Carbon tool steel wire rod and production method for controlling surface cracks of continuous casting billet

Abstract

The invention relates to a carbon tool steel wire rod and a production method for controlling surface cracks of a continuous casting billet. The steel wire rod comprises the following chemical components in percentage by mass: 1.08%-1.24% of C, 0.15%-0.35% of Si, 0.10%-0.35% of Mn, 0.0050%-0.012% of P, 0.0030%-0.012% of S, 0.0005%-0.0015% of total oxygen, 0.0003%-0.0020% of W, 0.0006%-0.0018% of Als and the balance of Fe and inevitable impurities. The carbon tool steel wire rod with the carbon content being about 1.2% is systematically designed from the aspects of chemical components, a smelting process and a rolling process, a traditional die casting production process is replaced with continuous casting, and the surface crack rating of a continuous casting blank is smaller than or equal to 0.5 grade.

Description

Technical Field

[0001] This invention relates to the field of wire rod production technology, and in particular to a carbon tool steel wire rod and a production method for controlling surface cracks 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 tough alloy tool steel wire and its manufacturing method". In addition to Fe, the tool steel wire 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 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, performing quenching and tempering heat treatment: 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 has excellent resistance to torsional fracture, but its carbon content 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 carbon tool steel wire rod and a production method for controlling surface cracks in continuously cast billets. For carbon tool steel wire rods with a carbon content of about 1.2%, a systematic design is carried out from aspects such as chemical composition, smelting process and rolling process. Continuous casting is used instead of the traditional ingot casting production process, and the surface crack rating of the continuously cast billet is ≤0.5.

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

[0007] A carbon tool steel wire rod, the chemical composition of which, by mass percentage, is: C: 1.08%–1.24%, Si: 0.15%–0.35%, Mn: 0.10%–0.35%, P: 0.0050%–0.012%, S: 0.0030%–0.012%, total oxygen: 0.0005%–0.0015%, W: 0.0003%–0.0020%, Als: 0.0006%–0.0018%, with the balance being Fe and unavoidable impurities.

[0008] The tensile strength of the wire rod is 950-1100 MPa.

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

[0010] A production method for controlling surface cracks on continuously cast billets using carbon tool steel wire rod, wherein the following processes are controlled during wire rod production:

[0011] 1) Smelting and continuous casting: After converter smelting, the oxygen activity of the molten steel is controlled at 100-240 ppm; the refining time in the LF furnace is controlled at 35-50 min, the refining temperature is controlled at 1490-1560℃, and argon blowing and stirring are used in the refining process, with an argon flow rate of 100-360 NL / min; the cross-sectional size of the continuously cast billet is 300-340 mm × 390-420 mm; the continuous casting speed is 0.40-0.50 m / min, the superheat of continuous casting is ≤30℃, and the fluctuation of the molten steel surface in the crystallizer is controlled within ±2 mm; the surface temperature of the billet during the continuous casting process is 870℃-900℃, and the current intensity of the electromagnetic stirring at the end of solidification is 300-600 A;

[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 steel billet is heated in the heating furnace for a total heating time of 200-230 minutes, with a soaking temperature of 1050-1080℃ and a soaking time of 50-70 minutes; the air-fuel ratio in the heating furnace is 1.9-2.4; after the heated steel billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling, it is then subjected to wire rod production; the wire rod temperature when exiting the pre-finishing mill is 980-995℃, the temperature when entering the finishing mill is 870-920℃, and the temperature when entering the double-module mill is 880-910℃; the wire rod production temperature is controlled at 880-910℃.

[0014] 4) Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The phase change temperature of the wire rod is controlled at 620-680℃ and the phase change time is 35-50s.

[0015] The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 10% of the total weight.

[0016] Alloys used in the converter furnace and refining process are pre-baked for no less than 4 hours.

[0017] When tapping steel from the converter, slag-blocking markers are used to block slag, and the slag layer thickness in the molten steel ladle after tapping is ≤60mm.

[0018] The surface crack grade of the continuously cast billet is ≤0.5.

[0019] After the steel billet exits the heating furnace, it undergoes high-pressure water descaling treatment with a descaling pressure ≥18MPa.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] For carbon tool steel wire rods 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 to replace the traditional mold casting production process, and the surface crack rating of the continuous casting billet was ≤0.5. Detailed Implementation

[0022] The carbon tool steel wire rod of the present invention has the following chemical composition by mass percentage: C: 1.08%–1.24%, Si: 0.15%–0.35%, Mn: 0.10%–0.35%, P: 0.0050%–0.012%, S: 0.0030%–0.012%, total oxygen: 0.0005%–0.0015%, W: 0.0003%–0.0020%, Als: 0.0006%–0.0018%, with the balance being Fe and unavoidable impurities.

[0023] The rationale for selecting the chemical composition and content of the carbon tool steel wire rod described in this invention, as well as the role of each element, are as follows:

[0024] Excessive carbon content in wire rod will cause the tool steel produced 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 1.08% and 1.24%.

[0025] 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 0.15%–0.35%.

[0026] Manganese is an element that can improve the strength of wire rod, which helps ensure that the tool steel produced from wire rod meets the tensile strength requirements. Manganese also lowers the eutectoid transformation temperature of steel, refines the pearlite structure of the wire rod, and improves the deformation capacity during the processing of wire rod into tool steel. Manganese can also reduce the tendency for surface cracks to appear in steel billets during straightening. Therefore, this invention controls the manganese content in the wire rod to be between 0.10% and 0.35%.

[0027] Phosphorus reduces the deformation capacity of wire rod during tool steel processing, causing cracking and breakage of the wire. Therefore, this invention controls the phosphorus content in wire rod to 0.0050% to 0.012%.

[0028] 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 caused by crystalline inclusions. Therefore, this invention controls the sulfur content in the wire rod to 0.0030% to 0.012%.

[0029] When the oxygen content is low, the inclusions in the wire rod have high melting points and poor deformability, making them prone to cracking between the inclusions and the matrix, which is detrimental to the processing of tool steel. When the oxygen content is too high, the inclusions in the steel are large, which easily leads to the appearance of micro-cracks during the processing of wire rod into steel wire, and thus causes the steel wire to crack. Therefore, this invention controls the total oxygen content in the wire rod at 0.0005% to 0.0015%.

[0030] 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 in wire rods during ultra-fine wire drawing and stranding, and improves the cold working performance of the wire rods. It also reduces the tendency for surface cracks to appear in continuously cast billets during straightening. However, excessively high tungsten content in the wire rods leads to excessive work hardening during drawing, which is detrimental to improving the wire rod's machinability. Therefore, this invention controls the tungsten content in the wire rods to be between 0.0003% and 0.0020%.

[0031] Excessive acid-soluble aluminum in steel results in coarser inclusions, which is detrimental to the processing of tool steel; conversely, excessively low aluminum content reduces the precipitation of AlN and other phases in the steel, hindering grain refinement during billet heating and rolling. This invention controls the acid-soluble aluminum content in wire rod to between 0.0006% and 0.0018%.

[0032] The present invention discloses a production method for controlling surface cracks on continuously cast billets using carbon tool steel wire rods. The following processes are controlled during wire rod production:

[0033] 1) Smelting and continuous casting: After converter smelting, the oxygen activity of the molten steel is controlled at 100-240 ppm; the refining time in the LF furnace is controlled at 35-50 min, the refining temperature is controlled at 1490-1560℃, and argon blowing and stirring are used in the refining process, with an argon flow rate of 100-360 NL / min; the cross-sectional size of the continuously cast billet is 300-340 mm × 390-420 mm; the continuous casting speed is 0.40-0.50 m / min, the superheat of continuous casting is ≤30℃, and the fluctuation of the molten steel surface in the crystallizer is controlled within ±2 mm; the surface temperature of the billet during the continuous casting process is 870℃-900℃, and the current intensity of the electromagnetic stirring at the end of solidification is 300-600 A;

[0034] 2) Rolling of continuously cast billets: Rolling the continuously cast billets into square billets of 150-170mm × 150-170mm;

[0035] 3) Wire rod rolling: The steel billet is heated in the heating furnace for a total heating time of 200-230 minutes, with a soaking temperature of 1050-1080℃ and a soaking time of 50-70 minutes; the air-fuel ratio in the heating furnace is 1.9-2.4; after the heated steel billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling, it is then subjected to wire rod production; the wire rod temperature when exiting the pre-finishing mill is 980-995℃, the temperature when entering the finishing mill is 870-920℃, and the temperature when entering the double-module mill is 880-910℃; the wire rod production temperature is controlled at 880-910℃.

[0036] 4) Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The phase change temperature of the wire rod is controlled at 620-680℃ and the phase change time is 35-50s.

[0037] The process involves smelting molten iron and scrap steel, with the scrap steel accounting for 5% to 10% of the total weight.

[0038] Alloys used in the converter furnace and refining process are pre-baked for no less than 4 hours.

[0039] When tapping steel from the converter, slag-blocking markers are used to block slag, and the slag layer thickness in the molten steel ladle after tapping is ≤60mm.

[0040] The surface crack grade of the continuously cast billet is ≤0.5.

[0041] After the steel billet exits the heating furnace, it undergoes high-pressure water descaling treatment with a descaling pressure ≥18MPa.

[0042] The finished wire rod specifications are ø12~ø16mm. The tensile strength of the wire rod is 950~1100MPa.

[0043] 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.

[0044] Example:

[0045] The chemical composition of the carbon tool steel wire rods in each embodiment is shown in Table 1, the production process parameters are shown in Table 2, and the finished product performance and surface crack grade of the continuously cast billet are shown in Table 3.

[0046] Table 1 Chemical composition of carbon tool steel wire rod (mass percentage, %)

[0047]

[0048] Table 2 Production process parameters for carbon tool steel wire rod

[0049]

[0050] Table 3 Finished Product Performance and Surface Crack Grades of Continuously Cast Billets

[0051]

[0052] 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 carbon tool steel wire rod, characterized in that, The chemical composition of the wire rod, by mass percentage, is: C: 1.08%–1.24%, Si: 0.15%–0.35%, Mn: 0.10%–0.35%, P: 0.0050%–0.012%, S: 0.0030%–0.012%, total oxygen: 0.0005%–0.0015%, W: 0.0003%–0.0020%, Als: 0.0006%–0.0018%, with the balance being Fe and unavoidable impurities.

2. The carbon tool steel wire rod according to claim 1, characterized in that, The tensile strength of the wire rod is 950-1100 MPa.

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

4. A production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod as described in claim 1, 2, or 3, characterized in that, The following processes are controlled during wire rod production: 1) Smelting and continuous casting: After converter smelting, the oxygen activity of the molten steel is controlled at 100-240 ppm; the refining time in the LF furnace is controlled at 35-50 min, the refining temperature is controlled at 1490-1560℃, and argon blowing and stirring are used in the refining process, with an argon flow rate of 100-360 NL / min; the cross-sectional size of the continuously cast billet is 300-340 mm × 390-420 mm; the continuous casting speed is 0.40-0.50 m / min, the superheat of continuous casting is ≤30℃, and the fluctuation of the molten steel surface in the crystallizer is controlled within ±2 mm; the surface temperature of the billet during the continuous casting process is 870℃-900℃, and the current intensity of the electromagnetic stirring at the end of solidification is 300-600 A; 2) Rolling of continuously cast billets: Rolling the continuously cast billets into square billets of 150-170mm × 150-170mm; 3) Wire rod rolling: The steel billet is heated in the heating furnace for a total heating time of 200-230 minutes, with a soaking temperature of 1050-1080℃ and a soaking time of 50-70 minutes; the air-fuel ratio in the heating furnace is 1.9-2.4; after the heated steel billet undergoes roughing, intermediate rolling, pre-finishing, and finishing rolling, it is then subjected to wire rod production; the wire rod temperature when exiting the pre-finishing mill is 980-995℃, the temperature when entering the finishing mill is 870-920℃, and the temperature when entering the double-module mill is 880-910℃; the wire rod production temperature is controlled at 880-910℃. 4) Wire rod cooling: After spinning, the wire rod is cooled on the air-cooled roller conveyor. The phase change temperature of the wire rod is controlled at 620-680℃ and the phase change time is 35-50s.

5. The production method for controlling surface cracks in continuously cast billets using carbon 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 10% of the total weight.

6. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 4, characterized in that, Alloys used in the converter furnace and refining process are pre-baked for no less than 4 hours.

7. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 4, characterized in that, When tapping steel from the converter, slag-blocking markers are used to block slag, and the slag layer thickness in the molten steel ladle after tapping is ≤60mm.

8. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 4, characterized in that, The surface crack grade of the continuously cast billet is ≤0.

5.

9. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 4, characterized in that, After the steel billet exits the heating furnace, it undergoes high-pressure water descaling treatment with a descaling pressure ≥18MPa.

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