Tool steel wire rod and process for producing the same

Abstract

The present application relates to a kind of tool steel wire rod and its production process, wire rod chemical composition is according to 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%, the balance is Fe and inevitable impurities.For the tool steel wire rod of carbon content 1.2% or so, from chemical composition, smelting process and rolling process each aspect carries out system design, using continuous casting instead of traditional mould casting production process, the low multiple porosity and shrinkage hole grade of continuous casting billet are all not greater than 1.0 level, and high-efficiency production of super-high-carbon tool steel wire rod is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wire rod production, and in particular to a tool steel wire rod and a production process thereof. BACKGROUND

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

[0003] At present, tool steel wire rods with a carbon content of about 1.2% basically use die casting billets, which have the problems of high production cost and low production efficiency. If the continuous casting process is used instead of the die casting process, it will help to reduce production cost and improve production efficiency.

[0004] A Chinese invention patent with the authorized announcement number CN117051308B discloses a "production method of tool steel wire rod". The production process flow includes hot metal pretreatment, converter smelting, CAS refining, LF refining, continuous casting, pit slow cooling of continuous casting billets, continuous casting billet grinding, 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, and the rest is Fe and a small amount of impurities. Through slow cooling, grinding, heating, rolling and controlled cooling of the casting billet, the hot-rolled wire rod forms a bainite + martensite structure, preventing the finished wire rod from being self-cut after baling. However, the carbon content in the wire rod is only 0.65%-0.75%, which is not suitable for the production of ultra-high carbon tool steel wire rod with a carbon content of about 1.2%. SUMMARY

[0005] The present application provides a tool steel wire rod and a production process thereof. For tool steel wire rods with a carbon content of about 1.2%, the chemical composition, smelting process and rolling process are systematically designed. The continuous casting process is used instead of the traditional die casting production process. The macroscopic porosity and shrinkage hole grade of the continuous casting billet are not greater than 1.0 grade, and the efficient production of ultra-high carbon tool steel wire rod is realized.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0007] A tool steel wire rod, the wire rod chemical composition in terms of 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%, the balance of Fe and inevitable impurities.

[0008] The wire rod tensile strength is 980~1040MPa.

[0009] The wire rod finished product specification is ø12~ø16mm.

[0010] A tool steel wire rod production process, comprising the following processes:

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

[0012] 2) continuous casting billet rolling: the continuous casting billet is rolled into 150~170mm×150~170mm square billet;

[0013] 3) wire rod rolling: the billet is heated into the heating furnace, the total heating time is 210~260min, the soaking section temperature is 1070~1090℃, and the soaking section holding time is 60~70min; after the heated billet is subjected to rough rolling, intermediate rolling, pre-precision rolling and precision rolling, the wire rod is operated; the temperature of the wire rod when it comes out of the pre-precision rolling mill is 980~995℃; the temperature when it enters the precision rolling mill is 870~910℃, and the temperature when it enters the double module rolling mill is 880~900℃; the double module rolling speed is 20~24m / s, and the last pass rolling deformation is 5%~15%; the wire rod spinning temperature is controlled at 880~900℃;

[0014] 4) wire rod cooling: the wire rod after spinning is cooled on the air cooling roller way, the phase change temperature is controlled at 670~690℃, and the phase change time is 30~45s.

[0015] The weight ratio of scrap steel is 5%-12%, and the mass percentage of Cr in the scrap steel is less than or equal to 0.06%, and the mass percentage of Ni in the scrap steel is less than or equal to 0.08%.

[0016] The LF refining ladle is pre-baked, and the baking time is not less than 6h.

[0017] The macroscopic porosity grade of the continuous casting billet is less than or equal to 1.0, and the shrinkage hole grade is less than or equal to 1.0.

[0018] Compared with the prior art, the tool steel wire rod has the following beneficial effects:

[0019] The tool steel wire rod is designed from the aspects of chemical composition, smelting process and rolling process, the traditional mold casting production process is replaced by the continuous casting process, the macroscopic porosity and shrinkage hole grade of the continuous casting billet are both less than or equal to 1.0, and the high-efficiency production of the ultra-high carbon tool steel wire rod is realized. DETAILED DESCRIPTION

[0020] The tool steel wire rod has the following chemical composition: the mass percentage of C is 1.12%-1.23%, the mass percentage of Si is 0.15%-0.32%, the mass percentage of Mn is 0.15%-0.40%, the mass percentage of P is 0.0050%-0.013%, the mass percentage of S is 0.0040%-0.015%, the mass percentage of N is 0.0025%-0.0040%, the mass percentage of W is 0.0005%-0.0018%, the mass percentage of Sb is 0.0004%-0.0021%, and the rest is Fe and inevitable impurities.

[0021] The selection reasons of the chemical composition and content of the tool steel wire rod and the effects of the elements are as follows:

[0022] If the carbon content in the wire rod is too high, the hardness of the tool steel processed from the wire rod will exceed the requirement; if the carbon content in the wire rod is too low, the hardness requirement of the tool steel cannot be met; therefore, the carbon content in the wire rod is controlled to be 1.12%-1.23%.

[0023] The eutectoid transformation temperature of the steel is increased by the silicon element, which leads to the coarse pearlite structure of the wire rod, and is not conducive to the complex deformation in the processing of the high-carbon tool steel; meanwhile, the silicon is the main deoxidizing element in the high-carbon steel, but if the silicon content in the steel is too high, coarse silicates and impurities will appear after the deoxidization of the molten steel, and if the silicon content is too low, the deformation ability of the tool steel in the processing will be reduced due to the insufficient deoxidization of the molten steel; therefore, the silicon content in the wire rod is controlled to be 0.15%-0.32%.

[0024] Manganese is an element that can improve the strength of wire rod, and is beneficial to ensure that the tool steel processed from the wire rod meets the hardness requirement; the manganese element also has the effect of reducing the eutectoid transformation temperature of the steel, can refine the pearlite structure of the wire rod, and improve the deformation capacity of the wire rod in the process of being processed into tool steel. In addition, the manganese element can also reduce the trend of leakage in the continuous casting process. Therefore, the content of manganese in the wire rod is controlled at 0.15% to 0.40% in the application.

[0025] Phosphorus can reduce the deformation capacity of the wire rod in the process of being processed into tool steel, and cause the wire to crack and break, so the content of phosphorus in the wire rod is controlled at 0.0050% to 0.013% in the application.

[0026] Higher sulfur content in the steel can reduce the cold working performance of the wire rod. However, since the MnS inclusions have good deformation capacity, a proper amount of sulfur in the steel can reduce the harm of the spinel inclusions, so the content of sulfur in the wire rod is controlled at 0.0040% to 0.015% in the application.

[0027] Nitrogen element can cause work hardening in the process of tool steel processing, which is not conducive to the improvement of the processing performance of tool steel. However, a certain amount of nitrogen in the steel can form precipitates, which can inhibit the expansion of micro-cracks in the steel and reduce the crack sensitivity of the tool steel. Therefore, the content of nitrogen in the wire rod is controlled at 0.0025% to 0.0040% in the application.

[0028] Tungsten element dissolves into iron to form a solid solution, which can reduce the strength difference between ferrite and cementite in sorbite structure, reduce the risk of micro-cracks in the process of wire rod being processed into tool steel, and improve the cold working performance of the wire rod. Tungsten element can also improve the smoothness of continuous casting and eliminate the possibility of leakage of continuous casting billet at high temperature. However, if the content of tungsten in the wire rod is too high, the work hardening in the process of wire rod drawing is too significant, which is not conducive to the improvement of the processing performance of the wire rod. Therefore, the content of tungsten in the wire rod is controlled at 0.0005% to 0.0018% in the application.

[0029] Antimony can make high-carbon tool steel have certain corrosion resistance, reduce the oxidation rate of the wire rod in the oxidation process, and is beneficial to the improvement of the mechanical phosphorus removal performance of the wire rod after oxidation scale, and the improvement of the mechanical phosphorus removal performance of the wire rod without pickling. Therefore, the content of antimony in the wire rod is controlled at 0.0004% to 0.0021% in the application.

[0030] The production process of the tool steel wire rod in the application includes the following processes:

[0031] 1) Smelting and continuous casting: the oxygen activity of the molten steel is controlled at 120-200 ppm after converter smelting; the LF refining time is controlled at 35-55 min, and the LF refining temperature is controlled at 1490-1540°C; argon is blown and stirred during the refining process, and the argon flow rate is 100-300 NL / min; the cross-sectional size of the continuous casting billet is 300-340 mm x 390-420 mm; the refractory material in the tundish top nozzle contains Al2O3≥85% and SiO2≤10% by mass percentage; the tundish slide contains 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°C, and the crystallizer molten steel liquid level fluctuation is controlled within ±3 mm;

[0032] 2) Continuous casting billet rolling: the continuous casting billet is rolled into a square billet with a size of 150-170 mm x 150-170 mm;

[0033] 3) Wire rod rolling: the billet is heated in a heating furnace, the total heating time is 210-260 min, the soaking section temperature is 1070-1090°C, and the soaking section holding time is 60-70 min; after the heated billet is subjected to rough rolling, intermediate rolling, pre-precision rolling, and precision rolling, wire rod is drawn; the temperature of the wire rod when it comes out of the pre-precision rolling mill is 980-995°C; the temperature when it enters the precision rolling mill is 870-910°C, and the temperature when it enters the double-module rolling mill is 880-900°C; the double-module rolling speed is 20-24 m / s, and the last pass rolling deformation is 5%-15%; the wire rod drawing temperature is controlled at 880-900°C; by setting a higher drawing temperature, the cooling speed of the wire rod on the air cooling roller is improved, thereby laying a foundation for controlling the final structure of the wire rod.

[0034] 4) Wire rod cooling: the wire rod after drawing is cooled on the air cooling roller, and the phase transition temperature is controlled at 670-690°C, and the phase transition time is 30-45 s.

[0035] The molten iron + scrap steel is smelted, and the weight ratio of scrap steel is 5%-12%, and the mass percentage of Cr in the scrap steel is ≤0.06%, and the mass percentage of Ni is ≤0.08%.

[0036] The molten steel ladle is pre-baked before LF refining, and the baking time is not less than 6 h.

[0037] The macroscopic porosity grade of the continuous casting billet is ≤1.0 grade, and the shrinkage hole grade is ≤1.0 grade.

[0038] The finished wire rod specification is ø12-ø16 mm. The tensile strength of the wire rod is 980-1040 MPa.

[0039] In order to more directly reflect the present application, the embodiments of the present application are further described in combination with examples. The following examples are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can obviously obtain the technical solutions within the technical range disclosed by the present application, including simple changes or equivalent replacements, which are all within the protection scope of the present application.

[0040] Examples:

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

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

[0043]

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

[0045]

[0046] Table 3 Finished product performance of tool steel wire rod

[0047]

[0048] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can obviously obtain the technical solutions within the technical range disclosed by the present application, including simple changes or equivalent replacements, which are all within the protection scope of the present application.

Claims

1. A process for the production of a tool steel wire rod, characterized in that, The chemical composition of the wire rod is as follows in percentage by mass: 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%, and the balance of Fe and inevitable impurities; the finished wire rod has a size of ø12-ø16mm; The production process of the tool steel wire rod comprises the following steps: 1) smelting and continuous casting: the oxygen activity of the molten steel is controlled at 120-200ppm after the molten steel is smelted by a converter; the LF refining time is controlled at 35-55min, and the LF refining temperature is controlled at 1490-1540℃; argon is blown and stirred during the refining process, and the argon flow is 100-300NL / min; the cross section size of the continuous casting billet is 300-340mm×390-420mm; the refractory material in the upper nozzle of the tundish has Al2O3≥85% and SiO2≤10% by mass percentage; the refractory material in the sliding plate of the tundish has Al2O3≥80% and SiO2≤10% by mass percentage; the continuous casting speed is controlled at 0.45-0.55m / min, the superheat degree of the continuous casting is ≤30℃, and the liquid level fluctuation of the crystallizer is controlled within ±3mm; 2) rolling of the continuous casting billet: the continuous casting billet is rolled into a square billet with a size of 150-170mm×150-170mm; 3) wire rod rolling: the billet is heated in a heating furnace, the total heating time is 210-260min, the temperature in the soaking section is 1070-1090℃, and the soaking time in the soaking section is 60-70min; after the heated billet is subjected to rough rolling, intermediate rolling, pre-precision rolling and precision rolling, wire rod is discharged; the temperature of the wire rod when it is discharged from the pre-precision rolling mill is 980-995℃; the temperature when it is fed into the precision rolling mill is 870-910℃, and the temperature when it is fed into the double-module rolling mill is 880-900℃; the rolling speed of the double-module rolling mill is 20-24m / s, the deformation of the last pass is 5%-15%, and the wire rod discharge temperature is controlled at 880-900℃; 4) cooling of the wire rod: the wire rod after discharging is cooled on the air cooling roller, the phase transition temperature is controlled at 670-690℃, and the phase transition time is 30-45s.

2. A process for the production of a tool steel wire rod as claimed in claim 1, characterized in that, The tensile strength of the wire rod is 980-1040MPa.

3. A process for the production of a tool steel wire rod as claimed in claim 1, characterized in that, The molten iron and scrap steel are smelted, and the weight ratio of the scrap steel is 5%-12%, and the scrap steel has Cr≤0.06% and Ni≤0.08% by mass percentage.

4. The process as claimed in claim 1, wherein, The molten steel ladle is pre-baked before LF refining, and the baking time is not less than 6h.

5. The process as claimed in claim 1, wherein, The macroscopic porosity grade of the continuous casting billet is ≤1.0 grade, and the shrinkage hole grade is ≤1.0 grade.

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