Steel for driving gear of excavator and manufacturing method thereof

Abstract

The invention relates to steel for an excavator driving gear and a manufacturing method thereof. The steel for the excavator driving gear comprises the following chemical components in percentage by mass: 0.24 to 0.28 percent of C, 0.30 to 0.45 percent of Si, 0.80 to 0.95 percent of Mn, 1.15 to 1.30 percent of Cr, less than or equal to 0.015 percent of P, 0.025 to 0.035 percent of S, 0.018 to 0.030 percent of Al, 0.0012 to 0.0018 percent of B, 0.05 to 0.10 percent of Cu, 0.16 to 0.28 percent of Ni, 0.06 to 0.12 percent of Mo, less than or equal to 0.003 percent of Sn, less than or equal to 0.003 percent of Sb, 0.006 to 0.0095 percent of N, less than or equal to 0.0010 percent of O and the balance of Fe and inevitable impurities. The method comprises the following steps: smelting in an electric furnace, refining in a refining furnace, vacuum degassing in a VD furnace, continuous casting, overall heating of a continuous casting blank, rolling into round steel, precise temperature control air cooling, and uniform slow cooling in a pit. The steel has the characteristics that the steel oxygen content O is smaller than or equal to 0.0010%, the steel oxide sum index K2 (O) is smaller than or equal to 20, the round bar center segregation is smaller than or equal to 0.5 level, the steel structure is uniform pearlite and ferrite, the diameter of the pearlite and the diameter of the ferrite are 18-25 micrometers, the hardness discrete value of each rolled round bar with the same furnace number is controlled to be smaller than or equal to 15 HBW, and the bending degree of the round bars is smaller than or equal to 2.0 mm / m.

Description

Technical Field

[0002] The invention belongs to the technical field of special steel smelting, and in particular relates to steel for excavator drive gears and a manufacturing method thereof. Background Art

[0004] The excavator drive gear is an important component of the excavator rear axle. It mainly plays the role of torque conversion, speed regulation, load adaptation and driving travel. Torque conversion: convert the high-speed and low-torque power of the engine into a larger torque suitable for the operation of the excavator to drive the excavator to travel under different working conditions; speed regulation: cooperate with other transmission components to achieve the adjustment and control of the excavator's travel speed; load adaptation: can adapt to the different loads borne by the excavator during operations such as excavation and loading, and ensure the stable operation of the travel system; driving travel: directly drive the excavator's crawler or tire to rotate, and realize the forward, backward and steering movements of the equipment. Therefore, the excavator rear axle drive gear needs to be made of materials with good toughness to ensure the specific excellent toughness, load-bearing capacity and fatigue life of the drive gear. The steel of the present invention greatly improves the performance of the excavator rear axle drive gear by strictly controlling the oxygen content, total oxides, center segregation of steel, and discreteness of steel hardness. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a steel for excavator drive gear and a manufacturing method thereof in view of the above-mentioned prior art. The steel of the present invention has the following characteristics: the oxygen content of the steel O: ≤0.0010%, the total oxide index of the steel K2(O) ≤20, the center segregation of the round bar ≤0.5 level, the steel structure is uniform pearlite and ferrite, the diameter of the pearlite and ferrite is 18-25um, the discrete value of the hardness of each rolled round bar of the same furnace number is controlled to be ≤15HBW, and the curvature of the round bar is ≤2.0mm / m.

[0007] The technical solution adopted by the present invention to solve the above-mentioned problem is: a steel for excavator driving gear, the chemical composition weight percentage of the steel is C: 0.24-0.28%, Si: 0.30-0.45%, Mn: 0.80-0.95%, Cr: 1.15-1.30%, P: ≤0.015%, S: 0.025-0.035%, Al: 0.018-0.030%, B: 0.0012-0.0018%, Cu: 0.05-0.10%, Ni: 0.16-0.28%, Mo: 0.06-0.12%, Sn: ≤0.003%, Sb≤0.003%, N: 0.006-0.0095%, O: ≤0.0010%, and the balance is Fe and unavoidable impurities.

[0008] The main functions and design basis of each chemical element of the steel of the present invention are:

[0009] C: Carbon is the most important element in the steel of the present invention. Carbon can significantly increase the hardness of the steel. An appropriate amount of carbon is beneficial to improving the strength of the steel, but it will significantly reduce the toughness of the steel, and too high a carbon content will form a more serious central carbon segregation. Therefore, the carbon content of the steel of the present invention is selected in the range of C: 0.24-0.28%.

[0010] Si: Silicon can play a role in deoxidation and can also appropriately increase the hardness of the steel. Therefore, the selection range of silicon in the steel of the present invention is Si: 0.30-0.45%.

[0011] Mn: Adding a certain amount of manganese to the steel of the present invention helps to improve the toughness and impact resistance of the steel and improve the hardenability of the steel. Therefore, the manganese element selection range of the steel of the present invention is Mn: 0.80-0.95%.

[0012] Cr: Adding chromium to steel can improve the hardenability of the steel, thereby improving the strength and hardness of the steel. Therefore, the chromium content of the present invention is selected within the range of Cr: 1.15-1.30%.

[0013] P: Too high phosphorus content in steel will reduce the toughness of the steel. Therefore, the phosphorus content in the steel of the present invention needs to be controlled at a relatively low level, and the selection range of phosphorus content is P: ≤0.015%.

[0014] S: Sulfur can combine with manganese in steel to form manganese sulfide inclusions. Only a small amount of manganese sulfide inclusions are needed in the steel to significantly improve the cutting performance of the steel, facilitate chip breaking during the cutting process, and reduce tool wear. Therefore, the sulfur content of the steel of the present invention is selected in the range of S: 0.025-0.035%.

[0015] Al: The aluminum element of the steel of the present invention mainly plays the role of deoxidation and grain refinement. The aluminum element is added in the form of pre-adding aluminum particles to the refining ladle; in the early stage of refining, aluminum powder is floated on the slag surface for diffusion deoxidation, and aluminum wire is added for deep deoxidation. The molten steel is deoxidized in this aluminum deoxidation manner, and the oxygen content of the steel is O:≤0.0010%, and the total oxide index of the steel is K2(O)≤20. After the molten steel is vacuum degassed, the nitrogen content in the steel is accurately increased by bottom blowing nitrogen to ensure that the aluminum element in the molten steel combines with the nitrogen element to form AlN, and the Al / N control range is 3.0-3.2.

[0016] B: Adding a small amount of boron can significantly improve the hardenability and hardness of steel, and boron helps to refine the pearlite and ferrite structure of steel. During the rapid air cooling process of the steel of the present invention, the boron element will precipitate in large quantities at the grain boundary at the junction of pearlite and ferrite grains and segregate at the grain boundary, thereby inhibiting the rapid growth of pearlite and ferrite structures. The grain boundary is the interface between pearlite and ferrite grains. The atomic arrangement at the grain boundary is irregular and the energy is high. The grains are easy to grow rapidly here, and the segregation of boron can reduce the energy of the grain boundary, making it difficult for grain growth, thereby playing a role in controlling the size of pearlite and ferrite grain diameters. Therefore, the boron content of the steel of the present invention needs to be controlled within a narrow range of B: 0.0012~0.0018%.

[0017] Cu: Adding a small amount of copper to steel enhances the corrosion resistance and rust resistance of the steel. The copper element selection range of the steel of the present invention is Cu: 0.05-0.10%.

[0018] Ni: Nickel can improve the strength, toughness and corrosion resistance of steel and prevent the steel from being oxidized and corroded during use. The nickel element selection range of the steel of the present invention is Ni: 0.16-0.28%.

[0019] Mo: Molybdenum can improve the strength and hardness of steel, and can also improve the high temperature resistance and corrosion resistance of steel. The molybdenum element selection range of the steel of the present invention is Mo: 0.06-0.12%.

[0020] Sn, Sb: Tin and antimony are easy to be segregated at the grain boundary, which promotes the embrittlement of the grain boundary, so that the pearlite structure and the ferrite structure of the steel of the present invention are easy to grow rapidly and disorderly during the cooling process after rolling, resulting in uncontrolled diameters of the pearlite structure and ferrite structure of the steel, and it is very easy to form coarse ferrite structure and pearlite structure. Therefore, the presence of tin and antimony elements must be strictly limited. The selection range of tin and antimony elements in the steel of the present invention is Sn: ≤0.003%, Sb: ≤0.003%.

[0021] N: Aluminum and nitrogen can combine to form aluminum nitride, which plays a role in refining the austenite grain size of steel. The aluminum content in the steel after vacuum degassing in the VD furnace is measured, and then the nitrogen content in the steel is accurately increased by bottom blowing nitrogen. The nitrogen content in the steel is accurately increased by controlling the flow rate and pressure of the bottom blowing nitrogen to ensure that the Al / N in the molten steel is controlled at 3.0-3.2. The nitrogen element selection range of the steel of the present invention is N: 0.006-0.0095%.

[0022] O: The steel of the present invention adopts aluminum deoxidation to control the oxygen content in the steel, and the deoxidation method is to pre-add aluminum particles to the refining ladle; in the early stage of refining, diffusion deoxidation is carried out by floating aluminum powder on the slag surface, and deep deoxidation is carried out by adding aluminum wire at the same time. The molten steel is deoxidized by this aluminum deoxidation method, and the oxygen content of the steel is controlled to be O:≤0.0010%.

[0023] The above-mentioned steel for excavator drive gear and the manufacturing method thereof include the following process steps:

[0024] (1) A 100t electric furnace is used for smelting, with no less than 60% molten iron and the rest high-quality scrap steel added to reduce the residual tin and antimony content. 0.9-1.2kg / t of aluminum particles are pre-added to the refining ladle, and the diameter of the aluminum particles is 10-15mm. During the steel-tapping process of the electric furnace, the steel-tapping speed of the molten steel is 350-470kg / s, and the total steel-tapping time is 220-270s. By pre-adding aluminum particles of reasonable weight and size into the refining ladle, and controlling the steel-tapping speed and total steel-tapping time of the molten steel, the molten steel is evenly mixed with the aluminum particles in the ladle during the process of entering the refining ladle and fully contacting, the best steel-molten pre-deoxidation effect can be achieved. In the early stage of refining, aluminum powder and calcium silicon powder are floated on the slag surface to diffuse deoxidation and make white slag; at the same time, aluminum wire is fed to perform deep deoxidation. The white slag is kept for 15-20 minutes during the refining process. In order to allow the oxygen elements in the molten steel to fully diffuse into the slag, the white slag must be kept for a period of time during the refining process, because the main components of the white slag are calcium oxide (CaO), silicon dioxide (SiO 2 ), aluminum oxide (Al 2 O 3 ) and other oxides, calcium oxide (CaO) and silicon dioxide (SiO 2 ) and aluminum oxide (Al 2 O 3) and other oxides can react with oxygen in molten steel, thereby reducing the oxygen content in the molten steel and improving the quality of the molten steel; white slag has excellent adsorption properties and can adsorb oxides in molten steel, thereby improving the purity of the molten steel; white slag can cover the surface of molten steel, reduce the contact between molten steel and air, prevent the molten steel from being oxidized, and also reduce the loss of heat in molten steel, ensuring the stability of molten steel temperature during the refining process. Alloys are added during the refining process to adjust the chemical composition of the molten steel, and then a VD vacuum degassing furnace is used to reduce the hydrogen content in the steel. The aluminum content in the molten steel after vacuum degassing is measured, and the molten steel after vacuum degassing is accurately increased by bottom nitrogen blowing. The ladle bottom blowing nitrogen flow rate is controlled at 50-60L / s, the bottom blowing nitrogen pressure is 0.6-0.8MPa, and the bottom blowing nitrogen time is 5-7min. After nitrogen increase, the Al / N in the molten steel is accurately controlled at 3.0-3.2, so that the Al and N elements in the steel are combined to form AlN to prevent the presence of elemental nitrogen. The presence of elemental nitrogen will affect the toughness of the steel, because the presence of nitrogen atoms will limit the deformation ability of the crystal structure at low temperatures, so elemental nitrogen will increase the cold brittle tendency of the steel. In a low temperature environment, the toughness of the steel will decrease significantly, making the steel more susceptible to brittle fracture.

[0025] (2) The continuous casting process uses a tundish covering agent and a mold protective slag to protect the casting. The thickness of the tundish covering agent melting layer, sintering layer and powder slag layer is adjusted by controlling the amount and time of the tundish covering agent. The tundish covering agent melting layer is thinner, with a thickness controlled to be 0.8-1cm; the sintering layer is controlled to be thicker, with a thickness of 1.5-2cm; the powder slag layer is controlled to be relatively thick, with a thickness of 5-7cm. The molten layer of the tundish covering agent is in direct contact with the molten steel, and only a relatively thin molten layer thickness is required to play the role of absorbing microscopic oxides. If the molten layer is too thick, the consumption of the covering agent will increase, thereby increasing the production cost. The thickness of the molten layer of the tundish covering agent is controlled to be 0.8-1cm; the sintered layer of the tundish covering agent is honeycomb-shaped, loose and porous, and has good thermal insulation performance, which can prevent the heat of the molten steel from being lost during the casting process. In order to ensure the excellent thermal insulation effect of the molten steel, it is necessary to ensure that the sintered layer of the tundish covering agent has a certain thickness, but an overly thick sintered layer will hinder the further floating and removal of oxides in the molten steel, and reduce the purity of the molten steel. The thickness of the sintered layer of the tundish covering agent is controlled to be 1.5-2cm; the powder slag layer of the tundish covering agent covers the outermost layer of the molten steel, which plays the role of heat insulation and heat preservation, isolating the air and preventing the secondary oxidation of the molten steel. Therefore, the powder slag layer needs to be relatively thick, but too much powder slag layer means that the use of the covering agent increases, which increases the production cost. The thickness of the powder slag layer of the tundish covering agent is controlled to be 5-7cm. During the casting process, the mold protection slag is added in a frequent and thin manner. The powder slag layer of the mold protection slag can prevent the heat loss of the molten steel and reduce the radiation heat loss. By controlling the thickness of the powder slag layer to a certain extent, the superheat of the molten steel can be reduced and stabilized. Although the powder slag layer has a good thermal insulation effect, a too thick layer may cause the molten steel temperature at the meniscus of the crystallizer to be too high, affecting the temperature gradient in the initial stage of solidification, which is not conducive to the uniformity of the solidification structure of the ingot, resulting in serious segregation of the continuous casting ingot. The thickness of the powder slag layer is controlled to be 3-4cm; a sintered layer of the mold protection slag with a certain thickness can prevent the molten steel from contacting with the air and prevent the secondary oxidation of the molten steel. At the same time, it can It absorbs the microscopic oxides floating in the molten steel and plays a role in purifying the molten steel. However, an overly thick sintered layer will hinder the transfer of heat from the molten steel to the crystallizer, resulting in uneven heat transfer during the solidification of the molten steel in the crystallizer, causing abnormal solidification structure of the ingot, and aggravating the segregation of the continuous casting ingot. The thickness of the sintered layer is controlled to be 0.5-0.8cm; the mold protective slag slag layer has a lubricating effect and can reduce the resistance of the billet. If the thickness is too thin, cracks will appear on the surface of the ingot. If the thickness is too thick, the heat transfer capacity of the crystallizer will be weakened, resulting in poor solidification uniformity of the ingot, thereby aggravating the segregation of the continuous casting ingot. Therefore, the thickness of the mold protective slag slag layer is controlled to be 1.1-1.5cm. The superheat of the casting process is controlled to be 12-18℃. When the superheat is high, the segregation of solute elements in the solidification process of the ingot is aggravated, and the continuous casting ingot after solidification forms a serious central segregation; when the superheat is low, the fluidity of the molten steel deteriorates, which is very likely to cause nozzle blockage and affect the smooth pouring.

[0026] (3) The continuous casting billet is heated to 1100-1200℃ as a whole and then rolled into round bars. The spacing of the round bars on the cooling bed after the rolling mill is kept at 0.7-0.8m. Fans are placed at intervals of 0.5-0.6m at the bottom of the cooling bed. The blowing angle of the fan is 90° perpendicular to the wind direction of the round bars. The temperature sensor is turned on to monitor the temperature change of the round bars in real time. The real-time air volume of each fan is controlled by a computer to achieve uniform cooling of the steel. The cooling rate of each part of each steel can be controlled at 10-11℃ / s. The stable cooling rate is conducive to the transformation of the austenite structure inside the steel into a ferrite structure with relatively uniform diameter. The steel that has been air-cooled to 650℃ is slowly cooled to room temperature in a tic-tac-toe arrangement in the pit. The tic-tac-toe arrangement for slow cooling in the pit can ensure that all parts of the steel can obtain a relatively uniform cooling rate after entering the pit, reduce the temperature gradient, and thus reduce thermal stress, which can reduce the bending deformation of the steel. By achieving a uniform slow cooling rate, the remaining austenite structure can be slowly transformed into a pearlite structure with a relatively uniform diameter, thereby improving the uniformity and size consistency of the ferrite and pearlite structures inside the steel.

[0027] The present invention is directed to a steel for driving gears of excavators, which adopts low carbon and low oxygen in composition, and adds a small amount of sulfur, aluminum, boron, copper, nickel and molybdenum to the steel. The electric furnace adopts a high iron-to-water ratio and is smelted with high-quality scrap steel to reduce the content of residual elements tin and antimony; the refining ladle adopts a method of pre-deoxidation by pre-adding aluminum particles and controlling the steel-out speed and steel-out time of the electric furnace; in the early stage of refining, aluminum particles and silicon-calcium powder are used for diffusion deoxidation to make white slag on the slag surface, and aluminum wire is fed into the molten steel for deep deoxidation. After vacuum degassing in the VD furnace, the aluminum content in the molten steel is measured, and the nitrogen content in the steel is accurately controlled by controlling the flow, pressure and time of bottom blowing nitrogen, and finally the accurate control of Al / N of the steel is realized. The continuous casting process adopts the tundish covering agent and the crystallizer protective slag to protect the casting to prevent the molten steel from being oxidized during the casting process, and at the same time, the low superheat stable casting of the molten steel can be realized. The continuous casting ingot is heated as a whole and rolled into round bars. The cooling speed of the round bars on the cooling bed is accurately controlled by a fan. The steel cooled to 650°C is put into the pit and slowly cooled in a tic-tac-toe pattern until room temperature, so as to control the diameter of the pearlite and ferrite structure of the steel, the discrete value of the hardness of the round bars and the curvature of the round bars.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] The oxygen content of the steel of the present invention is O:≤0.0010%, the total oxide index K2(O) of the steel is ≤20, the steel structure is uniform pearlite and ferrite, the diameter of the pearlite and ferrite is 18-25um, the center segregation of the round bar is ≤0.5 level, the discrete value of the hardness of each rolled round bar of the same furnace number is controlled to be ≤15HBW, and the curvature of the round bar is ≤2.0mm / m. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0032] Example 1 and Example 2:

[0033] The two embodiments involve a method for manufacturing steel for excavator drive gears: 100t electric furnace smelting → refining in refining furnace → vacuum degassing in VD furnace → continuous casting of billets (300mm*340mm) → heating of continuous casting billets as a whole → rolling into round bars → uniform air cooling → uniform slow cooling to room temperature in a pit. Two batches of steel for excavator drive gears were manufactured.

[0034] A 100t electric furnace was used for smelting, and 62% (Example 1) and 73% (Example 2) of molten iron were added, and the rest was high-quality scrap steel to reduce the content of residual elements tin and antimony. 0.9kg / t (Example 1) and 1.2kg / t (Example 2) of aluminum particles were pre-added to the refining ladle, and the diameter of the aluminum particles was 10mm (Example 1) and 15mm (Example 2). During the electric furnace tapping process, the tapping speed of the molten steel was 352kg / s (Example 1) and 469kg / s (Example 2), and the total tapping time was 268s (Example 1) and 223s (Example 2). In the early stage of refining, diffusion deoxidation is carried out by floating aluminum powder and silicon-calcium powder on the slag surface to make white slag; at the same time, deep deoxidation is carried out by feeding aluminum wire. The white slag retention time during the refining process is 15 minutes (Example 1) and 20 minutes (Example 2). During the refining process, alloys are added to adjust the chemical composition of the molten steel, and then a VD furnace vacuum degassing furnace is used to reduce the hydrogen content in the steel. The aluminum content in the molten steel after vacuum degassing is measured. The molten steel after vacuum degassing is accurately increased by bottom nitrogen blowing. The ladle bottom blowing nitrogen flow rate is controlled at 50L / s (Example 1) and 60L / s (Example 2), the bottom blowing nitrogen pressure is 0.6MPa (Example 1) and 0.8MPa (Example 2), the bottom blowing nitrogen time is 5min (Example 1) and 7min (Example 2), and the Al / N in the molten steel after the lifting is accurately controlled at 3.02 (Example 1) and 3.19 (Example 2).

[0035] The continuous casting process uses a tundish covering agent and a crystallizer protective slag to protect the casting. The thickness of the tundish covering agent melting layer, sintering layer and powder slag layer is adjusted by controlling the amount and time of the tundish covering agent. The tundish covering agent melting layer is thinner, and the thickness is controlled to be 0.8cm (Example 1) and 1cm (Example 2); the sintering layer is controlled to be thicker, and the thickness is 1.5cm (Example 1) and 2cm (Example 2); the powder slag layer is controlled to be relatively thick, and the thickness is 5.1cm (Example 1) and 7cm (Example 2). The casting process adopts the method of frequent and thin addition to add the crystallizer protective slag, and the thickness of the powder slag layer is 3cm (Example 1) and 3.9cm (Example 2), the thickness of the sintering layer is 0.5cm (Example 1) and 0.8cm (Example 2), the thickness of the liquid slag layer is 1.1cm (Example 1) and 1.5cm (Example 2), and the superheat of the casting process is controlled to be 18℃ (Example 1) and 12℃ (Example 2).

[0036] The continuous casting billet is heated as a whole to 1103°C (Example 1) and 1199°C (Example 2), and then rolled into round bars. The spacing between the round bars on the cooling bed after leaving the rolling mill is maintained at 0.7m (Example 1) and 0.8m (Example 2). Fans are placed at intervals of 0.5m (Example 1) and 0.6m (Example 2) at the bottom of the cooling bed. The blowing angle of the fan is 90° perpendicular to the wind direction of the round bars. The temperature sensor is turned on to monitor the temperature change of the round bars in real time. The real-time air volume of each fan is controlled by a computer to achieve uniform cooling of the steel. The cooling rate of each part of each steel can be controlled at 11°C / s (Example 1) and 10°C / s (Example 1). The steel cooled to 650°C by air is slowly cooled to room temperature in a tic-tac-toe arrangement in the pit.

[0037] The smelting compositions of the steels obtained in Example 1 and Example 2 are shown in Table 1.

[0038] Table 1 Melting composition (wt%)

[0039]

[0040] The total oxide index K2(O) of the round rods prepared in Example 1 and Example 2 is 17 (Example 1) and 10 (Example 2); the center segregation of the round rods prepared in Example 1 and Example 2 is 0.5 (Example 1) and 0 (Example 2); the diameters of the pearlite and ferrite structures of the round rods prepared in Example 1 and Example 2 are shown in Table 2.

[0041] Table 2

[0042]

[0043] The measured values ​​of the hardness of the round bars obtained in Example 1 and Example 2 are shown in Table 3;

[0044] Table 3

[0045]

[0046] The maximum curvature of the round bars obtained in Example 1 and Example 2 is 1.8 mm / m (Example 1) and 2.0 mm / m (Example 2).

[0047] The present invention is directed to a steel for driving gears of excavators, which adopts low carbon and low oxygen in composition, and adds a small amount of sulfur, aluminum, boron, copper, nickel and molybdenum to the steel. The electric furnace adopts a high iron-to-water ratio and is smelted with high-quality scrap steel to reduce the content of residual elements tin and antimony; the refining ladle adopts a method of pre-deoxidation by pre-adding aluminum particles and controlling the steel-out speed and steel-out time of the electric furnace; in the early stage of refining, aluminum particles and silicon-calcium powder are used for diffusion deoxidation to make white slag on the slag surface, and aluminum wire is fed into the molten steel for deep deoxidation. After vacuum degassing in the VD furnace, the aluminum content in the molten steel is measured, and the nitrogen content in the steel is accurately controlled by controlling the flow, pressure and time of bottom blowing nitrogen, and finally the accurate control of Al / N of the steel is realized. The continuous casting process adopts the tundish covering agent and the crystallizer protective slag to protect the casting to prevent the molten steel from being oxidized during the casting process, and at the same time, the low superheat stable casting of the molten steel can be realized. After the continuous casting billet is heated as a whole, it is rolled into a round bar. The round bar on the cooling bed uses a fan to accurately control the cooling speed of the round bar. The steel cooled to 650°C is slowly cooled in a tic-tac-toe arrangement until room temperature in the pit, so as to achieve the purpose of controlling the diameter of the pearlite and ferrite structure of the steel, the discrete value of the hardness of the round bar and the curvature of the round bar. Finally, a steel for excavator driving gear was invented, characterized in that: the oxygen content of the steel is O: ≤0.0010%, the total oxide index of the steel is K2 (O) ≤20, the steel structure is uniform pearlite and ferrite, the diameter of pearlite and ferrite is 18-25um, the center segregation of the round bar is ≤0.5 level, the discrete value of the hardness of each rolled round bar with the same furnace number is controlled to be ≤15HBW, and the curvature of the round bar is ≤2.0mm / m. The present invention manufactures a steel for excavator driving gear, filling the domestic gap.

[0048] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A steel for excavator driving gear, characterized in that: The chemical composition of the steel is as follows by weight: C: 0.24-0.28%, Si: 0.30-0.45%, Mn: 0.80-0.95%, Cr: 1.15-1.30%, P: ≤0.015%, S: 0.025-0.035%, Al: 0.018-0.030%, B: 0.0012-0.0018%, Cu: 0.05-0.10%, Ni: 0.16-0.28%, Mo: 0.06-0.12%, Sn: ≤0.003%, Sb≤0.003%, N: 0.006-0.0095%, O: ≤0.0010%, and the balance is Fe and unavoidable impurities.

2. The steel for excavator driving gear according to claim 1, characterized in that: The oxygen content of the steel is O:≤0.0010%, the total oxide index of the steel K2(O)≤20, and the center segregation of the round bar is ≤0.5 level.

3. The steel for excavator driving gear according to claim 1, characterized in that: The steel structure is uniform pearlite and ferrite, the diameter of the pearlite and ferrite is 18-25um, the discrete value of hardness of each rolled round bar of the same furnace number is controlled to be ≤15HBW, and the curvature of the round bar is ≤2.0mm / m.

4. A method for manufacturing steel for excavator drive gears according to claim 1, characterized in that: The method comprises the following steps: 1) A 100t electric furnace is used for smelting, with no less than 60% molten iron and the rest being high-quality scrap steel. In the early stage of refining, aluminum powder and calcium silicon powder are floated on the slag surface for diffusion deoxidation to produce white slag. At the same time, aluminum wire is fed for deep deoxidation. The white slag is kept for 15-20 minutes during the refining process. Alloys are added during the refining process to adjust the chemical composition of the molten steel. Then, a VD furnace vacuum degassing furnace is used to reduce the hydrogen content in the steel. The aluminum content in the molten steel after vacuum degassing is measured. The nitrogen content in the molten steel after vacuum degassing is accurately increased by bottom nitrogen blowing. 2) The continuous casting process uses tundish covering agent and mold protection slag to protect the casting. By controlling the amount and time of adding the tundish covering agent, the thickness of the tundish covering agent melting layer, sintering layer and powder slag layer can be adjusted to obtain a casting billet that meets the chemical composition requirements; 3) The continuous casting billet is heated to 1100-1200℃ as a whole, and then rolled into round bars. The round bars after leaving the rolling mill are cooled on the cooling bed. The steel cooled to 650℃ by air is put into the pit and slowly cooled to room temperature in a tic-tac-toe arrangement.

5. The method for manufacturing steel for excavator drive gear according to claim 4, characterized in that: In step 1), 0.9-1.2 kg / t of aluminum particles are pre-added to the refining ladle, and the diameter of the aluminum particles is 10-15 mm. During the steel tapping process of the electric furnace, the steel tapping speed of the molten steel is 350-470 kg / s, and the total steel tapping time is 220-270 s.

6. The method for manufacturing steel for excavator drive gear according to claim 4, characterized in that: Step 1) After medium vacuum degassing, the nitrogen content is controlled by the following method: the nitrogen flow rate of the ladle bottom blowing is controlled at 50-60L / s, the pressure of the bottom blowing nitrogen is 0.6-0.8MPa, the bottom blowing nitrogen time is 5-7min, and the Al / N in the molten steel is accurately controlled at 3.0-3.2 after nitrogen lifting.

7. The method for manufacturing steel for excavator drive gear according to claim 4, characterized in that: In step 2), the molten layer of the tundish covering agent is relatively thin, with a thickness controlled to be 0.8-1 cm; the sintered layer is controlled to be thicker, with a thickness of 1.5-2 cm; and the powder slag layer is controlled to be relatively thick, with a thickness of 5-7 cm.

8. The method for manufacturing steel for excavator drive gear according to claim 4, characterized in that In step 2), the thickness of the mold protective slag liquid slag layer is controlled to be 1.1-1.5 cm. The superheat during the casting process is controlled at 12-18°C.

9. The method for manufacturing steel for excavator drive gear according to claim 4, characterized in that Step 3) The distance between the round bars after the rolling mill on the cooling bed is maintained at 0.7-0.8m, and fans are placed at intervals of 0.5-0.6m at the bottom of the cooling bed. The blowing angle of the fans is 90° perpendicular to the wind direction of the round bars. The temperature sensor is turned on to monitor the temperature changes of the round bars in real time. The real-time air volume of each fan is controlled by a computer to achieve uniform cooling of the steel. The cooling speed of each part of each steel is controlled at 10-11℃ / s.

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