Tool steel wire rod and production process thereof

Abstract

The invention relates to a tool steel wire rod and a production process thereof. The tool steel wire rod comprises the following chemical components in percentage by mass: 1.12%-1.23% of C, 0.15%-0.32% of Si, 0.15%-0.40% of Mn, 0.0050%-0.013% of P, 0.0040%-0.015% of S, 0.0025%-0.0040% of N, 0.0005%-0.0018% of W, 0.0004%-0.0021% of Sb and the balance of Fe and inevitable impurities. For the tool steel wire rod with the carbon content of about 1.2%, systematic design is conducted from the aspects of chemical components, the smelting process and the rolling process, continuous casting is adopted to replace a traditional die casting production process, the macroporosity and the shrinkage cavity grade of a continuous casting blank are both not larger than 1.0 grade, and efficient production of the ultrahigh-carbon tool steel wire rod is achieved.

Description

Technical Field

[0001] This invention relates to the field of wire rod production technology, and in particular to a tool steel wire rod and its production process. Background Technology

[0002] High-strength tool steel wire is a wire product made of tool steel through special processing. It combines the excellent properties of tool steel (high hardness, high wear resistance, good red hardness, etc.) with the geometric shape of wire. It is suitable for precision wire applications that require high strength, wear resistance, and heat resistance, and has broad application prospects.

[0003] Currently, tool steel wire rods with a carbon content of around 1.2% are mainly produced using die casting, which results in high production costs and low production efficiency. Replacing die casting with continuous casting would help reduce production costs and improve production efficiency.

[0004] Chinese invention patent CN117051308B discloses a "method for producing tool steel wire rod". The production process includes hot metal pretreatment, converter smelting, CAS refining, LF refining, continuous casting, slow cooling of continuously cast billets in the pit, grinding of continuously cast billets, heating, rolling, cooling, finished product inspection, and warehousing. The chemical composition of the steel by weight percentage is: C=0.65~0.75, Si=1.00~1.40, Mn=0.50~0.80, P≤0.025, S≤0.025, Cr=0.30~0.60, Mo=0.40~0.50, V=0.10~0.25, Ni=0.10~0.30, Nb=0.010~0.030, with the remainder being Fe and a small amount of impurities. By slow cooling, grinding, heating, rolling, and controlled cooling of the cast billet, hot-rolled wire rods form a bainitic + martensitic structure, preventing spontaneous breakage after bundling. However, the carbon content in this wire rod is only 0.65% to 0.75%, making it unsuitable for the production of ultra-high carbon tool steel wire rods with a carbon content of around 1.2%. Summary of the Invention

[0005] This invention provides a tool steel wire rod and its production process. For tool steel wire rod with a carbon content of about 1.2%, a systematic design is carried out from the aspects of chemical composition, smelting process and rolling process. Continuous casting is adopted to replace the traditional mold casting production process. The low porosity and shrinkage cavity grade of the continuous casting billet are no greater than grade 1.0, and the high-efficiency production of ultra-high carbon tool steel wire rod is achieved.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A tool steel wire rod, the chemical composition of which, by mass percentage, is: C: 1.12%–1.23%, Si: 0.15%–0.32%, Mn: 0.15%–0.40%, P: 0.0050%–0.013%, S: 0.0040%–0.015%, N: 0.0025%–0.0040%, W: 0.0005%–0.0018%, Sb: 0.0004%–0.0021%, with the balance being Fe and unavoidable impurities.

[0008] The tensile strength of the wire rod is 980-1040 MPa.

[0009] The finished wire rod specifications are ø12~ø16mm.

[0010] A manufacturing process for tool steel wire rod includes the following steps:

[0011] 1) Smelting and continuous casting: After smelting in the converter, the oxygen activity of the molten steel is controlled at 120-200 ppm; the LF refining time is controlled at 35-55 min, and the LF refining temperature is controlled at 1490-1540℃; argon blowing and stirring are carried out during the refining process, and the argon flow rate is 100-300 NL / min; the cross-sectional size of the continuously cast billet is 300-340 mm × 390-420 mm; the refractory material of the tundish nozzle is Al2O3≥85% and SiO2≤10% by mass percentage; the tundish slide plate is Al2O3≥80% and SiO2≤10% by mass percentage; the continuous casting speed is controlled at 0.45-0.55 m / min, the continuous casting superheat is ≤30℃, and the fluctuation of the molten steel surface in the crystallizer is controlled within ±3 mm.

[0012] 2) Rolling of continuously cast billets: Rolling the continuously cast billets into square billets of 150-170mm × 150-170mm;

[0013] 3) Wire rod rolling: The billet is heated in the heating furnace for a total heating time of 210–260 min, with a soaking temperature of 1070–1090℃ and a soaking time of 60–70 min. After heating, the billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling before wire rod production. The wire rod exiting the pre-finishing mill has a temperature of 980–995℃; entering the finishing mill has a temperature of 870–910℃; and entering the twin-module mill has a temperature of 880–900℃. The twin-module rolling speed is 20–24 m / s, and the deformation in the last pass is 5%–15%. The wire rod production temperature is controlled at 880–900℃.

[0014] 4) Wire rod cooling: After spinning, the wire rod is cooled on an air-cooled roller conveyor, and the phase change temperature is controlled at 670-690℃ and the phase change time is 30-45s.

[0015] The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 12% of the total weight. The scrap steel contains Cr ≤ 0.06% and Ni ≤ 0.08% by mass percentage.

[0016] Before LF refining, the molten steel ladle is preheated for no less than 6 hours.

[0017] The low porosity grade of the continuously cast billet is ≤1.0, and the shrinkage grade is ≤1.0.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] For tool steel wire rods with a carbon content of around 1.2%, a systematic design was carried out in terms of chemical composition, smelting process and rolling process. Continuous casting was adopted to replace the traditional ingot casting production process. The low porosity and shrinkage cavity grade of the continuous casting billet are no greater than grade 1.0, and the high-efficiency production of ultra-high carbon tool steel wire rods was achieved. Detailed Implementation

[0020] The tool steel wire rod of the present invention has the following chemical composition by mass percentage: C: 1.12%–1.23%, Si: 0.15%–0.32%, Mn: 0.15%–0.40%, P: 0.0050%–0.013%, S: 0.0040%–0.015%, N: 0.0025%–0.0040%, W: 0.0005%–0.0018%, Sb: 0.0004%–0.0021%, with the balance being Fe and unavoidable impurities.

[0021] The rationale for selecting the chemical composition and content of the tool steel wire rod described in this invention, as well as the role of each element, are as follows:

[0022] Excessive carbon content in wire rod will cause the tool steel processed from it to exceed the required hardness; conversely, insufficient carbon content will fail to meet the hardness requirements for tool steel. Therefore, this invention controls the carbon content in the wire rod to be between 1.12% and 1.23%.

[0023] Silicon increases the eutectoid transformation temperature of steel, resulting in coarse pearlite structure in wire rod, which is detrimental to the complex deformation processes of high-carbon tool steel. Simultaneously, silicon is a major deoxidizing element in high-carbon steel; however, excessive silicon content leads to coarse silicates and impurities after deoxidation, while insufficient silicon content reduces the deformation capacity of tool steel during processing. Therefore, this invention controls the silicon content in wire rod to 0.15%–0.32%.

[0024] Manganese is an element that improves the strength of wire rod, which helps ensure that tool steel processed from wire rod meets hardness requirements. Manganese also lowers the eutectoid transformation temperature of steel, refines the pearlite structure of wire rod, and improves the deformation capacity during the processing of wire rod into tool steel. Furthermore, manganese can reduce the tendency for leakage during continuous casting. Therefore, this invention controls the manganese content in wire rod to be between 0.15% and 0.40%.

[0025] Phosphorus reduces the deformation capacity of wire rod during the processing into tool steel, causing cracking and breakage of the steel wire. Therefore, the present invention controls the phosphorus content in wire rod to be between 0.0050% and 0.013%.

[0026] High sulfur content in steel reduces the cold working performance of wire rod. However, since MnS inclusions have good deformability, an appropriate amount of sulfur in the steel can reduce the harm of crystalline inclusions. Therefore, this invention controls the sulfur content in the wire rod to 0.0040% to 0.015%.

[0027] Nitrogen can cause work hardening during the machining process of tool steel, which is detrimental to improving the machinability of tool steel. However, a certain amount of nitrogen can form precipitates in steel, which can inhibit the propagation of microcracks in the steel and reduce the crack sensitivity of tool steel. Therefore, this invention controls the nitrogen content in wire rod to be between 0.0025% and 0.0040%.

[0028] Tungsten dissolves in iron to form a solid solution, which reduces the strength difference between ferrite and cementite in the sorbite structure, lowers the risk of microcracks during the processing of wire rod into tool steel, and improves the cold working performance of the wire rod. Tungsten also improves the smoothness of continuous casting and eliminates the possibility of leakage during high-temperature casting. However, excessively high tungsten content in the wire rod leads to excessive work hardening during the drawing process, which is detrimental to improving the wire rod's machinability. Therefore, this invention controls the tungsten content in the wire rod to between 0.0005% and 0.0018%.

[0029] Antimony can impart a certain degree of corrosion resistance to high-carbon tool steel, reduce the oxidation rate of wire rod during the oxidation process, and improve the mechanical descaling performance of iron oxide scale on wire rod, thus improving the mechanical descaling performance of wire rod without acid washing. Therefore, this invention controls the antimony content in wire rod to be between 0.0004% and 0.0021%.

[0030] The manufacturing process of tool steel wire rod according to the present invention includes the following steps:

[0031] 1) Smelting and continuous casting: After smelting in the converter, the oxygen activity of the molten steel is controlled at 120-200 ppm; the LF refining time is controlled at 35-55 min, and the LF refining temperature is controlled at 1490-1540℃; argon blowing and stirring are carried out during the refining process, and the argon flow rate is 100-300 NL / min; the cross-sectional size of the continuously cast billet is 300-340 mm × 390-420 mm; the refractory material of the tundish nozzle is Al2O3≥85% and SiO2≤10% by mass percentage; the tundish slide plate is Al2O3≥80% and SiO2≤10% by mass percentage; the continuous casting speed is controlled at 0.45-0.55 m / min, the continuous casting superheat is ≤30℃, and the fluctuation of the molten steel surface in the crystallizer is controlled within ±3 mm.

[0032] 2) Rolling of continuously cast billets: Rolling the continuously cast billets into square billets of 150-170mm × 150-170mm;

[0033] 3) Wire rod rolling: The billet is heated in the heating furnace for a total heating time of 210–260 min, with a soaking temperature of 1070–1090℃ and a soaking time of 60–70 min. After heating, the billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling before wire rod production. The wire rod exiting the pre-finishing mill has a temperature of 980–995℃; entering the finishing mill has a temperature of 870–910℃; and entering the twin-module mill has a temperature of 880–900℃. The twin-module rolling speed is 20–24 m / s, and the deformation in the last pass is 5%–15%. The wire rod production temperature is controlled at 880–900℃. Setting a higher production temperature helps to increase the cooling rate of the wire rod on the air-cooled roller table, thus laying the foundation for controlling the final microstructure of the wire rod.

[0034] 4) Wire rod cooling: After spinning, the wire rod is cooled on an air-cooled roller conveyor, and the phase change temperature is controlled at 670-690℃ and the phase change time is 30-45s.

[0035] The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 12% of the total weight. The scrap steel contains Cr ≤ 0.06% and Ni ≤ 0.08% by mass percentage.

[0036] Before LF refining, the molten steel ladle is preheated for no less than 6 hours.

[0037] The low porosity grade of the continuously cast billet is ≤1.0, and the shrinkage grade is ≤1.0.

[0038] The finished wire rod specifications are ø12~ø16mm. The tensile strength of the wire rod is 980~1040MPa.

[0039] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0040] Example:

[0041] The chemical composition of the tool steel wire rods in each embodiment is shown in Table 1, the production process parameters are shown in Table 2, and the performance of the finished product is shown in Table 3.

[0042] Table 1 Chemical composition of tool steel wire rod (mass percentage, %)

[0043]

[0044] Table 2. Production process parameters for tool steel wire rod

[0045]

[0046] Table 3 Performance of Finished Tool Steel Wire Rods

[0047]

[0048] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A tool steel wire rod, characterized in that, The chemical composition of the wire rod, by mass percentage, is: C: 1.12%–1.23%, Si: 0.15%–0.32%, Mn: 0.15%–0.40%, P: 0.0050%–0.013%, S: 0.0040%–0.015%, N: 0.0025%–0.0040%, W: 0.0005%–0.0018%, Sb: 0.0004%–0.0021%, with the balance being Fe and unavoidable impurities.

2. The tool steel wire rod according to claim 1, characterized in that, The tensile strength of the wire rod is 980-1040 MPa.

3. The tool steel wire rod according to claim 1, characterized in that, The finished wire rod specifications are ø12~ø16mm.

4. A manufacturing process for tool steel wire rod as described in claim 1, 2, or 3, characterized in that, The process includes the following: 1) Smelting and continuous casting: After smelting in the converter, the oxygen activity of the molten steel is controlled at 120-200 ppm; the LF refining time is controlled at 35-55 min, and the LF refining temperature is controlled at 1490-1540℃; argon blowing and stirring are carried out during the refining process, and the argon flow rate is 100-300 NL / min; the cross-sectional size of the continuously cast billet is 300-340 mm × 390-420 mm; the refractory material of the tundish nozzle is Al2O3≥85% and SiO2≤10% by mass percentage; the tundish slide plate is Al2O3≥80% and SiO2≤10% by mass percentage; the continuous casting speed is controlled at 0.45-0.55 m / min, the continuous casting superheat is ≤30℃, and the fluctuation of the molten steel surface in the crystallizer is controlled within ±3 mm. 2) Rolling of continuously cast billets: Rolling the continuously cast billets into square billets of 150-170mm × 150-170mm; 3) Wire rod rolling: The billet is heated in the heating furnace for a total heating time of 210–260 min, with a soaking temperature of 1070–1090℃ and a soaking time of 60–70 min. After heating, the billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling before wire rod production. The wire rod exiting the pre-finishing mill has a temperature of 980–995℃; entering the finishing mill has a temperature of 870–910℃; and entering the twin-module mill has a temperature of 880–900℃. The twin-module rolling speed is 20–24 m / s, and the deformation in the last pass is 5%–15%. The wire rod production temperature is controlled at 880–900℃. 4) Wire rod cooling: After spinning, the wire rod is cooled on an air-cooled roller conveyor, and the phase change temperature is controlled at 670-690℃ and the phase change time is 30-45s.

5. The manufacturing process of tool steel wire rod according to claim 4, characterized in that, The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 12% of the total weight. The scrap steel contains Cr ≤ 0.06% and Ni ≤ 0.08% by mass percentage.

6. The manufacturing process of tool steel wire rod according to claim 4, characterized in that, Before LF refining, the molten steel ladle is preheated for no less than 6 hours.

7. The manufacturing process of tool steel wire rod according to claim 4, characterized in that, The low porosity grade of the continuously cast billet is ≤1.0, and the shrinkage grade is ≤1.0.

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