CN116904852A - CrMnTi series gear steel with good low-temperature toughness and production method thereof - Google Patents

CrMnTi series gear steel with good low-temperature toughness and production method thereof Download PDF

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CN116904852A
CN116904852A CN202310795413.2A CN202310795413A CN116904852A CN 116904852 A CN116904852 A CN 116904852A CN 202310795413 A CN202310795413 A CN 202310795413A CN 116904852 A CN116904852 A CN 116904852A
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steel
equal
temperature
continuous casting
crmnti
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马立国
郭大勇
刘鹤
孙浩
高航
杨辉
黄旺祥
王秉喜
张博
潘阳
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Angang Steel Co Ltd
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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
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • 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
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • 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
    • C22C38/40—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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    • 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
    • C22C38/40—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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    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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    • 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
    • C21D2211/001—Austenite
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    • C21—METALLURGY OF IRON
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • 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
    • C21D2211/009—Pearlite
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Abstract

The application discloses CrMnTi series gear steel with good low-temperature toughness and a production method thereof, belonging to the field of steel for gear steel bars. Comprising the following steps: c:0.18% -0.22%, si:0.20% -0.30%, mn:0.90% -1.10%, cr:1.00% -1.20%, mo:0.10% -0.20%, ti:0.040% -0.065%, W:0.05% -0.15%; ni:0.05% -0.10%; al:0.020% -0.040%, B:0.0020% -0.0040%, N:0.010% -0.016%, mg:0.0035% -0.0065%, ca:0.0040% -0.0080%; the balance being Fe and unavoidable impurities. The gear steel provided by the application has good toughness at low temperature.

Description

CrMnTi series gear steel with good low-temperature toughness and production method thereof
Technical Field
The application belongs to the field of steel for gear steel bars, and particularly relates to CrMnTi gear steel with good low-temperature toughness and a production method thereof.
Background
In recent years, the automobile industry has increasingly higher requirements on the quality and performance of gear steel, and a plurality of automobile gear manufacturers have further put strict requirements on the quality technical indexes of the gear steel, and the gear steel mainly comprises the following components: narrow end hardenability bands, low oxygen and inclusion content, fine grains, good workability, good surface quality, etc. For example: the technical index of the carburized gear steel for one gas specifies that the oxygen content is less than 20ppm, the hardenability bandwidth is less than or equal to 6HRC, and the grain size requirement is superior to grade 5.
In the prior art, the patent application with publication number CN101096742 discloses a high-strength gear steel for automobiles: the weight percentages of the components are as follows: c:0.20-0.40, si:0.20-0.50, mn:0.50-1.00, cr:0.80-1.30, nb:0.015-0.080, V:0.030-0.090, mo:0.15-0.55, al:0.015-0.050, and the balance of Fe and unavoidable impurities. According to the patent application, after a trace of Nb and V are added, the grain size, hardenability and bandwidth of the gear steel are obviously optimized, so that the heat treatment deformation of gears produced in batches is smaller, and the pairing rate is improved; meanwhile, the comprehensive mechanical property of the gear steel is increased, and the service life is prolonged; and the cost is low.
The patent application with publication number of CN108342640B discloses a high-hardenability gear steel and a manufacturing method thereof: the mass percentages of the chemical elements are as follows: c:0.19% -0.25%, si:0.15% -0.35%, mn:0.70% -1.05%, cr:0.70% -0.80%, ni:0.40% -0.65%, cu is more than 0 and less than or equal to 0.20%, mo:0.33-0.40%, al:0.020-0.050%, ti:0.003-0.010%, b:0.05-0.08%, B:0.0001-0.0003%, N:0.0080% -0.0150%, and the balance of Fe and other unavoidable impurities. The gear steel of the patent application has high strength and good toughness. However, when the steel is not drawn, the steel quality defects such as exceeding of the band structure and poor deformation ability of the nonmetallic inclusion are liable to occur due to the control of the segregation of the components such as C, mn and S and the nonmetallic inclusion modification treatment, and microcrack defects in the steel are liable to occur.
None of the gear steels disclosed in the above patent applications have good low temperature toughness.
Disclosure of Invention
The application provides CrMnTi series gear steel with good low-temperature toughness and a production method thereof, aiming at the problems.
The first aspect of the application provides CrMnTi series gear steel with good low-temperature toughness, which comprises the following chemical components in percentage by mass:
c:0.18% -0.22%, si:0.20% -0.30%, mn:0.90% -1.10%, cr:1.00% -1.20%, mo:0.10% -0.20%, ti:0.040% -0.065%, W:0.05% -0.15%, ni:0.05% -0.10%, al:0.020% -0.040%, B:0.0020% -0.0040%, N:0.010% -0.016%, mg:0.0035% -0.0065%, ca:0.0040% -0.0080%, and the balance of Fe and unavoidable impurities;
mg and Ca in the steel satisfy the relation: mg+Ca is more than or equal to 0.0080% and less than or equal to 0.0120%;
ti and N in the steel satisfy the relation: ti/N is more than or equal to 4.
Further, the gear steel is producedThe quenching degree J9 of the standard bar is 34-40HRC, and the permeability J15 is more than or equal to 22HRC.
Further, the nonmetallic inclusion in the gear steel satisfies: class A is less than or equal to 2.0, class B is less than or equal to 2.0, class C is less than or equal to 1.0, and class D is less than or equal to 1.0.
Further, the tensile strength of the gear steel is more than 960MPa, the elongation after break is more than 6%, the shrinkage after break is more than 26%, and the low-temperature impact energy at the temperature of minus 40 ℃ is more than 30J.
The second aspect of the application provides a method for producing the gear steel, comprising the following steps:
(1) LF refining: in the LF refining, the heating time of an electrode is controlled to be 20-25min, coarse adjustment and fine adjustment are carried out for two component adjustment, wherein the coarse adjustment is to add 0.5-0.8kg/t aluminum powder for deoxidization operation, and the fine adjustment is to control the content of C, si, mn and Cr of a target;
(2) Vacuum degassing by VD: the VD vacuum degassing comprises the steps of carrying out soft blowing on argon for 5-15min after the VD is broken and the VD pressure maintaining time is 10-20min, and standing for 10-15min after the soft blowing is finished;
(3) Continuous casting: the continuous casting comprises protection casting, wherein the electromagnetic stirring voltage of a crystallizer in the protection casting is 100-200V, the current intensity is 150-280A, and the frequency is 3-8Hz; the electromagnetic stirring voltage of the solidification end is 280-380V, the current intensity is 200-350A, and the frequency is 2-8Hz;
(4) Rolling: the rolling comprises the preheating section temperature less than or equal to 850 ℃, the heating section temperature 1050-1150 ℃ and the soaking section temperature 1140-1180 ℃;
and (3) performing high-pressure water descaling control on the continuous casting blank before rolling: single-pass multi-nozzle water spraying high-pressure descaling, wherein the water descaling pressure is more than or equal to 20MPa, and the water descaling rate is more than or equal to 95%;
and (3) controlling the process temperature: the initial rolling temperature is more than or equal to 1000 ℃ and the final rolling temperature is 900-960 ℃;
(5) Slowly cooling steel materials: the slow cooling of the steel comprises the slow cooling time being more than 24 hours, and the temperature of the steel which is discharged out of a slow cooling pit is lower than 200 ℃.
Further, the section size of the continuous casting blank in continuous casting is 250-350mm multiplied by 350-450mm, the superheat degree of the tundish is controlled at 20-30 ℃, the continuous casting blank is at a constant drawing speed, and the speed of the constant drawing speed control is 0.50-0.70m/min.
The principle of adding each element in the application is as follows:
c: the element C is used to ensure the strength of the steel material and to improve the hardenability of the steel material. If the mass percentage of carbon is less than 0.18%, the hardenability and strength of the gear steel cannot be improved, and if the mass percentage of carbon is more than 0.22%, the fatigue performance and machinability of the gear steel are reduced. Therefore, the mass percentage of C is controlled to be 0.18-0.22%;
si: the Si element acts as a deoxidizer in the steel. Since Si does not form carbide in steel but exists in ferrite in the form of solid solution, i.e., has remarkable solid solution strengthening ferrite, the effect of reducing plasticity of steel materials is achieved. In addition, si can promote grain boundary segregation of P, S element, and properly embrittle grain boundaries. Therefore, the content of Si is properly reduced, and the mass percentage of Si is controlled to be 0.20-0.30 percent;
mn: the Mn element has remarkable solid solution strengthening effect in addition to the functions of deoxidizing agent and desulfurizing agent. In addition, mn and S can form MnS inclusion, so that a notch effect and a lubricant function are achieved during gear machining, and the cutting performance of the steel material is improved. Therefore, the mass percentage of Mn is controlled to be 0.90-1.10%;
cr: cr is a forming element of medium-strength carbide, and can obviously improve the comprehensive properties of the steel material, such as strength, wear resistance and the like. In addition, cr also reduces the activity of C to prevent decarburization during heating, rolling and heat treatment. However, too high a content of Cr deteriorates machinability of the steel material, and also increases alloy addition costs. Therefore, the mass percentage of Cr needs to be controlled to be 1.00% -1.20%;
mo: molybdenum is used as a strong carbide forming element in steel, so that nucleation and growth of carbide can be strongly hindered, meanwhile, the hardenability can be effectively improved, the combined effect of molybdenum and manganese can be remarkably improved, the stability of austenite can be remarkably improved, and the hardenability of steel is improved. The Mo element can delay pearlite transformation, promote the formation of acicular ferrite tissues, and can effectively inhibit the formation of banded tissues by adding a proper amount of Mo, so that the mass percentage of the Mo is controlled to be 0.10-0.20%;
ti: the Ti element is added to mainly refine the austenite grain size so as to ensure that the austenite grain size of the steel is finer than 5 grades. In addition, the influence of titanium on the hardenability is complex, on one hand, tiC can be formed by combining with C, the TiC is difficult to dissolve in austenite, the stability of supercooled austenite is reduced, the effect of reducing the hardenability is achieved, and meanwhile, the titanium can refine grains and improve the hardenability of steel. The influence of Ti element on the hardenability of steel is small within the range of 0.040-0.065%, and the oversize and excessive content of TiN inclusion can be avoided; meanwhile, ti in the steel is preferentially combined with N to form TiN, so that B element in the steel can exist in an effective B mode, and the stability of the hardenability of the steel is affected.
W: w can obviously prevent precipitation of austenite grain boundary carbide, refine grains, improve the performances of strength, plasticity, impact toughness, hydrogen embrittlement sensitivity and the like of steel, and the content of W is controlled to be 0.05-0.15%;
ni: can enhance the cross sliding capability of the matrix, reduce the cold-brittle transition temperature and improve the toughness. The carburizing steel can also obtain a surface layer with small carbon gradient and certain toughness, so that the Ni content is controlled to be 0.05-0.10%;
al: adding Al (0.020% -0.040%) with a certain content to refine crystal grains and deoxidize so as to ensure that the austenite grain size of the steel is finer than 5 grades, obtain extremely low oxygen content and reduce the quantity and size of nonmetallic inclusion in the steel;
b: the B element exists in the steel in the form of acid-soluble boron, so that the hardenability of the steel is improved, and some precious alloy elements are replaced; the acid insoluble boron in the form of carbon and nitride can refine grains and improve the toughness of the steel, so that the content of B is controlled to be 0.0020-0.0040 percent;
n: n and C, al, B, ti are combined and separated out to form corresponding precipitates for refining grains, and the relative content of Al and B which are taken as positive effects is considered to be controlled to be 0.010-0.016;
mg: is commonly used as a steelmaking deoxidizer and a desulfurizing agent. Reacting with O, S in molten steel to generate magnesium oxide or sulfide, reducing [ O ] and [ S ] in the molten steel to lower levels, and floating generated inclusions or removing the generated inclusions from the molten steel by adsorption of protective slag to play a role in deoxidization and desulfurization; the addition of trace Mg can improve the composition, size, shape and the like of inclusions in steel, and enhance the deformation and machinability of the inclusions in the steel. So the content of Mg is controlled to be 0.0035-0.0065 percent;
ca: the main inclusion in Al deoxidized steel is Al 2 O 3 While Al is 2 O 3 The steel has high inclusion hardness and sharp edges, the matrix is very easy to scratch in the subsequent processing process of the steel, and due to the high melting point, the steel is easy to adhere to the inner wall of the water gap, the smooth casting is affected, and serious accidents such as water gap blockage and the like can be caused. To avoid pure Al 2 O 3 Formation of inclusions, the Ca treatment process is adopted to lead Al to 2 O 3 The impurities react with CaO to generate low-melting-point calcium aluminate impurities, and the MnS impurities in the steel are converted into CaS or CaO.Al 2 O 3 The CaS composite inclusion improves isotropy of the steel sheet and improves properties of the steel matrix. Therefore, the component of Ca is designed to be 0.0040-0.0080%.
The beneficial effects are that:
the application adds Mg and Ca elements and adjusts the percentage of each element, adopts Ca treatment process to lead Al to be 2 O 3 The impurities react with CaO to generate low-melting-point calcium aluminate impurities, so that nozzle flocculation in the molten steel pouring process is avoided, and simultaneously, the MnS impurities in the steel are converted into CaS or CaO.Al 2 O 3 The CaS composite inclusion improves the isotropy of the steel plate and the performance of the steel substrate; the size of the oxide core in the magnesium treated steel is smaller than that in the calcium treated steel, indicating that magnesium treatment is advantageous for forming finer oxide inclusions in the steel and for reducing the precipitation of MnS at the grain boundaries. Realizes the non-gold effect by the unique and composite effect of Mg and Ca elements on non-metallic inclusions in steelBelongs to inclusion removal and modification, so that the gear steel has good toughness at low temperature. The ratio of Ti to N is further limited, so that the austenite grain size of the steel is adjusted, and the hardenability is improved.
Produced by the applicationThe quenching degree J9 of the standard bar is 34-40HRC, and J15 is more than or equal to 22HRC; nonmetallic inclusions in the steel are of class A less than or equal to 2.0, class B less than or equal to 2.0, class C less than or equal to 1.0, class D less than or equal to 1.0, austenite grain size is finer than 5, and banded structure is less than or equal to 2; mechanical properties of gear steel measured after tempering heat treatment: the tensile strength is more than 960MPa, the elongation after break is more than 6%, the shrinkage after break is more than 26%, and the low-temperature impact energy at minus 40 ℃ is more than 30J.
Detailed Description
The technical solutions of the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
The first aspect of the application provides CrMnTi series gear steel with good low-temperature toughness, which comprises the following chemical components in percentage by mass:
c:0.18-0.22%, si:0.20-0.30%, mn:0.90-1.10%, cr:1.00-1.20, mo:0.10-0.20%, ti:0.040-0.065%, W:0.05-0.15%, ni:0.05-0.10%, al:0.020-0.040%, B:0.0020-0.0040%, N:0.010-0.016%, mg:0.0035-0.0065%, ca:0.0040-0.0080%, and Fe and unavoidable impurities in balance;
mg and Ca in the steel satisfy the relation: mg+Ca is more than or equal to 0.0080% and less than or equal to 0.0120%;
ti and N in the steel satisfy the relation: ti/N is more than or equal to 4.
The second aspect of the application provides a production method of CrMnTi series gear steel with good low-temperature toughness, which comprises the following steps: molten iron pretreatment, converter smelting, LF furnace refining, VD refining, billet continuous casting (for short continuous casting), heating, rolling, slow cooling of steel, finishing, checking and warehousing. Many of these methods are the same as the prior art methods, and will not be further described herein, focusing on the distinguishing methods.
The method comprises LF refining, VD vacuum degassing, continuous casting, rolling and slow cooling of steel.
LF refining:
the primary tasks of LF refining are component fine adjustment, temperature control and slag forming operation, and the nitrogen increase of molten steel is controlled by adopting micro-positive pressure operation, large slag amount and heating time limitation. Performing slag forming operation with lime and fluorite, and controlling the electrode heating time to 20-25min. And (3) performing component adjustment twice, adding 0.5-0.8kg/t aluminum powder for deoxidization during coarse adjustment, and adjusting the C, si, mn, cr content in the steel according to the target during fine adjustment. And after the treatment is finished, proper thick slag treatment is carried out, so that the stability of the VD process is ensured.
Vacuum degassing by VD:
the high alkalinity and low oxidability top slag is adopted for control, and the processes of VD vacuum treatment, soft argon blowing and the like are matched, so that the cleanliness of molten steel can be ensured, and the total oxygen and hydrogen content in the steel can be reduced. The VD dwell time is controlled at 15min, argon is blown for 10min after the VD is broken, and the vacuum furnace is kept stand for 10-15min after the soft blowing is finished, so that the impurities are ensured to float upwards sufficiently, and the ladle is moved out to realize the component target control.
Continuous casting:
the section size of the continuous casting billet is (250-350) mm x (350-450) mm, the superheat degree of the tundish is controlled at 20-30 ℃, and the constant drawing speed (the drawing speed of the casting billet is controlled at 0.50-0.70 m/min); protection pouring (ladle, adding low-oxidability alkaline covering agent into molten steel in a tundish, large ladle to tundish, adopting a protection sleeve for the tundish to a crystallizer and blowing argon for protection, and adding high-quality protecting slag into the crystallizer); crystallizer + solidification end electromagnetic stirring: the electromagnetic stirring voltage of the crystallizer is 100-200V, the current intensity is 150-280A, and the frequency is 3-8Hz; the electromagnetic stirring voltage at the solidification end is 280-380V, the current intensity is 200-350A, and the frequency is 2-8Hz. By adopting an electromagnetic stirring process, nonmetallic inclusion in molten steel can be promoted to float upwards, the particle size of the inclusion in steel is reduced, and the inclusion is uniformly distributed; element segregation of the steel is reduced, so that the structure is uniform, and the defect of strip-shaped structure of the steel is reduced; the number and the depth of surface defects such as transverse cracks, longitudinal cracks, corner cracks and the like of the steel billet are reduced, and high-quality raw materials are provided for the rod with no scratch on the rolling surface;
rolling:
continuous casting billet heating system: the temperature of the preheating section is less than or equal to 850 ℃, the temperature of the heating section is 1050-1150 ℃, and the temperature of the soaking section is 1140-1180 ℃;
and (3) high-pressure water descaling control of the continuous casting billet before rolling: single-pass multi-nozzle water spraying high-pressure descaling, wherein the water descaling pressure is more than or equal to 20MPa, and the water descaling rate is more than or equal to 95%;
and (3) controlling the process temperature: the initial rolling temperature is more than or equal to 1000 ℃ and the final rolling temperature is 900-960 ℃;
slowly cooling steel materials: and (3) pit-entering slow cooling, wherein the slow cooling pit is required to be dried, the pit-entering slow cooling is performed at the temperature of more than 500 ℃, the slow cooling time is more than 24 hours, the slow cooling pit is ensured to be discharged at the temperature of less than 200 ℃, and finally the CrMnTi series gear steel is prepared.
The following are specific examples.
Example 1
LF refining: the primary tasks of LF refining are component fine adjustment, temperature control and slag forming operation, and the nitrogen increase of molten steel is controlled by adopting micro-positive pressure operation, large slag amount and heating time limitation. And (3) performing slag forming operation by using lime and fluorite, and controlling the heating time of the electrode to be 20min. And (3) performing component adjustment twice, adding 0.8kg/t aluminum powder for deoxidization during rough adjustment, and adjusting the C, si, mn, cr content in the steel according to the target during fine adjustment. And after the treatment is finished, proper thick slag treatment is carried out, so that the stability of the VD process is ensured.
Vacuum degassing by VD: the high alkalinity and low oxidability top slag is adopted for control, and the processes of VD vacuum treatment, soft argon blowing and the like are matched, so that the cleanliness of molten steel can be ensured, and the total oxygen and hydrogen content in the steel can be reduced. The VD dwell time is controlled at 15min, argon is blown for 10min after the VD is broken, and the vacuum furnace is kept stand for 13min after the soft blowing is finished, so that the impurities are ensured to float upwards sufficiently, and the ladle is moved out to realize the component target control.
Continuous casting: the section size of the continuous casting blank is 320mm multiplied by 410mm, the superheat degree of the tundish is controlled at 25 ℃, and the constant pulling speed (the pulling speed of the casting blank is controlled at 0.55 m/min); protection pouring (ladle, adding low-oxidability alkaline covering agent into molten steel in a tundish, large ladle to tundish, adopting a protection sleeve for the tundish to a crystallizer and blowing argon for protection, and adding high-quality protecting slag into the crystallizer); crystallizer + solidification end electromagnetic stirring: the electromagnetic stirring voltage of the crystallizer is 100V, the current intensity is 200A, and the frequency is 4Hz; the electromagnetic stirring voltage of the solidification tail end is 300V, the current intensity is 250A, and the frequency is 5Hz;
rolling: continuous casting billet heating system: the temperature of the preheating section is 840 ℃, the temperature of the heating section is 1130 ℃, and the temperature of the soaking section is 1165 ℃; and (3) high-pressure water descaling control of the continuous casting billet before rolling: single-pass multi-nozzle water spraying high-pressure descaling, water descaling pressure of 23MPa and water descaling rate of 97%; and (3) controlling the process temperature: the initial rolling temperature is 1030 ℃ and the final rolling temperature is 930 ℃; slowly cooling steel materials: and (3) pit-entering slow cooling, wherein the slow cooling pit is required to be dried, pit-entering slow cooling is carried out at 550 ℃ for 26 hours, the slow cooling time is ensured to be lower than 200 ℃, and the CrMnTi series gear steel is finally prepared.
Example 2
LF refining: the primary tasks of LF refining are component fine adjustment, temperature control and slag forming operation, and the nitrogen increase of molten steel is controlled by adopting micro-positive pressure operation, large slag amount and heating time limitation. And (3) performing slag forming operation by using lime and fluorite, and controlling the heating time of the electrode to be 22min. And (3) performing component adjustment twice, adding 0.7kg/t aluminum powder for deoxidization during rough adjustment, and adjusting the C, si, mn, cr content in the steel according to the target during fine adjustment. And after the treatment is finished, proper thick slag treatment is carried out, so that the stability of the VD process is ensured.
Vacuum degassing by VD: the high alkalinity and low oxidability top slag is adopted for control, and the processes of VD vacuum treatment, soft argon blowing and the like are matched, so that the cleanliness of molten steel can be ensured, and the total oxygen and hydrogen content in the steel can be reduced. The VD dwell time is controlled at 15min, argon is blown for 10min after the VD is broken, and the vacuum furnace is kept stand for 13min after the soft blowing is finished, so that the impurities are ensured to float upwards sufficiently, and the ladle is moved out to realize the component target control.
Continuous casting: the section size of the continuous casting blank is 320mm multiplied by 410mm, the superheat degree of the tundish is controlled at 25 ℃, and the constant pulling speed (the pulling speed of the casting blank is controlled at 0.55 m/min); protection pouring (ladle, adding low-oxidability alkaline covering agent into molten steel in a tundish, large ladle to tundish, adopting a protection sleeve for the tundish to a crystallizer and blowing argon for protection, and adding high-quality protecting slag into the crystallizer); crystallizer + solidification end electromagnetic stirring: the electromagnetic stirring voltage of the crystallizer is 120V, the current intensity is 230A, and the frequency is 6Hz; the electromagnetic stirring voltage at the solidification end is 330V, the current intensity is 280A, and the frequency is 6Hz;
rolling: continuous casting billet heating system: the temperature of the preheating section is 830 ℃, the temperature of the heating section is 1125 ℃, and the temperature of the soaking section is 1160 ℃; and (3) high-pressure water descaling control of the continuous casting billet before rolling: single-pass multi-nozzle water spray high-pressure descaling, water descaling pressure of 22MPa and water descaling rate of 98%; and (3) controlling the process temperature: the initial rolling temperature is 1020 ℃, and the final rolling temperature is 950 ℃; slowly cooling steel materials: and (3) pit-entering slow cooling, wherein the slow cooling pit is required to be dried, the pit-entering slow cooling is carried out at 535 ℃ for 24 hours, the slow cooling time is ensured to be lower than 200 ℃, the pit-entering slow cooling pit is ensured, and finally the CrMnTi series gear steel is prepared.
Example 3
LF refining: the primary tasks of LF refining are component fine adjustment, temperature control and slag forming operation, and the nitrogen increase of molten steel is controlled by adopting micro-positive pressure operation, large slag amount and heating time limitation. And (3) performing slag forming operation by using lime and fluorite, and controlling the heating time of the electrode to be 25 minutes. And (3) performing component adjustment twice, adding 0.6kg/t aluminum powder for deoxidization during rough adjustment, and adjusting the C, si, mn, cr content in the steel according to the target during fine adjustment. And after the treatment is finished, proper thick slag treatment is carried out, so that the stability of the VD process is ensured.
Vacuum degassing by VD: the high alkalinity and low oxidability top slag is adopted for control, and the processes of VD vacuum treatment, soft argon blowing and the like are matched, so that the cleanliness of molten steel can be ensured, and the total oxygen and hydrogen content in the steel can be reduced. The VD dwell time is controlled at 15min, argon is blown for 10min after the VD is broken, and the vacuum furnace is kept stand for 14min after the soft blowing is finished, so that the impurities are ensured to float upwards sufficiently, and the ladle is moved out to realize the component target control.
Continuous casting: the section size of the continuous casting blank is 320mm multiplied by 410mm, the superheat degree of the tundish is controlled at 27 ℃, and the constant pulling speed (the pulling speed of the casting blank is controlled at 0.60 m/min); protection pouring (ladle, adding low-oxidability alkaline covering agent into molten steel in a tundish, large ladle to tundish, adopting a protection sleeve for the tundish to a crystallizer and blowing argon for protection, and adding high-quality protecting slag into the crystallizer); crystallizer + solidification end electromagnetic stirring: the electromagnetic stirring voltage of the crystallizer is 180V, the current intensity is 240A, and the frequency is 7Hz; the electromagnetic stirring voltage at the solidification end is 350V, the current intensity is 320A, and the frequency is 5Hz;
rolling: continuous casting billet heating system: the preheating section temperature is 850 ℃, the heating section temperature is 1120 ℃, and the soaking section temperature is 1150 ℃; and (3) high-pressure water descaling control of the continuous casting billet before rolling: single-pass multi-nozzle water spray high-pressure descaling, water descaling pressure of 24MPa and water descaling rate of 98%; and (3) controlling the process temperature: the initial rolling temperature is 1030 ℃ and the final rolling temperature is 930 ℃; slowly cooling steel materials: and (3) pit-entering slow cooling, wherein the slow cooling pit is required to be dried, the pit-entering slow cooling is carried out at 540 ℃, the slow cooling time is more than 24 hours, the slow cooling pit is ensured to be discharged at the temperature lower than 200 ℃, and finally the CrMnTi series gear steel is prepared.
Example 4
LF refining: the primary tasks of LF refining are component fine adjustment, temperature control and slag forming operation, and the nitrogen increase of molten steel is controlled by adopting micro-positive pressure operation, large slag amount and heating time limitation. And (3) performing slag forming operation by using lime and fluorite, and controlling the heating time of the electrode to be 23min. And (3) performing component adjustment twice, adding 0.7kg/t aluminum powder for deoxidization during rough adjustment, and adjusting the C, si, mn, cr content in the steel according to the target during fine adjustment. And after the treatment is finished, proper thick slag treatment is carried out, so that the stability of the VD process is ensured.
Vacuum degassing by VD: the high alkalinity and low oxidability top slag is adopted for control, and the processes of VD vacuum treatment, soft argon blowing and the like are matched, so that the cleanliness of molten steel can be ensured, and the total oxygen and hydrogen content in the steel can be reduced. The VD dwell time is controlled at 15min, argon is blown for 10min after the VD is broken, and the vacuum furnace is kept stand for 15min after the soft blowing is finished, so that the impurities are ensured to float upwards sufficiently, and the ladle is moved out to realize the component target control.
Continuous casting: the section size of the continuous casting blank is 320mm multiplied by 410mm, the superheat degree of the tundish is controlled at 25 ℃, and the constant pulling speed (the pulling speed of the casting blank is controlled at 0.60 m/min); protection pouring (ladle, adding low-oxidability alkaline covering agent into molten steel in a tundish, large ladle to tundish, adopting a protection sleeve for the tundish to a crystallizer and blowing argon for protection, and adding high-quality protecting slag into the crystallizer); crystallizer + solidification end electromagnetic stirring: the electromagnetic stirring voltage of the crystallizer is 200V, the current intensity is 260A, and the frequency is 7Hz; the electromagnetic stirring voltage at the solidification end is 350V, the current intensity is 300A, and the frequency is 5Hz;
rolling: continuous casting billet heating system: the temperature of the preheating section is 830 ℃, the temperature of the heating section is 1060 ℃, and the temperature of the soaking section is 1170 ℃; and (3) high-pressure water descaling control of the continuous casting billet before rolling: single-pass multi-nozzle water spray high-pressure descaling, water descaling pressure of 23MPa and water descaling rate of 96%; and (3) controlling the process temperature: the initial rolling temperature is 1025 ℃, and the final rolling temperature is 940 ℃; slowly cooling steel materials: and (3) pit-entering slow cooling, wherein the slow cooling pit is required to be dried, pit-entering slow cooling is carried out at 545 ℃ for 25 hours, the slow cooling time is ensured to be lower than 200 ℃, the pit-entering slow cooling pit is ensured, and finally the CrMnTi series gear steel is prepared.
Steelmaking is carried out according to the chemical compositions and the content designed by the application and the comparative example 1, gear steel bars are produced through the processes of LF refining, VD vacuum treatment, continuous casting, heating, rolling, slow cooling and the like, and the actual measured chemical compositions are shown in the table 1.
TABLE 1 chemical composition (wt.%)
The nonmetallic inclusion and austenite grain size and the strip structure test result of the steel are shown in Table 2; the steel is normalized after heat preservation for 1 hour at 910 ℃ and end quenching at 880 ℃ for 30 minutes, and the quenching performance is shown in Table 2.
TABLE 2 examination results of nonmetallic inclusion, austenite grain size, strip structure, and hardenability of steel
Produced by the applicationThe mechanical properties of the bars after tempering heat treatment are shown in Table 3 (the heat treatment schedule is regulated in Table 4).
TABLE 3 mechanical Properties of steels after Heat treatment
Table 4 Heat treatment System for Steel products
The indexes of nonmetallic inclusion, austenite grain size, banded structure, hardenability and mechanical property of the gear steel bar produced by the method are all superior to the national standard control range, the low-temperature impact performance is greatly improved, and the use requirement of a low-temperature environment can be met.
The foregoing disclosure is illustrative of the present application and is not to be construed as limiting the scope of the application, which is defined by the appended claims.

Claims (6)

1. The CrMnTi series gear steel with good low-temperature toughness is characterized by comprising the following chemical components in percentage by mass:
c:0.18% -0.22%, si:0.20% -0.30%, mn:0.90% -1.10%, cr:1.00% -1.20%, mo:0.10% -0.20%, ti:0.040% -0.065%, W:0.05% -0.15%, ni:0.05% -0.10%, al:0.020% -0.040%, B:0.0020% -0.0040%, N:0.010% -0.016%, mg:0.0035% -0.0065%, ca:0.0040% -0.0080%, and the balance of Fe and unavoidable impurities;
mg and Ca in the steel satisfy the relation: mg+Ca is more than or equal to 0.0080% and less than or equal to 0.0120%;
ti and N in the steel satisfy the relation: ti/N is more than or equal to 4.
2. CrMnTi-based gear steel with good low-temperature toughness according to claim 1, characterized in that it is producedThe quenching degree J9 of the standard bar is 34-40HRC, and the permeability J15 is more than or equal to 22HRC.
3. The CrMnTi-based gear steel with good low temperature toughness according to claim 1, wherein nonmetallic inclusion in the gear steel satisfies: class A is less than or equal to 2.0, class B is less than or equal to 2.0, class C is less than or equal to 1.0, and class D is less than or equal to 1.0.
4. The CrMnTi-based gear steel with good low-temperature toughness according to claim 1, wherein the gear steel has a tensile strength of more than 960MPa, an elongation after break of more than 6%, a shrinkage after break of more than 26%, and a low-temperature impact energy of more than 30J at-40 ℃.
5. A method of producing a gear steel according to any one of claims 1 to 4, comprising the steps of:
(1) LF refining: in the LF refining, the heating time of an electrode is controlled to be 20-25min, coarse adjustment and fine adjustment are carried out for two component adjustment, wherein the coarse adjustment is to add 0.5-0.8kg/t aluminum powder for deoxidization operation, and the fine adjustment is to control the content of C, si, mn and Cr of a target;
(2) Vacuum degassing by VD: the VD vacuum degassing comprises the steps of carrying out soft blowing on argon for 5-15min after the VD is broken and the VD pressure maintaining time is 10-20min, and standing for 10-15min after the soft blowing is finished;
(3) Continuous casting: the continuous casting comprises protection casting, wherein the electromagnetic stirring voltage of a crystallizer in the protection casting is 100-200V, the current intensity is 150-280A, and the frequency is 3-8Hz; the electromagnetic stirring voltage of the solidification end is 280-380V, the current intensity is 200-350A, and the frequency is 2-8Hz;
(4) Rolling: the rolling comprises the preheating section temperature less than or equal to 850 ℃, the heating section temperature 1050-1150 ℃ and the soaking section temperature 1140-1180 ℃;
and (3) performing high-pressure water descaling control on the continuous casting blank before rolling: single-pass multi-nozzle water spraying high-pressure descaling, wherein the water descaling pressure is more than or equal to 20MPa, and the water descaling rate is more than or equal to 95%;
and (3) controlling the process temperature: the initial rolling temperature is more than or equal to 1000 ℃ and the final rolling temperature is 900-960 ℃;
(5) Slowly cooling steel materials: the slow cooling of the steel comprises the slow cooling time being more than 24 hours, and the temperature of the steel which is discharged out of a slow cooling pit is lower than 200 ℃.
6. The method for producing CrMnTi gear steel with excellent low temperature toughness according to claim 5, wherein the cross-sectional dimension of the continuous casting slab in the continuous casting is 250-350mm x 350-450mm, the superheat degree of the tundish is controlled at 20-30 ℃, the continuous casting slab is at a constant drawing speed, and the speed of the constant drawing speed control is 0.50-0.70m/min.
CN202310795413.2A 2023-06-30 2023-06-30 CrMnTi series gear steel with good low-temperature toughness and production method thereof Pending CN116904852A (en)

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