Control process for reusing kr desulfurization slag on bearing steel

Abstract

The present application belongs to the field of steel production, and relates to a control process for recycling KR desulfurization slag in bearing steel, so as to solve the problem that KR desulfurization slag is difficult to be used in bearing steel production due to high sulfur and high oxidizability. In the present application, KR desulfurization slag is directly added into a ladle as slag material when the converter is tapped, and the control of the slag is realized through the deoxidization and slagging of an LF refining furnace. A specific amount of silicon carbide is added in the early stage of LF refining to quickly form reducing white slag, and lime is additionally added to adjust the composition and basicity of the slag, so as to control the oxidizability (TFe < 0.5%) and basicity (R is 3-5) of the refining slag. Through the control of the refining process, the recycling of KR desulfurization slag is realized under the premise of guaranteeing the cleanliness index of bearing steel, and the purpose of reducing cost and increasing efficiency is achieved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, specifically to a control process for the reuse of KR desulfurization slag on bearing steel. Background Technology

[0002] KR desulfurization is a common process in molten iron pretreatment. The desulfurization slag produced mainly consists of oxides of CaO, SiO2, S, and Fe. Its high alkalinity and high sulfur content pose environmental risks to traditional landfill disposal. Therefore, existing desulfurization slag is mostly used in roadbed materials or cement additives, but the added value is low. In addition, there are other methods of applying KR desulfurization slag in converter smelting and some high-sulfur steel production processes. For example, Chinese patent application CN202411688627.0, "A method for resource recycling of KR desulfurization slag in a converter," applies KR desulfurization slag to the converter smelting process. By optimizing the early-stage smelting process parameters of the converter, the CaO and iron resources in the KR desulfurization slag are utilized to the maximum extent, thereby reducing costs. Chinese patent application CN202110201652.1, "A process for producing high-sulfur steel by recycling slag," introduces a process for producing high-sulfur steel with an S content between 0.2% and 0.4% using KR desulfurization slag, which also achieves cost reduction. However, for bearing steel, there is no literature documenting the use of high-sulfur, high-oxidizing KR desulfurization slag, because its high sulfur content directly contaminates the molten steel, and its high oxidizing properties (high TFe content) generate a large number of oxide inclusions, seriously impairing the fatigue life of bearing steel.

[0003] This invention involves adding KR desulfurization slag to bearing steel and controlling the process through LF refining. Then, the total oxygen content and inclusions of the rolled product are tested to determine its impact on the purity of the molten steel. This makes it possible to reuse KR desulfurization slag in bearing steel, thereby reducing costs without affecting the quality of the bearing steel. Summary of the Invention

[0004] The purpose of this invention is to develop a reuse control process for applying KR desulfurization slag to bearing steel. This process can not only reduce the production cost of bearing steel, but also ensure the product quality of bearing steel.

[0005] The main components of the KR desulfurization slag are: CaO: 60~70%, SiO2: 8~12%, MgO <3%, Al2O3 <3%, S: 0.8~2.0%, TFe: 8~15%, F <3%, and the remainder are some residual elements.

[0006] The bearing steel has the following composition by mass percentage: C: 0.95-1.05%, Si: 0.15-0.35%, Mn: 0.25-0.45%, S≤0.020%, Cr: 1.40-1.65%, Al: 0.005-0.030%, with the remainder being iron and residual elements.

[0007] A controlled process for the reuse of KR desulfurization slag on bearing steel, characterized by the following key points:

[0008] (i) Converter tapping: The tapping temperature is required to be ≥1600℃. According to the ladle weighing display, when about 1 / 3 of the steel is tapped from the converter, 1.0~1.2kg / t of aluminum blocks are added as deoxidizer. After the steel is tapped, 4.5~5.0kg / t of KR desulfurization slag is directly hoisted into the argon station as top slag using an overhead crane.

[0009] (ii) LF refining: The ladle is transported to the LF refining furnace for refining. The LF refining furnace uses silicon carbide for slag surface deoxidation. Because KR desulfurization slag with high oxidizing properties is added, more silicon carbide needs to be added in the early stage of LF refining so that white slag can be formed as soon as possible in the first 10 minutes of smelting. The total amount used in the furnace is 1.6~2.0 kg / t.

[0010] Within 30 minutes before smelting in the LF refining furnace, lime is added in batches at a rate of 3.0~4.5 kg / t, and no further additions are made thereafter.

[0011] Throughout the LF refining process, the bottom-blown argon flow rate is controlled at 100~200 Nm. 3 / h;

[0012] After the initial slag formation in the LF refining furnace, samples are taken every 10-15 minutes to adjust the composition, and the adjustment is carried out in 2-3 times to avoid adding too much at once. As a preferred option, 50%-70% of the silicon carbide is added within 10 minutes before refining to achieve rapid white slag formation, and the remaining part is added in small batches during the refining process to maintain the reducibility of the slag.

[0013] The composition of the refining slag at the end of LF smelting is as follows: CaO: 50~55%, SiO2: 10~15%, MgO: 3~8%, Al2O3: 22~30%, S: 0.4~0.8%, TFe<0.5%, basicity R (CaO / SiO2): 3~5, and the remainder are some residual elements.

[0014] (III) Vacuum Treatment: After LF refining, the sample is transferred to RH for vacuum treatment. The vacuum level is reduced to within 67 Pa, and the holding time is ≥15 min. Then, soft blowing is performed for ≥10 min, with a soft blowing flow rate of 30~50 Nm³. 3 / h;

[0015] (iv) The material is transferred to the continuous casting machine for casting. Protective measures are taken throughout the continuous casting process. Finally, a sample of the rolled material is taken for total oxygen content and 50 MHz water immersion testing.

[0016] This invention relates to a controlled process for the reuse of KR desulfurization slag in bearing steel. The invention utilizes a combination of control measures in LF refining to eliminate the adverse effects of KR slag. In step (I), the tapping temperature, top slag, and the amount of aluminum blocks added ensure the deoxidation of the steel slag. Step (II) requires the rapid formation of white slag in the early stages, using approximately 60% silicon carbide; afterwards, only a small amount is needed for slag preservation. Within 30 minutes before smelting in the LF refining furnace, lime is added in batches at 3.0~3.5 kg / t. This serves two purposes: first, to increase the slag layer thickness to ensure arc submersion; and second, to increase the desulfurization capacity of the refining slag. Through enhanced deoxidation, adjustment of alkalinity, and process control, precise control of the reducibility and composition of the refining slag is ultimately achieved. The addition of lime is designed to ensure the arc submersion effect of the refining slag and prevent slag splashing. The RH vacuum treatment step improves the purity of the molten steel and further promotes the removal of inclusions by soft blowing, preventing secondary oxidation during continuous casting and contamination of the molten steel. Finally, the level of inclusions in the steel is evaluated by the total oxygen content of the rolled product, the metallographic inclusion grade, and the results of water immersion testing, so as to ensure that the use of KR desulfurization slag will not affect the product quality.

[0017] In traditional bearing steel refining processes, a large amount of expensive pre-melted synthetic slag is typically added during the LF refining stage to ensure desulfurization and cleanliness. This invention directly replaces this costly synthetic slag with low-cost KR desulfurization slag, reducing the cost per ton of steel. Detailed Implementation

[0018] The following detailed demonstration of the effects of the present invention is based on specific embodiments: Taking on-site production as an example, the process route is 120-ton converter → 120-ton LF refining furnace → RH refining furnace → 8-machine 8-strand continuous casting machine.

[0019] Before the implementation of this invention, the KR desulfurization slag used is required to be cooled, crushed and screened to obtain slag with a particle size between 3-30mm, and bagged for later use. The moisture content of the slag is tested to be less than 0.5%.

[0020] Example 1:

[0021] The finished steel composition is: C: 0.975%, Si: 0.193%, Mn: 0.287%, S: 0.009%, Cr: 1.426%, Al: 0.0154%. A top-and-bottom blown converter is used, with a tapping temperature of 1614℃. During tapping, 130kg of aluminum blocks are first added for deoxidation, followed by the addition of high-carbon ferrochrome, high-carbon ferromanganese, and ferrosilicon alloy. After tapping, 600kg of KR desulfurization slag is hoisted into the argon station using an overhead crane.

[0022] After the steel is tapped from the converter, the molten steel is transferred to the LF furnace for smelting. Ten minutes before smelting, 120 kg of silicon carbide is added for slag surface deoxidation, rapidly forming white slag. Small amounts of silicon carbide are then continuously used for slag retention, with a total of 200 kg used in the entire furnace. Thirty minutes before smelting, lime is added in two batches of approximately 200 kg each, totaling about 400 kg, for slag conditioning. Samples are taken three times during the process to adjust the composition. At the end of smelting, the sulfur content in the steel decreased from 0.017% to 0.009%, with a desulfurization rate of 47.06%. The refined slag at this point is analyzed, and the main components are shown in the table below.

[0023]

[0024] The molten steel is then hoisted to the RH refining furnace for vacuum treatment. It is held under pressure for 15 minutes at a vacuum level of ≤67Pa, and then softly blown for 16 minutes before being hoisted to the continuous casting furnace for casting. The long nozzle of the continuous casting ladle is protected by argon blowing, and a covering agent is used in the tundish to isolate the air and prevent secondary oxidation.

[0025] Finally, the total oxygen content and water immersion testing were performed on the rolled material samples. The oxygen content was tested in two batches, yielding values ​​of 4.3 ppm and 4.4 ppm respectively. A total of 5243 mm samples were tested using 50MHz water immersion testing. 2 Four defects were found, one per 1000mm. 2 On average, there are about 0.76 defects. Metallographic inclusions are classified as follows: A fine grade 0.5, A coarse grade 0, B fine grade 0, B coarse grade 0, C fine grade 0, C coarse grade 0, D fine grade 1.0, D coarse grade 0.5, and Ds class 0.

[0026] According to national standards for high-carbon chromium bearing steel (such as GB / T 18254) and the technical requirements of high-end customers, the sulfur content requirement for bearing steel is S≤0.015% (or 0.020%), the total oxygen content is typically required to be TO≤9ppm, and the inclusion rating requirements are stringent. The steel obtained in this invention has a sulfur content of 0.009% and a total oxygen content of only 4.3~4.4ppm, and both 50MHz water immersion testing and metallographic inclusion ratings are better than or far below the upper limit requirements of the standards. This proves that the product obtained by the process of this invention fully meets or exceeds the quality requirements of high-quality bearing steel.

[0027] Example 2:

[0028] The finished steel composition is: C: 0.991%, Si: 0.194%, Mn: 0.309%, S: 0.005%, Cr: 1.433%, Al: 0.0142%. A top-and-bottom blown converter is used, with a tapping temperature of 1612℃. During tapping, 130kg of aluminum blocks are first added for deoxidation, followed by the addition of high-carbon ferrochrome, high-carbon ferromanganese, and ferrosilicon alloy. After tapping, 600kg of KR desulfurization slag is hoisted into the argon station using an overhead crane.

[0029] After the steel is tapped from the converter, the molten steel is transferred to the LF furnace for smelting. Ten minutes before smelting, 140 kg of silicon carbide is added for slag surface deoxidation, rapidly forming white slag. Small amounts of silicon carbide are then continuously used for slag retention, with a total of 220 kg used in the entire furnace. Thirty minutes before smelting, lime is added in two batches (200 kg and 300 kg respectively), totaling 500 kg, for slag conditioning. Samples are taken three times during the process to adjust the composition. At the end of smelting, the sulfur content in the steel decreased from 0.021% to 0.005%, with a desulfurization rate of 76.19%. The refined slag at this point is analyzed, and the main components are shown in the table below.

[0030]

[0031] The molten steel is then hoisted to the RH refining furnace for vacuum treatment. It is held under vacuum of ≤67Pa for 16 minutes, then soft-blown for 18 minutes after the vacuum is broken, and then hoisted to the continuous casting furnace for casting. The long nozzle of the continuous casting ladle is protected by argon blowing, and a covering agent is used in the tundish to isolate the air and prevent secondary oxidation.

[0032] Finally, the total oxygen content and water immersion testing were performed on the rolled material samples. The oxygen content was tested in two batches, yielding values ​​of 4.0 ppm and 4.2 ppm respectively. A total of 5032 mm of material was tested using 50MHz water immersion testing. 2 Five defects were found, one per 1000mm. 2 On average, there are approximately 0.99 defects. Metallographic inclusions are classified as follows: A fine grade 0.5, A coarse grade 0.5, B fine grade 0, B coarse grade 0, C fine grade 0, C coarse grade 0, D fine grade 1.0, D coarse grade 0.5, and Ds class 0.

[0033] Comparative Example 1:

[0034] The finished steel composition is: C: 0.978%, Si: 0.189%, Mn: 0.292%, S: 0.008%, Cr: 1.458%, Al: 0.0139%. A top-and-bottom blown converter is used, and the tapping temperature is 1623℃. During tapping, 130kg of aluminum blocks are first added for deoxidation, followed by high-carbon ferrochrome, high-carbon ferromanganese, and ferrosilicon alloy. Finally, 400kg of lime and 500kg of synthetic slag (mainly composed of CaO and Al2O3) are added.

[0035] After the steel is tapped from the converter, the molten steel is transferred to the LF furnace for smelting. Ten minutes before smelting, 60 kg of silicon carbide is added to deoxidize the slag surface, forming white slag. Small amounts of silicon carbide are then continuously used for slag preservation, with a total of 150 kg of silicon carbide used in the entire furnace. 210 kg of lime is added in the early stages of smelting to adjust the slag composition. Samples are taken three times during the process for composition adjustment. At the end of smelting, the sulfur content in the steel decreases from 0.020% to 0.008%, achieving a desulfurization rate of 60%. The refined slag at this point is analyzed, and its main components are shown in the table below.

[0036]

[0037] The molten steel is then hoisted to the RH refining furnace for vacuum treatment. It is held under pressure for 15 minutes at a vacuum level of ≤67Pa, and then softly blown for 14 minutes before being hoisted to the continuous casting furnace for casting. The long nozzle of the continuous casting ladle is protected by argon blowing, and a covering agent is used in the tundish to isolate air and prevent secondary oxidation.

[0038] Finally, the rolled material samples were tested for total oxygen content and water immersion flaw detection. The oxygen content was tested in two batches, yielding values ​​of 4.7 ppm and 4.8 ppm respectively. A total of 6793 mm of material was tested for water immersion flaw detection. 2 Eight defects were found, per 1000mm 2 On average, there are about 1.18 defects. Metallographic inclusions are classified as follows: A fine grade 0, A coarse grade 0.5, B fine grade 0, B coarse grade 0, C fine grade 0, C coarse grade 0, D fine grade 1.0, D coarse grade 0.5, and Ds class 0.5.

[0039] Comparative Example 2:

[0040] The finished steel composition is: C: 0.991%, Si: 0.192%, Mn: 0.289%, S: 0.008%, Cr: 1.438%, Al: 0.0127%. A top-and-bottom blown converter is used, with a tapping temperature of 1610℃. During tapping, 130kg of aluminum blocks are first added for deoxidation, followed by the addition of high-carbon ferrochrome, high-carbon ferromanganese, and ferrosilicon alloy. After tapping, 600kg of KR desulfurization slag is hoisted into the argon station using an overhead crane.

[0041] After the steel is tapped from the converter, the molten steel is transferred to the LF furnace for smelting. Ten minutes before smelting, 70 kg of silicon carbide is added for slag surface deoxidation, and then silicon carbide is continuously added for further deoxidation, using a total of 150 kg of silicon carbide for the entire furnace. 200 kg of lime is added in the early stages of smelting to adjust the slag composition. Samples are taken three times during the process for composition adjustment. At the end of smelting, the sulfur content in the steel decreases from 0.015% to 0.009%, with a desulfurization rate of 40%. The refined slag at this point is analyzed, and the main components are shown in the table below.

[0042]

[0043] The molten steel is then hoisted to the RH refining furnace for vacuum treatment. It is held under vacuum of ≤67Pa for 15 minutes, then soft-blown for 15 minutes after the vacuum is broken, and then hoisted to the continuous casting furnace for casting. The long nozzle of the continuous casting ladle is protected by argon blowing, and a covering agent is used in the tundish to isolate the air and prevent secondary oxidation.

[0044] Finally, the total oxygen content and water immersion testing were performed on the rolled material samples. The oxygen content was tested in two batches, yielding values ​​of 6.6 ppm and 6.5 ppm respectively. A total of 4298 mm of material was tested for water immersion flaws. 2 24 defects were found, per 1000mm 2 On average, there were approximately 5.58 defects. Metallographic inclusions were classified as follows: A (fine) 0.5 grade, A (coarse) 0.5 grade, B (fine) 0 grade, B (coarse) 1.5 grade, C (fine) 0 grade, C (coarse) 0 grade, D (fine) 1.0 grade, D (coarse) 0.5 grade, and Ds (class 2.0 grade).

[0045] The experimental example uses KR desulfurization slag for smelting. Compared to the conventional process in Comparative Example 1, its LF refining requires more detailed deoxidation operations, but it saves on the cost of adding synthetic slag, which has a higher converter cost, resulting in a total cost reduction of approximately 6 yuan / t. Furthermore, the total oxygen content of the rolled product, water immersion testing results, and metallographic inclusion detection results did not deteriorate. In contrast, Comparative Example 2, after adding KR desulfurization slag and smelting using the conventional process, resulted in higher oxidative properties in the refined slag, increased inclusion levels in the rolled product, and a greater number of large inclusions, adversely affecting product quality. This example reduces slag costs while maintaining quality, demonstrating the feasibility of using KR desulfurization slag in the smelting of bearing steel according to this invention.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A control process for the reuse of KR desulfurization slag on bearing steel, characterized in that, Includes the following steps: (1) Converter tapping: Control the tapping temperature to be no less than 1600℃. When tapping, add aluminum blocks into the ladle for deoxidation and add KR desulfurization slag as top slag. (2) LF refining: The ladle is transported to the LF refining furnace, and silicon carbide is used for slag surface deoxidation at a rate of 1.6~2.0 kg / t, so that the slag can quickly form white slag in the early stage of smelting; 3.0~3.5 kg / t of lime is added in batches within 30 minutes before smelting in the LF refining furnace, and no more lime is added thereafter; through sampling analysis and composition adjustment, the composition of the refining slag at the end of LF smelting is controlled as follows: CaO: 50~55%, SiO2: 10~15%, TFe<0.5%, basicity R (CaO / SiO2): 3~5; (3) Vacuum treatment and continuous casting: The molten steel after LF refining is subjected to RH vacuum treatment, and then continuous casting is carried out under protective casting conditions.

2. The control process for reusing KR desulfurization slag on bearing steel according to claim 1, characterized in that: In step (1), the amount of aluminum blocks added is 1.0~1.2 kg / t, and the amount of KR desulfurization slag added is 5.0 kg / t.

3. The control process for reusing KR desulfurization slag on bearing steel according to claim 1, characterized in that: Step (2) Silicon carbide is added within 10 minutes before LF smelting to achieve white slag formation as quickly as possible within 10 minutes before smelting.

4. The control process for reusing KR desulfurization slag on bearing steel according to claim 1, characterized in that: During the LF refining process, the bottom-blown argon flow rate is controlled at 100~200 Nm. 3 / h.

5. The control process for reusing KR desulfurization slag on bearing steel according to claim 1, characterized in that: The vacuum degree of the RH vacuum treatment reaches within 67 Pa, the pressure holding time is not less than 15 min, and then soft blowing is performed.