CN113061799B - High-cleanliness spring steel and production method thereof - Google Patents
High-cleanliness spring steel and production method thereof Download PDFInfo
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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
- C22C33/06—Making ferrous alloys by melting using master alloys
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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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- 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
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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
- C21C7/064—Dephosphorising; Desulfurising
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- 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
- C21C7/068—Decarburising
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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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- C21C7/072—Treatment with gases
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- C—CHEMISTRY; METALLURGY
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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
- C21C7/076—Use of slags or fluxes as treating agents
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- C—CHEMISTRY; METALLURGY
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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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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- 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
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses high-cleanliness spring steel and a production method thereof. The production method comprises the following steps: desulfurizing the molten iron until S in the molten iron is less than or equal to 0.0015 percent; mixing molten iron and scrap steel into molten steel, carrying out desiliconization, dephosphorization and oxygen blowing decarburization to obtain the molten steel with the temperature of 1630-1660 ℃, C0.10-0.35%, O less than or equal to 0.045%, P less than or equal to 0.011% and S0.003-0.008%, pushing off slag, tapping and carrying out deoxidation alloying, wherein the flow rates of argon gas blown to the bottom of a steel ladle during tapping and after tapping are respectively 800-1000 NL/min and 100-200 NL/min; then refining the molten steel to adjust chemical components and inclusions, wherein the flow rates of argon blown from the bottom of the steel ladle during slag feeding and alloying treatment, power-on heating and other time are respectively 300-500 NL/min, 200-300 NL/min and 50-100 NL/min; then, vacuum refining and vacuum breaking soft stirring are sequentially carried out, and the flow of argon blown from the bottom of the steel ladle is 20-50 NL/min and 50-100 NL/min respectively; and casting the mixture into a billet. The high-cleanness product prepared by the production methodThe density of inclusions with the size of more than 5 mu m in the net degree spring steel is less than or equal to 0.5 per mm2The length-width product of the largest inclusion is less than or equal to 900 mu m2And has high cleanliness.
Description
Technical Field
The invention belongs to the technical field of steel smelting, and particularly relates to high-cleanliness spring steel and a production method of the high-cleanliness spring steel.
Background
The spring is used as a safety bearing part and widely applied to the fields of automobiles, machinery, railways and the like, frequently bears high-cycle alternating load in the service process, and the failure mode is mainly fatigue fracture. Numerous studies have shown that inclusions are a significant cause of fatigue failure.
As the bonding force of the inclusions and the spring matrix is weak and the difference of the elastic modulus of the inclusions and the spring matrix is large, stress concentration can be generated on the interface of the inclusions and the spring matrix in the service process of the spring, when the stress exceeds a certain range, a crack source can be formed at the inclusions, and cracks can be gradually enlarged under the action of continuous alternating load, so that the spring is finally fractured. In view of the problems of large size of inclusions, large quantity density of inclusions and the like existing in the spring steel prepared by the production process in the technical field at present, the performance of the existing spring steel cannot meet the market demand at present.
Disclosure of Invention
In order to solve at least one of the above technical problems, the present invention aims to provide a method for producing a high-cleanliness spring steel, and also relates to a high-cleanliness spring steel produced by the production method.
In order to achieve one of the above objects, an embodiment of the present invention provides a method for producing a high-cleanliness spring steel, the method comprising the steps of,
pretreatment: desulfurizing the molten iron until S in the molten iron is less than or equal to 0.0015 percent;
smelting in a converter: mixing the pretreated molten iron and scrap steel to form molten steel, carrying out desiliconization, dephosphorization and oxygen blowing decarburization to obtain the molten steel with the temperature of 1630-1660 ℃, the temperature of C0.10-0.35%, O less than or equal to 0.045%, P less than or equal to 0.011% and S0.003-0.008%, slag stopping and tapping, and carrying out deoxidation alloying treatment on the molten steel, wherein the flow of argon blown at the bottom of the steel ladle during tapping is 800-1000 NL/min, and the flow of argon blown at the bottom of the steel ladle after tapping is finished is 100-200 NL/min;
refining: carrying out chemical component adjustment and inclusion regulation on molten steel smelted by a converter, wherein the flow rate of argon blown at the bottom of a steel ladle during slag charge addition and alloying treatment is 300-500 NL/min, the flow rate of argon blown at the bottom of the steel ladle during power-on heating is 200-300 NL/min, and the flow rate of argon blown at the bottom of the steel ladle during the rest time is 50-100 NL/min;
vacuum refining: the method comprises a vacuum refining stage and a vacuum breaking soft stirring stage which are sequentially carried out, wherein the flow of argon blown from the bottom of the ladle in the vacuum refining stage is 20-50 NL/min, and the flow of argon blown from the bottom of the ladle in the vacuum breaking soft stirring stage is 50-100 NL/min;
continuous casting: casting the molten steel into a steel billet, wherein the steel billet comprises the following chemical components in percentage by mass: 0.35 to 0.85 percent of C, 0.5 to 2.0 percent of Si, 0.2 to 1.5 percent of Mn, 0.2 to 1.0 percent of Cr, and the balance of Fe and inevitable impurity elements.
Thus, according to the production method of one embodiment of the invention, on one hand, through operations such as desulfurization, desilicication, dephosphorization, oxygen blowing decarburization, deoxidation alloying, chemical composition adjustment, vacuum refining degassing and the like, the precise control of the chemical composition of the steel is realized, the number of inclusions in the steel can be reduced, the size of the inclusions can be reduced, and the purity and the fatigue resistance of the steel can be improved. The sulfur content in the molten iron and the molten steel is reduced to a lower level through a pretreatment process and a converter smelting process, slag entrapment or strong slag-metal reaction caused by massive desulfurization in a refining process is avoided, and therefore the generation of large-size inclusions in the molten steel is reduced, the types of the inclusions can be effectively controlled, and the sizes of the inclusions are reduced. On the other hand, the whole-flow steel ladle adopts a medium-small bottom blowing flow, so that floating and removal of impurities can be promoted, the removal degree of the impurities (namely, the size and the number density of the impurities) is increased, and the cleanliness of steel products is improved, so that chemical components and the impurities are effectively and accurately controlled, the scouring erosion of molten steel on the steel ladle refractory wall can be reduced, the influence of the eroded refractory wall on the cleanliness of the molten steel is reduced, the prepared steel products have high cleanliness, and the prepared spring steel has high cleanliness and excellent fatigue resistance. In addition, the consumption of gas is reduced, and the cost is reduced. During the deoxidation alloying process, the steel ladle is controlled to adopt larger bottom blowing argon gas flow during tapping, so that molten steel deoxidation and uniform components can be quickly completed, the flow of the bottom blowing argon gas of the steel ladle is reduced after tapping is completed, the upward floating of a deoxidation product can be promoted, and slag entrapment is avoided; in the refining process, the uniformity of slag melting and alloy components can be promoted by controlling the flow rate of bottom-blown argon of the steel ladle to be 300-500 NL/min during slag feeding and alloying treatment, slag entrapment can be avoided by controlling the flow rate of bottom-blown argon of the steel ladle to be lower during and after tapping, and floating and removal of inclusions are promoted; in the vacuum refining process, molten steel is exposed to vacuum and impurities are removed through bottom blowing stirring in the vacuum refining stage, deep vacuum degassing can be kept through controlling the flow of bottom blowing argon to be 20-50 NL/min, severe slag-metal reaction and slag entrapment caused by large volume increase when bubbles float to a vacuum interface are avoided, impurities can be gradually gathered at the upper middle part of the molten steel through air breaking soft stirring, and the impurities can float and be removed after standing for a period of time. In conclusion, the production method can obviously reduce the content of various impurity elements, effectively control the size and the quantity of endogenous inclusions, and avoid the generation of a large amount of exogenous brittle inclusions, thereby obtaining the spring steel with high cleanliness.
In a further improvement of an embodiment of the present invention, the blast furnace hot metal is desulfurized in a KR desulfurization apparatus in the pretreatment step, and the blast furnace hot metal satisfies, before desulfurization: the temperature is not less than 1360 ℃, 4.0-4.5% of C, not more than 0.040% of S, 0.20-0.60% of Si, not more than 0.04% of Ti, not more than 0.10% of P, and the balance of Fe and other inevitable impurity elements. The desulfurization effect of the pretreatment process can be ensured by optimizing the temperature and the components of the equipment and the blast furnace molten iron, and the low-Ti molten iron is adopted for smelting, so that the phenomenon that slag is discharged to cause Ti return can be effectively avoided, and further the phenomenon that fragile inclusions such as titanium oxide and titanium nitride are separated out in the continuous casting process is avoided.
As a further improvement of an embodiment of the present invention, the chemical components of the desulfurizing agent used in the pretreatment process include, by mass: 80-90% of CaO and CaF210-15% and the balance of unavoidable impurity components. By the components and the proportion of the desulfurizing agent, the desulfurizing effect of the pretreatment process can be ensured, the sulfur content in molten iron is reduced to a lower level, slag entrapment or strong slag-metal reaction caused by a large amount of desulfurization in the refining process is avoided, so that the generation of large-size inclusion in the molten steel is reduced, the type of the inclusion can be effectively controlled, and the size of the inclusion is reduced.
As a further improvement of one embodiment of the invention, the sliding plate slag blocking adopted in the converter smelting process has a good slag blocking effect, and can effectively avoid the problems of Ti return, P return and the like caused by slag falling, thereby avoiding the precipitation of titanium oxide and titanium nitride brittle inclusions in the continuous casting process and improving the cleanliness of steel.
In the smelting process of the converter, a recarburizer, ferrosilicon and manganese metal are added into a steel ladle to perform deoxidation alloying treatment on molten steel, wherein N in the recarburizer is less than or equal to 0.0065%, Al in the ferrosilicon is less than or equal to 0.05%, and Ti is less than or equal to 0.02%. On one hand, the oxygen content in the molten steel can be effectively reduced, and the content of alumina formed in the deoxidation process is greatly reduced; on the other hand, the increase of Al and Ti contents in molten steel caused by the deoxidation alloying process can be avoided, so that the generation of alumina, titanium oxide and magnesium aluminate spinel brittle inclusions is effectively avoided, and the cleanliness of steel is improved.
As a further improvement of one embodiment of the invention, in the refining process, the slag basicity of the slag charge is 2.5-3.0, which is beneficial to adsorbing a large amount of acidic inclusions generated in the smelting process of the converter and reducing SiO in molten steel2The content of the similar inclusions is reduced, and the corrosion to the refractory material wall of the steel ladle is reduced.
As an embodiment of the inventionIn the refining process, the chemical components of the slag charge comprise the following components in percentage by mass: 55-60% of CaO and SiO2 20～25％，MgO 6～12％；CaF2 2～5％； Al2O3Less than or equal to 5 percent; the T.Fe + MnO content is less than or equal to 2 percent, so that the slag charge has higher slag basicity, and the SiO in the molten steel is effectively reduced2The content of the similar impurities is reduced, and the corrosion to the wall of the ladle refractory material is reduced.
In a further improvement of an embodiment of the present invention, in the vacuum refining process, the vacuum degree in the vacuum refining stage is not more than 150Pa, and the vacuum treatment time is not less than 15 min. The vacuum degree and the vacuum treatment time during vacuum refining are controlled to meet the requirement on the vacuum degree, so that gas in molten steel is effectively removed, severe slag-metal reaction and slag entrapment are avoided, alloy components of the molten steel are finely adjusted, and inclusions are removed.
As a further improvement of one embodiment of the invention, in the continuous casting process, the superheat degree of the tundish is controlled to be 30-38 ℃ by adopting electromagnetic induction heating, and the liquid level fluctuation of the crystallizer is less than or equal to 2 mm. On the one hand, adopt higher superheat degree to cast in the continuous casting process, can make the molten steel have better mobility to be favorable to the inclusion come-up, on the other hand can stir the molten steel through electromagnetic induction heating for the speed that the molten steel flows and the speed of inclusion come-up, with the liquid level fluctuation control of crystallizer within 2mm simultaneously, can stop the emergence of crystallizer curling sediment, reduce the production of inclusion, improve the cleanliness factor of molten steel.
In a further improvement of an embodiment of the present invention, in the continuous casting step, the rolling reduction is 12 to 20 mm. By adopting a large reduction, segregation of various elements in the billet can be reduced, and formation of precipitate inclusions can be reduced.
In order to achieve one of the above objects, an embodiment of the present invention further provides a high-cleanliness spring steel, which is prepared by the above production method. The high-cleanliness spring steel has high cleanliness and fatigue resistance, and can be applied to spring products with high requirements on spring performance, such as automobile suspension springs.
In a further improvement of an embodiment of the present invention, in the high-cleanliness spring steel, P is less than or equal to 0.012%, S is less than or equal to 0.004%, T.O is less than or equal to 0.0020%, N is less than or equal to 0.0030%, H is less than or equal to 0.0002%, Al is less than or equal to 0.0020%, and Ti is less than or equal to 0.0009%. In other words, the high-cleanliness spring steel controls the content of harmful impurity elements in a lower range, so that the number of inclusions is small, the sizes of the inclusions are small, and the high requirement of the current industry on the cleanliness of the spring steel can be met.
As a further improvement of an embodiment of the present invention, in the high-cleanliness spring steel, the density of inclusions having a size of 5 μm or more is 0.5 pieces/mm or less2The length-width product of the largest inclusion is less than or equal to 900 mu m2The method not only meets the high requirement of the current industry on the cleanliness of the spring steel, but also can realize the large-scale production of the spring steel with high cleanliness.
Detailed Description
An embodiment of the invention provides a production method of high-cleanliness spring steel and the high-cleanliness spring steel prepared by the production method.
The respective steps in the method for producing the high-cleanliness spring steel will be described in detail below.
(1) Pretreatment procedure
And desulfurizing the molten iron until S in the molten iron is less than or equal to 0.0015 percent. Wherein the slagging-off rate of the desulfurization is more than or equal to 97 percent, and the temperature of the desulfurized molten iron is more than or equal to 1310 ℃.
Preferably, the blast furnace molten iron is adopted to carry out desulphurization in a KR desulphurization device, and the blast furnace molten iron meets the following requirements before desulphurization: the temperature is not less than 1360 ℃, 4.0-4.5% of C, not more than 0.040% of S, 0.20-0.60% of Si, not more than 0.04% of Ti, not more than 0.10% of P, and the balance of Fe and other inevitable impurity elements.
Preferably, the chemical components of the desulfurizing agent adopted in the pretreatment process comprise, by mass: 80-90% of CaO and CaF210-15% and the balance of inevitable impurity components.
(2) Converter smelting process
Mixing the pretreated molten iron and scrap steel to form molten steel, performing desilicication, dephosphorization, oxygen blowing and decarburization to obtain the molten steel with the temperature of 1630-1660 ℃, C0.10-0.35%, O not more than 0.045%, P not more than 0.011% and S0.003-0.008%, slag blocking and tapping, and performing deoxidation alloying treatment on the molten steel, wherein the flow of argon blowing at the bottom of a steel ladle is 800-1000 NL/min during tapping, and the flow of argon blowing at the bottom of the steel ladle is 100-200 NL/min after tapping is completed.
The charging amount of the converter is 145-150 t, the molten iron ratio is 78-83%, the scrap steel is high-quality scrap steel with the thickness not less than 2mm, and the steel tapping amount of the converter is 133-136 t. The high-quality steel scrap refers to waste steel with S less than or equal to 0.012 percent, P less than or equal to 0.015 percent and Ti less than or equal to 0.035 percent, so that the sulfur return amount in the molten steel can be reduced, the slag-metal reaction in the refining process is effectively reduced, and the generation of large-size inclusions in the molten steel is reduced.
Preferably, a sliding plate is adopted for slag blocking in the converter smelting process.
Furthermore, in the smelting process of the converter, a recarburizing agent, ferrosilicon and manganese metal are added into a steel ladle to perform deoxidation alloying treatment on the molten steel, wherein N in the recarburizing agent is less than or equal to 0.0065%, Al in the ferrosilicon is less than or equal to 0.05%, and Ti is less than or equal to 0.02%.
Specifically, when tapping is started, ferrosilicon, manganese metal and 30% of carburant are added into a steel ladle for deoxidation alloying, when 85% of the tapping is finished, the rest of carburant is added, and lime and synthetic slag are added for slagging after the tapping is finished, so that the severe boiling of molten steel can be avoided, safety accidents can be prevented, the carburant can be dissolved into the molten steel, the deoxidation alloying process is accelerated, and excessive air is prevented from entering the molten steel.
(3) Refining procedure
And carrying out chemical component adjustment and inclusion regulation on the molten steel smelted by the converter, wherein the flow rate of argon blown at the bottom of the steel ladle during slag charge addition and alloying treatment is 300-500 NL/min, the flow rate of argon blown at the bottom of the steel ladle during power-on temperature rise is 200-300 NL/min, and the flow rate of argon blown at the bottom of the steel ladle during the rest time is 50-100 NL/min.
Specifically, the molten steel smelted by the converter is sent into an LF furnace for chemical component adjustment and inclusion regulation, and steel is tapped after the molten steel components, the slag components and the molten steel temperature reach the standard.
Preferably, the slag alkalinity of the slag is 2.5-3.0.
Preferably, the chemical components of the slag comprise, by mass: 55-60% of CaO and SiO2 20～25％，MgO 6～12％；CaF2 2～5％；Al2O3≤5％；T.Fe+MnO≤2％。
(4) Vacuum refining step
And delivering the refined molten steel to a VD furnace, and sequentially carrying out a vacuum refining stage and an air breaking soft stirring stage, wherein the flow of argon blown from the bottom of the steel ladle in the vacuum refining stage is 20-50 NL/min, and the flow of argon blown from the bottom of the steel ladle in the air breaking soft stirring stage is 50-100 NL/min.
Preferably, the vacuum degree of the vacuum refining stage is less than or equal to 150Pa, and the vacuum treatment time is more than or equal to 15 min.
Preferably, the time of the air-breaking soft stirring stage is more than or equal to 25 min.
(5) Continuous casting procedure
Casting the molten steel into a steel billet, wherein the steel billet comprises the following chemical components in percentage by mass: 0.35 to 0.85 percent of C, 0.5 to 2.0 percent of Si, 0.2 to 1.5 percent of Mn, 0.2 to 1.0 percent of Cr, and the balance of Fe and inevitable impurity elements.
Specifically, bloom continuous casting can be adopted, molten steel is allowed to stand for more than 15min on a continuous casting platform, then casting is started, the whole continuous casting process is protected for casting, the nitrogen increment is controlled to be less than or equal to 0.0002%, and the continuous casting drawing speed is 0.65-0.70 m/min.
Preferably, the superheat degree of the tundish is controlled to be 30-38 ℃ by adopting electromagnetic induction heating during continuous casting, and the liquid level fluctuation of the crystallizer is controlled to be less than or equal to 2 mm.
Preferably, the rolling reduction during continuous casting is 12-20 mm.
Furthermore, the high-cleanliness spring steel is prepared by the production method, wherein P is less than or equal to 0.012 percent, S is less than or equal to 0.004 percent, T.O is less than or equal to 0.0020 percent, N is less than or equal to 0.0030 percent, H is less than or equal to 0.0002 percent, Al is less than or equal to 0.0020 percent, and Ti is less than or equal to 0.0009 percent.
And, the high-cleanliness spring steelIn the above, the density of inclusions with a size of 5 μm or more is not more than 0.5/mm2The length-width product of the largest inclusion is less than or equal to 900 mu m2(ii) a The grade of the A-type, B-type, C-type and D-type inclusions does not exceed 1.0 grade through rating measurement.
As described above, the production method of the present invention is obtained by a large number of experimental studies, and the respective steps in the production method will be further described below with reference to specific examples.
Example 1
(1) Pretreatment of
Taking blast furnace molten iron to desulfurize in a KR desulfurizing device, wherein the adopted desulfurizing agent comprises the following chemical components in percentage by mass: 80-90% of CaO and CaF210-15% and the balance of unavoidable impurity components; the slagging-off rate of desulfurization is 97%.
Wherein the temperature, C content, S content, Si content, Ti content, P content of the molten iron of the blast furnace, the temperature of the desulfurized molten iron, and the S content information of the desulfurized molten iron are shown in Table 1.
[ Table 1]
(2) Smelting in a converter
Mixing the pretreated molten iron and high-quality scrap steel with the thickness of 2mm into molten steel, loading the molten steel into a converter, and carrying out desilicication, dephosphorization and oxygen blowing decarburization, wherein the loading amount of the converter is 145t, the molten iron ratio is 78%, and the high-quality scrap steel meets the following requirements: less than or equal to 0.012 percent of S, less than or equal to 0.015 percent of P and less than or equal to 0.035 percent of Ti;
the method comprises the following steps of adopting a sliding plate to block slag and block slag for tapping, adding ferrosilicon, manganese metal and 30% of carburant into a steel ladle for deoxidation alloying when tapping begins, adding the rest carburant when tapping reaches 85%, and adding lime and synthetic slag for slagging after tapping ends, wherein N in the carburant is less than or equal to 0.0065%, Al in the ferrosilicon is less than or equal to 0.05%, and Ti is less than or equal to 0.02%;
and (3) opening bottom blowing argon gas in the whole process of the steel ladle during tapping, wherein the flow of the argon gas blown from the bottom of the steel ladle during tapping is 800NL/min, the flow of the argon gas blown from the bottom of the steel ladle after tapping is 100NL/min, the tapping quantity is 133t, and the temperature of the molten steel and the component content information of the molten steel are measured after tapping is finished and are shown in the table 2.
[ Table 2]
(3) Refining
And (4) sending the molten steel smelted by the converter into an LF furnace for chemical component adjustment and inclusion regulation, and tapping after the molten steel components, the slag components and the molten steel temperature reach the standard.
And the flow of the argon blown from the bottom of the steel ladle at the rest time is 50NL/min, and the flow of the argon blown from the bottom of the steel ladle at the rest time is 200NL/min when the steel ladle is electrified and the temperature is raised.
The slag alkalinity of the slag is 2.5, and the slag comprises the following chemical components in percentage by mass: 55-60% of CaO and SiO2 20～25％，MgO 6～12％；CaF2 2～5％；Al2O3≤5％；T.Fe+MnO≤2％。
(4) Vacuum refining
And (3) delivering the refined molten steel to a vacuum chamber of a VD furnace, carrying out vacuum refining, and then breaking the vacuum for soft stirring. Wherein the vacuum degree of the vacuum chamber in the vacuum refining stage is 150Pa, the flow of argon blown from the bottom of the ladle is 20NL/min, and the vacuum treatment time is 15 min; the flow of argon blown from the bottom of the steel ladle in the breaking soft stirring stage is 50NL/min, and the time in the breaking soft stirring stage is 25 min.
(5) Continuous casting of bloom
And (2) sending the molten steel after vacuum refining to a continuous casting platform, standing for 15min, then casting, protecting the casting in the whole continuous casting process, controlling the superheat degree of a tundish to be 30 ℃ by adopting electromagnetic induction heating equipment, controlling the nitrogen increment in the continuous casting process to be 0.0002%, controlling the liquid level fluctuation of a crystallizer to be less than or equal to 2mm, controlling the continuous casting pulling speed to be 0.65m/min, and controlling the reduction amount to be 12 mm.
The high-cleanliness spring steel billets were prepared by the above production method, and the mass percentages of the harmful impurity elements therein were determined to be shown in table 3.
[ Table 3]
| Element(s) | P | S | T.O | N | H | Al | Ti |
| Mass percent of | 0.0097 | 0.004 | 0.002 | 0.003 | 0.0002 | 0.002 | 0.0009 |
The detection shows that the type of the inclusion in the high-cleanliness spring steel is low-melting-point spherical CaO & SiO2、 CaO·Al2O3·2SiO2Isosilicate inclusions, the number density of inclusions more than 5 mu m is 0.5 per mm2The length-width product of the largest inclusion is900μm2And the A, B, C, D-type inclusion ratings were all 1.0.
Example 2
(1) Pretreatment of
Taking blast furnace molten iron to carry out desulfurization in a KR desulfurization device, wherein the adopted desulfurizer comprises the following chemical components in percentage by mass: 80-90% of CaO and CaF210-15% of the total weight of the composition, and the balance of inevitable impurity components; the slagging-off rate of the desulfurization is 98 percent.
Wherein, the temperature, C content, S content, Si content, Ti content, P content of the blast furnace molten iron, the temperature of the desulfurized molten iron, and the S content information of the desulfurized molten iron are shown in Table 4.
[ Table 4]
(2) Smelting in a converter
Mixing the pretreated molten iron and high-quality scrap steel with the thickness of 3mm to form molten steel, feeding the molten steel into a converter, and carrying out desiliconization, dephosphorization and oxygen blowing decarburization, wherein the loading amount of the converter is 147t, the molten iron ratio is 80%, and the high-quality scrap steel meets the following requirements: less than or equal to 0.012 percent of S, less than or equal to 0.015 percent of P and less than or equal to 0.035 percent of Ti;
the method comprises the following steps of adopting a sliding plate to block slag and block slag for tapping, adding ferrosilicon, manganese metal and 30% of carburant into a steel ladle for deoxidation alloying when tapping begins, adding the rest carburant when tapping reaches 85%, and adding lime and synthetic slag for slagging after tapping ends, wherein N in the carburant is less than or equal to 0.0065%, Al in the ferrosilicon is less than or equal to 0.05%, and Ti is less than or equal to 0.02%;
and (3) opening bottom blowing argon gas in the whole process of the steel ladle during tapping, wherein the flow rate of the argon gas blown from the bottom of the steel ladle during tapping is 900NL/min, the flow rate of the argon gas blown from the bottom of the steel ladle after tapping is 150NL/min, the tapping amount is 135t, and the temperature of the molten steel and the component content information of the molten steel are measured after tapping is finished and are shown in a table 5.
[ Table 5]
(3) Refining
And (4) sending the molten steel smelted by the converter into an LF furnace for chemical component adjustment and inclusion regulation, and tapping after the molten steel components, the slag components and the molten steel temperature reach the standard.
And the flow of the argon blown from the bottom of the steel ladle at the rest time is 80NL/min, and the flow of the argon blown from the bottom of the steel ladle at the rest time is 250NL/min when the steel ladle is electrified and the temperature is raised.
The slag alkalinity of the slag charge is 2.8, and the chemical components of the slag charge comprise the following components in percentage by mass: 55-60% of CaO and SiO2 20～25％，MgO 6～12％；CaF2 2～5％；Al2O3≤5％；T.Fe+MnO≤2％。
(4) Vacuum refining
And (3) delivering the refined molten steel to a vacuum chamber of a VD furnace, carrying out vacuum refining, and then breaking the vacuum for soft stirring. Wherein the vacuum degree of the vacuum chamber in the vacuum refining stage is 120Pa, the flow of argon blown from the bottom of the ladle is 35NL/min, and the vacuum treatment time is 20 min; the flow of argon blown from the bottom of the steel ladle in the air breaking soft stirring stage is 70NL/min, and the time in the air breaking soft stirring stage is 30 min.
(5) Continuous casting of bloom
And (3) sending the molten steel after vacuum refining to a continuous casting platform, standing for 19min, then casting, protecting the whole continuous casting process, controlling the superheat degree of a tundish to be 35 ℃ by adopting electromagnetic induction heating equipment, controlling the nitrogen increasing amount in the continuous casting process to be 0.0001%, controlling the liquid level fluctuation of a crystallizer to be less than or equal to 1.5mm, controlling the continuous casting drawing speed to be 0.67m/min, and controlling the reduction amount to be 17 mm.
The high-cleanliness spring steel billets were prepared by the above production method, and the mass percentages of the harmful impurity elements therein were determined to be shown in table 6.
[ Table 6]
| Element(s) | P | S | T.O | N | H | Al | Ti |
| By mass percent% | 0.012 | 0.002 | 0.001 | 0.002 | 0.00015 | 0.001 | 0.0008 |
The detection shows that the type of the inclusion in the high-cleanliness spring steel is low-melting-point spherical CaO & SiO2、 CaO·Al2O3·2SiO2Equal silicate inclusions, and the number density of inclusions more than 5 mu m is 0.35 per mm2The length-width product of the largest inclusion is 810 μm2And the A, B, C, D-type inclusions are all rated on a 0.5 scale.
Example 3
(1) Pretreatment of
Taking blast furnace molten iron to desulfurize in a KR desulfurizing device, wherein the adopted desulfurizing agent comprises the following chemical components in percentage by mass: 80-90% of CaO and CaF2 10～15% and the balance of unavoidable impurity components; the slagging-off rate of the desulfurization is 99 percent.
Wherein, the temperature, the C content, the S content, the Si content, the Ti content, the P content of the blast furnace molten iron, the temperature of the desulfurized molten iron and the S content information of the desulfurized molten iron are shown in Table 7.
[ Table 7]
(2) Smelting in a converter
Mixing the pretreated molten iron and high-quality scrap steel with the thickness of 4mm into molten steel, loading the molten steel into a converter, and carrying out desiliconization, dephosphorization and oxygen blowing decarburization, wherein the loading amount of the converter is 150t, the molten iron ratio is 83%, and the high-quality scrap steel meets the following requirements: less than or equal to 0.012 percent of S, less than or equal to 0.015 percent of P and less than or equal to 0.035 percent of Ti;
the method comprises the following steps of (1) adopting a sliding plate to block slag and tapping, adding ferrosilicon, manganese metal and 30% of carburant into a ladle for deoxidation alloying when tapping begins, adding the rest carburant when tapping reaches 85%, and adding lime and synthetic slag for slagging after tapping ends, wherein N in the carburant is less than or equal to 0.0065%, Al in the ferrosilicon is less than or equal to 0.05%, and Ti is less than or equal to 0.02%;
and (3) opening bottom blowing argon gas in the whole process of the steel ladle during tapping, wherein the flow of the argon gas blown from the bottom of the steel ladle during tapping is 1000NL/min, the flow of the argon gas blown from the bottom of the steel ladle after tapping is 200NL/min, the tapping amount is 136t, and the temperature of the molten steel and the component content information of the molten steel are measured after tapping is finished and are shown in a table 8.
[ Table 8]
(3) Refining
And (4) sending the molten steel smelted by the converter into an LF furnace for chemical component adjustment and inclusion regulation until the molten steel components, the slag components and the molten steel temperature all reach the standard, and then tapping.
Wherein, the bottom blowing argon is opened in the whole process of the steel ladle, the flow of the steel ladle bottom blowing argon is 500NL/min during slag charge adding and alloying treatment, the flow of the steel ladle bottom blowing argon is 300NL/min during power-on temperature rise, and the flow of the steel ladle bottom blowing argon is 100NL/min in the rest time.
The slag alkalinity of the slag charge is 3.0, and the chemical components of the slag charge comprise the following components in percentage by mass: 55-60% of CaO and SiO2 20～25％，MgO 6～12％；CaF2 2～5％；Al2O3≤5％；T.Fe+MnO≤2％。
(4) Vacuum refining
And (3) delivering the refined molten steel to a vacuum chamber of a VD furnace, carrying out vacuum refining, and then breaking the vacuum for soft stirring. Wherein the vacuum degree of the vacuum chamber in the vacuum refining stage is 100Pa, the flow of argon blown from the bottom of the ladle is 50NL/min, and the vacuum treatment time is 25 min; the flow of argon blown from the bottom of the steel ladle in the breaking soft stirring stage is 100NL/min, and the time in the breaking soft stirring stage is 35 min.
(5) Continuous bloom casting
And (3) sending the molten steel after vacuum refining to a continuous casting platform, standing for 25min, then casting, protecting the casting in the whole continuous casting process, controlling the superheat degree of a tundish to be 38 ℃ by adopting electromagnetic induction heating equipment, controlling the nitrogen increment in the continuous casting process to be 0.0001%, controlling the liquid level fluctuation of a crystallizer to be less than or equal to 1mm, controlling the continuous casting drawing speed to be 0.70m/min, and controlling the reduction to be 20 mm.
The high-cleanliness spring steel billets were prepared by the above production method, and the mass percentages of the harmful impurity elements therein were determined to be shown in table 9.
[ Table 9]
| Element(s) | P | S | T.O | N | H | Al | Ti |
| By mass percent% | 0.0104 | 0.001 | 0.0009 | 0.001 | 0.0001 | 0.0009 | 0.0007 |
The detection proves that the type of the inclusions in the high-cleanliness spring steel is low-melting-point spherical CaO & SiO2、 CaO·Al2O3·2SiO2Equal silicate inclusions, number density of inclusions above 5 μm 0.2/mm2The length-width product of the largest inclusion is 700 μm2And the A, B, C, D-type inclusions are all rated on a 0.5 scale.
Claims (5)
1. A production method of high-cleanliness spring steel is characterized by comprising the following steps of,
pretreatment: the method comprises the following steps of desulfurizing by using blast furnace molten iron until S in the molten iron is less than or equal to 0.0015%, wherein the blast furnace molten iron meets the following requirements before desulfurization: the temperature is more than or equal to 1360 ℃, the C is 4.0-4.5%, the S is less than or equal to 0.040%, the Si is 0.20-0.60%, the Ti is less than or equal to 0.04%, the P is less than or equal to 0.10%, and the balance of Fe and other inevitable impurity elements, wherein the adopted desulfurizer comprises the following chemical components in percentage by mass: 80-90% of CaO and CaF210-15% and the balance of unavoidable impurity components;
smelting in a converter: mixing the pretreated molten iron and scrap steel to form molten steel, carrying out desiliconization, dephosphorization, oxygen blowing and decarburization to obtain the molten steel with the temperature of 1630-1660 ℃, C0.10-0.35%, O not more than 0.045%, P not more than 0.011%, and S0.003-0.008%, pushing off slag by using a sliding plate, tapping, carrying out deoxidation alloying treatment on the molten steel, adding ferrosilicon, manganese metal and 30% of carburant into a steel ladle when tapping starts, adding the rest carburant when tapping is 85%, wherein N in the carburant is not more than 0.0065%, Al in the ferrosilicon is not more than 0.05%, Ti is not more than 0.02%, the flow of argon blowing at the bottom of the steel ladle during tapping is 800-1000 NL/min, and the flow of argon blowing at the bottom after tapping is finished is 100-200 NL/min;
refining: the method comprises the following steps of carrying out chemical component adjustment and inclusion regulation on molten steel after converter smelting, wherein the flow of argon blown from the bottom of a steel ladle during slag charge addition and alloying treatment is 300-500 NL/min, the flow of argon blown from the bottom of the steel ladle during power-on temperature rise is 200-300 NL/min, the flow of argon blown from the bottom of the steel ladle during the rest time is 50-100 NL/min, the slag alkalinity of slag charge is 2.5-3.0, and the chemical components of the slag charge comprise the following components in percentage by mass: 55-60% of CaO and SiO2 20~25%，MgO 6~12%；CaF2 2~5%；Al2O3≤5%；T.Fe+MnO≤2%；
Vacuum refining: the method comprises a vacuum refining stage and an emptying soft stirring stage which are sequentially carried out, wherein the flow of argon blown from the bottom of the steel ladle in the vacuum refining stage is 20-50 NL/min, the vacuum degree is less than or equal to 150Pa, the vacuum treatment time is more than or equal to 15min, and the flow of argon blown from the bottom of the steel ladle in the emptying soft stirring stage is 50-100 NL/min;
continuous casting: the method comprises the following steps of casting molten steel into a steel billet, controlling the superheat degree of a tundish to be 30-38 ℃ by adopting electromagnetic induction heating, controlling the liquid level fluctuation of a crystallizer to be less than or equal to 2mm, and controlling the reduction amount to be 12-20 mm, wherein the steel billet comprises the following chemical components in percentage by mass: 0.35 to 0.85 percent of C, 0.5 to 2.0 percent of Si, 0.2 to 1.5 percent of Mn, 0.2 to 1.0 percent of Cr, and the balance of Fe and inevitable impurity elements.
2. The method for producing a high-cleanliness spring steel according to claim 1, wherein in the pretreatment step, the blast furnace molten iron is desulfurized in a KR desulfurization apparatus.
3. A high-cleanliness spring steel characterized by being produced by the production method according to any one of claims 1 to 2.
4. The high-cleanliness spring steel according to claim 3, wherein P is 0.012% or less, S is 0.004% or less, T.O is 0.0020% or less, N is 0.0030% or less, H is 0.0002% or less, Al is 0.0020% or less, and Ti is 0.0009% or less.
5. The high-cleanliness spring steel according to claim 3, wherein the density of inclusions having a size of 5 μm or more is 0.5 pieces/mm or less2The length-width product of the largest inclusion is less than or equal to 900 mu m2。
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