Tool steel wire rod and production method for controlling segregation of continuous casting billet

Abstract

The invention relates to a tool steel wire rod and a production method for controlling segregation of a continuous casting billet. The tool steel wire rod comprises the following chemical components in percentage by mass: 1.10%-1.20% of C, 0.10%-0.35% of Si, 0.10%-0.30% of Mn, 0.0040%-0.015% of P, 0.0030%-0.014% of S, 0.00050%-0.0018% of As, 0.0005%-0.0020% of W, 0.00004%-0.0005% of Se and the balance of Fe and inevitable impurities. According to the method, system design is conducted on the ultrahigh-carbon tool steel wire rod with the carbon content being about 1.2% from the aspects of chemical components, the smelting process and the rolling process, continuous casting is adopted for replacing a traditional die casting production process, the carbon segregation index of a continuous casting blank does not exceed 1.07, and segregation of the continuous casting blank is effectively controlled.

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 a production method for controlling segregation in continuously cast billets. 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 patent application CN114318125A discloses a "high-strength and high-toughness alloy tool steel wire", which, in addition to Fe, contains the following chemical elements in the following mass percentages: C: 0.60-0.90 wt.%, Si: 1.00-3.00 wt.%, Mn: 0.45-1.00 wt.%, Cr: 0.45-1.00 wt.%, Mo: 0.20-0.60 wt.%; the microstructure of the high-strength and high-toughness alloy tool steel wire is tempered martensite + dispersed spherical carbides. The manufacturing method of high-strength and high-toughness alloy tool steel wire includes the following steps: (1) smelting, casting, and rolling into wire rod; (2) offline spheroidizing annealing; (3) after processing into wire, heat treatment is carried out: heating to the austenitizing temperature of 820-960℃, holding for 0.5-1h, quenching and cooling to room temperature at a rate of 1-50℃ / s; reheating to 200-400℃ for tempering, holding for 0.5-3h. The high-strength and high-toughness alloy tool steel wire produced has excellent resistance to torsional fracture and can be applied in the field of hardware tools. It mainly focuses on the resistance to torsional fracture of tool steel wire, and the carbon content in the wire is only 0.60%-0.90%, which is not suitable for the production of tool steel wire with a carbon content of about 1.2%. Summary of the Invention

[0005] This invention provides a tool steel wire rod and a production method for controlling segregation in continuously cast billets. It systematically designs various aspects of ultra-high carbon tool steel wire rod with a carbon content of about 1.2%, including chemical composition, smelting process and rolling process. It adopts continuous casting instead of the traditional ingot casting production process, so that the carbon segregation index of the continuously cast billet does not exceed 1.07, effectively controlling the segregation of the continuously cast billet.

[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: 1.10%–1.20%, Si: 0.10%–0.35%, Mn: 0.10%–0.30%, P: 0.0040%–0.015%, S: 0.0030%–0.014%, As: 0.00050%–0.0018%, W: 0.0005%–0.0020%, Se: 0.00004%–0.0005%, with the balance being Fe and unavoidable impurities.

[0008] The tensile strength of wire rod is 980–1120 MPa.

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

[0010] A production method for controlling segregation in continuously cast billets using tool steel wire rod, the wire rod production process including steel smelting, continuous casting, continuous rolling, wire rod rolling, and wire rod cooling; details are as follows:

[0011] 1) Steelmaking: The sulfur content of the molten iron after desulfurization pretreatment is ≤0.0050%; the oxygen activity of the molten steel after converter smelting is controlled at 90-260ppm; the refining time in the LF furnace is controlled at 35-60min, and the refining temperature in the LF furnace is controlled at 1480-1570℃; argon blowing and stirring are carried out during the refining process, and the argon flow rate is 100-400NL / min.

[0012] 2) Continuous casting: The cross-sectional dimensions of the continuously cast billet are 300~340mm×390~420mm; the casting speed is controlled at 0.40~0.55m / min, the superheat is ≤25℃, the electromagnetic stirring current intensity of the crystallizer is 600~800A; the electromagnetic stirring current intensity at the end of solidification is 300~600A, and the stirring frequency is 3~5Hz;

[0013] 3) Continuous rolling: Rolling the continuously cast billet into a square billet with a cross-sectional size of 150-170mm × 150-170mm;

[0014] 4) Wire rod rolling: The billet is heated in the heating furnace for a total heating time of 220-260 minutes, with a soaking temperature of 1080-1120℃ and a soaking time of 55-65 minutes. 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 is at 970-990℃; the temperature entering the finishing mill is 870-920℃; and the temperature entering the double-module mill is 890-900℃. The deformation in the last pass of the double-module mill is 10%-15%. The wire rod production temperature is controlled at 880-910℃.

[0015] 5) Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The phase change temperature is controlled at 660-690℃ and the phase change time is controlled at 35-60s.

[0016] The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 10% of the total weight.

[0017] The carbon segregation index of the continuously cast billet is ≤1.07.

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

[0019] For ultra-high carbon tool steel wire rod with a carbon content of about 1.2%, a systematic design was carried out in terms of chemical composition, smelting process and rolling process. Continuous casting was adopted instead of the traditional ingot casting production process, so that the carbon segregation index of the continuous casting billet does not exceed 1.07, effectively controlling the segregation of the continuous casting billet. Detailed Implementation

[0020] The tool steel wire rod of the present invention has the following chemical composition by mass percentage: C: 1.10%–1.20%, Si: 0.10%–0.35%, Mn: 0.10%–0.30%, P: 0.0040%–0.015%, S: 0.0030%–0.014%, As: 0.00050%–0.0018%, W: 0.0005%–0.0020%, Se: 0.00004%–0.0005%, 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 user's hardness requirements and will severely worsen the segregation of continuously cast billets. Insufficient carbon content will fail to meet the hardness requirements of tool steel. Therefore, this invention controls the carbon content in the wire rod to be between 1.10% and 1.20%.

[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 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 0.10%–0.35%.

[0024] Manganese is an element that can improve the strength of wire rod, which helps ensure that the tool steel processed from wire rod meets the hardness requirements. Manganese also has the effect of lowering the eutectoid transformation temperature of steel, refining the pearlite structure of wire rod, and improving the deformation capacity during the processing of wire rod into tool steel. However, excessive manganese content can lead to increased segregation. Therefore, this invention controls the manganese content in wire rod to be between 0.10% and 0.30%.

[0025] Phosphorus reduces the deformability of wire rod during the processing into tool steel, causing cracking and breakage of the wire. Furthermore, excessively high phosphorus content in steel can lead to increased segregation. Therefore, this invention controls the phosphorus content in wire rod to between 0.0040% and 0.015%.

[0026] High sulfur content in steel reduces the cold working performance of wire rod, and excessive sulfur content can lead to increased segregation. However, since MnS inclusions have good deformability, an appropriate amount of sulfur in the steel can reduce the harm caused by crystalline inclusions. Therefore, this invention controls the sulfur content in the wire rod to 0.0030% to 0.014%.

[0027] Arsenic readily accumulates at grain boundaries in steel, reducing system energy, stabilizing austenite, and decreasing the grain size of the wire rod. Excessive arsenic content in steel reduces the drawing properties of the wire rod and the performance of the tool steel made from it. Therefore, this invention controls the arsenic content in the wire rod to between 0.0005% and 0.0018%.

[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. The combination of tungsten and carbon can, to some extent, reduce carbon diffusion and prevent excessive accumulation at grain boundaries, which could lead to severe precipitation of cementite and worsen the steel's microstructure segregation. However, if the tungsten content in the wire rod is too high, the work hardening during the drawing process becomes too significant, which is detrimental to improving the wire rod's processing performance. Therefore, this invention controls the tungsten content in the wire rod to be between 0.0005% and 0.0020%.

[0029] Selenium forms selenides in steel with elements such as manganese and niobium. These selenides are finer than sulfides and have a more significant inhibitory effect on the propagation of microcracks, reducing the crack susceptibility during the processing of wire rod into tool steel. However, excessively high selenium content in steel can reduce the drawing properties of the wire rod. Therefore, this invention controls the selenium content in the wire rod to between 0.00004% and 0.0005%.

[0030] The present invention discloses a production method for controlling segregation in continuously cast billets using tool steel wire rod. The wire rod production process includes steel smelting, continuous casting, continuous rolling, wire rod rolling, and wire rod cooling; specifically as follows:

[0031] 1) Steelmaking: The sulfur content of the molten iron is ≤0.0050% after desulfurization pretreatment; the oxygen activity of the molten steel is controlled at 90-260ppm after converter smelting; the refining time in the LF furnace is controlled at 35-60min, and the refining temperature in the LF furnace is controlled at 1480-1570℃; the refining process is stirred by argon blowing, and the argon flow rate is 100-400NL / min.

[0032] 2) Continuous casting: The cross-sectional dimensions of the continuously cast billet are 300~340mm×390~420mm; the casting speed is controlled at 0.40~0.55m / min, the superheat is ≤25℃, the electromagnetic stirring current intensity of the crystallizer is 600~800A; the electromagnetic stirring current intensity at the end of solidification is 300~600A, and the stirring frequency is 3~5Hz.

[0033] 3) Continuous rolling: Rolling the continuously cast billet into a square billet with a cross-sectional size of 150-170mm × 150-170mm.

[0034] 4) Wire rod rolling: The billet is heated in the heating furnace for a total heating time of 220-260 minutes, with a soaking temperature of 1080-1120℃ and a soaking time of 55-65 minutes. 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 970-990℃; entering the finishing mill has a temperature of 870-920℃; entering the double-module mill has a temperature of 890-900℃, with a deformation of 10%-15% in the final pass of the double-module mill. The wire rod production temperature is controlled at 880-910℃. 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.

[0035] 5) Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The phase change temperature is controlled at 660-690℃ and the phase change time is controlled at 35-60s.

[0036] The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 10% of the total weight.

[0037] The carbon segregation index of the continuously cast billet is ≤1.07, and the tensile strength of the wire rod is 980~1120MPa. The finished wire rod specifications are ø12~ø16mm.

[0038] 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.

[0039] Example:

[0040] The chemical composition of the tool steel wire rods in each embodiment is shown in Table 1, and the production process parameters and finished product performance are shown in Table 2.

[0041] Table 1 Chemical composition of tool steel wire rod (mass percentage, %)

[0042]

[0043] Table 2. Production process parameters and finished product performance of tool steel wire rod

[0044]

[0045] 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 production method for controlling segregation in continuously cast billets using tool steel wire rod, characterized in that, The chemical composition of the wire rod, by mass percentage, is: C: 1.10%–1.20%, Si: 0.10%–0.35%, Mn: 0.10%–0.30%, P: 0.0040%–0.015%, S: 0.0030%–0.014%, As: 0.00050%–0.0018%, W: 0.0005%–0.0020%, Se: 0.00004%–0.0005%, with the balance being Fe and unavoidable impurities. The wire rod production process includes steel smelting, continuous casting, continuous rolling, wire rod rolling, and wire rod cooling; details are as follows: 1) Steelmaking: The sulfur content of the molten iron after desulfurization pretreatment is ≤0.0050%; the oxygen activity of the molten steel after converter smelting is controlled at 90-260ppm; the refining time in the LF furnace is controlled at 35-60min, and the refining temperature in the LF furnace is controlled at 1480-1570℃; argon blowing and stirring are carried out during the refining process, and the argon flow rate is 100-400NL / min. 2) Continuous casting: The cross-sectional dimensions of the continuously cast billet are 300~340mm×390~420mm; the casting speed is controlled at 0.40~0.55m / min, the superheat is ≤25℃, the electromagnetic stirring current intensity of the crystallizer is 600~800A; the electromagnetic stirring current intensity at the end of solidification is 300~600A, and the stirring frequency is 3~5Hz; 3) Continuous rolling: Rolling the continuously cast billet into a square billet with a cross-sectional size of 150-170mm × 150-170mm; 4) Wire rod rolling: The billet is heated in the heating furnace for a total heating time of 220-260 minutes, with a soaking temperature of 1080-1120℃ and a soaking time of 55-65 minutes. 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 is at 970-990℃; the temperature entering the finishing mill is 870-920℃; and the temperature entering the double-module mill is 890-900℃. The deformation in the last pass of the double-module mill is 10%-15%. The wire rod production temperature is controlled at 880-910℃. 5) Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The phase change temperature is controlled at 660-690℃ and the phase change time is controlled at 35-60s.

2. The production method for controlling segregation of continuously cast billets using tool steel wire rod according to claim 1, characterized in that, The tensile strength of wire rod is 980–1120 MPa.

3. The production method for controlling segregation of continuously cast billets using tool steel wire rod according to claim 1, characterized in that, The finished wire rod specifications are ø12~ø16mm.

4. The production method for controlling segregation of continuously cast billets using tool steel wire rod according to claim 1, characterized in that, The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 10% of the total weight.

5. The production method for controlling segregation of continuously cast billets using tool steel wire rod according to claim 1, characterized in that, The carbon segregation index of the continuously cast billet is ≤1.07.

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