A medium carbon alloy steel transmission output shaft and its preparation method

Abstract

The invention discloses a transmission output shaft made of medium-carbon alloy steel and a preparation method thereof. The transmission output shaft comprises C: 0.40%-0.50%, Si: 0.10%-0.37%, Mn: 0.40%-0.90%, Cr: 0.45%-1.30%, Ni: 1.00%-2.00%, V: 0.05%-0.30%, Mo: 0.15%-0.40%, S: ≤0.025%, P: ≤0.025%, Cu: ≤0.25%, and the remainder is Fe, so that the elements play a synergistic role with each other, a new carburizing heat treatment process is developed, and the geometrical dimension deformation requirements of parts after carburizing heat treatment are met. The transmission output shaft made of medium-carbon alloy steel has high static torsional strength and fatigue life, ensures that the parts have high strength and the core has good toughness, and solves the problem of low strength of the output shaft of a large torque transmission.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical industry, and relates to a transmission output shaft made of medium carbon alloy steel and a preparation method thereof. Background Art

[0002] As an important part of the automobile power system, the transmission plays a role in changing the torque, speed and driving direction, so that the driving force, speed and driving direction of the automobile can adapt to different working conditions, and at the same time, it also makes the engine power more fully and reasonably utilized. Heavy trucks have a heavy load, usually between 14 tons and 100 tons; and because of the complex and changeable road conditions in my country, the requirements for transmission reliability are getting higher and higher. The transmission output shaft transmits the torque transmitted from the engine to the transmission to the drive shaft. Its structural schematic diagram and cross-sectional diagram are shown in Figure 1. The design length of the output shaft is 250~300mm, and the outer diameter is There are splines at both ends, one end is a coarse spline and the other end is a fine spline. The spline shaft head at the fine spline end has threads, and the large spline end has an inner hole. Generally, low-carbon alloy steel, such as 17CrNiMo6 or 20CrNi3, is selected. The parts are carburized and heat treated to obtain high surface hardness and good core toughness, so that they have excellent fatigue and impact properties.

[0003] As the transmission develops towards high torque, high power density and light weight, the performance requirements for the transmission output shaft are getting higher and higher. Heavy truck transmissions with input torque of 2400N.m-3200N.m are the focus of future development. According to the transmission ratio and the provisions of "QC / T568 Technical Conditions and Bench Test Methods for Automobile Mechanical Transmission Assembly", the transmission output static torsional strength is required to reach 72KN.m or even higher, but the static torsional strength of the materials currently used cannot meet this requirement.

[0004] To improve the static torsional strength of shaft parts, the industry currently uses induction quenching treatment of medium carbon steel, such as the public patents CN107470852 B, CN105714087A, CN107470852B, etc., to obtain high static torsional strength. However, due to the complex structure of the output shaft of the heavy truck transmission, the large spline, small spline and the intermediate optical axis have different diameters, and the surface needs to be induction hardened. The design of the process parameters of induction heating is difficult; at the same time, the inner hole of the large spline needs a high surface hardness to improve wear resistance because the bearing is assembled, but the inner hole wall is thin. If the induction heating parameters are not designed reasonably, it is very easy to overlap with the hardened layer generated by surface induction, causing cracks at the end of the output shaft. Medium carbon steel is rarely carburized heat treated because its high hardenability will cause the core hardness of shaft parts to be too high, thereby increasing brittleness; and there may also be large deformation during heat treatment, which may cause the parts to be unable to be assembled and used. In summary, the existing technology has the problem of low strength of the output shaft of the large torque transmission, and the hardness of the core is too high, which leads to increased brittleness and the problem of being unable to be assembled. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a transmission output shaft made of medium carbon alloy steel and a preparation method thereof, which ensures that the part has high strength while having good toughness in the core and meets the requirements for geometric deformation of the part after carburizing heat treatment, thereby solving the problem of low strength of the spline output shaft of a high-torque transmission.

[0006] The present invention is achieved through the following technical solutions:

[0007] A transmission output shaft made of medium carbon alloy steel, comprising:

[0008] Calculated by mass percentage, it includes the following components:

[0009] C: 0.40% ~ 0.50%, Si: 0.10% ~ 0.37%, Mn: 0.40% ~ 0.90%, Cr: 0.45% ~ 1.30%, Ni: 1.00% ~ 2.00%, V: 0.05% ~ 0.30%, Mo: 0.15% ~ 0.40%, S: 0 ~ 0.025%, P: 0 ~ 0.025%, Cu: 0 ~ 0.25%, and the rest is Fe.

[0010] Preferably, the surface hardness of the transmission output shaft made of medium carbon alloy steel reaches 50-55HRC, and the core hardness is 40-45HRC.

[0011] Preferably, the static torsional strength of the transmission output shaft made of medium carbon alloy steel is at least 83 KN·m.

[0012] Preferably, the surface microstructure of the transmission output shaft made of medium carbon alloy steel is tempered troostite, and the core microstructure is tempered troostite.

[0013] A method for preparing a transmission output shaft made of medium carbon alloy steel, comprising:

[0014] The component materials are weighed according to the following mass percentages: C: 0.40%-0.50%, Si: 0.10%-0.37%, Mn: 0.40%-0.90%, Cr: 0.45%-1.30%, Ni: 1.00%-2.00%, V: 0.05%-0.30%, Mo: 0.15%-0.40%, S: 0-0.025%, P: 0-0.025%, Cu: 0-0.25%, and the remainder is Fe. They are melted and smelted, and are successively refined outside the furnace, vacuum degassing and cast to form a round steel bar. The round steel bar is then forged to obtain an output shaft blank, the output shaft blank is normalized, and the output shaft semi-finished product is obtained after fine machining. The output shaft semi-finished product is then placed in a carburizing furnace for carburizing treatment, and is successively heated, strongly carburized, diffused, heat-insulated, oil-cooled, and tempered and air-cooled to obtain a transmission output shaft made of medium-carbon alloy steel.

[0015] Preferably, the specific process of forging is:

[0016] According to the specifications of the parts, the round steel bars are cut into the required size, and then the cut round steel bars are subjected to medium frequency induction heating to 1050℃~1250℃, and are rolled into output shaft blanks through a wedge cross rolling process.

[0017] Preferably, the process conditions for normalizing the output shaft blank are: heating to a temperature of 900°C to 930°C, keeping warm for 2 to 5 hours, then cooling to 600°C to 670°C with the furnace, keeping warm for 2 to 4 hours, cooling out of the furnace, and the hardness is required to be controlled at 170 to 240 HBW.

[0018] Preferably, the specific processing process of the finishing treatment is:

[0019] The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

[0020] Preferably, the carburizing heat treatment process is specifically as follows: rapidly heating to 855-885°C and keeping warm for 20-30 minutes, the carbon potential in the heating stage is 0.70-0.85C%; heating to 910-935°C for strong infiltration for 100-140 minutes, and the carbon potential in the strong infiltration stage is 1.0-1.15C%; then diffusing at 910-935°C for 130-150 minutes, and the carbon potential in the diffusion stage is 0.70-0.85C%; finally, rapidly cooling to 840-865°C and keeping warm for 30-50 minutes, and the carbon potential in the insulation stage is 0.60-0.75C%; after carburizing heat treatment, pulling from the rear chamber of the furnace to the front chamber for oil-cooling quenching, cooling with graded cooling oil, the oil temperature is 60-80°C, the stirring time is 30-50 minutes, and the stirring speed is 100-200rpm. After the oil cooling is completed, drain the oil for 15 to 30 minutes. After cleaning, heat the output shaft again to 400°C to 460°C for tempering, keep it in a nitrogen atmosphere for 2h to 5h, and then air-cool it to room temperature to obtain a medium-carbon alloy steel transmission output shaft.

[0021] Preferably, the atmosphere for the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is: the nitrogen flow rate is 4.0 to 6.0 m 3 / h, methanol flow rate is 4.5~5.5L / h.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] The invention provides a transmission output shaft made of medium-carbon alloy steel and a preparation method thereof. By optimizing the ratio of chemical elements in the alloy, the chemical composition of the transmission output shaft is C: 0.40%-0.50%, Si: 0.10%-0.37%, Mn: 0.40%-0.90%, Cr: 0.45%-1.30%, Ni: 1.00%-2.00%, V: 0.05%-0.30%, Mo: 0.15%-0.40%, S: allowable residual content ≤0.025%, P: allowable residual content ≤0.025%, Cu: allowable residual content ≤0.25%, and the remainder is Fe, so that the elements play a synergistic role with each other, and a new carburizing heat treatment process is developed to ensure that the core of the part has good toughness while obtaining high strength, and meet the geometrical dimension deformation requirements of the part after the carburizing heat treatment, so that the transmission output shaft made of medium-carbon alloy steel has high static torsional strength and fatigue life, thereby solving the problem of low strength of the spline output shaft of a large torque transmission.

[0024] Furthermore, carbon is the main element of steel. The carbon content plays a decisive role in the core hardness and hardenability of parts after carburizing and quenching. If the carbon content is too low, the hardenability is poor and the strength decreases; if the carbon content is too high, the forgeability and weldability deteriorate. Therefore, the C content is controlled at 0.40% to 0.50%.

[0025] Furthermore, it exists as a solid solution in ferrite and austenite, strongly promoting the graphitization of C; increasing the annealing, normalizing and quenching temperatures; improving wear resistance, and the Si content is controlled at 0.10% to 0.37%;

[0026] Furthermore, manganese is a good deoxidizer and desulfurizer, forming MnS, eliminating hot brittleness and improving hot working properties; significantly improving the strength of medium and low carbon pearlite steel, and reducing ductility; reducing the critical cooling rate of steel and improving the hardenability of steel. The Mn content is controlled at 0.40% to 0.90%;

[0027] Furthermore, phosphorus is generally a harmful element, which drastically reduces plasticity and toughness and increases cold brittleness. Sulfur is a harmful element in most cases, mixed in solid steel as FeS, which has severe FeS segregation, causing the steel to crack easily during hot processing (hot brittleness). Adding Mn can prevent hot brittleness, and the content in high-quality steel is <0.04%. In mechanical manufacturing, in order to improve the cutting performance of certain steels, the sulfur content is artificially increased to form sulfides to interrupt the continuity of the matrix.

[0028] Furthermore, chromium is a carbide-forming element, which improves the wear resistance of the carburized layer; reduces the critical cooling rate of steel, improves the hardenability of steel; increases the strength and hardness of steel and the tough-brittle transition temperature, improves the mechanical properties, and the Cr content is controlled at 0.45% to 1.30%;

[0029] Furthermore, nickel and Fe are infinitely dissolved in solid solution and are the main elements for forming and stabilizing austenite; strengthening ferrite, refining and increasing pearlite, improving strength; improving fatigue resistance, reducing steel sensitivity to notches, and improving low-temperature toughness of steel. The content of Ni is controlled at 1.00% to 2.00%.

[0030] Furthermore, molybdenum has a solid solution strengthening effect on ferrite, improves carbide stability, improves steel strength; improves tempering resistance and high temperature strength; reduces the critical cooling rate of steel and improves the hardenability of steel; Mo content is controlled at 0.15% to 0.40%

[0031] Furthermore, vanadium has a strong chemical affinity with carbon and nitrogen, and is easy to form vanadium carbide or vanadium nitride, which plays a role in fine grain strengthening and precipitation strengthening of alloy steel. The V content is controlled at 0.05% to 0.30%.

[0032] Furthermore, after carburizing heat treatment, the surface hardness of the parts reaches 50-55HRC, the core hardness is 40-45HRC, the surface microstructure is tempered troostite, and the core microstructure is also tempered troostite. Through the single static torsional strength test, the static torsional strength reaches 83KN·m, which meets the static torsional strength requirements of the output shaft of the high-torque transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of the transmission output shaft, FIG. (a) is a main view, and FIG. (b) is a cross-sectional view;

[0034] Figure 2 The surface microstructure of the transmission output shaft made of medium carbon alloy steel;

[0035] Figure 3 The core microstructure of the transmission output shaft made of medium carbon alloy steel. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0038] The present invention proposes to develop a high-performance medium-carbon alloy steel material and a new carburizing heat treatment process, so that the static torsional strength of the output shaft meets the requirements of a large torque transmission. The chemical composition of the medium-carbon steel is C: 0.40% to 0.50%, Si: 0.10% to 0.37%, Mn: 0.40% to 0.90%, Cr: 0.45% to 1.30%, Ni: 1.00% to 2.00%, V: 0.05% to 0.30%, Mo: 0.15% to 0.40%, S: 0 to 0.025%, P: 0 to 0.025%, Cu: 0 to 0.25%, and the remainder is Fe.

[0039] 1) Carbon:

[0040] Carbon is the main element of steel. The carbon content plays a decisive role in the core hardness and hardenability of parts after carburizing and quenching. If the carbon content is too low, the hardenability is poor and the strength decreases; if the carbon content is too high, the forgeability and weldability deteriorate. Therefore, the C content is controlled at 0.40% to 0.50%.

[0041] 2) Silicon

[0042] It exists in ferrite and austenite as a solid solution, strongly promoting the graphitization of C; increasing the annealing, normalizing and quenching temperatures; improving wear resistance, and the Si content is controlled at 0.10% to 0.37%;

[0043] 3) Manganese

[0044] Manganese is a good deoxidizer and desulfurizer, forming MnS, eliminating hot brittleness and improving hot working performance; significantly improving the strength of medium and low carbon pearlite steel, and reducing ductility; reducing the critical cooling rate of steel and improving the hardenability of steel. The Mn content is controlled at 0.40% to 0.90%;

[0045] 4) Phosphorus

[0046] Phosphorus is generally a harmful element that drastically reduces plasticity and toughness and increases cold brittleness.

[0047] 5) Sulfur

[0048] Sulfur is a harmful element in most cases. It is mixed in solid steel as FeS. FeS segregation is serious, which makes the steel easy to crack (hot brittleness) during hot processing. Adding Mn can prevent hot brittleness. The content in high-quality steel is less than 0.04%. In mechanical manufacturing, in order to improve the cutting performance of certain steels, the sulfur content is artificially increased to form sulfides to interrupt the continuity of the matrix.

[0049] 6) Chromium

[0050] Carbide-forming elements improve the wear resistance of the carburized layer; reduce the critical cooling rate of steel and improve the hardenability of steel; increase the strength and hardness of steel and the tough-brittle transition temperature, and improve the mechanical properties. The Cr content is controlled at 0.45% to 1.30%;

[0051] 7) Nickel

[0052] Nickel is infinitely dissolved in Fe and is the main element for forming and stabilizing austenite; it strengthens ferrite, refines and increases pearlite, and improves strength; it improves fatigue resistance, reduces steel's sensitivity to notches, and improves steel's low-temperature toughness. The Ni content is controlled at 1.00% to 2.00%.

[0053] 8) Molybdenum

[0054] Molybdenum has a solid solution strengthening effect on ferrite, improves carbide stability, improves steel strength; improves tempering resistance and high temperature strength; reduces the critical cooling rate of steel and improves the hardenability of steel; Mo content is controlled at 0.15% to 0.40%

[0055] 9) Vanadium

[0056] Vanadium has a strong chemical affinity with carbon and nitrogen, and is easy to form vanadium carbide or vanadium nitride, which plays a role in fine grain strengthening and precipitation strengthening of alloy steel. The V content is controlled at 0.05% to 0.30%.

[0057] The specific process is as follows:

[0058] 1) According to the chemical composition of the material, the round steel bar is made by electric furnace or converter smelting and external refining (LF) + vacuum degassing (VD or RH) + continuous casting / mold casting process.

[0059] 2) Forging

[0060] According to the specifications of the parts, the round steel bars are cut into the required size, and then the cut round steel bars are subjected to medium frequency induction heating to 1050℃~1250℃, and are rolled into output shaft blanks through a wedge cross rolling process.

[0061] 3) Normalizing

[0062] In order to facilitate the processing of the output shaft blank and improve the internal microstructure, the output shaft blank obtained in step 2) is normalized, heated to 900°C-930°C, kept warm for 2-5 hours, cooled to 600°C-670°C with the furnace, kept warm for 2-4 hours, and cooled out of the furnace. The hardness is required to be controlled at 170-240 HBW;

[0063] 4) Finishing

[0064] The cooled output shaft blank is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling, and knurling to obtain a semi-finished output shaft;

[0065] 5) Carburizing heat treatment

[0066] The processed output shaft parts are placed in a carburizing furnace for carburizing treatment. The carburizing atmosphere is nitrogen and methanol. After heating, strong carburizing, diffusion, heat preservation, oil cooling, tempering and air cooling, the parts are obtained. Among them:

[0067] The ratio of nitrogen and methanol in the carburizing medium is: nitrogen flow rate is 4.0~6.0m 3 / h, methanol flow rate is 4.5~5.5L / h;

[0068] The specific carburizing heat treatment process is as follows: quickly heat up to 855-885°C and keep warm for 20-30 minutes, the carbon potential in the heating stage is 0.70-0.85C%; heat up to 910-935°C for strong infiltration for 100-140 minutes, and the carbon potential in the strong infiltration stage is 1.0-1.15C%; then diffuse at 910-935°C for 130-150 minutes, and the carbon potential in the diffusion stage is 0.70-0.85C%; finally, quickly cool down to 840-865°C and keep warm for 30-50 minutes, and the carbon potential in the insulation stage is 0.60-0.75C%.

[0069] After carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil cooling quenching. The cooling is carried out using graded cooling oil. The oil temperature is 60-80°C, the stirring time is 30-50 minutes, and the stirring speed is 100-200rpm. After the oil cooling is completed, the oil is drained for 15-30 minutes. After cleaning, the output shaft is heated to 400-460°C again for tempering treatment, kept in a nitrogen atmosphere for 2h-5h, and then air-cooled to room temperature to obtain the output shaft parts.

[0070] After carburizing heat treatment, the surface hardness of the parts reaches 50-55HRC, and the core hardness is 40-45HRC. Figure 2 and Figure 3 As shown, the surface microstructure is tempered troostite, and the core microstructure is also tempered troostite. Through the single static torsional strength test, the static torsional strength reaches 83KN·m, which meets the static torsional strength requirements of the output shaft of the large torque transmission.

[0071] Embodiment 1,

[0072] A method for preparing a transmission output shaft made of medium carbon alloy steel, comprising:

[0073] The component materials are weighed according to the following mass percentages: C: 0.40%, Si: 0.37%, Mn: 0.40%~0.90%, Cr: 0.45%, Ni: 2.00%, V: 0.05%, Mo: 0.40%, S: 0, P: 0.025%, Cu: 0, and the balance is Fe, and melt smelting is carried out, and then the round steel rod is made into an output shaft blank by forging, and the output shaft blank is normalized and finely processed to obtain an output shaft semi-finished product, and then the output shaft semi-finished product is placed in a carburizing furnace for carburizing treatment, and then heated, strongly carburized, diffused, heat-insulated, oil-cooled and tempered and air-cooled to obtain a transmission output shaft made of medium carbon alloy steel.

[0074] The specific process of forging is: cutting the round steel bar into the required size according to the part specifications, then heating the cut round steel bar to 1050° C. by medium frequency induction heating, and rolling it into an output shaft blank by wedge cross rolling process.

[0075] The process conditions for normalizing the output shaft blank are as follows: heating the blank to 900°C, keeping it warm for 2 hours, then cooling it to 600°C in the furnace, keeping it warm for 2 hours, cooling it out of the furnace, and the hardness is required to be controlled at 170HBW.

[0076] The specific processing process of the finishing process is as follows:

[0077] The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

[0078] The carburizing heat treatment process is specifically as follows: quickly heating to 885°C and keeping warm for 30 minutes, the carbon potential in the heating stage is 0.85C%; heating to 935°C for strong penetration, the time is 140 minutes, and the carbon potential in the strong penetration stage is 1.15C%; then diffusion is carried out at 910-935°C for 150 minutes, and the carbon potential in the diffusion stage is 0.85C%; finally, the temperature is quickly cooled to 865°C and kept warm for 50 minutes, and the carbon potential in the insulation stage is 0.75C%; after carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil cooling quenching, and graded cooling oil is used for cooling, the oil temperature is 80°C, the stirring time is 50 minutes, and the stirring speed is 00rpm. After the oil cooling is completed, drain the oil for 15-30 minutes. After cleaning, the output shaft is heated to 460°C again for tempering treatment, kept warm for 5 hours in a nitrogen atmosphere, and then air-cooled to room temperature to obtain a transmission output shaft made of medium carbon alloy steel.

[0079] The atmosphere for the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is such that the nitrogen flow rate is 4.0 m 3 / h, and the methanol flow rate is 4.5L / h.

[0080] Embodiment 2,

[0081] A method for preparing a transmission output shaft made of medium carbon alloy steel, comprising:

[0082] The component materials are weighed according to the following mass percentages: C: 0.50%, Si: 0.10%, Mn: 0.40%~0.90%, Cr: 1.30%, Ni: 1.00%, V: 0.30%, Mo: 0.15%, S: 0.025%, P: 0, Cu: 0.25%, and the rest is Fe, and melt smelting is carried out, and then the round steel rod is made into an output shaft blank by forging, and the output shaft blank is normalized and finished to obtain an output shaft semi-finished product. The output shaft semi-finished product is placed in a carburizing furnace for carburizing treatment, and then heated, strongly carburized, diffused, kept warm, oil cooled and tempered and air cooled to obtain a transmission output shaft made of medium carbon alloy steel.

[0083] The specific forging process is: the round steel bar is cut into required sizes according to the part specifications, the cut round steel bar is then subjected to medium frequency induction heating to 11250° C., and then rolled into an output shaft blank through a wedge cross rolling process.

[0084] The process conditions for normalizing the output shaft blank are as follows: heating the blank to 930°C, keeping it warm for 5 hours, then cooling it to 670°C in the furnace, keeping it warm for 4 hours, cooling it out of the furnace, and the hardness is required to be controlled at 240HBW.

[0085] The specific processing process of the finishing process is as follows:

[0086] The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

[0087] The carburizing heat treatment process is specifically as follows: quickly heating to 855°C and keeping warm for 20 minutes, the carbon potential in the heating stage is 0.70C%; heating to 910°C for strong penetration, the time is 1000 minutes, the carbon potential in the strong penetration stage is 1.0C%; then diffusion is carried out at 910°C for 130 minutes, the carbon potential in the diffusion stage is 0.70C%; finally, the temperature is quickly reduced to 840°C and kept warm for 30 minutes, the carbon potential in the insulation stage is 0.60C%; after carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil cooling quenching, and graded cooling oil is used for cooling, the oil temperature is 60°C, the stirring time is 30 minutes, and the stirring speed is 100rpm. After the oil cooling is completed, drain the oil for 15 minutes. After cleaning, the output shaft is heated to 400°C again for tempering treatment, kept warm for 2 hours in a nitrogen atmosphere, and then air-cooled to room temperature to obtain a transmission output shaft made of medium carbon alloy steel.

[0088] The atmosphere for the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is 6.0 m 3 / h, and the methanol flow rate is 4.5L / h.

[0089] Embodiment 3,

[0090] A method for preparing a transmission output shaft made of medium carbon alloy steel, comprising:

[0091] The component materials are weighed according to the following mass percentages: C: 0.45%, Si: 0.21%, Mn: 0.65%, Cr: 0.75%, Ni: 1.3%, V: 0.15%, Mo: 0.25%, S: 0.015%, P: 0.01%, Cu: 0.15%, and the remainder is Fe, and melt smelting is carried out, and then the round steel rods are made through out-of-furnace refining, vacuum degassing + and continuous casting / die casting processes, and then the round steel rods are forged to obtain an output shaft blank, and the output shaft blank is normalized and finely processed to obtain an output shaft semi-finished product, and then the output shaft semi-finished product is placed in a carburizing furnace for carburizing treatment, and then heated, strongly carburized, diffused, kept warm, oil cooled and tempered and air cooled to obtain a transmission output shaft made of medium carbon alloy steel.

[0092] The specific process of forging is: cutting the round steel bar into the required size according to the part specifications, then heating the cut round steel bar to 1100° C. by medium frequency induction heating, and rolling it into an output shaft blank by wedge cross rolling process.

[0093] The process conditions for normalizing the output shaft blank are as follows: heating the blank to 920°C, keeping it warm for 3 hours, then cooling it to 630°C in the furnace, keeping it warm for 3 hours, cooling it out of the furnace, and the hardness is required to be controlled at 190HBW.

[0094] The specific processing process of the finishing process is as follows:

[0095] The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

[0096] The carburizing heat treatment process is specifically as follows: quickly heating to 865°C and keeping warm for 25 minutes, the carbon potential in the heating stage is 0.77C%; heating to 920°C for strong penetration, the time is 120 minutes, the carbon potential in the strong penetration stage is 1.11C%; then diffusion is carried out at 920°C, the time is 140 minutes, the carbon potential in the diffusion stage is 0.85C%; finally, the temperature is quickly reduced to 850°C and kept warm for 40 minutes, the carbon potential in the insulation stage is 0.7C%; after carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil cooling quenching, and graded cooling oil is used for cooling, the oil temperature is 70°C, the stirring time is 40 minutes, and the stirring speed is 150rpm. After the oil cooling is completed, drain the oil for 20 minutes. After cleaning, the output shaft is heated to 430°C again for tempering treatment, kept warm in a nitrogen atmosphere for 3 hours, and then air-cooled to room temperature to obtain a transmission output shaft made of medium carbon alloy steel.

[0097] The atmosphere for the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is 5.0 m 3 / h, methanol flow rate is 5.0L / h.

[0098] Embodiment 4,

[0099] A method for preparing a transmission output shaft made of medium carbon alloy steel, comprising:

[0100] The component materials are weighed according to the following mass percentages: C: 0.47%, Si: 0.28%, Mn: 0.85%, Cr: 1.1%, Ni: 1.8%, V: 0.25%, Mo: 0.35%, S: 0.0008%, P: 0.001%, Cu: 0.1%, and the remainder is Fe, and melt smelting is carried out, and then the round steel rods are made through out-of-furnace refining, vacuum degassing + and continuous casting / die casting processes, and then the round steel rods are forged to obtain an output shaft blank, and the output shaft blank is normalized and finished to obtain an output shaft semi-finished product, and then the output shaft semi-finished product is placed in a carburizing furnace for carburizing treatment, and then heated, strongly carburized, diffused, kept warm, oil cooled and tempered and air cooled to obtain a transmission output shaft made of medium carbon alloy steel.

[0101] The specific process of forging is: cutting the round steel bar into the required size according to the part specifications, then heating the cut round steel bar to 1200° C. by medium frequency induction heating, and rolling it into an output shaft blank by wedge cross rolling process.

[0102] The process conditions for normalizing the output shaft blank are as follows: heating the blank to 925°C, keeping it warm for 4 hours, then cooling it to 655°C in the furnace, keeping it warm for 3 hours, cooling it out of the furnace, and the hardness is required to be controlled at 220HBW.

[0103] The specific processing process of the finishing process is as follows:

[0104] The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

[0105] The carburizing heat treatment process is specifically as follows: quickly heating to 870°C and keeping warm for 25 minutes, the carbon potential in the heating stage is 0.82C%; heating to 930°C for strong penetration, the time is 130 minutes, the carbon potential in the strong penetration stage is 1.14C%; then diffusion is carried out at 930°C, the time is 140 minutes, the carbon potential in the diffusion stage is 0.82C%; finally, the temperature is quickly reduced to 860°C and kept warm for 45 minutes, the carbon potential in the insulation stage is 0.71C%; after carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil cooling quenching, and graded cooling oil is used for cooling, the oil temperature is 75°C, the stirring time is 45 minutes, and the stirring speed is 180rpm. After the oil cooling is completed, drain the oil for 25 minutes. After cleaning, the output shaft is heated to 450°C again for tempering treatment, kept warm in a nitrogen atmosphere for 4 hours, and then air-cooled to room temperature to obtain a transmission output shaft made of medium carbon alloy steel.

[0106] The atmosphere for the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is such that the nitrogen flow rate is 4.5m 3 / h, methanol flow rate is 5L / h.

[0107] Embodiment 5,

[0108] A method for preparing a transmission output shaft made of medium carbon alloy steel, comprising:

[0109] The component materials are weighed according to the following mass percentages: C: 0.50%, Si: 0.10%, Mn: 0.40%~0.90%, Cr: 1.30%, Ni: 2.00%, V: 0.30%, Mo: 0.40%, S: 0, P: 0, Cu: 0, and the rest is Fe, and melt smelting is carried out, and then the round steel rods are made through out-of-furnace refining, vacuum degassing + and continuous casting / die casting processes, and then the round steel rods are forged to obtain an output shaft blank, and the output shaft blank is normalized and finely processed to obtain an output shaft semi-finished product, and then the output shaft semi-finished product is placed in a carburizing furnace for carburizing treatment, and then heated, strongly carburized, diffused, kept warm, oil cooled and tempered and air cooled to obtain a transmission output shaft made of medium carbon alloy steel.

[0110] The specific process of forging is: cutting the round steel bar into the required size according to the part specifications, then heating the cut round steel bar to 1250° C. by medium frequency induction heating, and rolling it into an output shaft blank by wedge cross rolling process.

[0111] The process conditions for normalizing the output shaft blank are as follows: heating the blank to 930°C, keeping it warm for 5 hours, then cooling it to 650°C in the furnace, keeping it warm for 4 hours, cooling it out of the furnace, and the hardness is required to be controlled at 190HBW.

[0112] The specific processing process of the finishing process is as follows:

[0113] The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

[0114] The carburizing heat treatment process is specifically as follows: quickly heating to 885°C and keeping warm for 30 minutes, the carbon potential in the heating stage is 0.85C%; heating to 935°C for strong penetration, the time is 100 minutes, the carbon potential in the strong penetration stage is 1.15C%; then diffusion is carried out at 935°C for 130 minutes, the carbon potential in the diffusion stage is 0.70C%; finally, the temperature is quickly reduced to 840-865°C and kept warm for 30 minutes, the carbon potential in the insulation stage is 0.75C%; after carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil cooling quenching, and graded cooling oil is used for cooling, the oil temperature is 80°C, the stirring time is 50 minutes, and the stirring speed is 200rpm. After the oil cooling is completed, drain the oil for 30 minutes. After cleaning, the output shaft is heated to 460°C again for tempering treatment, kept warm in a nitrogen atmosphere for 5 hours, and then air-cooled to room temperature to obtain a transmission output shaft made of medium carbon alloy steel.

[0115] The atmosphere for the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is 6.0 m 3 / h, and the methanol flow rate is 5.5L / h.

[0116] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A transmission output shaft made of medium carbon alloy steel, characterized in that: Calculated by mass percentage, it includes the following components: C: 0.40%~0.50%, Si: 0.10%~0.37%, Mn: 0.40%~0.90%, Cr: 0.45%~1.30%, Ni: 1.00%~2.00%, V: 0.05%~0.30%, Mo: 0.15%~0.40%, S: 0~0.025%, P: 0~0.025%, Cu: 0~0.25%, the rest is Fe; The static torsional strength of the medium carbon alloy steel transmission output shaft is at least ; The surface microstructure of the medium carbon alloy steel transmission output shaft is tempered troostite, and the core microstructure is tempered troostite; The method for preparing a transmission output shaft made of medium carbon alloy steel comprises: The component materials are weighed according to the following mass percentages: C: 0.40%~0.50%, Si: 0.10%~0.37%, Mn: 0.40%~0.90%, Cr: 0.45%~1.30%, Ni: 1.00%~2.00%, V: 0.05%~0.30%, Mo: 0.15%~0.40%, S: 0~0.025%, P: 0~0.025%, Cu: 0~0.25%, and the balance is Fe, and melt smelting is performed, and then the round steel rod is made by refining outside the furnace, vacuum degassing and casting processes in sequence, and then the prepared round steel rod is forged to obtain an output shaft blank, and the output shaft blank is normalized and finely processed to obtain an output shaft semi-finished product, and then the output shaft semi-finished product is placed in a carburizing furnace for carburizing treatment, and then heated, strongly infiltrated, diffused, heat-insulated, oil-cooled and tempered and air-cooled in sequence to obtain a transmission output shaft made of medium carbon alloy steel; The carburizing treatment process is specifically as follows: rapidly heating to 855-885°C and keeping warm for 20-30 minutes, the carbon potential in the heating stage is 0.70-0.85C; heating to 910-935°C for strong infiltration for 100-140 minutes, the carbon potential in the strong infiltration stage is 1.0-1.15C; then diffusion is carried out at 910-935°C for 130-150 minutes, the carbon potential in the diffusion stage is 0.70-0.85C; finally, rapidly cooling to 840-865°C and keeping warm for 30-50 minutes. min, and the carbon potential in the insulation stage is 0.60~0.75C; after carburizing heat treatment, it is pulled from the rear chamber of the furnace to the front chamber for oil-cooling quenching, and graded cooling oil is used for cooling. The oil temperature is 60~80℃, the stirring time is 30~50min, and the stirring speed is 100~200rpm; after oil cooling, the oil is drained for 15~30min; after cleaning, the output shaft is heated to 400℃~460℃ again for tempering treatment, and is kept in a nitrogen atmosphere for 2h~5h and then air-cooled to room temperature to obtain a transmission output shaft made of medium carbon alloy steel.

2. The transmission output shaft made of medium carbon alloy steel according to claim 1, characterized in that: The surface hardness of the medium carbon alloy steel transmission output shaft reaches 50-55HRC, and the core hardness is 40-45HRC.

3. According to claim 1, the transmission output shaft made of medium carbon alloy steel, the specific forging process is: According to the specifications of the parts, the round steel bars are cut into the required size, and then the cut round steel bars are subjected to medium frequency induction heating to 1050℃~1250℃, and are rolled into output shaft blanks through wedge cross rolling process.

4. According to the transmission output shaft made of medium carbon alloy steel as described in claim 1, the process conditions for normalizing treatment of the output shaft blank are: heating temperature reaches 900℃~930℃, keeping warm for 2~5h, then cooling to 600℃~670℃ with the furnace, keeping warm for 2~4h, cooling out of the furnace, and the hardness is required to be controlled at 170~240HBW.

5. According to the medium carbon alloy steel transmission output shaft of claim 1, the specific processing process of the finishing treatment is: The output shaft blank after normalizing treatment is processed, and the processing steps are rough turning, deep hole drilling, fine turning, inner hole boring, oil hole drilling and knurling to obtain the output shaft semi-finished product.

6. According to the medium carbon alloy steel transmission output shaft of claim 1, the atmosphere of the carburizing treatment is nitrogen and methanol, wherein the ratio of nitrogen to methanol is 4.0-6.0 m 3 / h, methanol flow rate is 4.5~5.5L / h.

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