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

Abstract

The present application relates to a kind of carbon tool steel wire rod and the production method for controlling continuous casting billet surface crack, and the chemical composition of wire rod is as follows: 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%, the balance is Fe and inevitable impurities.The present application is aimed at carbon tool steel wire rod with carbon content of about 1.2%, and is systematically designed from aspects of chemical composition, smelting process and rolling process, uses continuous casting instead of traditional mold casting production process, and the surface crack rating of continuous casting billet is ≤0.5 level.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wire rod production, and particularly relates to a carbon tool steel wire rod and a production method for controlling surface cracks of continuous casting billets. 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 (high hardness, high wear resistance, good red hardness, etc.) of tool steel and the geometric shape of wire rod, and is suitable for precise wire rod application occasions 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 mold casting billets, which has the problems of high production cost and low production efficiency. If the continuous casting process is used instead of the mold casting process, it is beneficial to reduce production cost and improve production efficiency.

[0004] A Chinese patent application with publication number CN114318125A discloses "a high-strength and high-toughness alloy tool steel wire rod and a manufacturing method thereof". The tool steel wire rod contains the following chemical elements in addition to Fe: C: 0.60-0.90wt.%, Si: 1.00-3.00wt.%, Mn: 0.45-1.00wt.%, Cr: 0.45-1.00wt.%, Mo: 0.20-0.60wt.%. The microstructure of the tool steel wire rod is tempered martensite + dispersed spherical carbides. The manufacturing method of the high-strength and high-toughness alloy tool steel wire rod includes the following steps: (1) smelting, casting and rolling into a wire rod; (2) offline spheroidizing annealing; (3) after the wire rod is made through the processing process, quenching and tempering heat treatment is performed: heating to austenitizing temperature 820-960℃, holding for 0.5-1h, quenching to room temperature at a speed of 1-50℃ / s; again heating to 200-400℃ for tempering, holding for 0.5-3h. The high-strength and high-toughness alloy tool steel wire rod has excellent torsional fracture resistance, but its carbon content is only 0.60%-0.90%, which is not suitable for the production of tool steel wire rods with a carbon content of about 1.2%. SUMMARY

[0005] The present application provides a carbon tool steel wire rod and a production method for controlling surface cracks of continuous casting billets. For carbon tool steel wire rods with a carbon content of about 1.2%, the chemical composition, smelting process and rolling process are systematically designed, and the continuous casting process is used instead of the traditional mold casting production process, and the surface crack rating of the continuous casting billet is ≤0.5.

[0006] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

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

[0008] The wire rod tensile strength is 950~1100MPa.

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

[0010] A production method for controlling surface cracks of continuous casting billet of carbon tool steel wire rod, the following processes are controlled in wire rod production:

[0011] 1) Smelting and continuous casting: the oxygen activity of molten steel after converter smelting is controlled at 100~240ppm; the LF furnace refining time is controlled at 35~50min, the refining temperature is controlled at 1490~1560℃, argon blowing stirring is adopted in the refining process, and the argon flow is 100~360NL / min; the continuous casting billet section size is 300~340mm×390~420mm; the continuous casting speed is 0.40~0.50m / min, the continuous casting superheat is ≤30℃, and the continuous casting mold liquid level fluctuation is controlled within ±2mm; the billet surface temperature during continuous casting trolley process is 870℃~900℃, and the current intensity of electromagnetic stirring at the solidification end is 300~600A;

[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 enters the heating furnace for heating, the total heating time is 200~230min, the soaking section temperature is 1050~1080℃, and the soaking section holding time is 50~70min; the air-fuel ratio in the heating furnace is 1.9~2.4; after the heated billet is subjected to rough rolling, intermediate rolling, pre-precision rolling and precision rolling, wire rod laying operation is carried out; 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 870~920℃, and the temperature when it enters the double-module rolling mill is 880~910℃; the wire rod laying temperature is controlled at 880~910℃;

[0014] 4) Wire rod cooling: the wire rod after laying is cooled on the air cooling roller way, the phase change temperature of the wire rod is controlled at 620~680℃, and the phase change time is 35~50s.

[0015] Adopting hot metal + scrap steel smelting, the scrap steel weight ratio is 5%~10%.

[0016] The alloy used in the converter post-furnace and refining process is pre-baked, and the baking time is not less than 4h.

[0017] The slag is marked during tapping, and the thickness of the slag layer in the molten steel tank after tapping is ≤60mm.

[0018] The surface crack grade of the continuous casting billet is ≤0.5 grade.

[0019] The billet is subjected to high-pressure water descaling treatment after being discharged from the heating furnace, and the descaling pressure is ≥18MPa.

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

[0021] The carbon content of the carbon tool steel wire rod is about 1.2%, and the wire rod is designed from the aspects of chemical composition, smelting process and rolling process, the continuous casting is used instead of the traditional mold casting production process, and the surface crack rating of the continuous casting billet is ≤0.5 grade. DETAILED DESCRIPTION

[0022] The chemical composition of the carbon tool steel wire rod is as follows: C: 1.08% to 1.24%, Si: 0.15% to 0.35%, Mn: 0.10% to 0.35%, P: 0.0050% to 0.012%, S: 0.0030% to 0.012%, total oxygen: 0.0005% to 0.0015%, W: 0.0003% to 0.0020%, Als: 0.0006% to 0.0018%, and the balance is Fe and inevitable impurities.

[0023] The selection reasons and the effects of the chemical composition and the content of the carbon tool steel wire rod are as follows:

[0024] 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 1.08% to 1.24%.

[0025] Silicon element increases the eutectoid transformation temperature of the steel, resulting in coarse pearlite structure of the wire rod, which is not conducive to the complex deformation in the tool steel processing process. Meanwhile, silicon is the main deoxidizing element in 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 in the tool steel processing process will be reduced due to insufficient deoxidization of the molten steel. Therefore, the silicon content in the wire rod is controlled to be 0.15% to 0.35%.

[0026] Manganese is an element that can improve the strength of wire rod, which is conducive to ensure that the tool steel after wire rod processing meets the tensile strength requirements; manganese element also has the effect of reducing the eutectoid transformation temperature of steel, which can refine the pearlite structure of wire rod and improve the deformation capacity of tool steel during wire rod processing. Manganese element can also reduce the tendency of surface cracks of billet during straightening process. Therefore, the manganese content in the wire rod is controlled at 0.10%-0.35% in the application.

[0027] Phosphorus can reduce the deformation capacity of wire rod during tool steel processing, causing steel wire cracking and breaking, so the phosphorus content in the wire rod is controlled at 0.0050%-0.012% in the application.

[0028] Higher sulfur content in steel can reduce the cold working performance of wire rod. However, since MnS inclusions have good deformation capacity, a certain amount of sulfur in steel can reduce the harm of crystalline inclusions, so the sulfur content in the wire rod is controlled at 0.0030%-0.012% in the application.

[0029] When the oxygen content is low, the inclusions in the wire rod have high melting point and poor deformation capacity, and cracks are prone to occur between the inclusions and the matrix, which is not conducive to the processing of tool steel; when the oxygen content is too high, the size of inclusions in steel is large, which can easily cause the occurrence of micro-cracks during the processing of wire rod into steel wire, and then cause the cracking of steel wire. Therefore, the total oxygen content in the wire rod is controlled at 0.0005%-0.0015% in the application.

[0030] 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 ultra-fine steel wire drawing and plying, and improve the cold working performance of wire rod. At the same time, it can also reduce the tendency of surface cracks of continuous casting billet during straightening process. However, if the tungsten content in the wire rod is too high, the work hardening during wire rod drawing process is too significant, which is not conducive to the improvement of wire rod processing performance. Therefore, the tungsten content in the wire rod is controlled at 0.0003%-0.0020% in the application.

[0031] Excessive acid-soluble aluminum in steel can make the inclusions in steel relatively coarse, which is not conducive to the processing of tool steel; when the aluminum content is too low, the amount of AlN and other precipitated phases in steel is reduced, which is not conducive to the grain refinement during billet heating and rolling. The acid-soluble aluminum content in the wire rod is controlled at 0.0006%-0.0018% in the application.

[0032] The production method for controlling surface cracks of continuous casting billet of the carbon tool steel wire rod disclosed in the application controls the following processes in wire rod production:

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

[0034] 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;

[0035] 3) Wire rod rolling: the billet is heated in a heating furnace, the total heating time is 200-230 min, the soaking section temperature is 1050-1080 °C, and the soaking section holding time is 50-70 min; the air-fuel ratio in the heating furnace is 1.9-2.4; after heating, the billet is subjected to rough rolling, intermediate rolling, pre-precision rolling, and precision rolling, and then 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 870-920 °C, and the temperature when it enters the double-module rolling mill is 880-910 °C; the wire rod drawing temperature is controlled at 880-910 °C;

[0036] 4) Wire rod cooling: the wire rod after drawing is cooled on the air cooling roller, the phase change temperature of the wire rod is controlled at 620-680 °C, and the phase change time is 35-50 s.

[0037] The molten iron + scrap steel is smelted, and the weight ratio of scrap steel is 5%-10%.

[0038] The alloys used after the converter and during the refining process are pre-baked, and the baking time is not less than 4 h.

[0039] The slag is marked when the converter is tapped, and the slag layer thickness in the molten steel tank after tapping is ≤60 mm.

[0040] The surface crack grade of the continuous casting billet is ≤0.5 grade.

[0041] The billet is subjected to high-pressure water descaling treatment after coming out of the heating furnace, and the descaling pressure is ≥18 MPa.

[0042] The wire rod finished product specification is ø12-ø16 mm. The tensile strength of the wire rod is 950-1100 MPa.

[0043] 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 obtain the technical solutions which are obvious within the technical range disclosed by the present application, including simple changes or equivalent replacements, all of which are within the protection scope of the present application.

[0044] Examples:

[0045] The chemical components of the carbon 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 and continuous casting billet surface crack grade are shown in Table 3.

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

[0047]

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

[0049]

[0050] Table 3 Finished product performance and continuous casting billet surface crack grade

[0051]

[0052] 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 obtain the technical solutions which are obvious within the technical range disclosed by the present application, including simple changes or equivalent replacements, all of which are within the protection scope of the present application.

Claims

1. A production method for controlling surface cracks in continuously cast billets using 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; the tensile strength of the wire rod is 950–1100 MPa; the finished wire rod specifications are ø12–ø16 mm; 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, and the refining temperature is controlled at 1490-1560℃. Argon blowing and stirring are used in the refining process, and the argon flow rate is 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℃; 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℃; the current intensity of the electromagnetic stirring at the end of solidification is 300-600 A; the surface crack grade of the continuously cast billet is ≤0.

5. 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.

2. The production method for controlling surface cracks in continuously cast billets using carbon 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.

3. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 1, characterized in that, Alloys used in the converter furnace and refining process are pre-baked for no less than 4 hours.

4. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 1, 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.

5. The production method for controlling surface cracks in continuously cast billets using carbon tool steel wire rod according to claim 1, 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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