CN115478230A - Cold-forged gear steel and manufacturing method thereof - Google Patents
Cold-forged gear steel and manufacturing method thereof Download PDFInfo
- Publication number
- CN115478230A CN115478230A CN202110601013.4A CN202110601013A CN115478230A CN 115478230 A CN115478230 A CN 115478230A CN 202110601013 A CN202110601013 A CN 202110601013A CN 115478230 A CN115478230 A CN 115478230A
- Authority
- CN
- China
- Prior art keywords
- cold
- gear steel
- steel
- forging
- forged
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 175
- 239000010959 steel Substances 0.000 title claims abstract description 175
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 28
- 238000010273 cold forging Methods 0.000 claims abstract description 64
- 238000000034 method Methods 0.000 claims abstract description 37
- 239000000126 substance Substances 0.000 claims abstract description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 5
- 238000001816 cooling Methods 0.000 claims description 46
- 238000010438 heat treatment Methods 0.000 claims description 44
- 238000005242 forging Methods 0.000 claims description 30
- 238000005096 rolling process Methods 0.000 claims description 25
- 230000009467 reduction Effects 0.000 claims description 13
- 238000000137 annealing Methods 0.000 claims description 12
- 229910000859 α-Fe Inorganic materials 0.000 claims description 9
- 238000003723 Smelting Methods 0.000 claims description 8
- 238000005266 casting Methods 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 5
- 238000007599 discharging Methods 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 4
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- 229910052717 sulfur Inorganic materials 0.000 claims 1
- 239000013078 crystal Substances 0.000 abstract description 6
- 238000005255 carburizing Methods 0.000 abstract description 4
- 230000008569 process Effects 0.000 description 30
- 229910001566 austenite Inorganic materials 0.000 description 27
- 230000000052 comparative effect Effects 0.000 description 25
- 239000000463 material Substances 0.000 description 19
- 238000012545 processing Methods 0.000 description 8
- 238000004321 preservation Methods 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 238000003754 machining Methods 0.000 description 5
- 230000006911 nucleation Effects 0.000 description 5
- 238000010899 nucleation Methods 0.000 description 5
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 4
- 125000004122 cyclic group Chemical group 0.000 description 4
- OXNIZHLAWKMVMX-UHFFFAOYSA-N picric acid Chemical compound OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O OXNIZHLAWKMVMX-UHFFFAOYSA-N 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000005520 cutting process Methods 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 239000012071 phase Substances 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000007670 refining Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 229910052729 chemical element Inorganic materials 0.000 description 1
- 238000003776 cleavage reaction Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 229910052593 corundum Inorganic materials 0.000 description 1
- 238000004512 die casting Methods 0.000 description 1
- 238000011143 downstream manufacturing Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000007017 scission Effects 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 229910001845 yogo sapphire Inorganic materials 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Abstract
The invention discloses cold forging gear steel, which comprises the following chemical components in percentage by weight: c:0.16 to 0.19wt%, si:0.15 to 0.25wt%, mn:1.00 to 1.20wt%, cr:1.0 to 1.10wt%, al:0.02 to 0.04wt%, N: 0.010-0.016 wt%. Also disclosed is a method for manufacturing a cold-forged gear steel having strength of not more than 450MPa and excellent plasticity and elongation, while maintaining fine crystal grains without coarsening by carburizing at 950 ℃.
Description
Technical Field
The invention relates to the field of alloy steel, in particular to cold-forging gear steel and a manufacturing method thereof.
Background
The gear is a key part of the zero-speed gearbox of the automobile. With the rapid development of the automobile industry, the demand of the transmission is high for a long time in the face of a wide automobile market. Because the shape of gear is comparatively special, has higher to the size precision requirement, and gear production is carried out to many enterprises adoption hot forging back finish machining technology mode, and not only the utilization ratio of material is lower on the one hand, and on the other hand hot forging needs the energy resource consumption higher, can increase the processing cost, and can produce environmental pollution.
Therefore, part processing enterprises adopt the cold forging technology to produce gears, and the part cold forging processing has many-sided advantages: (1) The near-net-shaped body has high size and shape and position precision, and can provide an ideal blank for subsequent high-efficiency and high-precision processing; (2) For the net-shaped parts, a plurality of parts do not need subsequent processing, so that the waste of raw materials is greatly reduced; (3) The production efficiency is high, the energy consumption is low, the manufacturing cost can be effectively reduced, the manufacturing period is shortened, the competitiveness of the product is improved, and the performance and the quality of the precision forming product are greatly improved compared with the product processed by traditional cutting; (4) Compared with the traditional forming process, the part cold forging technology has the advantages that the production conditions are improved, and the pollution to the environment is greatly reduced; (5) In the aspect of cold precision forming of the part cold forging technology, due to the reduction of heat treatment procedures and the improvement of a flash-free process, the energy consumption and the pollution degree are greatly reduced. Therefore, the cold forging technology is more suitable for the future trend of clean manufacturing and green environmental protection, and can create favorable conditions for sustainable development.
However, in the cold forging pinion steel on the market at present, due to insufficient plasticity of the material, the cold forging part directly cracks after forging or microcracks exist inside the material, so that the rejection rate of the part is high, and the part processing cost is increased. In addition, although many cold-forged gear steels have excellent plasticity, the material strength is high (greater than 500 MPa), and during the forging process, the loss of the die is increased due to the high material strength, and the downstream forging cost is also increased.
Meanwhile, a high-temperature carburizing process is often needed in the machining process of cold-forged gears, so that a hardened layer with higher hardness is formed on the surface of gear steel, the contact fatigue strength is improved, and the fatigue service life of the gears is further prolonged.
Disclosure of Invention
The invention aims to solve the problems that cold-forged gear steel is easy to crack and has high strength to aggravate the loss of a die. The invention provides cold forging gear steel and a manufacturing method thereof, wherein the cold forging gear steel has the strength of not more than 450MPa and excellent plasticity and elongation, and simultaneously the cold forging gear steel can keep fine crystal grains and does not generate coarsening when carburized at 950 ℃.
In order to solve the technical problem, the embodiment of the invention discloses cold forging gear steel which comprises the following chemical components in percentage by weight: c:0.16 to 0.19wt%, si:0.15 to 0.25wt%, mn:1.00 to 1.20wt%, cr:1.0 to 1.10wt%, al:0.02 to 0.04wt%, N: 0.010-0.016 wt%.
By adopting the technical scheme, the cold forging gear steel has the strength not exceeding 450MPa and excellent plasticity and elongation, and meanwhile, the cold forging gear steel can keep fine crystal grains and does not generate coarsening when carburized at 950 ℃.
According to another specific embodiment of the present invention, an embodiment of the present invention discloses a cold-forged pinion steel, further comprising: the balance being Fe and other unavoidable impurities.
According to another specific embodiment of the present invention, an embodiment of the present invention discloses a cold-forged gear steel, further comprising: 0 < Ca < 0.004 wt%, 0 < Ti < 0.008 wt%.
According to another embodiment of the present invention, an embodiment of the present invention discloses a cold-forged gear steel, the other inevitable impurities including: less than or equal to 0.003wt% of S, less than or equal to 0.015wt% of P and less than or equal to 0.0030wt% of O.
According to another embodiment of the present invention, there is disclosed a cold-forged gear steel having a microstructure of ferrite and spherical carbide.
According to another specific embodiment of the invention, the embodiment of the invention discloses cold-forging gear steel, and the performance of the cold-forging gear steel meets at least one of yield strength of 180-220 MPa, tensile strength of 380-430 MPa, elongation of more than or equal to 37% and reduction of area of more than or equal to 65%.
The embodiment of the invention also discloses a manufacturing method of the cold forging gear steel, the composition of the cold forging gear steel is as described in the above, and the manufacturing method comprises the following steps:
smelting and casting;
heating;
forging or rolling, and air-cooling to room temperature;
spheroidizing annealing: heating to 700 ℃, keeping the temperature for 1h, heating to 750-770 ℃, keeping the temperature for 4-6h, then cooling to 700-720 ℃ at a cooling rate of 10-15 ℃/h, keeping the temperature for 3-5h, then cooling to 670-690 ℃ at a cooling rate of 10-15 ℃/h, keeping the temperature for 4-6h, then cooling to below 500 ℃ at a cooling rate of 15-20 ℃/h, and then discharging and cooling to room temperature.
By adopting the technical scheme, the obtained cold forging gear steel has the strength not exceeding 450MPa and excellent plasticity and elongation, and meanwhile, the cold forging gear steel can keep fine crystal grains and does not generate coarsening when carburized at 950 ℃.
According to another specific embodiment of the invention, the embodiment of the invention discloses a manufacturing method of cold forging gear steel, wherein in the heating step, the heating temperature is controlled to be 1100-1200 ℃, and the heating time is controlled to be 4-5 h.
According to another embodiment of the invention, the forging or rolling temperature is 860 to 980 ℃.
Drawings
FIG. 1 is a metallographic picture of a cold-forged gear steel which is provided in example 3 of the present invention;
FIG. 2 is an austenite grain size morphology chart of cold-forged gear steel provided by embodiment 3 of the present invention, which is measured after heat preservation at 950 ℃ for 4h, water-cooling quenching and picric acid corrosion.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure. While the invention will be described in conjunction with the preferred embodiments, it is not intended that the features of the invention be limited to that embodiment. On the contrary, the invention is described in connection with the embodiments for the purpose of covering alternatives or modifications that may be extended based on the claims of the present invention. In the following description, numerous specific details are included to provide a thorough understanding of the invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been left out of the description in order to avoid obscuring or obscuring the focus of the present invention. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
Hereinafter, the component system of the present invention will be described in terms of weight percent.
C：0.16～0.19wt％
In the cold forging gear steel, a proper amount of C element is added, so that the steel material has good hardenability and proper strength, and the wear resistance required by the steel material processed into a final part is improved, but the hardness of the steel material is increased due to the over-high content of the C element in the steel material, so that the strength of the steel material is over-high in the subsequent processing process, the loss of a die in the cold forging process is increased, and the downstream processing cost is further increased. If the content of C element in the steel is too low, the steel cannot obtain high tensile strength, the structural strength of the gear core is low, the deformation resistance of the gear is reduced, and the fatigue life of the gear is shortened. And the C element is a key element influencing hardenability, so that the C element content in the cold-forging gear steel is 0.16-0.19 wt% to realize narrow hardenability of the gear steel.
Si：0.15～0.25wt％
In the cold-forging gear steel of the present invention, si is a ferrite-forming element, and has a strong solid solution strengthening effect, and the strength of the steel material can be improved. In addition, si element can also reduce the diffusion capability of C element in ferrite, so that proper amount of Si element can effectively avoid the formation and precipitation of coarse carbide at the defect site during spheroidizing annealing. However, since the Si element content in the steel material is too high and the plasticity of the steel material is lowered, the Si element content in the cold-forged gear steel of the present invention is 0.15 to 0.25wt%.
Mn：1.00～1.20wt％
In the cold forging gear steel, mn element is a core element influencing the hardenability of the gear steel, and when a proper amount of S element exists in the steel, mn element and S easily form plastic MnS, so that the chip breaking effect can be effectively improved and the cutting performance can be improved in the subsequent gear finish machining process. It should be noted that too high content of Mn element in the steel material may increase the strength and hardness of the steel material, and may increase the loss of the die during the subsequent cold forging process. Therefore, in order to improve the free-cutting property of the material, avoid the higher strength of the steel and ensure certain hardenability of the gear steel, the content of Mn element in the cold forging gear steel is 1.00-1.20 wt%.
Cr：1.0-1.10wt％
In the cold-forging gear steel, cr can greatly influence the hardenability of the gear steel, in order to reduce the hardenability fluctuation range of the gear steel, and in addition, cr is a strong carbide forming element, cr23C7 type carbide is easily formed in the steel, and the carbide can be used as nucleation particles in the subsequent spheroidizing annealing heat treatment process, so that the nucleation energy is reduced, and the spheroidizing speed is accelerated. If the Cr element content in the steel is too high, coarse carbides are formed, and the cold formability is deteriorated. The content of Cr element in the cold forging gear steel is 1.0-1.10wt%.
Al：0.02～0.04wt％
In the cold forging gear steel, al has good deoxidation effect in the steel making process, oxygen in the steel can be effectively reduced, fine AlN precipitation can be formed, the AlN can inhibit growth of austenite grains in the subsequent cooling process, and the AlN is dispersed and distributed in grain boundaries in the gear carburizing process, so that the austenite grains can be effectively prevented from coarsening in the high-temperature carburizing process. However, too high an Al content in the steel results in the formation of large Al oxides and large-sized B-type inclusions, and coarse alumina hard inclusions deteriorate the fatigue properties of the steel and also cause chipping during machining. Therefore, in order to effectively exert the beneficial effects of the Al element in the invention, the content of the Al element in the cold forging gear steel is 0.02-0.04 wt%.
N：0.010～0.016wt％
In the cold forging gear steel, although the N element can form AlN or TiN in the steel and can play a role in refining austenite grains, the increase of the content of the N element in the steel can lead to the increase of the enrichment amount of the N element at a defect part and simultaneously form coarse nitride precipitation grains, thereby influencing the fatigue life of the steel. Therefore, the content of the N element in the cold forging gear steel is 0.010-0.016 wt%.
Further, the cold-forging pinion steel of the present invention further includes: 0 < Ca < 0.004 wt%, 0 < Ti < 0.008 wt%.
Ca: in the cold forging gear steel, a proper amount of Ca element is added into the steel, so that the castability of molten steel can be effectively improved, and the water gap blockage caused during steel casting is avoided. However, too high Ca content in the steel is not preferable, and too high Ca content causes large-size DS-type inclusions in the steel, which adversely affects the fatigue life of the gear. Therefore, the content of Ca element in the cold-forged gear steel according to the present invention is 0 < Ca.ltoreq.0.004% by weight.
Ti: in the cold forging gear steel, ti element can form corresponding compounds with C and N in the steel, wherein the formation temperature of TiN is above 1400 ℃, and TiN is usually precipitated in a liquid phase or delta ferrite, thereby realizing the purpose of refining austenite grains. However, if the content of Ti element in the steel is too high, coarse TiN precipitates, and the fatigue properties of the steel are lowered. Therefore, the content of Ti element in the cold-forged gear steel according to the present invention is 0 < Ti ≦ 0.008% by weight.
Further, in the cold-forged gear steel according to the present invention, the other inevitable impurities include: less than or equal to 0.003wt% of S, less than or equal to 0.015wt% of P and less than or equal to 0.0030wt% of O.
S: s is easily combined with Fe to form a FeS phase with a melting point of 989 ℃, which causes hot brittleness of the steel during hot working. Therefore, in order to avoid hot shortness of the steel, the content of the element S in the cold-forged gear steel of the present invention is controlled to be S.ltoreq.0.003 wt%.
P: p combines with Fe to form hard and brittle Fe 3 The P phase causes cold brittleness of the steel in the cold machining process, so that the plasticity of the steel is deteriorated, the steel is broken along the grain under the action of impact load to form a large cleavage plane, and the P element in the steel is deviated at the grain boundary, so that the binding energy of the grain boundary is reduced, and the plasticity of the steel is deteriorated. Therefore, in order to avoid the brittleness of the steel becoming high, the content of the P element in the cold-forged gear steel of the present invention is controlled to be P.ltoreq.0.015 wt%.
O: the O element can form Al2O3, tiO and the like with Al and Ti elements in steel, so in order to ensure the uniformity of the steel structure, the content of the O element in the cold forging gear steel is controlled to be less than or equal to 0.0030wt percent.
Furthermore, the microstructure of the cold forging gear steel is ferrite and spherical carbide, so that the cold forging gear steel has good plasticity.
Furthermore, the performance of the cold forging gear steel meets at least one of yield strength of 180-220 MPa, tensile strength of 380-430 MPa, elongation of more than or equal to 37% and reduction of area of more than or equal to 65%.
In addition, the cold forging gear steel is subjected to heat preservation at 1150 ℃ for 30min, then is subjected to air cooling to room temperature, is subjected to heat preservation at 950 ℃ for 4h, finally is subjected to water cooling quenching, and is subjected to picric acid corrosion, austenite grain size data is obtained through testing, and results show that grain size results are all above grade 6, further show that the austenite grains of the cold forging gear steel subjected to cyclic heating and cooling are fine, and also show that the cold forging gear steel provided by the invention has good fatigue resistance.
The yield strength of the obtained cold forging gear steel is 180-220 MPa, the tensile strength is 380-430 MPa, the elongation is larger than or equal to 37%, the reduction of area is larger than or equal to 68%, the cold forging gear steel obtained by the manufacturing method has excellent plasticity and processing characteristics, austenite grain refinement can be kept under the condition of high-temperature carburization at 950 ℃, specifically, the cold forging gear steel is subjected to heat preservation at 1150 ℃ for 30min, then is subjected to air cooling to room temperature, is subjected to heat preservation at 950 ℃ for 4h, finally is subjected to water cooling quenching, and after bitter acid corrosion, austenite grain size data are obtained through testing, the result shows that the grain size result is more than 6 grades, further shows that the austenite grain size of the cold forging gear steel after cyclic heating and cooling is fine, and also shows that the cold forging gear steel provided by the invention can effectively avoid fatigue life reduction caused by grains.
The invention provides a method for manufacturing cold-forging gear steel, the components of the cold-forging gear steel are as described above, and the method comprises the following steps:
smelting and casting;
heating;
forging or rolling, and air-cooling to room temperature;
spheroidizing annealing: heating to 700 ℃ and preserving heat for 1h, heating to 750-770 ℃ and preserving heat for 4-6h, then cooling to 700-720 ℃ at a cooling rate of 10-15 ℃/h and preserving heat for 3-5h, then cooling to 670-690 ℃ at a cooling rate of 10-15 ℃/h and preserving heat for 4-6h, then cooling to below 500 ℃ at a cooling rate of 15-20 ℃/h, and then discharging and cooling to room temperature.
Here, in the smelting and casting steps, smelting may be performed using an electric furnace or a converter, and casting may be performed using die casting or continuous casting.
Here, in the forging or rolling step, a forging or rolling process may be employed. If the forging process is adopted, the gear steel can be directly forged to the final size of the cold-forged gear steel; if the rolling process is adopted, the billet can also be directly rolled to the final size of the cold-forged pinion steel, and in other embodiments, the rolling process is adopted, and the billet can be firstly rolled to the specified intermediate billet size, and then the obtained intermediate billet is heated and rolled to obtain the final size of the cold-forged pinion steel.
Further, in the heating step, the heating temperature is controlled to be 1100-1200 ℃, and the heating time is 4-5 h.
Specifically, in the heating step, the billet is heated and austenitized at a heating temperature of 1080-1200 ℃, elements in the steel are subjected to uniform diffusion, and segregation of the material is reduced, so that the cold-forged gear steel has good structural uniformity and small hardenability fluctuation in the subsequent forging or rolling and cooling processes.
Furthermore, in the forging or rolling step, the forging or rolling temperature is 860-980 ℃, so that the deformation resistance of the intermediate blank is low.
In the method for manufacturing cold-forged pinion steel according to the present invention,
(1) By controlling the process conditions, particularly the heat treatment process parameters, the forged or rolled bar is controlled and then a spheroidizing annealing process is adopted, so that the cold-forged round steel cold-forged gear steel prepared by the manufacturing method of the invention obtains a matrix structure of ferrite and spherical carbide, and a large amount of ferrite is arranged on the matrix, thereby effectively ensuring that the cold-forged gear steel has good plasticity, eliminating the internal stress of the steel and having good tissue uniformity.
(2) By adopting the precipitation of AlN at a crystal boundary, the austenite grain size of steel is controlled, alN does not dissolve at 950 ℃ and can effectively prevent the crystal boundary migration, and in addition, alN precipitates as dispersed mass points, so that nucleation points can be formed in the spheroidizing annealing process, the nucleation power is reduced, the spheroidizing speed is improved, and meanwhile, the nucleation number of carbide during spheroidizing is increased, so that the carbide is more fully spheroidized.
(3) In the spheroidizing annealing process, a means of precise temperature control and cooling control is adopted, so that the spheroidizing efficiency is improved, carbides in the structure are fully spheroidized, and the cold forging plasticity of steel is improved.
In conclusion, the invention fully utilizes the influence of various alloy elements on phase change and microstructure through reasonable chemical composition design and is matched with a specific heat treatment process, thereby forming a uniform ferrite + spheroidized carbide matrix structure. Meanwhile, the contents of P, N and O elements in the cold forging gear steel are effectively controlled, the cold forging gear steel is guaranteed to have the strength not exceeding 450MPa and excellent plasticity and elongation, the yield strength is 180-220 MPa, the tensile strength is 380-430 MPa, the elongation is larger than or equal to 37%, the reduction of area is larger than or equal to 68%, austenite grains can be kept to be refined under the high-temperature carburization condition of 950 ℃, and the reduction of fatigue life caused by the fact that the grains are large can be effectively avoided.
In addition, the cold forging gear steel has reasonable chemical composition and process design and loose process window, can realize batch commercial production on a bar production line, and has good popularization prospect and application value.
Examples 1 to 9
The cold-forged gear steels of examples 1 to 9 were all produced by the following steps:
smelting and casting: smelting and casting according to chemical components shown in the table 1 to obtain a billet, wherein an electric furnace or a converter is adopted for smelting;
heating: heating the steel billet at 1100-1200 ℃ for 4-5 h;
forging or rolling: forging or rolling the heated billet to obtain an intermediate billet, heating, forging or rolling the intermediate billet again to obtain a bar, wherein the forging or rolling temperature is 860-980 ℃, and then air-cooling to room temperature, the heating temperature is 1100-1200 ℃, and the heating time is 4-5 h;
spheroidizing annealing: heating to 700 ℃ and preserving heat for 1h, heating to 750-770 ℃ and preserving heat for 4-6h, then cooling to 700-720 ℃ at a cooling rate of 10-15 ℃/h and preserving heat for 3-5h, then cooling to 670-690 ℃ at a cooling rate of 10-15 ℃/h and preserving heat for 4-6h, then cooling to below 500 ℃ at a cooling rate of 15-20 ℃/h, and then discharging and cooling to room temperature.
In examples 1 to 9, the billet was rolled by a rolling process in the forging or rolling step. In the rolling process, the finishing temperature is controlled to be 860-980 ℃ in examples 1-9, the billet is rolled into an intermediate billet with the size of 215 x 215mm, then the intermediate billet is heated again, and after the intermediate billet leaves the heating furnace, the intermediate billet is rolled again to roll the intermediate billet into the specification of 215 x 215mm
The specification of the bar is
The rod material is subjected to spheroidizing annealing to obtain the rod material with the specification of
The cold-forged gear steel of (1).
In some embodiments provided by the invention, the cold forging gear steel can be directly rolled by controlling the finishing temperature to 860-980 ℃. Correspondingly, in other embodiments provided by the invention, a forging process can be adopted, and the cold forging gear steel can be directly forged by controlling the forging temperature to be 860-980 ℃. For example, in the forging or rolling step of example 6, the forging process was used to directly forge the steel to the specification of 860 to 980 ℃ by controlling the forging temperature
The cold-forged gear steel of (1).
TABLE 1 weight percents (wt%) of chemical elements in cold-forged gear steels provided in examples 1 to 9 and comparative examples 1 to 4
The "diameter" in Table 1 means the diameter of cold-forged gear steel, and the diameters of cold-forged gear steel in examples 1 to 9 and comparative examples 1 to 4 were each in the range of 20 to 50 mm.
TABLE 2-1 Process parameters in the manufacturing method of Cold-forged Gear Steel provided in examples 1-9 and comparative examples 1-4
Examples 1-9 and comparative examples 1-4 specifically included rolling, heating, rolling or forging processes at the forging or rolling step, as shown in table 2-1.
TABLE 2-2 Process parameters in the manufacturing method of Cold-forged Gear Steel provided in examples 1-9 and comparative examples 1-4
The cold-forged gear steels of examples 1 to 9 and comparative examples 1 to 4 obtained according to tables 1, 2 to 1 and 2 to 2 were subjected to mechanical property tests according to the GB/T228 metal material room temperature tensile method, and the test results are shown in Table 3, in which the cold-forged gear steels of examples 1 to 9 had yield strengths of 180 to 220MPa, tensile strengths of 380 to 430MPa, elongations of not less than 37% and reductions in area of not less than 68%.
TABLE 3 mechanical properties of cold-forged gear steels provided in examples 1 to 9 and comparative examples 1 to 4
As shown in table 1, table 2-2 and table 3, the cold-forged gear steel in comparative example 2 has a C element content of 0.212wt% and a Mn element content of 1.33wt%, and after mechanical testing, the cold-forged gear steel has a yield strength of more than 220MPa, a tensile strength of more than 430MPa, an elongation of less than 37% and a reduction of area of less than 68%, because the C element content and the Mn element content in the cold-forged gear steel in comparative example 2 are both too high, which results in an increase in strength, an increase in hardness and a poor hardenability of the cold-forged gear steel, and thus increases the loss of the die in the subsequent cold-forging process. In the spheroidizing annealing step of the manufacturing method of the cold-forged gear steel of comparative example 4, the heating temperature is 780 ℃ and the heat preservation time is 8h, the yield strength of the cold-forged gear steel after mechanical testing is more than 220MPa, the tensile strength is more than 430MPa, the elongation is less than 37% and the reduction of area is less than 68%, because the heating temperature of the spheroidizing annealing step in comparative example 4 is higher than 770 ℃ and the heat preservation time is more than 6h, the strength, the hardness and the hardenability of the cold-forged gear steel are increased, and the loss of a die is increased in the subsequent cold forging process.
Table 4 shows prior austenite grain size data obtained by cold forging gear steels of examples 1 to 9 and comparative examples 1 to 4 provided in tables 1, 2 to 2, and 3, heat-retaining at 1150 ℃ for 30min, then air-cooling to room temperature, heat-retaining at 950 ℃ for 4h, and finally water-cooling quenching and picric acid etching. As shown in Table 4, the maximum austenite grain size grades of the cold-forged gear steels provided in examples 1 to 9 are not lower than 6, which further indicates that the austenite grains of the cold-forged gear steels after cyclic heating and cooling are fine, and also indicates that the cold-forged gear steels provided by the present invention can effectively avoid the fatigue life reduction caused by coarse grains.
TABLE 4 Austenite grain sizes of cold-forged gear steels provided in examples 1 to 9 and comparative examples 1 to 4
| Number of | Maximum grain size level |
| Example 1 | 8.0 |
| Example 2 | 7.0 |
| Example 3 | 6.5 |
| Example 4 | 7.5 |
| Example 5 | 7.0 |
| Example 6 | 7.0 |
| Example 7 | 7.5 |
| Example 8 | 7.0 |
| Example 9 | 6.5 |
| Comparative example 1 | 4.0 |
| Comparative example 2 | 6.5 |
| Comparative example 3 | 5.5 |
| Comparative example 4 | 7.0 |
As shown in table 1, table 2-2 and table 4, the austenite grain size of the cold-forged gear steel of comparative example 1 after the 950 ℃ high temperature carburization process was 4.0 and less than 6.0 because the Cr element content of the cold-forged gear steel of comparative example 1 was 1.26wt%, the N element content was 0.0068wt%, the Cr element content of the steel was too high, coarse carbides were formed, the cold deformability was deteriorated, and the N element content was too low, the effect of refining austenite grains was weak, resulting in the austenite grain size of the cold-forged gear steel of comparative example 1 shown in table 4 being small and the austenite grains being large, which also indicates that the cold-forged gear steel provided by comparative example 1 in table 1 was poor in fatigue resistance. The austenite grain size of the cold-forged gear steel of comparative example 3 after being subjected to the high temperature carburization process at 950 ℃ is 5.5 and less than 6.0 because the heating temperature is more than 1200 ℃ in the heating step and the heating temperature of the intermediate blank is more than 1200 ℃ in the forging or rolling step of the manufacturing method of the cold-forged gear steel of comparative example 3, resulting in the influence of the uniform diffusion of each element during the heating austenitization, the structural uniformity of the cold-forged gear steel is poor, resulting in the austenite grain size of the cold-forged gear steel of comparative example 3 shown in table 4 being small and the austenite grain size being large, which also indicates that the fatigue resistance of the cold-forged gear steel provided by comparative example 3 in table 1 is poor.
As shown in FIG. 1, the microstructure of the cold-forged gear steel provided in example 3 of the present invention was observed under 500 times conditions using Leica DM6000, which included: ferrite F and spherical carbide SC.
As shown in fig. 2, the cold-forged gear steel provided in example 3 of the present invention was heat-insulated at 1150 ℃ for 30min, then air-cooled to room temperature, and then heat-insulated at 950 ℃ for 4h, and finally water-cooled quenched, and after picric acid corrosion, the austenite grain size was obtained by testing, and observed at 100 times using Leica DM6000, the austenite grain size a:36.83 μm, B:37.77 μm, C:38.32 mu m and 6.5-grade austenite grain size, further illustrates that the austenite grain size of the cold forging gear steel after cyclic heating and cooling is fine, and also illustrates that the cold forging gear steel provided by the invention can effectively avoid the fatigue life reduction caused by coarse grains.
While the invention has been described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed. Various changes in form and detail, including simple deductions or substitutions, may be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (10)
1. The cold-forging gear steel is characterized by comprising the following chemical components in percentage by weight:
C：0.16～0.19wt％、Si：0.15～0.25wt％、Mn：1.00～1.20wt％、Cr：1.0-1.10wt％、Al：0.02～0.04wt％，N：0.010～0.016wt％。
2. the cold-forged gear steel according to claim 1, further comprising: the balance being Fe and other unavoidable impurities.
3. The cold-forged gear steel according to claim 1 or 2, further comprising: 0 < Ca < 0.004 wt%, 0 < Ti < 0.008 wt%.
4. The cold-forged gear steel according to claim 2, wherein said other inevitable impurities include: less than or equal to 0.003 weight percent of S, less than or equal to 0.015 weight percent of P and less than or equal to 0.0030 weight percent of O.
5. The cold-forged gear steel as claimed in claim 1, wherein said microstructure of said cold-forged gear steel is ferrite and spherical carbide.
6. The cold-forged gear steel according to claim 1, wherein the properties of the cold-forged gear steel satisfy at least one of a yield strength of 180 to 220MPa, a tensile strength of 380 to 430MPa, an elongation of not less than 37% and a reduction of area of not less than 68%.
7. A method for producing a cold-forged gear steel, characterized in that the composition of the cold-forged gear steel is as set forth in any one of claims 1 to 6, the method comprising:
smelting and casting;
heating;
forging or rolling, and air-cooling to room temperature;
spheroidizing annealing: heating to 700 ℃ and preserving heat for 1h, heating to 750-770 ℃ and preserving heat for 4-6h, then cooling to 700-720 ℃ at a cooling rate of 10-15 ℃/h and preserving heat for 3-5h, then cooling to 670-690 ℃ at a cooling rate of 10-15 ℃/h and preserving heat for 4-6h, then cooling to below 500 ℃ at a cooling rate of 15-20 ℃/h, and then discharging and cooling to room temperature.
8. The method for producing cold-forged gear steel according to claim 7, wherein in said heating step, the heating temperature is controlled to 1100 to 1200 ℃ and the heating time is controlled to 4 to 5 hours.
9. The method for producing a cold-forged gear steel as claimed in claim 7, wherein the temperature of said forging or said rolling is 860 to 980 ℃.
10. The method for producing cold-forged gear steel according to claim 7, wherein said forging or rolling step further comprises heating at 1100 to 1200 ℃ for 4 to 5 hours.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110601013.4A CN115478230A (en) | 2021-05-31 | 2021-05-31 | Cold-forged gear steel and manufacturing method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110601013.4A CN115478230A (en) | 2021-05-31 | 2021-05-31 | Cold-forged gear steel and manufacturing method thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN115478230A true CN115478230A (en) | 2022-12-16 |
Family
ID=84419775
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202110601013.4A Pending CN115478230A (en) | 2021-05-31 | 2021-05-31 | Cold-forged gear steel and manufacturing method thereof |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115478230A (en) |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1947928A (en) * | 2005-10-14 | 2007-04-18 | 大同特殊钢株式会社 | Manufacturing method of block with perfect cold-forging property |
| CN101255531A (en) * | 2008-03-26 | 2008-09-03 | 莱芜钢铁股份有限公司 | Production method of low-Ti pinion steel |
| CN101289731A (en) * | 2008-05-09 | 2008-10-22 | 莱芜钢铁股份有限公司 | CrMnTi narrow hardenability strip pinion steels and method of manufacture |
| JP2010168628A (en) * | 2009-01-23 | 2010-08-05 | Jfe Steel Corp | Production method for steel for carburizing excellent in cold forgeability |
| CN106011648A (en) * | 2016-07-22 | 2016-10-12 | 武汉钢铁股份有限公司 | Gear steel and production method thereof |
| CN111334722A (en) * | 2018-12-18 | 2020-06-26 | 南京工程学院 | Carburized gear with uniform structure and refined grains and manufacturing method thereof |
-
2021
- 2021-05-31 CN CN202110601013.4A patent/CN115478230A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1947928A (en) * | 2005-10-14 | 2007-04-18 | 大同特殊钢株式会社 | Manufacturing method of block with perfect cold-forging property |
| CN101255531A (en) * | 2008-03-26 | 2008-09-03 | 莱芜钢铁股份有限公司 | Production method of low-Ti pinion steel |
| CN101289731A (en) * | 2008-05-09 | 2008-10-22 | 莱芜钢铁股份有限公司 | CrMnTi narrow hardenability strip pinion steels and method of manufacture |
| JP2010168628A (en) * | 2009-01-23 | 2010-08-05 | Jfe Steel Corp | Production method for steel for carburizing excellent in cold forgeability |
| CN106011648A (en) * | 2016-07-22 | 2016-10-12 | 武汉钢铁股份有限公司 | Gear steel and production method thereof |
| CN111334722A (en) * | 2018-12-18 | 2020-06-26 | 南京工程学院 | Carburized gear with uniform structure and refined grains and manufacturing method thereof |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN101705439B (en) | Low-temperature high-toughness F460 grade super strength steel plate for building ship and manufacturing method thereof | |
| CN110863158B (en) | High-performance Mn-Cr series steel for wind power output gear and production method thereof | |
| CN111424219B (en) | Method for manufacturing gear shaft steel capable of being directly subjected to cold forging | |
| CN101348884B (en) | 440MPa grade niobium-containing high-strength IF steel and manufacturing method thereof | |
| TW201708568A (en) | Wire for bolt excellent in acid cleaning property and delayed fracture resistance after quenching and tempering, and bolt | |
| CN111218620B (en) | High-yield-ratio cold-rolled dual-phase steel and manufacturing method thereof | |
| CN111850399B (en) | Corrosion-resistant plastic die steel with good wear resistance and preparation method thereof | |
| CN102345074A (en) | Intermediate-carbon high-speed cutting saw blade matrix steel and production method thereof | |
| KR20230159857A (en) | Steel for high-temperature carburized gear shafts and manufacturing method thereof | |
| CN112430771B (en) | Cold-rolled steel plate for precision stamping high-speed cutting chain saw blade and manufacturing method thereof | |
| CN104928577B (en) | A kind of steel plate and its manufacture method with high hole expansibility and excellent application of slip performance | |
| CN108998730B (en) | Hypereutectoid tool steel and manufacturing method thereof | |
| JP2001303172A (en) | Case hardening boron steel for cold forging free from formation of abnormal structure in carburiazation and its producing method | |
| CN115449703B (en) | Isothermal annealing gear steel bar applicable to cold forging and manufacturing method thereof | |
| CN110791706A (en) | Austenitic coarse-grain structural steel for cold forging and preparation method of wire rod of austenitic coarse-grain structural steel | |
| CN113832389B (en) | Cold extrusion round steel and manufacturing method thereof | |
| CN110066966A (en) | A kind of low internal stress titaniferous high-strength steel and production method | |
| CN115478230A (en) | Cold-forged gear steel and manufacturing method thereof | |
| CN112813361A (en) | Steel for hardware tools and preparation method thereof | |
| CN114763594A (en) | Cold-rolled steel sheet and method for manufacturing cold-rolled steel sheet | |
| CN115369311B (en) | Cold forging steel and manufacturing method thereof | |
| CN115029618B (en) | Cold forging gear steel with narrow hardenability and manufacturing method thereof | |
| CN115058658B (en) | Crankshaft, steel for crankshaft and preparation method thereof | |
| CN117626106A (en) | Energy-saving cold forging steel and manufacturing method thereof | |
| CN116640983A (en) | Non-quenched and tempered steel for high-pressure oil pump body of electric control common rail fuel injection system and preparation method of non-quenched and tempered steel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| RJ01 | Rejection of invention patent application after publication |
Application publication date: 20221216 |