CN114959502A - Nb microalloyed fine-grain high-torque output gear steel, manufacturing method thereof and machining process for producing gears - Google Patents
Nb microalloyed fine-grain high-torque output gear steel, manufacturing method thereof and machining process for producing gears Download PDFInfo
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Abstract
The invention provides Nb microalloyed fine grain high torque output gear steel, a manufacturing method thereof and a processing technology for producing gears, and the Nb microalloyed fine grain high torque output gear steel comprises the following components: c: 0.24-0.33%, Si: 0.15-0.40%, Mn: 1.00-1.80%, Cr: 1.60-2.00%, Mo: 0.30-0.50%, Ni: 1.10-1.50%, Al: 0.030 to 0.050%, Nb: 0.020-0.050%; p: less than or equal to 0.010 percent, S: less than or equal to 0.020%, T.O: less than or equal to 15ppm, [ H ] less than or equal to 1.0ppm, [ N ]: 0.0090-0.0130% and the balance of Fe and inevitable impurity elements. The rotary bending fatigue strength of the gear produced after infiltration is more than or equal to 1000MPa, the torsional fatigue strength is more than or equal to 620MPa, and the austenite grain size is more than or equal to 10.0 grade.
Description
Technical Field
The invention belongs to the field of gear steel, and relates to Nb microalloyed fine-grain high-torque output gear steel, a manufacturing method thereof and a machining process for producing gears, which are suitable for manufacturing high-torque automobile variable speed output gear steel.
Background
The new energy automobile is a key direction for the development of the automobile industry in the future due to the characteristics of low pollution, high efficiency and the like. Compared with the traditional fuel vehicle, the reduction/differential gear has high rotating speed and large instantaneous torque, is an important bottleneck restricting the development of new energy vehicles, and is a key difficult problem to be solved urgently.
The common technology for increasing the torque of the gear steel comprises increasing the alloy content, increasing the hardenability and increasing the martensite content to improve the torque; the other technical scheme is to add micro-alloying elements such as Nb and V to refine grains and improve torque, but the cost increase brought by the technical schemes causes the technical schemes to encounter huge resistance in popularization.
The currently common new energy gear steel material is 17CrNiMo6 gear steel, and the hardenability control range is J9: 37-47 HRC, J15: 34-46 HRC, J25: 31 to 43 HRC. However, with the requirement of high output torque, the residual performance of the existing gear steel material is insufficient, and the design requirement of a new energy automobile in the future cannot be met. Although the performance of 20Cr2Ni4 is better than that of 17CrNiMo6, the alloy cost is too high, the material popularization difficulty is high, and the alloy is only applied in a small amount. Therefore, there is a need to develop a low-cost gear material with high hardenability, high output torque and excellent toughness to meet the requirements of the automobile industry for low-cost high-output torque high-performance gear steel.
The Chinese patent, publication No. CN108866439A, invention patent with publication No. 2018, 11 and 23, discloses Nb and Ti composite microalloyed high-temperature vacuum carburized heavy-load gear steel, and through the composite microalloyed design, the carburized temperature is increased, crystal grains are refined, but the hardenability is not strictly required, and the requirements of low-cost high-output-torque high-performance gear steel cannot be met.
Chinese patent, publication No. CN 104109816A, invention patent of publication No. 2014, 10, 22, discloses a CrNiMo gear steel with high hardenability, the invention effectively improves the hardenability of materials by improving elements such as Cr, Ni and the like in a higher range, and the hardenability can reach J9: 40-46HRC, J15: 39-44HRC, J25: 38-44 HRC; and the content control of Al and N ensures that austenite grains do not grow obviously in the carburizing process, and improves the fatigue resistance and the comprehensive mechanical property of the carburizing alloy steel. Although the hardenability is further improved, the content of Ni and Mo is extremely high, and the cost is greatly increased by adding noble metals such as V, Nb, and the requirement of low-cost high-output-torque high-performance gear steel cannot be met.
Chinese patent, publication No. CN107604253A, invention patent with publication date of 2018, 1 month and 19 days, discloses Mn-Cr series carburizing steel with high hardenability, the invention effectively improves the hardenability of the material containing B by improving elements such as C, Mn, Cr and the like in a higher range, and the hardenability can reach J9: 40-46HRC, J15: 34-40HRC, J25: 30.5-33.5 HRC; and the content control of Al and N ensures that the austenite grains do not grow obviously in the carburizing process. Although the hardenability is further improved, the demand for low-cost, high-output torque, and high-performance gear steel has not yet been satisfied.
At present, CrNiMo gear steel has good obdurability, and a certain technology accumulation is generated in the development of CrNiMo gear steel, but the requirements of improving hardenability and high output torque, and greatly reducing the cost, wherein the performance of the CrNiMo gear steel is equivalent to that of 20Cr2Ni4, cannot be achieved at present. Therefore, the development of a new technical means for improving hardenability, toughness, high output torque and low-cost high-performance gear steel is urgently needed to meet the continuous development of the automobile industry
Disclosure of Invention
The invention aims to provide Nb microalloyed fine grain high-torque output gear steel and a manufacturing method thereof, wherein the end hardenability of the Nb microalloyed fine grain high-torque output gear steel can meet the following requirements that J9: 39-46 HRC, J15: 38-44HRC, J25: 36-42 HRC.
The invention also aims to provide a processing technology for producing gears by utilizing the Nb microalloyed fine-grain high-torque output gear steel, and the invention designs and matches the processing technology according to the steel components, and the rotary bending fatigue strength is more than or equal to 1000MPa, the torsional fatigue strength is more than or equal to 620MPa, and the austenite grain size is more than or equal to 10.0 grade after carburization.
The specific technical scheme of the invention is as follows:
the invention provides Nb microalloyed fine-grain high-torque output gear steel which comprises the following components in percentage by mass:
c: 0.24-0.33%, Si: 0.15-0.40%, Mn: 1.00-1.80%, Cr: 1.60-2.00%, Mo: 0.30-0.50%, Ni: 1.10-1.50%, Al: 0.030 to 0.050%, Nb: 0.020-0.050%; p: less than or equal to 0.010%, S: less than or equal to 0.020%, T.O: less than or equal to 15ppm, [ H ] less than or equal to 1.0ppm, [ N ]: 0.0090-0.0130% and the balance of Fe and inevitable impurity elements.
The Nb microalloyed fine grain high-torque output pinion steel also meets the requirements; Al-1.52X N, Alf is 0.020% -0.030%.
The invention provides a method for manufacturing Nb microalloyed fine-grain high-torque output gear steel, which comprises the following process flows of:
smelting, refining, vacuum treatment, round billet/square billet continuous casting and round steel rolling.
The rolling process comprises heating, rolling and slow cooling.
The heating process comprises the following steps: controlling the soaking temperature of the steel billet in the heating furnace to be 1230-1280 ℃; the total time of preheating, heating and soaking the round steel is controlled to be 6.0 h-10.0 h, wherein the time of the soaking period is not less than 300 min.
And (3) rolling: the initial rolling temperature is 1150-1200 ℃, and the final rolling temperature is 880-950 ℃.
And (3) slow cooling: and cooling the rolled steel plate to 500-550 ℃ by a cooling bed, entering a pit for slow cooling for more than or equal to 24 hours, and polishing and peeling the rolled steel plate after the rolled steel plate is taken out of the pit to ensure that the surface has no decarburization and zero defect.
The steel produced by the manufacturing method can meet the end hardenability of J9: 39-46 HRC, J15: 38-44HRC, J25: 36-42 HRC.
The invention provides a processing technology for producing a gear by adopting the Nb microalloying fine grain high-torque output gear steel, which comprises the following process flows of: blanking, forging, carburizing heat treatment, tempering, finishing and flaw detection, wherein the carburizing heat treatment process comprises the following steps: heating the part blank to 880 +/-5 ℃ in a carburizing furnace, keeping the temperature for more than 30min, then heating to 930 +/-5 ℃ for carburizing, wherein the carburizing time is more than 6h, then cooling the part blank to room temperature with oil at the temperature of less than 180 ℃.
The gear produced by the processing technology has the rotating bending fatigue strength of more than or equal to 1000MPa, the torsional fatigue strength of more than or equal to 620MPa and the austenite grain size of more than or equal to 10.0 grade.
The design concept of the invention is as follows:
c: c is the most basic effective strengthening element in steel, is the most effective element influencing hardenability, and is low in cost, in order to ensure that the pinion steel has sufficient strength and sufficient hardenability, the content of C needs to be increased, the increase of the content of C is beneficial to improving the hardness of a core matrix, so that the content of carbon in martensite laths in the matrix is increased, the increase of the content of the core carbon is beneficial to improving the content of the core residual austenite, the residual austenite can increase the coordinated deformability of the matrix, so that coordinated deformation is realized under the action of high torque, cracks are not easy to initiate, the increase of the martensite hardness is far greater than the hardness reduction brought by the increase of the residual austenite, the increase of the core hardness can increase the static torsion strength, so that the content of carbon is not less than 0.24, but the excessively high content of carbon has great damage to the toughness, and the content of carbon is not higher than 0.33% for CrNiMo pinion steel. So that the carbon content is determined to be 0.24-0.33%
Si: si is a deoxidizer, and can improve the hardenability of the gear steel by simultaneously improving the strong hardness of the steel through solid solution strengthening, the content of Si is not less than 0.15 percent, but the excessive silicon increases the activity of C, promotes the decarburization and graphitization tendency of the steel during rolling and heat treatment, makes a carburized layer easy to oxidize, and therefore the content of Si is not more than 0.40 percent. The content of Si is controlled between 0.15 and 0.40 percent.
Mn: mn can enlarge an austenite phase region, improve the hardenability of steel and the hardness of ferrite and austenite of the steel, and improve the stability of an austenite structure. However, excessive Mn lowers the ductility of the steel, and the toughness of the steel deteriorates during hot rolling. The Mn content is controlled to be 1.00-1.80.
Cr: cr can improve the hardenability and the strength of steel, Cr is combined with carbon in steel grades to form carbide, the carbide is precipitated in fine carbide after tempering, the precipitated carbide is enriched among martensite laths to inhibit the laths from moving under stress, dislocation in martensite can be tangled to improve the strength and the fatigue resistance, so the Cr content is not less than 1.60%, but at the same time, too high Cr can form a carbide film to influence the carburizing effect and reduce the performance of a carburized layer, so the Cr content cannot be higher than 2.00%. The Cr content is controlled to be 1.60-2.00%.
Mo: mo can obviously improve the hardenability of steel and prevent temper brittleness and overheating tendency. In addition, the reasonable matching of the Mo element and the Cr element can obviously improve the hardenability and the tempering resistance, and the Mo can refine grains. And if the Mo content is too low, the effect is limited, if the Mo content is too high, the formation of a grain boundary ferrite film is promoted, the thermoplasticity of the steel is not facilitated, the reheating crack tendency of the steel is increased, and the cost is higher. Therefore, the Mo content is controlled to be 0.30 to 0.50%.
Ni: ni can effectively improve the core toughness of steel, reduce ductile-brittle transition temperature, improve low-temperature impact performance and improve the fatigue strength of steel materials, and the other function of Ni in the project is to improve the fault energy, improve the dislocation crossing potential barrier and improve the anti-torsion performance, while the cost of Ni is higher, and the high content of Ni can reduce the machinability after hot working. Therefore, the Ni content is controlled within 1.10-1.50%.
Al: al is an effective deoxidizer and forms fine AlN grains, and when the Al content is less than 0.030%, the effect is not significant, and when it is more than 0.040%, coarse inclusions are likely to be formed, deteriorating the performance of the steel. Therefore, the adding time of Al in the steel-making process needs to be adjusted specially, and the content of Al is ensured to be controlled to be 0.030-0.050%.
Nb: nb is an effective refined grain microalloying element, can form a carbonitride nail rolling crystal boundary with C, N elements in steel to inhibit austenite grain growth, has less refined grain content and unobvious refined grain content, and simultaneously has solid-dissolved Nb content capable of improving hardenability, so that the core hardness is improved, the static torsion strength is increased, the content is higher than 0.020%, but the excessive Nb content easily causes the excessive Nb inclusion to influence the fatigue performance, and the Nb content is ensured to be controlled to be 0.020-0.050%.
P and S: the sulfur is easy to form MnS inclusion with manganese in the steel, so that the steel is hot-brittle, but the small amount of S is added, the machinability of the gear steel can be obviously improved while the product performance is not influenced, and the MnS has the effect of refining grains; p is an element with strong segregation tendency, increases the cold brittleness of steel, reduces the plasticity and is harmful to the uniformity of the product structure and performance. Controlling P to be less than or equal to 0.010 percent, and S: less than or equal to 0.020%.
T.O and [ H ]: forming oxide inclusions in the steel by the T.O, and controlling the T.O to be less than or equal to 15 ppm; [H] white spots are formed in steel, the product performance is seriously influenced, and the [ H ] is controlled to be less than or equal to 1.0 ppm.
[ N ]: can form compounds with Nb, B, Al and the like to refine grains, reasonable Al/[ N ] has obvious effect on grain refinement, and excessive [ N ] can form continuous casting defects such as bubbles and the like. Therefore, the content of [ N ] should be controlled to 0.0090-0.0130%.
If the content of free aluminum exceeds 0.050%, the hardenability of the steel is not significantly improved, and therefore, the content of Alf is controlled to be 0.020% to 0.030%.
The steel for the gear of the automobile transmission, which is produced by adopting specific components and a reasonable preparation method and has high hardenability and low cost, is subjected to end hardenability performance inspection according to GB/T225, the control of the end hardenability J9, J15 and J25 is greatly improved compared with that of a CiNiMo system, and the cost is greatly reduced compared with that of 20Cr2Ni 4.
Drawings
FIG. 1 is a graph of grains after carburization in example 1;
FIG. 2 is a graph of grains after carburization in example 2;
FIG. 3 is a graph of grains after carburization in example 3;
FIG. 4 is a graph of grains after carburization in comparative example 1;
FIG. 5 is a graph of grains after carburization in comparative example 2;
FIG. 6 is a graph of grains after carburization in comparative example 3;
fig. 7 is a graph of the grain after carburization in comparative example 4.
Detailed Description
Examples 1 to 3 are a 3-furnace co-production of gear steel using the composition, comparative examples 1 to 3 are the steel composition of example 1 but not the manufacturing method of the invention, and comparative example 4 is a 20Cr2Ni4 steel and a conventional rolling process. The balance not shown in table 1 is Fe and inevitable impurities.
The following is a specific example of the steel for an automobile transmission gear with high hardenability and low cost of the present invention.
TABLE 1 inventive and comparative examples chemical composition (unit: [ N ] is ppm, others are wt%)
The manufacturing method of each of the above examples and comparative examples includes the following process flows:
smelting, refining, vacuum treatment, round billet/square billet continuous casting and round steel rolling.
The rolling process comprises heating, rolling and slow cooling.
The heating process comprises the following steps: controlling the soaking temperature of the steel billet in the heating furnace to be 1230-1280 ℃; the total time of preheating, heating and soaking the round steel is controlled to be 6.0 h-10.0 h, wherein the time of the soaking period is not less than 300 min.
And (3) rolling: the initial rolling temperature is 1150-1200 ℃, and the final rolling temperature is 880-950 ℃.
And (3) slow cooling: and cooling the rolled steel plate to 500-550 ℃ by a cooling bed, entering a pit for slow cooling for more than or equal to 24 hours, and polishing and peeling the rolled steel plate after the rolled steel plate is taken out of the pit to ensure that the surface has no decarburization and zero defect.
The specific process parameters for each example and comparative example are shown in table 2.
TABLE 2 production parameters of rolled steel in examples and comparative examples
Table 3 shows the end hardenability values of the inventive examples, and it can be seen from Table 3 that the hardenability control values J9, J15, J25 of the inventive steels for gears are within the range required by the steel for high torque automobile transmission output gears, and the hardenability control values are comparable to those of the comparative steels, but the cost is lower.
TABLE 3 end hardenability values (HRC) for the examples of the invention
| Examples | J9 | J15 | J25 |
| Require to make a request for | 39～46 | 38～44 | 36～42 |
| Example 1 | 43.5 | 42.2 | 39.2 |
| Example 2 | 44.1 | 41.8 | 41.2 |
| Example 3 | 44.3 | 42.7 | 42.5 |
| Comparative example 1 | 42.5 | 40.0 | 38.7 |
| Comparative example 2 | 40.2 | 39.1 | 38.3 |
| Comparative example 3 | 40.1 | 37.0 | 36.6 |
| Comparative example 4 | 40.3 | 38.8 | 35.5 |
The steel of each example and each comparative example is subjected to blanking, forging, carburizing heat treatment, tempering, finishing and flaw detection to produce the gear, wherein the carburizing heat treatment process comprises the following steps: heating the part blank to 880 +/-5 ℃ in a carburizing furnace, preserving heat for 35min, then heating to 930 +/-5 ℃ for carburizing, wherein the carburizing time is 6.5h, then cooling oil to room temperature, and the oil temperature is less than 180 ℃, and obtaining the product performance shown in the table 4.
Table 4 shows that the grain sizes of the gear steels of examples 1 to 5 of the present invention after carburization are all above grade 10, as shown in Table 4.
TABLE 4 grain size of grain size grade after carburization in accordance with the examples of the present invention
The steel provided by the invention is subjected to carburization treatment, the rotary bending fatigue strength of a product is more than or equal to 1000MPa, the torsional fatigue strength is more than or equal to 620MPa, and the austenite grain size is more than or equal to 10.0 grade.
Claims (10)
1. The Nb microalloyed fine grain high-torque output gear steel is characterized by comprising the following components in percentage by mass:
c: 0.24-0.33%, Si: 0.15-0.40%, Mn: 1.00-1.80%, Cr: 1.60-2.00%, Mo: 0.30-0.50%, Ni: 1.10-1.50%, Al: 0.030 to 0.050%, Nb: 0.020-0.050%; p: less than or equal to 0.010 percent, S: less than or equal to 0.020%, T.O: less than or equal to 15ppm, [ H ] less than or equal to 1.0ppm, [ N ]: 0.0090-0.0130% and the balance of Fe and inevitable impurity elements.
2. The Nb microalloyed fine grain high torque output pinion steel as set forth in claim 1, whereinThe Nb microalloyed fine-grain high-torque output gear steel has the following components: Alf-Al-1.52X [ N ]]，Al f 0.020% -0.030%.
3. A method of making the Nb microalloyed fine grain high torque output gear steel in accordance with claim 1 or 3, wherein the method of making includes the steps of:
smelting, refining, vacuum treatment, round billet continuous casting and finishing to obtain the finished product.
4. The method of manufacturing of claim 3, wherein the finishing stock comprises heating, rolling, and slow cooling.
5. The manufacturing method according to claim 4, wherein the heating: controlling the soaking temperature of the steel billet in the heating furnace to be 1230-1280 ℃; the total time of preheating, heating and soaking the round steel is controlled to be 6.0 h-10.0 h, wherein the time of the soaking period is not less than 300 min.
6. The manufacturing method according to claim 4, wherein the rolling: the initial rolling temperature is 1150-1200 ℃, and the final rolling temperature is 880-950 ℃.
7. The manufacturing method according to claim 4, wherein the slow cooling: and cooling the rolled steel plate to 500-550 ℃ by a cooling bed, and entering a pit for slow cooling for more than or equal to 24 hours.
8. The manufacturing method according to any one of claims 3 to 7, wherein the steel tip hardenability satisfies J9: 39-46, J15: 38-44HRC, J25: 36-42 HRC.
9. A process for producing gears from Nb microalloyed fine grain high torque output gear steel manufactured by the method of manufacture set forth in any one of claims 3 to 7, which comprises the carburizing heat treatment of: heating the part blank to 880 +/-5 ℃ in a carburizing furnace, keeping the temperature for more than 30min, then heating to 930 +/-5 ℃ for carburizing, wherein the carburizing time is more than 6h, then cooling the part blank to room temperature with oil at the temperature of less than 180 ℃.
10. The process according to claim 9, wherein the gear produced has a rotary bending fatigue strength of 1000MPa or more, a torsional fatigue strength of 620MPa or more, and an austenite grain size of 10.0 or more.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210769514.8A CN114959502B (en) | 2022-06-30 | 2022-06-30 | Nb microalloyed fine-grain high-torque output gear steel, manufacturing method thereof and processing technology for producing gears |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210769514.8A CN114959502B (en) | 2022-06-30 | 2022-06-30 | Nb microalloyed fine-grain high-torque output gear steel, manufacturing method thereof and processing technology for producing gears |
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| Publication Number | Publication Date |
|---|---|
| CN114959502A true CN114959502A (en) | 2022-08-30 |
| CN114959502B CN114959502B (en) | 2023-07-25 |
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| CN110846580A (en) * | 2019-12-05 | 2020-02-28 | 马鞍山钢铁股份有限公司 | high-Mo high-performance Mn-Cr series steel for wind power output gear and production method thereof |
| CN113631746A (en) * | 2019-03-29 | 2021-11-09 | 日本制铁株式会社 | Carburized component and method for manufacturing same |
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| JP2009068065A (en) * | 2007-09-12 | 2009-04-02 | Sanyo Special Steel Co Ltd | Case hardening steel excellent in bearing fatigue-strength, impact strength and bending fatigue-strength |
| US20140030136A1 (en) * | 2011-04-21 | 2014-01-30 | Sanyo Special Steel Co., Ltd. | Steel Material for Machine Structural Use Having Excellent Contact Pressure Fatigue Strength |
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