CN116043111A - Gear steel for wind power and production method thereof - Google Patents
Gear steel for wind power and production method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 104
- 239000010959 steel Substances 0.000 title claims abstract description 104
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 238000010438 heat treatment Methods 0.000 claims abstract description 15
- 238000005096 rolling process Methods 0.000 claims description 38
- 238000000034 method Methods 0.000 claims description 33
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 24
- 238000007670 refining Methods 0.000 claims description 24
- 229910052757 nitrogen Inorganic materials 0.000 claims description 22
- 239000002893 slag Substances 0.000 claims description 21
- 238000009749 continuous casting Methods 0.000 claims description 20
- 238000005266 casting Methods 0.000 claims description 19
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 19
- 229910052799 carbon Inorganic materials 0.000 claims description 15
- 238000001816 cooling Methods 0.000 claims description 13
- 229910052782 aluminium Inorganic materials 0.000 claims description 11
- 238000003756 stirring Methods 0.000 claims description 11
- 238000002791 soaking Methods 0.000 claims description 10
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052742 iron Inorganic materials 0.000 claims description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
- 238000010079 rubber tapping Methods 0.000 claims description 6
- 238000009849 vacuum degassing Methods 0.000 claims description 6
- 238000007664 blowing Methods 0.000 claims description 5
- 238000009792 diffusion process Methods 0.000 claims description 5
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims description 5
- 229910010271 silicon carbide Inorganic materials 0.000 claims description 5
- 238000009489 vacuum treatment Methods 0.000 claims description 5
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical group [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 4
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 4
- 239000004571 lime Substances 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 239000011574 phosphorus Substances 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000003723 Smelting Methods 0.000 claims description 3
- 238000010791 quenching Methods 0.000 claims description 3
- 230000000171 quenching effect Effects 0.000 claims description 3
- 239000002994 raw material Substances 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 2
- 238000010583 slow cooling Methods 0.000 claims description 2
- 239000013078 crystal Substances 0.000 abstract description 14
- 239000002245 particle Substances 0.000 abstract description 10
- 239000002131 composite material Substances 0.000 abstract description 8
- 230000000694 effects Effects 0.000 abstract description 7
- 238000005255 carburizing Methods 0.000 abstract description 6
- 230000000052 comparative effect Effects 0.000 description 19
- 238000001556 precipitation Methods 0.000 description 9
- 238000010586 diagram Methods 0.000 description 8
- 238000012360 testing method Methods 0.000 description 8
- 239000000203 mixture Substances 0.000 description 5
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000004321 preservation Methods 0.000 description 4
- 230000002159 abnormal effect Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000009827 uniform distribution Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- FHKPLLOSJHHKNU-INIZCTEOSA-N [(3S)-3-[8-(1-ethyl-5-methylpyrazol-4-yl)-9-methylpurin-6-yl]oxypyrrolidin-1-yl]-(oxan-4-yl)methanone Chemical compound C(C)N1N=CC(=C1C)C=1N(C2=NC=NC(=C2N=1)O[C@@H]1CN(CC1)C(=O)C1CCOCC1)C FHKPLLOSJHHKNU-INIZCTEOSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- RRZKHZBOZDIQJG-UHFFFAOYSA-N azane;manganese Chemical compound N.[Mn] RRZKHZBOZDIQJG-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
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- 238000005516 engineering process Methods 0.000 description 1
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- 239000004615 ingredient Substances 0.000 description 1
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- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
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- 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
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/076—Use of slags or fluxes as treating agents
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- 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
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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Abstract
The invention belongs to the technical field of gear steel, and particularly relates to gear steel for wind power and a production method thereof. Since the number of AlN and NbN second phase particles affects the degree of grain growth, alt/[ N ] in the steel is controlled within a range of 2-4 in order to ensure that a sufficient amount of AlN and NbN second phase particles are generated in the steel. In addition, the effect of the composite elements on grain growth is expressed by a simple linear formula, so that the stability of the gear steel structure for wind power is ensured, and the grain growth and the mixed crystal phenomenon of the forged piece after carburizing heat treatment at the temperature of 950-1000 ℃ for 15-40 hours are effectively avoided.
Description
Technical Field
The invention belongs to the technical field of gear steel, and particularly relates to gear steel for wind power and a production method thereof.
Background
In 2021, with the exit of land patch, the development of offshore wind power in china enters the scenic cycle. Ultra-large fans are increasingly favored by owners to reduce overall construction and maintenance costs. Aiming at the change, main host manufacturers at home and abroad push out the 8-12MW type of the fan, and more 'Jumbo' fans are produced, so that higher requirements are also put forward on the manufacture of various fan parts. On one hand, the gear for the fan is suitable for the severe environment of offshore wind power, and the gear is required to have high internal quality; on the other hand, the state energy-saving carbon reduction call is responded, a high-temperature carburization process with more advanced process is adopted, the carburization quenching temperature is improved, the high-temperature carburization time is shortened, and the carburization efficiency is improved.
A great deal of researches show that the carburization period can be reduced by increasing the carburization temperature, and the carburization treatment efficiency is obviously improved. However, due to the limitation of equipment conditions, the carburization treatment temperature of gears of most gear manufacturing enterprises in China is still controlled below 1000 ℃. Carburization at higher temperature is often carried out under vacuum condition, industrial high-temperature carburization equipment is expensive, and the technology is not mature enough, so that large-scale application is difficult. Some large modulus gears, due to the large size of the gears, often require 15 to 40 hours of carburizing heat treatment at temperatures below 1000 c, depending on the depth of carburized layer required. The tendency for grain growth during this process is very severe. In general carburized gear steel, al element is mostly added, and A1N fine crystal grain is used, but Al has poor high-temperature stability, is easily dissolved at 950 ℃ or more, and loses the effect of pinning grain boundaries. It has also been found that Nb can be added to steel during high temperature carburization at 1000 ℃ or less, and that grain boundaries are pinned by Nb (C, N) formation, thereby preventing abnormal growth of austenite grains. However, in the actual production process, the gear steel which is subjected to the composite microalloying of Al and Nb is very easy to generate mixed crystal phenomenon after carburization heat treatment for more than or equal to 15 hours at the temperature of more than 950 ℃, the grain size of individual parts reaches 3 grades, and the grain size is very poor and is often more than 3 grades. It can be seen that simple Al and Nb composite microalloying is difficult to adapt to the long-time high-temperature carburization requirement of gears.
Disclosure of Invention
The invention aims to provide gear steel for wind power and a production method thereof. To ensure that enough AlN and NbN second phase particles are generated in the steel, alt/[ N ] in the steel is controlled to be in the range of 2-4. In addition, the effect of the composite elements on grain growth is expressed by a simple linear formula, so that the stability of the gear steel structure for wind power is ensured, and the grain growth and the mixed crystal phenomenon of the forged piece after carburizing heat treatment at the temperature of 950-1000 ℃ for 15-40 hours are effectively avoided.
The technical problems to be solved by the invention are realized by adopting the following technical scheme:
the gear steel for wind power comprises the following chemical components in percentage by weight: c:0.15 to 0.23 percent, si:0.17 to 0.35 percent, mn:0.50 to 1.20 percent, cr:1.10 to 1.80 percent, mo:0.20 to 0.35 percent, ni:0 to 1.70 percent, nb:0.015 to 0.050 percent, P: less than or equal to 0.020%, S: less than or equal to 0.015 percent, alt: 0.020-0.040%, cu: less than or equal to 0.20 percent, ti less than or equal to 0.010 percent, [ O ]: less than or equal to 0.0015 percent, and [ N ]: less than or equal to 0.015 percent, [ H ]: less than or equal to 0.00015 percent, and the balance of Fe and other unavoidable impurities;
wherein, the content of the elements is less than or equal to 0.7 percent and less than or equal to 1/5Cr+1/5Mo+1/15Ni+20Nb+15Al+10Ti-1/6Mn-1/6P-C, and Alt/[ N ] is 2-4, wherein, the symbols of the elements represent the mass percentage of the corresponding elements in the steel.
The invention limits 0.7 percent to less than or equal to 1/5Cr+1/5Mo+1/15Ni+20Nb+15Al+10Ti-1/6Mn-1/6P-C, and has the function of ensuring that the average grain size of the forging is more than or equal to 7 grade and the range is less than 3 grade after carburizing heat treatment for 15-40 hours at the temperature of 950-1000 ℃.
The technical scheme of the invention is as follows: the hardenability of the steel is checked by quenching at 860 ℃, J1.5:40-48HRC, J5:39-48hrc, j25:31-39HRC;
the class A inclusion in the steel is less than or equal to 1.5 level, the class B inclusion is less than or equal to 1.0 level, the class C inclusion is less than or equal to 0.5 level, the class D inclusion is less than or equal to 0.5 level, and the class Ds is less than or equal to 0.5 level.
The invention also discloses a production method of the gear steel for wind power, which comprises the following steps:
1) Smelting in an electric furnace: the scrap steel and molten iron are adopted as raw materials, the proportion of molten iron into a furnace is 65-75%, the terminal carbon of an electric furnace is controlled to be more than or equal to 0.08%, the terminal phosphorus is controlled to be less than or equal to 0.010%, a proper amount of pure aluminum ingot is added into steel for deoxidization in the tapping process of the electric furnace, and the Alt content in the steel after refining in place is controlled to be 0.050-0.070%;
2) LF refining;
3) Vacuum treatment is carried out on the VD furnace, and nitrogen increasing treatment is carried out after the vacuum breaking;
4) Continuous casting: the continuous casting process adopts a whole-process protection casting process, and the nitrogen increment of molten steel in the continuous casting process is controlled to be less than or equal to 3ppm;
the superheat degree of molten steel is controlled at 20-35 ℃, the specific water quantity is 0.08-0.13L/kg, the proportion of the foot roller section, the secondary cooling section 1 and the secondary cooling section 2 is 6:4:3, the electromagnetic stirring current of a crystallizer is less than or equal to 150A, and the electromagnetic stirring current of the tail end is more than or equal to 200A;
5) Rolling: the casting blank adopts a cold charging heating process, the total heating time is controlled to be 7.5-9.0 hours, wherein the time of a soaking period is more than or equal to 1.5 hours, and the temperature of the soaking period is controlled to be 1200-1240 ℃;
rolling by adopting a rough rolling cogging and finish rolling forming mode, waiting for 3-5 min before starting rolling, controlling the starting rolling temperature to 1070-1180 ℃, controlling the reduction of a rough rolling single pass to be more than or equal to 50mm, controlling the finishing rolling temperature to 900-1030 ℃, and preserving heat before sawing the steel;
6) Slowly cooling.
The technical scheme of the invention is as follows: the LF refining step of the step 2) comprises the following specific steps: making refining slag by using lime and refining premelting slag, and controlling Al in the refining slag 2 O 3 The content is 25-32%, the slag alkalinity R is controlled within 5-7, silicon carbide and carburant are used for diffusion deoxidation in the refining process, the content of sigma Fe in the refined final slag is less than or equal to 0.5%, and the refining time of molten steel in LF is 45-55 min.
The technical scheme of the invention is as follows: the vacuum treatment of the VD furnace comprises the following specific steps: vacuum degassing is carried out by utilizing a VD furnace, the thickness of slag is controlled to be 80-100 mm before charging, the holding time of molten steel is not less than 67Pa, and the molten steel is maintained for 15min or more, after the vacuum degassing, 1.8-2.2 m/ton of steel is fed into the steel for nitrogen increasing, and the soft blowing time of the molten steel is controlled to be 15-25 min.
The technical scheme of the invention is as follows: the step 6) of slow cooling specifically comprises the following steps: the temperature of the upper cooling bed is controlled between 650 and 750 ℃.
The technical scheme of the invention is as follows: step 4) continuous casting is carried out by adopting a large round billet continuous casting machine for casting, and the section of a casting blank is
The rolling specification of the step 5) rolling is
Summary of the invention: to avoid abnormal grain growth of gears during high temperature carburization, it is necessary to: 1. the steel has enough second phase particles to play a role of pinning grain boundaries; 2. the second phase particles are uniformly distributed, and abnormal growth of crystal grains in a local area is avoided.
The invention adopts Al,Nb and N composite microalloying design aims to ensure that second phase particles such as AlN, nbN and the like are generated in steel, and grain boundaries are pinned in the carburizing heat treatment process to prevent the grains from growing. The relative atomic mass ratio of aluminum to nitrogen in AlN is about 3:2, but the aluminum in the steel is in Al 2 O 3 AlN, acid-soluble aluminum and other forms exist, and Alt/[ N ] in steel is subjected to Al and Nb composite conditions]The second phase particles such as AlN, nbN and the like can be generated in a sufficient amount in the steel by controlling the content within the range of 2-4. In addition, an excessive amount of N causes defects in the surface quality of the steel, adversely affects the production, and therefore the nitrogen content cannot be increased without limitation.
In addition, the invention fully utilizes the effect of alloy elements such as Cr, mo, ni and the like for stabilizing austenite grains, the elements such as Cr, mo and the like can form stable carbide with carbon in steel, the growth of the grains is prevented, and the Ni element has a certain blocking effect on the growth of the austenite grains. The effect of the composite element is not necessarily a simple superposition of the effects of the single element.
In a certain chemical composition range, the invention analyzes a large amount of test data, expresses the effect of the composite element on grain growth through a simple linear formula, can conveniently guide the subsequent production process, and has certain reference significance for developing new materials.
In the continuous casting process, the invention integrally adopts a weak cooling process, the water quantity is properly increased in the early stage, the electromagnetic stirring current of the crystallizer is controlled within 150A, the growth of columnar crystals of the casting blank can be better promoted, the electromagnetic stirring current at the tail end is controlled above 200A at the final stage of solidification, and the uniformity of the core casting blank is improved. Thus, the uniformity of the whole cross section of the casting blank can be well ensured.
In the rolling process, the soaking period is longer than or equal to 1.5h, the soaking period temperature is controlled at 1200-1240 ℃, the component uniformity of the casting blank is further improved, the temperature is waited to be reduced for 3-5 min before rolling, the surface temperature of the casting blank is greatly reduced, the core deformation of the casting blank in the cogging process is facilitated, the finishing temperature is controlled at 900-1030 ℃, and the hot rolling state grain size is ensured to be controlled to be more than 8 grades. The primary grain size of the steel also affects the size of the austenite grains. In addition, studies have shown that,as shown in FIG. 9, FIG. 9 shows the Time (Time) and Temperature (Temperature) required for precipitation of Nb (C, N) per unit amount under the same strain rate (. Epsilon.) condition, and the strain amount
The higher the temperature, the longer the time required for precipitation of Nb (C, N) per unit amount, and the shortest the time required for precipitation of Nb (C, N) per unit amount when the temperature reaches 900 ℃; similarly, the larger the strain amount, the shorter the time required for Nb (C, N) precipitation per unit amount at the same temperature, and since the rate of Nb (C, N) precipitation reaches a maximum value at 900 ℃ under the same strain rate condition, the steel is kept warm after rolling and before sawing, and Nb (C, N) precipitation is promoted.
Compared with the prior art, the invention has the beneficial effects that:
(1) The gear steel for wind power ensures that the grain size of the gear steel after carburizing heat treatment for 15-40 hours at 950-1000 ℃ is more than or equal to 7 levels by stably controlling the alloy content in the steel, and simultaneously stably controls the hardenability of the steel.
(2) The production method of the gear steel for wind power adopts good steelmaking cleanliness control, a continuous casting process full-protection casting process, a reasonable electromagnetic stirring process and a large compression ratio rolling process, ensures uniform and stable components and tissues of round steel, and has excellent steel performance.
(3) The production method of the gear steel for wind power adopts reasonable rolling temperature control, strengthens precipitation of second phase particles in steel in the cooling process after rolling, and stabilizes the grain size of the steel.
Drawings
FIG. 1 is a grain size diagram of a cross-sectional edge portion of a gear steel for wind power in example 1;
FIG. 2 is a grain size diagram of a 1/2R part of a cross section of gear steel for wind power in example 1;
FIG. 3 is a grain size diagram of a cross-sectional edge portion of a gear steel for wind power in example 2;
FIG. 4 is a grain size diagram of a 1/2R part of a cross section of gear steel for wind power in example 2;
FIG. 5 is a grain size diagram of a cross-sectional edge portion of a gear steel for wind power in comparative example 1;
FIG. 6 is a grain size diagram of a cross-sectional edge portion of a gear steel for wind power in comparative example 2;
FIG. 7 is a grain size diagram of a cross-sectional edge portion of a gear steel for wind power in comparative example 3;
FIG. 8 is a grain size diagram of a 1/2R part of a cross section of a gear steel for wind power in comparative example 3;
FIG. 9 is a graph showing the precipitation rate of Nb (C, N) under different strain conditions.
Detailed Description
The following describes the invention in more detail with reference to examples, which are not intended to limit the invention thereto.
The invention discloses a production method of gear steel for wind power, which comprises the following steps:
1) Smelting by using an electric furnace, wherein scrap steel and molten iron are used as raw materials, the proportion of molten iron into the furnace is 65-75%, the terminal carbon of the electric furnace is controlled to be more than or equal to 0.08%, the terminal phosphorus is controlled to be less than or equal to 0.010%, a proper amount of pure aluminum ingot is added into steel for deoxidization in the tapping process of the electric furnace, and the Alt content in the steel after refining in place is controlled to be 0.050-0.070%.
Making refining slag by using lime and refining premelting slag, and controlling Al in the refining slag 2 O 3 The content is 25-32%, the slag alkalinity R is controlled within 5-7, silicon carbide and carburant are used for diffusion deoxidation in the refining process, the content of sigma Fe in the refined final slag is less than or equal to 0.5%, and the refining time of molten steel in LF is 45-55 min.
Vacuum degassing is carried out on a VD furnace, the thickness of slag is controlled to be 80-100 mm before the furnace is charged, the holding time of molten steel is more than or equal to 15min below 67Pa, after the vacuum degassing is carried out, manganese nitride wires are fed into steel for increasing nitrogen by 1.8-2.2 m/ton of steel, and the soft blowing time of molten steel is controlled to be 15-25 min.
2) The continuous casting process adopts a whole-process protection casting process, and the nitrogen increment of molten steel in the continuous casting process is controlled to be less than or equal to 3ppm.
3) Casting by a large round billet continuous casting machine, wherein the section of a casting blank is
The superheat degree of molten steel is controlled at 20-35 ℃, the specific water quantity is 0.08-0.13L/kg, the proportion of the foot roller section, the secondary cooling section 1 and the secondary cooling section 2 is 6:4:3, the electromagnetic stirring current of a crystallizer is less than or equal to 150A, and the electromagnetic stirring current of the tail end is more than or equal to 200A;
4) The casting blank adopts a cold charging heating process, the total heating time is controlled to be 7.5-9.0 hours, wherein the time of a soaking period is more than or equal to 1.5 hours, and the temperature of the soaking period is controlled to be 1200-1240 ℃.
Adopting rough rolling cogging and finish rolling forming mode to roll, waiting for 3-5 min before starting rolling, controlling the starting rolling temperature at 1070-1180 ℃, and the reduction of rough rolling single pass is more than or equal to 50mm, and the rolling specification is that
The final rolling temperature is controlled to 900-1030 ℃, the heat preservation is carried out before sawing the steel, and the upper cooling bed temperature is controlled to 650-750 ℃.
The gear steel for wind power is primarily refined by adopting a 120-ton electric furnace, high-quality self-circulation scrap steel is adopted, the ratio of added molten iron is 65-75%, the terminal carbon is more than or equal to 0.08%, the terminal phosphorus is less than or equal to 0.010%, and the tapping temperature is 1628-1640 ℃. 115-120 tons of electric furnace tapping are carried out, 660kg of lime, 400kg of refining premelting slag and 135kg of pure aluminum blocks are added in the tapping process, and alloy is prepared according to the component. After LF is in place, a carburant and silicon carbide are used for diffusion deoxidation, the dosage of the silicon carbide is 50kg, alloy is distributed according to target components after the diffusion deoxidation is completed, and the molten steel refining period is 50-60min.
Slag is removed before molten steel enters a VD station, 1/3 slag amount is removed, vacuum treatment is carried out for 25min, the temperature is kept below 67Pa for 15min, a finished product sample is taken and analyzed after soft blowing is carried out for 3min, the total soft blowing time after breaking is more than or equal to 20min, and steel is added after proper temperature measurement.
Wherein, table 1 is the parameters of the continuous casting process of the embodiment of the invention; table 2 shows parameters of the continuous casting process according to the embodiment of the invention; table 3 shows the melting analysis ingredients of the examples of the present invention; table 4 shows the results of the gas test in accordance with the examples of the present invention; table 5 shows the test results of the mechanical properties of the steel materials according to the examples of the present invention; table 6 shows the hardenability test results of the steel products according to the examples of the present invention; table 7 shows the grain size rating of examples of the present invention.
TABLE 1 parameters of the continuous casting process according to the examples of the invention
| Casting section | Electric stirring current of crystallizer | Terminal electric stirring current | |
| Example 1 | Φ500mm | 150A | 200A |
| Example 2 | Φ650mm | 100A | 225A |
| Comparative example 1 | Φ500mm | 150A | 200A |
| Comparative example 2 | Φ500mm | 150A | 200A |
| Comparative example 3 | Φ500mm | 225A | 150A |
TABLE 2 Steel Rolling Process parameters according to the examples of the invention
| Rolling specification | Soaking temperature | Soaking time | Finishing temperature | Whether or not to keep warm after rolling | |
| Example 1 | |
1200～1240℃ | 1.67～2h | 923～958℃ | Is that |
| Example 2 | Φ240mm | 1220～1240℃ | 1.5～2.2h | 915～955℃ | Is that |
| Comparative example 1 | |
1200～1240℃ | 1.67～2h | 923～958℃ | Is that |
| Comparative example 2 | |
1200～1240℃ | 1.67～2h | 923～958℃ | Is that |
| Comparative example 3 | |
1200～1240℃ | 1.67～2h | 953～988℃ | Whether or not |
TABLE 3 melting analysis Components according to examples of the invention
TABLE 4 results of gas tests per ppm in examples of the invention
| O | N | H | |
| Example 1 | 11.8 | 84.9 | 0.1 |
| Example 2 | 8 | 88.6 | 0.7 |
| Comparative example 1 | 7.5 | 33 | 0.2 |
| Comparative example 2 | 8.8 | 80 | 0.1 |
| Comparative example 3 | 9 | 90 | 0.2 |
TABLE 5 mechanical test results of the inventive example steels
TABLE 6 HRC results of hardenability test of the inventive example steels
| J1.5 | J9 | J15 | |
| Example 1 | 43.8 | 43.63 | 38.8 |
| Example 2 | 43.9 | 40 | 30.2 |
| Comparative example 1 | 43.1 | 40.2 | 31.1 |
| Comparative example 2 | 47.5 | 44.1 | 39.2 |
| Comparative example 3 | 44.2 | 43.8 | 37.6 |
TABLE 7 grain size rating of the examples of the invention
As shown in Table 7 and FIGS. 1 to 4, it can be seen from the grain size test results that the average grain sizes at the edges and 1/2R of examples 1 and 2 are not less than 7.5 grade, the difference is not more than 2.5 grade, the growth of crystal grains is effectively inhibited, and the mixed crystal phenomenon does not occur under the condition of heat preservation at 980 ℃ for 40 h.
In comparative example 1, although the composition satisfies 0.7% or less 1/5Cr+ 1/5Mo+ 1/15Ni+20Nb+15Al+10Ti-1/6Mn-1/6P-C, the crystal grains were locally grown abnormally at the edges of the rolled material, and as shown in Table 7 and FIG. 5, the average grain size at the edge portion was 6.5 grade, the difference was 5 grade, and the mixed crystal phenomenon was observed under the condition of heat preservation at 980℃for 20 hours. Therefore, it was revealed that, even if the content of the microalloy components such as Al and Nb is satisfactory, but the nitrogen content is not satisfactory, that is, alt/[ N ] is greater than 4, as shown in tables 3 and 4, a sufficient amount of second phase particles such as AlN, nbN and the like cannot be produced, and the mixed crystal phenomenon is also caused.
The comparative example 2 was subjected to nitrogen enrichment, but the chemical composition was not 0.7% or less 1/5Cr+ 1/5Mo+ 1/15Ni+20Nb+15Al+10Ti-1/6Mn-1/6P-C, and after 20 hours of heat treatment, the average grain size at the edge portion was 5.0 grade, the difference was 3.5 grade, and the mixed crystal phenomenon was observed under the condition of heat preservation at 980℃for 20 hours as shown in Table 7 and FIG. 6.
According to the invention, the relation among the components and the Alt/[ N ] have obvious influence on the grain size and the range of the subsequent carburization treatment structure grain size of the gear steel, and the average grain size is more than or equal to 7 grade and the range is less than 3 grade after the carburization heat treatment for 15-40 hours at the temperature of 950-1000 ℃ only when the two components are satisfied.
Comparative example 3 is similar to example 1 in composition, but it is different from the continuous casting and rolling processes, and is disadvantageous in uniform distribution of the composition and rapid mass precipitation of second phase particles such as Nb (C, N), and as shown in table 7 and fig. 8, the average grain size at the edge portion is 5.5 grade, the difference is 3.5 grade, resulting in coarse and mixed crystal grains at 1/2R of the rolled material. It is described that the subsequent continuous casting and rolling have an important influence on the uniform distribution of crystal grains.
Claims (7)
1. The gear steel for wind power is characterized by comprising the following chemical components in percentage by weight: c:0.15 to 0.23 percent, si:0.17 to 0.35 percent, mn:0.50 to 1.20 percent, cr:1.10 to 1.80 percent, mo:0.20 to 0.35 percent, ni:0 to 1.70 percent, nb:0.015 to 0.050 percent, P: less than or equal to 0.020%, S: less than or equal to 0.015 percent, alt: 0.020-0.040%, cu: less than or equal to 0.20 percent, ti less than or equal to 0.010 percent, [ O ]: less than or equal to 0.0015 percent, and [ N ]: less than or equal to 0.015 percent, [ H ]: less than or equal to 0.00015 percent, and the balance of Fe and other unavoidable impurities;
wherein, the content of the elements is less than or equal to 0.7 percent and less than or equal to 1/5Cr+1/5Mo+1/15Ni+20Nb+15Al+10Ti-1/6Mn-1/6P-C, and Alt/[ N ] is 2-4, wherein, the symbols of the elements represent the mass percentage of the corresponding elements in the steel.
2. The gear steel for wind power according to claim 1, wherein: the hardenability of the steel is checked by quenching at 860 ℃, J1.5:40-48HRC, J5:39-48hrc, j25:31-39HRC;
the class A inclusion in the steel is less than or equal to 1.5 level, the class B inclusion is less than or equal to 1.0 level, the class C inclusion is less than or equal to 0.5 level, the class D inclusion is less than or equal to 0.5 level, and the class Ds is less than or equal to 0.5 level.
3. A method for producing the gear steel for wind power according to claim 1 or 2, comprising the steps of:
1) Smelting in an electric furnace: the scrap steel and molten iron are adopted as raw materials, the proportion of molten iron into a furnace is 65-75%, the terminal carbon of an electric furnace is controlled to be more than or equal to 0.08%, the terminal phosphorus is controlled to be less than or equal to 0.010%, a proper amount of pure aluminum ingot is added into steel for deoxidization in the tapping process of the electric furnace, and the Alt content in the steel after refining in place is controlled to be 0.050-0.070%;
2) LF refining;
3) Vacuum treatment is carried out on the VD furnace, and nitrogen increasing treatment is carried out after the vacuum breaking;
4) Continuous casting: the continuous casting process adopts a whole-process protection casting process, and the nitrogen increment of molten steel in the continuous casting process is controlled to be less than or equal to 3ppm;
the superheat degree of molten steel is controlled at 20-35 ℃, the specific water quantity is 0.08-0.13L/kg, the proportion of the foot roller section, the secondary cooling section 1 and the secondary cooling section 2 is 6:4:3, the electromagnetic stirring current of a crystallizer is less than or equal to 150A, and the electromagnetic stirring current of the tail end is more than or equal to 200A;
5) Rolling: the casting blank adopts a cold charging heating process, the total heating time is controlled to be 7.5-9.0 hours, wherein the time of a soaking period is more than or equal to 1.5 hours, and the temperature of the soaking period is controlled to be 1200-1240 ℃;
rolling by adopting a rough rolling cogging and finish rolling forming mode, waiting for 3-5 min before starting rolling, controlling the starting rolling temperature to 1070-1180 ℃, controlling the reduction of a rough rolling single pass to be more than or equal to 50mm, controlling the finishing rolling temperature to 900-1030 ℃, and preserving heat before sawing the steel;
6) Slowly cooling.
4. A method of producing a gear steel for wind power according to claim 3, wherein: the LF refining step of the step 2) comprises the following specific steps: making refining slag by using lime and refining premelting slag, and controlling Al in the refining slag 2 O 3 The content is 25-32%, the slag alkalinity R is controlled within 5-7, silicon carbide and carburant are used for diffusion deoxidation in the refining process, the content of sigma Fe in the refined final slag is less than or equal to 0.5%, and the refining time of molten steel in LF is 45-55 min.
5. A method of producing a gear steel for wind power according to claim 3, wherein: the vacuum treatment of the VD furnace comprises the following specific steps: vacuum degassing is carried out by utilizing a VD furnace, the thickness of slag is controlled to be 80-100 mm before charging, the holding time of molten steel is not less than 67Pa, and the molten steel is maintained for 15min or more, after the vacuum degassing, 1.8-2.2 m/ton of steel is fed into the steel for nitrogen increasing, and the soft blowing time of the molten steel is controlled to be 15-25 min.
6. A method of producing a gear steel for wind power according to claim 3, wherein: the step 6) of slow cooling specifically comprises the following steps: the temperature of the upper cooling bed is controlled between 650 and 750 ℃.
7. A method of producing a gear steel for wind power according to claim 3, wherein: step 4) continuous casting is carried out by adopting a large round billet continuous casting machine, and the section of a casting blank is phi 500-650 mm;
the rolling specification of the rolling in the step 5) is phi 120-260 mm.
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