Gear steel quality improvement control method

Abstract

The application discloses a gear steel quality improvement control method, which comprises hot metal desulfurization and vanadium extraction, semi-steel converter smelting, LF, RH and continuous casting processes; nitrogen-increasing agent alloy balls are added in the LF process, MnS nucleating agents are added in the RH process, and specified cooling solidification control technology is implemented. Through the method, the symmetry of the gear steel casting blank solidification structure is obviously improved, the distance range of the equiaxed crystal zone boundary and the casting blank surface is reduced from 30-40 mm to 10-12 mm, after being rolled into round bars, the distance range of the solidification structure equiaxed crystal trace zone boundary and the round bar surface is controlled to be less than or equal to 4 mm, the solute segregation degree range (circumferential direction) of the round bar at the same distance from the surface is less than or equal to 0.02, the grain size of the obtained gear steel is stabilized to 8.0 level, the maximum single particle area of MnS in the 0-50 mm area under the casting blank surface is reduced from 9 um 2 to 3-4 um 2 , and the inclusion distribution particle number range per unit area is reduced from 15-19 particles / mm 2 to 6-9 particles / mm 2 .

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and specifically relates to a method for improving and controlling the quality of gear steel. Background Technology

[0002] Gears are crucial mechanical components for power transmission. The stress on gears varies depending on their operating conditions and location, leading to differences in failure modes. These failure modes are influenced by numerous factors, including gear material, manufacturing process, lubrication, friction, gear geometry, and load patterns. The main failure modes include: tooth root fracture, tooth surface deformation due to tooth surface concavity, fatigue spalling, and wear (adhesive wear and abrasive wear). Based on these main failure modes, the performance requirements for gear steel are high crush resistance and resistance to pitting and spalling, good impact resistance and bending resistance, suitable hardenability and hardened layer depth and core hardness, good processability and machinability, and good deformation and dimensional stability. Automotive gears play a vital role in power transmission and speed change, making them a major representative of gears. Gear steel must possess good strength, toughness, and wear resistance, effectively withstanding impact, bending, and contact stress, while also exhibiting minimal deformation. During gear manufacturing, in addition to reasonable design and machining, heat treatments such as carburizing, quenching, or tempering are required to harden the surface for wear resistance and enhance the impact resistance of the base material. The quality of gear blanks largely determines the efficiency and quality control of gear production.

[0003] With the continuous development of continuous casting technology, the quality control technology of cast billets has been continuously improved. Currently, the production of automotive gear billets in China mainly relies on continuous casting of small square billets. As gear quality requirements continue to increase, the requirements for the density and homogeneity of gear steel billets are also becoming more stringent. There is currently a considerable amount of research on the homogeneity control of continuously cast billets, mostly focusing on controlling center segregation, i.e., reducing the accumulation of solute elements at the center of the billet. This is largely achieved by increasing the equiaxed crystal ratio to promote synchronous nucleation and solidification of the molten steel in the central region. For example, CN107262689A discloses a large square billet double-cold pressing convex foot roll structure and pressing process; CN106735013A discloses a continuous casting process to improve the quality of the head billet of a large square billet; CN107225148A discloses a rolling method for 22CrMoH gear steel; CN106967931A discloses a 20Cr2Ni4 gear steel and its production process; and CN106566998A discloses a manufacturing method for CrMo-based gear round steel. However, some key specific contents of "a method for improving and controlling the quality of gear steel" are not covered. In terms of production practice, in the process of straight arc or full arc continuous casting, the well-developed equiaxed crystal structure is accompanied by the problem of asymmetry between the inner and outer arcs. Under the action of grain sedimentation, the equiaxed crystal region is generally biased towards the outer arc side. The asymmetrical distribution of the solidification structure directly leads to the uneven distribution of solute concentration, especially the uneven distribution of semi-macroscopic segregation. The uneven distribution of solutes in the cast billet is inherited to varying degrees after rolling into round bars. During the rolling process, these uneven distributions undergo deformation and other changes due to matrix rheological effects, further exacerbating the uneven distribution of solute elements within the round bar. In gear manufacturing, this uneven distribution of solute elements leads to varying degrees of segregation in the CCT curves of the corresponding heat treatment regions. This results in differences in grain size and even microstructure type, ultimately causing deformation and other problems that directly worsen product quality.

[0004] Based on the above analysis, in order to effectively improve the macroscopic solute concentration uniformity in all directions of the cross-section of the gear steel continuous casting billet, improve the regional symmetry of the solidification structure, and thus promote a more uniform multi-scale segregation distribution on the round bar, and promote a more uniform phase transformation and stress distribution in the gear structure during gear processing and subsequent heat treatment; further refine the grain size of the gear steel and improve the grain size level; at the same time, control the fine dispersion of MnS inclusions in the 0~50mm area below the surface of the gear steel billet, and finally lay an important quality foundation for the high grain size level, high performance uniformity and high dimensional stability control of the gear. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention aims to provide a method for improving and controlling the quality of gear steel, comprising the following steps: desulfurization and vanadium extraction of molten iron → semi-steel converter smelting → LF refining → RH vacuum refining → continuous casting. The converter process mainly completes dephosphorization and deoxidation alloying treatment during steel tapping to initially adjust the content of the main chemical components in the gear steel. The LF process mainly completes refining and slag formation to promote the flotation and removal of non-metallic inclusions generated in the molten steel, and further finely controls the content of each alloy component based on the target composition. Simultaneously, the temperature of the molten steel is controlled by electrode heating to achieve precise and stable temperature control. Furthermore, based on the LF refining, the resulting molten steel undergoes real-time RH vacuum refining, and the vacuum degree and corresponding processing time are controlled during the refining process to effectively reduce the content of harmful gaseous elements in the molten steel to the target level.

[0006] To achieve the above-mentioned objectives, this invention provides a method for improving and controlling the quality of gear steel. The method includes the following steps: desulfurization and vanadium extraction of molten iron → semi-steel converter smelting → LF refining → RH vacuum refining → continuous casting; during the LF refining process, nitrogen-enhancing alloy balls are added; during the RH refining process, MnS nucleating agent is added; the solidification process of molten steel in the billet pool is controlled during the continuous casting process, and solidification is completed within the 1 / 4 arc-shaped area of ​​the billet. Based on this, cooling and solidification control is implemented step by step to control the growth, evolution, and composition of the solidification structure.

[0007] The nitrogen-enhancing agent alloy balls are spherical metal particles with a diameter of 19-21 mm. The wall thickness of the iron-coated layer of the metal particles is 2.0-2.2 mm, and the inner diameter of the metal particles is 15-17 mm. Nitrogen-enhancing agent core particles with a diameter of 2.0-3.0 mm are encased within the inner cavity. The nitrogen-enhancing agent alloy balls consist of an innermost layer of nitrogen-enhancing agent and an outer layer of iron-coated layer surrounding the nitrogen-enhancing agent. This design is highly feasible, has low production costs, and produces a high and stable alloy yield, avoiding re-contamination of the molten steel by the additives. The function of the iron-coated layer is to encapsulate the nitrogen-enhancing agent core particles, increasing the specific gravity of the metal particles and thus improving the nitrogen-enhancing agent yield. The mass percentage content of each component in the iron-coated layer (weight-adding layer) is: iron: 97.0%-99.0%, with the balance being unavoidable impurities.

[0008] The mass percentage content of each component in the nitrogen-enhancing agent core is as follows: calcium: 5.1%~8.2%, silicon: 37.0%~39.0%, nitrogen: 34.0%~37.0%, clay: 4.0%~5.0%, with the balance being iron and unavoidable impurities.

[0009] The MnS nucleating agent consists of spherical metal particles with a diameter of 19-21 mm. The metal particles have an iron-coated layer with a wall thickness of 2.0-2.2 mm and an inner cavity diameter of 15-17 mm, encapsulating nucleating agent core particles with a diameter of 2.0-3.0 mm within the inner cavity. The iron-coated layer encapsulates the nucleating agent core particles, increasing the specific gravity of the metal particles and thus improving the yield of the nucleating agent. The mass percentage content of each component in the iron-coated layer (weight-adding layer) is as follows: iron: 97.0%-99.0%, with the balance being unavoidable impurities.

[0010] The mass percentage content of each component in the nucleating agent core is as follows: calcium: 15.0%~18.0%, silicon: 35.0%~37.0%, magnesium: 19.0%~25.0%, clay: 4.0%~5.0%, with the balance being iron and unavoidable impurities.

[0011] Furthermore, in the converter smelting process, ferrosilicon is added during the converter tapping process to deoxidize the molten steel, wherein the amount of ferrosilicon added is 3.0~4.0 kg / t. 钢 After deoxidation, the molten steel is alloyed, and the content of key chemical components is initially adjusted to reach 70%~90% of the target component content. After alloying, active lime is added to the ladle at a rate of 2.5~3.5 kg / t. 钢 The oxygen activity of the molten steel in the ladle is measured. Based on the oxygen activity measurement results, aluminum wire is fed in. The diameter of the aluminum wire is Φ15mm~Φ16mm, and the feeding length is controlled at 15m / ppm[O].

[0012] Furthermore, in the LF refining process, the nitrogen-enhancing agent alloy balls are added at an amount of 0.9~1.2 kg / t. 钢 Implementation; Als in molten steel is controlled at 0.030%~0.040%; after LF refining, CaSi wire is added at 1.5~2.0 m / ppm[S].

[0013] Furthermore, during the RH vacuum refining process, the vacuum level in the vacuum chamber is required to be reduced to ≤3 mbar, and the vacuum level is maintained at <3 mbar for ≥11 min. After ≥1 min of cyclic treatment at <3 mbar, the MnS nucleating agent can be added to the vacuum chamber. The addition process requires uniform weight distribution, and the addition time is controlled within 2-3 min. The amount of nucleating agent added is based on the S content analysis results of the sample taken from the molten steel entering the RH station, specifically: 0.10~0.13 kg / (t). 钢• 10ppm [S]). After vacuum depressurization, the CaSi line described in the LF process is added according to the difference of [S]% in the molten steel when it leaves and enters the RH process. The amount of feed is controlled at 8~8.5m for every 1ppm increase in sulfur in the RH process. After the CaSi line is added, the molten steel is allowed to stand for more than 5 minutes before casting can begin.

[0014] The CaSi core powder content in the LF and RH processes is 130~140 g / m, and the mass content of key components is: calcium content ≥28%, silicon content 45%~53%, with the balance being unavoidable impurities.

[0015] Furthermore, in the continuous casting process, a designated cooling and solidification control process is implemented, and argon blowing protection must be maintained throughout the casting process. Specifically, the "designated cooling and solidification control process" includes: controlling the superheat of the molten steel at 30~35℃; setting the M-EMS stirring current intensity to 100~200A; maintaining the secondary cooling coverage area for 7~10m from the bottom of the crystallizer; and setting the secondary cooling water ratio to 0.84~0.92 L / kg. 钢 Control; F-EMS is stirred at a distance of 7.5~11m from the bottom of the crystallizer, and the stirring current intensity is set at 200~300A; the billet temperature in the straightening zone rises to 920~970℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention provides a method for improving and controlling the quality of gear steel. It can effectively enhance the macroscopic solute concentration uniformity in all directions of the cross-section of the continuously cast gear steel billet, improve the regional symmetry of the solidification structure, refine the gear steel grains, and increase the grain size. The high symmetry of the solidification structure and multi-scale homogeneity results in a more uniform multi-scale segregation distribution on the round bar obtained from the billet rolling process. This, in turn, leads to a more uniform phase transformation and stress distribution in the gear structure during gear machining and subsequent heat treatment, laying an important quality foundation for the high-performance uniformity and high dimensional stability control of gears. Increasing the nitrogen content in the gear steel and controlling the aluminum-nitrogen ratio can suppress the excessive growth of austenite grains during the phase transformation process through the precipitated AlN particles, thereby refining the gear steel grain size and improving the grain size. Finely dispersing MnS inclusions in the 0-50mm region below the surface of the gear steel billet provides an important positive condition for the stable control of gear tooth quality.

[0018] By employing this method, the symmetry of the solidification structure of gear steel billets is significantly improved. The difference in distance between the equiaxed crystal region boundary and the billet surface is reduced from 30-40 mm to 10-12 mm. After rolling into round bars, the difference in distance between the equiaxed crystal trace region boundary and the round bar surface is controlled to ≤4 mm, and the difference in solute segregation (circumferential) at the same radial distance from the surface of the round bar is ≤0.02. The resulting gear steel grain size stabilizes from grade 6.0-7.0 to grade 8.0; the maximum single MnS particle area in the 0-50 mm region below the surface of the gear steel billet is reduced from 9 μm. 2 Miniaturization to 3~4μm 2 The number of particles per unit area of ​​the inclusions varied from 15 to 19 particles / mm. 2 Reduced to 6~9 particles / mm 2 . Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the nitrogen-enhancing agent alloy ball / MnS nucleating agent of the present invention;

[0020] In the figure: 1 represents the innermost nitrogen-enhancing agent core particle or MnS nucleating agent core particle; 2 represents the coating layer covering the nitrogen-enhancing agent core particle / MnS nucleating agent core particle; D is the outer diameter of the nitrogen-enhancing agent alloy ball / MnS nucleating agent; and d is the inner diameter of the nitrogen-enhancing agent alloy ball / MnS nucleating agent. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0022] Example 1

[0023] A method for improving and controlling the quality of gear steel, the method comprising the following steps: desulfurization and vanadium extraction of molten iron → semi-steel converter smelting → LF refining → RH vacuum refining → continuous casting; in the LF refining process, nitrogen-enhancing alloy balls are added; in the RH refining process, MnS nucleating agent is added.

[0024] (1) In the converter smelting process, aluminum ferrophosphate is added during the converter tapping process to deoxidize the molten steel, wherein the amount of aluminum ferrophosphate added is 3.5 kg / t. 钢 After deoxidation, the molten steel is alloyed, and the content of key chemical components is initially adjusted to reach 70%~90% of the target component content. After alloying, active lime is added to the ladle at a rate of 3.0 kg / t. 钢 .

[0025] (2) The oxygen activity of the molten steel in the ladle is measured, and aluminum wire is fed according to the oxygen activity measurement results. The feeding length is controlled at 15 m / ppm[O]; the diameter of the aluminum wire is Φ16mm.

[0026] (3) In the LF refining process, the nitrogen-enhancing alloy balls provided by the present invention are added at an amount of 1.2 kg / t. 钢 Implementation; control the Al content in the molten steel to 0.040%; after LF refining, feed CaSi wire at 1.7 m / ppm[S].

[0027] The nitrogen-enhancing agent alloy balls are spherical metal particles with a diameter of 19 mm. The metal particles are coated with an iron sheet with a wall thickness of 2.0 mm, and the inner cavity diameter of the metal particles is 15 mm. Further, nitrogen-enhancing agent core particles with a diameter of 2.0 mm are wrapped within the inner cavity. The mass percentage content of each component in the nitrogen-enhancing agent core particles is: calcium: 5.1%, silicon: 39.0%, nitrogen: 37.0%, clay: 5.0%, with the balance being iron and unavoidable impurities. The mass percentage content of each component in the iron sheet coating is: iron: 99.0%, with the balance being unavoidable impurities.

[0028] (4) During the RH vacuum refining process, the vacuum level in the vacuum chamber is required to be reduced to ≤3mbar and maintained at <3mbar for ≥11min. After 1min of cyclic treatment at <3mbar, MnS nucleating agent is added to the vacuum chamber. The addition process requires uniform weight distribution and the addition time is controlled within 2min. The amount of nucleating agent added is based on the S content test results of the sample taken from the RH molten steel entering the station, specifically: 0.10 kg / (t 钢 • 10ppm [S]). After vacuum depressurization, the CaSi line described in the LF process is fed according to the difference of [S]% in the molten steel when it leaves and enters the RH process. The feeding amount is controlled at 8.2m for every 1ppm increase in sulfur in the RH process. After the CaSi line is fed, the molten steel is allowed to stand for 5.5min before casting begins.

[0029] The MnS nucleating agent consists of spherical metal particles with a diameter of 20.4 mm. The metal particles have a 2.2 mm thick iron sheet wall and an inner cavity diameter of 16 mm, encapsulating a 3.0 mm diameter nucleating agent core particle within the cavity. The mass percentage content of each component in the nucleating agent core particle is as follows: calcium: 18.0%, silicon: 35.0%, magnesium: 25.0%, clay: 4.0%, with the balance being iron and unavoidable impurities. The mass percentage content of each component in the iron sheet weighting layer is as follows: iron: 97.0%, with the balance being unavoidable impurities.

[0030] The CaSi core powder content of LF and RH is 136 g / m, and the mass content of key components is: calcium content 28%, silicon content 53%, and the balance is unavoidable impurities.

[0031] (5) In the continuous casting process, the specified cooling and solidification control process of this invention shall be implemented, and argon blowing protection shall be carried out throughout the casting process.

[0032] The "specified cooling and solidification control process" for the continuous casting process specifically refers to: controlling the superheat of the molten steel at 30~35℃; setting the M-EMS stirring current intensity to 100A; and setting the length of the secondary cooling coverage area to 10m from the bottom of the crystallizer, with a secondary cooling water ratio of 0.84 L / kg. 钢 Control; F-EMS is stirred at a position 11m away from the bottom of the crystallizer, and the stirring current intensity is set at 200A; the billet temperature in the straightening zone rises to 970℃.

[0033] Through the above quality improvement and control methods, the symmetry of the solidification structure of the gear steel billet was significantly improved. The range of distance between the boundary of the equiaxed crystal zone and the billet surface was reduced from 30-40 mm to 15 mm. After rolling into round bars, the range of distance between the boundary of the equiaxed crystal trace zone and the surface of the round bar was controlled within 5 mm, and the range of solute segregation (circumferential) at the same radial distance from the surface of the round bar was 0.02. The resulting gear steel grain size was improved from grade 6.0 to grade 7.0.

[0034] Example 2

[0035] A method for improving and controlling the quality of gear steel, the method comprising the following steps: desulfurization and vanadium extraction of molten iron → semi-steel converter smelting → LF refining → RH vacuum refining → continuous casting; in the LF refining process, nitrogen-enhancing alloy balls are added; in the RH refining process, MnS nucleating agent is added.

[0036] (1) In the converter smelting process, aluminum ferrophosphate is added to the molten steel during the tapping process to deoxidize the steel, wherein the amount of aluminum ferrophosphate added is 3.0 kg / t. 钢 After deoxidation, the molten steel is alloyed, and the content of key chemical components is initially adjusted to reach 70%~90% of the target component content. After alloying, active lime is added to the ladle at a rate of 3.5 kg / t. 钢 .

[0037] (2) The oxygen activity of the molten steel in the ladle is measured, and aluminum wire is fed according to the oxygen activity measurement results. The feeding length is controlled at 15 m / ppm[O]; the diameter of the aluminum wire is Φ15mm.

[0038] (3) In the LF refining process, the nitrogen-enhancing alloy balls provided by the present invention are added at an amount of 1.12 kg / t. 钢Implementation; control the Al content in the molten steel to 0.030%; after LF refining, feed CaSi wire at 2.0 m / ppm[S].

[0039] The nitrogen-enhancing agent alloy balls are spherical metal particles with a diameter of 20 mm. The metal particles are coated with an iron sheet with a wall thickness of 2.0 mm, and the inner cavity diameter of the metal particles is 16 mm. Further, nitrogen-enhancing agent core particles with a diameter of 2.5 mm are wrapped within the inner cavity. The mass percentage content of each component in the nitrogen-enhancing agent core particles is as follows: calcium: 8.2%, silicon: 39.0%, nitrogen: 34.0%, clay: 4.0%, with the balance being iron and unavoidable impurities. The mass percentage content of each component in the iron sheet coating is as follows: iron: 97.0%, with the balance being unavoidable impurities.

[0040] (4) During the RH vacuum refining process, the vacuum level in the vacuum chamber is required to be reduced to ≤3mbar and maintained at <3mbar for ≥11min. After 1min of cyclic treatment at <3mbar, MnS nucleating agent is added to the vacuum chamber. The addition process requires uniform weight distribution and the addition time is controlled within 3min. The amount of nucleating agent added is based on the S content test results of the sample taken from the RH molten steel entering the station, specifically: 0.13 kg / (t 钢 • 10ppm [S]). After vacuum depressurization, the CaSi line described in the LF process is added according to the difference of [S]% in the molten steel when it leaves and enters the RH process. The amount of feed is controlled at 8.5m for every 1ppm increase in sulfur in the RH process. After the CaSi line is added, the molten steel is allowed to stand for 5.5min before casting begins.

[0041] The MnS nucleating agent consists of spherical metal particles with a diameter of 19.2 mm. The metal particles have a 2.1 mm thick iron sheet wall and an inner cavity diameter of 15 mm, within which a nucleating agent core particle with a diameter of 2.5 mm is encapsulated. The mass percentage content of each component in the nucleating agent core particle is as follows: calcium: 15.0%, silicon: 37.0%, magnesium: 19.0%, clay: 5.0%, with the balance being iron and unavoidable impurities. The mass percentage content of each component in the iron sheet weighting layer is as follows: iron: 98.0%, with the balance being unavoidable impurities.

[0042] The CaSi core powder content of LF and RH is 130 g / m, and the mass content of key components is: calcium content 30%, silicon content 45%, and the balance is unavoidable impurities.

[0043] (5) In the continuous casting process, the specified cooling and solidification control process of this technical solution shall be implemented, and argon blowing protection shall be carried out throughout the casting process.

[0044] The "specified cooling and solidification control process" for the continuous casting process specifically refers to: controlling the superheat of the molten steel at 30~35℃; setting the M-EMS stirring current intensity to 100A; and setting the length of the secondary cooling coverage area to 10m from the bottom of the crystallizer, with a secondary cooling water ratio of 0.84 L / kg. 钢 Control; F-EMS is stirred at a position 11m away from the bottom of the crystallizer, and the stirring current intensity is set at 200A; the billet temperature in the straightening zone rises to 970℃.

[0045] Through the above quality improvement and control methods, the symmetry of the solidification structure of the gear steel billet was significantly improved. The range of distance between the boundary of the equiaxed crystal zone and the billet surface was reduced from 30-40 mm to 10 mm. After rolling into round bars, the range of distance between the boundary of the equiaxed crystal trace zone and the surface of the round bar was controlled within 3 mm, and the range of solute segregation (circumferential) at the same radial distance from the surface of the round bar was 0.014. The resulting gear steel grain size was improved from grade 6.0 to grade 7.0.

[0046] Example 3

[0047] A method for improving and controlling the quality of gear steel, the method comprising the following steps: desulfurization and vanadium extraction of molten iron → semi-steel converter smelting → LF refining → RH vacuum refining → continuous casting; in the LF refining process, nitrogen-enhancing alloy balls are added; in the RH refining process, MnS nucleating agent is added.

[0048] (1) In the converter smelting process, aluminum ferrophosphate is added during the tapping process of the converter to deoxidize the molten steel, wherein the amount of aluminum ferrophosphate added is 4.0 kg / t. 钢 After deoxidation, the molten steel is alloyed, and the content of key chemical components is initially adjusted to reach 70%~90% of the target component content. After alloying, active lime is added to the ladle at a rate of 2.5 kg / t. 钢 .

[0049] (2) The oxygen activity of the molten steel in the ladle is measured, and aluminum wire is fed according to the oxygen activity measurement results. The feeding length is controlled at 15 m / ppm[O]; the diameter of the aluminum wire is Φ16mm.

[0050] (3) In the LF refining process, the nitrogen-enhancing alloy balls provided by the present invention are added at a rate of 0.9 kg / t. 钢 Implementation; control the Al content in the molten steel to 0.034%; after LF refining, feed CaSi wire at 1.5 m / ppm[S].

[0051] The nitrogen-enhancing agent alloy balls are spherical metal particles with a diameter of 19 mm. The metal particles are coated with an iron sheet with a wall thickness of 2.0 mm, and the inner cavity diameter of the metal particles is 15 mm. Further, nitrogen-enhancing agent core particles with a diameter of 2.2 mm are wrapped within the inner cavity. The mass percentage content of each component in the nitrogen-enhancing agent core particles is: calcium: 6.5%, silicon: 38.0%, nitrogen: 36.0%, clay: 4.5%, with the balance being iron and unavoidable impurities. The mass percentage content of each component in the iron sheet coating is: iron: 97.0%, with the balance being unavoidable impurities.

[0052] (4) During the RH vacuum refining process, the vacuum level in the vacuum chamber is required to be reduced to ≤3mbar and maintained at <3mbar for ≥11min. After 1.5min of cyclic treatment at <3mbar, MnS nucleating agent is added to the vacuum chamber. The addition process requires uniform weight distribution and the addition time is controlled at 2.5min. The amount of nucleating agent added is based on the S content test results of the sample taken from the RH molten steel entering the station, specifically: 0.114 kg / (t 钢 • 10ppm [S]). After vacuum depressurization, the CaSi line described in the LF process is added according to the difference of [S]% in the molten steel when it leaves and enters the RH process. The amount of feed is controlled at 8m for every 1ppm increase in sulfur in the RH process. After the CaSi line is added, the molten steel is allowed to stand for 6.5min before casting begins.

[0053] The MnS nucleating agent consists of spherical metal particles with a diameter of 21 mm. The metal particles have a 2.0 mm thick iron sheet wall and an inner cavity diameter of 17 mm, encapsulating a 2.5 mm diameter nucleating agent core particle within the cavity. The mass percentage content of each component in the nucleating agent core particle is as follows: calcium: 17.0%, silicon: 36.0%, magnesium: 22.0%, clay: 4.5%, with the balance being iron and unavoidable impurities. The mass percentage content of each component in the iron sheet weighting layer is as follows: iron: 98.0%, with the balance being unavoidable impurities.

[0054] The CaSi wire core powder content of LF and RH is 140 g / m, and the mass content of key components is: calcium content 30%, silicon content 49%, and the balance is unavoidable impurities.

[0055] (5) In the continuous casting process, the specified cooling and solidification control process of this technical solution shall be implemented, and argon blowing protection shall be carried out throughout the casting process.

[0056] The "specified cooling and solidification control process" for the continuous casting process specifically refers to: controlling the superheat of the molten steel at 30~35℃; setting the M-EMS stirring current intensity to 150A; and setting the length of the secondary cooling coverage area to 9m from the bottom of the crystallizer, with a secondary cooling water ratio of 0.87 L / kg. 钢Control; F-EMS is used to stir at a distance of 9.5m from the bottom of the crystallizer, and the stirring current intensity is set at 250A; the billet temperature in the straightening zone rises to 950℃.

[0057] Through the above quality improvement and control methods, the symmetry of the solidification structure of the gear steel billet was significantly improved. The range of distance between the boundary of the equiaxed crystal zone and the billet surface was reduced from 30-40 mm to 12 mm. After rolling into round bars, the range of distance between the boundary of the equiaxed crystal trace zone and the surface of the round bar was controlled at 4 mm. The range of solute segregation (circumferential direction) at the same radial distance from the surface of the round bar was 0.018. The resulting gear steel grain size was improved from grade 6.0 to grade 7.0.

[0058] Comparative Example

[0059] In the converter smelting process, ferroaluminum is added during the tapping process to deoxidize the molten steel, with the amount of ferroaluminum added being 3.0~4.0 kg / t. 钢 After deoxidation, the molten steel is alloyed, and the content of key chemical components is initially adjusted to reach 70%~90% of the target component content. After alloying, active lime is added to the ladle at a rate of 2.5~3.5 kg / t. 钢 .

[0060] Furthermore, the oxygen activity of the molten steel in the ladle is measured, and aluminum wire is fed according to the oxygen activity measurement results. The diameter of the aluminum wire is Φ15mm~Φ16mm, and the feeding length is controlled at 15 m / ppm[O].

[0061] Furthermore, in the LF refining process, the Alt content in the molten steel is controlled at 0.040~0.060%. Even further, after the LF refining is completed, CaSi wire is fed at 1.5~2.0 m / ppm[S].

[0062] The CaSi wire core powder has a content of 130~140g / m, and the mass content of key components is: calcium content ≥28%, silicon content 45~53%, and the balance is unavoidable impurities.

[0063] Furthermore, during the RH vacuum refining process, the vacuum level in the vacuum chamber is required to be reduced to ≤3mbar, and the vacuum level is maintained at <3mbar for ≥11 minutes. After vacuum depressurization, the CaSi line from the LF process is added based on the difference in [S]% between the RH process exiting and entering the molten steel. The feeding amount is controlled at 8~8.5m for every 1ppm increase in sulfur in the RH process. After the CaSi line is added, the molten steel is allowed to stand for >5 minutes before casting can begin.

[0064] The distance difference between the equiaxed crystal zone boundary and the surface of the gear steel billet produced by this process is 30~40mm. After being rolled into a round bar, the distance difference between the equiaxed crystal trace zone boundary and the surface of the round bar is 7~9mm. The solute segregation difference (circumferential) at the same radial distance from the surface of the round bar reaches 0.04. The resulting gear steel has a grain size of 6.0~7.0 grade. The maximum single MnS particle area in the 0~50mm region below the surface of the gear steel billet is 9μm. 2 The number of particles per unit area of ​​the inclusions varies greatly, ranging from 15 to 19 particles / mm. 2 .

[0065] Through the comparison of the above embodiments and comparative examples, it can be seen that the gear steel quality improvement and control method provided by the present invention effectively improves the macroscopic solute concentration uniformity in all directions of the cross-section of the gear steel continuous casting billet, improves the regional symmetry of the solidification structure, and thus promotes a more uniform multi-scale segregation distribution on the round bar, and promotes a more uniform phase transformation and stress distribution in the gear structure during gear processing and subsequent heat treatment. Increasing the nitrogen content in the gear steel and controlling the aluminum-nitrogen ratio can suppress the excessive growth of austenite grains during the phase transformation process through the precipitated AlN particles, thereby achieving grain refinement and improving the grain size level of the gear steel. Ultimately, this lays an important quality foundation for the high-performance uniformity and high dimensional stability control of gears.

[0066] By employing this method, the symmetry of the solidification structure of gear steel billets is significantly improved. The difference in distance between the equiaxed crystal region boundary and the billet surface is reduced from 30-40 mm to 10-12 mm. After rolling into round bars, the difference in distance between the equiaxed crystal trace region boundary and the round bar surface is controlled to ≤4 mm, and the difference in solute segregation (circumferential) at the same radial distance from the surface of the round bar is ≤0.02. The resulting gear steel grain size stabilizes from grade 6.0-7.0 to grade 8.0. The maximum single MnS particle area in the 0-50 mm region below the surface of the gear steel billet is reduced from 9 μm. 2 Miniaturization to 3~4μm 2 The number of particles per unit area of ​​the inclusions varied from 15 to 19 particles / mm. 2 Reduced to 6~9 particles / mm 2 .

[0067] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for improving and controlling the quality of gear steel, characterized in that, The method includes the following steps: molten iron desulfurization and vanadium extraction → semi-steel converter smelting → LF refining → RH vacuum refining → continuous casting; during the LF refining process, nitrogen-enhancing alloy balls are added; during the RH refining process, MnS nucleating agent is added; a specified cooling and solidification control process is implemented to control the solidification process of the molten steel in the billet pool during the continuous casting process, and solidification is completed within the 1 / 4 arc-shaped area of ​​the billet. The nitrogen-enhancing agent alloy ball is a spherical metal particle with a diameter of 19~21mm. The metal particle has a metal sheet coating with a wall thickness of 2.0~2.2mm and an inner cavity diameter of 15~17mm. The inner cavity contains a nitrogen-enhancing agent core particle with a particle diameter of 2.0~3.0mm. The MnS nucleating agent is a spherical metal particle with a diameter of 19-21 mm. The metal particle has a metal sheet coating with a wall thickness of 2.0-2.2 mm and an inner cavity diameter of 15-17 mm. The inner cavity contains a nucleating agent core particle with a diameter of 2.0-3.0 mm. The mass percentage content of each component in the nitrogen-enhancing agent core particles is as follows: calcium: 5.1%~8.2%, silicon: 37.0%~39.0%, nitrogen: 34.0%~37.0%, clay: 4.0%~5.0%, with the balance being iron and unavoidable impurities; The mass percentage content of each component in the nucleating agent core is as follows: calcium: 15.0%~18.0%, silicon: 35.0%~37.0%, magnesium: 19.0%~25.0%, clay: 4.0%~5.0%, with the balance being iron and unavoidable impurities.

2. The method according to claim 1, characterized in that, In the semi-steel converter smelting process, ferrosilicon is added during the converter tapping process to deoxidize the molten steel, wherein the amount of ferrosilicon added is 3.0~4.0 kg / t. 钢 After deoxidation, the molten steel is alloyed. After alloying, quicklime is added to the ladle at a rate of 2.5~3.5 kg / t. 钢 The oxygen activity of the molten steel in the ladle is measured, and aluminum wire is fed according to the oxygen activity measurement results. The diameter of the aluminum wire is Φ15mm~Φ16mm, and the feeding length is controlled at 15m / ppm[O].

3. The method according to claim 1, characterized in that, In the LF refining process, the nitrogen-enhancing agent alloy balls are added at a rate of 0.9~1.2 kg / t. 钢 Implementation; Als in molten steel is controlled at 0.030%~0.040%; after LF refining, CaSi wire is added at 1.5~2.0m / ppm[S].

4. The method according to claim 1, characterized in that, During the RH vacuum refining process, the vacuum level in the vacuum chamber is reduced to ≤3 mbar and maintained at <3 mbar for ≥11 min. After ≥1 min of cyclic treatment at <3 mbar, the MnS nucleating agent is added to the vacuum chamber. The addition time is controlled at 2~3 min. The amount of nucleating agent added is based on the S content test results of the sample taken from the molten steel entering the RH station, specifically: 0.10~0.13 kg / (t). 钢 • 10ppm[S]); After vacuum depressurization, add CaSi line according to the difference of [S]% in the molten steel when leaving and entering the RH process. The amount of feed is controlled at 8~8.5m for every 1ppm increase in sulfur in the RH process. After the CaSi line is added, let the molten steel stand for more than 5min before casting.

5. The method according to claim 1, characterized in that, The CaSi core powder content in the LF and RH processes is 130~140g / m, and the mass content of key components is: calcium content ≥28%, silicon content 45%~53%, with the balance being unavoidable impurities.

6. The method according to claim 1, characterized in that, In the continuous casting process, a designated cooling and solidification control process is implemented, and argon blowing protection is used throughout the casting process. Specifically, the "designated cooling and solidification control process" includes: controlling the superheat of the molten steel at 30~35℃; setting the M-EMS stirring current intensity to 100~200A; extending the secondary cooling coverage area 7~10m from the bottom of the crystallizer; and setting the secondary cooling water ratio to 0.84~0.92L / kg. 钢 Control; F-EMS is stirred at a distance of 7.5~11m from the bottom of the crystallizer, and the stirring current intensity is set at 200~300A; the billet temperature in the straightening zone rises to 920~970℃.

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