Production method for realizing RH-free vacuum treatment of high manganese steel

Abstract

The invention discloses an RH-free vacuum treatment production method for high-manganese steel, and belongs to the technical field of ferrous metallurgy, according to the method, through four procedures of converter smelting, steel ladle alloying and pre-deoxidation, LF furnace deep refining and continuous casting, a Zr-Mg-Ca composite microalloying system is constructed, and narrow-range component control and precise process regulation and control are combined, so that the RH-free vacuum treatment production method for the high-manganese steel is obtained. According to the high-manganese steel produced through the method, the gas content is stably controlled to be that [H] is smaller than or equal to 1.5 ppm, [O] is smaller than or equal to 15 ppm, and [N] is smaller than or equal to 60 ppm, the rating of various inclusions is smaller than or equal to 1.0 grade, the impact toughness is remarkably superior to that of a traditional process product, meanwhile, the smelting period is shortened, and the production cost is saved.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a production method for achieving RH-free vacuum treatment of high manganese steel. Background Technology

[0002] High-manganese steel, especially high-manganese austenitic steel, is widely used in cryogenic storage tanks, railway frogs, excavator bucket teeth, and bulletproof steel plates—operating conditions subject to strong impacts and severe wear—due to its extremely high work hardening ability, good low-temperature toughness, and wear resistance. However, the smelting of high-manganese steel has always been a challenge in the metallurgical field, mainly in the following aspects: Controlling gas content is difficult: Manganese has a strong affinity for both oxygen and nitrogen. During smelting, especially when a large amount of ferromanganese alloy is added, the content of gases such as oxygen, nitrogen, and hydrogen in the molten steel is easily increased. High oxygen content will form a large number of inclusions such as MnO, which will worsen the fatigue performance of the steel; high nitrogen content can improve strength to some extent, but it will significantly reduce plasticity and toughness and increase the tendency for cold brittleness; high hydrogen content will lead to serious defects such as white spots and hydrogen-induced cracks.

[0003] Cleanliness control challenges: Inclusions in high manganese steel, especially hard, non-deformable inclusions such as Al2O3 and MnO·Al2O3, can become stress concentration points during steel processing and use, inducing cracks and severely impairing its impact toughness and fatigue life.

[0004] Reliance on traditional processes and cost issues: To effectively reduce the gas and inclusion content in steel, modern high-quality steelmaking generally adopts a long process of "converter / electric furnace → LF ladle refining → RH vacuum circulation degassing". RH vacuum treatment can very effectively remove hydrogen and nitrogen and promote the flotation of deoxidation products. However, RH equipment requires huge investment, has high operating costs, and a long processing cycle (usually 20-40 minutes), which seriously restricts production pace and cost control.

[0005] While some existing technologies have attempted to simplify the refining process of high-manganese steel, most have yielded unsatisfactory results. For example, relying solely on strong deoxidation in an LF furnace and argon blowing for stirring makes it difficult to stably control the hydrogen content below 2.0 ppm and the nitrogen content below 80 ppm, and also suffers from large fluctuations in composition control and incomplete removal of inclusions. Patent CN202210946337.6, "A High-Cleanliness High-Manganese Steel and Its Production Method," proposes purifying molten steel by adding rare earth elements. However, rare earth elements are chemically reactive, have low and unstable yields, and easily form large-sized rare earth oxides or oxysulfides, which become harmful inclusions. Another patent, CN202310548812.9, "A Method for Converter Smelting of High-Manganese Steel," focuses on "process control" innovation at the front end of the high-manganese steel process (converter smelting), but fails to systematically solve the problems of oxygen and hydrogen control, and cannot achieve RH-free vacuum treatment.

[0006] Therefore, developing a smelting method that can stably produce high-manganese steel with low gas content, high cleanliness, and excellent performance without relying on RH vacuum treatment is of great practical significance and economic value for reducing production costs, improving production efficiency, and promoting the application of high-manganese steel in a wider range of fields. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a production method for achieving RH-free vacuum treatment of high manganese steel.

[0008] To solve the above technical problems, the technical solution of the present invention is as follows: A production method for achieving RH-free vacuum treatment of high manganese steel specifically includes the following steps: (1) Converter smelting: A converter is used for primary refining, and the tapping temperature is controlled at 1620-1680℃. Slag-blocking technology is used during tapping to control the slag layer thickness in the ladle to be no more than 50mm. (2) Alloying and pre-deoxidation of steel ladle: During the tapping process, ferromanganese alloy, ferrosilicon, aluminum blocks and composite refining agent are added to the ladle in sequence, and argon gas is blown in and stirred throughout the process, with an argon gas flow rate of 20-50 NL / min; (3) LF furnace deep refining: The ladle is hoisted to the LF furnace station, powered on and heated, and CaO-Al2O3-based synthetic refining slag is added to the slag surface. The white slag refining time is kept at no less than 25 minutes, and the (FeO+MnO) content in the slag is controlled at ≤0.8% during the white slag process, so as to accurately control the final composition of the molten steel. Before the refining process is completed, adjust the argon flow rate to 5-15 NL / min and perform soft argon blowing treatment for no less than 15 minutes. At the same time, feed calcium iron wire and magnesium wire into the core of the molten steel through a wire feeder. (4) Continuous casting: After LF refining, the molten steel is directly transported to the continuous casting machine for pouring. A long nozzle + argon gas sealing protection pouring method is adopted to control the superheat of the molten steel in the tundish at 15-30℃, and electromagnetic stirring of the crystallizer and the end electromagnetic stirring are applied.

[0009] In a further preferred embodiment of the present invention, the ferromanganese alloy in step (2) is a low-carbon or medium-carbon ferromanganese alloy with low phosphorus and low nitrogen content, and its [N] content ≤ 0.02% and [P] content ≤ 0.15%, and the amount added ensures that the final Mn content of the molten steel is 10.0-25.0%; the amount of ferrosilicon added makes the Si content of the molten steel reach 0.20-0.50%; the amount of aluminum block added makes the acid-soluble aluminum [Al]s content of the molten steel controlled at 0.020-0.050%.

[0010] In a further preferred embodiment of the present invention, the composite refining agent in step (2) is composed of CaO, CaF2 and Al2O3 in a mass ratio of (6-8):(1-2):(1-2), and the amount added is 0.8-1.5% of the weight of molten steel.

[0011] In a further preferred embodiment of the present invention, the final composition of the molten steel in step (3) is precisely controlled as follows by weight percentage: C: 0.4-1.0%, Si: 0.25-0.45%, Mn: 13.0-25.0%, P: ≤0.020%, S: ≤0.005%, [Al]s: 0.025-0.045%, Zr: 0.005-0.020%, Ca: 0.008-0.015%, Mg: 0.008-0.025%, with the remainder being Fe and unavoidable impurities.

[0012] The beneficial effects of this invention are: The present invention adds a trace amount of Zr to molten steel, which can preferentially combine with [N] to form fine, high-melting-point ZrN particles. These ZrN particles can act as heterogeneous nucleation nuclei during the solidification of molten steel, refine the grains, and more importantly, "fix" the free nitrogen in the steel, significantly reducing the content of dissolved nitrogen, thereby effectively eliminating the deteriorating effect of nitrogen on the toughness of high manganese steel. This invention adds Mg to molten steel. Mg is a surface-active element with a high vapor pressure. In molten steel, it floats to the surface in the form of bubbles. During the floating process, the trace amounts of Mg bubbles can act as "carriers" for [H] and [N], carrying hydrogen and nitrogen atoms to the slag phase, thus achieving a "microbubble degassing" effect. At the same time, Mg can modify residual oxide inclusions, making them spheroidized and refined, and reducing their harm to toughness. This invention adds Ca to molten steel. Ca treatment is a mature inclusion modification technology. In this invention, Ca reacts with inclusions such as Al2O3 to generate low-melting-point, spherical calcium aluminate, which is not easily deformed during rolling, avoiding the generation of chain inclusions and significantly improving the fatigue performance and isotropy of the steel. The synergistic effect of these three factors constitutes a deep purification and microstructure control system of "fixed nitrogen (Zr), carried gas (Mg), and spheroidized inclusions (Ca)," which essentially makes up for the lack of degassing and impurity removal capabilities after the removal of RH.

[0013] This invention completely eliminates the need for RH vacuum treatment, shortens the smelting cycle, reduces production costs, and has extremely significant economic benefits. Furthermore, the high-manganese steel produced using this invention can have its gas content stably controlled at: [H] ≤ 1.5 ppm, [O] ≤ 15 ppm, [N] ≤ 60 ppm. This level fully meets or even exceeds the requirements for gas content in high-end applications. At the same time, the total oxygen (T[O]) content in the steel of this invention is low, and the rating of all kinds of inclusions is ≤ 1.0. The inclusions are basically small, dispersed, and spherical. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the high-manganese steel RH-free vacuum treatment method of the present invention. Detailed Implementation

[0015] To make the content of this invention easier to understand, the invention will be further described in detail below based on specific embodiments. Example 1

[0016] This embodiment provides a production method for Mn13 type high manganese wear-resistant steel that does not require RH vacuum treatment, such as... Figure 1 As shown, the specific steps include: (1) Converter smelting: A converter is used for primary refining, and the tapping temperature is controlled at 1655℃. Slag-blocking technology is used during tapping to control the slag layer thickness in the ladle to 45mm. (2) Alloying and pre-deoxidation of steel ladle: Starting when the steel is 1 / 4 full, low-nitrogen, low-carbon ferromanganese, ferrosilicon, aluminum blocks, and a composite refining agent are added to the ladle. The low-nitrogen, low-carbon ferromanganese ([N]=0.018%) and [P] content are 0.12%, and the amount added ensures that the final Mn content of the molten steel is 13.0%. The amount of ferrosilicon added brings the Si content of the molten steel to 0.45%. The amount of aluminum blocks added controls the acid-soluble aluminum [Al]s content of the molten steel at 0.045%. Argon gas is blown in and stirred throughout the process at a flow rate of 35 NL / min. The composite refining agent is a mixture of CaO, CaF2, and Al2O3 in a ratio of 8:1.8:1.3, and the amount added is 0.8% of the weight of the molten steel. (3) LF furnace deep refining: The ladle is hoisted to the LF furnace position, energized and heated, and CaO-Al2O3-based synthetic refining slag is added to the slag surface. The white slag refining time is maintained for 30 minutes, and the (FeO+MnO) content in the slag is controlled at 0.7% during the white slag process. The final composition of the molten steel is precisely controlled, and the specific weight percentages are as follows: C: 1.0%, Si: 0.45%, Mn: 13.0%, P: ≤0.020%, S: ≤0.005%, [Al]s: 0.045%, Zr: 0.020%, Ca: 0.010%, Mg: 0.008%, with the remainder being Fe and unavoidable impurities. Before the refining process is completed, adjust the argon flow rate to 10 NL / min and perform soft argon blowing for 20 minutes. At the same time, feed calcium iron wire and magnesium wire into the core of the molten steel through a wire feeder. (4) Continuous casting: After LF refining, the molten steel is directly transported to the continuous casting machine for pouring. A long nozzle + argon gas sealing protection pouring method is adopted to control the superheat of the molten steel in the tundish at 22°C, and electromagnetic stirring of the crystallizer and the end electromagnetic stirring are applied.

[0017] The results of sampling and analysis of the final cast billet are as follows: Gas content: [H]=1.2 ppm, [O]=12 ppm, [N]=48 ppm.

[0018] Inclusion rating: Class A (sulfides) 1.0, Class B (alumina) 1.0, Class D (spherical oxides) 0.5.

[0019] Mechanical properties: The core impact toughness at -40℃ (KV2) of the 50mm rolled steel plate is 152J. Example 2

[0020] This embodiment provides a production method for Mn18 high-manganese wear-resistant steel that does not require RH vacuum treatment, specifically including the following steps: (1) Converter smelting: A converter is used for primary refining, and the tapping temperature is controlled at 1625℃. Slag-blocking technology is used during tapping to control the slag layer thickness in the ladle to 40mm. (2) Alloying and pre-deoxidation of steel ladle: Starting when the steel is 1 / 4 full, low-nitrogen, low-carbon ferromanganese, ferrosilicon, aluminum blocks, and a composite refining agent are added to the ladle. The low-nitrogen, low-carbon ferromanganese ([N]=0.018%) has a [P] content of 0.10%, and the amount added ensures that the final Mn content of the molten steel is 18.0%. The amount of ferrosilicon added brings the Si content of the molten steel to 0.35%. The amount of aluminum blocks added controls the acid-soluble aluminum [Al]s content of the molten steel at 0.035%. Argon gas is blown in and stirred throughout the process at a flow rate of 45 NL / min. The composite refining agent is a mixture of CaO, CaF2, and Al2O3 in a ratio of 7:1.5:1.5, and the amount added is 1.2% of the weight of the molten steel. (3) LF furnace deep refining: The ladle is hoisted to the LF furnace position, energized and heated, and CaO-Al2O3-based synthetic refining slag is added to the slag surface. The white slag refining time is maintained for 30 minutes, and the (FeO+MnO) content in the slag is controlled at 0.5% during the white slag process. The final composition of the molten steel is precisely controlled, and the specific weight percentages are as follows: C: 0.75%, Si: 0.35%, Mn: 18.0%, P: ≤0.020%, S: ≤0.005%, [Al]s: 0.035%, Zr: 0.012%, Ca: 0.015%, Mg: 0.015%, with the remainder being Fe and unavoidable impurities. Before the refining process is completed, adjust the argon flow rate to 15 NL / min and perform soft argon blowing treatment for no less than 15 minutes. At the same time, feed calcium iron wire and magnesium wire into the core of the molten steel through a wire feeder. (4) Continuous casting: After LF refining, the molten steel is directly transported to the continuous casting machine for pouring. A long nozzle + argon gas sealing protection pouring method is adopted to control the superheat of the molten steel in the tundish at 23°C, and electromagnetic stirring of the crystallizer and the end electromagnetic stirring are applied.

[0021] The results of sampling and analysis of the final cast billet are as follows: Gas content: [H]=1.1 ppm, [O]=14 ppm, [N]=43 ppm.

[0022] Inclusion rating: Class A (sulfides) 1.0 grade, Class B (alumina) 0.5 grade, Class D (spherical oxides) 0.5 grade.

[0023] Mechanical properties: For 50mm rolled steel plates, the core impact toughness at -40℃ KV2 is 136J. Example 3

[0024] This embodiment provides a production method for high-manganese low-temperature steel Mn25 that does not require RH vacuum treatment, specifically including the following steps: (1) Converter smelting: A converter is used for primary refining, and the tapping temperature is controlled at 1670℃. Slag-blocking technology is used during tapping to control the slag layer thickness in the ladle to 35mm. (2) Alloying and pre-deoxidation of steel ladle: Starting when the steel is 1 / 4 full, low-nitrogen, low-carbon ferromanganese, ferrosilicon, aluminum blocks, and a composite refining agent are added to the ladle. The low-nitrogen, low-carbon ferromanganese ([N]=0.018%) and [P] content are 0.10%, and the amount added ensures that the final Mn content of the molten steel is 25.0%. The amount of ferrosilicon added makes the Si content of the molten steel reach 0.25%. The amount of aluminum blocks added controls the acid-soluble aluminum [Al]s content of the molten steel at 0.025%. Argon gas is blown in and stirred throughout the process at a flow rate of 35 NL / min. The composite refining agent is a mixture of CaO, CaF2, and Al2O3 in a ratio of 6.5:2.0:1.0, and the amount added is 1.5% of the weight of the molten steel. (3) LF furnace deep refining: The ladle is hoisted to the LF furnace position, energized and heated, and CaO-Al2O3-based synthetic refining slag is added to the slag surface. The white slag refining time is maintained for 35 minutes, and the (FeO+MnO) content in the slag is controlled at 0.6% during the white slag process. The final composition of the molten steel is precisely controlled, and the specific weight percentages are as follows: C: 0.4%, Si: 0.25%, Mn: 25.0%, P: ≤0.020%, S: ≤0.005%, [Al]s: 0.025%, Zr: 0.006%, Ca: 0.012%, Mg: 0.025%, with the remainder being Fe and unavoidable impurities. Before the refining process is completed, adjust the argon flow rate to 5 NL / min and perform soft argon blowing for 25 minutes. At the same time, feed calcium iron wire and magnesium wire into the core of the molten steel through a wire feeder. (4) Continuous casting: After LF refining, the molten steel is directly transported to the continuous casting machine for pouring. A long nozzle + argon gas sealing protection pouring method is adopted to control the superheat of the molten steel in the tundish at 18°C, and electromagnetic stirring of the crystallizer and the end electromagnetic stirring are applied.

[0025] The results of sampling and analysis of the final cast billet are as follows: Gas content: [H]=1.0 ppm, [O]=10 ppm, [N]=42 ppm.

[0026] Inclusion rating: Class A 1.0, Class B 0.5, Class D 1.0.

[0027] Mechanical properties: For 50mm rolled steel plates, the core impact toughness at -196℃ KV2 is 131J. Comparative Example 1

[0028] The conventional process for producing Mn13 high-manganese wear-resistant steel with the same target composition as in Example 1 was employed: converter → LF → RH → continuous casting. The differences between this conventional process and the process in Example 1 are: ① the addition of an RH process, with a processing time of 25 minutes and a vacuum degree of 0.3 mbar; ② the absence of Zr and Mg, with only Ca treatment performed. Other processes remained consistent with those in Example 1. Analysis of samples from the final cast billet yielded the following results: Gas content: [H]=1.5 ppm, [O]=18 ppm, [N]=75 ppm.

[0029] Inclusion rating: Class A (sulfides) 1.5, Class B (alumina) 2.0, Class D (spherical oxides) 1.5.

[0030] Mechanical properties: The 50mm steel plate was rolled using the same rolling process as in Example 1, and the core impact toughness at -40℃ KV2 was 86J. Comparative Example 2

[0031] The conventional process for producing Mn18 high-manganese wear-resistant steel with the same target composition as in Example 2 was employed: converter → LF → RH → continuous casting. The differences between this conventional process and the process in Example 2 are: ① the addition of an RH process, with a processing time of 35 minutes and a vacuum degree of 0.4 mbar; ② the absence of Zr and Mg, with only Ca treatment performed. Other processes remained consistent with those in Example 1. Sampling and analysis of the final cast billet yielded the following results: Gas content: [H]=1.8 ppm, [O]=20 ppm, [N]=83 ppm.

[0032] Inclusion rating: Class A (sulfides) 2.0, Class B (alumina) 1.5, Class D (spherical oxides) 1.5.

[0033] Mechanical properties: The 50mm steel plate was rolled using the same rolling process as in Example 1, and the core impact toughness at -40℃ KV2 was 74J. Comparative Example 3

[0034] The same Mn25 high-manganese low-temperature steel with the same target composition as in Example 3 was produced using the same process route as in Example 3. However, the differences between this process and the process in Example 3 are: ① no Zr was added; ② the amount of Mg fed was significantly reduced, and the Mg content in the molten steel was only 0.0006%.

[0035] The results of sampling and analysis of the final cast billet are as follows: Gas concentrations: [H] = 1.8 ppm, [O] = 25 ppm, [N] = 120 ppm. Nitrogen content is severely exceeded.

[0036] Inclusion rating: Class A 1.5, Class B 2.0, Class D 1.5.

[0037] Mechanical properties: A 50mm steel plate was rolled using the same rolling process as in Example 2. The core impact toughness at -196℃ KV2 was only 52J, indicating a significant deterioration in toughness. Therefore, a comparison between the embodiments and the comparative examples shows that: (1) The gas content (especially nitrogen content) and cleanliness of the method of the present invention (Examples 1 and 2) after RH is removed are better than or equivalent to the traditional RH process (Comparative Examples 1 and 2), and the impact toughness is significantly improved.

[0038] (2) Example 3 and Comparative Example 3 demonstrate that without the “Zr-Mg-Ca” composite microalloying technology of the present invention, conventional LF refining alone cannot effectively control the nitrogen content, resulting in unqualified product toughness, highlighting the importance of the core technology of the present invention.

[0039] In summary, this invention, through systematic component design and process innovation, successfully achieves RH-free vacuum treatment of high manganese steel, reducing costs and improving efficiency while ensuring high product quality, and has extremely high industrial application value.

[0040] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A production method for achieving RH-free vacuum treatment of high manganese steel, characterized in that: Specifically, the following steps are included: (1) Converter smelting: A converter is used for primary refining, and the tapping temperature is controlled at 1620-1680℃. Slag-blocking technology is used during tapping to control the slag layer thickness in the ladle to be no more than 50mm. (2) Alloying and pre-deoxidation of steel ladle: During the tapping process, ferromanganese alloy, ferrosilicon, aluminum blocks and composite refining agent are added to the ladle in sequence, and argon gas is blown in and stirred throughout the process, with an argon gas flow rate of 20-50 NL / min; (3) LF furnace deep refining: The ladle is hoisted to the LF furnace station, powered on and heated, and CaO-Al2O3-based synthetic refining slag is added to the slag surface. The white slag refining time is kept at no less than 25 minutes, and the (FeO+MnO) content in the slag is controlled at ≤0.8% during the white slag process, so as to accurately control the final composition of the molten steel. Before the refining process is completed, adjust the argon flow rate to 5-15 NL / min and perform soft argon blowing treatment for no less than 15 minutes. At the same time, feed calcium iron wire and magnesium wire into the core of the molten steel through a wire feeder. (4) Continuous casting: After LF refining, the molten steel is directly transported to the continuous casting machine for pouring. A long nozzle + argon gas sealing protection pouring method is adopted to control the superheat of the molten steel in the tundish at 15-30℃, and electromagnetic stirring of the crystallizer and the end electromagnetic stirring are applied.

2. The production method for achieving RH-free vacuum treatment of high manganese steel according to claim 1, characterized in that: In step (2), the ferromanganese alloy is a low-carbon or medium-carbon ferromanganese alloy with low phosphorus and low nitrogen, and its [N] content is ≤0.02% and [P] content is ≤0.15%. The amount added ensures that the final Mn content of the molten steel is 10.0-25.0%. The amount of ferrosilicon added makes the Si content of the molten steel reach 0.20-0.50%. The amount of aluminum block added controls the acid-soluble aluminum [Al] s content of the molten steel at 0.020-0.050%.

3. A production method for achieving RH-free vacuum treatment of high manganese steel according to claim 1, characterized in that: In step (2), the composite refining agent is composed of CaO, CaF2 and Al2O3 in a mass ratio of (6-8):(1-2):(1-2), and the amount added is 0.8-1.5% of the weight of the molten steel.

4. A production method for achieving RH-free vacuum treatment of high manganese steel according to claim 1, characterized in that: In step (3), the final composition of the molten steel is precisely controlled, and the specific weight percentages are as follows: C: 0.4-1.0%, Si: 0.25-0.45%, Mn: 13.0-25.0%, P: ≤0.020%, S: ≤0.005%, [Al]s: 0.025-0.045%, Zr: 0.005-0.020%, Ca: 0.008-0.015%, Mg: 0.008-0.025%, with the remainder being Fe and unavoidable impurities.

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