Carburized steel wire rod for large deformation cold working and manufacturing method thereof

Abstract

The present invention relates to a carburized steel wire rod for large deformation cold working and a manufacturing method thereof. The metallographic structure of the wire rod is spherical pearlite, the spheroidization rate is ≥95%, and the grain size is 7 to 9. After the wire rod is cold worked with a deformation of more than 80%, it is carburized in the temperature range of 930°C to 950°C for 1-3 hours without the formation of mixed crystals. A small amount of Cr, Ni, and Mo elements are added to low-carbon steel to improve the hardenability of the steel while still maintaining good plasticity. The addition of Nb and Al microalloying elements to disperse and precipitate carbonitrides to refine the grains significantly improves the plasticity and prevents excessive grain growth during heating and heat preservation at higher temperatures. Low Si control significantly reduces the degree of hardening during the cold working of the steel, avoiding a sharp decrease in the plasticity and toughness of the material during the cold working process. In the manufacturing method, the area reduction rate in the rough drawing process is controlled at 20-50%, followed by spheroidizing annealing. The large area reduction rate of the wire drawing causes dislocations to be generated inside the steel wire, which helps to significantly improve the spheroidization rate in the annealed state, reduce the tensile strength and hardness, and improve the plasticity.

Description

Technical Field

[0001] The invention relates to carburized wire rod steel and a manufacturing method thereof. Background Art

[0002] Multi-station cold heading machines have higher metal recovery rates, higher production efficiency and lower production costs. They have been widely used in the automotive parts industry. Since the material deforms greatly and deforms quickly during the cold heading process, the material is required to have excellent plasticity, deformation ability and metallographic structure.

[0003] Currently, domestically produced carburizing steels primarily include alloy structural steels such as 20Cr, 20CrMnTi, and 16MnCr5. These high alloy contents, compared to carbon steel, result in greater plasticity and cold forming resistance, making them unsuitable for large-deformation cold working. Carbon carburizing steels also have low hardenability, making it difficult to increase core strength. There is a need to develop a steel that combines the large-deformation cold working performance of carbon steel with excellent carburizing properties and hardenability.

[0004] During the cold forming process, due to the large local deformation and uneven overall deformation, coarse grains are likely to appear during the subsequent high-temperature carburizing heat treatment, affecting the carburizing effect. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a carburized steel wire rod for large deformation cold working and a manufacturing method thereof in view of the above-mentioned prior art.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] The chemical composition wt% of carburizing steel wire rod for large deformation cold working is C: 0.08~0.12%, Si: ≤0.10%, Mn: 0.50~0.70%, P: ≤0.025%, S: ≤0.010%, Cr: 0.25~0.35%, Ni: 0.10~0.20%, Mo: 0.01~0.10%, Al: 0.025~0.060%, N: 0.0050~0.0150%, Nb: 0.01~0.05%, and the rest is Fe and unavoidable impurities.

[0008] The chemical composition design basis of the carburizing steel of the present invention is as follows:

[0009] 1) Determination of C content

[0010] C is the most basic strengthening element in steel, but too much C will have an adverse effect on the toughness and plasticity of steel. The C content of the present invention is determined to be within the range of 0.08-0.12%. The steel material of the present invention belongs to the category of low carbon steel.

[0011] 2) Determination of Si content

[0012] Si increases the steel's sensitivity to overheating, cracking, and decarburization, significantly increasing the degree of cold working hardening and causing a sharp decrease in the material's plasticity and toughness. Furthermore, in carburized steel, Si reduces the carburized layer thickness and carbon concentration. The Si content in this invention is defined as ≤0.10%.

[0013] 3) Determination of Mn content

[0014] Manganese, as a deoxidizing element in the steelmaking process, improves the hardenability of steel. It also fixes the sulfur in the steel, forming MnS and (Fe,Mn)S, which are less detrimental to the steel's performance. This reduces or inhibits FeS production and prevents hot embrittlement. Therefore, a small amount of manganese (0.50-0.70%) in steel can improve its purity and performance. However, excessive Mn content in steel can lead to significant temper brittleness. Furthermore, Mn is a readily segregating element, particularly in the center of wire, negatively impacting drawability. Furthermore, Mn promotes grain growth, increasing the steel's overheat sensitivity and cracking tendency, while also reducing dimensional stability, adversely affecting customer use. To achieve excellent microstructure, mechanical properties, and cold workability, the Mn content in this invention is set within the range of 0.50-0.70%.

[0015] 4) Determination of Cr content

[0016] Cr is a carbide-forming element that improves the hardenability, wear resistance, and corrosion resistance of steel. Some of the Cr in steel replaces iron to form alloy cementite, improving the steel's tempering stability; some dissolves into ferrite, producing solid solution strengthening and increasing its strength and hardness. Cr also reduces the steel's tendency to overheat and the rate of surface decarburization. However, excessive Cr content combines with carbon in the steel to form large carbides. These insoluble carbides reduce the steel's toughness. Furthermore, excessive Cr content increases the steel's hardness, making it difficult for customers to process and use. Currently, Cr is present as a residual element in carbon steels, both domestically and internationally, generally requiring a content of ≤0.2%, and is not intentionally added. However, the present invention recognizes that adding Cr to steel can improve its strength, hardness, corrosion resistance, and wear resistance. However, excessive Cr addition can result in excessively hard steel, making it difficult to cold work. For these reasons, the present invention sets the Cr content range to 0.25-0.35%.

[0017] 5) Determination of Al content

[0018] Al is added to steel as a deoxidizing element. Besides reducing dissolved oxygen in molten steel, Al and N form dispersed, fine aluminum nitride, which refines grain size and increases the temperature at which grains coarsen. However, high Al content can easily form brittle inclusions such as Al₂O₃ during molten steel smelting, reducing the purity of the molten steel. Furthermore, high Al content can increase the austenite grain size of the steel and cause it to grow and coarsen. The Al content in the present invention is set within a range of 0.025-0.060%.

[0019] 6) Determination of Ni content

[0020] Ni is a non-carbide-forming element that exists in steel as a solid solution. When used in combination with Cr, it can significantly improve the hardenability of steel. The Ni content in the present invention is determined to be within the range of 0.10-0.20%.

[0021] 7) Determination of Mo content

[0022] Mo exists in the solid solution and carbides of steel, has a solid solution strengthening effect, can improve the hardenability and tempering stability of steel, can also refine the grain, improve the unevenness of carbides, thereby increasing the strength and toughness of steel. The range of Mo content in the present invention is determined to be 0.01-0.10%.

[0023] 8) Determination of Nb content

[0024] Nb is a typical microalloying element with a strong affinity for carbon and nitrogen, forming stable carbides and carbonitrides. The present invention utilizes a relatively high carburizing temperature. An appropriate amount of Nb can prevent excessive grain growth during the heating and holding process. However, high Nb content can affect the surface quality of the billet. The present invention defines a Nb content range of 0.01 to 0.05%.

[0025] 9) Determination of P and S content

[0026] Phosphorus (P) causes severe segregation during solidification in steel. P dissolves in ferrite, causing grain distortion and coarsening, and increasing cold brittleness. The P content in this invention is set to ≤ 0.025%. Sulphur (S) causes hot brittleness in steel, reducing its ductility and toughness. The S content in this invention is set to ≤ 0.010%.

[0027] 10) Determination of N content

[0028] Nitrogen has a strong affinity with Al and Nb, forming stable carbides and carbonitrides, refining grains and increasing the temperature at which steel grains coarsen. However, excessive nitrogen content will reduce the plasticity and toughness of the steel. The nitrogen content of the present invention is determined to be within the range of 0.0050-0.0150%.

[0029] A method for manufacturing carburized steel wire rod for large deformation cold working, comprising:

[0030] Step 1: Smelting and casting: Smelt molten steel according to the chemical composition of the wire rod and cast it into steel billets.

[0031] Step 2: Billeting: The steel billet is rolled to obtain an intermediate billet, which is then surface treated.

[0032] Step 3, wire rolling: the intermediate billet is heated in a heating furnace, the temperature of the high temperature section is controlled at 1010℃~1100℃, the holding time of the high temperature section is not less than 45min, the residual oxygen content in the furnace is ≤4.0%, so that the alloy elements are fully dissolved and evenly distributed; after the holding is completed, the intermediate billet is taken out of the furnace to remove the scale and surface oxide layer, and then rolled, rough rolling stage: the rolling temperature is 900~1000℃, the total compression ratio is ≥65%; secondary descaling is performed before intermediate rolling; finishing rolling stage: the finishing rolling temperature is 900~960℃, the total compression ratio is ≥95%; the temperature of the sizing mill is 930~9 60℃, the compression ratio of the last two passes is ≥30%; after sizing, the wire rod is spun at a temperature of 880℃~950℃. After spun, the wire rod coil is cooled by slow cooling. The roller speed of the wire rod coil is set to 0.10m / s~0.35m / s. Initially, 2~4 insulation covers are opened. The cooling rate of the wire rod at this stage is ensured to be ≥1.5℃ / s. The temperature of the wire rod entering the insulation cover is controlled to be 780~850℃, and the other insulation covers are closed. The residence time of the wire rod in the insulation cover is controlled to be more than 11min, and the cooling rate of the wire rod in the insulation cover is ensured to be ≤1℃ / s.

[0033] Step 4, deep processing: wire rod is carried out pickling back lime or phosphorus saponification coating (guarantee pickling quality, avoid lacking pickling or over-acid), carry out coarse drawing, wire drawing area reduction rate is controlled at 20~50% (wire drawing process prevents abrasion, carries out die lubrication, avoids the occurrence of defectives such as lubrication failure and causes crack), carry out spheroidizing annealing after the wire drawing, feed protective gas in the annealing furnace, control the interior oxygen content of the furnace below 20ppm, dew point is controlled at below-50 ℃, prevents decarburization from increasing, is heated to 730~740 ℃, is heat-insulated 5~9 hours, controlled cooling, adopts slow cooling mode in the furnace, rate of cooling is controlled at 10~20 ℃ / h, slowly cools to come out of the stove below 200 ℃; Carry out pickling phosphorus saponification coating (in order to meet the demand of follow-up large deformation amount cold heading lubrication) before the wire drawing, fine drawing area reduction rate is controlled at 3~10%, and the metallographic structure of gained carburized steel wire rod is spherical pearlite, and spheroidization rate 〉=95%, and grain size is 7~9 grades.

[0034] The above manufacturing method is preferably suitable for producing carburizing steel wire rods with specifications of Φ4.0 to Φ20 mm.

[0035] The tensile strength of the carburized steel wire rod obtained based on the above manufacturing method is ≤400MPa, the area reduction is ≥70%, the deformation is above 80%, and no mixed crystals appear when carburized in the temperature range of 930℃ to 950℃ for 1-3 hours after cold working.

[0036] Preferably, in step one, high-quality molten iron, scrap steel and raw and auxiliary materials are used for molten steel smelting to reduce the content of harmful elements in the molten steel. The molten steel smelting involves primary smelting in a converter, LF refining, vacuum degassing and argon blowing and stirring. The converter slag is made to remove C and P, and the purpose of tapping is to avoid slag. One of the purposes of vacuum treatment is to control the hydrogen content to be lower than 1.0 ppm. The molten steel is cast into a billet using a continuous casting process. The pouring superheat during the continuous casting process does not exceed 35°C. Soft pressure reduction and electromagnetic stirring are implemented in the continuous casting process to improve the segregation of the billet. The entire continuous casting process adopts protective pouring to isolate the billet from the air to prevent secondary oxidation.

[0037] Preferably, in step 2, the continuous casting billet is heated in a heating furnace at a high temperature of 1150-1270°C to fully dissolve the alloy components in the steel, and the billet is cut into a cross-section of 150*150mm. 2 ~200*200mm 2 The intermediate billet is taken off the line and slowly cooled after the billet is opened.

[0038] The reason why the wire rod of the present application can be carburized without the formation of mixed crystals after large deformation cold working is that: in terms of element design, the chemical composition design of Al, Nb and N with appropriate proportions is adopted, which can form stable carbides and carbonitrides in the steel, refine the grains, increase the temperature of steel grain coarsening, and prevent mixed crystals. In order to ensure that there are as many solid-solution aluminum and nitrogen as possible, so that the subsequent heat treatment can precipitate fine and dispersed carbide and carbonitride particles, thereby preventing grain growth during high-temperature carburizing. At the same time, in order to avoid stress concentration during the rolling process, reduce lattice distortion, and facilitate recovery of recrystallization, the heating and rolling processes adopt a "double high" process, high-temperature heating and high-temperature rolling, to ensure that there are as many solid-solution elements as possible. These solid-solution elements form stable carbide and carbonitride particles in the steel during the subsequent heat treatment. These particles play the role of pinning the grains, preventing the growth of grains and the formation of mixed crystals during the heat treatment.

[0039] Compared with the prior art, the advantages of the present invention are:

[0040] (1) Chemical composition optimization: Adding a small amount of Cr, Ni, and Mo elements to low-carbon steel can improve the hardenability of the steel while still maintaining good plasticity. The comprehensive addition of Nb and Al microalloying elements, which are dispersed and precipitated in the form of carbonitrides, can refine the grains, significantly improve the plasticity, and prevent excessive grain growth during heating and holding at high temperatures. By controlling low Si, the degree of hardening during cold working of the steel can be significantly reduced, avoiding a sharp drop in plasticity and toughness during cold working of the material.

[0041] (2) During molten steel smelting, a converter is used to produce molten steel with low S and P content. LF refining + vacuum degassing helps to produce molten steel with uniform chemical composition and purity. The continuous casting process is used to improve production efficiency and facilitate the control of the internal quality of the billet.

[0042] (3) In the deep processing process, the area reduction rate in the rough drawing process is controlled at 20-50%, and then spheroidizing annealing is performed. The large area reduction rate of wire drawing causes dislocations to be generated inside the steel wire, which helps to significantly improve the spheroidization rate of the annealed state, reduce the tensile strength (tensile strength ≤ 400 MPa) and hardness, and improve the plasticity (area reduction ≥ 70%).

[0043] (4) After the steel wire is cold worked with a deformation of more than 80%, it is carburized at 930°C-950°C for 1-3 hours without the formation of mixed crystals. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below with reference to the examples. The examples are illustrative and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0045] Example 1

[0046] The carburizing steel wire for large deformation cold working involved in this embodiment contains the following components and their mass percentages: C: 0.09%, Si: 0.04%, Mn: 0.55%, P: 0.012%, S: 0.002%, Cr: 0.28%, Ni: 0.13%, Mo: 0.02%, Al: 0.045%, N: 0.0100%, Nb: 0.02%, and the balance is Fe and unavoidable impurity elements.

[0047] The production process of carburizing steel wire for large deformation cold working is as follows:

[0048] According to the chemical composition, the smelting raw materials are configured and carried out in sequence: BOF converter smelting → LF refining → RH vacuum degassing → continuous casting (the continuous casting billet specification is 390*510mm 2 )→ continuous casting billet heating→ billet opening (intermediate billet specification 200*200mm 2 )→intermediate billet surface treatment→wire heating→high-pressure water descaling→controlled rolling and controlled cooling→pickling and coating→rough drawing→annealing→pickling and phosphorus saponification→finishing drawing→finished product.

[0049] The specific process of the above-mentioned heating, rolling and cooling stages is as follows: heating the produced intermediate billet to 1030℃ and keeping it warm for 60min, the residual oxygen content in the furnace is 2.1%, descaling is carried out with high-pressure water after being discharged from the furnace, and then rolling is carried out, the rough rolling start temperature is 955℃, the total compression ratio is 65%; the finishing rolling temperature is 935℃, the total compression ratio of the intermediate and finishing rolling is 99.6%; the sizing temperature is 945℃, and the compression ratio of the last two passes is 43%; the wire drawing temperature is 923℃, the roller speed is 0.25m / s, the initial insulation covers are opened for 2 times, the initial cooling rate is ≥1.5℃ / s, the temperature of the wire rod entering the insulation cover is 780~850℃, and the wire rod is slowly cooled at a speed of ≤1℃ / s in the insulation cover.

[0050] The obtained hot-rolled wire rod is drawn with a 38.12% reduction rate, spheroidized annealing at 935℃ for 8 hours, and slowly cooled in the furnace with a cooling rate controlled below 10℃ / h until it is cooled to below 200℃. The reduction rate of the finished product is 6.66%r.

[0051] The steel formed by the above manufacturing process has good hardenability, excellent surface quality, good plasticity and low deformation resistance. The deformation amount is 93% and then carburized at 950℃ for 3 hours without mixed crystals. Its spheroidization rate, mechanical properties and cracking ratio are shown in Table 1.

[0052] Example 2

[0053] The carburizing steel wire for large deformation cold working involved in this embodiment contains the following components and their mass percentages: C: 0.10%, Si: 0.06%, Mn: 0.54%, P: 0.015%, S: 0.002%, Cr: 0.27%, Ni: 0.13%, Mo: 0.02%, Al: 0.047%, N: 0.0110%, Nb: 0.02%, and the balance is iron and unavoidable impurity elements.

[0054] The production process of carburizing steel wire for large deformation cold working is as follows:

[0055] According to the chemical composition, the smelting raw materials are configured and carried out in sequence: BOF converter smelting → LF refining → RH vacuum degassing → continuous casting (the continuous casting billet specification is 390*510mm 2 )→ continuous casting billet heating→ billet opening (intermediate billet specification 200*200mm 2 )→intermediate billet surface treatment→wire heating→high-pressure water descaling→controlled rolling and controlled cooling→pickling and coating→rough drawing→annealing→pickling and phosphorus saponification→finishing drawing→finished product.

[0056] The specific process of the above-mentioned heating, rolling and cooling stages is as follows: heating the intermediate billet to 1045℃ and keeping it warm for 55 minutes, the residual oxygen content in the furnace is 1.1%, descaling is carried out with high-pressure water after being taken out of the furnace, and then rolling is carried out, the rough rolling start temperature is 965℃, and the total compression ratio is 65%; the finishing rolling temperature is 955℃, and the total compression ratio of the intermediate and finishing rolling is 99.6%; the sizing temperature is 953℃, and the compression ratio of the last two passes is 43%; the wire drawing temperature is 933℃, the roller speed is 0.25m / s, two initial insulation covers are opened, and the other insulation covers are closed. The wire rod coil is first quickly cooled on the roller, and then slowly cooled in the cover.

[0057] The obtained hot-rolled wire rod is rough-drawn with a 27.75% area reduction, annealed at 935°C for 8 hours, and cooled to below 200°C using a furnace slow cooling process with a cooling rate controlled at 15°C / h. The finished product has a 5.8% area reduction.

[0058] The steel formed by the above manufacturing process has good hardenability, excellent surface quality, good plasticity and low deformation resistance. After 88% cold working and carburization at 940℃ for 3 hours, no mixed crystals appear. Its spheroidization rate, mechanical properties and cracking ratio are shown in Table 1.

[0059] Example 3

[0060] The carburizing steel wire for large deformation cold working involved in this embodiment contains the following components and their mass percentages: C: 0.09%, Si: 0.05%, Mn: 0.55%, P: 0.011%, S: 0.002%, Cr: 0.28%, Ni: 0.12%, Cu: 0.02%, Mo: 0.04%, Al: 0.046%, N: 0.0100%, Nb: 0.02%, and the balance is iron and unavoidable impurity elements.

[0061] The production process of carburizing steel wire for large deformation cold working is as follows:

[0062] According to the chemical composition, the smelting raw materials are configured and carried out in sequence: BOF converter smelting → LF refining → RH vacuum degassing → continuous casting (the continuous casting billet specification is 390*510mm 2 )→ continuous casting billet heating→ billet opening (intermediate billet specification 200*200mm 2 )→intermediate billet surface treatment→wire heating→high-pressure water descaling→controlled rolling and controlled cooling→pickling and coating→rough drawing→annealing→pickling and phosphorus saponification→finishing drawing→finished product.

[0063] The specific process of the above-mentioned heating, rolling and cooling stages is as follows: heating the intermediate billet to 1088°C and keeping it warm for 58 minutes, the residual oxygen content in the furnace is 3.4%, descaling is carried out with high-pressure water after being taken out of the furnace, and then rolling is carried out, the rough rolling start temperature is 975°C, the total compression ratio is 68%; the finishing rolling temperature is 953°C, the total compression ratio of the intermediate and finishing rolling is 96.5%; the sizing temperature is 947°C, and the compression ratio of the last two passes is 34%; the wire drawing temperature is 923°C, the roller speed is 0.30m / s, 3 initial insulation covers are opened, and the remaining insulation covers are closed.

[0064] The obtained hot-rolled wire rod is drawn with a 28.4% area reduction rate, annealed at 935°C for 8 hours, and slowly cooled in the furnace with a cooling rate controlled at 15°C / h until it is cooled to below 200°C. The area reduction rate of the finished product is 5.38%.

[0065] The steel formed by the above manufacturing process has good hardenability, excellent surface quality, good plasticity and low deformation resistance. No mixed crystals appear when the deformation is 85% cold worked and carburized at 940℃ for 2 hours. The spheroidization rate, mechanical properties and cracking ratio are shown in Table 1.

[0066] Table 1

[0067]

Claims

1. A method for manufacturing carburized steel wire rod for large deformation cold working, characterized in that: The chemical composition wt% of the wire rod is C: 0.08-0.12%, Si: ≤0.10%, Mn: 0.50-0.70%, P: ≤0.025%, S: ≤0.010%, Cr: 0.25-0.35%, Ni: 0.10-0.20%, Mo: 0.01-0.10%, Al: 0.025-0.060%, N: 0.0050-0.0150%, Nb: 0.01-0.05%, and the rest is Fe and unavoidable impurities; The method steps include: Step 1: Smelting and casting: smelting molten steel according to the chemical composition of the wire rod and casting to obtain steel billets; Step 2: Billeting: The steel billet is rolled to obtain an intermediate billet, and the intermediate billet is surface treated; Step 3, wire rolling: the intermediate billet is heated in a heating furnace, the temperature of the high temperature section is controlled at 1010℃~1100℃, the holding time of the high temperature section is not less than 45min, the residual oxygen content in the furnace is ≤4.0%, so that the alloy elements are fully dissolved and evenly distributed; after the holding is completed, the intermediate billet is taken out of the furnace to remove the scale and surface oxide layer, and then rolled, rough rolling stage: the rolling temperature is 900~1000℃, the total compression ratio is ≥65%; secondary descaling is performed before intermediate rolling; finishing rolling stage: the finishing rolling temperature is 900~960℃, the total compression ratio is ≥95%; the temperature of the sizing mill is 930~9 60℃, the compression ratio of the last two passes is ≥30%; after sizing, the wire rod is spun at a temperature of 880℃~950℃. After spun, the wire rod coil is cooled by slow cooling. The roller speed of the wire rod coil is set to 0.10m / s~0.35m / s. Initially, 2~4 insulation covers are opened. The cooling rate of the wire rod at this stage is ensured to be ≥1.5℃ / s. The temperature of the wire rod entering the insulation cover is controlled to be 780~850℃. The other insulation covers are closed. The residence time of the wire rod in the insulation cover is controlled to be more than 11 minutes. The cooling rate of the wire rod in the insulation cover is ensured to be ≤1℃ / s. Step 4, deep processing: pickling the wire rod and then applying lime or phosphorus saponification coating, rough drawing, controlling the wire drawing reduction rate at 20-50%, spheroidizing annealing after wire drawing, introducing protective gas into the annealing furnace, controlling the oxygen content in the furnace below 20ppm, controlling the dew point below -50°C to prevent decarburization from increasing, heating to 730-740°C, keeping warm for 5-9 hours, controlling cooling, adopting the slow cooling method in the furnace, controlling the cooling rate at 10-20°C / h, slowly cooling to below 200°C and taking out of the furnace; pickling and phosphorus saponification coating before wire drawing, controlling the fine drawing reduction rate at 3-10%, the metallographic structure of the obtained carburized steel wire rod is spherical pearlite, the spheroidization rate is ≥95%, and the grain size is 7-9.

2. The method according to claim 1, wherein: The specifications of the carburizing steel wire rod are Φ4.0~Φ20mm.

3. The method according to claim 1, wherein: The obtained carburized steel wire rod has a tensile strength of ≤400MPa, a surface reduction of ≥70%, a deformation of more than 80%, and no mixed crystals appear when carburized in a temperature range of 930°C to 950°C for 1-3 hours after cold working.

4. The method according to claim 1, wherein: Step 1: The molten steel is smelted using high-quality molten iron, scrap steel and raw and auxiliary materials to reduce the content of harmful elements in the molten steel. The molten steel smelting involves primary smelting in a converter, LF refining, vacuum degassing and argon blowing and stirring. The converter slag is used to remove C and P, and the purpose of tapping is to avoid slagging. One of the purposes of vacuum treatment is to control the hydrogen content below 1.0ppm. The molten steel is cast into steel billets using a continuous casting process. The pouring superheat during the continuous casting process does not exceed 35°C. Soft pressure and electromagnetic stirring are implemented in the continuous casting process to improve the segregation of the cast billets. Protective casting is used throughout the continuous casting process to isolate the cast billets from air to prevent secondary oxidation.

5. The method according to claim 1, wherein: Step 2: The continuous casting billet is heated in a heating furnace at a temperature of 1150-1270°C to fully dissolve the alloy components in the steel and then cut into 150mm billets. 2 ~200mm 2 The intermediate billet is taken off the line and slowly cooled after the billet is opened.

Images