Accurate control method for Al2O3 / MnO value in 1215MS steel refining slag

Abstract

The invention discloses an accurate control method for Al2O3 / MnO value in 1215MS steel refining slag, which comprises the following steps: adding ferro-aluminum when 1 / 4 of converter tapping is performed, adding lime and wollastonite when 1 / 3 of converter tapping is performed, and controlling the converter slag amount in the tapping process to be 1-4kg / t steel; in the LF refining heating process, aluminum slag and metallurgical lime are added; the adding amount of the aluminum slag is controlled to be 3.3-4.0 kg / t, 2.6-3.2 kg / t or 2.0-2.7 kg / t steel; in the LF refining heating process, the temperature is controlled to be 1600-1620 DEG C, and aluminum cut shots, lime and wollastonite are added in batches for strong stirring and slagging; according to the method, Al2O3 / MnO in the refining slag can be accurately controlled within the range of 1.90-2.20, the content of dissolved oxygen in molten steel at the LF refining end point can be accurately controlled, the LF refining period is shortened, the proportion of fusiform sulfide inclusions in steel is effectively increased, and the cutting performance of a product is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel refining outside a furnace, and in particular relates to a method for accurately controlling the Al2O3 / MnO value in 1215MS steel refining slag. Background Art

[0002] 1215MS is a high oxygen-sulfur free-cutting steel. It is mainly used in mechanical manufacturing industries such as office appliances, instrumentation, and non-load-bearing parts of automobiles due to its high cutting efficiency, low tool wear, good surface finish, and low processing cost. It is an increasingly widely used green, low-carbon, and energy-saving steel material. 1215MS steel needs to maintain a certain oxygen content, which is conducive to the formation of oxide nucleation particles such as MnO and FeO, reducing the average diameter and aspect ratio of MnS inclusions precipitated during steel solidification, and improving the cutting performance of this steel.

[0003] LF is an important process link between steelmaking and continuous casting due to its good functions of temperature rise, alloy fine-tuning, deoxidation, desulfurization and non-metallic inclusion control. It is widely used in the refining treatment of primary molten steel. At present, domestic steel mills produce 1215MS steel, and they all need to adjust the oxygen content in the steel through the LF refining process to control the distribution of sulfide inclusions.

[0004] 1215MS steel is a weakly deoxidized steel with strict requirements on the Al and Si contents in the steel. High Al and Si contents in the steel are prone to form hard Al2O3 and SiO2 aluminum silicates, which will cause tool wear during cutting. Customers hope that the Al and Si contents of this steel are as low as possible. Therefore, 1215MS steel mainly relies on Mn in the steel to balance the oxygen in the steel. The oxygen balance between slag and steel is mainly achieved by controlling the Al2O3 / MnO value of the refined slag. At present, the Al2O3 / MnO value of the refined slag in the refining process of 1215MS steel is not accurately controlled, resulting in unstable control of oxygen content and sulfide aspect ratio, which not only affects the LF smelting cycle, but also affects the stability of the quality of 1215MS steel products.

[0005] Chinese patent CN117403147A discloses a high-oxygen and high-sulfur free-cutting steel 1215MS and its oxygen-controlled LF smelting method. The converter is used for low-carbon steel tapping. Aluminum iron, low-carbon manganese iron and sulfur iron are used for deoxidation and alloying during the steel tapping process. Silicon carbide and calcium carbide are used for slag surface deoxidation during refining. The Al2O3 content in the slag is not adjusted, and the precise control of the Al2O3 / MnO value in the slag cannot be achieved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for accurately controlling the Al2O3 / MnO value in 1215MS steel refining slag. The method can accurately control the Al2O3 / MnO in the refining slag within the range of 1.90 to 2.20, so that the oxygen content of the slag and the molten steel can quickly reach a balanced state, which is beneficial to accurately control the dissolved oxygen content of the molten steel at the end point of LF refining, shorten the LF refining cycle by 20 to 30%, effectively increase the proportion of spindle-shaped sulfide inclusions in the steel, and improve the cutting performance of the product.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag, the method comprising:

[0009] When the converter is 1 / 4 of the steel is tapped, add aluminum iron, and when the converter is 1 / 3 of the steel is tapped, add lime and wollastonite, and control the slag amount of the converter during the tapping process to 1-4kg / t steel;

[0010] During the LF refining and heating process, aluminum slag and metallurgical lime are added; when the manganese yield of converter steel is ≤75%, the amount of aluminum slag added is controlled to be 3.3-4.0kg / t steel; when 75%< converter steel manganese yield ≤80%, the amount of aluminum slag added is controlled to be 2.6-3.2kg / t steel; when the manganese yield of converter steel is >80%, the amount of aluminum slag added is controlled to be 2.0-2.7kg / t;

[0011] During the LF refining heating process, the temperature is controlled at 1600-1620°C, and aluminum cut shots, lime and wollastonite are added in batches for strong stirring and slag making; the argon blowing flow rate is 500-800NL / min.

[0012] Furthermore, when the converter is 1 / 4 of the steel is tapped, the amount of aluminum and iron added is m 铝铁 Calculated from the final oxygen content of the converter w[O], m 铝铁 =-491.50w[O] 2 +100.65w[O]-2.22,m 铝铁 The unit of is kg / t steel, and the unit of w[O] is %. The formula for the amount of aluminum and iron added is to accurately control the degree of deoxidation, the dissolved oxygen content of molten steel and the Al2O3 / MnO ratio in the slag.

[0013] When 1 / 3 of the steel is discharged from the converter, the amount of lime and wollastonite added is 3-5kg / t steel and 2-4kg / t steel respectively.

[0014] During LF refining heating, adjust the arc power P arc Matching with the total slag amount M, the arc submergence efficiency is optimized, and the relationship between the two satisfies P arc =5.857M 2 +485.0M-332.4,Parc The unit of is kW, and the unit of M is kg / t. The formula of arc power changing with slag amount will affect whether the slag amount can cover and bury the arc during heating, affect the arc heating efficiency, and thus affect the refining power consumption.

[0015] The aluminum slag contains 5-15% by mass of metal Al, 40-50% by mass of Al2O3, 10-20% by mass of CaO, ≤5% by mass of SiO2 and 10-15% by mass of MgCO3. The aluminum slag is added into the ladle in 3-4 times.

[0016] The added amount of metallurgical lime is 4-6 kg / t steel; the metallurgical lime is added to the ladle in 3-4 times.

[0017] During the LF refining and slag-making process, the addition amounts of aluminum cut shot, lime and wollastonite are 0.2-0.8kg / t steel, 1.0-3.0kg / t steel and 2.0-4.0kg / t steel respectively. They are evenly divided into 3-4 batches and added to the ladle. The argon blowing flow rate is adjusted for strong stirring to promote the oxygen between the slag and the molten steel to quickly reach a balanced state.

[0018] The weight percentages of the components in the refined slag are: CaO 40.0-45.0%, SiO2 18.0-21.0%, Al2O3 17.0-20.0%, MnO 8.0-10.0%, Al2O3 / MnO 1.90-2.20.

[0019] During the slag making process, the argon blowing flow rate Q Ar According to the slag layer thickness h s Dynamic adjustment, Q Ar =644.61-57.91h s +7.13h s 2 -0.192h s 3 ;Q Ar The unit is NL / min, h s The unit is cm. The thicker the slag layer, the greater the argon blowing flow rate required for slag making and stirring. As the slag making material is added, the thickness of the slag layer gradually increases, and the argon blowing flow rate needs to be dynamically adjusted accordingly. If the argon blowing flow rate is maintained at 600NL / min throughout the process, the argon blowing flow rate for slag making is too small, which affects the stirring and mass transfer effect and requires extended stirring time; if the argon blowing flow rate is maintained at 700NL / min throughout the process, it is easy for the flow rate to be too large in the early stage and too small in the later stage; if the argon blowing flow rate is maintained at 800NL / min throughout the process, the argon blowing flow rate for slag making is too large, which is easy to cause the molten steel to leak oxygen and extend the deoxidation time, which will ultimately affect the slag making time.

[0020] During the LF refining process of 1215MS steel, the process of oxygen transfer from manganese oxide in the slag to the molten steel (oxygen transfer) is: (MnO) = [Mn] + [O];

[0021] The process of adding aluminum to steel to react with oxygen in the molten steel to deoxidize (deoxidize) is: [Al] + [O] = (Al2O3);

[0022] The comprehensive overall reaction formula of the two, that is, the reaction of manganese oxide in aluminum reduction slag, is:

[0023] 2[Al]+3(MnO)=3[Mn]+(Al2O3);

[0024] In the above reaction formula, the small brackets () represent the substances in the slag, and the square brackets [] represent the substances in the molten steel.

[0025] 1215MS is a weakly deoxidized steel. It is necessary to maintain 45-65ppm dissolved oxygen in the molten steel. The Al2O3 / MnO ratio in the refined slag is controlled to achieve a dynamic balance between the oxygen transfer and deoxidation processes and to maintain a certain amount of dissolved oxygen in the molten steel. If the Al2O3 / MnO ratio in the refined slag is large, the Al2O3 content is high and the MnO content is low, aluminum over-reduces MnO in the slag, and the ability of MnO to transfer oxygen to the molten steel is weak, then the dissolved oxygen content balanced with the molten steel is low; if the Al2O3 / MnO ratio in the refined slag is small, the Al2O3 content is low and the MnO content is high, there is insufficient MnO in the aluminum-reduced slag, and the ability of MnO to transfer oxygen to the molten steel is strong, and the oxygen balanced with the molten steel will be high. The method disclosed in the present invention can accurately control the Al2O3 / MnO value in the refined slag to be between 1.90 and 2.20, so that the oxygen transfer and deoxidation processes can quickly reach a dynamic balance.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) The present invention optimizes the design of the LF refining process of 1215MS steel, especially controls the amount of aluminum slag added in the LF refining heating process according to the manganese yield in the steel tapping alloying process, thereby facilitating the precise control of the Al2O3 / MnO value; at the same time, it is assisted by the control of the amount of slag lowered during converter steel tapping, the slag adjustment control during the steel tapping process, refining heating and refining slag making process, and the dynamic control of the argon flow rate in the refining slag making process according to the slag thickness, thereby facilitating further ensuring the precise control of the Al2O3 / MnO value.

[0028] 2) The method for accurately controlling the Al2O3 / MnO value of 1215MS steel of the present invention realizes that the oxygen content of the slag and the molten steel quickly reaches a balanced state by accurately controlling the Al2O3 / MnO in the refining slag, which is beneficial to accurately control the dissolved oxygen content of the molten steel at the end point of LF refining, shortens the LF refining cycle by 20-30%, effectively improves the control level of spindle-shaped sulfide inclusions in the steel, and improves the cutting performance of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a metallographic diagram of sulfide inclusions in the cross section of the wire made of 1215MS steel in Example 1. DETAILED DESCRIPTION

[0030] The present invention provides a method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag, which is as follows:

[0031] The dissolved oxygen content w[O] in the molten steel is measured before tapping the converter, and the amount of slag discharged from the converter is controlled to be 1-4 kg / t steel.

[0032] According to the different dissolved oxygen content of molten steel at the end of the converter, 1-3kg / t of ferroaluminum is added when 1 / 4 of the converter is tapped, and 3-5kg / t of lime and 2-4kg / t of wollastonite are added when 1 / 3 of the converter is tapped. 铝铁 The relationship between (kg / t) and the final oxygen content of the converter w[O](%) is m 铝铁 =-491.50w[O] 2 +100.65w[O]-2.22.

[0033] During the LF refining and heating process, 2-4kg / t aluminum slag and 4-6kg / t lime are added, the argon flow rate is controlled at 150-250NL / min, the temperature of the LF heating process is controlled at 1600-1620℃, and the aluminum slag and lime are added in 3-5 times. Specifically, when the manganese yield of steel is ≤75%, the total amount of aluminum slag added is controlled to be 3.3-4.0kg / t; when 75%<manganese yield of steel is ≤80%, the total amount of aluminum slag added is controlled to be 2.6-3.2kg / t; when the manganese yield of steel is>80%, the total amount of aluminum slag added is controlled to be 2.0-2.7kg / t. The mass percentage of metal Al in aluminum slag is 5-15%, the Al2O3 content is 40-50%, the CaO content is 10-20%, the SiO2 content is ≤5%, and the MgCO3 content is 10-15%.

[0034] LF heating process, adjust the arc power P arc Matching with the total slag volume M, the arc submerged efficiency is optimized. Specifically, the arc power P arc The total slag volume M satisfies P arc =5.857M 2+485.0M-332.4,P arc The unit of is kW, and the unit of M is kg / t.

[0035] During the LF slag making process, 0.2-0.8kg / t aluminum cut shot, 0-2kg / t lime and 2-4kg / t wollastonite are added in 3-4 batches, and the argon blowing flow rate is dynamically adjusted to 500-800NL / min according to the thickness of the slag layer for stirring. The Al content in the aluminum cut shot is ≥99%, and the particle size is ≤5mm. Specifically, the argon blowing flow rate Q Ar (NL / min) and slag layer thickness h s (cm) is: Q Ar =644.61-57.91h s +7.13h s 2 -0.192h s 3 In the slag making process of the present invention, by controlling the argon gas flow rate and the thickness of the slag layer, the exposed area of ​​the molten steel can be controlled, the oxygen between the slag and the molten steel can be promoted to quickly reach a balanced state, and the dissolved oxygen content of the molten steel can be accurately controlled.

[0036] The present invention is described in detail below with reference to the embodiments.

[0037] Examples 1-8

[0038] Examples 1-8 are all implemented on a 150t LF furnace, and the steel grade produced is 1215MS steel. Specifically, the oxygen is determined at the converter end point. According to the different oxygen content of the molten steel at the converter end point, 1-3kg / t of aluminum and iron are added when the converter is 1 / 4 of the steel being tapped, 3-5kg / t of lime and 2-4kg / t of wollastonite are added when the steel is 1 / 3 of the steel being tapped, and the amount of slag discharged from the converter during the tapping process is controlled to be 1-4kg / t of steel.

[0039] During the LF refining heating process, the amount of aluminum slag and lime added during the LF heating process is determined according to the manganese recovery rate and the amount of slag during the steelmaking process. 2-4kg / t aluminum slag and 4-6kg / t lime are added in 3-4 times. The argon flow rate is controlled at 150-250NL / min. During the heating process, the arc power and gear are dynamically adjusted according to the change in slag amount to optimize the arc submerged efficiency. The temperature of the LF heating process is controlled at 1600-1620℃.

[0040] During the LF slag making process, 0.2-0.8kg / t aluminum cut shot, 1.0-3.0kg / t lime and 2.0-4.0kg / t wollastonite are added in 3-4 batches, and the aluminum slag and aluminum cut shot are combined to quickly diffuse and deoxidize the slag surface and adjust the Al2O3 content in the slag, so that the (MnO) in the slag and the Als in the molten steel react to reach a balanced state, which is beneficial to accurately control the dissolved oxygen content [O] in the molten steel and improve the distribution of sulfide inclusions.

[0041] The mass percentage of metal Al in aluminum slag is 5-15%, Al2O3 content is 40-50%, CaO content is 10-20%, SiO2 content is ≤5%, and MgCO3 content is 10-15%. The Al content in aluminum cut shot is ≥99% and the particle size is ≤5mm.

[0042] In addition, the argon blowing flow rate is dynamically and accurately adjusted to 500-800NL / min for stirring according to the thickness of the slag layer, the exposed leakage area of ​​the molten steel is controlled, the oxygen between the slag and the molten steel is promoted to quickly reach a state of equilibrium, the dissolved oxygen content of the molten steel is accurately controlled, the distribution of the sulfide inclusion morphology is improved, the ratio of spindle-shaped sulfides is increased, and the cutting performance of the product is improved.

[0043] Comparative Examples 1-6

[0044] The smelting process flow of 1215MS steel in Comparative Example 1-6 is basically the same as that in Example 1-8, and the main difference lies in the different operation modes, process parameters and additive addition amounts of each process step. In Comparative Example 1-6, relative to Example 1-8, the aluminum slag and aluminum cut shot used in Example 1-8 are replaced by silicon carbide, and the mass percentage of SiC in the silicon carbide is ≥90%, and the particle size is ≤5mm.

[0045] The control parameters of the converter steel-making process of Examples 1-8 and Comparative Examples 1-6 are detailed in Table 1, the refining control parameters of the LF furnace are detailed in Table 2, the arc power (single-phase) parameters of the LF furnace electrode gear are detailed in Table 3, and the comparison of the refined slag composition and implementation effect is detailed in Table 4.

[0046] Table 1 Control parameters of converter steel-making process

[0047]

[0048]

[0049] Table 2 LF furnace heating process control parameters

[0050]

[0051]

[0052] Table 3 LF furnace electrode gear arc power (single phase) / kW

[0053]

[0054] Table 4 LF furnace slag making process control parameters

[0055]

[0056]

[0057] Table 5 Refining slag composition and implementation effect

[0058]

[0059]

[0060] Note: The sulfide inclusion spindle rate is the metallographic result of the wire cross section, which refers to the ratio of spindle-shaped sulfides with a sulfide inclusion length / width ratio of ≤4. The higher the sulfide spindle rate in the steel, the better the turning performance of the steel.

[0061] In summary, 1-5 is compared with comparative example 1-6, in embodiment 1-8 of the present invention, the amount of slag, manganese recovery rate, and aluminum iron, lime, wollastonite, aluminum slag, and aluminum cut shot are precisely controlled during the converter steel tapping process, steel tapping, heating, and slag making, and the arc power and gear are dynamically adjusted according to the change in the slag amount during the heating process to optimize the arc submerged arc efficiency. The average refining power consumption of embodiment 1-8 is reduced by 7.4 k·W / t compared with the average value of the refining power consumption of comparative example 1-6; in the slag making process of embodiment 1-8 of the present invention, the argon blowing flow rate is dynamically and precisely adjusted according to the thickness of the slag layer for stirring, the exposed area of ​​the molten steel is controlled, the stirring time prolonged due to the small argon blowing flow rate during the slag making process or the deoxidation time prolonged due to the exposed oxygen absorption of the molten steel due to the large argon blowing flow rate, etc., so as to promote the oxygen between the slag and the molten steel to quickly reach a balanced state, and significantly improve the control accuracy of the Al2O3 / MnO value of 1215MS steel. The average slag making time of embodiment 1-8 is reduced by 4.6 min compared with the average value of comparative example 1-6.

[0062] Combined with Table 1-5, compared with Comparative Examples 1-6, the Al2O3 / MnO value of the refined slag of Example 1-8 can be precisely controlled within the range of 1.9 to 2.2, so that the oxygen content of the slag and the molten steel can quickly reach a dynamic equilibrium state, the refining cycle can be reduced by more than 20%, and the dissolved oxygen content [O] of the molten steel at the end of refining can be precisely controlled within the range of 50 to 60 ppm, and the total oxygen content T·[O] of the ingot can be precisely controlled within the range of 125 to 135 ppm. The oxygen content in the steel is appropriate, and the spindle rate of sulfide inclusions with an aspect ratio of ≤4 is above 84%, which is 26.9% higher than the average spindle rate of sulfide inclusions with an aspect ratio of ≤4 in Comparative Examples 1-6, thereby improving the morphology and distribution of sulfides and improving the cutting performance of the product.

[0063] The detailed description of a method for accurately controlling the Al2O3 / MnO value in a 1215MS steel refined slag with reference to the above-mentioned embodiment is illustrative rather than restrictive, and several embodiments may be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag, characterized in that: The method comprises: When the converter is 1 / 4 of the steel is tapped, add aluminum iron, and when the converter is 1 / 3 of the steel is tapped, add lime and wollastonite, and control the slag amount of the converter during the tapping process to 1-4kg / t steel; During the LF refining and heating process, aluminum slag and metallurgical lime are added; when the manganese yield of converter steel is ≤75%, the amount of aluminum slag added is controlled to be 3.3-4.0kg / t steel; when 75%< converter steel manganese yield ≤80%, the amount of aluminum slag added is controlled to be 2.6-3.2kg / t steel; when the manganese yield of converter steel is >80%, the amount of aluminum slag added is controlled to be 2.0-2.7kg / t; During the LF refining heating process, the temperature is controlled at 1600-1620°C, and aluminum cut shots, lime and wollastonite are added in batches for strong stirring and slag making; the argon blowing flow rate is 500-800NL / min.

2. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: When 1 / 4 of the steel is tapped from the converter, the amount of aluminum and iron added is m 铝铁 Calculated from the final oxygen content of the converter w[O], m 铝铁 =-491.50w[O] 2 +100.65w[O]-2.22,m 铝铁 The unit of is kg / t steel, and the unit of w[O] is %.

3. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: When 1 / 3 of the steel is discharged from the converter, the amount of lime and wollastonite added is 3-5kg / t steel and 2-4kg / t steel respectively.

4. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: During LF refining heating, adjust the arc power P arc Matching with the total slag amount M, the arc submergence efficiency is optimized, and the relationship between the two satisfies P arc =5.857M 2 +485.0M-332.4,P arc The unit of is kW, and the unit of M is kg / t.

5. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: The mass percentage of metal Al in the aluminum slag is 5-15%, the Al2O3 content is 40-50%, the CaO content is 10-20%, the SiO2 content is ≤5%, and the MgCO3 content is 10-15%.

6. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: The amount of metallurgical lime added is 4-6kg / t steel.

7. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: During the LF refining and slag making process, the addition amounts of aluminum cut shot, lime and wollastonite are 0.2-0.8kg / t steel, 1.0-3.0kg / t steel and 2.0-4.0kg / t steel respectively.

8. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: The weight percentages of the components in the refined slag are: CaO 40.0-45.0%, SiO2 18.0-21.0%, Al2O3 17.0-20.0%, MnO 8.0-10.0%, and Al2O3 / MnO 1.90-2.

20.

9. The method for accurately controlling the Al2O3 / MnO value in 1215MS steel refined slag according to claim 1, characterized in that: During the slag making process, the argon blowing flow rate Q Ar According to the slag layer thickness h s Dynamic adjustment, Q Ar =644.61-57.91h s +7.13h s 2 -0.192h s 3 ;Q Ar The unit is NL / min, h s The unit is cm.

Images