Smelting method of steel containing sulfur and aluminum

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a smelting method of sulfur-containing aluminum-containing steel, which comprises the steps of converter smelting, LF refining, RH treatment and continuous casting, wherein LF refining specifically comprises the steps that 10-20 kg of aluminum wires and 60-80 kg of high-purity silicon carbide are added for slag surface diffusion deoxidation after electrification is conducted for 3 minutes; sampling and analyzing after supplying power for 15 minutes, wherein the target temperature liquidus is + 40 DEG C; 150 kg of lime is supplemented into the furnace, and 100-200 kg of silicon carbide is added in batches to make high-alkalinity slag for deoxidation; 60-80 kg of quartz sand is added into slag in the middle and later stages of refining, and the alkalinity of the furnace is reduced. According to the method for controlling the refining alkalinity in stages, the possibility that the molten steel is poor in castability due to calcium sulfide is greatly improved, so that multi-furnace continuous casting of the molten steel is achieved, and high economic, environmental and social benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a method for smelting sulfur-containing and aluminum-containing steel. Background Art

[0002] With the development of the mechanical processing industry, especially the rapid development of the automobile industry, the demand for free-cutting steel in my country has increased rapidly. The requirements for the mechanical properties of materials are getting higher and higher, and they are required to have good processing performance. Therefore, high-cleanliness steel with good cutting performance has a huge market potential.

[0003] Free-cutting steel can be divided into sulfur free-cutting steel, lead free-cutting steel, calcium free-cutting steel, and selenium, tellurium, bismuth, and tin free-cutting steel according to the free-cutting elements added. Lead free-cutting steel is less used at present because the lead vapor produced during steelmaking and rolling pollutes the environment and damages refractory materials. The high cost of other elements such as calcium, selenium, tellurium, and bismuth limits their promotion and application. The effect of tin on the properties of steel other than the mechanical properties at room temperature needs to be further studied, and tin free-cutting steel is not yet mature. Sulfur free-cutting steel is currently the largest type of free-cutting steel, accounting for more than 90% of the free-cutting steel output.

[0004] At present, weak deoxidation is generally used in the production of this type of steel. The oxygen content of sulfur-based free-cutting steel is generally controlled at 100-150ppm to ensure the sulfur recovery rate when smelting this type of steel. However, due to the high oxygen content in the steel, the inclusion content in the steel is difficult to control, which seriously affects the cleanliness of the steel.

[0005] Therefore, the production of high-quality low-oxygen sulfur free-cutting steel is of great significance, but there are great difficulties in smelting:

[0006] In terms of castability: (1) The Al content in steel is relatively high, and the deoxidation process mainly generates Al2O3 inclusions. If you want to strengthen the adsorption of the deoxidation product Al2O3, you should use a high CaO / Al2O3 refined slag to remove Al2O3 inclusions as much as possible during the LF and RH processes; at the same time, in order to inhibit the oxidizing components (MnO, FeO, SiO2) in the slag from reacting with the molten steel [Al] to generate high-melting-point oxides, you should use a high-basicity, low-oxygen potential slag. (2) Steel also contains a high S content. The high content of [S] in steel is easy to react with the ladle top slag to generate a large amount of high-melting-point CaS. On the contrary, in order to inhibit the reaction of [S] with steel slag (CaO) to generate CaS, you should use a low-basicity, high-oxygen potential slag. There is a thermodynamic contradiction between these two aspects. How to coordinate the metallurgical reaction effects of the above two aspects is very difficult in theory and in actual process. Therefore, in order to improve the castability of molten steel, it is necessary to make technical breakthroughs in the slag making and deoxidation system of refined slag.

[0007] Cleanliness: Due to the high [Al] content of this type of steel, Al2O3 inclusions generated by deoxidation reaction, and the high S content of this type of steel, [S] reacts with (CaO) to generate (CaS), which are high melting point inclusions and are difficult to remove during the smelting process. Therefore, this type of steel has great difficulty in controlling inclusions. For this reason, this application proposes a smelting method for sulfur-containing and aluminum-containing steel. Summary of the invention

[0008] The present invention aims at the above-mentioned technical problems, overcomes the shortcomings of the prior art, and provides a smelting method for sulfur-containing and aluminum-containing steel. The method controls the refining basicity in stages, controls the high-basicity reducing slag in the early stage of refining, adopts high-power stirring to achieve deoxidation and desulfurization, obtains molten steel with low oxygen potential and high purity, reduces the slag basicity and the stirring power in the later stage of LF, reduces the slag basicity while maintaining the molten steel with low oxygen potential and high purity, and avoids the generation of a large amount of calcium sulfide after adding the sulfur line. The possibility of poor castability of molten steel caused by calcium sulfide is greatly improved.

[0009] The smelting method of sulfur-containing aluminum-containing steel in this scheme specifically includes converter smelting, LF refining, RH treatment and continuous casting;

[0010] LF refining specifically includes: 3 minutes after power on, add 10-20kg of aluminum wire and 60-80kg of high-purity silicon carbide to deoxidize the slag surface; 15 minutes after power on, take samples for analysis, the target temperature liquidus is +40℃; add 150kg of lime after sampling, add 100-200kg of silicon carbide in batches until the reducing atmosphere in the furnace is strong (a large amount of white smoke overflows), stop adding silicon carbide to avoid excessive calcium carbide slag formation, and then slowly increase the argon flow rate according to the atmosphere in the furnace to the maximum value required by the standard. If the arc is well submerged, the furnace has basically formed foam slag. The refining process ensures that the aluminum content in the molten steel is ≥0.015%; the sulfur slag content in the molten steel is controlled to be less than 0.008%; in the middle and late stages of refining, add 60-80kg / furnace of quartz sand to the slag to reduce the furnace basicity.

[0011] The technical solution further defined in the present invention is:

[0012] Furthermore, the converter smelting includes: adding molten iron and scrap steel into the converter, bottom blowing to supply argon and top blowing to supply oxygen, adding slag-making materials into the converter in batches, and obtaining crude molten steel at a steel tapping temperature of 1600-1630°C.

[0013] Furthermore, during the steel-making process, 1.2 kg of aluminum per ton of steel is used for deoxidation, 550 kg of slag lime per furnace and 200 kg of refined slag per ton of furnace are added along with the steel flow.

[0014] Furthermore, in the early stage of LF refining, 3 minutes before power-on, the argon flow rate was controlled at 50-100NL / min to allow the slag to be slightly stirred.

[0015] Furthermore, the RH treatment specifically includes feeding the molten steel into the RH furnace, feeding a sulfur line into the molten steel to increase sulfur, performing vacuum treatment, adjusting the components such as calcium, aluminum, and sulfur, and the target temperature is 1560°C.

[0016] The beneficial effects of the present invention are:

[0017] The present invention controls the refining basicity in stages, controls the high-basicity reducing slag in the early stage of refining, adopts high-power stirring to achieve deoxidation and desulfurization, obtains molten steel with low oxygen potential and high purity, reduces the slag basicity and reduces the stirring power in the late stage of LF, reduces the slag basicity while maintaining the molten steel with low oxygen potential and high purity, avoids the generation of a large amount of calcium sulfide after adding the sulfur line, greatly improves the possibility of poor castability of molten steel caused by calcium sulfide, thereby realizing multi-furnace continuous casting of molten steel, and has higher economic, environmental and social benefits. DETAILED DESCRIPTION

[0018] This embodiment provides a smelting method of sulfur-containing aluminum-containing steel, including converter smelting - converter tapping (slag control, deoxidation and alloying) - LF refining (adding quartz sand during slag making) - RH - continuous casting. The composition and percentage of sulfur-containing aluminum-containing steel are shown in Table 1 below.

[0019] Table 1

[0020] Element C Mn si P s Cr Ni Cu Mo Alt o N scope 0.45-0.47 0.82-0.88 0.20-0.30 ≤0.020 0.022-0.025 0.16-0.20 ≤0.10 ≤0.15 0.020-0.050 0.024-0.026 ≤20 70-120 Standard value 0.46 0.85 0.24 ≤0.020 0.023 0.18 ≤0.10 ≤0.15 0.030 0.025 ≤20 ≥80 determination 0.44-0.48 0.75-0.90 0.15-0.35 ≤0.022 0.022-0.035 0.15-0.20 ≤0.15 ≤0.20 0.020-0.050 0.024-0.035 ≤20 60-200

[0021] The specific steps are as follows:

[0022] (1) Converter blowing control: Add molten iron and scrap steel into the converter, bottom blowing to supply argon and top blowing to supply oxygen, add slag-making materials in batches into the converter, and the tapping temperature is 1600-1630℃, thereby obtaining crude molten steel (about 120 tons). During the tapping process, 1.2 kg of aluminum is used per ton of steel for deoxidation, and 550 kg of slag lime per furnace and 200 kg of refined slag per ton of furnace are added along with the steel flow;

[0023] (2) LF process: 3 minutes after power on, aluminum wire (10-20kg) and high-purity silicon carbide 60-80kg (which can be adjusted appropriately according to the post-furnace sample C) are used to deoxidize the slag surface in the early stage of slagging. After power on for about 15 minutes, sample 1 for analysis. The target temperature liquidus line is +40℃. Subsequently, 150kg of lime is added in small batches and multiple batches to add silicon carbide (total silicon carbide amount is 100-200kg) to maintain white slag in the process. The smelting process ensures that [AL] ≥ 0.015%. Deep deoxidation and desulfurization are carried out. The desulfurization intensity is increased in the early stage of refining. The final sulfur is less than 0.008%, but desulfurization cannot be achieved by increasing the amount of lime. After deoxidation and desulfurization are completed in the middle and late stages of refining, the target temperature is 1595℃. 60-80kg of quartz sand is added to the slag to reduce the basicity of the slag and increase the (SiO2) in the slag. At the same time, the bottom blowing stirring intensity is reduced. The slag is continuously powered and silicon carbide is added for diffusion deoxidation. After the chemical composition adjustment is completed, the molten steel is sent to the RH furnace at a target temperature of 1610℃.

[0024] (3)RH: After the molten steel arrives at the station, it is directly fed into the sulfur line to increase sulfur, and then vacuum treated. After breaking the air, samples are taken for analysis, and the components such as calcium, aluminum, and sulfur are adjusted. After the components and temperature (target 1560℃) are qualified, they are hoisted to the continuous casting machine for casting.

[0025] (4) Continuous casting: After the vacuum furnace soft blowing is completed, the steel is hoisted for casting. It is very important to protect the continuous casting and prevent secondary oxidation.

[0026] The target slag composition and percentage at the end of refining are shown in Table 2 below:

[0027] Table 2

[0028] TFe CaO <![CDATA[SiO2]]> MgO <![CDATA[Al2O3]]> R1 ≤0.3 52-56 10-14 ＜7 29-33 3.5-5.5

[0029] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for smelting sulfur-containing and aluminum-containing steel, characterized in that: Including converter smelting, LF refining, RH treatment and continuous casting; LF refining specifically includes: 3 minutes after power-on, add 10-20kg of aluminum wire and 60-80kg of high-purity silicon carbide to deoxidize the slag surface; take samples for analysis 15 minutes after power-on, with the target temperature liquidus line +40°C; add 150kg of lime into the furnace, and add 100-200kg of silicon carbide in batches to make high-basicity slag for deoxidation; ensure that the aluminum content in the molten steel is ≥0.015%; control the end point of the sulfur slag content in the molten steel to be less than 0.008%; add 60-80kg of quartz sand into the slag in the middle and late stages of refining to reduce the furnace basicity.

2. The smelting method according to claim 1, characterized in that: The converter smelting comprises: adding molten iron and scrap steel into the converter, supplying argon by bottom blowing and oxygen by top blowing, adding slag-making materials into the converter in batches, and obtaining crude molten steel at a tapping temperature of 1600-1680°C.

3. The smelting method according to claim 2, characterized in that: During the steel-making process, 1.2 kg of aluminum per ton of steel is used for deoxidation, and 550 kg of slag lime per furnace and 200 kg of refined slag per ton of furnace are added along with the steel flow.

4. The smelting method according to claim 1, characterized in that: In the early stage of LF refining, 3 minutes before power-on, the argon flow rate is controlled at 50-100NL / min to allow the slag to be slightly stirred.

5. The smelting method according to claim 1, characterized in that: The RH treatment specifically includes feeding molten steel into an RH furnace, feeding a sulfur line into the molten steel to increase sulfur, performing vacuum treatment, adjusting components such as calcium, aluminum, and sulfur, and the target temperature is 1560°C.