Electroslag remelting process for specially-smelted stainless steel

Abstract

The invention relates to the field of metal smelting, and discloses a specially-smelted stainless steel electroslag remelting process which comprises the steps of raw material pretreatment, slagging and primary deoxidation, secondary treatment and addition of a deoxidizing agent, protective electroslag remelting, stepped heat preservation and cooling and finished product treatment. The method is characterized in that a staged deoxidation strategy is adopted, first, single aluminum particles are subjected to primary deoxidation, and then a composite deoxidizer composed of the aluminum particles and the nickel-magnesium alloy is pretreated through an electroslag redissolution auxiliary device and then is automatically added; argon subjected to drying treatment is introduced in the electroslag process, a protective atmosphere is formed through an annular gas distribution pipeline, and the melting rate of a metal electrode is controlled to be 4-6 kg / min; and in the cooling stage, the protection atmosphere is maintained until the ingot body is cooled to a preset value. The method solves the problems of non-uniform deoxidation, many oxide inclusions, poor protection effect and the like in the traditional process, obviously improves the purity and surface quality of the electroslag ingot, and is suitable for electroslag remelting production of high-precision metal materials.

Description

Technical Field

[0001] This invention relates to the field of metal smelting, and more specifically to an electroslag remelting process for special stainless steel. Background Technology

[0002] Electroslag remelting technology, as a core process in the production of high-purity metallic materials such as special stainless steel, plays a crucial role in improving material purity and performance stability. However, existing processes still have many limitations. In the preparation of consumable electrode billets and deoxidation treatment, traditional processes often employ single refining methods, making it difficult to accurately control the purity and compositional stability of the molten steel. In particular, the residual Al content in Ti-containing steel lacks proper control, leading to severe Ti element loss and large yield fluctuations during electroslag remelting. At the same time, deoxidation often relies on single or simple mixed deoxidizers, resulting in incomplete deoxidation and excessive oxide inclusions (especially fine D-type inclusions) in the molten steel, seriously affecting material purity.

[0003] The shortcomings of slag system selection and pretreatment are equally prominent: for Ti-containing stainless steel, the existing slag system composition ratios lack specificity and have not formed a suitable five-element slag system. Furthermore, improper control of pretreatment temperature and time leads to high melting point and poor fluidity of the slag, resulting in poor adsorption of inclusions and easily causing defects such as slag grooves and inclusions on the surface of steel ingots. In addition, insufficient baking of slag material and residual moisture can easily cause porosity during electroslag treatment, further deteriorating the material quality and making it difficult to meet the stringent requirements for inclusion control in special stainless steel.

[0004] Inadequate ingot design and cooling processes further exacerbate quality problems: existing electroslag ingots are mostly short and thick with a low filling ratio, resulting in uneven heat distribution and uneven slag thickness, which reduces yield and easily leads to surface defects; the cooling process often relies on natural cooling or simple heat preservation, which easily generates large thermal stress inside the ingot, causing cracks; at the same time, insufficient control over the dryness, pressure, and gas distribution of the protective gas (such as argon) makes the molten steel prone to secondary oxidation, exacerbating surface roughness. These problems result in low first-pass yield of special-grade stainless steel electroslag ingots, high risk of forging fracture, and difficulty in meeting relevant standards and users' technical requirements for high-purity and high-stability materials. Summary of the Invention

[0005] The present invention aims to provide a special electroslag remelting process for stainless steel to solve the technical problems of insufficient surface smoothness and easy cracking of ingots in the existing electroslag remelting process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a special stainless steel electroslag remelting process, comprising the following steps: S1. Preparation of consumable electrode billets: The consumable electrode billets are smelted using an electric furnace + LF + VOD / AOD ladle refining process, and the residual Al content in the Ti-containing steel electrode billets is controlled to be 0.08%~0.20%; S2. Slag pretreatment: Ti-containing stainless steel adopts a five-element slag system, which is CaF2 53±5%, CaO 20±2%, MgO 3.0±2.0%, Al2O3 20±5%, TiO2 4.0±1.0% by weight. The slag is baked at 700~800℃ for more than 6 hours. S3. Slag formation and electroslag remelting: For small ingots, the arc is directly initiated using metal electrodes, while for large ingots, carbon electrodes are used to form slag. The electroslag remelting voltage is controlled at 58~62V and the current at 2800~3200A. S4. Deoxidation treatment: Si-Mn-Ca and ANS composite deoxidizers are used for pre-deoxidation and final deoxidation during the electrode billet smelting stage. S5. Cooling and forming: The ingot is slender and elongated. After remelting, it is cooled by step heat preservation and argon gas protection throughout the process. S6. Finished product processing: Surface grinding and quality inspection of electroslag ingots.

[0007] Preferably, as an improvement, the internal control range of the chemical composition of the consumable electrode blank in step S1 is: C 0.03~0.06%, Si 0.2~0.5%, Mn 1.3~1.8%, P ≤0.030%, S ≤0.020%.

[0008] Preferably, as an improvement, the five-element slag system in step S2 is, by weight percentage, CaF2 53%, CaO 20%, MgO 3%, Al2O3 20%, and TiO 24%.

[0009] Preferably, as an improvement, in step S3, the slag formation time of the carbon electrode is ≤ 15 minutes, the melting rate of the metal electrode is 5~7 kg / min, and the current and voltage fluctuation range is ≤ ±3%.

[0010] Preferably, as an improvement, in step S3, the small ingot is Φ220~260 and the large ingot is Φ≥260.

[0011] Preferably, as an improvement, the amount of composite deoxidizer added in step S4 is 0.3~0.5 kg per 100 kg of molten steel, and the particle size is 1~2 mm.

[0012] Preferably, as an improvement, the filling ratio of the elongated ingot in step S5 is 0.6~0.8, wherein the dimensions of the Φ220 ingot are Φ210mm at the top, Φ240mm at the bottom, and 1100mm in height. Preferably, as an improvement, the stepped heat preservation and cooling in step S5 is as follows: first, heat preservation at 1050℃ for 20~25 minutes, and then cooling down to below 150℃ at a rate of 60~80℃ / h.

[0013] Preferably, as an improvement, in step S5, the argon gas dew point is ≤-45℃, the inlet pressure is 3.5~4MPa, and it is blown in through an annular gas distribution channel.

[0014] Preferably, as an improvement, the surface grinding in step S6 uses an 80-120 mesh grinding wheel.

[0015] Advantages of this solution: 1. Significantly improves the purity of electroslag ingots and effectively controls non-metallic inclusions. By optimizing the pre-deoxidation and final deoxidation processes of the electrode billet, a Si-Mn-Ca and ANS composite deoxidizer is used to form easily removable large-particle Class C inclusions; the new slag system enhances adsorption capacity, reducing the fineness of Class D inclusions in low-carbon stainless steel by 0.5 to 1.0 grade, and reducing macroscopic segregation in low-magnification microstructures of Ti-containing steel, meeting the stringent requirements for inclusions in high-end applications.

[0016] 2. Improve the recovery rate and compositional stability of easily oxidized elements. For Ti-containing steel, control the residual Al content of consumable electrodes and combine it with the balancing effect of TiO2 in the five-element slag system to reduce Ti element burn-off, making the Ti recovery rate more stable and reducing Ti segregation at the beginning and end of the ingot; optimize the internal control range of the chemical composition of the electrode billet to further ensure compositional consistency.

[0017] 3. Improve the surface quality of electroslag ingots and reduce surface defects. By adjusting the slag composition ratio to improve fluidity and optimizing the electroslag process parameters, the slag temperature at the edge of the crystallizer inner wall is increased, forming a thin and uniform slag skin. This effectively reduces defects such as large slag grooves and slag inclusions in steel ingots, resulting in a significant improvement in surface quality.

[0018] 4. Improve the low-magnification pass rate and mechanical property stability of electroslag ingots. The new slag system and process optimization have significantly improved the low-magnification first-pass pass rate of Ti-containing steel electroslag ingots, and the pass rate of low-carbon stainless steel has also increased simultaneously; controlling the shape of the molten metal pool and the quality of crystallization reduces defects such as shrinkage cavities and porosity, lowers the risk of forging cracks, and makes the mechanical properties more stable after hot working.

[0019] 5. Improve yield and reduce production costs. The adoption of a slender ingot design reduces head and tail losses, thus improving the overall yield. The electric furnace + VOD process has lower smelting costs compared to medium-frequency induction furnaces and can utilize a large amount of alloy recycled material, further reducing raw material costs.

[0020] 6. Reduce smelting power consumption and achieve energy saving and efficiency improvement. The elongated ingot shape increases the filling ratio, and combined with the multi-element high-resistivity slag system, it reduces the heat radiation loss on the slag surface, which significantly reduces the power consumption of electroslag ingot smelting, conforms to the concept of green production, and can save considerable electricity costs based on the current production volume. Attached Figure Description

[0021] Figure 1 A schematic diagram of the surface of an ingot produced using a special stainless steel electroslag remelting process according to the present invention; Figure 2 A schematic diagram of the surface of an ingot produced by the existing electroslag remelting process. Detailed Implementation

[0022] The following detailed description illustrates the specific implementation method: Example: I. A special stainless steel electroslag remelting process, comprising the following steps: 1. Preparation of consumable electrode blank 1Cr18Ni9Ti consumable electrode billets were smelted using a 15-ton electric furnace + LF + VOD ladle refining process. The residual Al content was controlled at 0.12%, and the internal chemical composition was as follows: C 0.05%, Si 0.35%, Mn 1.5%, P 0.025%, S 0.015%, Cr 17.45%, Ni 9.6%, and Ti 0.65%. The temperature of the molten steel entering the VOD was controlled at 1620±5℃ in the LF furnace, with a composition adjustment accuracy of ≤0.01%, resulting in longitudinal segregation of the electrode billet ≤0.5 grade and shrinkage cavities and porosity defects ≤0.3 grade.

[0023] 2. Slag Pretreatment Ti-containing stainless steel uses a five-element slag system: CaF2 53%, CaO 20%, MgO 3%, Al2O3 20%, and TiO2 4%. The slag is placed in a baking furnace and heated to 750℃ at a rate of 100℃ / h, and baked at a constant temperature for 8 hours. The moisture content is measured to be 0.008% (≤0.01%).

[0024] 3. Slag remelting and electroslag remelting For Φ260 large ingots, a 50mm diameter carbon electrode was used for slag formation, with a slag formation time of 12 minutes. Electroslag remelting parameters were: voltage 60V, current 3000A (fluctuation ±2%), and metal electrode melting rate 6kg / min. An infrared thermometer was used to monitor the molten pool temperature every 30 seconds, maintaining it at 1600±10℃. The electrode descent speed was adjusted to ensure the height of the upper cylindrical section of the molten pool was 12mm.

[0025] 4. Deoxygenation treatment In the electrode billet smelting stage, a Si-Mn-Ca and ANS composite deoxidizer (particle size 1.5mm) is used, with an addition amount of 0.4kg per 100kg of molten steel. The nickel-magnesium alloy (Ni 55%, Mg 44.5%) is mixed with aluminum particles at a mass ratio of 3:7, crushed by a jaw crusher, stirred at 40Hz for 8 minutes, and then sieved through a 120-mesh screen, achieving a mixing uniformity ≥95%.

[0026] 5. Cooling and molding The ingot is a slender Φ260mm ingot: Φ250mm at the top, Φ280mm at the bottom, and 1400mm in height, with a filling ratio of 0.7. After remelting, it undergoes stepped cooling: held at 1050℃ for 22 minutes, then cooled to 140℃ at a rate of 70℃ / h (taking 13 hours). Argon gas is used throughout the process: dew point -48℃, pressure 3.8MPa, injected through an annular gas distribution channel (3mm diameter, 12mm spacing) at a flow rate of 2.5L / min.

[0027] 6. Finished Product Processing The surface of the electroslag ingot was ground with a 100-grit grinding wheel to control the roughness Ra=10μm. A fluorescent flaw detector was used to inspect the head, tail, and the area around the drainage holes, finding no defects. Samples were taken from the top, middle, and bottom of the ingot, and spectral analysis showed the following compositional deviations: C ±0.003%, Ti ±0.04%, both ≤±0.05%.

[0028] II. Implementation Results Data Table 1 Comparison of low magnification mass and inclusion control

[0029] Table 1 clearly presents the differences between the traditional process and the patented process in the core quality indicators of electroslag ingots. The significant increase in the first-pass yield of Ti-containing steel directly reflects the significant inhibitory effect of the new slag system on crystallization defects, reducing problems such as shrinkage cavities and porosity. The reduction in the fine D-type inclusions in low-carbon stainless steel confirms that the quaternary slag system has a stronger ability to adsorb microparticles. Overall, the new process, through optimizing the slag system composition and controlling the molten pool, makes the internal quality of electroslag ingots more stable, providing a reliable foundation for subsequent forging processing.

[0030] Table 2. Maximum yield of various electroslag ingot types before and after electroslag ingot optimization design.

[0031] As shown in Table 2, the slender ingot design increases the height and reduces the proportion of head and tail cuts, which directly leads to improved production efficiency by increasing the overall yield. Compared with traditional ingots, it is more in line with the needs of high-efficiency production.

[0032] Table 3 Comparison of Energy Consumption and Cost

[0033] Table 3 data fully demonstrates the economic and green attributes of this patented process. The significant reduction in smelting power consumption stems from the reduced heat loss after increasing the filling ratio with slender ingots. Combined with the energy-saving characteristics of the multi-element high-resistivity slag system, considerable electricity costs can be saved based on the current production volume. The cost advantage of the electric furnace plus VOD process, as well as the efficient utilization of alloy return materials, further reduces raw material expenditures, making the overall production cost more competitive than traditional processes.

[0034] The surface of the ingot prepared using the special stainless steel electroslag remelting process of this invention is as follows: Figure 1 As shown, comparison Figure 2 Using existing technology, the surface quality of electroslag steel ingots can be significantly improved. After the electroslag steel ingots are forged and rolled into finished products, low-magnification sampling tests show no inclusion defects.

[0035] Table 4. Comparison of Low Magnitude and Chemical Composition of the Five-Element Slag System and the Original Quaternary Slag System

[0036] Table 4 shows that the Ti yield of Ti-containing steel produced by the pentagonal slag system is stable, and the Ti segregation at the head and tail of the ingot is smaller compared with the original quaternary slag system. Compared with the original quaternary slag system, the low-magnification macroscopic segregation of the microstructure after electroslag remelting and billet forming of the pentagonal slag steel ingot is also smaller.

[0037] In summary, this process fully demonstrates its significant advantages in the production of special-purpose stainless steel. Regarding quality stability, the synergistic effect of the pentagonal slag system and deoxidizer significantly improves the first-pass yield of Ti-containing steel at low magnification, and noticeably reduces the fine inclusions (Class D inclusions) in low-carbon steel. Larger inclusions are more easily removed by the slag system, resulting in more stable crystallization quality. In terms of composition control, the balance between the residual Al content in the electrode billet and the TiO2 in the pentagonal slag system increases Ti yield, reduces head-to-tail deviation, and ensures compositional uniformity.

[0038] In terms of production economics, the elongated ingot shape reduces head and tail losses, improving the overall yield; the electric furnace combined with VOD process reduces smelting power consumption, significantly reducing production costs, resulting in considerable cost savings based on current output. In summary, this process, through multifaceted optimization, achieves a dual improvement in the quality and efficiency of special-purpose stainless steel.

[0039] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A special electroslag remelting process for stainless steel, characterized in that: Includes the following steps: S1. Preparation of consumable electrode billets: The consumable electrode billets are smelted using an electric furnace + LF + VOD / AOD ladle refining process, and the residual Al content in the Ti-containing steel electrode billets is controlled to be 0.08%~0.20%; S2. Slag pretreatment: Ti-containing stainless steel adopts a five-element slag system, which is CaF2 53±5%, CaO 20±2%, MgO 3.0±2.0%, Al2O3 20±5%, TiO2 4.0±1.0% by weight. The slag is baked at 700~800℃ for more than 6 hours. S3. Slag formation and electroslag remelting: For small ingots, the arc is directly initiated using metal electrodes, while for large ingots, carbon electrodes are used to form slag. The electroslag remelting voltage is controlled at 58~62V and the current at 2800~3200A. S4. Deoxidation treatment: Si-Mn-Ca and ANS composite deoxidizers are used for pre-deoxidation and final deoxidation during the electrode billet smelting stage. S5. Cooling and forming: The ingot is slender and elongated. After remelting, it is cooled by step heat preservation and argon gas protection throughout the process. S6. Finished product processing: Surface grinding and quality inspection of electroslag ingots.

2. The electroslag remelting process for special stainless steel according to claim 1, characterized in that: The internal control range of chemical composition of the consumable electrode blank in step S1 is: C 0.03~0.06%, Si 0.2~0.5%, Mn 1.3~1.8%, P ≤0.030%, S≤0.020%.

3. The electroslag remelting process for special stainless steel according to claim 2, characterized in that: In step S2, the five-element slag system is composed of CaF2 53%, CaO 20%, MgO 3%, Al2O3 20%, and TiO2 4% by weight percentage.

4. The electroslag remelting process for special stainless steel according to claim 3, characterized in that: In step S3, the carbon electrode slag formation time is ≤ 15 minutes, the metal electrode melting rate is 5~7 kg / min, and the current and voltage fluctuation range is ≤ ±3%.

5. The electroslag remelting process for special stainless steel according to claim 4, characterized in that: In step S3, the small ingot size is Φ220~260, and the large ingot size is Φ≥260.

6. The electroslag remelting process for special stainless steel according to claim 5, characterized in that: In step S4, the amount of composite deoxidizer added is 0.3~0.5 kg per 100 kg of molten steel, and the particle size is 1~2 mm.

7. The electroslag remelting process for special stainless steel according to claim 6, characterized in that: In step S5, the filling ratio of the elongated ingot is 0.6~0.8, wherein the dimensions of the Φ220 ingot are Φ210mm at the top, Φ240mm at the bottom, and 1100mm in height.

8. The electroslag remelting process for special stainless steel according to claim 7, characterized in that: The stepped heat preservation and cooling in step S5 is as follows: first, maintain the temperature at 1050℃ for 20~25 minutes, and then cool down to below 150℃ at a rate of 60~80℃ / h.

9. The electroslag remelting process for special stainless steel according to claim 8, characterized in that: In step S5, the argon gas has a dew point of ≤-45℃, is introduced at a pressure of 3.5~4MPa, and is blown in through an annular gas distribution channel.

10. The electroslag remelting process for special stainless steel according to claim 9, characterized in that: In step S6, surface grinding is performed using an 80-120 mesh grinding wheel.

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