CN114395657A - High-cleanness electroslag bearing steel for railway freight car and smelting method thereof - Google Patents
High-cleanness electroslag bearing steel for railway freight car and smelting method thereof Download PDFInfo
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- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
- C22B9/16—Remelting metals
- C22B9/18—Electroslag remelting
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- 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
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
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- 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
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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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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Abstract
The invention provides high-cleanness electroslag bearing steel for a railway wagon and a smelting method thereof, wherein a process route of 'primary smelting furnace + LF refining + RH vacuum degassing + protective pouring + protective atmosphere electroslag remelting' is adopted; the content of oxygen, calcium and magnesium impurity elements and inclusions is obviously reduced by strictly controlling the aluminum content, the LF refining slag component, the electroslag remelting furnace slag component in the whole process and limiting the vacuum degassing mode; the invention has the advantages that the electric slag bearing steel for the railway freight car produced by the process has higher cleanliness, and the inclusions are finer and more dispersed; the contents of oxygen, calcium and magnesium impurity elements are respectively not more than 0.0007%, 0.0003% and 0.0003%, and Ds inclusion is not more than 0.5 grade, so that the high fatigue performance of the carburizing bearing steel is effectively ensured.
Description
Technical Field
The invention belongs to the field of ferrous metallurgy production, and particularly relates to high-cleanness electroslag bearing steel for a railway wagon and a smelting method thereof, which are particularly suitable for smelting high-cleanness carburizing bearing steel varieties.
Background
The railway freight transportation has a series of advantages of large transportation volume, low cost, high safety and the like, and plays an important role in the field of modern transportation. The bearing is one of key basic components and plays a very important role in the service life of the railway wagon. G20CrNi2Mo is a typical carburized bearing steel with high hardness, wear resistance, and dimensional stability on the surface and high toughness inside. The rolling bearing ring of the railway freight car in China is made of the steel.
Electroslag remelting (ESR) is a typical special refining process and has the advantages of obviously removing large-size nonmetallic inclusions, improving steel ingot solidification structures and the like. Therefore, the railway department (now the China railway general company) has always required that the special steel enterprises in China need to adopt the external refining and electroslag remelting process to produce the G20CrNi2Mo bearing steel. The cleanliness of steel (oxygen content and inclusions) is an important factor affecting the fatigue life of bearing steel. With the development of the Chinese railway freight car to load 70t class, 120 km/h and 150 km/h operation mileage, the railway bearing needs higher bearing capacity, longer service life and higher reliability, which also puts higher requirements on the cleanliness of electroslag bearing steel.
In order to improve the cleanliness of carburizing bearing steel, chinese patent CN104532102A discloses a new process for manufacturing large-specification carburizing bearing steel G20CrNi4A for wind power, the process adopts a technical route of 'electric furnace + LF + VD degassing + die casting + protective atmosphere electroslag remelting', and the process has the following limitations: (1) VD slag steel reacts violently, and the aluminum loss is large; performing aluminum supplement operation after VD to cause the cleanliness of molten steel to be poor; (2) in the VD process, the stirring is violent, the slag overflow phenomenon is serious, and simultaneously, the slag entrainment of molten steel is easy to occur, and more large-particle impurities are generated; (3) the electroslag remelting process adopts traditional pseudo-ginseng slag and has limited adsorption effect on the inclusions of the consumable electrode. Chinese patent CN 107904498A discloses a carburizing bearing steel for a railway wagon and a preparation method thereof, the process adopts a technical route of 'primary smelting (electric furnace or converter) + LF refining + vacuum degassing (VD or RH) + continuous casting', but the invention does not explicitly describe key technical parameters such as slag components and the like in the smelting process. Further, the manner of degassing is not limited, and as noted above, VD degassing has inherent limitations that are detrimental to high cleanliness control. The document (discussion of G20CrNi2MoA carburizing bearing steel production process) reports a process route of 'electric furnace + LF + VD degassing + electroslag remelting', and the addition of aluminum wires before VD breaks the steel slag balance established in the LF refining process, and is also not beneficial to the control of the cleanliness of molten steel. Chinese patent CN112030065A discloses a carburizing bearing steel and a preparation method thereof, the invention mainly focuses on material component design, and plays a role in refining crystal grains and improving the uniformity of a structure by adding a proper amount of Nb and V, but does not relate to the control of technical parameters in a smelting process.
These processes and methods are helpful in improving the cleanliness of carburized bearing steels, but have limited improvements due to the lack of systematic control of key technological parameters, such as molten steel aluminum content, slag composition, etc. Therefore, how to provide the electroslag bearing steel for the railway wagon and the smelting method thereof is a problem which is urgently solved by the personnel in the field, and the electroslag ingot with high cleanliness is produced by finely controlling key process parameters of the whole process.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for smelting electroslag bearing steel for a high-cleanness railway wagon. The method adopts a process route of 'primary smelting furnace + LF refining + RH vacuum degassing + protective casting + protective atmosphere electroslag remelting'. The cleanliness of the carburizing bearing steel is obviously improved by strictly controlling the aluminum content, the LF refining slag component, the electroslag remelting furnace slag component in the whole process and limiting the vacuum degassing mode.
The invention firstly provides the electroslag bearing steel for the railway freight car, which comprises the following elements in percentage by mass: ω [ C ]: 0.19 to 0.23%, and [ omega ] Si: 0.25 to 0.35%, and [ omega ] Mn: 0.55-0.65%, ω [ Cr ]: 0.45-0.60%, ω [ Ni ]: 1.70-1.90%, and ω [ Mo ]: 0.20 to 0.30%, and [ omega ] Al: 0.015-0.025%, omega [ S ] < 0.0015%, omega [ P ] < 0.013%, omega [ Ca ] less than or equal to 0.0003%, omega [ Mg ] less than or equal to 0.0003%, omega [ O ] less than or equal to 0.0007%, and the balance of Fe and unavoidable impurity elements; ds inclusions are not greater than 0.5 grade.
The invention also provides a smelting method of the electroslag bearing steel for the railway wagon, which adopts a process route of 'primary smelting furnace + LF refining + RH vacuum degassing + protective pouring + protective atmosphere electroslag remelting', and obviously reduces the contents of oxygen, calcium and magnesium impurity elements and impurities by strictly controlling the aluminum content, the LF refining slag component, the electroslag remelting furnace slag component in the whole process and limiting the vacuum degassing mode. Wherein the oxygen content of the electroslag ingot is not more than 0.0007 percent, and the contents of Ca and Mg are not more than 0.0003 percent.
And after the primary smelting is finished, the aluminum content range after tapping is omega [ Al ]: 0.04-0.05%;
the range of the aluminum content at the end of the LF refining is omega [ Al ]: 0.025-0.035%;
the slag composition range at the end of LF refining is as follows: ω (CaO): 52 to 56%, omega (SiO)2)：8～12％、ω(Al2O3)：22～27％、ω(MgO)：3～5％、ω(FeO)<0.7％；
The degassing mode is RH vacuum degassing;
the slag after electroslag remelting and slagging comprises the following components in range: omega (CaF)2)：40～55％、ω(CaO)：10～15％、ω(Al2O3)：30～40％、ω(SiO2)：1～3％、ω(MgO)：3～5％。
Further, wherein:
(1) the primary smelting furnace comprises a converter or an electric arc furnace and mainly realizes the tasks of dephosphorization, decarburization, temperature rise and the like;
tapping conditions after primary smelting are as follows: the control range of the carbon content is 0.06-0.15%, and the temperature of the molten steel is 1600-1650 ℃.
Tapping: the operations of deoxidation, alloying and slagging of the aluminum ingot are sequentially completed; wherein, the slagging is preferably calcium-aluminum pre-melted slag; and (3) carrying out aluminum deoxidation, alloying and slagging operation in sequence in the tapping process, wherein the aluminum content range after tapping is as follows: ω [ Al ]: 0.042-0.046%, and the slag discharge amount of tapping is controlled to be less than 2 kg/ton steel.
(2) In the LF refining process, operations such as slagging, heating, fine adjustment of molten steel components and the like are mainly performed, so that the deep removal of dissolved oxygen and inclusion oxygen is realized; electrifying and heating the steel ladle after the steel ladle arrives at the station, and then adding lime to adjust the components of the slag;
the LF refining time is 40-60 min, aluminum is not added in the LF refining process, the aluminum content is gradually reduced under the reaction action of slag steel, and when the refining is finished, the aluminum content in molten steel is omega [ Al ]]: 0.028-0.032%; the slag composition satisfies the following conditions: ω (CaO): 53.5 to 54.7% of [ omega ] (SiO)2)：8～10.46％、ω(Al2O3)：22～25.6％、ω(MgO)：3～3.74％、ω(FeO)<0.7 percent. The whole refining time is 40-60 min.
(3) RH vacuum degassing process: the metallurgical effect of degassing and removing impurities is achieved by carrying out vacuum treatment on the molten steel;
controlling the electrode vacuum time to be 25-35 min, and controlling the vacuum degree to be less than or equal to 67 Pa; after the air is broken, carrying out soft stirring, wherein the soft blowing time is 20-30 min; and when the soft stirring is finished, the temperature of the molten steel is 1520-1570 ℃.
(4) The protective pouring process comprises continuous casting or die casting, and is mainly used for preventing the secondary oxidation of molten steel;
the chemical components of the cast and formed continuous casting billet meet the following requirements: ω [ C ]: 0.19 to 0.23%, and [ omega ] Si: 0.25 to 0.35%, and [ omega ] Mn: 0.55-0.65%, ω [ Cr ]: 0.45-0.60%, ω [ Ni ]: 1.70-1.90%, and ω [ Mo ]: 0.20 to 0.30%, and [ omega ] Al: 0.02-0.03%, omega [ S ] < 0.0025%, omega [ P ] < 0.015%, omega [ Ca ] < 0.0008%, omega [ Mg ] < 0.0005%, omega [ O ] < 0.0010%, the rest is Fe and unavoidable impurity elements.
(5) Electroslag remelting in protective atmosphere: mainly realizes the removal of large-size impurities in the electrode blank and the improvementThe task of improving the solidification structure of the steel ingot is fulfilled; the protective gas is preferably argon, graphite electrodes are used for slagging, and the components of slag after slagging meet the following requirements: omega (CaF)2)：48.76～52.73％、ω(CaO)：10～13.4％、ω(Al2O3)：30～34.5％、ω(SiO2): 1-1.68%, ω (MgO): 3-5%; the slag amount is 30-35 kg per ton steel; in the whole remelting process, the average melting speed of the electrode blank is 6-10 kg/min, and the surface temperature of the slag pool is 1650-1750 ℃.
The smelting method is particularly applied to smelting carburized bearing steel G20CrNi2Mo and similar bearing steel grades.
In the chemical composition design of the electroslag bearing steel for the railway freight car produced according to the invention, aluminum, oxygen, calcium and magnesium are key elements, and the reason for limiting the value range is explained as follows:
aluminum element: the deoxidizing elements in bearing steel determine, to a large extent, the oxygen content in the steel. When the Al content is lower than 0.015 percent, the equilibrium dissolved oxygen content in the molten steel is higher; when the content is higher than 0.025%, the change of dissolved oxygen is not obvious; therefore, the Al content is controlled within the range of 0.015 to 0.025%.
Oxygen element: key impurity elements in bearing steel; an excessively high oxygen content means that a larger number of inclusions will reduce the fatigue life of the bearing steel, and therefore the oxygen content is controlled to not more than 0.0007%.
Calcium element: the content of which determines the inclusion characteristics to a large extent. The calcium content exceeds 3ppm, and therefore, a low melting point calcium aluminate is easily formed. Stress concentration is easily caused around inclusions in the service process of the bearing, and the fatigue life is further reduced; therefore, the calcium content is controlled to be not more than 0.0003%.
Magnesium element: forming element of magnesium aluminate spinel inclusion. The magnesium aluminate spinel has a regular shape, is easy to aggregate to form large-size cluster-shaped inclusions, and can also reduce the fatigue life of the bearing steel; therefore, the magnesium content is controlled to not more than 0.0003%.
The key control points of the invention are the aluminum content in the whole process, the slag components in the LF refining and electroslag remelting processes.
Wherein, the design principle of the aluminum content is as follows:
(1) the control principle of the aluminum in the invention is that the aluminum is controlled in the whole process, the aluminum is added at one time in the tapping process, adjustment is not needed in the later period, the aluminum content is gradually reduced to a target value through the slag steel reaction, and the excellent effects are that the endogenous inclusion in the deoxidation is generated early and the removal is carried out in enough time.
(2) In order to ensure the later deoxidation efficiency, the aluminum content is controlled to be 0.04-0.05% after tapping. In the LF refining process, the slag steel reaction is accompanied with the continuous reduction of the oxygen potential in the aluminum in the steel and the slag, and the balance between the slag steel is achieved when the reaction is carried out to a certain degree. And controlling the aluminum content to be 0.025-0.035% at the end of LF. In the RH vacuum degassing process, because the reaction between slag steel is weak, the change of the aluminum content is small, the casting is carried out in the protective atmosphere, and the aluminum content in the cast and formed continuous casting billet meets 0.02-0.03%.
(3) The key for improving the cleanliness of the electroslag ingot is to reduce the generation of impurities in the electroslag remelting process; the oxidation degree of aluminum can be reduced by designing the slag components matched with the electrode blank; the control range of the aluminum content of the electroslag ingot is 0.015-0.025%.
The design principle of the slag component in the LF refining process is as follows:
when omega (CaO + MgO)/omega (SiO)2)>7, the melting point of the slag is higher, the fluidity is not good, and the absorption of impurities is not facilitated; in addition, the alkalinity of the slag is too high, so that low-melting-point calcium aluminate inclusions are easily generated in molten steel, and the fatigue life of the bearing steel is seriously damaged. When omega (CaO + MgO)/omega (Al)2O3)<2, at this time, Al in the slag2O3Higher, it is also not good for the adsorption of the impurities.
The control of the cleanliness of molten steel in the electroslag remelting process is closely related to slag components, and the design principle of the slag components is as follows:
(1) when ω (CaF)2)>At 55%, CaF2The slag composition is unstable due to excessive variation; when ω (CaF)2)<At 40%, the slag resistance furnace is large, so that the slag temperature is easily overhigh, the melting speed is too high, and the absorption and removal of impurities in the consumable electrode are not facilitated.
(2)Al2O3The content is controlled to be 30-40Percent, the reaction degree between slag steel is lower, the oxidation of the aluminum of the consumable electrode is less, and the generated alumina inclusions are less; the CaO content is controlled to be 10-15%, on one hand, the adsorption of inclusions is guaranteed, and on the other hand, the generation of calcium aluminate inclusions can be prevented.
Compared with the prior art, the invention realizes the advanced realization of the electroslag bearing steel for smelting iron road-cargo vehicles: the method comprises the steps of adopting a full-flow control idea of molten steel cleanliness, controlling technological parameters such as the end point carbon content of a converter, the aluminum addition amount in the tapping process, slag components in the LF refining process and the like, and limiting a vacuum degassing mode to obtain an electrode blank with good cleanliness; and further, by controlling technological parameters such as slag components for electroslag remelting, slag bath temperature and the like, a high-cleanness electroslag ingot is obtained. The oxygen content of the electroslag ingot can be stably kept to be not more than 0.0007%, the calcium and magnesium contents can be stably kept to be not more than 0.0003%, and the high fatigue performance of the carburizing bearing steel is effectively ensured.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments.
Example 1:
the embodiment provides a method for smelting electroslag bearing steel for a railway wagon, which comprises the following steps:
(1) a converter process: rapidly completing the tasks of temperature rise, decarburization, dephosphorization and the like through oxygen blowing and slagging operations; the carbon content of the molten steel before tapping is 0.12 percent, and the temperature is 1620 ℃; aluminum ingots are sequentially added for deoxidation in the tapping process, nickel plates, low-titanium high-chromium, ferromanganese, ferromolybdenum and the like are added for alloying, and calcium aluminate premelting slag and lime are added for slagging; after tapping, the aluminum content was 0.046%.
(2) An LF refining procedure: and electrifying the steel ladle to raise the temperature after the steel ladle arrives at the station, and then adding lime to quickly form white slag. Alloy, carbon powder and the like are added in the refining process to ensure that the molten steel meets the component requirements, but aluminum is not added. Adding proper amount of lime and silicon carbide, and keeping white slag. Chemical formation of slag at the end of refiningThe method comprises the following steps: 54.7% of omega (CaO), omega (Al)2O3)24.4％，ω(SiO2)9.46 percent of the total weight, 3.68 percent of omega (MgO), 0.47 percent of omega (FeO), and 0.032 percent of aluminum in molten steel; the slag amount is 17 kg/ton steel; LF refining time was 47 min.
(3) RH degassing process: the vacuum was maintained at 67Pa for 32 min. And soft blowing for 25min after breaking the air. At the end of the soft stirring, the temperature of the molten steel was 1550 ℃.
(4) And (3) continuous casting process: adopting full argon protection pouring to prevent the molten steel from contacting with air to generate secondary oxidation; the liquid levels in the tundish and the crystallizer are kept stable in the continuous casting process, so that slag entrapment is prevented;
the casting-molded continuous casting billet comprises the following chemical components: 0.21% of omega C, 0.27% of omega Si, 0.58% of omega Mn, 0.50% of omega Cr, 1.87% of omega Ni, 0.25% of omega Mo, 0.028% of omega Al, 0.0015% of omega S, 0.012% of omega P, 0.0007% of omega Ca, 0.0004% of omega Mg and 0.0009% of omega O.
(5) An electroslag remelting process: the reaction is carried out in an argon protective atmosphere. Starting arc by using a graphite electrode, wherein the slag melting time is 30 min; the slag component is omega (CaF) after slagging is finished2)48.76％，ω(Al2O3)33.4％，ω(CaO)13.4％，ω(MgO)4.52％，ω(SiO2)1.68 percent, and the slag amount is 32 kg/ton steel; the average temperature of the surface of the slag pool in the whole smelting process is 1674 ℃, and the average melting speed is 7.2 kg/min;
the chemical components of electroslag ingot are 0.21% of omega C, 0.26% of omega Si, 0.57% of omega Mn, 0.50% of omega Cr, 1.87% of omega Ni, 0.25% of omega Mo, 0.022% of omega Al, 0.0010% of omega S, 0.011% of omega P, 0.0002% of omega Ca, 0.0003% of omega Mg and 0.0006% of omega O; ds inclusion grade 0.5.
Example 2:
the embodiment provides a method for smelting electroslag bearing steel for a railway wagon, which comprises the following steps:
(1) a converter process: rapidly completing the tasks of temperature rise, decarburization, dephosphorization and the like through oxygen blowing and slagging operations; the carbon content of the molten steel before tapping is 0.08 percent, and the temperature is 1640 ℃; aluminum ingots are sequentially added for deoxidation in the tapping process, nickel plates, low-titanium high-chromium, ferromanganese, ferromolybdenum and the like are added for alloying, and calcium aluminate premelting slag and lime are added for slagging; after tapping, the aluminum content was 0.042%.
(2) An LF refining procedure: electrifying and heating the steel ladle after the steel ladle arrives at the station, and then adding lime to quickly form white slag; alloy, carbon powder and the like are added in the refining process to ensure that the molten steel meets the component requirements, but aluminum is not added; adding a proper amount of lime and silicon carbide, and keeping white slag;
the chemical components of the slag at the end of refining are as follows: 53.5% of omega (CaO), omega (Al)2O3)25.6％，ω(SiO2)10.46 percent, 3.74 percent of omega (MgO), 0.58 percent of omega (FeO), and the aluminum content in the molten steel is 0.028 percent; the amount of slag is 17.6kg per ton of steel; LF refining time is 52 min;
(3) RH degassing process: keeping the extreme vacuum time for 29min, and keeping the vacuum degree at 67 Pa; soft blowing for 27min after breaking; when the soft stirring is finished, the temperature of the molten steel is 1545 ℃.
(4) And (3) continuous casting process: and the molten steel is poured under the protection of full argon to prevent the molten steel from contacting with air to generate secondary oxidation. The liquid levels in the tundish and the crystallizer are kept stable in the continuous casting process, so that slag entrapment is prevented;
the casting-molded continuous casting billet comprises the following chemical components: omega C0.22%, omega Si 0.32%, omega Mn 0.59%, omega Cr 0.51%, omega Ni 1.88%, omega Mo 0.24%, omega Al 0.022%, omega S0.0018%, omega P0.013%, omega Ca 0.0006%, omega Mg 0.0003%, omega O0.0010%.
(5) An electroslag remelting process: the reaction is carried out in an argon protective atmosphere. And (4) starting arc by adopting a graphite electrode, wherein the slagging time is 30 min. The slag component is omega (CaF) after slagging is finished2)52.73％，ω(Al2O3)34.5％，ω(CaO)13.2％，ω(MgO)3.48％，ω(SiO2)1.48 percent; the amount of slag is 33kg per ton of steel; the average temperature of the surface of the slag pool in the whole smelting process is 1725 ℃, and the average melting speed is 7.7 kg/min;
the chemical components of electroslag ingot are omega C0.22%, omega Si 0.29%, omega Mn 0.58%, omega Cr 0.50%, omega Ni 1.87%, omega Mo 0.24%, omega Al 0.016%, omega S0.0011%, omega P0.012%, omega Ca 0.0001%, omega Mg 0.0002% and omega O0.0007%; ds inclusion class 0.
Comparative example 1:
the comparative example provides a smelting method of electroslag bearing steel for a railway wagon, and the method comprises the following steps:
(1) a converter process: the tasks of temperature rise, decarburization, dephosphorization and the like are rapidly completed through oxygen blowing and slagging operations. The carbon content of the molten steel before tapping is 0.05 percent, and the temperature is 1670 ℃. And aluminum ingots are sequentially added for deoxidation in the tapping process, nickel plates, low-titanium high-chromium, ferromanganese, ferromolybdenum and the like are added for alloying, and calcium aluminate premelting slag and lime are added for slagging. After tapping, the aluminum content was 0.023%.
(2) An LF refining procedure: and electrifying the steel ladle to raise the temperature after the steel ladle arrives at the station, and then adding lime to quickly form white slag. Alloy, carbon powder and the like are added in the refining process to ensure that the molten steel meets the component requirements. Adding a proper amount of lime and silicon carbide, and keeping white slag; adding aluminum wires twice in the refining process;
the chemical components of the slag at the end of refining are as follows: 54.3% of omega (CaO), omega (Al)2O3)24.2％，ω(SiO2)11.54 percent, 4.14 percent of omega (MgO), 0.66 percent of omega (FeO), and 0.027 percent of aluminum in molten steel; the amount of slag was 17.4 kg/ton steel. The LF refining time is 54 min.
(3) RH degassing process: keeping the extreme vacuum time for 31min, keeping the vacuum degree at 67Pa, and soft-blowing for 29min after breaking the air; at the end of the soft stirring, the temperature of the molten steel was 1533 ℃.
(4) And the molten steel is poured under the protection of full argon to prevent the molten steel from contacting with air to generate secondary oxidation. The liquid levels in the tundish and the crystallizer are kept stable in the continuous casting process, so that slag entrapment is prevented. The casting-molded continuous casting billet comprises the following chemical components: 0.22% of omega C, 0.33% of omega Si, 0.60% of omega Mn, 0.51% of omega Cr, 1.88% of omega Ni, 0.24% of omega Mo, 0.021% of omega Al, 0.0017% of omega S, 0.013% of omega P, 0.0006% of omega Ca, 0.0003% of omega Mg and 0.0011% of omega O.
(5) An electroslag remelting process: the reaction is carried out in an argon protective atmosphere. And (4) starting arc by adopting a graphite electrode, wherein the slagging time is 30 min. The slag component is omega (CaF) after slagging is finished2)50.48％，ω(Al2O3)32.5％，ω(CaO)12.6％，ω(MgO)4.45％，ω(SiO2)2.16 percent, and the slag amount is 32.5 kg/ton steel; the average temperature of the surface of the slag pool in the whole smelting process is 1712The average melting speed is 7.5kg/min at the temperature of;
the chemical components of electroslag ingot are 0.22% of omega C, 0.31% of omega Si, 0.59% of omega Mn, 0.51% of omega Cr, 1.87% of omega Ni, 0.24% of omega Mo, 0.016% of omega Al, 0.0012% of omega S, 0.012% of omega P, 0.0002% of omega Ca, 0.0002% of omega Mg and 0.0009% of omega O; ds inclusion grade 0.5.
Compared with example 1, the converter of the comparative example is seriously overoxidized, the aluminum addition amount is insufficient in the tapping process, and the aluminum content after tapping is only 0.023%. And the LF refining process is supplemented with aluminum twice, so that the control of the cleanliness of the continuous casting billet is not facilitated, and the oxygen content of the continuous casting billet reaches 0.0011%. On the premise that the electroslag remelting process completely meets the requirements, the contents of calcium and magnesium and Ds inclusion in an electroslag ingot are within expected values, but the oxygen content is higher and reaches 0.0009%. Relevant research shows that the oxygen content of bearing steel is reduced from 10ppm to 5ppm, and the fatigue life is doubled. Therefore, it is necessary to control the oxygen content to an extremely low level. Comparing the data in comparative example 1, the reduction in oxygen content of example 1 by 3ppm will significantly improve the fatigue life of the bearing steel.
Comparative example 2:
comparative example 2 the converter process, LF refining process, and electroslag remelting process were identical to those of example 1, except for the vacuum degassing. VD is selected for degassing, the extreme vacuum time is kept for 32min, and the vacuum degree is 67 Pa. And after the air is broken, the content of aluminum in the molten steel is 0.014%, an aluminum wire is added, and the molten steel is subjected to soft blowing for 26 min. The continuous casting adopts full protection pouring, and prevents the molten steel from contacting with air and generating secondary oxidation. The casting-molded continuous casting billet comprises the following chemical components: omega C0.22%, omega Si 0.32%, omega Mn 0.59%, omega Cr 0.50%, omega Ni 1.87%, omega Mo 0.25%, omega Al 0.024%, omega S0.0014%, omega P0.012%, omega Ca 0.0005%, omega Mg 0.0002%, omega O0.0013%. The chemical components of the electroslag ingot are as follows: omega C0.22%, omega Si 0.30%, omega Mn 0.58%, omega Cr 0.50%, omega Ni 1.87%, omega Mo 0.25%, omega Al 0.016%, omega S0.0012%, omega P0.011%, omega Ca 0.0004%, omega Mg 0.0002%, omega O0.0010%; ds inclusion grade 0.5.
Compared with the example 1, the comparative example adopts VD for vacuum degassing, the slag steel reacts violently, the aluminum oxidation is serious, and a large amount of impurities are generated. After the aluminum wire is supplemented, although the aluminum content is within the target range, the oxygen content of the continuous casting billet is higher and reaches 0.0013%. On the premise that the electroslag remelting process completely meets the requirements, the calcium and magnesium contents and Ds inclusion levels in the electroslag ingot are within expected values, but the oxygen content is higher and reaches 0.0010%, compared with example 1, the oxygen content is increased by 4ppm, and the fatigue life of the bearing steel is seriously influenced.
Comparative example 3:
comparative example 3 the converter process, LF refining process, vacuum degassing, and continuous casting process were the same as example 1, except for the control of slag components in the electroslag remelting process.
The electroslag remelting process is carried out in an argon protective atmosphere. Starting arc by using a graphite electrode, wherein the slagging time is 30min, and the slag component is omega (CaF) after slagging is finished2)46.46％，ω(Al2O3)27.5％，ω(CaO)22.5％，ω(MgO)4.76％，ω(SiO2)1.76 percent. The amount of slag was 33.4 kg/ton steel. The average temperature of the surface of the slag pool in the whole smelting process is 1698 ℃, and the average melting speed is 7.3 kg/min. The chemical composition of electroslag ingot is omega C]0.21％，ω[Si]0.28％，ω[Mn]0.57％，ω[Cr]0.50％，ω[Ni]1.87％，ω[Mo]0.25％，ω[Al]0.019％，ω[S]0.0008％，ω[P]0.010％，ω[Ca]0.0005％，ω[Mg]0.0004％，ω[O]0.0006 percent; ds inclusion level 1.0.
Compared with example 1, the content of CaO in the slag used in the electroslag remelting process of comparative example 3 is higher, reaching 22.5%. Although the oxygen content of the electroslag ingot is within the target range, the calcium content and the Ds inclusion level both exceed the target values, and the expected effect cannot be achieved.
It can be seen that the main differences between the examples and the comparative examples are the control of the carbon content at the end point of the converter, the control of the aluminum content in the whole process, the selection of the degassing mode and the control of the slag component for electroslag remelting. The embodiment strictly controls each process link, and obtains unexpected remarkable effect. As can be seen from the comparison example, when some conditions can not be met, more ideal smelting effect can not be achieved. According to the method provided by the invention, by accurately controlling the key process parameters of the whole process, the obtained electroslag ingot is lower in oxygen, calcium and magnesium element content, and is smaller and more dispersive in inclusion, and higher in cleanliness.
Description of the drawings: the above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention; thus, while the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.
Claims (9)
1. The electroslag bearing steel for the high-cleanness railway wagon is characterized in that the element content of the electroslag bearing steel expressed by mass fraction is as follows: ω [ C ]: 0.19 to 0.23%, and [ omega ] Si: 0.25 to 0.35%, and [ omega ] Mn: 0.55-0.65%, ω [ Cr ]: 0.45-0.60%, ω [ Ni ]: 1.70-1.90%, and ω [ Mo ]: 0.20 to 0.30%, and [ omega ] Al: 0.015-0.025%, omega [ S ] < 0.0015%, omega [ P ] < 0.013%, omega [ Ca ] less than or equal to 0.0003%, omega [ Mg ] less than or equal to 0.0003%, omega [ O ] less than or equal to 0.0007%, the balance being Fe and unavoidable impurities; ds inclusions are not greater than 0.5 grade.
2. The method for smelting the electroslag bearing steel for the high-cleanness railway wagon according to claim 1, wherein the smelting method adopts a process route of 'primary smelting furnace + LF refining + RH vacuum degassing + protective casting + protective atmosphere electroslag remelting', and the content of oxygen, calcium and magnesium impurity elements and inclusions is remarkably reduced by strictly controlling the aluminum content, the LF refining slag component, the electroslag remelting furnace slag component and limiting the vacuum degassing mode in the whole process; wherein the oxygen content of the electroslag ingot is not more than 0.0007 percent, and the calcium and magnesium contents are not more than 0.0003 percent;
and after the primary smelting is finished, the aluminum content range after tapping is omega [ Al ]: 0.04-0.05%;
the range of the aluminum content at the end of the LF refining is omega [ Al ]: 0.025-0.035%;
the slag composition range at the end of LF refining is as follows: ω (CaO): 52 to 56%, omega (SiO)2)：8～12％、ω(Al2O3)：22～27％、ω(MgO)：3～5％、ω(FeO)<0.7％；
The degassing mode is RH vacuum degassing;
the slag after electroslag remelting and slagging comprises the following components in range: omega (CaF)2)：40～55％、ω(CaO)：10～15％、ω(Al2O3)：30～40％、ω(SiO2)：1～3％、ω(MgO)：3～5％。
3. The method for smelting electroslag bearing steel for high-cleanliness railway wagon according to claim 2, wherein the primary smelting furnace comprises a converter or an electric arc furnace; the requirements of the primary smelting end and the tapping process are as follows:
(1) at the end of primary smelting, the carbon content of molten steel is omega C: 0.06-0.15% and the temperature of the molten steel is 1600-1650 ℃.
(2) And (3) carrying out aluminum deoxidation, alloying and slagging operation in sequence in the tapping process, wherein the aluminum content range after tapping is as follows: ω [ Al ]: 0.042-0.046%, and the slag discharge amount of tapping is controlled to be less than 2 kg/ton steel.
4. The method for smelting electroslag bearing steel for high-cleanness railway freight cars according to claim 2, wherein the LF refining process comprises the following steps: the LF refining time is 40-60 min, aluminum is not added in the refining process, the aluminum content is gradually reduced under the reaction of slag steel, and omega Al is controlled when the refining is finished]: 0.028-0.032%; the slag composition satisfies the following conditions: ω (CaO): 53.5 to 54.7% of [ omega ] (SiO)2)：8～10.46％、ω(Al2O3)：22～25.6％、ω(MgO)：3～3.74％、ω(FeO)<0.7％。
5. The method for smelting the electroslag bearing steel for the high-cleanness railway wagon according to claim 2, wherein the degassing method adopts RH vacuum degassing, the extreme vacuum time is controlled to be 25-35 min, the vacuum degree is less than or equal to 67Pa, the soft blowing time after the vacuum breaking is 20-30 min, and the temperature of molten steel is 1520-1570 ℃ after the soft stirring is finished.
6. The method for smelting the electroslag bearing steel for the high-cleanness railway wagon according to claim 2, wherein the chemical components of the continuously cast billet which is cast and formed meet the following requirements: ω [ C ]: 0.19 to 0.23%, and [ omega ] Si: 0.25 to 0.35%, and [ omega ] Mn: 0.55-0.65%, ω [ Cr ]: 0.45-0.60%, ω [ Ni ]: 1.70-1.90%, and ω [ Mo ]: 0.20 to 0.30%, and [ omega ] Al: 0.02-0.03%, omega [ S ] < 0.0025%, omega [ P ] < 0.015%, omega [ Ca ] < 0.0008%, omega [ Mg ] < 0.0005%, omega [ O ] < 0.0010%, the rest is Fe and unavoidable impurity elements.
7. The method for smelting the electroslag bearing steel for the high-cleanness railway wagon according to claim 2, wherein the electroslag remelting is carried out in a protective atmosphere, graphite electrodes are used for slagging, and the slag components after slagging meet the following requirements: omega (CaF)2)：48.76～52.73％、ω(CaO)：10～13.4％、ω(Al2O3)：30～34.5％、ω(SiO2): 1-1.68%, ω (MgO): 3-5%; the amount of slag is 30-35 kg per ton of steel.
8. The method for smelting the electroslag bearing steel for the high-cleanness railway wagon according to claim 2, wherein the average melting speed of the electrode blank in the electroslag remelting process is 6-10 kg/min, and the control range of the surface temperature of the slag is 1650-1750 ℃.
9. The smelting method according to any one of claims 2 to 8, which is particularly applied to smelting of carburizing bearing steel G20CrNi2Mo and similar bearing steel grades.
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