the molten steel is: C 0.16~0.22wt.%, Si 0.10~0.25wt.%, Mn 1.10~1.40wt.%, Cr 1.00~1.30wt.%, P≤0.025wt.%, S 0.02~0.03wt.%, Ni≤0.25wt.%, Mo≤0.08wt.%, Al 0.03~0.04wt.%, Ca 0.0005~0.001wt.%, Mg≤0.0005wt.%, N 0.008~0.014wt.%, with the balance being Fe and unavoidable impurity elements.

[0019] In addition, after RH vacuum treatment, nitrogen-containing cored wire is added to increase the N content to 0.008~0.014 wt.%, meeting the composition requirements. The molten steel is then subjected to weak stirring, a conventional technique well-known to those skilled in the art, aimed at promoting homogenization of the steel composition. Optionally, the weak stirring time is controlled to 5~10 min, and the weak stirring method is argon blowing. During argon blowing, exposed molten steel is prevented. The argon blowing flow rate has no specific requirements and can be adjusted according to site conditions, preferably 10~30 NL / min. Continuous casting is then carried out; during continuous casting, protective pouring is performed to reduce the formation of foreign inclusions; subsequently, the continuously cast billet is rolled into bars.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: by using the process of the present invention, a large number of composite inclusions with small-sized Al2O3 inclusions containing a small amount of Ca and Mg as the core and surrounded by (Ca,Mn)S can be obtained in steel, which significantly reduces the formation of large-sized aggregated Ca-Mg-Al-O inclusions that cause defects in flaw detection. The obtained bars are ultrasonically tested according to the GB / T4162A standard, and the pass rate is steadily increased to over 98%. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0022] Figure 1 It is the morphology and size of large inclusions that cause defects in ultrasonic testing.

[0023] Figure 2 It is the surface scanning analysis result of large-sized inclusions that cause defects in ultrasonic testing.

[0024] Figure 3 It is the position of the composition of large-sized inclusions that cause defects in ultrasonic testing in the CaO-MgO-Al2O3 phase diagram.

[0025] Figure 4 This is a typical distribution of inclusions in the steel prepared in Example 1.

[0026] Figure 5 This is a typical morphology of inclusions in the steel prepared in Example 1.

[0027] Figure 6 The position of the core oxide composition in the composite inclusions of the steel prepared in Examples 1, 2, and 3 in the CaO-MgO-Al2O3 phase diagram. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: The production process of 170t converter-LF refining-RH refining-continuous casting is adopted. The C content at the time of steel tapping is 0.11wt.%, the steel tapping temperature is 1625℃, the steel tapping amount is 165 tons, and the Al iron addition amount is 200kg.

[0030] When the LF refining process arrived at the station, the Al content was 0.043 wt.%, and the main components of the slag were: CaO 56.5 wt.%, SiO2 7.2 wt.%, Al2O3 28.1 wt.%, MgO 4.8 wt.%, FeO 0.71 wt.%, MnO 0.61 wt.%, and a binary basicity of 7.8. Silicon carbide was used for slag surface deoxidation during the LF refining process, with a total addition of 70 kg. 100 kg of lime was added after 20 minutes of refining.

[0031] At the end of LF refining, the Al content was 0.026 wt.%, the S content was 0.004 wt.%, and the Ca content was 0.008 wt.%.

[0032] The RH vacuum treatment time was 40 min. After 30 min, Al-iron was added to increase the Al content to 0.035 wt.%, and after 35 min, S-iron was added to increase the S content to 0.025 wt.%. After the vacuum treatment was completed, CrN cored wire was added to increase the N content to 0.0130 wt.%.

[0033] The steel liquid obtained at the end of RH refining has the following composition: C 0.21wt.%, Si 0.19wt.%, Mn 1.39wt.%, Cr 1.28wt.%, P 0.022wt.%, S 0.025wt.%, Ni 0.13wt.%, Mo 0.03wt.%, Al 0.035wt.%, Ca 0.0007wt.%, Mg 0.0004wt.%, N 0.0130wt.%, with the balance being Fe and unavoidable impurity elements. The steel liquid is then weakly stirred for 8 minutes, followed by continuous casting. The continuously cast billets are then rolled to obtain bars.

[0034] Example 2: The production process of 170t converter-LF refining-RH refining-continuous casting was adopted. The C content at tapping was 0.10wt.%, the tapping temperature was 1629℃, the tapping amount was 166 tons, and the Al iron addition amount was 210kg.

[0035] Upon arrival at the LF refining station, the Al content was 0.046 wt.%, and the slag composition was: CaO 55.8 wt.%, SiO2 7.0 wt.%, Al2O3 28.8 wt.%, MgO 5.3 wt.%, FeO 0.73 wt.%, MnO 0.56 wt.%, and binary basicity 8.0. Silicon carbide was used for slag surface deoxidation during the LF refining process, with a total addition of 80 kg. 120 kg of lime was added after 20 minutes of refining.

[0036] At the end of LF refining, the Al content was 0.027 wt.%, the S content was 0.003 wt.%, and the Ca content was 0.010 wt.%.

[0037] The RH vacuum treatment time was 40 min. At 30 min, Al-iron was added to increase the Al content to 0.037 wt.%, and at 35 min, S-iron was added to increase the S content to 0.024 wt.%. After the vacuum treatment was completed, CrN cored wire was added to increase the N content to 0.0135 wt.%.

[0038] The steel liquid obtained at the end of RH refining has the following composition: C 0.17wt.%, Si 0.19wt.%, Mn 1.17wt.%, Cr 1.24wt.%, P 0.016wt.%, S 0.024wt.%, Ni 0.13wt.%, Mo 0.03wt.%, Al 0.037wt.%, Ca 0.0008wt.%, Mg 0.0004wt.%, N 0.0135wt.%, with the balance being Fe and unavoidable impurity elements. The steel liquid is then weakly stirred for 6 minutes, followed by continuous casting. The continuously cast billets are then rolled to obtain bars.

[0039] Example 3: The production process of 170t converter-LF refining-RH refining-continuous casting was adopted. The C content at tapping was 0.09wt.%, the tapping temperature was 1632℃, the tapping amount was 164 tons, and the Al iron addition amount was 200kg.

[0040] Upon arrival at the LF refining station, the Al content was 0.041 wt.%, and the slag composition was: CaO 57.3 wt.%, SiO2 7.6 wt.%, Al2O3 28.0 wt.%, MgO 5.1 wt.%, FeO 0.77 wt.%, MnO 0.64 wt.%, and binary basicity 7.5. Silicon carbide was used for slag surface deoxidation during the LF refining process, with a total addition of 60 kg. 90 kg of lime was added after 20 minutes of refining.

[0041] At the time of LF discharge, the Al content was 0.028 wt.%, the S content was 0.005 wt.%, and the Ca content was 0.007 wt.%.

[0042] The RH vacuum treatment time was 40 min. After 30 min, Al-iron was added to increase the Al content to 0.036 wt.%, and after 35 min, S-iron was added to increase the S content to 0.025 wt.%. After the vacuum treatment was completed, CrN cored wire was added to increase the N content to 0.0137 wt.%.

[0043] The steel liquid obtained at the end of RH refining has the following composition: C 0.18wt.%, Si 0.17wt.%, Mn 1.16wt.%, Cr 1.24wt.%, P 0.02wt.%, S 0.025wt.%, Ni 0.13wt.%, Mo 0.03wt.%, Al 0.036wt.%, Ca 0.0006wt.%, Mg 0.0004wt.%, N 0.0137wt.%, with the balance being Fe and unavoidable impurity elements. The steel liquid is then weakly stirred for 7 minutes, followed by continuous casting. The continuously cast billets are then rolled to obtain bars.

[0044] Comparative Example 1: The main difference between Comparative Example 1 and the requirements of the invention lies in the carbon content of the steel tapped from the primary refining furnace. The carbon content of the tapped steel is 0.05 wt.%, which does not meet the requirements. Other operating processes meet the requirements of the invention.

[0045] Comparative Example 2: The main difference between Comparative Example 2 and the requirements of the invention lies in the initial slag composition of LF refining. The slag composition is CaO 54.5wt.%, SiO2 7.0wt.%, Al2O3 32.3wt.%, MgO 4.8wt.%, FeO 0.68wt.%, MnO 0.59wt.%, and binary basicity 7.8. The Al2O3 content does not meet the requirements of the invention, but other operating processes meet the requirements of the invention.

[0046] Experiment: Ultrasonic scanning flaw detection was performed on the bars in Examples 1-3 and Comparative Examples 1-2 using the GB / T 4162 Class A standard. The pass rate was tested, and the test results are shown in Table 1.

[0047] Table 1. Sample pass rates in Examples 1-3 and Comparative Examples 1-2

[0048]

[0049] The typical distribution and morphology of inclusions in Example 1 are as follows: Figure 4 , Figure 5 As shown in the figure. It can be seen that the rods obtained in Example 1 contain a large number of composite inclusions. The black portion of each composite inclusion is the core oxide, mainly Al2O3 containing small amounts of Ca and Mg. The position of its composition in the CaO-MgO-Al2O3 phase diagram is shown below. Figure 6 As shown, the gray part is the outer (Ca,Mn)S. This composite inclusion exists alone and does not aggregate, thus effectively avoiding the formation of large-sized aggregated Ca-Mg-Al-O inclusions.

[0050] The typical distribution and morphology of inclusions in the rods obtained in Example 2 are basically the same as those in Example 1. There are a large number of composite inclusions with Al2O3 containing a small amount of Ca and Mg as the core and (Ca,Mn)S as the periphery. They exist alone and do not aggregate, thus effectively avoiding the formation of large-sized aggregated Ca-Mg-Al-O inclusions.

[0051] The typical distribution and morphology of inclusions in the rods obtained in Example 3 are basically the same as those in Example 1. There are a large number of composite inclusions with Al2O3 containing a small amount of Ca and Mg as the core and (Ca,Mn)S as the periphery, which effectively avoids the formation of large-sized aggregated Ca-Mg-Al-O inclusions.

[0052] In Comparative Example 1, because the C content in the tapped steel was lower than the requirements of the invention, the number of inclusions formed during the tapping process was too large and difficult to be completely absorbed and removed during the refining process. At the end of RH refining, there were still a large number of 35% (CaO+MgO)-65% Al2O3 inclusions in the molten steel that were not removed. During the solidification process, these inclusions agglomerated into large-sized inclusions and were retained in the steel.

[0053] In Comparative Example 2, since the Al2O3 content was higher than the invention requirement when the LF arrived at the station, its ability to absorb Al2O3 inclusions was greatly reduced. The inclusions formed during the tapping process were difficult to be fully absorbed by the slag and remained in the molten steel. At the end of RH refining, there were still a large amount of 35% (CaO+MgO)-65% Al2O3 inclusions in the molten steel that had not been removed. During solidification, these inclusions agglomerated into large-sized inclusions and remained in the steel.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0055] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A metallurgical process for reducing ultrasonic flaw detection defects in 20MnCrS5 gear steel for automobiles, characterized in that: The process route includes converter → LF refining → RH refining → continuous casting; among which: When tapping steel from the converter, the carbon content should be controlled to be no less than 0.08 wt.%, and the tapping temperature should be no less than 1600℃. When the LF refinery arrives at the station, the Al content is controlled to be no less than 0.04 wt.%, and when it leaves the station, the Al content is controlled to be no less than 0.025 wt.%. At the end of LF refining, the sulfur content in the molten steel should be controlled to be no higher than 0.005 wt.%. The RH vacuum treatment time is 25~45min. Add Al iron 10min before the end of the RH vacuum treatment and add S iron 5min later. After RH vacuum treatment, nitrogen-containing cored wire is added to increase the N content to 0.008~0.014 wt.%, and continuous casting is carried out after the alloy liquid composition is kept uniform. During continuous casting, protective pouring is performed, and the continuously cast billet is rolled into bars; wherein: During the converter tapping process, when 1 / 3 of the steel has been tapped, Al blocks are added for deoxidation at a rate of 1.1~1.5 kg / ton of steel. When 2 / 3 of the steel has been tapped, ferrochrome, ferromanganese, ferrosilicon, pre-melted slag, and lime are added sequentially. By adjusting the amount of pre-melted slag and lime added during the tapping process, the main component composition range of the LF refining slag delivered to the station is controlled as follows: CaO 53~58 wt.%, SiO2 5~8 wt.%, Al2O3 25~30 wt.%, MgO 3~7 wt.%, FeO+MnO≤2 wt.%, binary basicity 6~8. Silicon carbide is used for slag surface deoxidation during the LF refining process, with a total addition amount of 0.3~1.0 kg / ton of steel. Lime is added 20 minutes after refining, with an addition amount of 0.5~1.5 kg / ton of steel. At the end of RH refining, the composition of the molten steel is controlled as follows: C 0.16~0.22wt.%, Si 0.10~0.25wt.%, Mn 1.10~1.40wt.%, Cr 1.00~1.30wt.%, P≤0.025wt.%, S 0.02~0.03wt.%, Ni≤0.25wt.%, Mo≤0.08wt.%, Al 0.03~0.04wt.%, Ca 0.0005~0.001wt.%, Mg≤0.0005wt.%, N 0.008~0.014wt.%, with the balance being Fe and unavoidable impurity elements.

2. The 20MnCrS5 gear steel prepared by the process according to claim 1.

3. The 20MnCrS5 gear steel according to claim 2, characterized in that: The ultrasonic flaw detection pass rate of the 20MnCrS5 gear steel is ≥98%.

Images