A method for producing composite gear steel ingots

Abstract

The invention provides a method for producing a composite gear steel ingot. The composite gear steel ingot is formed by casting a ingot shell formed by powder pressing with molten steel. The method specifically comprises the following steps: S1, producing the ingot shell online by using powder metallurgy technology; S2, injecting the molten steel in a tundish into the ingot shell through an immersed nozzle by a continuous casting machine for casting, and forming the ingot after cooling. The powder composition adopts a high-carbon CrNiMo gear steel composition system, and the composition is calculated by mass percentage as follows: C: 1.00-1.10%, Si: 0.05-0.15%, Mn: 0.5-0.6%, P: ≤0.015%, S: ≤0.015%, Cr: 1.5-1.8%, Ni: 1.7-1.8%, Mo: 0.3-0.4%, lubricant: 0.4-0.6%, and the remainder is Fe and unavoidable impurities. The present invention can produce composite gear steel ingots online, with the shell and interior of the ingot being made of different materials. The produced ingots can meet the requirements of wear resistance and hardness at the gear tooth position, while ensuring the overall toughness and processability of the gear, and has the advantages of short process, high production efficiency and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a method for producing composite gear steel castings. Background Art

[0002] The gear manufacturing process generally includes the following steps: forging the blank, normalizing, rough turning, UT testing, pre-heat vertical turning, scribing, drilling, hobbing, chamfering, carburizing and quenching, shot peening, post-heat finish turning, CNC vertical grinding, grinding, MT testing, burn detection, spline insertion, cleaning, and installation. Carburizing and shot peening are intended to improve the wear resistance and hardness of the teeth. However, because gear steel is currently made entirely of the same steel, even after implementing these processes to improve wear resistance and hardness, insufficient tooth hardness persists, leading to frequent tooth breakage during gear steel use. Furthermore, carburizing, as an energy-intensive process, is both costly and energy-intensive.

[0003] Composite materials in the metallurgical field generally include two-layer composites and three-layer composites. Two-layer composites refer to materials with different materials on the upper and lower surfaces, while three-layer composites refer to materials with different materials on the upper, lower surfaces, and interior. Different materials can perform different functions. For example, a composite gear steel blank with high alloy content on the upper and lower surfaces and low alloy content in the inner thickness can improve wear resistance and hardness at the tooth position, while the low alloy content in the inner thickness can improve the overall toughness and workability of the gear.

[0004] A Chinese invention patent with the publication number "CN100377814C" discloses an efficient forming method for cladding materials. The method comprises the following steps: the cladding metal is kept warm by a cladding metal temperature-controlled crucible, flows through a cladding metal insulation chamber, and is then injected into a mold formed by a cladding metal crystallizer and a core metal pouring pipe to solidify into a cladding metal tube. The core metal liquid is then poured into the metal tube, whereupon the core metal solidifies in the solidified cladding metal tube and forms a composite ingot with the cladding metal tube. However, this method requires two containers (tundishes or ladles) for holding different molten metals, resulting in complex equipment. Furthermore, based on the current level of continuous casting technology, it is very difficult to manufacture a cladding metal tube by horizontal continuous casting. This technology does not explain how the core metal pouring pipe cools the cladding metal liquid, nor does it explain how to achieve the demolding problem between the solidified cladding metal tube and the cladding metal crystallizer and the core metal pouring pipe.

[0005] A Chinese invention patent with publication number "CN109128691B" discloses a process for preparing composite ingots for high-carbon, high-alloy steel plates. The process includes the following steps: raw material ingot preparation; raw material ingot processing, including high-carbon and high-alloy steel raw material ingot processing, including groove processing and thinning processing; preheating and welding the edge or surfacing the transition layer to prepare the composite ingot; milling and cleaning the welded composite ingot to obtain the composite ingot; vacuum treating and welding the composite ingot to obtain the composite ingot; and heating the composite ingot. The method disclosed in this invention requires grinding the steel plates to be welded to remove the iron oxide scale, and then using vacuum welding to weld the different steel plates into a single piece. This method requires surface processing and vacuum welding of the steel plates, resulting in low production efficiency and high costs.

[0006] From the above, it can be seen that the currently published technologies for composite ingots mainly include two categories: one is to cast a steel shell first, and then cast molten steel of another material into the inside of the steel shell to form a composite ingot, but this method requires two containers for holding different metal liquids, the equipment is relatively complex, and it is extremely difficult to cast a defect-free steel shell with the existing continuous casting technology level; the other is to use vacuum welding to weld two pieces of metal materials with smooth surfaces together to form a composite ingot, but the steel plate needs to be surface polished and the iron oxide scale removed, which has the disadvantages of low production efficiency and high cost.

[0007] In summary, the metallurgical field currently lacks an operable method for producing composite gear steel billets by continuous steel casting. Summary of the Invention

[0008] To address the deficiencies in the prior art, the present invention provides a method for producing composite gear steel ingots. First, powder metallurgy technology is used to press out an ingot shell online. Molten steel is then injected into the shell through an immersed nozzle. Under the high temperature of the molten steel, a sintering reaction occurs in the shell, thereby increasing the strength of the shell. Subsequently, the ingot is hot-rolled into a round bar-type gear steel blank, and the density of the ingot is further improved during the rolling process.

[0009] The technical solution specifically adopted in the present invention is:

[0010] The invention discloses a method for producing a composite gear steel ingot, wherein a ingot shell formed by powder pressing is cast with molten steel to form the composite gear steel ingot.

[0011] The specific steps include:

[0012] S1, using powder metallurgy technology to produce in-line casting shell: using a mold to press powder into casting shell;

[0013] S2, injecting molten steel into the ingot shell through the submerged nozzle: a tundish filled with molten steel is arranged above the submerged nozzle, and the continuous casting machine injects the molten steel in the tundish into the ingot shell through the submerged nozzle for casting, and forms a ingot after cooling.

[0014] Preferably, the composition of the powder in S1 adopts a high-carbon content CrNiMo gear steel component system, recorded as the first metal, and is calculated in percentage by mass as follows: C: 1.00-1.10%, Si: 0.05-0.15%, Mn: 0.5-0.6%, P: ≤0.015%, S: ≤0.015%, Cr: 1.5-1.8%, Ni: 1.7-1.8%, Mo: 0.3-0.4%, lubricant: 0.4-0.6%, and the rest is Fe and unavoidable impurities.

[0015] Preferably, the particle size of the powder in S1 is: 600 mesh ≤ the particle size of the powder ≤ 100 mesh.

[0016] Wherein, the lubricant in S1 is a special lubricant for powder metallurgy gears.

[0017] Preferably, the blank shell of the ingot in S1 has a blank size of 100-300 mm*100-300 mm rectangular blank, and the mold has a gap with a rectangular tube cross-section. The gap in the mold is a maze-like tortuous direction from top to bottom to improve the powder pressing force and the strength after pressing.

[0018] Preferably, the maze-like zigzag movement of the powder along the gap under the action of the pressing force is as follows: the powder first moves downward, then horizontally, then upward, then horizontally, then downward, then horizontally, then upward, then horizontally, and then downward along the gap in the mold to form the final rectangular billet shell. Multiple zigzag movements can increase the resistance to powder movement and improve the density and strength of the billet shell after pressing.

[0019] Preferably, the powder is uniformly fed into a mold for pressing a composite gear steel ingot shell, and the pressing machine presses the powder into an ingot shell in a sinusoidal motion, with a pressing frequency of 150 to 200 times / min and a pressing amplitude of 2 to 4 mm. The thickness of the ingot shell after pressing is 5 to 45 mm, and the density is 6.8 to 7.2 g / cm 3 .

[0020] Preferably, the composition of the molten steel in S2 adopts the 20CrMnTi composition system, recorded as the second metal, and the mass percentage is: C: 0.17~0.24%, Si: 0.17~0.30%, Mn: 0.8~1.0%, P: ≤0.015%, S: ≤0.015%, Ti: 0.04-0.06%, and the rest is Fe and unavoidable impurities.

[0021] After the molten steel is injected into the ingot shell, the temperature difference between the ingot shell after pressing and the molten steel reaches more than 1500℃, while the temperature of the molten steel and the solidus temperature is only about 100℃. Therefore, the molten steel will quickly solidify a second metal layer on the inner surface of the ingot shell. The ingot shell and the second metal layer work together to resist the static pressure of the molten steel.

[0022] Preferably, in said S2, the pulling speed of the casting billet is controlled to be 1-2 m / min by a flow control device, and said flow control device is a stopper rod or a nozzle slider.

[0023] Among them, the crystallizer protection slag is added to the top of the molten steel in the shell of the ingot in S2 to prevent the secondary oxidation of the molten steel and to keep it warm.

[0024] The shell of the ingot in S2 is supported by small-diameter support rollers on all sides, the diameter of the support rollers is 40 to 180 mm, and the roller spacing is 60 to 250 mm.

[0025] Preferably, the diameter of the support roller from the molten steel surface at the top of the ingot shell to 4m downward is 40-50mm, and the roller spacing is 50-70mm; the diameter of the support roller from 4m to 12m is 70-80mm, and the roller spacing is 90-110mm; the diameter of the support roller from 12m downward is 120-140mm, and the roller spacing is 150-250mm.

[0026] Cooling water can be sprayed between the two rollers to control the outer surface temperature of the ingot shell. Before the ingot is straightened, the outer surface temperature of the ingot shell is controlled below 1080°C, and when the outer surface temperature of the ingot shell is lower than 1040°C, cooling water is not sprayed on the outer surface of the ingot shell. The higher temperature is conducive to the rapid sintering reaction of the ingot shell pressed and formed by powder metallurgy.

[0027] After the inside of the ingot is completely solidified, the arc-shaped ingot continuous casting machine cuts the ingot into a fixed length.

[0028] Among them, the ingot is cut to a fixed length and then heated in a heating furnace. The ingot shell formed by powder metallurgy is further sintered in the heating furnace, and then rough rolled and final rolled to form a round bar gear steel blank.

[0029] Preferably, the heating time of the cast billet in the heating furnace is 2 to 3 hours, and the temperature of the soaking section of the heating furnace is 1230 to 1270°C.

[0030] Preferably, the starting rolling temperature during the rolling process is 1170-1230°C, the finishing rolling temperature is 900-950°C, and the billet compression ratio during the rolling process is ≥5, so as to improve the density of the billet shell formed by powder metallurgy.

[0031] Beneficial effects of the present invention:

[0032] 1) The present invention can produce composite gear steel ingots online, wherein the shell and interior of the ingot are made of different materials. Only a container for holding molten steel is required, and subsequent physical processing and vacuum welding are unnecessary. Furthermore, the heat of the molten steel is used to self-sinter the shell of the ingot pressed and formed by powder metallurgy, thereby saving sintering costs and having the advantages of a short process, high production efficiency, and low cost.

[0033] 2) The ingot produced by the present invention is hot-rolled to form a composite gear steel blank, which has a high alloy content in the surface layer and a low alloy content in the inner thickness. The surface of the material has high hardness and high wear resistance, while the core has high toughness and strength, reducing high-energy consumption processes such as carburizing and nitriding in conventional gear production, meeting the requirements of wear resistance and hardness at the tooth position, and ensuring the overall toughness and processability of the gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the vertical flow direction of powder during the process of pressing the composite gear steel ingot shell provided by the present invention;

[0035] Figure 2 for Figure 1 Schematic diagram of the cross section at AA in the middle;

[0036] Figure 3 A schematic vertical cross-sectional view of a mold for pressing a composite gear steel ingot shell provided by the present invention;

[0037] In the figure, 1. Powder; 2. Vertical cross-section of the upper part of the mold for pressing the composite gear steel ingot shell; 3. Vertical cross-section of the lower part of the mold for pressing the composite gear steel ingot shell; 4. The outermost gap in the mold has a cross-sectional shape of a rectangular tube; 5. The innermost gap in the mold has a cross-sectional shape of a rectangular tube. DETAILED DESCRIPTION

[0038] The following is explained in conjunction with specific embodiments:

[0039] Example 1:

[0040] 1. Online production of ingot shells using powder metallurgy technology

[0041] The composition of powder 1 adopts the CrNiMo gear steel composition system with a high carbon content, which is recorded as the first metal. The mass percentage is as follows: C: 1.03%, Si: 0.07%, Mn: 0.54%, P: 0.007%, S: 0.003%, Ni: 1.74%, Cr: 1.53%, Mo: 0.32%, lubricant: 0.5%, and the rest is Fe and unavoidable impurities.

[0042] The particle size of the powder 1 is 200 mesh, and the lubricant is a special lubricant for powder metallurgy gears.

[0043] The size of the billet shell is a rectangular billet of 180mm*220mm. The powder 1 is pressed into the billet shell by a mold. The mold has a gap with a rectangular cross-section. The gap in the mold is a maze-like zigzag direction from top to bottom. Figure 1 、 Figure 2 As shown, the powder 1 moves along the maze-like gap under the action of the pressing force as follows: first downward, then horizontal, then upward, then horizontal, then downward, then horizontal, then upward, then horizontal, then downward, and the powder 1 is gradually pressed from the outermost edge 4 to the innermost edge 5; the cross-sectional view of the mold for pressing the composite gear steel ingot shell is shown in FIG. Figure 3 As shown, it is composed of an upper mold part and a lower mold part, and the gap formed by the combination is the movement trajectory of the above-mentioned powder 1 in the mold.

[0044] Powder 1 is uniformly fed into a mold for pressing composite gear steel ingot shells. The pressing machine presses the powder downward in a sinusoidal motion, and the powder moves along the gap to form ingot shells. The pressing frequency is 170 times / min, the pressing amplitude is 3mm, and the thickness of the ingot shell after pressing is 10mm. The density of the ingot shell is 6.9g / cm 3 .

[0045] 2. Injecting molten steel into the billet shell through the submerged nozzle to form the billet

[0046] A tundish filled with molten steel is arranged above the submerged nozzle. The continuous casting machine injects the molten steel in the tundish into the billet shell through the submerged nozzle, and controls the billet pulling speed to 1.5m / min through the stopper rod. Crystallizer protection slag is added to the top of the molten steel in the billet shell to prevent secondary oxidation of the molten steel and keep it warm.

[0047] The composition of the molten steel adopts the 20CrMnTi composition system, which is recorded as the second metal, and the mass percentage is: C: 0.19%, Si: 0.22%, Mn: 0.93%, P: 0.008%, S: 0.005%, Ti: 0.052%, and the rest is Fe and unavoidable impurities.

[0048] The ingot shell is supported by small diameter support rollers on all sides. The diameter of the support rollers from the molten steel surface at the top of the ingot shell to 4m downwards is 40mm, and the roller spacing is 60mm. The diameter of the support rollers from 4m to 12m is 80mm, and the roller spacing is 110mm. The diameter of the support rollers from 12m downwards is 120mm, and the roller spacing is 150mm.

[0049] Cooling water is sprayed between the two rollers to control the outer surface temperature of the ingot shell. Before the ingot is straightened, the outer surface temperature of the ingot shell is controlled below 1080℃, and when the outer surface temperature of the ingot shell is lower than 1040℃, cooling water is not sprayed on the outer surface of the ingot shell.

[0050] In this embodiment, it is not necessary to spray water for cooling the outer surface of the ingot shell from the molten steel liquid level in the crystallizer downward to 1.8m, because within this distance, heat exchange occurs between the molten steel and the ingot shell, and the molten steel gradually heats the outer surface of the ingot shell to 1040°C, and a second metal layer is rapidly solidified on the inner surface of the ingot shell. After testing, the shell thickness from the molten steel liquid level at the top of the ingot shell to 1.8m downward is 32mm, and the ingot shell of this thickness is fully capable of resisting the static pressure of the molten steel; starting from 1.8m, cooling water is sprayed between the two rollers to control the outer surface temperature of the ingot shell. Before the ingot is straightened, the outer surface temperature of the ingot shell is controlled within the range of 1040-1080°C. According to calculation, the total specific water volume for cooling the ingot is 0.12m 3 Water / t steel.

[0051] The ingot continuous casting machine is an arc-shaped continuous casting machine with an arc radius of 10m. The position where the ingot is completely solidified is 15m below the molten steel surface at the top of the ingot shell. After the ingot runs to the position of the cutting equipment, the cutting equipment cuts the ingot to a fixed length.

[0052] 3. The ingot is hot rolled into round bar gear steel blank

[0053] The ingots cut to length are heated in a heating furnace for 2.5 hours. The temperature of the soaking section of the heating furnace is 1250°C. The shell of the ingot formed by powder metallurgy is further sintered in the heating furnace. Then, they are rough rolled and finished rolled to form round bar gear steel blanks. The starting rolling temperature during the rolling process is 1180°C, the finishing rolling temperature is 910°C, and the ingot compression ratio is 8.

[0054] After testing, the first metal layer is within a depth of 1mm from the surface of the gear steel blank, the second metal layer is below a depth of 2mm from the surface of the gear steel blank, and the transitional component layer is within a depth of 1mm to 2mm from the surface of the gear steel blank. The mass percentage of each component is shown in Table 1 below:

[0055] Table 1. Composition test of gear steel blank in Example 1 (%)

[0056]

[0057] As can be seen in Table 1 above, the composite gear steel blanks produced using this method exhibit significant compositional differences between their surface and interior. The surface contains higher levels of elements such as C and Cr, which enhance hardenability and hardenability. This eliminates the need for carburizing to increase surface carbon, which helps improve the hardness and wear resistance of the finished gear surface, thereby increasing the gear's service life. Testing has shown that the hardness of the gear teeth produced using this composite gear steel blank after quenching is 85HRC, and the hardness of the core is 35HRC. In contrast, the hardness of the gear teeth produced using a normal non-composite gear steel blank after carburizing and quenching is 59HRC. The technology provided by this invention increases the hardness of the gear teeth by approximately 50% without reducing the toughness of the gear core.

[0058] In addition, in the composite gear steel blank produced by this method, the first metal layer containing a high content of precious alloys (Mo, Ni) is only within a depth of 1 mm from the surface of the gear steel blank, and the rest of the position is still a second metal layer with a low alloy content and no precious alloys. While ensuring the toughness of the gear core, the total amount of precious alloy added is small. The present invention has the effect of saving resources and reducing the cost of gear production.

[0059] Example 2:

[0060] The powder 1 in this embodiment adopts a high-carbon CrNiMo gear steel component system, which is recorded as the first metal and has the following mass percentages: C: 1.09%, Si: 0.14%, Mn: 0.58%, P: 0.015%, S: 0.015%, Ni: 1.75%, Cr: 1.8%, Mo: 0.4%, lubricant: 0.6%, and the rest is Fe and unavoidable impurities; the particle size of the powder 1 is 600 mesh, and the lubricant is a special lubricant for powder metallurgy gears.

[0061] The composition of the molten steel adopts the 20CrMnTi composition system, recorded as the second metal, and the mass percentage is: C: 0.23%, Si: 0.29%, Mn: 0.95%, P: 0.014%, S: 0.014%, Ti: 0.058%, and the rest is Fe and inevitable impurities.

[0062] The same method as in Example 1 was used to produce a composite gear steel blank. After testing, the first metal layer was within a depth of 1 mm from the surface of the gear steel blank, the second metal layer was within a depth of 2 mm from the surface of the gear steel blank, and the transitional component layer was within a depth of 1 mm to 2 mm from the surface of the gear steel blank. The mass percentage of each component is shown in Table 2 below:

[0063] Table 2. Composition test of gear steel blank in Example 2 (%)

[0064]

[0065] It can be seen from Table 2 above that there are obvious composition differences between the surface and interior of the composite gear steel blank produced by this method. After testing, the hardness of the gear teeth produced by quenching the composite gear steel blank is 89HRC, and the hardness of the core is 37HRC.

[0066] Example 3:

[0067] The powder 1 in this embodiment adopts a high-carbon CrNiMo gear steel component system, which is recorded as the first metal and has the following mass percentages: C: 1.05%, Si: 0.1%, Mn: 0.55%, P: 0.009%, S: 0.002%, Ni: 1.75%, Cr: 1.65%, Mo: 0.35%, lubricant: 0.5%, and the rest is Fe and unavoidable impurities; the particle size of the powder 1 is 400 mesh, and the lubricant is a special lubricant for powder metallurgy gears.

[0068] The composition of the molten steel adopts the 20CrMnTi composition system, which is recorded as the second metal, and the mass percentage is: C: 0.2%, Si: 0.25%, Mn: 0.9%, P: 0.007%, S: 0.004%, Ti: 0.052%, and the rest is Fe and unavoidable impurities.

[0069] The same method as in Example 1 was used to produce a composite gear steel blank. After testing, the first metal layer was within a depth of 1 mm from the surface of the gear steel blank, the second metal layer was within a depth of 2 mm from the surface of the gear steel blank, and the transitional component layer was within a depth of 1 mm to 2 mm from the surface of the gear steel blank. The mass percentage of each component is shown in Table 2 below:

[0070] Table 3. Composition detection of gear steel blank in Example 3 (%)

[0071]

[0072]

[0073] It can be seen from Table 3 above that there are obvious composition differences between the surface and interior of the composite gear steel blank produced by this method. After testing, the hardness of the gear teeth produced by quenching the composite gear steel blank is 87HRC, and the hardness of the core is 36HRC.

[0074] Comparative Example 1:

[0075] The powder 1 in this comparative example adopts a low-carbon CrNiMo gear steel composition system, which is recorded as the first metal, and its mass percentage is as follows: C: 0.18%, Si: 0.10%, Mn: 0.56%, P: 0.008%, S: 0.002%, Ni: 1.75%, Cr: 1.54%, Mo: 0.33%, lubricant: 0.45%, and the rest is Fe and unavoidable impurities.

[0076] The component system of the molten steel (second metal) and the method for producing the composite ingot are the same as those in Example 1.

[0077] After testing, the first metal layer is within a depth of 1mm from the surface of the gear steel blank, the second metal layer is below a depth of 2mm from the surface of the gear steel blank, and the transitional component layer is within a depth of 1mm to 2mm from the surface of the gear steel blank. The mass percentage of each component is shown in Table 4 below:

[0078] Table 4. Composition test of gear steel blank of comparative example 1 (%)

[0079]

[0080] After testing, the hardness of the gear teeth produced by quenching the composite gear steel blank is 43HRC, which is lower than the hardness of the gear teeth produced in Example 1. This shows that powder with high carbon content is beneficial to improving the hardness of the gear teeth after quenching.

[0081] Comparative Example 2:

[0082] This comparative example does not adopt the composite gear steel ingot casting method described in Example 1, but instead adopts a conventional method to produce ingots. The produced ingots are not composite ingots, and the composition of the surface and core of the ingots is the same. The composition of the ingots adopts a high-carbon CrNiMo gear steel composition system, and the specific composition, in percentage by mass, is as follows: C: 1.03%, Si: 0.07%, Mn: 0.54%, P: 0.007%, S: 0.003%, Ni: 1.74%, Cr: 1.53%, Mo: 0.32%, and the remainder is Fe and unavoidable impurities.

[0083] First, the molten steel is condensed in a crystallizer to form a billet shell. After the billet leaves the crystallizer, water is sprayed on the billet surface for secondary cooling to ensure that the inside of the billet is completely solidified. The solidified billet is then hot rolled into a gear steel blank.

[0084] Testing revealed that the gear produced from this quenched gear steel blank had a hardness of 86 HRC at the teeth and 82 HRC at the core. The high core hardness resulted in poor toughness, making the gear susceptible to overall fracture under alternating loads during use, resulting in a short gear lifespan. Comparative Example 2, which did not utilize the technical method provided in Example 1, resulted in the gear teeth and core having identical compositions. While this improved the hardness of the teeth, it sacrificed overall toughness, shortening the gear's lifespan.

[0085] Comparative Example 3:

[0086] This comparative example adopts the same traditional method as comparative example 2 to produce the casting blank, and in order to ensure the overall toughness of the gear, the composition of the casting blank adopts the 20CrMnTi composition system, which is calculated by mass percentage as follows: C: 0.19%, Si: 0.24%, Mn: 0.95%, P: 0.007%, S: 0.004%, Ti: 0.052%, and the rest is Fe and unavoidable impurities.

[0087] Testing revealed that the gears produced using this gear steel blank after carburizing and quenching had a hardness of 59 HRC at the teeth and 36 HRC at the core. The carbon content at a thickness of 0.8 mm in the teeth after carburizing was 0.52%, approximately 0.51% lower than the carbon content at a thickness of 1 mm in the gears of Example 1. Compared to Example 1, not only was the gear carburizing process increased, resulting in high energy consumption and a lengthy process, but the hardness of the gear teeth was still lower than that of Example 1. This is because the entire gear steel blank in this example utilizes a low-carbon composition, and the carburizing process can only increase the carbon content at a thickness of approximately 0.3 to 0.5% in the teeth, resulting in a still-low hardness and a high risk of tooth breakage.

[0088] In summary, the present invention provides a method for producing composite gear steel ingots, and also provides a high-carbon content CrNiMo gear steel component system for preparing composite gear steel ingot shells. Composite gear steel ingots with ingot shells and ingot interiors made of different materials can be produced online without the need for subsequent physical processing and vacuum welding. The produced ingots can meet the requirements of wear resistance and hardness at the gear tooth position, while ensuring the overall toughness and processability of the gear.

Claims

1. A method for producing composite gear steel ingots, characterized in that: The composite gear steel ingot is formed by casting the ingot shell formed by powder pressing with molten steel; The specific steps include: S1, using powder metallurgy technology to produce in-line casting shell: using a mold to press powder into casting shell; S2, injecting molten steel into the ingot shell through the submerged nozzle: a container containing molten steel is arranged above the submerged nozzle, and the continuous casting machine injects the molten steel in the tundish into the ingot shell through the submerged nozzle for casting, and forms a cast ingot after cooling; The powder in S1 adopts a high-carbon CrNiMo gear steel composition system, and its mass percentage is as follows: C: 1.00-1.10%, Si: 0.05-0.15%, Mn: 0.5-0.6%, P: ≤0.015%, S: ≤0.015%, Cr: 1.5-1.8%, Ni: 1.7-1.8%, Mo: 0.3-0.4%, lubricant: 0.4-0.6%, and the rest is Fe and unavoidable impurities; Step S1: The mold has a slit with a rectangular cross-section, and the slit in the mold is a maze-like zigzag from top to bottom: the powder moves along the slit in the mold first downward, then horizontally, then upward, then horizontally, then downward, then horizontally, then upward, then horizontally, and then downward to form a final rectangular billet shell; The composition of the molten steel in S2 adopts the 20CrMnTi composition system; In the step S2, mold protection slag is added to the top of the molten steel in the slab shell; the slab shell is supported by small-diameter support rollers on all sides, the diameter of the support rollers from the molten steel surface at the top of the slab shell to 4m downward is 40-50mm, the roller spacing is 50-70mm, the diameter of the support rollers from 4m to 12m is 70-80mm, the roller spacing is 90-110mm, and the diameter of the support rollers from 12m downward is 120-140mm, the roller spacing is 150-250mm; The ingot is hot rolled into a composite gear steel blank; wherein, the heating time of the ingot in the heating furnace is 2 to 3 hours, and the temperature of the soaking section of the heating furnace is 1230 to 1270°C; the starting rolling temperature in the hot rolling process is 1170 to 1230°C, the finishing rolling temperature is 900 to 950°C, and the ingot compression ratio is ≥5.

2. The method for producing composite gear steel ingot according to claim 1, characterized in that: The particle size of the powder in S1 is: 600 mesh ≤ the particle size of the powder ≤ 100 mesh.

3. The method for producing composite gear steel ingot according to claim 1, wherein: The size of the billet shell in the S1 is a rectangular billet with a size of 100-300 mm*100-300 mm.

4. The method for producing composite gear steel ingot according to claim 1, wherein: The powder in S1 is uniformly fed into a mold for pressing a composite gear steel ingot shell. The pressing machine presses the powder into an ingot shell in a sinusoidal motion. The pressing frequency is 150 to 200 times / min, the pressing amplitude is 2 to 4 mm, and the thickness of the ingot shell after pressing is 5 to 45 mm and the density is 6.8 to 7.2 g / cm 3 .

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