High-density gear steel and production process thereof

Abstract

The high-density gear steel comprises the following chemical components in percentage by mass: 0.17 to 0.25 percent of C, 0.20 to 0.45 percent of Si, 0.50 to 0.95 percent of Mn, 0.80 to 1.30 percent of Cr, 0.20 to 0.50 percent of Mo, less than or equal to 0.010 percent of S, less than or equal to 0.015 percent of P, less than or equal to 0.035 percent of Als, 0.015 to 0.050 percent of Nb, less than or equal to 0.0040 percent of N, less than or equal to 0.0012 percent of O, less than or equal to 0.00015 percent of H and the balance of Fe and inevitable impurities during smelting. And rolling and heat treatment technologies are combined, so that the gear steel material with the density higher than 0.95 is developed.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and particularly relates to a high-density gear steel and its production process. Background Art

[0002] Gear steel is a general term for alloy materials that can be used for machining gears. It is one of the key materials with relatively high requirements among special alloy materials used in fields such as new energy wind power, rail transit, mechanical equipment, automobile manufacturing, and shipbuilding. Since gears are the core components of mechanical equipment, there are very high requirements for the performance, service life, running smoothness, safety, etc. of the gear steel materials.

[0003] As a basic part of the machinery industry, gears are subjected to various forces such as impact force, contact stress, pulsating bending stress, and friction force of variable loads during operation. At the same time, they are also affected by various factors such as machining accuracy, assembly accuracy, and grinding of foreign hard particles. They are the parts that are extremely easy to damage among various parts. Therefore, it is required that the gear steel for manufacturing gears has high strength and toughness, fatigue strength, and wear resistance. Four quality indicators for evaluating gear steel: (1) Specific hardenability and narrow hardenability bandwidth; (2) High purity; (3) Fine and uniform grains; (4) Good surface quality. Among them, narrow composition control, low oxygen content, and low inclusion content are the keys to ensuring the quality of gear steel.

[0004] The density of steel is directly related to factors such as porosity, cracks, segregation, gas content, cleanliness, and grain structure of the steel. This index reflects the density of the matrix structure of the steel and directly affects the strength and toughness, wear resistance, homogenization level, and the ability to withstand alternating impact loads of the steel. Therefore, it is urgent to develop a high-density gear steel and its production process to meet the needs of high-end gears. Summary of the Invention

[0005] In view of the above deficiencies, the present invention provides a production process for high-density gear steel. By optimizing the smelting and continuous casting process and combining rolling and heat treatment technologies, a gear steel material with a density higher than 0.95 is developed.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions: A high-density gear steel, the chemical composition of which is by mass percentage: C: 0.17 - 0.25%, Si: 0.20 - 0.45%, Mn: 0.50 - 0.95%, Cr: 0.80 - 1.30%, Mo: 0.20 - 0.50%, S: ≤0.010%, P: ≤0.015%, Als: ≤0.035%, Nb: 0.015 - 0.050%, N: ≤0.0040%, O: ≤0.0012%, H: ≤0.00015%, and the balance is Fe and impurities inevitably present during smelting.

[0007] Furthermore, the non-metallic inclusions of the gear steel meet the following requirements: the A-type coarse series is not more than grade 1.5, the B-type fine series is not more than grade 1.5, the B-type coarse series is not more than grade 0.5, the C-type fine series is not more than grade 0.5, the C-type coarse series is grade 0, the D-type fine series is not more than grade 1.0, the D-type coarse series is not more than grade 0.5, and the Ds-type is not more than grade 0.5.

[0008] Furthermore, there are no macroscopic inclusions, and the requirements of level 3 or above of SEP 1927-2010 for immersion ultrasonic testing are met; the microscopic inclusions are fine and uniform, and there are no inclusions larger than 30 μm.

[0009] A production process of high-density gear steel, characterized by comprising the following steps: putting raw materials into a converter or an electric furnace for steelmaking, then transferring them to an LF furnace for refining, then performing vacuum degassing treatment in VD or RH, carrying out continuous casting after degassing, slow cooling for rolling forming, air cooling or slow cooling, straightening or heat treatment, and skinning after rolling, and slow cooling in a pit.

[0010] Furthermore, the carbon temperature at the end of primary smelting is double-controlled to reduce the oxygen content of the molten steel; the LF furnace adopts a high-alkalinity refining slag system, controls FeO + MnO in the slag ≤ 0.5%, and controls the bottom blowing argon gas flow in stages of large - small - medium.

[0011] Furthermore, extend the vacuum treatment time and soft blowing time to ensure the floating of inclusions; the time below 67 Pa during the vacuum treatment process ≥ 15 min, and the soft blowing time ≥ 20 min; the soft blowing time is not less than 20 min to ensure that the molten steel surface is not exposed during the soft blowing process and avoid secondary oxidation of the molten steel.

[0012] Furthermore, carry out full-process protected casting during continuous casting, and operate with three constants of constant drawing speed, constant liquid level, and constant casting temperature.

[0013] Low drawing speed, weak secondary cooling and dynamic control technology, and the total specific water volume is controlled at 0.03 - 0.095 L / kg; control the temperature of the round billet entering the straightening machine ≥ 920 °C.

[0014] Adjust the electromagnetic stirring parameters and increase the current in two sections.

[0015] Online heat preservation and offline slow cooling, the slow cooling time is not less than 24 hours, and the slow cooling pit is preheated to 500 °C.

[0016] Furthermore, an appropriate compression ratio can compact the structure inside the billet, weld holes and cracks, and homogenize the segregated components, making the properties of the steel consistent. The compression ratio for round steel rolling is ≥12. The cast billet is rolled into the finished size using a one-fire rolling process or a two-fire rolling process. Among them: for the one-fire rolling process, the starting rolling temperature is ≥1050°C, and the finishing rolling temperature is ≤950°C; the temperature for entering the cooling bed is ≤670°C. In the two-fire rolling process, the starting rolling temperature for blooming is ≥1050°C, and the finishing rolling temperature for blooming is ≥870°C; the heating temperature for the intermediate billet is 1150 - 1250°C, and the heating time is 3 - 10 h; the starting rolling temperature for finishing is ≥1030°C, and the finishing rolling temperature for finishing is ≥850°C.

[0017] For the low magnification structure inspection of the gear steel continuous casting round billet produced by the method of the present invention, the center porosity shall be ≤1.5 grades, the shrinkage cavity shall be ≤0.5 grades, and there shall be no defects such as center cracks, intermediate cracks, subsurface air bubbles, and subsurface cracks.

[0018] The low magnification structure of the rolled material is inspected according to the GB / T 1979 standard. There shall be no visible shrinkage cavity, air bubble, crack, inclusion, delamination, turned skin, white spot, and intergranular crack on the acid-etched low magnification structure test piece of the cross-section of the round steel. The acid-etched low magnification structure shall comply with the provisions of Table 1.

[0019] Table 1 Low Magnification Structure Inspection

[0020] General porosity Central porosity Ingot shape segregation Central segregation General punctiform segregation Edge punctiform segregation ≤1.0 ≤0.5 Not allowed ≤1.0 Not allowed Not allowed

[0021] The density index of the gear steel produced by the method of the present invention is as follows:

[0022] The average apparent density measured by the Originalposition statistic distributionanalysis (OPA) (hereinafter referred to as in-situ analysis) is ≥0.95. Description of the Drawings

[0023] Figure 1 The figure shows the schematic diagram of the rolling deformation process of gear steel in the two-fire rolling process.

[0024] Figure 2 The figure shows the low magnification photo of a φ500mm continuous casting round billet with 0.5 grades of porosity and 0.5 grades of shrinkage cavity;

[0025] Figure 3 The figure shows the low magnification photo of a φ90mm rolled material;

[0026] Figure 4 The figure shows the in-situ analysis diagram of the round steel in Example 1, with a density of 0.9573;

[0027] Figure 5 The figure shows the density distribution state diagram of the round steel in Example 1;

[0028] Figure 6 Shown is the in-situ analysis diagram of round steel in Example 2, with a relative density of 0.9628. Specific Embodiments

[0029] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments:

[0030] In the present invention, unless otherwise specified, the technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the technical field to which the present invention pertains.

[0031] In the present invention, unless otherwise specified, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0032] In the present invention, unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods without special instructions, and the materials, reagents, etc. used can be obtained from commercial sources without special instructions.

[0033] Example 1

[0034] 1) The chemical composition of the gear steel produced in this example is shown in the following table:

[0035] Table 2 Melting Chemical Composition

[0036]

[0037] The gear steel in this example is produced according to the following steps: batching → 100-ton electric furnace → LF furnace refining + VD vacuum degassing treatment → continuous casting (φ500mm) → hot charging / temperature-controlled slow cooling → rolling and blooming (265×265mm) → slow cooling in the pit → rolling into finished products (φ90mm) → slow cooling in the pit.

[0038] 2) Electric furnace smelting:

[0039] Charging system: The prepared materials are added to the electric furnace. The amount of hot metal added is 103 tons, and the amount of scrap steel is 22.5 tons. The residual elements in the scrap steel charged are strictly controlled. Heavy, medium, cut billets and other scrap steels are proportioned according to 1:3:1:5.

[0040] End point: C: 0.116%, P: 0.0107%, the binary basicity of the slag is 2.83, the residual elements [Cu] 0.03% and [Ni] 0.02%, meeting the standard requirements; the tapping temperature is 1592°C.

[0041] 3) Deoxidation and alloying: 0.25kg / t of high-purity silicon carbide and 0.8kg / t of calcined coal recarburizer (fixed carbon content > 95%) are added to the ladle for pre-deoxidation; aluminum ingots are used for precipitation deoxidation, with an addition amount of 0.8kg / t of steel; 9.6kg / t of manganese silicon alloy, 20kg / t of chromium iron, and 5.5kg / t of ferromolybdenum are added during the steelmaking process; the ingredients are added according to the target values, and no alloy is added during the refining process.

[0042] 4) LF refining furnace smelting: control the basicity of the final slag to 3.2, the (FeO+MnO) content in the slag to 0.35%, the Al2O3 content to 26.7%, use silicon carbide + aluminum particles for diffusion deoxidation, the silicon carbide addition amount is 1.2kg / t steel, the aluminum particles are 0.25kg / t steel, double bricks are argon-blown, and the single brick argon flow rate is 720NL / min. VD furnace vacuum refining: the vacuum degree is less than 67Pa and the holding time is 18 minutes; the ladle soft blowing is 30×2L / min, based on the slight movement of the slag surface and no exposed molten steel, the time is 22 minutes; the tundish continuous casting is the 7th furnace, and the exit temperature is 1559℃.

[0043] 5) Continuous casting: casting round billets with a cross-section of φ500mm, drawing speed of 0.27m / min, superheat of 22℃, and weak cooling water distribution mode; argon is blown in the tundish throughout the production process, and the tundish cover is sealed; the crystallizer liquid level fluctuation is ≤±3mm; the amount of molten steel in the tundish is 45t; the temperature of the billet entering the straightening machine is 952℃; the billet is cut and slowly cooled on the ground, and the slow cooling time is 46 hours.

[0044] 6) Rolling process: the temperature of the ingot soaking section is 1210℃, the heating time is 6.5h, the ingot starting and rolling temperature is 1085℃, the final rolling temperature is 988℃, and the intermediate ingot size is 265mm×265mm; the intermediate ingot heating temperature is 1220℃, the holding time is 4h, the finished product starting and rolling temperature is 1050℃, the finished product final rolling temperature is 960℃, the head cutting length is 220mm, and the tail cutting length is 450mm.

[0045] Example 2

[0046] 1) The chemical composition of the gear steel produced in this embodiment is shown in the following table:

[0047] Table 3 Melting chemical composition

[0048]

[0049] The gear steel in this embodiment is produced according to the following steps: batching → 100-ton electric furnace → LF furnace refining + VD vacuum degassing treatment → continuous casting (φ500mm) → hot delivery / temperature control slow cooling → steel rolling (265×265mm) → pit slow cooling → rolled into product (φ75mm) → pit slow cooling.

[0050] 2) Electric furnace smelting:

[0051] Charging system: The prepared materials are added to the electric furnace. The amount of hot metal added is 102.9 tons, and the amount of scrap steel is 21.8 tons. The residual elements in the scrap steel charged into the furnace are strictly controlled. Heavy, medium, cut billets and other scrap steels are proportioned according to 1:3:1:5.

[0052] End point: C: 0.12%, P: 0.009%, the binary basicity of the slag is 3.04, the residual elements [Cu] 0.03%, [Ni] 0.02%, meeting the standard requirements; the tapping temperature is 1587 °C.

[0053] 3) Deoxidation and alloying: Silicon carbide and carburizer are added to the ladle for preliminary deoxidation. The addition amount of calcined coal carburizer (fixed carbon content > 95%) is 0.8 kg / t of steel, and the addition amount of high-purity silicon carbide is 0.25 kg / t of steel; aluminum ingots are used for precipitation deoxidation, and the addition amount is 0.8 kg / t of steel; during tapping, the addition amount of ferromanganese-silicon alloy is 9.7 kg / t of steel, the addition amount of ferrochrome is 20 kg / t of steel, and the addition amount of ferromolybdenum is 5.5 kg / t of steel.

[0054] 4) LF refining furnace smelting: Control the basicity of the final refining slag to 3.4, (FeO + MnO) in the slag is 0.42%, and the Al2O3 content is 27.6%. Use silicon carbide + aluminum pellets (the addition amount of silicon carbide is 1.2 kg / t of steel, and the addition amount of aluminum pellets is 0.25 kg / t of steel) for diffusion deoxidation, blow argon with double bricks, and the argon flow rate of single brick is 720 NL / min. VD furnace vacuum refining: The vacuum degree is less than 67 Pa and the holding time is 18 minutes; the ladle soft blowing is 30×2 L / min, with the slag surface slightly moving and not exposing the molten steel as the standard, and the time is 25 minutes; the 9th furnace is continuously cast in the tundish, and the tapping temperature is 1557 °C.

[0055] 5) Continuous casting: Pouring section is φ500mm round billet, casting speed is 0.27 m / min, superheat is 21 °C, and weak cooling water distribution mode is adopted; during the production process, argon is blown throughout the tundish, and the tundish cover is sealed; the liquid level fluctuation in the mold is ≤ ±3 mm; the amount of molten steel in the tundish is 45 t; the temperature of the cast billet entering the straightening machine is 950 °C; after the cast billet is cut, it is cooled slowly on the ground, and the slow cooling time is 46 hours.

[0056] 6) Rolling process: The soaking section temperature of the cast billet is 1210 °C, the heating time is 6.5 h, the blooming rolling start temperature is 1090 °C, the finishing rolling temperature is 990 °C, and the size of the intermediate billet is 265 mm×265 mm; the heating temperature of the intermediate billet is 1220 °C, the holding time is 4 h, the rolling start temperature of the finished product is 1055 °C, the finishing rolling temperature of the finished product is 963 °C, the cutting head length is 240 mm, and the cutting tail length is 430 mm.

[0057] 7) Density detection of φ75mm round steel:

[0058] The density detection result of the round steel is 0.9628, see the attachment for details Figure 6 .

[0059] The present invention has been described in detail above. For those skilled in the art, without departing from the spirit and scope of the present invention and without the need for unnecessary experiments, the present invention can be implemented within a relatively wide range under equivalent parameters, concentrations, and conditions. Although specific embodiments of the present invention are given, it should be understood that the present invention can be further improved. In short, according to the principle of the present invention, this application intends to cover any modifications, uses, or improvements to the present invention, including those that depart from the scope disclosed in this application but are made by using conventional techniques known in the art.

Claims

1. A high-density gear steel, characterized in that: Its chemical composition by mass percentage is: C: 0.17~0.25%, Si: 0.20~0.45%, Mn: 0.50~0.95%, Cr: 0.80~1.30%, Mo: 0.20~0.50%, S: ≤0.010%, P: ≤0.015%, Als: ≤0.035%, Nb: 0.015~0.050%, N: ≤0.0040%, O: ≤0.0012%, H: ≤0.00015%, and the balance is Fe and inevitable impurities during smelting.

2. The high-density gear steel according to claim 1, characterized in that: The non-metallic inclusions of the gear steel meet the following requirements: the coarse inclusions of Class A shall not exceed Grade 1.5, the fine inclusions of Class B shall not exceed Grade 1.5 and the coarse inclusions of Class B shall not exceed Grade 0.5, the fine inclusions of Class C shall not exceed Grade 0.5 and the coarse inclusions of Class C shall be Grade 0, the fine inclusions of Class D shall not exceed Grade 1.0 and the coarse inclusions of Class D shall not exceed Grade 0.5, and the Ds inclusions shall not exceed Grade 0.

5.

3. The high-density gear steel according to claim 1, characterized in that: There are no macroscopic inclusions, and the water immersion ultrasonic test meets the requirements of SEP 1927-2010 level 3 and above; the microscopic inclusions are small and uniform, and there are no inclusions larger than 30μm.

4. A production process for high-density gear steel as described in claims 1-3, characterized in that: The method comprises the following steps: placing the raw materials into a converter or an electric furnace for steelmaking, and then transferring the raw materials into an LF furnace for refining, and then performing vacuum degassing treatment in a VD or RH, performing continuous casting after degassing, performing rolling forming by slow cooling, air cooling or slow cooling after rolling, straightening or heat treatment, peeling, and slow cooling in a pit.

5. A production process for high-density gear steel as claimed in claim 4, characterized in that: LF adopts high basicity refining slag system, controls FeO+MnO in the slag ≤ 0.5%, and controls the bottom blowing argon flow rate in stages from large to small to medium.

6. A production process for high-density gear steel as claimed in claim 4, characterized in that: The vacuum treatment process should be below 67Pa for ≥15min, and the soft blowing time should be ≥20min; the soft blowing time should not be less than 20min.

7. A production process for high-density gear steel as claimed in claim 4, characterized in that: The continuous casting process is protected by pouring, and the continuous casting operation is performed with constant casting speed, constant liquid level and constant pouring temperature; Low drawing speed, secondary cooling, weak cooling and dynamic control technology, the total specific water volume is controlled at 0.03~0.095L / kg; the temperature of the round billet entering the drawing and straightening machine is controlled to be ≥920℃; the electromagnetic stirring parameters are adjusted, and the current of the two sections is increased; online insulation and offline slow cooling, the slow cooling time is not less than 24 hours, and the slow cooling pit is preheated to 500℃.

8. A production process for high-density gear steel as claimed in claim 4, characterized in that: The round steel rolling reduction ratio is ≥12; the ingot is rolled into finished product size using a one-fire process or a two-fire process.

9. A production process for high-density gear steel as claimed in claim 8, characterized in that: The first rolling temperature of the one-fire rolling process is ≥1050°C, the final rolling temperature is ≤950°C; and the upper cooling bed temperature is ≤670°C.

10. A production process for high-density gear steel as claimed in claim 8, characterized in that: In the two-fire timber forming process, the slab rolling temperature is ≥1050°C, and the slab final rolling temperature is ≥870°C; the intermediate billet heating temperature is 1150-1250°C, and the heating time is 3-10h; the finished product rolling temperature is ≥1030°C, and the finished product final rolling temperature is ≥850°C.

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