CN115261702B - Smelting method of hot-rolled spring steel and hot-rolled spring steel prepared by smelting method - Google Patents
Smelting method of hot-rolled spring steel and hot-rolled spring steel prepared by smelting method 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
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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
- C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
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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
- C21C7/076—Use of slags or fluxes as treating agents
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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
- C21C7/10—Handling in a vacuum
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Abstract
The invention discloses a smelting method of hot rolled spring steel, which comprises the following steps: smelting in a converter, and carrying out weak deoxidization on molten steel during tapping; LF refining comprises a first stage and a second stage, wherein the first stage comprises a first aluminum wire feeding step of feeding aluminum wires into molten steel, the target alkalinity of refining slag in the first stage is 4-7, the second stage comprises a second aluminum wire feeding step of feeding aluminum wires into molten steel, and the target alkalinity of refining slag in the second stage is 2-3; vacuum treatment; and (5) continuous casting. The invention is beneficial to reducing the oxygen content and the titanium content in the hot-rolled spring steel and controlling the inclusion in the hot-rolled spring steel. The invention also discloses hot rolled spring steel.
Description
Technical Field
The invention relates to the field of steel smelting, in particular to a smelting method of hot-rolled spring steel and the hot-rolled spring steel prepared by the smelting method.
Background
The hot-rolled spring steel is mainly applied to the diaphragm spring clutch of the automobile, the diaphragm spring clutch has a special structure and a severe service environment, and fatigue damage occurs to the hot-rolled spring steel due to the fact that the hot-rolled spring steel continuously bears alternating loads in strong pressure and high temperature. The metallurgical quality of hot rolled spring steel is therefore very critical. At present, high-grade hot-rolled spring steel in China is imported from abroad, and the domestic field is still blank.
Oxygen and non-metal oxides in steel reduce the fatigue life and impact toughness of the steel and are the main causes of fatigue failure cracks. For critical parts of automobiles with high safety requirements, the oxygen content and nonmetallic oxide inclusions need to be strictly controlled. Ti can fix N element in molten steel and can form TiN. However, if the titanium content is too high, large particles of TiC, tiN and TiCN are formed, deteriorating toughness and fatigue resistance of the steel, and thus the titanium content needs to be controlled. For high grade hot rolled spring steels, there is also a need to reduce class a sulfide inclusions in order to achieve a stable long fatigue life. The quality fluctuation of the hot rolled high-grade spring steel produced by the domestic prior smelting method is large, the inclusion interval A is 1.5-2.5 grade, the inclusion interval B is 1.5-2.5 grade, the oxygen content interval is 14-31ppm, and the steel contains large-particle TiN, so that the steel is difficult to reach the level of similar products abroad.
The invention patent application publication number CN106222362A discloses a refining method of spring steel, wherein the alkalinity of LF refining slag is controlled to be 1.8-2.5, and the refining slag comprises the following components: caO 50-60 wt%, siO 2 22～28wt％，Al 2 O 3 3～6wt％，MgO10～15wt％，MnO+FeO 0.5～1wt％，CaF 2 2 to 4.5 weight percent, si is adopted for deoxidization in refining, thereby achieving the purpose of reducing nonmetallic inclusion in steel. The invention patent No. CN102162068B discloses spring steel and a manufacturing and heat treatment method thereof, wherein the production process is electric furnace-LF-VD-continuous casting-rolling-heat treatment, LF refining slag alkalinity is 2.5-3.0, and Si is adopted for deoxidation during refining to obtain high-quality spring steel. The invention patent publication No. CN201810936796 discloses an LF refining method of spring steel, which achieves the effect of improving inclusions by accurately controlling refining slag and fully utilizing the adsorption effect of the refining slag. The refining slag system comprises the following components: caO 55-60 wt%, siO 2 11～15wt％，Al 2 O 3 18～19wt％，MgO 11～15wt％，CaF 2 2-3 wt% and others; al is adopted for deoxidation in refining.
The high alkalinity refining slag is favorable for deoxidation and desulfurization of molten steel, but has high viscosity and poor adsorption inclusion effect, and easily causes the B-type inclusion in steel to exceed standard, thereby influencing the fatigue performance of spring steel. Adding CaF into refining slag 2 The viscosity of the slag can be effectively reduced, but the slag is seriously harmful to the environment.
The invention patent No. CN104056871B discloses a spring steel wire rod production process for controlling inclusions, which adopts Si/Mn deoxidization smelting process, refining slag component CaO 25-50wt%, siO 2 35～55wt％，Al 2 O 3 3 to 10 weight percent of MgO, 5 to 20 weight percent of FeO+MnO is less than or equal to 5 weight percent, the alkalinity is controlled to be 0.7 to 2.0, and the target control range of the inclusion is SiO 2 ：40-70％，Al 2 O 3 ：10-25％，CaO：20-50% of the total weight of the composition; caO and SiO 2 The content ratio is 0.2-1.0, and CaO-SiO with low melting point is obtained 2 ·Al 2 O 3 The size of the system inclusions is mostly controlled below 5 mu m. The invention patent application publication number CN103510020A discloses a spring steel wire rod and a method for controlling inclusions of the spring steel wire rod, and adopts low-alkalinity refining slag to deoxidize silicon and manganese to realize that the titanium content in steel is not more than 0.0015 percent and the width dimension of the inclusions is not more than 10um.
The adoption of the low-alkalinity refining slag silicomanganese deoxidizing process can reduce the quantity of large-particle TiN and B-class inclusions, but the oxygen content in steel is too high (more than or equal to 20 ppm), silicate inclusions in steel are easy to exceed standard, and meanwhile, the low-alkalinity slag has serious corrosion to steel ladle refractory materials.
Disclosure of Invention
The invention aims to solve the problems that the oxygen content and the titanium content in the hot rolled spring steel are too high and inclusions are not easy to control. The invention provides a smelting method of hot-rolled spring steel, which is beneficial to reducing the oxygen content and the titanium content in the hot-rolled spring steel and controlling inclusions in the hot-rolled spring steel.
In order to solve the technical problems, the invention discloses a smelting method of hot rolled spring steel, which comprises the following steps: smelting in a converter, and carrying out weak deoxidization on molten steel during tapping; LF refining comprises a first stage and a second stage, wherein the first stage comprises a first aluminum wire feeding step of feeding aluminum wires into molten steel, the target alkalinity of refining slag in the first stage is 4-7, the second stage comprises a second aluminum wire feeding step of feeding aluminum wires into molten steel, and the target alkalinity of refining slag in the second stage is 2-3; vacuum treatment; and (5) continuous casting.
In LF refining, the adjustment of the alkalinity and the components of the refining slag are needed, wherein the adjustment of the alkalinity and the components of the refining slag are usually selected as targets, and the control of the refining slag is carried out by adding a slag former and the like so as to lead the alkalinity and the components of the refining slag to reach the targets. The specific alkalinity value is the target alkalinity of the refining slag, and the specific component proportion is the target component of the refining slag.
According to the invention, the converter tapping is used for weak deoxidation, so that the reduction of Ti oxide in the converter slag is avoided, and the Ti is prevented from entering molten steel. Feeding aluminum wires in batches in an LF refining process, so as to avoid the reaction of aluminum and refining slag as much as possible and avoid Ti entering molten steel due to reduction of Ti oxide in the refining slag; and aluminum wires are fed in batches in the LF refining process, so that aluminum can be ensured to fully enter molten steel for dispersion deoxidization, and a dispersed small particle deoxidization product is formed. The target alkalinity of the refining slag is adjusted from 4-7 in the first stage to 2-3 in the second stage, the high alkalinity in the first stage is favorable for desulfurization and deoxidation, the low alkalinity in the second stage can reduce alumina inclusion, and the low alkalinity can inhibit the increase of Ti in molten steel and reduce large-particle TiN inclusion.
Optionally, in the continuous casting step, a magnesia covering agent is adopted in a ladle pouring area, and a calcia covering agent is adopted in a tundish pouring area.
The tundish adopts two covering agents, a ladle pouring area adopts a magnesium covering agent, the formation of large-particle calcium aluminate inclusions of molten steel slag is avoided, the pouring area of the tundish adopts a calcium covering agent, the upper layer of the calcium covering agent adopts carbonized rice hulls to cover the whole, and the inclusions in the molten steel are effectively adsorbed and removed while keeping warm, so that the inclusions in the hot rolled spring steel can be further controlled by selecting the tundish covering agent.
Optionally, in the converter smelting step, the molten steel is weakly deoxidized with a deoxidizer containing no aluminum at the time of tapping.
Optionally, the aluminum-free deoxidizer is a calcium carbide deoxidizer.
Optionally, the aluminum wire feeding amount of the first aluminum wire feeding step and the second aluminum wire feeding step is 0.3-0.4kg/t steel.
Optionally, the refining slag is CaO-Al 2 O 3 -SiO 2 -MgO-Na 2 O system, the target components of the refining slag in the first stage are CaO:48 to 56 weight percent of Al 2 O 3 ：28～34wt％，SiO 2 ：8～12wt％，MgO：4～6wt％，Na 2 O:1 to 3 weight percent, wherein MnO+FeO is more than 0 weight percent and less than or equal to 0.5 weight percent, and the target components of the refining slag in the second stage are as follows: caO:46 to 54 weight percent of Al 2 O 3 ：21～27wt％，SiO 2 ：18～24wt％，MgO：4～6wt％，Na 2 O：1～3wt％，0wt％＜MnO+FeO≤0.5wt％。
Optionally, a carbonized rice hull is used to cover the top of the calcareous covering agent.
The invention also discloses hot rolled spring steel, which is prepared by the smelting method.
The smelting method of the hot-rolled spring steel is beneficial to reducing the oxygen content and the titanium content in the hot-rolled spring steel and controlling inclusions in the hot-rolled spring steel.
Optionally, the oxygen content of the hot rolled spring steel is less than or equal to 0.0015wt%, the titanium content is less than or equal to 0.0015wt%, the diameter of TiN inclusions is less than or equal to 27um, the A and B, C, D inclusions are all less than or equal to 1.0 level, and the Ds inclusions are all less than or equal to 0.5 level.
The process provided by the invention has strong operability and is easy to control; the high-alkalinity low-viscosity fluorine-free refining slag reduces the corrosion of steel ladle refractory materials and avoids the damage of fluorine to the environment.
Detailed Description
Further advantages and effects of the present invention will become apparent to those skilled in the art from the disclosure of the present specification, by describing the embodiments of the present invention with specific examples. While the description of the invention will be described in connection with the preferred embodiments, it is not intended to limit the inventive features to the implementation. Rather, the purpose of the invention described in connection with the embodiments is to cover other alternatives or modifications, which may be extended by the claims based on the invention. The following description contains many specific details for the purpose of providing a thorough understanding of the present invention. The invention may be practiced without these specific details. Furthermore, some specific details are omitted from the description in order to avoid obscuring the invention. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
In the description of the present embodiment, it should be noted that the positional or positional relationship indicated by the terms such as "upper", "lower", etc. are positional or positional relationships based on the conventional arrangement of the present invention in use, are merely for convenience of describing the present invention and simplifying the description, and are not indicative or implying that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention.
The terms "first," "second," and the like are used merely to distinguish between descriptions and are not to be construed as indicating or implying relative importance.
To make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
The invention discloses a smelting method of hot rolled spring steel, which comprises the following steps: smelting in a converter, and carrying out weak deoxidization on molten steel during tapping; LF refining comprises a first stage and a second stage, wherein the first stage comprises a first aluminum wire feeding step of feeding aluminum wires into molten steel, the target alkalinity of refining slag in the first stage is 4-7, the second stage comprises a second aluminum wire feeding step of feeding aluminum wires into molten steel, and the target alkalinity of refining slag in the second stage is 2-3; vacuum treatment; and (5) continuous casting.
According to the invention, the converter tapping is used for weakly deoxidizing, so that Ti is prevented from entering molten steel due to reduction of Ti oxide in the converter slag, the titanium content in the steel is reduced, and the diameter of TiN inclusions in the steel is reduced. Aluminum wires are fed in batches in the LF refining process, so that the reaction of aluminum and refining slag is avoided as much as possible, ti entering molten steel caused by reduction of Ti oxide in the refining slag is avoided, the titanium content in the steel is reduced, and the diameter of TiN inclusions in the steel is reduced; and aluminum wires are fed in batches in the LF refining process, so that aluminum can be ensured to fully enter molten steel for dispersion deoxidization, and dispersed small-particle deoxidization products are formed, thereby being beneficial to reducing the oxygen content in steel and controlling inclusion.
The target alkalinity of the refining slag is adjusted from 4-7 in the first stage to 2-3 in the second stage, the high alkalinity in the first stage is favorable for desulfurization and deoxidation, the oxygen content in steel is reduced, the inclusion is controlled, the low alkalinity in the second stage can reduce alumina inclusion, the low alkalinity can inhibit the increase of Ti in molten steel, and the large-particle TiN inclusion is reduced.
When the target alkalinity of the refining slag in the first stage is less than 4, the deoxidation of molten steel is not facilitated; when the target alkalinity of the refining slag in the first stage is more than 7, the viscosity of the slag is too high, which is not beneficial to the adsorption removal of impurities in the steel. Therefore, the target alkalinity of the refining slag in the first stage should be controlled to be 4-7.
When the target alkalinity of the refining slag in the second stage is less than 2, the deoxidizing effect is poor, and oxygen is easily added into the steel; when the target alkalinity of the refining slag in the second stage is more than 3, alumina inclusions in the steel are increased, and the control is not easy. Therefore, the target alkalinity of the refining slag in the second stage should be controlled to be 2-3.
Optionally, in the continuous casting step, a magnesia covering agent is adopted in a ladle pouring area, and a calcia covering agent is adopted in a tundish pouring area.
The ladle flow injection area adopts a magnesium covering agent to avoid the formation of large-particle calcium aluminate inclusions by molten steel slag, thereby reducing the level of Ds inclusion. The pouring area of the tundish adopts a calcareous covering agent to effectively adsorb and remove impurities in molten steel.
Optionally, in the converter smelting step, the molten steel is weakly deoxidized with a deoxidizer containing no aluminum at the time of tapping.
Optionally, the aluminum-free deoxidizer is a calcium carbide deoxidizer, and the addition amount of the calcium carbide deoxidizer is 0.6-0.9kg/t steel.
Optionally, the aluminum wire feeding amount of the first aluminum wire feeding step and the second aluminum wire feeding step is 0.3-0.4kg/t steel.
When the aluminum wire feeding amount is less than 0.3kg/t of steel, the deoxidizing effect is poor, and the oxygen content in the steel is high; when the aluminum wire feeding amount is more than 0.4kg/t steel, excessive aluminum oxide inclusions are easily formed in molten steel, and the inclusions are aggregated, so that the B-class inclusions exceed the standard.
Optionally, the refining slag is CaO-Al 2 O 3 -SiO 2 -MgO-Na 2 O system, the target components of the refining slag in the first stage are CaO:48 to 56 weight percent of Al 2 O 3 ：28～34wt％，SiO 2 ：8～12wt％，MgO：4～6wt％，Na 2 O:1 to 3 weight percent, wherein MnO+FeO is more than 0 weight percent and less than or equal to 0.5 weight percent, and the target components of the refining slag in the second stage are as follows: caO:46 to 54 weight percent of Al 2 O 3 ：21～27wt％，SiO 2 ：18～24wt％，MgO：4～6wt％，Na 2 O：1～3wt％，0wt％＜MnO+FeO≤0.5wt％。
The refining slag is CaO-Al 2 O 3 -SiO 2 -MgO-Na 2 O system, wherein CaO-Al 2 O 3 -SiO 2 The ternary slag system is a common refining slag system, and the addition of MgO is beneficial to reducing corrosion resistance material of the steel ladle, na 2 O is beneficial to improving the plasticity of the hot rolled spring steel. MnO and FeO are reaction products obtained by oxidizing trace oxygen, manganese and iron in molten steel and enter slag to form. The target components of the refining slag in the first stage are selected from CaO:48 to 56 weight percent of Al 2 O 3 ：28～34wt％，SiO 2 ：8～12wt％，MgO：4～6wt％，Na 2 O:1 to 3 weight percent, the range of MnO+FeO less than or equal to 0.5 weight percent, and the high alkalinity slag system has good deoxidization effect, low viscosity, low melting point and good inclusion adsorption performance. The target components of the refining slag in the second stage are selected from CaO:46 to 54 weight percent of Al 2 O 3 ：21～27wt％，SiO 2 ：18～24wt％，MgO：4～6wt％，Na 2 O:1 to 3 weight percent, wherein MnO+FeO is more than 0 weight percent and less than or equal to 0.5 weight percent, the alkalinity of refining slag is properly reduced, and B-type inclusions in steel can be better controlled.
Optionally, carbonized rice hulls are covered above the calcareous covering agent, so that the effect of heat preservation of molten steel is achieved.
Specifically, the smelting method of the hot rolled spring steel disclosed by the invention comprises the following steps:
(1) Smelting in a converter: molten iron and scrap steel are used as raw materials for converter smelting, and the molten iron accounts for 80-90 wt% of the raw materials. Slag retention and slag splashing are forbidden in the first furnace before the converter production. The phosphorus content of the converter is less than or equal to 0.005wt percent, and the blowing stop temperature is 1645-1665 ℃. The tapping adopts a front slide plate and a rear slide plate to stop slag. Adding high-purity ferrosilicon and electrolytic manganese into a ladle at the early stage of tapping to carry out alloying, adding low-nitrogen carbon powder to carry out carbon matching, adding a deoxidizer which is not aluminum-containing and is used for calcium carbide to carry out deoxidization, adding lime and part of LF premelting slag, and supplementing the LF premelting slag after tapping is finished. The alloy is added in the sequence of adding high-purity ferrosilicon, then adding low-nitrogen carbon powder and then adding electrolytic manganese.
(2) LF refining: the ladle is moved into an LF refining station, an aluminum wire is fed by a wire feeder, and the adding amount of the steel is 0.3-0.4 kg/t. Adding lime and Na 2 Energizing slagging of slagging agents such as O, adjusting refining slag components, na 2 The addition amount of O is 0.1-0.15 kg-And t steel. CaO-Al as refining slag 2 O 3 -SiO 2 -MgO-Na 2 O system, alkalinity 4-7, target component weight percentage is CaO:48 to 56 weight percent of Al 2 O 3 ：28～34wt％，SiO 2 ：8～12wt％，MgO：4～6wt％，Na 2 O:1 to 3 weight percent, and MnO+FeO is more than 0 weight percent and less than or equal to 0.5 weight percent. And after melting refining slag, taking a molten steel sample to analyze molten steel components, feeding aluminum wires, and adding 0.3-0.4kg/t of steel for the second time. And supplementing alloy components according to the analyzed molten steel components. Adjusting slag system at the end of refining, wherein the alkalinity is 2-3, and the target components are CaO:46 to 54 weight percent of Al 2 O 3 ：21～27wt％，SiO 2 ：18～24wt％，MgO：4～6wt％，Na 2 O：1～3wt％，0wt％＜MnO+FeO≤0.5wt％。
(3) Vacuum treatment: and carrying out vacuum treatment on the ladle subjected to LF refining, wherein a vacuum refining method (VD) or a molten steel vacuum circulation degassing method (RH) can be adopted. The absolute vacuum degree of the RH method is less than or equal to 67Pa, the pure degassing time is more than 7min, and the soft blowing and the sedation are carried out for 15-25min; the absolute vacuum degree of the VD method is less than or equal to 300Pa, the high vacuum time is 15-20min, and the soft blowing and the sedation are 15-25min.
(4) Continuous casting: and (3) hanging the sedated molten steel to a casting platform, wherein argon protection casting is adopted for a long nozzle in the whole casting process, two covering agents are adopted for a tundish, a magnesia covering agent is adopted for a ladle pouring area, a calcareous covering agent is adopted for a tundish pouring area, and the upper layer of the calcareous covering agent is completely covered by carbonized rice hulls.
Wherein Na is added into the refining slag 2 O can improve the plasticity of hot rolled spring steel inclusions, while when Na 2 When the addition amount of O is less than 0.1kg/t of steel, the effect of improving plasticity is not obvious, and when Na is used 2 When the addition amount of O is more than 0.15kg/t of steel, a large amount of smoke is generated, causing environmental problems, thus Na 2 The addition amount of O is 0.1-0.15 kg/t steel.
The invention also discloses hot rolled spring steel, which is prepared by the smelting method.
Optionally, the oxygen content of the spring steel is less than or equal to 0.0015wt%, the titanium content is less than or equal to 0.0015wt%, the diameter of TiN inclusions is less than or equal to 27um, the A inclusions and the B, C, D inclusions are all less than or equal to 1.0 level, and the Ds inclusions are all less than or equal to 0.5 level.
Optionally, the hot rolled spring steel comprises the following components: c:0.76 to 0.84 weight percent, 0.10 to 0.35 weight percent of Si, 0.30 to 0.6 weight percent of Mn, cr:0.09 to 0.30 weight percent, 0 to less than or equal to 0.020 weight percent of P, 0 to less than or equal to 0.005 weight percent of S, 0 to less than or equal to 0.0070 weight percent of N, 0 to less than or equal to 0.0015 weight percent of O,0 to less than or equal to 0.0015 weight percent of Ti, and the balance of Fe and unavoidable impurities.
The performance requirements of spring steel are mainly strength and elasticity, and the purpose of high carbon is to improve the strength limit and the yield limit. The proper amount of Si and Mn is added to improve the hardenability and the tempering stability of the steel, so that the spring steel has higher hardness and strength at the same tempering temperature, but the excessive content of Si and Mn can increase the overheating and decarburization of the steel. By adding a certain amount of Cr, on the one hand, overheating and decarburization can be prevented and, at the same time, hardenability can be improved. However, the content of Si and Cr is too high, pearlite transformation is inhibited in the heat treatment process, and the strength and elasticity of the spring steel are poor; p, S is a harmful element in steel, and the reduction of the content is beneficial to improving the fatigue life; decreasing N, O, ti content can reduce oxide and titanium nitride inclusions and improve fatigue performance.
Example 1
(1) Smelting in a converter: smelting by adopting a converter with nominal capacity of 300t, taking molten iron and scrap steel as raw materials, adding 275t of molten iron and 45t of high-quality scrap steel. Slag retention and slag splashing are forbidden in the first furnace before the converter production. The addition amount of the first slag lime is 4t, and the light burned dolomite is 1t. Slag top-blowing flow 55000Nm 3 /h, oxygen supply 1500Nm 3 The back top-blown flow rate is reduced to 45000Nm 3 And/h. High-carbon drawing operation is carried out, the carbon content at the stopping blowing end point of the converter is 0.2 weight percent, the phosphorus content is 0.005 weight percent, and the stopping blowing temperature is 1648 ℃. The tapping adopts a front slide plate and a rear slide plate to stop slag. And (3) sequentially adding high-purity ferrosilicon and electrolytic manganese into the steel for alloying, adding low-nitrogen carbon powder for carbon matching and calcium carbide for deoxidizing, and coarsely adjusting the content of the element components in the molten steel to meet the lower limit value of each element component in the molten steel. 600kg of lime is added in tapping, 800kg of LF premelting slag is added immediately after alloying, and 800kg of LF premelting slag is added after tapping is finished.
(2) LF refining: the ladle is moved into an LF refining station, an aluminum wire is fed by a wire feeder, and the adding amount of the aluminum wire is 0.3kg/t steel. Lime 1t and silicon carbide balls 0.2t are added,Na 2 the addition amount of O is 0.1kg/t steel. The alkalinity of refining slag is 4, and the components are 48 percent of CaO and 31 percent of Al by weight percent 2 O 3 ，12％SiO 2 ，5.5％MgO，3％Na 2 O,0.5% MnO+FeO. After the refining slag is completely melted, sampling and analyzing the molten steel components, and feeding aluminum wires into the molten steel, wherein the adding amount of the second aluminum wires is 0.3kg/t of steel. And supplementing alloy components according to the analyzed molten steel components. Adding 600kg silicon carbide balls at the final stage of refining to adjust slag system, wherein the alkalinity is 2, and the refining slag comprises 46% of CaO and 24% of Al by weight percent 2 O 3 ，23％SiO 2 ，4.3％MgO，2.5％Na 2 O，0.2％MnO+FeO。
(3) RH treatment: and (3) conveying the ladle subjected to LF refining to an RH station for vacuum treatment, wherein the absolute vacuum degree is 65Pa, the pure degassing time is 7min, and the soft blowing and the sedation are carried out for 20min.
(4) Continuous casting: and (3) hanging the sedated molten steel to a casting platform, and casting the long nozzle by adopting argon protection in the whole casting process. Two tundish covering agents are adopted, a magnesia covering agent is adopted in a ladle flow injection area, a calcareous covering agent is adopted in a pouring area, and the upper layer of the calcareous covering agent is completely covered by carbonized rice hulls.
(5) Rolling: and rolling the casting blank to obtain the hot rolled spring steel.
Example 2
(1) Smelting in a converter: smelting by adopting a converter with nominal capacity of 300t, taking molten iron and scrap steel as raw materials, adding 274t of molten iron and 44t of high-quality scrap steel. Slag retention and slag splashing are forbidden in the first furnace before the converter production. The addition amount of the first slag lime is 3t, and the light burned dolomite is 1t. Slag top-blowing flow 55000Nm 3 /h, oxygen supply 1500Nm 3 The back top-blown flow rate is reduced to 45000Nm 3 And/h. The carbon content at the stop blowing end point of the converter is 0.035wt percent, the phosphorus content is 0.005wt percent, and the stop blowing temperature is 1660 ℃. The tapping adopts a front slide plate and a rear slide plate to stop slag. And (3) sequentially adding high-purity ferrosilicon and electrolytic manganese into the steel for alloying, adding low-nitrogen carbon powder for compounding carbon and calcium carbide for deoxidizing, and meeting the lower limit value of each element component in the molten steel by coarsely adjusting the content of the element component in the molten steel. 800kg of lime is added in tapping, LF premelting slag 1t is added immediately after alloying, and LF premelting slag 1t is added after tapping is finished.
(2) LF refining: will beThe ladle is moved into an LF refining station, an aluminum wire is fed by a wire feeder, and the adding amount of the steel is 0.35 kg/t. Lime 1t, na 2 The addition amount of O was 0.1kg/t of steel. The alkalinity of the refining slag is 7, and the components of the refining slag are 56 percent of CaO and 28 percent of Al by weight percent 2 O 3 ，8％SiO 2 ，4.5％MgO，3％Na 2 O,0.5% MnO+FeO. After the refining slag is completely melted, sampling and analyzing the molten steel components, and feeding aluminum wires into the molten steel, wherein the second aluminum wire is added into the molten steel at the amount of 0.35 kg/t. And supplementing alloy components according to the analyzed molten steel components. 400kg of silicon carbide balls are added at the end of refining to adjust slag system, the alkalinity is 3, and the components of the refining slag are 52.5 percent CaO and 23 percent Al by weight percent 2 O 3 ，18％SiO 2 ，4％MgO，2.3％Na 2 O，0.2％MnO+FeO。
(3) RH treatment: and (3) conveying the ladle subjected to the LF treatment to an RH station for vacuum treatment, wherein the absolute vacuum degree is 60Pa, the pure degassing time is 8min, and the soft blowing and the sedation are carried out for 21min.
(4) Continuous casting: and (3) hanging the sedated molten steel to a casting platform, and casting the long nozzle by adopting argon protection in the whole casting process. Two tundish covering agents are adopted, a magnesia covering agent is adopted in a ladle flow injection area, a calcareous covering agent is adopted in a pouring area, and the upper layer of the calcareous covering agent is completely covered by carbonized rice hulls.
(5) Rolling: and rolling the casting blank to obtain the hot rolled spring steel.
Example 3
(1) Smelting in a converter: smelting by adopting a converter with nominal capacity of 300t, taking molten iron and scrap steel as raw materials, adding 274t of molten iron and 44t of high-quality scrap steel. Slag retention and slag splashing are forbidden in the first furnace before the converter production. The addition amount of the first slag lime is 3t, and the light burned dolomite is 1t. Slag top-blowing flow 55000Nm 3 /h, oxygen supply 1500Nm 3 The back top-blown flow rate is reduced to 45000Nm 3 And/h. The carbon content at the stop blowing end point of the converter is 0.035wt percent, the phosphorus content is 0.005wt percent, and the stop blowing temperature is 1660 ℃. The tapping adopts a front slide plate and a rear slide plate to stop slag. And (3) sequentially adding high-purity ferrosilicon and electrolytic manganese into the steel for alloying, adding low-nitrogen carbon powder for compounding carbon and calcium carbide for deoxidizing, and meeting the lower limit value of each element component in the molten steel by coarsely adjusting the content of the element component in the molten steel. 800kg of lime is added into the steel tapping, and LF premelting slag is added immediately after alloying1t, and then supplementing LF premelting slag 1t after tapping.
(2) LF refining: the ladle is moved into an LF refining station, an aluminum wire is fed by a wire feeder, and the addition amount of the steel is 0.35 kg/t. Lime 1t, silicon carbide balls 100kg, na 2 The addition amount of O is 0.1kg/t steel. The alkalinity of the refining slag is 5.5, the components are 52.5 percent of CaO and 30 percent of Al by weight percent 2 O 3 ，9.5％SiO 2 ，4.5％MgO，3％Na 2 O,0.5% MnO+FeO. After the refining slag is completely melted, sampling and analyzing the molten steel components, and feeding aluminum wires into the molten steel, wherein the second aluminum wire is added into the molten steel at the amount of 0.35 kg/t. And supplementing alloy components according to the analyzed molten steel components. 600kg of low-alkalinity premelting slag is added at the end of refining to adjust slag system, the alkalinity is 2.5, and the components of the refining slag are 50 percent CaO and 23 percent Al by weight percent 2 O 3 ，20％SiO 2 ，4％MgO，2.5％Na 2 O，0.5％MnO+FeO。
(3) RH treatment: and (3) conveying the ladle subjected to the LF treatment to an RH station for vacuum treatment, wherein the absolute vacuum degree is 60Pa, the pure degassing time is 8min, and the soft blowing and the sedation are carried out for 21min.
(4) Continuous casting: and (3) hanging the sedated molten steel to a casting platform, and casting the long nozzle by adopting argon protection in the whole casting process. Two tundish covering agents are adopted, a magnesia covering agent is adopted in a ladle flow injection area, a calcareous covering agent is adopted in a pouring area, and the upper layer of the calcareous covering agent is completely covered by carbonized rice hulls.
(5) Rolling: and rolling the casting blank to obtain the hot rolled spring steel.
Comparative example
(1) Smelting in a converter: smelting by adopting a converter with nominal capacity of 300t, taking molten iron and scrap steel as raw materials, adding 275t of molten iron and 44t of high-quality scrap steel. Lime and dolomite are added into the converter for slagging and dephosphorization, the carbon content of the stopping blowing end point is 0.035wt percent, the phosphorus content is 0.005wt percent, and the stopping blowing temperature is 1655 ℃. The tapping adopts a front slide plate and a rear slide plate to stop slag. And (3) 1/3 of tapping is sequentially added with high-purity ferrosilicon and electrolytic manganese for alloying, and low-nitrogen carbon powder is added for carbon distribution, and 0.5kg/t of aluminum ingot is added for deoxidizing, so that the lower limit value of each element component in the molten steel is met by roughly adjusting the content of the element component in the molten steel. 800kg of lime is added in tapping, LF premelting slag 1t is added immediately after alloying, and LF premelting slag 1t is added after tapping is finished.
(2) LF refining: and transferring the ladle into an LF refining station for electrifying slag, sampling and analyzing molten steel components after the refining slag is melted, adding lime and aluminum, electrifying and melting, and supplementing alloy components according to the analyzed molten steel components. Lime was added at 1t, silicon carbide balls at 400kg, and aluminum was added at 0.3kg/t of steel. The alkalinity of the refining slag is 3, and the components are 51 percent CaO and 17 percent SiO by weight percent 2 ，26％Al 2 O 3 ，5.5％MgO，0.5％FeO+MnO。
(3) RH treatment: and (3) conveying the ladle subjected to the LF treatment to an RH station for vacuum treatment, wherein the absolute vacuum degree is 60Pa, the pure degassing time is 8min, and the soft blowing and the sedation are carried out for 21min.
(4) Continuous casting: and (3) hanging the sedated molten steel to a slab casting platform, wherein argon protection casting is adopted in the whole casting process, a double-layer covering agent is adopted in a tundish, an amorphous pre-melted calcareous covering agent is adopted in a bottom layer, and carbonized rice hulls are adopted in an upper layer to cover the whole casting process.
(5) Rolling: and rolling the casting blank to obtain the hot rolled spring steel.
The hot rolled spring steel obtained in the examples and the comparative examples was subjected to component detection according to the following specific test method: JISG 1253-2002 iron and steel-photoemission spectroscopy methods, specific results are shown in table 1:
TABLE 1 composition (wt.%) of hot rolled spring steel
| C | Si | Mn | Cr | P | S | N | O | Ti | |
| Example 1 | 0.82 | 0.17 | 0.41 | 0.11 | 0.013 | 0.001 | 0.004 | 0.0009 | 0.0013 |
| Example 2 | 0.81 | 0.16 | 0.40 | 0.10 | 0.014 | 0.001 | 0.004 | 0.0010 | 0.0015 |
| Example 3 | 0.79 | 0.19 | 0.41 | 0.12 | 0.014 | 0.001 | 0.004 | 0.0010 | 0.0015 |
| Comparative example | 0.82 | 0.18 | 0.41 | 0.12 | 0.015 | 0.001 | 0.004 | 0.0016 | 0.0029 |
The hot rolled spring steels obtained in examples and comparative examples were rated for A, B, C, D, ds class inclusions and the diameter of TiN inclusions was measured, the detection criteria being based on: GB/T10561-2005/ISO 4967:1998 (E): the test surface is positioned at 1/4 of the width of the cross section parallel to the longitudinal axis of the steel material, and the area of the polished surface is 200mm 2 The morphology and distribution of inclusions were observed with a metallographic microscope at a field of view enlarged 100 times, and the grade of A, B, C, D and Ds inclusion was evaluated against a standard chart. The diameter of TiN inclusion was measured by the same test sample and observation method. The specific results are shown in Table 2:
TABLE 2 inclusions in hot rolled spring steels
As is clear from tables 1 and 2, the hot rolled spring steels obtained in examples 1 to 3 have an oxygen content of 0.0015wt% or less, a titanium content of 0.0015wt% or less, tiN inclusions of 27 μm or less, and inclusions of 1.0 or less in both of A and B, C, D, and Ds of 0.5 or less. In the comparative example, aluminum ingot is used for deoxidizing molten steel in the converter smelting process, aluminum is added once in the LF refining process, and refining slag is adjusted once, namely, the aluminum ingot is adjusted to be conventional refining slag with the alkalinity of 3, so that the oxygen content of the hot rolled spring steel obtained in the comparative example is up to 0.0016wt%, the titanium content is up to 0.0029wt%, the diameter of TiN inclusion is up to 32um, class B inclusion is 1.5, class D inclusion is 1.5, and class Ds inclusion is 1.5.
In summary, according to the smelting method of the hot rolled spring steel, provided by the invention, through weak deoxidization of converter tapping, batch feeding of aluminum wires in an LF refining process and adjustment of target alkalinity of refining slag from 4-7 in the first stage to 2-3 in the second stage, oxygen content and titanium content in the hot rolled spring steel can be effectively reduced, and inclusions in the hot rolled spring steel can be effectively controlled.
While the invention has been described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is a further detailed description of the invention in connection with specific embodiments, and it is not intended to limit the invention to the specific embodiments described. Various changes in form and detail may be made therein by those skilled in the art, including a few simple inferences or alternatives, without departing from the spirit and scope of the present invention.
Claims (12)
1. The smelting method of the hot rolled spring steel is characterized by comprising the following steps of:
smelting in a converter, and carrying out weak deoxidization on molten steel during tapping;
LF refining comprises a first stage and a second stage, wherein the first stage comprises a first aluminum wire feeding step of feeding aluminum wires into molten steel, the target alkalinity of refining slag in the first stage is 4-7, the second stage comprises a second aluminum wire feeding step of feeding aluminum wires into molten steel, and the target alkalinity of refining slag in the second stage is 2-3;
vacuum treatment;
continuous casting;
wherein in the LF refining step, refining slag is CaO-Al 2 O 3 -SiO 2 -MgO-Na 2 O is; the target components of the refining slag in the first stage are as follows: caO:48-56wt%, al 2 O 3 ：28-34wt%，SiO 2 ：8-12wt%，MgO：4-6wt%，Na 2 O:1 to 3 weight percent, wherein MnO+FeO is more than 0 weight percent and less than or equal to 0.5 weight percent; the target components of the refining slag in the second stage are as follows: caO:46-54wt%, al 2 O 3 ：21-27wt%，SiO 2 ：18-24wt%，MgO：4-6wt%，Na 2 O：1-3wt%，0wt%＜MnO+FeO≤0.5wt%。
2. The method of claim 1, wherein in the continuous casting step, a magnesium covering agent is used in a ladle pouring area, and a calcium covering agent is used in a tundish pouring area.
3. The method according to claim 1 or 2, wherein in the converter smelting step, the converter blowing-off P content is not more than 0.005wt%, and the blowing-off temperature is 1645 to 1665 ℃.
4. The method according to claim 1 or 2, wherein in the converter smelting step, the molten steel is weakly deoxidized with an aluminum-free deoxidizer at the time of tapping.
5. The method according to claim 4, wherein the aluminum-free deoxidizer is a calcium carbide deoxidizer.
6. The smelting process according to claim 1 or 2, wherein the aluminum wire feeding amount of the first aluminum wire feeding step and the second aluminum wire feeding step is 0.3 to 0.4kg/t steel.
7. The smelting method according to claim 5, wherein the calcium carbide deoxidizer is added in an amount of 0.6 to 0.9kg/t of steel.
8. The smelting method according to claim 1 or 2, wherein in the vacuum treatment step, vacuum treatment is performed by using a VD method or an RH method: in the VD method, the absolute vacuum degree is less than or equal to 300Pa, the high vacuum time is 15-20min, and the soft blowing and sedation time is 15-25min; in RH method, absolute vacuum degree is less than or equal to 67Pa, pure degassing time is more than 7min, and soft blowing and sedation time is 15-25min.
9. The method of claim 2, wherein the carbonaceous rice hulls are coated on top of the calcareous coating agent.
10. A hot rolled spring steel prepared by the smelting process of any one of claims 1-9.
11. The hot rolled spring steel as claimed in claim 10, wherein the hot rolled spring steel has an oxygen content of 0.0015wt% or less, a titanium content of 0.0015wt% or less, a diameter of TiN inclusions of 27um or less, a class a, B, C, D inclusions of 1.0 or less, and a class Ds inclusion of 0.5 or less.
12. The hot rolled spring steel as claimed in claim 10, wherein the hot rolled spring steel has the following composition: c:0.76% -0.84%, si:0.10% -0.35%, mn:0.30% -0.60%, cr:0.09% -0.30%,0 < P is less than or equal to 0.020%,0 < S is less than or equal to 0.005%,0 < N is less than or equal to 0.0070%,0 < O is less than or equal to 0.0015%,0 < Ti is less than or equal to 0.0015%, and the balance is Fe and unavoidable impurities.
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