Low-carbon low-silicon high-sulfur steel oxygen content accurate control method

Abstract

The application discloses a low-carbon low-silicon high-sulfur steel oxygen content accurate control method, which comprises the following steps: controlling the converter final slag basicity at 2.0-2.5; adopting a step-by-step weak deoxidization process in the converter tapping process, sequentially adding low-carbon manganese iron, high-sulfur ferrous sulfide and phosphorus iron alloy when tapping 1 / 2, and adding lime and wollastonite when tapping 3 / 4; according to the dissolved oxygen content w[O] Ar precise aluminum wire feeding; adding lime, raw dolomite and wollastonite in batches in the LF heating process; adding aluminum-based reducing agent after the heating is completed, adding lime and wollastonite for slagging; after the slagging is completed, alloy fine adjustment, aluminum wire feeding or slag surface iron oxide skin adding is carried out; the LF is subjected to secondary heating, and pure calcium cored wire is fed after the heating is completed, and the station is softly blown; the cast blank after continuous casting is subjected to light pressing; the application solves the problem of large oxygen content control fluctuation in the smelting process, realizes accurate control of the molten steel oxygen content, and obtains a cast blank with good sulfide inclusion form, good surface quality and excellent cutting performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel metallurgy, and particularly relates to a method for precisely controlling oxygen content of low-carbon low-silicon high-sulfur steel. BACKGROUND

[0002] Sulfur is one of the main impurity elements in general steel, which can cause problems such as "hot brittleness" and reduction of toughness of steel. However, adding a certain amount of sulfur element in steel can form MnS inclusions capable of cutting the continuity of the steel matrix, which can play a role of stress concentration source in the machining process of steel parts, improve the cutting performance of steel, and reduce tool wear.

[0003] There are mainly three types of morphologies of manganese sulfide in low-carbon high-sulfur steel: type I MnS is spherical or fusiform, and is precipitated with an oxide core; type II MnS is fan-shaped or chain-shaped, and is spontaneously nucleated and grown; and type III MnS is polyhedral, and is spontaneously nucleated and grown. Type I MnS inclusions contain an oxide core, and are small in size, not easy to deform in the rolling process, and not easy to be stretched into a long strip, and the spherical or fusiform morphology can effectively cut the steel matrix to improve the cutting chip breaking performance. Type II and III MnS are irregularly distributed in a chain shape, a network shape or an angular shape, are spontaneously nucleated and grown, are large in size, and are single-phase MnS which is easy to deform, and are easily deformed into a long strip in the rolling process, which is not conducive to cutting performance.

[0004] Oxygen content of molten steel is one of the key elements affecting the morphology of MnS, and a certain oxygen content is beneficial to increase the nucleation particles of FeO, MnO and other oxides, reduce the average diameter and aspect ratio of MnS inclusions, increase the proportion of type I composite MnS inclusions, and improve the cutting performance of medium-high sulfur steel. The document "Xia Yunjin, Wang Fujing, Wang Jinlong, et al., Influence of Oxygen Content on Sulfide Formation Behavior in Free-cutting Steel, Journal of University of Science and Technology Beijing, Vol. 32, No. 10" discloses that when the oxygen content is as high as 0.022%, a large amount of MnO-based low-melting point liquid oxides are formed at the initial stage of solidification, which promotes the transformation of the formation mode of MnS from eutectic form to monotectic form, type I MnS is formed, and the liquid-phase inclusions rich in oxygen are formed at the beginning, and single-phase MnS is mainly precipitated at the end. When the oxygen content is below 0.01%, the amount of MnO-based low-melting point liquid oxides formed at the initial stage of solidification is small, most of the MnS is precipitated in a eutectic form under a supersaturated state at the end of solidification, and type II MnS is formed. It can be seen that under the premise of not affecting the cleanliness of the molten steel, appropriately increasing the oxygen content in the steel is beneficial to the control of MnS inclusions, but too high oxygen content is easy to produce skin gas bubbles, scarring and other surface defects of the casting blank. In the rolling process, the local surface of the matrix is disconnected from the matrix to produce a skin defect. Although the document discloses the influence of oxygen content on the sulfide formation behavior in free-cutting steel, it does not disclose how to precisely control the oxygen content in the steel.

[0005] Chinese patent CN 115386800 A discloses a low-carbon high-manganese sulfur environmentally friendly free-cutting steel and its manufacturing method. Aluminum iron, manganese iron, and sulfur iron are added during tapping to deoxidize and alloy. Silicon iron and aluminum are used for steel deoxidization during refining. Pre-melted wollastonite and lime are used for slag making. In this patent, the slag surface is not deoxidized, the silicon content of the molten steel is high, and the oxygen content of the molten steel fluctuates greatly, which is not conducive to the accurate control of the total oxygen content of the casting blank, and adversely affects the cutting stability of low-carbon high-sulfur steel and the wear of the cutting tool.

[0006] Chinese patent CN 111286580 A discloses a low-carbon tellurium-containing high-sulfur free-cutting steel casting blank and its production method. Silicon-manganese alloy and alloy are used for pre-deoxidization of the molten steel during tapping. Silicon iron powder or iron oxide scale is added for oxygen control during LF refining. Silicon-manganese, silicon iron, and other silicon-containing raw materials are used for oxygen control. This method can easily cause the silicon content of the molten steel to exceed the standard, and the addition of tellurium elements can modify inclusions, which has a certain effect on cutting performance, but the addition of tellurium elements is difficult and costly, which is not conducive to stable mass production.

[0007] Chinese patent CN 117403147 A discloses a high-oxygen high-sulfur free-cutting steel 1215MS and its oxygen control LF smelting method. Aluminum iron, low-carbon manganese iron, and sulfur iron are used for deoxidization and alloying during tapping. Silicon carbide and calcium carbide are used for slag surface deoxidization during refining. Silicon carbide can easily increase the silicon and carbon content of the molten steel, the silicon content of the molten steel is high, and low-carbon tapping is required in the converter, the molten steel is highly oxidizing, the deoxidization cost is high, and it cannot meet the low-silicon content requirements of medium and high-end users.

[0008] It can be seen that the above-mentioned prior art does not specifically focus on the control of the silicon content in the steel during the smelting of high-sulfur steel. Low-carbon high-sulfur steel has a high oxygen content in the molten steel and belongs to weakly deoxidized steel. Silicon and aluminum easily form a large amount of high-melting-point hard inclusions such as silicates and aluminum oxides, which can cause tool wear during cutting processing. Medium and high-end customers hope that the silicon and aluminum content in the steel is as low as possible, and there are strict requirements for the silicon and aluminum content in the steel. SUMMARY

[0009] To solve the above technical problems, the present application provides a low-carbon low-silicon high-sulfur steel oxygen content precise control method. According to the characteristics of low-carbon low-silicon high-sulfur steel, the converter steelmaking, LF refining, and continuous casting production processes are controlled to solve the problem of large fluctuation in oxygen content control during the smelting process, achieve precise control of the oxygen content of the molten steel, and obtain a casting blank with good sulfide inclusion morphology, good surface quality, and excellent cutting performance.

[0010] The technical scheme adopted by the present application is as follows:

[0011] The present application provides a low-carbon low-silicon high-sulfur steel oxygen content precise control method, which includes the following steps:

[0012] a. Converter smelting: smelting with molten iron, desulfurization slag iron, scrap steel; the basicity of converter final slag is controlled at 2.0-2.5; no phosphorus and sulfur is removed;

[0013] b. Carbon is left at the end of the converter and argon is blown at the bottom for strong stirring;

[0014] c. The converter tapping process adopts a step-by-step weak deoxidation process, and at 1 / 2 of the tapping, low-carbon ferromanganese with a mass percentage of C ≤0.2%, high-sulfur ferrous sulfide with a mass percentage of S of 50-55%, and phosphorus iron alloy are sequentially added; at 3 / 4 of the tapping, lime and wollastonite are added; a slide plate is used to block the slag, and the amount of converter slag is controlled to be ≤3 kg / t;

[0015] d. The temperature and oxygen are measured at the argon blowing station, and the dissolved oxygen content w[O] Ar The results are accurate, and after the aluminum wire is fed, the dissolved oxygen content of the molten steel is controlled to be 30-80 ppm; the feeding amount l Al of the aluminum wire is calculated according to Formula One: Formula One wherein, m st is the weight of the molten steel, in t; η is an empirical parameter of the deoxidation efficiency of the aluminum wire, when the C at the end of the converter is ≥0.060%, η is 1.15-1.25; when the C at the end of the converter is <0.060%, η is 1.25-1.45; ρ Al is the density of aluminum, in kg / m 3 ; d is the diameter of the aluminum wire, in m; w Al is the mass percentage of aluminum in the aluminum wire, %; l Al is in m; w[O] Ar is in ppm;

[0016] e. The LF station is used for heating, and lime, raw dolomite, and wollastonite are added in batches during the heating process;

[0017] f. After the heating is completed, an aluminum-based reducing agent is added for slag surface diffusion deoxidation, and lime and wollastonite are added for slagging;

[0018] g. After the slagging is completed, alloy fine adjustment, aluminum wire feeding, or slag surface iron oxide skin addition is performed to control the dissolved oxygen content of the molten steel at the end point to be 45-65 ppm;

[0019] h. The LF is used for secondary heating, and after the heating is completed, a pure calcium cored wire is fed to modify the sulfide inclusions, and the wire is fed and then soft blown out of the station;

[0020] i. Continuous casting: the cast blank after continuous casting is subjected to light pressing;

[0021] The weight percentages of carbon, silicon, and sulfur in the low-carbon low-silicon high-sulfur steel are respectively: C ≤0.090%, Si ≤0.010%, and S 0.30-0.50%.

[0022] In step a, the mass percentage of molten iron is 83-93%, the mass percentage of desulfurized slag iron is 2-6%, and the rest is scrap steel; the S content at the end of the converter is 0.030-0.060%, and the P content is 0.035-0.045%.

[0023] In step a, the mass percentage of iron in the desulfurized slag iron is ≥50%, and the mass percentage of sulfur is 1.5-2.5%.

[0024] Further, the mass percentage of T·Fe in the final slag of the converter is 12-15%.

[0025] In step b, the mass percentage of carbon at the end of the converter is 0.060%-0.080%, the mass percentage of oxygen at the end of the converter is 300-400 ppm, and the end temperature is 1620-1660°C; the argon flow rate at the end of the converter is 0.10-0.12 Nm 3 / min·t, and the stirring time is 1.5-2.5 min. The carbon is left at the end of the converter, the oxidizing property at the end of the converter is reduced, a large flow of bottom blowing is used for strong stirring, and the carbon-oxygen reaction is promoted to reduce the oxygen content of the primary refined molten steel.

[0026] In step c, the addition amounts of low-carbon manganese iron, high-sulfur ferrous sulfide, and phosphorus iron alloy are 17.5±0.2 kg / t steel, 22.3*(w[S] CC -w[S] BOF )±0.05 kg / t steel, and 39.7*(w[P CC -w[P BOF )±0.05 kg / t steel, respectively, where w[S CC , w[P CC are the target values of the mass percentages of sulfur and phosphorus in the finished product, and w[S BOF , w[P BOF are the mass percentages of sulfur and phosphorus at the end of the converter; the addition amounts of lime and wollastonite are 3.0-3.5 kg / t steel and 1.5-2.0 kg / t steel, respectively.

[0027] In step c, the mass percentages of the components in the low-carbon manganese iron are: Mn 85-90%, C≤0.2%, and Si≤0.5%; the mass percentages of the components in the high-sulfur ferrous sulfide are: S 50-55%, C≤0.1%, and Si≤0.5%; and the mass percentages of the components in the phosphorus iron are: P 26-30%, C≤0.1%, and Si≤0.5%.

[0028] In step d, the Al content in the aluminum wire is ≥99.5%, and the diameter is 9.5-10.5 mm.

[0029] In step e, the adding amount of lime, raw dolomite and wollastonite is 0.6-1.6 kg / t steel, 0.8-1.2 kg / t steel and 1.0-2.0 kg / t steel respectively, and they are added in 4-5 batches; the electric arc energy is used to fully melt the slag, the raw dolomite MgCO3=MgO+CO2 is decomposed to play the role of foaming agent and refractory agent; the electric arc gear is adjusted to match the submerged arc slag thickness during the heating process to make the electric arc submerged arc efficiency optimal.

[0030] Further, the lime CaO content is ≥90%, the raw dolomite MgCO3 content is ≥40%, and the wollastonite SiO2 content is ≥45%.

[0031] In step f, the total amount of 0.6-1.0 kg / t steel of the environment-friendly aluminum-based reducing agent, 0.2-0.4 kg / t steel of lime and 0.3-0.8 kg / t steel of wollastonite is added in 3-5 batches; the target composition of the refining slag is 43-48% of CaO, 22-27% of SiO2, 14-16% of Al2O3, 6-8% of MgO, 6-10% of T·Fe+MnO, and the basicity CaO / SiO2 is 1.6-2.2; in the environment-friendly aluminum-based reducing agent, the metal Al content is 18-22%, the Al2O3 content is 20-30%, the CaO content is 25-45%, the SiO2 content is ≤5%, the particle size is 5-30 mm, and the density is 2.3-2.7 kg / cm 3 The environment-friendly aluminum-based reducing agent is added in small batches and multiple batches during the slag making process to diffuse and deoxidize the slag surface, the lime and the wollastonite are accurately controlled to control the composition and basicity of the refining slag, and the oxygen between the slag and the molten steel is quickly balanced.

[0032] In step g, 0.075 kg / t steel of aluminum wire can reduce 10 ppm of dissolved oxygen; 0.227 kg / t steel of iron scale added to the slag surface can increase 10 ppm of dissolved oxygen.

[0033] In step h, the sulfide form and composition are controlled by the parameter denaturation degree γ Ca of the modification and denaturation reaction, the calculation method of the denaturation degree γ Ca is shown in Formula Two:

[0034] Formula Two Wherein, w[Ca] is the calcium content of the molten steel, unit is %; w[O] is the dissolved oxygen content of the molten steel, unit is %; w[S] is the sulfur content of the molten steel, unit is %; γ Ca The control range is 0.2-0.4; after the wire feeding, soft blowing is performed for 10-15 min to leave the station.

[0035] Further, the length l CaThe relationship with the calcium percentage content w[Ca] of the molten steel is shown in formula three: Wherein, l Ca The length of the solid core pure calcium cored wire, in units of m; m st The weight of the molten steel, in units of t; m Ca The weight of the calcium core, in units of g / m; alpha Ca The percentage content of electrolytic calcium in the calcium core, %; eta Ca The calcium line yield, 20% to 30%; the percentage content of electrolytic calcium in the calcium core of the solid core pure calcium cored wire is greater than or equal to 97%, the calcium-iron ratio Ca / Fe is greater than or equal to 0.22, and the weight of the calcium core is greater than or equal to 55 g / m.

[0036] In step i, the total reduction of light pressing is 10-20 mm, and the light pressing of 2, 3, 4, 5, and 6 devices is controlled, and the reduction is 1-3 mm, 2-4 mm, 3-5 mm, 3-5 mm, and 1-3 mm, respectively. The casting blank light pressing technology is adopted, the bubbles oxygen adsorbed on the surface of the casting blank is extruded and discharged, the reduction is accurately controlled, and the casting blank with good surface quality and small sulfur segregation is obtained.

[0037] The low-carbon low-silicon high-sulfur steel includes the following chemical components in percentage by weight: C≤0.090%, Si≤0.010%, S 0.30-0.50%, P: 0.040-0.080%, T·[O] 0.010%-0.015%, dissolved [O] 0.0040%-0.0070%, Alt≤0.0050%, Mn / S 3-5, and the rest is Fe and inevitable impurities.

[0038] The low-carbon low-silicon high-sulfur steel oxygen content precise control method provided by the application realizes the precise control of the end oxygen content of the low-carbon low-silicon high-sulfur steel refining molten steel through the above process, and the sulfides are denatured and treated according to the oxygen content and the casting blank light pressing is used to discharge the bubble oxygen on the surface of the casting blank, so that the spindle-shaped type I MnS inclusions are generated in the form of oxides in the solidification process of the molten steel, and the casting blank with good surface quality and small sulfur segregation and the product with good sulfide inclusion form and excellent cutting performance are obtained.

[0039] Compared with the prior art, the application has the following beneficial effects:

[0040] 1) According to the characteristics of the low-carbon low-silicon high-sulfur steel, sulfur and phosphorus are beneficial alloying elements of the steel, part of the desulfurization slag iron is added in the converter, the slag is smelted, sulfur and phosphorus are not removed, high-sulfur and high-phosphorus primary smelting steel is obtained, the cost of sulfur-iron and phosphorus-iron alloy is reduced; on the other hand, the metal iron and slag in the desulfurization slag iron can be recovered, the cost of steel and slag in the converter is reduced, the treatment cost of the desulfurization slag iron and the problem of solid waste stacking are reduced, which is beneficial to environmental protection;

[0041] 2) According to the characteristics of low-carbon low-silicon high-sulfur steel, a full-process precise oxygen control process method is designed, carbon is left in the converter end point and the steel is discharged, the end point oxygen content is reduced; in the process of discharging, the amount of under-slag is strictly controlled, and a step-by-step weak deoxidation process is adopted; the argon station accurately feeds aluminum wire according to the oxygen content and the end point oxidizing property, and controls the oxygen content of the discharged molten steel; the LF refining adopts the environment-friendly aluminum-based reducing agent to realize rapid diffusion deoxidation on the slag surface, so that the oxygen content of the slag and the molten steel reaches a balanced state, the aluminum wire or the slag surface is fed with iron oxide scale to accurately control the dissolved oxygen content of the molten steel at the LF refining end point, and according to the sulfur and oxygen contents, the sulfides are modified to control the sulfide form and composition;

[0042] 3) According to the characteristics of low-carbon low-silicon high-sulfur steel, the billet light press-down technology is adopted to accurately control the press-down amount, the bubbles of oxygen adsorbed on the surface of the billet in the solidification process are squeezed out, and high-quality billets with good surface quality and small sulfur segregation are obtained to improve the cutting performance of the products. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a low-power photograph of the transverse and longitudinal section of the billet of Example 1, wherein the left photograph is a transverse section and the right photograph is a longitudinal section.

[0044] Figure 2 It is a sulfide inclusion metallographic photograph of the transverse section of the wire of Example 1. DETAILED DESCRIPTION

[0045] The application will be described in detail below in combination with examples.

[0046] The desulfurization slag iron used in each example and comparative example is of the same batch, and in the desulfurization slag iron, the mass percentage of iron is ≥50%, and the mass percentage of sulfur is 1.5-2.5%.

[0047] The low-carbon ferromanganese, high-sulfur ferrous sulfide, phosphorus iron, aluminum wire and other alloys used in each example and comparative example are of the same batch, wherein in the low-carbon ferromanganese, the mass percentage of each component is: Mn: 85-90%, C≤0.2%, Si≤0.5%; in the high-sulfur ferrous sulfide, the mass percentage of each component is: S: 50-55%, C≤0.1%, Si≤0.5%; in the phosphorus iron, the mass percentage of each component is: P: 26-30%, C≤0.1%, Si≤0.5%.

[0048] The lime, raw dolomite and wollastonite used in each example and comparative example are of the same batch, wherein in the lime, the CaO content is ≥90%, in the raw dolomite, the MgCO3 content is ≥40%, and in the wollastonite, the SiO2 content is ≥45%.

[0049] The environmental protection aluminum-based reducing agent used in each embodiment and comparative example is the same batch, the metal Al content in the environmental protection aluminum-based reducing agent is 18-22%, the Al2O3 content is 20-30%, the CaO content is 25-45%, the SiO2 content is ≤5%, the particle size is 5-30 mm, and the density is 2.3-2.7 kg / cm 3 .

[0050] The solid core pure calcium cored wire used in each embodiment and comparative example is the same batch, the electrolytic calcium percentage content is 99%, the calcium-iron ratio Ca / Fe is ≥0.22, and the calcium core weight is 57 g / m.

[0051] The density of the aluminum wire used in each embodiment and comparative example is 2.7 kg / cm 3 , the diameter is 10 mm, and the Al content is 99.7%.

[0052] The aluminum iron and silicon carbide used in the comparative example are the same batch, the Al mass percentage content in the aluminum iron is ≥40%, the particle size is 10-30 mm; the SiC mass percentage content in the silicon carbide is ≥90%, and the particle size is ≤5 mm.

[0053] The content referred to in the present document is mass percentage content, unless otherwise specified.

[0054] Embodiment 1

[0055] A low-carbon low-silicon high-sulfur steel oxygen content precise control method, comprising the following steps:

[0056] a. Converter smelting: the main raw material ratio of the converter is 87.6% of molten iron, 10.4% of scrap steel and 2.0% of desulfurization slag iron, the sulfur in the desulfurization slag iron is recovered by using the oxidizing atmosphere of the converter, the converter adopts less slag smelting to create low alkalinity to keep sulfur and phosphorus, the converter slag consumption is 29.0 kg / t of steel, the final slag alkalinity R is 2.3, the converter endpoint can not only obtain high-sulfur and high-phosphorus molten steel, the endpoint S content is 0.037%, and the endpoint P content is 0.043%; on the other hand, the iron-containing material in the desulfurization slag iron can also be recovered, which has the beneficial effect that the converter endpoint steel and iron material consumption is reduced to 1057.0 kg / t;

[0057] b. End-point carbon-remaining and tapping to reduce the endpoint oxidation, the endpoint temperature is 1638℃, the endpoint carbon is 0.074%, the endpoint oxygen content is 345 ppm, the final slag T·Fe content is 13.1%, and the endpoint bottom blowing intensity is 0.11 Nm 3 / min·t, and the strong stirring for 2 min promotes the further reaction of carbon and oxygen;

[0058] c. During the whole tapping process, the flow rate of the ladle was 1000 NL / min. When tapping was 1 / 2, 17.4 kg / t steel of low-carbon ferromanganese, 6.86 kg / t steel of high-sulfur ferrous sulfide, and 0.30 kg / t steel of phosphorus iron were added in turn; when tapping was 3 / 4, 3.2 kg / t steel of lime and 1.9 kg / t steel of wollastonite were added.

[0059] d. According to the results of the argon station oxygen determination of 125.6 ppm and the end-point carbon retention, the feeding aluminum wire was calculated to be 120 m (converted into pure aluminum consumption of 0.214 kg / t steel) according to Formula One, and the oxygen content at the argon station outlet was 42.6 ppm.

[0060] e. During the refining and heating process, a total amount of 1.23 kg / t steel of lime, 1.47 kg / t steel of wollastonite, and 0.92 kg / t steel of raw dolomite were added in four times, with the amount of each addition being 1 / 4 of the total amount, and the process electrode gear positions corresponding to each batch of material being 10 gears→8 gears→6 gears→4 gears. The raw dolomite MgCO3=MgO+CO2 decomposition reaction can act as a foaming agent and a furnace protection agent. The MgO content in the refining slag was 7.3%, which can reduce the erosion of the slag line magnesium carbon bricks.

[0061] f. After the heating was completed, a total amount of 0.83 kg / t steel of environmentally friendly aluminum-based reducing agent, 0.30 kg / t steel of lime, and 0.37 kg / t steel of wollastonite were added in small batches and multiple batches to perform slagging. The slagging material was added in three batches, with the amount of each addition being 1 / 3 of the total amount, and the interval between each addition being 3 min. The argon blowing and stirring flow rate during the slagging process was controlled to be 500-800 NL / min.

[0062] g. After the slagging was completed, the refining slag sample was taken. The slag basicity R was 1.9, and the T·Fe+MnO% mass percentage content was 8.3%. This can not only avoid the high T·Fe+MnO% content causing the slag to continuously transfer oxygen to the molten steel, but also better balance the dissolved oxygen content in the molten steel. The dissolved oxygen content at the end of the refining was 56.2 ppm.

[0063] h. The low-spatter solid-core pure calcium cored wire of 105 m needed to be fed was calculated according to Formula Two and Formula Three, and the modification degree γ was controlled to be 0.292. The soft blowing was performed for 14 min to exit the station. Ca

[0064] i. Continuous casting: The cast blank after continuous casting was subjected to light pressing down, and the total pressing down amount was 15 mm. The light pressing down was controlled at the 2nd, 3rd, 4th, 5th, and 6th devices, with the pressing down amounts being 2 mm, 3 mm, 4 mm, 4 mm, and 2 mm, respectively.

[0065] ​The casting blank C content is 0.060%, the Si content is 0.0051%, the T·[O] total oxygen content is 130.9ppm, the Mn / S is 3.77, the end point C and Si content is low, the T·[O] total oxygen content is appropriate, the surface quality is good, and the spindle rate of the sulfide inclusion length-width ratio ≤4 is 81.4%.

[0066] Example 2

[0067] A low-carbon low-silicon high-sulfur steel oxygen content accurate control method, comprising the following steps:

[0068] a. The furnace main raw material ratio is 88.2% of molten iron, 7.8% of scrap steel and 4.0% of desulfurization slag iron. The sulfur in the desulfurization slag iron is recovered by using the oxidizing atmosphere of the converter. The converter adopts less slag smelting to create low alkalinity to keep sulfur and phosphorus. The converter slag consumption is 27.3kg / t of steel, the final slag alkalinity R is 2.1, and the converter endpoint can not only obtain high-sulfur and high-phosphorus molten steel, but also can recover the iron-containing material in the desulfurization slag iron. The beneficial effect brought by it is that the converter endpoint steel iron material consumption is reduced to 1042.9kg / t of steel;

[0069] b. The end point leaves carbon and reduces the end point oxidation. The end point temperature is 1643℃, the end point carbon is 0.072%, the end point oxygen content is 359ppm, the end slag T·Fe content is 13.5%, and the end point bottom blowing intensity is 0.12Nm 3 / min·t, and the strong stirring is 1.8min to promote the further reaction of carbon and oxygen;

[0070] c. The ladle is full of large flow of 900NL / min during the whole process. At 1 / 2 of the tapping, 17.5kg / t of steel of low-carbon manganese iron, 6.71kg / t of steel of high-sulfur iron sulfide, and 0.42kg / t of steel of phosphorus iron are added in turn. At 3 / 4 of the tapping, 3.3kg / t of steel of lime and 1.8kg / t of steel of wollastonite are added;

[0071] d. According to the argon station fixed oxygen result 136.5ppm and the end point carbon leaving condition, the formula one is used to calculate the feeding aluminum wire 140m (converted into the pure aluminum consumption of 0.251kg / t of steel), and the argon station oxygen content is 48.3ppm;

[0072] e. During the refining and heating process, a total amount of 1.48kg / t of steel of lime, 1.48kg / t of steel of silicon carbide, and 1.02kg / t of steel of raw dolomite are added. The total amount is added in 5 times, and the amount of each time is 1 / 5 of the total amount. The process electrode gear position corresponding to each batch of material is 11gear→9gear→7gear→5gear→3gear. The added raw dolomite MgCO3=MgO+CO2 decomposition reaction can play the role of foaming agent and refractory agent. The MgO content in the refining slag is 7.4%, which can reduce the erosion of slag line magnesium carbon brick;

[0073] f、After the end of heating, a small batch of slag surface, a total of 0.90 kg / t steel of environmental protection aluminum-based reducing agent, 0.37 kg / t steel of lime, 0.37 kg / t steel of wollastonite is added to build slag, and the slag building material is added in 3 batches, the amount of each addition is 1 / 3 of the total amount, the interval between each addition is 3 min, and the argon blowing stirring flow is controlled to be 500-700 NL / min during the slag building process;

[0074] g、After the end of slag building, the refining slag sample is taken, the slag basicity R is 2.0, and the T·Fe+MnO mass percentage content is 7.8%, which can not only avoid the high T·Fe+MnO content to cause the slag to continuously transfer oxygen to the molten steel, but also can better balance the dissolved oxygen content in the molten steel, and the control of the aluminum wire feeding amount is 10 m, the dissolved oxygen content at the end of refining is 53.8 ppm,

[0075] h、According to formula two and formula three, 100 m of low spatter solid core pure calcium cored wire needs to be fed, the control of the modification degree γ Ca is 0.297, and the soft blowing is 13 min;

[0076] i、Continuous casting: The cast blank after continuous casting is subjected to light pressing, and the total pressing amount is 15 mm, the light pressing is controlled at 2, 3, 4, 5, and 6 racks, and the pressing amounts are 2 mm, 3 mm, 4 mm, 4 mm, and 2 mm respectively.

[0077] The cast blank C content is 0.058%, the Si content is 0.0057%, the T·[O] total oxygen content is 128.0 ppm, and the Mn / S is 3.80, the C and Si contents at the end are low, the T·[O] total oxygen content is appropriate, the surface quality is good, and the spindle rate of sulfide inclusions with a length-width ratio of ≤4 is 81.9%.

[0078] Example 3

[0079] A low-carbon low-silicon high-sulfur steel oxygen content accurate control method, comprising the following steps:

[0080] a、The main raw material ratio of the converter is 89.1% of molten iron, 4.9% of scrap steel, and 6.0% of desulfurization slag iron, the sulfur in the desulfurization slag iron is recovered by using the oxidizing atmosphere of the converter, the converter adopts less slag smelting to build low basicity to keep sulfur and phosphorus, the converter slag consumption is 25.2 kg / t steel, the final slag basicity R is 2.2, and the converter endpoint can not only obtain high-sulfur and high-phosphorus molten steel, the S content at the end is 0.058%, and the P content at the end is 0.039%; On the other hand, the iron-containing material in the desulfurization slag iron can be recovered, and the beneficial effect brought by it is that the converter endpoint steel and iron material consumption is reduced to 1029.1 kg / t steel;

[0081] b. End-point carbon-stopping tapping reduces end-point oxidizability, end-point temperature 1635°C, end-point carbon 0.069%, end-point oxygen content 368 ppm, end- point T-Fe content of slag 13.8%, end-point bottom blowing intensity 0.11 Nm 3 / min·t, strong stirring 2.0 min promotes further reaction of carbon and oxygen;

[0082] c. During tapping, a large flow of 900 NL / min is maintained throughout the ladle, at 1 / 2 of the tapping, 17.6 kg / t of steel of low-carbon ferromanganese, 6.35 kg / t of steel of high-sulfur ferrous sulfide, and 0.39 kg / t of steel of ferrophosphorus are sequentially added; at 3 / 4 of the tapping, 3.4 kg / t of steel of lime and 1.7 kg / t of steel of wollastonite are added;

[0083] d. According to the argon station fixed oxygen result 141.5 ppm and the end-point carbon-stopping condition, 150 m of aluminum wire is fed according to Formula One (converted into 0.271 kg / t of steel of pure aluminum consumption), and the argon station outlet oxygen content is 53.7 ppm;

[0084] e. During the refining and heating process, a total amount of 1.49 kg / t of steel of lime, 1.24 kg / t of steel of wollastonite, and 0.87 kg / t of steel of raw dolomite are added in four times, with each addition amount being 1 / 4 of the total amount, and the process electrode gear position corresponding to each batch of material being 9 gear → 7 gear → 5 gear → 3 gear; the raw dolomite MgCO3 = MgO + CO2 decomposition reaction can play the role of a foaming agent and a furnace protection agent, the MgO content in the refining slag is 7.2%, which can reduce the erosion of the slag line magnesium carbon brick;

[0085] f. After the heating is completed, a total amount of 0.97 kg / t of steel of environmental protection aluminum-based reducing agent, 0.38 kg / t of steel of lime, and 0.31 kg / t of steel of wollastonite are added in small batches and multiple batches to perform slagging, the slagging material is added in three batches, with each addition amount being 1 / 3 of the total amount, and the interval between each addition being 3 min, and the argon blowing and stirring flow during the slagging process is controlled to be 600-800 NL / min;

[0086] g. After the slagging is completed, the refining slag sample is taken, the slag basicity R is 2.1, and the T-Fe + MnO% mass percentage content is 7.1%, which can not only avoid the high T-Fe + MnO% content causing the slag continuously transferring oxygen to the molten steel, but also can better balance the dissolved oxygen content in the molten steel, 15 m of aluminum wire is fed to control the refining end-point dissolved oxygen content to be 57.3 ppm;

[0087] h. According to Formula Two and Formula Three, 110 m of low-spatter solid-core pure calcium cored wire needs to be fed, the modification degree γ Ca is controlled to be 0.288, and the soft blowing is 15 min;

[0088] i. Continuous casting: the cast blank after continuous casting is subjected to soft reduction, and the total reduction is 15 mm. The soft reduction is controlled at 2, 3, 4, 5, and 6 stands, and the reduction amounts are 2 mm, 3 mm, 4 mm, 4 mm, and 2 mm, respectively.

[0089] The cast blank C content is 0.059%, the Si content is 0.0053%, the T·[O] total oxygen content is 133.5 ppm, the Mn / S is 3.75, the end-point C and Si contents are low, the T·[O] total oxygen content is appropriate, the surface quality is good, and the spindle rate of the sulfide inclusions with a length-width ratio of ≤4 is 81.1%.

[0090] Comparative Example 1

[0091] The main raw material ratio of the converter is 85.9% molten iron and 14.1% scrap steel. The converter is smelted according to the conventional low-carbon steel, the converter slag consumption is 49.6 kg / t of steel, the final slag basicity R is 3.3, the end-point temperature is 1637℃, the end-point carbon content is 0.043%, the phosphorus content is 0.018%, the sulfur content is 0.019%, the oxygen content is 605 ppm, the end-point T·Fe content of the slag is 16.8%, and the steel and iron material consumption is 1070.4 kg / t of steel.

[0092] The converter slag amount is strictly controlled, and 1.5 kg / t of steel of aluminum iron, 18.8 kg / t of steel of low-carbon ferromanganese, 7.25 kg / t of steel of high-sulfur ferrous sulfide, 1.32 kg / t of steel of phosphorus iron, 1.8 kg / t of steel of lime, and 3.3 kg / t of steel of wollastonite are sequentially added during the tapping process. Argon station blowing is performed for 2 min, the oxygen is fixed at 71.0 ppm, and the aluminum iron conversion aluminum consumption is 0.589 kg / t of steel during the tapping process.

[0093] After entering the LF station, the temperature is raised to above 1580℃, after heating, the lime and wollastonite are added in batches to form slag, and silicon carbide is added on the slag surface for diffusion deoxidation. The oxygen capacity of silicon carbide de-sludge is relatively weak, the diffusion deoxidation rate is slow, and the high oxygen in the slag will continue to transfer oxygen to the molten steel, so multiple feeding of aluminum wire is required to reduce the oxygen content of the molten steel. During the slagging and stirring process, silicon carbide is easy to enter the molten steel, causing the molten steel to increase in silicon and carbon. In this embodiment, the total amount of lime added during the slagging process is 1.25 kg / t of steel, the total amount of wollastonite is 1.88 kg / t of steel, and the total amount of silicon carbide is 1.13 kg / t of steel. The T·Fe+MnO content in the slag at the end of the refining is 23.1%, the slag basicity R is 1.4, and the MgO content in the slag is 7.0%, which is relatively high (the general refining slag is ≤5%) due to the erosion and dissolution of the ladle slag line magnesium carbon brick. The dissolved oxygen content at the end of the refining is 73.8 ppm, and the silicon content is 0.0238%, which exceeds the composition requirements of the low-carbon low-silicon high-sulfur steel.

[0094] No soft reduction of the cast blank is performed after continuous casting;

[0095] The slab C content is 0.054%, the Si content is 0.0238%, the T·[O] total oxygen content is 158.8ppm, the Mn / S is 3.59, the Si content is relatively high, the cutting process aggravates the wear of the tool, and the high-end customer demand cannot be met, the T·[O] total oxygen content is relatively high, the overheating degree is high, the segregation is relatively serious, and the spindle rate of sulfide inclusions with a length-width ratio of less than 4 is only 50.8%.

[0096] Comparative Example 2

[0097] The main raw material ratio of the converter is 86.7% molten iron and 13.3% scrap steel, the converter is smelted according to the conventional low-carbon steel, the converter slag consumption is 50.5kg / t steel, the final slag basicity R is 3.4, the final temperature is 1645℃, the final carbon content is 0.039%, the sulfur content is 0.020%, the phosphorus content is 0.016%, the oxygen content is 667ppm, the T·Fe content of the final slag is 17.3%, and the steel and iron material consumption is 1071.1kg / t steel;

[0098] The converter slag amount is strictly controlled, and 1.7kg / t steel of aluminum iron, 19.0kg / t steel of low-carbon ferromanganese, 7.12kg / t steel of high-sulfur ferrous sulfide, 1.29kg / t steel of phosphorus iron, 3.7kg / t steel of lime, and 1.2kg / t steel of wollastonite are sequentially added during the tapping process; argon station blows argon for 2min, and the oxygen is 68.2ppm, and the aluminum iron conversion aluminum consumption is 0.681kg / t steel during the tapping process;

[0099] After entering the LF station, the temperature is raised to above 1580℃, after heating, the lime and wollastonite are added in batches to form slag, and silicon carbide is added on the slag surface to diffuse and deoxidize; the oxygen capacity of silicon carbide in the slag is relatively weak, the diffusion and deoxidization rate is slow, the high oxygen in the slag will continue to transfer oxygen to the molten steel, and multiple feeding of aluminum wire is required to reduce the oxygen content of the molten steel; during the slagging and stirring process, the silicon carbide is easy to enter the molten steel, causing the molten steel to increase in silicon and carbon; in this embodiment, the total amount of lime added during the slagging process is 2.50kg / t steel, the total amount of wollastonite is 1.25kg / t steel, and the total amount of silicon carbide is 0.64kg / t steel; the T·Fe+MnO content in the slag at the end of the refining is 4.6%, the slag basicity R is 2.6, and the MgO content in the slag is 6.8%, which is relatively high (the refining slag is generally ≤5%) due to the erosion and dissolution of the ladle slag line magnesium-carbon brick, the dissolved oxygen content at the end of the refining is 38.5ppm, and the silicon content is 0.0186%, which exceeds the composition requirements of the low-carbon low-silicon high-sulfur steel;

[0100] No light pressing of the cast slab is used after continuous casting;

[0101] The slab C content is 0.048%, the Si content is 0.0186%, the T·[O] total oxygen content is 93.5ppm, the Mn / S is 3.57, the Si content is high, the cutting process exacerbates the wear of the tool, and the T·[O] total oxygen content is low, the overheating degree is high, the segregation is more serious, and the spindle rate of sulfide inclusions with a length-width ratio of less than 4 is only 48.7%.

[0102] Comparative Example 3

[0103] With reference to Example 2, the following steps are included:

[0104] a. The main raw material ratio of the converter is 88.0% molten iron, 8.0% scrap steel and 4.0% desulfurization slag iron. The sulfur in the desulfurization slag iron is recovered by using the oxidizing atmosphere of the converter. The converter is used for less slag smelting to reduce the basicity and keep the sulfur and phosphorus. The converter slag consumption is 26.8kg / t steel, the final slag basicity R is 2.3, the converter endpoint obtains high sulfur and phosphorus molten steel, the endpoint S content is 0.043%, and the endpoint P content is 0.045%;

[0105] b. The endpoint carbon is discharged to reduce the endpoint oxidation. The endpoint temperature is 1641℃, the endpoint carbon is 0.079%, the endpoint oxygen content is 316ppm, the final slag T·Fe content is 12.1%, and the endpoint bottom blowing intensity is 0.11Nm / min·t. The strong stirring is 2.0min to promote the further reaction of carbon and oxygen; 3

[0106] c. The ladle is full of large flow 950NL / min during the whole process. At 1 / 2 of the tapping, 17.4kg / t steel of low-carbon ferromanganese, 6.86kg / t steel of high-sulfur ferrous sulfide and 0.22kg / t steel of phosphorus iron are added in turn. At 3 / 4 of the tapping, 3.2kg / t steel of lime and 1.8kg / t steel of wollastonite are added;

[0107] d. The argon station enters the station with indefinite oxygen. According to the on-site operation experience, 120m of aluminum wire is fed (converted to 0.215kg / t steel of pure aluminum consumption), and the oxygen content of the argon station is 23.5ppm. The low oxygen content of the molten steel is not conducive to the accurate molten steel dissolved oxygen content in the refining process;

[0108] e. During the refining heating process, 1.33kg / t steel of lime, 1.44kg / t steel of wollastonite and 0.93kg / t steel of raw dolomite are added in total, which are added in 4 times, and the amount of each addition is 1 / 4 of the total amount. The process electrode gear position corresponding to each batch of material is 10gear→8gear→6gear→4gear. The added raw dolomite MgCO3=MgO+CO2 decomposition reaction can play the role of foaming agent and refractory agent. The MgO content in the refining slag is 7.1%, which can reduce the erosion of the slag line magnesium carbon brick;

[0109] ​f、After the end of heating, small batches of lime and 0.36 kg / t steel of wollastonite were added to the slag surface in multiple batches to form slag, the slag forming material was added in 3 batches, the amount of each addition was 1 / 3 of the total amount, the interval between each addition was 3 min, and the argon stirring flow rate during the slag forming process was controlled at 600-800 NL / min;

[0110] g、After the end of slagging, the refining slag sample was taken, the slag basicity R was 2.1, and the T·Fe+MnO mass percentage content was 5.8%, the T·Fe+MnO content of the refining slag was low, which caused the dissolved oxygen content of the steel to be low, 0.467 kg / t steel of iron oxide scale was added to the slag surface to increase the oxygen content of the molten steel, the argon stirring flow rate was controlled at 300-500 NL / min for stirring for 8 min, and the dissolved oxygen content at the end of refining was 46.8 ppm, which was low;

[0111] h、According to formula two and formula three, 70 m of low-spatter solid-core pure calcium cored wire needs to be fed, the modification degree γ Ca was controlled to be 0.191, and soft blowing was performed for 12 min to exit the station; the sulfide modification degree γ Ca was low, and the sulfides were not completely modified;

[0112] i、Continuous casting: the cast blank after continuous casting was subjected to light pressing, the total pressing amount was 15 mm, and the light pressing was controlled at 2, 3, 4, 5, and 6 stands, and the pressing amounts were 2 mm, 3 mm, 4 mm, 4 mm, and 2 mm, respectively.

[0113] The C content of the cast blank was 0.065%, the Si content was 0.0054%, the T·[O] total oxygen content was 119.2 ppm, and the Mn / S was 3.73, the C and Si contents at the end point were low, the T·[O] total oxygen content was low, the surface quality was good, the sulfide modification degree γ Ca was low, and the spindle rate of sulfide inclusions with a length-width ratio of ≤4 was 70.8%.

[0114] Comparative Example 4

[0115] Referring to Example 2, the following steps were included:

[0116] a、The main raw material ratio of the converter was 88.5% of molten iron, 7.5% of scrap steel, and 4.0% of desulfurization slag iron, the sulfur in the desulfurization slag iron was recovered by using the oxidizing atmosphere of the converter, the converter was smelted with less slag, and the low basicity was used to keep the sulfur and phosphorus, the converter slag consumption was 28.4 kg / t steel, the final slag basicity R was 2.2, the high-sulfur and phosphorus molten steel was obtained at the end point of the converter, the S content at the end point was 0.051%, and the P content at the end point was 0.035%;

[0117] b. Converter endpoint failed to retain carbon, endpoint temperature 1647°C, endpoint carbon 0.041%, endpoint oxygen content 644 ppm, final slag T-Fe content 17.1%, endpoint bottom blowing intensity 0.10 Nm 3 / min·t, strong stirring 2.0 min to promote further reaction of carbon and oxygen;

[0118] c. During tapping, a large flow of 900 NL / min was maintained throughout the ladle, at 1 / 2 of the tapping, 18.7 kg / t of steel of low-carbon ferromanganese, 6.58 kg / t of steel of high-sulfur ferrous sulfide, and 0.60 kg / t of steel of phosphorus iron were sequentially added; at 3 / 4 of the tapping, 3.4 kg / t of steel of lime and 1.6 kg / t of steel of wollastonite were added;

[0119] d. The argon station had an undetermined oxygen content, according to the on-site operation experience, 150 m of aluminum wire was fed, which was converted to 0.270 kg / t of steel of pure aluminum consumption, the oxygen content of the argon station was 90.4 ppm, the oxygen content of the molten steel was high, which was not conducive to the accurate molten steel dissolved oxygen content in the refining process;

[0120] e. During the refining and heating process, a total of 1.40 kg / t of steel of lime, 1.30 kg / t of steel of wollastonite, and 1.1 kg / t of steel of raw dolomite were added, which were added in four times, each time the amount was 1 / 4 of the total amount, and the process electrode gear position corresponding to each batch of material was 9 gear→7 gear→5 gear→3 gear. The decomposition reaction of the added raw dolomite MgCO3=MgO+CO2 can act as a foaming agent and a furnace protection agent, the MgO content in the refining slag is 7.5%, which can reduce the erosion of the slag line magnesium carbon brick;

[0121] f. After the heating was completed, a total of 0.98 kg / t of steel of environmentally friendly aluminum-based reducing agent, 0.33 kg / t of steel of lime, and 0.46 kg / t of steel of wollastonite were added in small batches and multiple batches to form slag, the slag forming material was added in three batches, each time the amount was 1 / 3 of the total amount, and the interval between each addition was 3 min, and the argon blowing and stirring flow during the slag forming process was controlled at 600-800 NL / min;

[0122] g. After the slag forming was completed, the refining slag sample was taken, the slag basicity R was 1.8, and the T-Fe+MnO% mass percentage content was 10.1%, the T-Fe+MnO% content of the refining slag was high, which caused the slag to continuously transfer oxygen to the molten steel, the feeding of 65 m of aluminum wire controlled the refining endpoint dissolved oxygen content to be 64.2 ppm, and the refining endpoint dissolved oxygen content was high;

[0123] h. According to formula two and formula three, 150 m of low-spatter solid-core pure calcium cored wire needed to be fed, the control of the modification degree γ Ca was 0.409, and the soft blowing was 12 min out of the station;

[0124] i. Continuous casting: the cast blank after continuous casting is subjected to light pressing, and the total pressing amount is 15mm, and the light pressing is controlled at 2, 3, 4, 5, 6 frame devices, and the pressing amounts are 2mm, 3mm, 4mm, 4mm and 2mm respectively.

[0125] The cast blank C content is 0.047%, the Si content is 0.0048%, the T·[O] total oxygen content is 141.1ppm, the Mn / S is 3.80, the end point C and Si content is low, the T·[O] total oxygen content is high, the surface quality is good, the sulfide modification degree γ Ca The sulfide inclusion length-width ratio is less than or equal to 4, and the spindle rate is 81.2%.

[0126] In summary, the dissolved oxygen content [O] of the molten steel at the refining end point in the embodiments 1, 2 and 3 of the present application is accurately controlled at 50-60ppm, the total oxygen content T·[O] of the cast blank is accurately controlled at 125-135ppm, the oxygen content in the steel is appropriate, the spindle rate of the sulfide inclusion length-width ratio less than or equal to 4 is more than 80%, and compared with the average values of the comparative examples, the spindle rate is increased by 27.6%, 28.1% and 27.3% respectively, the sulfide morphology and distribution are improved, and the product cutting performance is improved.

[0127] The embodiments 1, 2 and 3 of the present application recover the desulfurization slag iron in the converter, smelt with less slag and low alkalinity slag process, obtain high-sulfur and high-phosphorus molten steel, the high-sulfur iron sulfide is reduced by 0.33kg / t, 0.48kg / t and 0.84kg / t respectively compared with the average values of the comparative examples 1 and 2, the phosphorus iron is reduced by 1.01kg / t, 0.89kg / t and 0.92kg / t respectively compared with the average values of the comparative examples 1 and 2, and the alloy consumption is reduced; another beneficial effect is that the metal iron in the desulfurization slag can be recovered at the same time, the converter steel material consumption is reduced by 13.8kg / t, 27.8kg / t and 41.7kg / t respectively compared with the average values of the comparative examples 1 and 2, and the slag consumption is reduced by 21.1kg / t, 22.8kg / t and 24.9kg / t respectively compared with the average values of the comparative examples 1 and 2;

[0128] The embodiments 1, 2 and 3 of the present application leave carbon and tap the molten steel in the converter, reduce the oxidation at the end point, the oxygen content at the end point is between 300-400ppm, utilize strong stirring by large flow bottom blowing, and stepwise weak deoxidation in the tapping process, and the deoxidation aluminum consumption is reduced by 0.42kg / t of steel, 0.38kg / t of steel and 0.36kg / t of steel respectively compared with the average values of the comparative examples 1 and 2;

[0129] The examples 1, 2 and 3 of the present application can quickly remove the middle oxygen by using the environment-friendly aluminum-based refining agent, realize the oxygen balance between the slag and the steel, accurately control the oxygen content of the molten steel, and avoid the silicon and carbon increase caused by the silicon carbide, the Si content of the examples is 0.0051%, 0.0057% and 0.0053% respectively, which is lower than 0.010%, and the Si content is reduced by more than 0.015% compared with the comparative examples, so that the high Si content silicate hard inclusions can be effectively avoided, the wear of the cutting tool in the cutting process is reduced, and the refining time of the examples 1, 2 and 3 is reduced by 17 min, 20 min and 15 min respectively compared with the average values of the comparative examples 1 and 2.

[0130] The examples 1, 2 and 3 of the present application use raw dolomite as a foaming agent and a furnace protection agent to reduce the melting loss of the magnesia-carbon brick of the ladle slag line, and the slag line erosion amount is reduced by 0.43 kg / t, 0.46 kg / t and 0.45 kg / t respectively compared with the average values of the comparative examples 1 and 2.

[0131] The examples 1, 2 and 3 of the present application adopt low superheat casting and billet light pressing down technology to accurately control the pressing down amount, extrude and discharge the bubble oxygen adsorbed on the surface of the billet in the solidification process, obtain high-quality billets with good surface quality and small segregation, and improve the cutting performance of the products.

[0132] The comparative example 3 is implemented according to the example 2, the aluminum wire is not accurately fed in the argon station, the aluminum wire is fed too much in the argon station according to the operation experience, the oxygen content of the argon station is 23.5 ppm, the T·Fe+MnO% content of the refining slag is 5.8%, the dissolved oxygen content of the steel is low, the iron oxide scale of 0.467 kg / t of steel needs to be added to the slag surface, and the stirring time is prolonged by 8 min to promote the transmission of oxygen from the iron oxide scale to the molten steel, the dissolved oxygen content of the molten steel at the refining end point is 46.8 ppm, the T·[O] total oxygen content of the billet is 119.2 ppm, and the dissolved oxygen content of the molten steel and the total oxygen content of the billet are low. Ca The comparative example 3 is implemented according to the example 2, the aluminum wire is not accurately fed in the argon station, the aluminum wire is fed too much in the argon station according to the operation experience, the oxygen content of the argon station is 23.5 ppm, the T·Fe+MnO% content of the refining slag is 5.8%, the dissolved oxygen content of the steel is low, the iron oxide scale of 0.467 kg / t of steel needs to be added to the slag surface, and the stirring time is prolonged by 8 min to promote the transmission of oxygen from the iron oxide scale to the molten steel, the dissolved oxygen content of the molten steel at the refining end point is 46.8 ppm, the T·[O] total oxygen content of the billet is 119.2 ppm, and the dissolved oxygen content of the molten steel and the total oxygen content of the billet are low. Ca The sulfide modification degree γ Ca The sulfide modification degree γ Ca The sulfide modification degree γ

[0133] Comparative Example 4, referring to Example 2, was implemented. The argon station was not accurately fed with oxygen at the entrance. The argon station fed less aluminum wire according to operating experience, resulting in an oxygen content of 90.4ppm at the exit of the argon station and a T·Fe+MnO% content of 10.1% in the refining slag, resulting in a higher dissolved oxygen content in equilibrium with the molten steel. It was necessary to feed 65m of aluminum wire to reduce the dissolved oxygen content at the end of refining. The dissolved oxygen content at the end of refining was 64.2ppm, and the total oxygen content of the ingot T·[O] was 141.1ppm. The dissolved oxygen content of the molten steel and the total oxygen content of the ingot were higher. 150m of low-sputtering solid pure calcium cored wire was fed, and the amount of calcium wire fed was too much to control the degree of modification. Ca The value is 0.409, and the sulfide denaturation degree γ Ca The value is relatively high, and the spindle rate of sulfide inclusions with an aspect ratio of ≤4 is 81.2%. The spindle rate does not increase with the high degree of denaturation γ Ca If it continues to increase, the excess calcium line will cause cost waste.

[0134] Table 1 Parameters of main raw materials, final molten steel and slag in converter smelting

[0135]

[0136]

[0137] Table 2 Converter tapping charging and argon station molten steel parameters

[0138]

[0139]

[0140] Table 3LF refining feed and related parameters

[0141]

[0142]

[0143] Table 4 Composition of slag sample at the end of LF refining

[0144]

[0145]

[0146] Table 5 Chemical composition control of ingot

[0147]

[0148]

[0149] Note: [O] is the mass percentage of dissolved oxygen at the end of LF refining; the rate of spindle-shaped sulfide inclusions is the electron microscope test result, indicating the ratio of spindle-shaped sulfide inclusions with a length / width ratio ≤4, and the higher the rate of spindle-shaped sulfide inclusions in the steel, the better the turning performance of the steel.

[0150] Table 6: Continuous casting related control parameters

[0151]

[0152] The foregoing detailed description of the low-carbon low-silicon high-sulfur steel oxygen content precise control method according to the above reference examples is illustrative rather than limiting, and several examples can be listed within the limited range, and thus variations and modifications without departing from the overall concept of the present application shall fall within the protection scope of the present application.

Claims

1. A method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel, characterized in that: The following steps are involved: a. Converter smelting: put in molten iron, desulfurized slag and scrap steel for smelting; the basicity of converter final slag is controlled at 2.0-2.5; phosphorus and sulfur are not removed; b. Carbon is retained and steel is tapped at the end of the converter, and argon is blown from the bottom for strong stirring; c. The converter tapping process adopts a step-by-step weak deoxidation process. Low-carbon ferromanganese with a C mass percentage of ≤0.2%, high-sulfur ferrosulphur and ferrophosphorus alloy with a S mass percentage of 50-55% are added in sequence when the steel is 1 / 2 tapped. Lime and wollastonite are added when the steel is 3 / 4 tapped. A slide plate is used to block the slag, and the amount of slag discharged from the converter is controlled to ≤3kg / t. d. Temperature measurement and oxygen determination at the argon blowing station, and the dissolved oxygen content w[O] determined by the argon blowing station Ar Results: After feeding aluminum wire accurately, the dissolved oxygen content of molten steel was controlled to be 30-80ppm; the feeding amount of aluminum wire was l Al for: Among them, m st is the weight of molten steel, in t; η is the empirical parameter of aluminum wire deoxidation efficiency, when the converter end point C ≥ 0.060%, η is 1.15 ~ 1.25; when the converter end point C < 0.060%, η is 1.25 ~ 1.45; ρ Al is the density of aluminum in kg / m 3 ; d is the diameter of the aluminum wire, in m; w Al is the mass percentage of aluminum in the aluminum wire, %; l Al The unit is m; w[O] Ar The unit is ppm; e. The LF station is heated, and lime, raw dolomite and wollastonite are added in batches during the heating process; f. After the heating is completed, an aluminum-based reducing agent is added to diffuse and deoxidize the slag surface, and lime and wollastonite are added to form slag; g. After slag making, perform alloy fine-tuning, feed aluminum wire or add iron oxide scale on the slag surface to control the endpoint dissolved oxygen content of the molten steel to 45-65ppm; h, LF is heated twice, after which pure calcium cored wire is fed in to denature the sulfide inclusions, and after feeding the wire, it is soft blown out of the station; i. Continuous casting: The billet after continuous casting is subjected to light reduction; The weight percentages of carbon, silicon and sulfur in the low-carbon, low-silicon and high-sulfur steel are respectively: C≤0.090%, Si≤0.010%, and S0.30-0.50%.

2. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step a, the mass percentage of molten iron is 83-93%, the mass percentage of desulfurized slag iron is 2-6%, and the rest is scrap steel; the S content at the converter end point is 0.030-0.060%, and the P content is 0.035-0.045%.

3. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step b, the mass percentage of carbon at the converter end point is 0.060-0.080%, the mass percentage of oxygen at the converter end point is 300-400 ppm, and the end point temperature is 1620-1660°C; the argon flow rate at the converter end point is 0.10-0.12 Nm 3 / min·t, stirring for 1.5 to 2.5 minutes.

4. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step c, the addition amounts of low carbon ferromanganese, high sulfur ferrosulfur and ferrophosphorus alloy are 17.5±0.2kg / t steel, 22.3*(w[S] CC -w[S] BOF )±0.05kg / t steel, 39.7*(w[P] CC -w[P] BOF )±0.05kg / t steel, where w[S] CC 、w[P] CC are the target values ​​of the mass percentage of sulfur and phosphorus in the finished product, w[S] BOF 、w[P] BOF They are the mass percentages of sulfur and phosphorus at the converter end point respectively; the added amounts of lime and wollastonite are 3.0-3.5 kg / t steel and 1.5-2.0 kg / t steel respectively.

5. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step c, the mass percentage of each component in the low-carbon ferromanganese is: Mn 85-90%, C≤0.2%, Si≤0.5%; the mass percentage of each component in the high-sulfur ferrosulfur is: S 50-55%, C≤0.1%, Si≤0.5%; the mass percentage of each component in the ferrophosphorus is: P 26-30%, C≤0.1%, Si≤0.5%.

6. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step e, the added amounts of lime, raw dolomite and wollastonite are 0.6-1.6 kg / t steel, 0.8-1.2 kg / t steel and 1.0-2.0 kg / t steel, respectively, and are added in 4-5 batches.

7. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step f, a total amount of 0.6-1.0 kg / t steel of an environmentally friendly aluminum-based reducing agent, 0.2-0.4 kg / t steel of lime, and 0.3-0.8 kg / t steel of wollastonite are added in small batches of 3-5 batches; the target composition of the refined slag is as follows by mass percentage: CaO 43-48%, SiO2 22-27%, Al2O3 14-16%, MgO 6-8%, T·Fe+MnO 6-10%, and a basicity CaO / SiO2 of 1.6-2.2; the environmentally friendly aluminum-based reducing agent has a metal Al content of 18-22%, an Al2O3 content of 20-30%, a CaO content of 25-45%, a SiO2 content of ≤5%, a particle size of 5-30 mm, and a density of 2.3-2.7 kg / cm 3 .

8. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step g, feeding 0.075 m / t steel of aluminum wire can reduce 10 ppm of dissolved oxygen; adding 0.227 kg / t steel of iron oxide scale to the slag surface can increase 10 ppm of dissolved oxygen.

9. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step h, the sulfide morphology and composition are determined by the parameter of the modification reaction degree γ Ca Take control: Wherein, w[Ca] is the percentage of calcium in molten steel, in %; w[O] is the percentage of dissolved oxygen in molten steel, in %; w[S] is the percentage of sulfur in molten steel, in %; γ Ca The control range is 0.2~0.4; After feeding the line, soft blow for 10 to 15 minutes before leaving the station.

10. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to claim 1, characterized in that: In step i, the total soft pressing amount is 10-20 mm, and the soft pressing devices 2, 3, 4, 5, and 6 are controlled to have a pressing amount of 1-3 mm, 2-4 mm, 3-5 mm, 3-5 mm, and 1-3 mm, respectively.

11. The method for accurately controlling the oxygen content of low-carbon, low-silicon, high-sulfur steel according to any one of claims 1 to 10, characterized in that: The low-carbon, low-silicon, high-sulfur steel includes the following chemical components in weight percentage: C≤0.090%, Si≤0.010%, S0.30-0.50%, P: 0.040-0.080%, T·[O]0.010%-0.015%, dissolved [O]0.0040%-0.0070%, Alt≤0.0050%, Mn / S 3-5, and the rest is Fe and unavoidable impurities.

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