A method for preparing high-strength and high-toughness cold-working die steel billet

Abstract

The invention provides a preparation method of a high-strength and high-toughness cold-working die steel billet, and relates to the field of cold-working die steel production. The method comprises the following steps: tapping a VD furnace, a ladle turret, a tundish, a crystallizer, secondary cooling, a drawing and leveling machine, flame cutting, and billet sizing; the total length of the crystallizer is 1500 mm, the width and height h1 of the crystallizer are 170 mm, the radius r1 of the four fillets of the crystallizer is 60 mm, and the side length h2 of the crystallizer is 50 mm; the temperature of the molten steel in the tundish is 1480-1500° C., the drawing speed is 0.6-0.8 m / min, and the water volume of the continuous casting machine crystallizer is 140-160 m 3 / h. The key technology and process designed by the present invention solves the problem of Cr 8 Mo 2 The SiV steel grade has the problem of locally forming oversized eutectic carbides due to component segregation during the solidification process, which improves the flaw detection pass rate and has certain economic benefits.

Description

Technical Field

[0001] The invention relates to the field of cold working die steel production, and in particular to a method for preparing a high-strength and high-toughness cold working die steel billet. Background Art

[0002] Cold working die steel is an important component of die steel and is widely used in blanking, stamping, cold extrusion, cold heading, drawing and stamping dies. The commonly used cold working die steels in my country mainly include low alloy cold working die steel Cr-W-Mn series, medium alloy cold working die steel A2 series and high alloy Cr 12 A2 steel has medium permeability and toughness, but is not suitable for manufacturing molds with high dimensional accuracy and mass production. 12 The series of high-chromium and high-carbon cold working die steels have good wear resistance, but the number of carbides is serious, especially when the specifications are large. Repeated pulling is still difficult to significantly improve the distribution of carbides, resulting in a decrease in deformation directionality and toughness.

[0003] In order to improve Cr 12 The number and toughness of carbides in cold working die steel, Japan Datong developed DC 53 , reducing the content of carbon and chromium, increasing the content of silicon and molybdenum, achieving the purpose of reducing the number of eutectic carbides and improving toughness. The domestic imitation grade is Cr8Mo2SiV. In China, this type of steel is mainly cast into ingots by ingot casting, and forged or rolled into finished products. However, due to the cooling conditions of die casting, due to component segregation during the solidification process, oversized eutectic carbides are formed locally, resulting in non-conformity in finished product flaw detection, affecting production efficiency and product quality. Summary of the invention

[0004] Based on the above technical problem that the existing Cr8Mo2SiV steel locally forms oversized eutectic carbides during the solidification process, a method for preparing a high-strength and high-toughness cold-working die steel billet is provided. The present invention mainly solves the eutectic carbide and segregation problems by designing the continuous casting billet section and continuous casting process.

[0005] The technical means adopted by the present invention are as follows:

[0006] A method for preparing a high-strength and high-toughness cold-working die steel billet comprises the following steps:

[0007] VD furnace tapping, ladle turret, tundish, crystallizer, secondary cooling, straightening machine, flame cutting, billet sizing;

[0008] The total length of the crystallizer is 1500mm, the temperature of the molten steel in the tundish is 1480~1500℃, the casting speed is 0.6~0.8m / min, and the water volume of the continuous casting machine crystallizer is 140~160m 3 / h.

[0009] Furthermore, the chemical composition of the high-strength and high-toughness cold-working die steel billet is as follows: C: 0.95%~1.05%, Si: 0.8%~1.2%, Mn: 0.3%~0.6%, P: ≤0.03%, S: ≤0.005%, Cr: 8.0%~9.0%, Mo: 2.0%~2.3%, V: 0.2%~0.4%, Cu: 0.1%~0.3%, Ni: 0.1%~0.3%, and the rest is iron and impurities generated by manufacturing.

[0010] Furthermore, before pouring, the baking time of the tundish is 2.1 to 2.3 hours, and the temperature of the tundish after baking is 700° C. to 800° C.

[0011] Furthermore, the temperature of the continuous casting molten steel is 1530-1550°C, and the temperature of the molten steel in the tundish is 1480-1500°C.

[0012] Furthermore, the working liquid level height of the tundish is 810-910 mm, the overflow molten steel height is 970 mm, the minimum molten steel liquid level depth is greater than 405 mm, and the stop-pouring liquid level depth is greater than 160 mm.

[0013] Furthermore, the starting pulling speed of the dummy rod is 0.2-0.4 m / min, and the normal pulling speed of the dummy rod is 1.9-2.1 m / min; before the pouring starts, the dummy head on the dummy rod is sent into the crystallizer 30-40 mm away.

[0014] Furthermore, the ladle starts pouring, and when the liquid level in the tundish exceeds 300mm, the temperature measurement operation is carried out. After completion, oxygen is used to burn the steel flow. When the liquid level of the crystallizer is 220mm away from the upper mouth, steel drawing begins and is gradually accelerated to stability.

[0015] Furthermore, the water flow rate of the crystallizer is 140-150m 3 / h.

[0016] Furthermore, after the continuous casting billet leaves the crystallizer, it is cooled in a second cooling section. The second cooling section adopts a three-stage cooling mode. The three-stage cooling mode includes zero stage, one stage and two stages, wherein: the number of nozzles in the zero stage is 18, the number of nozzles in the first stage is 42, and the number of nozzles in the second stage is 30, and the nozzles are arranged in a uniform distribution manner.

[0017] Furthermore, the specific water volume of the secondary cooling section is 0.8 to 2 L / kg.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The continuous casting square billet prepared by the present invention reduces the tendency of forming oversized eutectic carbides in terms of composition, so that oversized eutectic carbides will not be formed locally during the cooling process of the billet;

[0020] The continuous casting square billet prepared by the present invention has a specific cross-sectional structure with rounded corners, and the cooling speed of the cross-section is superior to that of an ordinary cross-section. The cross-section is beneficial to final pressure production and finished product flaw detection. Eutectic carbides in the final product are evenly dispersed, thereby improving the quality of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 This is a cross-sectional shape diagram of the continuous casting billet of the present invention.

[0023] Figure 2 This is the core structure diagram of the continuous casting billet in Example 1 of the present invention.

[0024] Figure 3 This is the core structure diagram of the continuous casting billet in Example 2 of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0026] The present invention provides a method for preparing a high-strength and high-toughness cold-working die steel billet, and the technical scheme is as follows:

[0027] (1) The grade of the high-strength and high-toughness cold-working die steel is Cr8Mo2SiV. Based on the national standard requirements, the preferred chemical composition of this patent is: C0.95-1.05, Si0.8-1.2, Mn0.3-0.6, P≤0.03, S≤0.005, Cr8.0-9.0, Mo2.0-2.3, V0.2-0.4, Cu0.1-0.3, Ni0.1-0.3.

[0028] (2) A continuous casting billet with a specific cross section is designed, as shown in the attached Figure 1 shown. Figure 1 In the figure, the width and height h1 of the crystallizer are both 170 mm, the radius r1 of the four corners is 60 mm, the side length h2 is 50 mm, and the total length of the crystallizer is 1500 mm.

[0029] (3) The general continuous casting process involved in the present invention is: VD furnace steel tapping → ladle turret → tundish → crystallizer → secondary cooling → straightening machine → flame cutting → billet sizing.

[0030] (4) Before pouring, the tundish is baked for 2.1-2.3 hours. First bake it on low heat for 50-70 minutes, and then bake it on high heat for 68-76 minutes.

[0031] (5) The temperature of the continuous casting molten steel (temperature measurement at the time of steel tapping from the VD furnace) is controlled at 1530-1550°C, and the temperature of the molten steel in the tundish is controlled at 1480-1500°C.

[0032] (6) The working liquid level height of the tundish is 810-910 mm, the overflow molten steel height is 970 mm, the minimum molten steel level depth is greater than 405 mm, and the stop pouring liquid level depth is greater than 160 mm.

[0033] (7) Starting pulling speed of the dummy rod: 0.2-0.4 m / min, normal pulling speed 1.9-2.1 m / min. Before pouring, the dummy head on the dummy rod is sent into the crystallizer about 30-40 mm.

[0034] (8) Add cold material.

[0035] (9) When the ladle starts pouring, when the liquid level in the tundish exceeds 300 mm, temperature measurement is carried out. After completion, the steel flow is burned with oxygen. When the liquid level in the crystallizer is 220 mm away from the upper mouth, steel drawing begins and is gradually accelerated to stability.

[0036] (10) Where: The water flow rate of the crystallizer is 140~150m 3 / h.

[0037] (11) After the continuous casting billet leaves the crystallizer, it is cooled in the secondary cooling section. The secondary cooling section adopts the commonly used three-stage cooling mode, namely, the zero stage, the first stage and the second stage. Among them, the number of nozzles in the zero stage is 18, the number of nozzles in the first stage is 42, and the number of nozzles in the second stage is 30, which are arranged in a uniform distribution.

[0038] (12) The above secondary cooling water volume is controlled at 0.8 to 2 L / kg.

[0039] (13) After the continuous casting billet comes out of the second cooling section and passes through the straightening machine, it is flame cut to a length of 5-8m.

[0040] Example 1

[0041] This embodiment uses the cross-sectional shape of the continuous casting billet and the continuous casting process designed by the present invention to produce a continuous casting square billet of cold-working die steel.

[0042] The details are as follows:

[0043] (1) The chemical composition of the cold working die steel used in the production of continuous casting square billets is: C: 0.98, Si: 1.0, Mn: 0.5, P: 0.02, S: 0.002, Cr: 8.8, Mo: 2.3, V: 0.4, Cu: 0.3, Ni: 0.28.

[0044] (2) The width and height of the crystallizer are both 170 mm, the radius of the four corners is 60 mm, the side length is 50 mm, and the total length of the crystallizer is 1500 mm.

[0045] (3) Before pouring, the tundish is baked for 2.1 hours, first baked on low heat for 55 minutes, then baked on high heat for 70 minutes.

[0046] (4) The temperature of the molten steel in continuous casting (temperature measurement at the tapping of the VD furnace) is controlled at 1530°C, and the temperature of the molten steel in the tundish is controlled at 1485°C.

[0047] (5) The working liquid level height of the tundish is 815mm, the overflow molten steel height is 970mm, the minimum molten steel level depth is 408mm, and the stop pouring liquid level depth is 170mm.

[0048] (6) Starting pulling speed of the dummy rod: 0.4m / min, normal pulling speed 2.0 / min. Before pouring, the dummy head on the dummy rod is sent into the crystallizer about 35mm.

[0049] (7) Add cold material.

[0050] (8) When the ladle starts pouring, when the liquid level in the tundish exceeds 300 mm, temperature measurement is carried out. After completion, the steel flow is burned with oxygen. When the liquid level in the crystallizer is 220 mm from the upper mouth, steel drawing begins and is gradually accelerated to a stable state.

[0051] (9) Where: The water flow rate of the crystallizer is 140m 3 / h.

[0052] (10) After the continuous casting billet leaves the crystallizer, it is cooled in the secondary cooling section. The secondary cooling section adopts the commonly used three-stage cooling mode, namely, the zero stage, the first stage and the second stage. Among them, the number of nozzles in the zero stage is 18, the number of nozzles in the first stage is 42, and the number of nozzles in the second stage is 30, which are arranged in a uniform distribution.

[0053] (11) The above secondary cooling water volume is controlled at 1.0L / kg.

[0054] (12) After the continuous casting billet comes out of the second cooling section and passes through the straightening machine, it is flame cut to a fixed length of 5m.

[0055] (13) The morphology of eutectic carbide in the center of continuous casting billet is as follows Figure 2 Shown

[0056] Example 2

[0057] This embodiment uses the cross-sectional shape of the continuous casting billet and the continuous casting process designed by the present invention to produce a continuous casting square billet of cold-working die steel.

[0058] The details are as follows:

[0059] (1) The chemical composition of the cold working die steel used in the production of continuous casting square billets is: C: 0.95, Si: 0.81, Mn: 0.3, P: 0.01, S: 0.005, Cr: 81, Mo: 2.0, V: 0.22, Cu: 0.12, Ni: 0.15.

[0060] (2) The width and height of the crystallizer are both 170 mm, the radius of the four corners is 60 mm, the side length is 50 mm, and the total length of the crystallizer is 1500 mm.

[0061] (3) Before pouring, the tundish is baked for 2.3 hours, first baked on low heat for 70 minutes, then baked on high heat for 75 minutes.

[0062] (4) The temperature of the molten steel in continuous casting (temperature measurement at the time of steel tapping from a VD furnace) is controlled at 1550°C, and the temperature of the molten steel in the tundish is controlled at 1500°C.

[0063] (5) The working liquid level height of the tundish is 905mm, the overflow molten steel height is 970mm, the minimum molten steel level depth is 410mm, and the stop pouring liquid level depth is 170mm.

[0064] (6) Starting pulling speed of the dummy rod: 0.2m / min, normal pulling speed 1.9 / min. Before pouring, the dummy head on the dummy rod is sent into the crystallizer about 35mm away.

[0065] (7) Add cold material.

[0066] (8) When the ladle starts pouring, when the liquid level in the tundish exceeds 300 mm, temperature measurement is carried out. After completion, the steel flow is burned with oxygen. When the liquid level in the crystallizer is 220 mm from the upper mouth, steel drawing begins and is gradually accelerated to a stable state.

[0067] (9) Where: The water flow rate of the crystallizer is 150m 3 / h.

[0068] (10) After the continuous casting billet leaves the crystallizer, it is cooled in the secondary cooling section. The secondary cooling section adopts the commonly used three-stage cooling mode, namely, the zero stage, the first stage and the second stage. Among them, the number of nozzles in the zero stage is 18, the number of nozzles in the first stage is 42, and the number of nozzles in the second stage is 30, which are arranged in a uniform distribution.

[0069] (11) The above secondary cooling water volume is controlled at 1.8L / kg.

[0070] (12) After the continuous casting billet comes out of the second cooling section and passes through the straightening machine, it is flame cut to a fixed length of 5m.

[0071] (13) The morphology of eutectic carbide in the center of continuous casting billet is as follows Figure 3 shown.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength and high-toughness cold-working die steel billet, characterized in that: The steps include: VD furnace tapping, ladle turret, tundish, crystallizer, secondary cooling, straightening machine, flame cutting, billet sizing; The total length of the crystallizer is 1500 mm, the width and height h1 of the crystallizer are 170 mm, the radius r1 of the four fillets of the crystallizer is 60 mm, and the side length h2 of the crystallizer is 50 mm; The temperature of molten steel in the tundish is 1480-1500℃, and the water volume of the continuous casting machine crystallizer is 140-160m 3 / h; the starting pulling speed of the dummy bar is 0.2-0.4m / min, and the normal pulling speed of the dummy bar is 1.9-2.1m / min; before pouring, the dummy head on the dummy bar is sent into the crystallizer 30-40mm; The steel grade of high-strength and high-toughness cold-working die steel billet is Cr8Mo2SiV, and the chemical composition of high-strength and high-toughness cold-working die steel billet is: C: 0.95% ~ 1.05%, Si: 0.8% ~ 1.2%, Mn: 0.3% ~ 0.6%, P: ≤ 0.03%, S: ≤ 0.005%, Cr: 8.0% ~ 9.0%, Mo: 2.0% ~ 2.3%, V: 0.2% ~ 0.4%, Cu: 0.1% ~ 0.3%, Ni: 0.1% ~ 0.3%, and the rest is iron and impurities generated by manufacturing; The working liquid level of the tundish is 810-910mm, the overflow molten steel height is 970mm, the minimum molten steel level depth is greater than 405mm, and the stop-casting liquid level depth is greater than 160mm; The ladle starts pouring, and when the liquid level in the tundish exceeds 300mm, the temperature measurement operation is carried out. After completion, the steel flow is burned with oxygen. When the liquid level of the crystallizer is 220mm away from the upper mouth, the steel drawing starts, and gradually accelerates to stability; After the continuous casting billet leaves the crystallizer, it is cooled in the second cooling section. The second cooling section adopts a three-stage cooling mode, which includes zero stage, one stage and two stages. Among them, the number of nozzles in the zero stage is 18, the number of nozzles in the first stage is 42, and the number of nozzles in the second stage is 30. The nozzles are arranged in a uniform distribution manner. The specific water volume of the secondary cooling section is 0.8 to 2 L / kg.

2. The method for preparing a high-strength and high-toughness cold-working die steel billet according to claim 1, characterized in that: Before pouring, the baking time of the tundish is 2.1 to 2.3 hours, and the temperature of the tundish after baking is 700°C to 800°C.

3. The method for preparing a high-strength and high-toughness cold-working die steel billet according to claim 1, characterized in that: The temperature of continuous casting molten steel is 1530~1550℃.

4. The method for preparing a high-strength and high-toughness cold-working die steel billet according to claim 1, characterized in that: The water volume of the continuous casting machine crystallizer is 140-150m 3 / h.

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