A high-efficiency desulfurized low-aluminum synthetic slag and smelting process for hard wire steel

Abstract

The present invention belongs to the technical field of steelmaking, specifically relating to a high-efficiency desulfurization low-aluminum synthetic slag and smelting process for hard wire steel. The composition requirements are: 40% ≤ CaO ≤ 50%, 35% ≤ CaF2 ≤ 40%, Al2O3 ≤ 2%, MgO ≥ 8%, and SiO2 ≤ 8%. The synthetic slag is mechanically pelletized from raw materials to form spheres with diameters of 2 mm to 50 mm, preventing the generation of smoke and dust during addition. Adding the low-aluminum synthetic slag to the converter tapping process reduces the desulfurization workload during refining and ensures a low Al content in the molten steel, reducing costs and improving steel purity. This allows for nodule-free continuous casting and stable casting.

Description

Technical Field

[0001] The invention belongs to the field of steelmaking production technology, and relates to a high-efficiency desulfurized low-aluminum synthetic slag for hard wire steel and a smelting process. Background Art

[0002] As a typical silicon-deoxidized steel, the general process routes of hard wire steel are "KR desulfurization → BOF → LF → CCM" and "BOF → LF → CCM". If the process passes the KR desulfurization treatment, the steel type does not need to undergo slag desulfurization during the LF refining process, but the cost is relatively high; without the KR treatment, the Al2O3 content in the refined slag must be controlled during slag desulfurization during the LF refining process, otherwise high-melting-point inclusions are easily generated, which will cause fluctuations in continuous casting nodules, thereby affecting smooth production.

[0003] Through searching and investigation, it is found that the synthetic slag invented so far is basically developed for the adsorption and removal of inclusions in aluminum-killed steel. Hard-wire steel generally adopts the slag making method of lime plus fluorite or cryolite. However, if fluorite is added alone, the erosion of the refractory material of the ladle will be aggravated, which will not only shorten the service life of the ladle, but also aggravate the reaction between the molten steel and the refractory material, which is not conducive to the control of the purity of the molten steel; and because cryolite contains Al element, it will react with the molten steel to generate high-melting-point calcium aluminate or spinel inclusions, which is not conducive to stable continuous casting.

[0004] For high-melting-point inclusions that have already appeared in hard wire steel, modification treatment is generally used in the literature. For example, the literature "Current Status and Progress of Modification Research on Type B Inclusions in High-Carbon Hard Wire Steel" introduces the mechanism and effect of modification treatment by calcium treatment, magnesium treatment and rare earth treatment respectively. However, calcium treatment can easily cause erosion of the stopper rod in the continuous casting tundish, and the amount of magnesium treatment is difficult to control, which can easily generate MgS inclusions and cause nodules. Rare earth treatment is also unstable. Therefore, although various modification treatments can solve the plasticization problem of high-melting-point inclusions, they are still difficult to control for actual production.

[0005] To this end, the present invention directly provides a highly efficient desulfurized synthetic slag with a low Al2O3 content. This eliminates the introduction of Al into ferrosilicon alloys and further reduces the formation of high-melting-point calcium aluminates or spinel inclusions by reducing slag-steel reactions, ensuring nodule-free continuous casting and stable casting. Summary of the Invention

[0006] The purpose of the present invention is to develop a high-efficiency desulfurization low-aluminum synthetic slag for hard wire steel and a process for smelting hard wire steel using the synthetic slag. This method can ensure that hard wire steel that does not undergo the KR desulfurization process can be stably and efficiently desulfurized during the LF refining process, and can also reduce the formation of high-melting-point calcium aluminate and spinel inclusions in the steel, thereby ensuring the purity of the molten steel and stable continuous casting.

[0007] The present invention provides a high-efficiency desulfurization low-aluminum synthetic slag for hard wire steel, the composition requirements of which are: 40%≤CaO≤50%, 35%≤CaF2≤40%, Al2O3≤2%, MgO≥8%, and SiO2≤8%. The synthetic slag is mechanically ball-pressed by raw materials to form balls with a diameter of 2mm to 50mm to prevent smoke and dust from being generated when added.

[0008] The present invention also provides a process for smelting hard wire steel using the synthetic slag:

[0009] (1) The molten iron is not subjected to KR desulfurization treatment, the converter tapping temperature is controlled between 1600 and 1620°C, silicon manganese, silicon carbide and high carbon ferrochrome are used for alloying, and ferrosilicon alloy is avoided. After alloying, 3.6 kg / t of the above-mentioned synthetic slag is added;

[0010] (2) In the LF refining furnace, 0.8 kg / t calcium carbide is used to deoxidize the slag surface of the molten steel. After the temperature rises to between 1500 and 1515 ° C, 0.4 to 0.8 kg / t of lime can be added to adjust the basicity of the refined slag to 2 to 4. This will enhance desulfurization while also preventing the formation of acidic slag due to low basicity of the refined slag, which will corrode the ladle refractory.

[0011] (3) After the LF smelting is completed, soft blowing is performed for 10-30 minutes to try to float the inclusions in the molten steel;

[0012] (4) Transfer to continuous casting for casting, and provide protective casting throughout the continuous casting process.

[0013] The mass percentage composition of the steel of the present invention is: C: 0.40-0.80%, Si: 0.15-0.30%, Mn: 0.5-0.8%, S: ≤0.015%, and the rest is iron and residual elements.

[0014] The present invention provides a low-aluminum synthetic slag for efficient desulfurization of hard wire steel. The design of the synthetic slag composition can not only meet the effect of slagging desulfurization, but also reduce the erosion of the ladle refractory material with a high MgO content, because the gradient of the MgO content in the refractory material and the refined slag is reduced and the saturation of MgO in the refined slag is increased. At the same time, the low Al2O3 content also reduces the slag-steel reaction to generate high-melting-point calcium aluminate or spinel inclusions. The use of molten iron that has not undergone KR desulfurization treatment in the smelting process is to reduce costs, so the desulfurization treatment needs to be completed by slag making in the LF refining furnace. The use of ferrosilicon alloy is avoided in order to reduce the residual Al element entering the molten steel. The alkalinity of the refined slag after adding lime is generally between 2 and 4, which meets the desulfurization of the molten steel while not forming acidic slag to corrode the ladle refractory material. The use of the synthetic slag of the present invention to smelt hard wire steel can ensure that the hard wire steel that does not undergo the KR desulfurization process can be stably and efficiently desulfurized during the LF refining process, and can also reduce the generation of high-melting-point calcium aluminate and spinel inclusions in the steel, thereby ensuring the purity of the molten steel and stable continuous casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an analysis diagram of inclusions in the steel in the continuous casting tundish of Example 1;

[0016] Figure 2 This is an analysis diagram of inclusions in the steel in the continuous casting tundish of Example 2;

[0017] Figure 3 This is an analysis diagram of inclusions in the steel in the continuous casting tundish of Comparative Example 1;

[0018] Figure 4 This is an analysis diagram of inclusions in the steel in the continuous casting tundish of comparative example 2. DETAILED DESCRIPTION

[0019] The effects of the present invention will be further demonstrated in detail below in conjunction with specific embodiments: a 130-ton converter and a 130-ton refining furnace are used to produce 82B and 60 steel grades.

[0020] Example 1

[0021] The steel grade is 82B, and the finished steel composition is: C: 0.84%, Si: 0.23%, Mn: 0.78%, S: 0.008%, Cr: 0.16%. Conventional blowing methods are used in a top-bottom combined-blown converter with 130 tons of molten steel. The converter's final temperature is 1618°C, and the final S content is 0.024%. When tapping the converter, 1050kg of silicon-manganese alloy, 250kg of silicon carbide, 110kg of high-carbon ferrochrome, 700kg of carbon balls, and 100kg of recarburizer are first added, followed by 500kg of synthetic slag. The synthetic slag composition is: CaO: 40%, CaF2: 38%, Al2O3: 1.3%, MgO: 8.3%, and SiO2: 6%.

[0022] After the molten steel is transported to the LF refining furnace, 80kg of calcium carbide is added to deoxidize the slag surface. After the temperature reaches 1515°C, the molten steel is sampled and 60kg of lime is added to adjust the refining slag. After the composition is fed back to the main control room, 250kg of high-carbon ferrochrome, 120kg of high-carbon ferromanganese, 150kg of silicon manganese, and 200kg of recarburizer are added. The power is then turned on for 3 minutes to raise the temperature to 1525°C, and soft blowing is carried out for 10 minutes. The initial slag removal time is 10 minutes, and the power-on, temperature increase, and composition adjustment time are approximately 30 minutes. The total refining time is 40 minutes. The sulfur content in the molten steel is reduced from 0.024% to 0.010%, and the desulfurization rate is 58.33%. The composition of the refining slag after LF refining is shown in Table 1 below:

[0023] Table 1 Refined slag composition (%)

[0024]

[0025] It can be seen that the synthetic slag contains about 8% MgO, while the MgO content in the refined slag after LF refining is only 8.77%, indicating that the erosion of the ladle refractory material is very small; in addition, the Al2O3 content is also significantly lower.

[0026] The continuous casting cycle is 36 minutes. When the molten steel is halfway poured, sampling is carried out in the impact zone of the tundish to detect inclusions. Figure 1 As shown in the figure, the main inclusions are low-melting-point CaO-SiO2 system inclusions. The steel throughput of this continuous casting is about 3,800 tons. The liquid level is stable during the continuous casting process, and there is no scrapped ingot due to nodule fluctuations.

[0027] Example 2

[0028] The steel grade is No. 60 steel, and the finished steel composition is: C: 0.59%, Si: 0.20%, Mn: 0.55%, S: 0.009%. Conventional blowing methods are used in a top-bottom combined-blown converter with 130 tons of molten steel. The converter's final temperature is 1612°C, and the final S content is 0.022%. When tapping the converter, 850kg of silicon-manganese alloy, 250kg of silicon carbide, 600kg of carbon balls, and 80kg of recarburizer are first added, followed by 500kg of synthetic slag. The synthetic slag composition is: CaO: 42%, CaF2: 39%, Al2O3: 1.0%, MgO: 8.9%, and SiO2: 7.2%.

[0029] After the molten steel was transported to the LF refining furnace, 80kg of calcium carbide was added to deoxidize the slag surface. After the temperature reached 1505°C, the molten steel was sampled and 160kg of lime was added to adjust the refining slag. After the composition was fed back to the main control room, 180kg of silicon manganese and 90kg of recarburizer were added. The power was then continued to be applied for 8 minutes to raise the temperature to 1535°C, followed by soft blowing for 13 minutes. The initial slagging time was 10 minutes, and the power-on, temperature increase, and composition adjustment time were approximately 37 minutes. The total refining time was 47 minutes. The sulfur content in the molten steel dropped from 0.022% to 0.009%, and the desulfurization rate was 59.09%. The composition of the refining slag after LF refining is shown in Table 2 below:

[0030] Table 2 Refined slag composition (%)

[0031]

[0032] The continuous casting cycle is 28 minutes. When the molten steel is halfway poured, sampling is carried out in the impact zone of the tundish to detect inclusions. Figure 2 As shown in the figure, the main inclusions are low-melting-point CaO-SiO2 system inclusions. The steel throughput of this continuous casting is about 6,100 tons. The liquid level is stable during the continuous casting process, and there is no scrapped ingot due to nodule fluctuations.

[0033] Comparative Example 1

[0034] The steel grade is 82B, and the finished steel composition is: C: 0.83%, Si: 0.23%, Mn: 0.75%, S: 0.009%, Cr: 0.15%. Conventional blowing methods are used in a top-bottom combined-blown converter with 130 tons of molten steel. The converter's final temperature is 1611°C, and the final S content is 0.025%. When tapping the converter, 1000kg of silicon-manganese alloy, 250kg of silicon carbide, 100kg of high-carbon ferrochrome, 700kg of carbon balls, and 100kg of recarburizer are added, followed by 300kg of lime.

[0035] Once the molten steel arrives at the LF refining furnace, 100kg of calcium carbide is added to deoxidize the slag surface. Then, 100kg of cryolite is added to deslagging. After the temperature reaches 1515°C, the molten steel is sampled and 100kg of lime is added to adjust the refining slag. After the composition is fed back to the main control room, 300kg of high-carbon ferrochrome, 100kg of high-carbon ferromanganese, and 160kg of recarburizer are added. The silicon content already meets the requirements and no further adjustment is required. The power is then applied for 3 minutes to raise the temperature to 1525°C, followed by soft blowing for 12 minutes. The initial deslagging time is 10 minutes, and the power-up, temperature increase, and composition adjustment time are approximately 35 minutes. The final total refining time is approximately 45 minutes. The sulfur content in the molten steel drops from 0.022% to 0.009%, and the desulfurization rate is 59.09%. The composition of the refining slag at the end of LF refining is shown in Table 3 below:

[0036] Table 3 Refined slag composition (%)

[0037]

[0038] The continuous casting cycle is 35 minutes. When the molten steel is halfway poured, sampling is carried out in the impact zone of the tundish to detect inclusions. Figure 3 As shown, it is mainly calcium aluminate with high melting point. The total steel volume of this continuous casting is about 4,000 tons. According to the fluctuation of the crystallizer liquid level exceeding ±5mm, the billets were selected and scrapped, and finally about 200 tons were scrapped.

[0039] Comparative Example 2

[0040] The steel grade is No. 60 steel, and the finished steel composition is: C: 0.60%, Si: 0.21%, Mn: 0.54%, S: 0.011%. A top-bottom combined-blowing converter is used, with 130 tons of molten steel, using conventional blowing methods. The converter's final temperature is 1603°C, and the final S content is 0.028%. When tapping the converter, 900kg of silicon-manganese alloy, 250kg of silicon carbide, 600kg of carbon balls, and 50kg of recarburizer are first added, followed by 300kg of lime.

[0041] Once the molten steel arrives at the LF refining furnace, 120 kg of calcium carbide is added to deoxidize the slag surface. Then, 130 kg of cryolite is added to deslagging. After the temperature reaches 1510°C, the molten steel is sampled and 150 kg of lime is added to adjust the slag. After the composition is fed back to the main control room, 200 kg of silicon manganese and 130 kg of recarburizer are added. The power is then turned on for another 8 minutes to raise the temperature to 1535°C, followed by soft blowing for 20 minutes. The initial deslagging time is 8 minutes, and the power-on, temperature increase, and composition adjustment time are approximately 34 minutes. The total refining time is approximately 42 minutes. The sulfur content in the molten steel drops from 0.028% to 0.011%, with a desulfurization rate of 60.71%. The composition of the refined slag at the end of LF refining is shown in Table 4 below:

[0042] Table 4 Refined slag composition (%)

[0043]

[0044] The continuous casting cycle is 30 minutes. When the molten steel is halfway poured, sampling is carried out in the impact zone of the tundish to detect inclusions. Figure 4 As shown, it is mainly calcium aluminate with high melting point. The total steel volume of this continuous casting is about 6,500 tons. According to the fluctuation of the crystallizer liquid level exceeding ±5mm, the billets were selected and scrapped, and finally about 450 tons were scrapped.

Claims

1. A smelting process for hard wire steel, characterized in that: The specific steps include: (1) The molten iron is not subjected to KR desulfurization treatment, the converter tapping temperature is controlled at 1600-1620°C, silicon manganese, silicon carbide and high carbon ferrochrome are used for alloying, and ferrosilicon alloy is avoided. After alloying, synthetic slag is added; the composition requirements of the synthetic slag are: 40%≤CaO≤50%, 35%≤CaF2≤40%, Al2O3≤2%, MgO≥8%, 6%≤SiO2≤8%; the particle size is 2-50 mm; (2) Calcium carbide is used to deoxidize the slag surface of the molten steel in the LF refining furnace. After the temperature is raised to 1500-1515°C, lime is added to adjust the basicity of the refined slag. The basicity of the refined slag is 2-4. (3) Soft blowing for 10 to 30 minutes after LF smelting; (4) Transfer to continuous casting for casting.

2. The smelting process of hard wire steel according to claim 1, characterized in that: The addition amount of synthetic slag is 3.6 kg / t steel.

3. The smelting process of hard wire steel according to claim 1, characterized in that: The dosage of calcium carbide is 0.8kg / t steel.

4. The smelting process of hard wire steel according to claim 1, characterized in that: The amount of lime added is 0.4 to 0.8 kg per ton of steel.

5. The smelting process of hard wire steel according to claim 1, characterized in that: Provide protective casting throughout the continuous casting process.

6. The high-efficiency desulfurization low-aluminum synthetic slag for hard wire steel according to claim 1, characterized in that: The mass percentage composition of the hard wire steel is: C: 0.40-0.80%, Si: 0.15-0.30%, Mn: 0.5-0.8%, S: ≤0.015%, and the rest is iron and residual elements.

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