Iron-chromium-aluminum series electrothermal alloy forging square billet and preparation method thereof

Abstract

The invention belongs to the technical field of metal material hot working, and particularly relates to an iron-chromium-aluminum series electrothermal alloy forging square billet and a preparation method thereof. The preparation method of the iron-chromium-aluminum series electrothermal alloy forged square billet comprises the following steps: carrying out hot working forging on a heated electroslag ingot to obtain a square billet; wherein the hot working forging is divided into the following three stages: an initial forging cogging stage, a middle-stage main forging stage and a final precision forging stage. The method can solve the problem of cracking of large-size electroslag ingots in the hot working process due to poor plasticity and toughness of materials, meets the use requirements of small-batch and multi-variety iron-chromium-aluminum electrothermal alloy series hot-rolled wires on square billet raw materials, and has the characteristics of low capital investment of production line equipment, high production efficiency and the like. And the method has the advantages of good square billet quality, low cost, high material compactness, improved material structure and performance and the like.

Description

Technical Field

[0001] This invention belongs to the field of hot working technology of metal materials, specifically relating to a forged square billet of iron-chromium-aluminum electrothermal alloy and its preparation method. Background Technology

[0002] Electrothermal alloy materials are widely used in industries such as industry, petrochemicals, and home appliances due to their excellent resistivity, resistance uniformity, and oxidation resistance. Among them, iron-chromium-aluminum alloys have become the most widely used and consumed materials in electrothermal applications due to their high resistivity, high thermal stability, long service life, high energy conversion efficiency, and low price. In particular, iron-chromium-aluminum wires and filaments have the largest market share.

[0003] The matrix of iron-chromium-aluminum alloy is ferrite, mainly composed of elements such as iron, chromium, and aluminum. At high temperatures, a dense oxide film easily forms on the alloy surface, with a maximum oxidation resistance temperature reaching 1400℃, significantly extending the high-temperature service life of the material. High Al content increases resistivity, which effectively converts electrical energy into heat energy, with a maximum resistivity reaching 1.6 μΩ·m. However, these characteristics result in poor plasticity and toughness, making ingot casting and electroslag ingot initial rolling production difficult. Furthermore, metal cracking and brittle fracture frequently occur during deformation processing. Some foreign companies have been forced to adopt powder metallurgy for production, but this has led to increased investment costs, making iron-chromium-aluminum one of the steel grades recognized worldwide as difficult to mass-produce.

[0004] Although my country is a major producer and user of iron-chromium-aluminum wire rods, its current production mainly relies on hot rolling of small-sized cylindrical electroslag ingots (tens of kilograms with a nominal cross-sectional diameter (d) ≤ 200 mm) smelted by private enterprises and billets produced by continuous casting in some large steel enterprises. However, the small electroslag ingots (tens of kilograms) face technical bottlenecks in terms of compositional stability, performance uniformity, production economy, and energy and environmental protection. Meanwhile, continuous casting of billets presents challenges such as high investment in production line equipment, high technical difficulty, large batch sizes, and inflexible production organization.

[0005] Therefore, there is an urgent need for a production line equipment that requires less capital investment, has high production efficiency, produces high-quality billets, has low cost, and can solve the cracking problem in the initial rolling process of die casting and electroslag ingots caused by poor material plasticity and toughness, so as to meet the billet raw material needs of small and medium batches and multiple varieties of iron-chromium-aluminum electrothermal alloy wire production. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a forged square billet of an iron-chromium-aluminum electrothermal alloy and its preparation method.

[0007] Specifically, the method for preparing the iron-chromium-aluminum electrothermal alloy forged square billet of the present invention includes: hot working and forging a heated electroslag ingot to obtain a square billet; wherein, the hot working and forging is divided into the following three stages: Initial forging stage: The electroslag ingot is forged into a forging billet with a rectangular cross-section. The hot working forging temperature range is 800~1050℃, the single-pass hammer reduction is 5~15mm, and the total reduction rate of the cross-section of the forging is 15%~20%. Mid-term main forging stage: hot working forging temperature range 750~1050℃, single-pass hammer reduction 40~60mm, total reduction rate of forging cross section 20%~60%; Final precision forging stage: hot working forging temperature range 700~1050℃, single-pass hammer reduction 0~5mm, total reduction rate of forging cross section 0~5%.

[0008] The above-mentioned method for preparing iron-chromium-aluminum electrothermal alloy forged square billets involves heating the electroslag ingot as follows: the electroslag ingot is heated in the furnace to a heating section temperature of 650~750℃ and held for 2~5 hours; then the electroslag ingot is heated at an average rate of 50~160℃ / h to a soaking section temperature of 1020~1200℃ and held for 2~5 hours.

[0009] In the above-mentioned method for preparing iron-chromium-aluminum electrothermal alloy forged square billets, the electroslag ingot is a cylindrical electroslag ingot with a nominal diameter of 350~450mm and a length of 500~1500mm.

[0010] The above-mentioned method for preparing iron-chromium-aluminum electrothermal alloy forged square billets, by weight percentage, the electroslag ingot comprises: C: 0~0.06%, Si: 0~0.60%, Mn: 0~0.50%, P≤0.025%, S≤0.010%, Cr: 11.50%~26.00%, Ni: 0~0.50%, Al: 3.00%~7.00%, with the balance being Fe and unavoidable impurities.

[0011] In the above-mentioned method for preparing iron-chromium-aluminum electrothermal alloy forged square billets, the electroslag ingot grade is 0Cr23Al5 or 0Cr25Al5.

[0012] The above-mentioned method for preparing iron-chromium-aluminum electrothermal alloy forged square billets has a cross-sectional side length range of 140~220mm.

[0013] On the other hand, the present invention also provides a forged square billet of iron-chromium-aluminum electrothermal alloy, which is prepared by the above-described preparation method.

[0014] The aforementioned iron-chromium-aluminum electrothermal alloy forged square billet, by weight percentage, comprises: C: 0~0.06%, Si: 0~0.60%, Mn: 0~0.50%, P≤0.025%, S≤0.010%, Cr: 11.50%~26.00%, Ni: 0~0.50%, Al: 3.00%~7.00%, with the balance being Fe and unavoidable impurities.

[0015] The aforementioned iron-chromium-aluminum electrothermal alloy forged square billet has a cross-sectional side length ranging from 140 to 220 mm.

[0016] The technical solution of the present invention has the following beneficial effects: The preparation method of the iron-chromium-aluminum electrothermal alloy forged square billet of the present invention can solve the cracking problem of large-size electroslag ingots during hot working caused by poor plasticity and toughness of materials, meet the use requirements of square billet raw materials for small batches and multiple varieties of iron-chromium-aluminum electrothermal alloy series hot-rolled wire rods, and has the advantages of low investment in production line equipment, good square billet quality, low cost, high material density, and improved material structure and properties. Attached Figure Description

[0017] Figure 1 The image shows the finished product of the iron-chromium-aluminum electrothermal alloy forging billet prepared in Example 1 after final forging.

[0018] Figure 2 The cross-sectional morphology of the forged square billet of the iron-chromium-aluminum electrothermal alloy prepared in Example 2 is shown. Detailed Implementation

[0019] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0020] This invention addresses the technical challenges of poor plasticity and toughness in iron-chromium-aluminum electrothermal alloys, leading to easy cracking during hot processing of large-sized electroslag ingots. It proposes a systematic method for preparing forged square billets. The inventive concept involves: using large-sized cylindrical electroslag ingots as raw materials; employing a two-stage heating process to improve material plasticity and suppress grain coarsening; then using a three-stage forging process—initial forging to break the surface structure, mid-stage main forging to weld defects and refine grains, and final precision forging to shape—effectively solving the processing cracking problem while controlling equipment investment. This yields square billets with high density, uniform structure, and excellent performance, meeting the production needs of high-end wire rods in multiple varieties and small-to-medium batches.

[0021] The electroslag ingot used in this invention is a large-sized cylindrical electroslag ingot with a nominal diameter of 350~450mm and a length of 500~1500mm. The cross-sectional side length of the prepared square billet ranges from 140~220mm.

[0022] In some preferred embodiments, the electroslag ingot comprises, by weight percentage: C: 0~0.06%, Si: 0~0.60%, Mn: 0~0.50%, P≤0.025%, S≤0.010%, Cr: 11.50%~26.00%, Ni: 0~0.50%, Al: 3.00%~7.00%, with the balance being Fe and unavoidable impurities.

[0023] Before electroslag remelting (ESR) ingots are forged, they need to be heated to improve the steel's plasticity, reduce deformation resistance, and improve the internal structure and properties of the metal for easier processing. To homogenize the internal structure and solvent carbides, and obtain sufficiently high plasticity, the ingot needs to be heated to a sufficiently high temperature and held at that temperature for a certain period to ensure good hot workability. However, ESR stainless steel has a ferritic structure at high temperatures. Ferrite grains begin to grow at 720-780℃, grow rapidly at 900℃, and grow dramatically above 1000℃. Excessively coarse ferrite grains significantly reduce hot workability. When heating large-sized ESR ingots of ESR, the heating time in the high-temperature zone should be minimized, especially the time spent in the high-temperature zone above 1000℃. At room temperature, the thermal conductivity of ESR alloys is 10-15 W / (m·K), lower than that of 304 stainless steel (14-16 W / (m·K)). Therefore, the large-size electroslag ingot of the present invention has an added heat preservation section during the heating process at medium and low temperatures to make the electroslag ingot obtain a more uniform preheating temperature. Afterwards, as the heating temperature increases, the thermal conductivity of the iron-chromium-aluminum electrothermal alloy will exceed that of 304 stainless steel. For example, at 800°C, the thermal conductivity of the iron-chromium-aluminum electrothermal alloy will rapidly increase to 30 W / (m·K), while the thermal conductivity of 304 stainless steel is about 23 W / (m·K). Therefore, the heat preservation time of the high-temperature homogenization section of the electroslag ingot can be appropriately shortened according to the homogenization temperature to save energy consumption.

[0024] In some preferred embodiments, the method for preparing the iron-chromium-aluminum electrothermal alloy forged billet of the present invention includes the following heating process for the electroslag ingot: the electroslag ingot is heated in the furnace to a heating section temperature of 650~750℃ and held for 2~5 hours; then the electroslag ingot is heated to a soaking section temperature of 1020~1200℃ at an average heating rate of 50~160℃ / h and held for 2~5 hours.

[0025] The heating process of this invention, which heats the electroslag ingot, not only avoids cracking and grain coarsening, but also promotes a certain degree of diffusion and homogenization of the component segregation inside the electroslag ingot, thus initially optimizing the as-cast microstructure. The final ingot is a forging billet with uniform internal and external temperature, controlled grain size, and optimal plasticity, capable of withstanding deformation in subsequent forging stages without becoming brittle.

[0026] Forging significantly improves the microstructure and properties of electroslag ingots of iron-chromium-aluminum electrothermal alloys. It eliminates solidification defects, improves the microstructure, and enhances the mechanical properties and reliability of the material, meeting the stringent service requirements of high-end applications for heating elements. Specific effects include: (1) Eliminate solidification casting defects of electroslag ingots and improve the density of steel ingots. The huge pressure during the forging process can effectively compact the internal pores and gaps of these electroslag ingots, thereby significantly improving the density of the material; at the same time, forging can break up the remaining inclusions and distribute them along the direction of metal flow lines, reducing their cutting effect on the matrix structure and reducing their risk as crack sources.

[0027] (2) Breaking up the coarse as-cast structure to achieve grain refinement. Due to the well-developed ferrite structure and coarse grains in the electroslag ingot of iron-chromium-aluminum stainless steel, the material has extremely poor plasticity and toughness. Through forging, the coarse as-cast ferrite grains in the electroslag ingot can be broken by external force, thereby achieving grain refinement.

[0028] (3) Improve the chemical composition segregation inside the electroslag ingot and enhance the uniformity of the material's microstructure and properties. Although the electroslag remelting process can effectively reduce macroscopic segregation, there is still a certain degree of microscopic chemical composition inhomogeneity at the microscale. The high-temperature heating and intense plastic deformation during the forging process can promote interatomic diffusion, which can redistribute alloying elements in the segregated areas, making the microstructure and properties of the entire forging more uniform and consistent, thereby ensuring that the heating elements prepared by the iron-chromium-aluminum electrothermal alloy have more uniform and stable electrothermal performance (resistivity, etc.).

[0029] In some preferred embodiments, the hot forging process of the iron-chromium-aluminum electrothermal alloy forging billet of the present invention is divided into the following three stages: Initial forging stage In the initial forging and billet opening stage, small deformation hot forging is used. The purpose is to break the coarse grains on the surface of the steel ingot, improve the plasticity of the steel ingot, and prepare it to withstand subsequent larger forging deformation processing.

[0030] In a further preferred embodiment, during the initial forging and billet-making stage, the electroslag ingot is forged into a forging billet with a rectangular cross-section, the hot working forging temperature range is 800~1050℃, the single-pass hammer reduction is 5~15mm, and the total reduction rate of the cross-section of the forging is 15%~20%.

[0031] Mid-term master forging stage In the mid-term main forging stage, hot working forging with large reduction deformation is adopted. The purpose is to completely weld the gaps inside the electroslag ingot, improve the density of the steel ingot, fully break and refine the grains, and make the inclusions and second phase inside the electroslag ingot elongated and extended along the main stress direction to form "fibrous structure", which significantly improves the mechanical properties of the material, such as mechanical properties and impact toughness.

[0032] Further preferred options include a hot forging temperature range of 750~1050℃ during the intermediate main forging stage, a single-pass hammer reduction of 40~60mm, and a total reduction rate of 20%~60% for the cross-sectional area of ​​the forging; Final forging stage The final precision forging stage employs hot forging with less deformation, the purpose of which is to bring the forging to the final required shape and size, and to make the surface of the obtained square billet forging smoother and flatter.

[0033] Further preferred options include a hot forging temperature range of 700~1050℃, a single-pass hammer reduction of 0~5mm, and a total reduction rate of 0~5% for the cross-section of the forging.

[0034] This method uses large-sized cylindrical electroslag ingots to prepare square billets through hot forging, which can solve the problem of hot working cracking caused by the poor plasticity and toughness of such materials. It has advantages such as low investment in production line equipment, high billet quality, low production cost, high material density, and improved material microstructure and properties. The prepared square billets can meet the high-quality requirements for billet raw materials of 0Cr23Al5, 0Cr25Al5 and other iron-chromium-aluminum electrothermal alloy wires.

[0035] Example The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0036] Example 1 An electroslag ingot of an iron-chromium-aluminum electrothermal alloy with the grade 0Cr23Al5, smelted by electroslag remelting, has the following chemical composition by mass percentage: C: 0.018%, Si: 0.33%, Mn: 0.38%, P: 0.017%, S: 0.001%, Cr: 20.76%, Ni: 0.08%, Al: 4.31%, with the balance being Fe and unavoidable impurities.

[0037] The cylindrical electroslag ingot obtained by electroslag remelting has a nominal diameter (d) of 350 mm and a length of 500 mm.

[0038] The electroslag ingot is placed in a heating furnace and heated to a heating section temperature of 680~720℃ and held for 3 hours. Then the electroslag ingot is heated to a soaking section temperature of 1060~1100℃ at an average heating rate of 80~120℃ / h and held for 3 hours.

[0039] The billet was prepared by forging in three hot working stages using a 1000-ton hydraulic high-speed forging machine.

[0040] Initial forging and billet opening stage of electroslag ingot: The electroslag ingot after the first heating is forged into a forging billet with a rectangular cross section. The hot working forging temperature range is 813~1037℃, the single-pass hammer reduction is 5~15mm, and the total reduction rate of the cross section of the forging is 18%.

[0041] Mid-term main forging stage of forging: forging billet after second heating, hot working forging temperature range of 752~1024, single-pass hammer reduction of 40~60mm, total reduction rate of cross-section of forging of 55%.

[0042] The final precision forging stage of the forging: to make the forging achieve the required shape and dimensional accuracy of the final square billet, the forging billet after the third heating, the hot working forging temperature range of 768~1023℃, the single-pass hammer reduction of 0~5mm, the total reduction rate of the cross-section of the forging of 4%, and the forging is processed into a finished square billet with a cross-sectional side length of 150mm.

[0043] The soft Φ5.5mm wire rod prepared from the above-mentioned forged square billet was tested for tensile strength R according to standard GB / T 1234-2012 "High Resistance Heating Alloys". m The strength is 619 MPa, and the elongation after fracture (A) is 26.5%, which meets the mechanical property requirements of the standard for soft alloy materials. Observation of the finished product after final forging of the iron-chromium-aluminum electrothermal alloy forging billet showed no hot working cracks (see...). Figure 1 ).

[0044] Example 2 An electroslag ingot of an iron-chromium-aluminum electrothermal alloy with the grade 0Cr25Al5, smelted by electroslag remelting, has the following chemical composition by mass percentage: C: 0.024%, Si: 0.35%, Mn: 0.33%, P: 0.018%, S: 0.001%, Cr: 23.25%, Ni: 0.11%, Al: 4.64%, with the balance being Fe and unavoidable impurities.

[0045] The cylindrical electroslag ingots obtained by electroslag remelting have a nominal diameter (d) ranging from 450 mm to 800 mm.

[0046] The electroslag ingot is placed in a heating furnace and heated to a heating section temperature of 680~720℃ and held for 5 hours. Then the electroslag ingot is heated to a soaking section temperature of 1140~1180℃ at an average heating rate of 50~90℃ / h and held for 4 hours.

[0047] The billet was prepared by forging in three hot working stages using a 1000-ton hydraulic high-speed forging machine.

[0048] Initial forging and billet opening stage of electroslag ingot: The electroslag ingot after the first heating is forged into a forging billet with a rectangular cross section. The hot working forging temperature range is 839~1036℃, the single-pass hammer reduction is 5~15mm, and the total reduction rate of the cross section of the forging is 16%.

[0049] Mid-term main forging stage of forging: Forging billet after second heating, hot working forging temperature range of 767~1025℃, single-pass hammer reduction of 40~60mm, total reduction rate of cross-section of forging of 51%.

[0050] The final precision forging stage of the forging: to make the forging achieve the shape and dimensional accuracy required for the final square billet, the forging billet after the third heating, the hot working forging temperature range of 732~1029℃, the single-pass hammer reduction of 0~5mm, the total reduction rate of the cross-section of the forging is 3%, and the forging is processed into a finished square billet with a cross-sectional side length of 220mm.

[0051] The soft Φ5.5mm wire rod prepared from the above-mentioned forged square billet was tested for tensile strength R according to standard GB / T 1234-2012 "High Resistance Heating Alloys". m The strength is 663 MPa and the elongation after fracture (A) is 28%, which meets the requirements of the standard for the mechanical properties of soft alloy materials. Observation of the cross-sectional morphology of the forged square billet of the iron-chromium-aluminum electrothermal alloy revealed no visible internal defects (see...). Figure 2 ).

[0052] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0053] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0054] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method of producing a wrought square billet of an iron-chromium-aluminum electric resistance alloy, characterized by, The application relates to a preparation method of a square billet. The heated electroslag ingot is subjected to hot working forging to obtain the square billet; wherein the hot working forging is divided into the following three stages: An initial forging and breaking stage: the electroslag ingot is forged into a rectangular cross-section forging blank, the hot working forging temperature interval is 800-1050 DEG C, the single pass hammer head compression amount is 5-15 mm, and the total cross-section reduction rate of the forging is 15%-20%; A middle main forging stage: the hot working forging temperature interval is 750-1050 DEG C, the single pass hammer head compression amount is 40-60 mm, and the total cross-section reduction rate of the forging is 20%-60%; A final finish forging stage: the hot working forging temperature interval is 700-1050 DEG C, the single pass hammer head compression amount is 0-5 mm, and the total cross-section reduction rate of the forging is 0-5%.

2. The production method according to claim 1, characterized by, The heating process of the electroslag ingot is as follows: the electroslag ingot is heated to a heating section temperature of 650-750 DEG C and is kept for 2-5 hours; then the electroslag ingot is heated to a soaking section temperature of 1020-1200 DEG C at an average heating rate of 50-160 DEG C / h, and the soaking section is kept for 2-5 hours.

3. The preparation method according to claim 1, characterized in that, The electroslag ingot is a cylindrical electroslag ingot with a nominal diameter of 350-450 mm and a length of 500-1500 mm.

4. The method of claim 1, wherein, The electroslag ingot comprises the following components in percentage by weight: C: 0-0.06%, Si: 0-0.60%, Mn: 0-0.50%, P: not more than 0.025%, S: not more than 0.010%, Cr: 11.50%-26.00%, Ni: 0-0.50%, Al: 3.00%-7.00%, and the balance is Fe and inevitable impurities.

5. The preparation method according to claim 1, characterized in that, The electroslag ingot is of a 0Cr23Al5 or 0Cr25Al5 grade.

6. The method of claim 1, wherein, The square billet has a cross-section side length size range of 140-220 mm.

7. A forged square billet of an iron-chromium-aluminum electrothermal alloy, characterized in that, The square billet is prepared by the preparation method.

8. The Fe-Cr-Al based electric resistance alloy forged bloom according to claim 7, wherein The square billet has a cross-section side length size range of 140-220 mm.

9. The Fe-Cr-Al based electric resistance alloy forged bloom according to claim 7, wherein The square billet has a cross-section side length size range of 140-220 mm.

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