A method for producing medium-carbon high-silicon steel round billet without surface cracks

Abstract

The present invention provides a method for producing a medium-carbon high-silicon steel round billet without surface cracks, and belongs to the field of metallurgical technology. The production method includes the steps of molten iron pre-desulfurization, converter smelting, LF refining, VD refining, and round billet continuous casting; the round billet continuous casting step uses a special protective slag for medium-carbon high-silicon steel; the mass number of oxygen and nitrogen content of the steel water in the middle package is controlled to be T[O]≤20ppm, [N]≤40ppm; the composition and weight ratio of the special protective slag for medium-carbon high-silicon steel are SiO2: 30.0-35.0%, CaO: 22.0-28.0%, MgO: 0.5-1.5%, Al2O3: 3.0-5.0%, Na2O: 10.0-12.0%, F: 3.0-5.0%, C: 12.5-15.5%. The present invention can realize the production of medium-carbon high-silicon steel round billets with high surface quality.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for producing a medium-carbon high-silicon steel round billet without surface cracks. Background Art

[0002] my country is a country with a large infrastructure construction. With the acceleration of infrastructure construction, the demand for drill steel used in mining coal, metal, rock and other mines is also increasing year by year. Drill steel belongs to the medium-carbon high-silicon series of steels. It has a good combination of strength and toughness, high fatigue strength, elastic limit, and relatively low notch sensitivity. It has been widely used in the production of cone drill rods and other drill accessories. However, in the actual production process, medium-carbon high-silicon steel round billets often have surface crack defects. This type of crack will be transmitted to the surface of the rolled material during the subsequent rolling process to form surface cracks. Due to the uneven depth of the cracks, it is often necessary to manually grind the surface cracks. For rolled materials with deeper cracks, they still cannot meet the manufacturer's size requirements after grinding, and they can only be scrapped, which greatly increases the cost and product yield rate during the product production process.

[0003] The Chinese patent application with application number CN201810147733.6 discloses "a high silicon steel and a production method". The high silicon steel referred to in the invention is low carbon high silicon steel, which has a large difference in composition from medium carbon high silicon steel, and its billet shape is a slab, which is not suitable for the production of medium carbon high silicon steel round billets. In the prior art, there is no method that can effectively solve the above technical problems of medium carbon high silicon steel. Summary of the invention

[0004] The invention provides a method for producing a medium-carbon high-silicon steel round billet without surface cracks. The medium-carbon high-silicon steel round billet obtained by the method has no surface crack defects.

[0005] In order to solve the above technical problems, the present invention adopts the following technical scheme: a method for producing a medium-carbon high-silicon steel round billet without surface cracks, the method comprising the steps of molten iron pre-desulfurization, converter smelting, LF refining, VD refining, and round billet continuous casting, and the specific control steps are as follows:

[0006] (1) Hot metal pre-desulfurization process: Before desulfurization, pre-slag is removed to make the exposed surface of hot metal ≥30%. After desulfurization, the slag on the surface of hot metal is removed to make the exposed surface of hot metal ≥90%. The temperature of hot metal outgoing from the station is ≥1300℃, ensuring that the hot metal [S] outgoing from the station is ≤0.010%;

[0007] (2) Converter smelting process: The composition and mass percentage of the molten steel at the end of smelting are: [C]: 0.375-0.395%, [S] ≤ 0.010%, [P] ≤ 0.0090%;

[0008] (3) LF refining process: The composition and mass percentage of the molten steel at the time of leaving the station are: [C]: 0.440-0.460%, [Si]: 1.20-1.30%, [Als]: 0.015-0.020%, [Mn]: 1.95-2.10%, [Mo]: 0.40-0.42%, [S] ≤ 0.003%, [P] ≤ 0.010%, [N] ≤ 0.0045%;

[0009] (4) VD refining process: The composition and mass percentage of the molten steel at the time of leaving the station are: [C]: 0.440-0.460%, [Si]: 1.20-1.30%, [Als]: 0.015-0.020%, [Mn]: 1.95-2.10%, [Mo]: 0.40-0.42%, [S] ≤ 0.003%, [P] ≤ 0.010%, [N] ≤ 0.0040%;

[0010] (5) Round billet continuous casting process: the temperature of the molten steel in the tundish is 1527-1537°C; the protective slag is a special protective slag for medium carbon high silicon steel; the oxygen and nitrogen content of the molten steel in the tundish is controlled to be T[O]≤20ppm, [N]≤40ppm; the composition and mass percentage of the special protective slag for medium carbon high silicon steel are: SiO 2 :30.0~35.0%, CaO: 22.0~28.0%, MgO: 0.5~1.5%, Al 2 O 3 :3.0~5.0%,Na 2 O: 10.0~12.0%, F: 3.0~5.0%, C: 12.5~15.5%, melting point is 1000~1100℃, viscosity is 1.60~2.20 poise.

[0011] In the converter smelting process of the present invention, lime is added according to the final slag basicity of 3.5-4.0, and the molten steel temperature at the smelting end point is 1640-1670°C.

[0012] In the converter smelting process of the present invention, the converter steel tapping adopts a front and rear double-block process, the front block adopts a slag blocking plug, and the rear block adopts a slide plate and a slag blocking mark to block the slag, and the lower slag thickness is ≤30mm.

[0013] In the converter smelting process of the present invention, the material addition starts when 1 / 5 of the steel is tapped, and the order of adding the material is lime, steel sand aluminum, ferrosilicon, and high carbon ferromanganese. The alloy and slag material are added before 4 / 5 of the steel is tapped, and the tapping time is ≥3 minutes.

[0014] In the LF refining process of the present invention, the molten steel and the slag are deoxidized respectively by the aluminum wire and the aluminum wire segment, and TFe+MnO≤1.0% in the final slag sample.

[0015] In the VD refining process of the present invention, the VD vacuum degree is ≤67Pa, and the argon gas blowing flow rate is 50-80Nm 3 / h, to ensure the denitrification effect of the molten steel, and then adjust the molten steel composition by adding titanium and the final alloy composition, and then maintain the pure degassing time ≥ 8min.

[0016] In the round billet continuous casting process of the present invention, the tundish uses a carbon-free and low-silicon covering agent, the tundish uses a slag retaining wall and a slag retaining weir, the tundish baking temperature is ≥1300°C, the baking time is ≥3h, the tundish uses a magnesium refractory material, an aluminum-carbon upper water inlet, an aluminum-carbon stopper rod and an immersed water inlet; a low pulling speed is used for casting, the pulling speed is ≤0.4m / min, the crystallizer water distribution adopts a slow cooling mode, and the crystallizer water volume is 1500-1600L / min; the secondary cooling zone adopts a cooling mode of weak in front and strong in the back, the water volume ratio of the front section and the rear section of the secondary cooling is 1:1.4-1.6, and the total water volume is 0.14-0.16L / kg.

[0017] The N content in the medium-carbon high-silicon steel round billet of the present invention is ≤40ppm, and the S content is ≤0.003%.

[0018] The specification of the medium carbon high silicon steel round billet of the present invention is φ200-600mm.

[0019] The medium carbon high silicon steel round billet of the present invention has no surface cracks.

[0020] The invention produces a medium-carbon high-silicon steel product without surface cracks after the round billet is subjected to a hot rolling process.

[0021] The beneficial effects of the above technical solution are: 1. The present invention controls the N content in the whole process of converter, LF, VD and continuous casting, so that the N content in the finished product is ≤40ppm, which greatly reduces the surface crack defects caused by the high-temperature precipitation of nitrides. 2. The configuration of molten iron pre-desulfurization + LF refining is adopted to ensure that the S element of the steel is controlled below 0.003%; the special protective slag for medium-carbon high-silicon steel is used to effectively reduce the low thermal conductivity caused by the composition characteristics of medium-carbon high-silicon steel, and various surface cracks caused by uneven shell of the ingot, thereby improving the surface quality of the round billet, and finally producing a medium-carbon high-silicon steel round billet without surface crack defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The surface quality diagram of the round billet produced by the prior art;

[0023] Figure 2 This is the surface quality diagram of the round billet in Example 1. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below in conjunction with specific embodiments.

[0025] Examples 1-6

[0026] The present invention discloses a method for producing a medium-carbon high-silicon steel round billet without surface cracks, wherein the process flow is as follows: molten iron pre-desulfurization → converter smelting → LF refining → VD refining → round billet continuous casting process, and the specific process control is as follows:

[0027] (1) Hot metal pre-desulfurization process: Before desulfurization, pre-slag is removed to make the exposed surface of the hot metal ≥30%. After desulfurization, the slag on the surface of the hot metal is removed to make the exposed surface of the hot metal ≥90%. The outlet hot metal temperature is ≥1300°C, ensuring that the outlet hot metal [S] is ≤0.010% to avoid rephosphorization caused by deep desulfurization of reducing slag in the refining process. The process parameter control of each embodiment is shown in Table 1.

[0028] (2) Converter smelting process:

[0029] A. The average temperature of the molten iron entering the furnace is 1270-1320℃, S≤0.010%, [P]: 0.090-0.140%; lime is added according to the final slag basicity of 3.5-4.0, the molten steel temperature at the end of smelting is 1640-1670℃, the FeO mass percentage in the final slag is ≤20%, and the components and mass percentages in the final molten steel are: [C]: 0.375-0.395%, [S]≤0.010%, [P]≤0.0090%;

[0030] B. The converter tapping adopts the front and rear double-blocking process, the front block adopts the slag blocking plug, the rear block adopts the slide plate and the slag blocking mark, and the lower slag thickness is ≤30mm. When 1 / 5 of the molten steel is tapped, the material addition begins, and the order of adding materials is lime, steel sand aluminum, ferrosilicon, and high carbon ferromanganese. The alloy and slag-making materials are added before 4 / 5 of the steel is tapped, and the tapping time is ≥3min. The process parameter control of each embodiment is shown in Table 1.

[0031] Table 1 Parameters of hot metal pre-desulfurization and converter smelting process in Example 1-6

[0032]

[0033] (3) LF refining process:

[0034] A. After the ladle enters the station, the temperature is measured and the sample is analyzed for composition, and the content of elements such as C, Mn, and Si is adjusted;

[0035] B. Deoxidize the molten steel and slag through aluminum wire and aluminum wire segment respectively, and TFe+MnO in the final slag sample is ≤1.0%;

[0036] C. The composition and mass percentage of the molten steel at the time of leaving the station are [C]: 0.440-0.460%, [Si]: 1.20-1.30%, [Als]: 0.015-0.020%, [Mn]: 1.95-2.10%, [Mo]: 0.40-0.42%, [S]≤0.003%, [P]≤0.010%, [N]≤0.0045%. The LF refining process parameter control of each embodiment is shown in Table 2.

[0037] Table 2 LF refining process parameters of Examples 1-6

[0038]

[0039] (4) VD refining process:

[0040] A. VD vacuum degree ≤ 67Pa, control the argon gas blowing flow rate to 50~80Nm 3 / h, to ensure the denitrification effect of molten steel. After 10-20 min of vacuum circulation, take samples for temperature measurement and composition analysis, adjust the molten steel composition with titanium and the final alloy composition, and then maintain the pure degassing time ≥ 8 min;

[0041] B. The composition and mass percentage of the molten steel at the time of leaving the station are [C]: 0.440-0.460%, [Si]: 1.20-1.30%, [Als]: 0.015-0.020%, [Mn]: 1.95-2.10%, [Mo]: 0.40-0.42%, [S]≤0.003%, [P]≤0.010%, [N]≤0.0040%. The VD refining process parameter control of each embodiment is shown in Table 3.

[0042] Table 3 VD refining process parameters of Examples 1-6

[0043]

[0044] (5) Round billet continuous casting process:

[0045] A. The tundish uses magnesium refractory, aluminum carbon upper nozzle, aluminum carbon stopper rod and submerged nozzle, uses carbon-free low-silicon covering agent, and the tundish adopts slag retaining wall and slag retaining weir; the tundish baking temperature is ≥1300℃, the baking time is ≥3h, the tundish molten steel temperature is controlled at 1527~1537℃, and the oxygen and nitrogen content of the molten steel in the tundish is controlled to be T[O]≤20ppm, [N]≤40ppm;

[0046] B. The protective slag is a special protective slag for medium carbon high silicon steel, and its composition and weight ratio are SiO 2 :30.0~35.0%, CaO: 22.0~28.0%, MgO: 0.5~1.5%, Al 2 O3 :3.0~5.0%,Na 2 O: 10.0-12.0%, F: 3.0-5.0%, C: 12.5-15.5%, melting point 1000-1100°C, viscosity 1.60-2.20 poise;

[0047] C. Round billet continuous casting process, low pulling speed is adopted for casting, the pulling speed is ≤0.4m / min, the water distribution of the crystallizer adopts slow cooling mode, and the water volume of the crystallizer is 1500~1600L / min; the secondary cooling zone adopts the cooling mode of weak front and strong back, the water volume ratio of the front and rear sections of the secondary cooling is 1:1.4 to 1:1.6, and the total water volume is 0.14~0.16L / kg.

[0048] The round billet continuous casting process parameter control of each embodiment is shown in Table 4 and Table 5.

[0049] Table 4 Round billet continuous casting process parameters of Examples 1-6

[0050]

[0051] Table 5 Composition, mass percentage and viscosity index of protective slag of Examples 1-6

[0052]

[0053] SiO 2 :30.0~35.0%, CaO: 22.0~28.0%, MgO: 0.5~1.5%, Al 2 O 3 :3.0~5.0%,Na 2 O: 10.0~12.0%, F: 3.0~5.0%, C: 12.5~15.5%.

[0054] The chemical composition of the medium carbon high silicon steel round billet produced by the above process is shown in Table 6. The N content in the medium carbon high silicon steel round billet is ≤40ppm, and S is ≤0.003%. No surface crack defects were found in the cold state inspection, which can well meet the quality requirements of the subsequent hot rolling process and the final product. Figure 1 This is the subcutaneous quality map of the round billet produced by the prior art. Figure 1 Obvious surface cracks can be seen.

[0055] Figure 2 The subcutaneous mass diagram of the round blank of Example 1 is shown by Figure 2 It can be seen that no surface cracks were found in the round billet produced by the inventive method. (The drawings of the other embodiments are the same and therefore omitted)

[0056] Table 6 Specifications, chemical composition and mass percentage of medium carbon high silicon steel round billets of Example 1-6

[0057]

[0058] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for producing a medium-carbon high-silicon steel round billet without surface cracks, characterized in that: The method includes molten iron pre-desulfurization, converter smelting, LF refining, VD refining, and round billet continuous casting processes, and the specific control steps are as follows: (1) Hot metal pre-desulfurization process: Before desulfurization, pre-slag is removed to make the exposed surface of hot metal ≥30%. After desulfurization, the slag on the surface of hot metal is removed to make the exposed surface of hot metal ≥90%. The temperature of hot metal outgoing from the station is ≥1300℃, ensuring that the hot metal [S] outgoing from the station is ≤0.010%; (2) Converter smelting process: lime is added according to the final slag basicity of 3.5-4.0, and the molten steel temperature at the end of smelting is 1640-1670℃; the components and mass percentages in the molten steel at the end of smelting are: [C]: 0.375-0.395%, [S] ≤ 0.010%, [P] ≤ 0.0090%; when 1 / 5 of the steel is tapped, the material addition begins, and the order of adding is lime, steel grit aluminum, ferrosilicon, and high carbon ferromanganese. Alloy and slag-making materials are added before 4 / 5 of the steel is tapped, and the tapping time is ≥ 3 min; (3) LF refining process: The molten steel and slag are deoxidized by aluminum wire and aluminum wire segment respectively, and TFe+MnO in the final slag sample is ≤1.0%; the composition and mass percentage of the molten steel at the time of leaving the station are: [C]: 0.440-0.460%, [Si]: 1.20-1.30%, [Als]: 0.015-0.020%, [Mn]: 1.95-2.10%, [Mo]: 0.40-0.42%, [S] ≤0.003%, [P] ≤0.010%, [N] ≤0.0045%; (4) VD refining process: VD vacuum degree ≤ 67Pa, argon gas blowing flow rate 50~80Nm 3 / h, to ensure the denitrification effect of molten steel, and then adjust the molten steel composition by titanium and the final alloy composition, and then maintain the pure degassing time ≥ 8min; the composition and mass percentage of molten steel at the time of leaving the station are: [C]: 0.440 ~ 0.460%, [Si]: 1.20 ~ 1.30%, [Als]: 0.015 ~ 0.020%, [Mn]: 1.95 ~ 2.10%, [Mo]: 0.40 ~ 0.42%, [S] ≤ 0.003%, [P] ≤ 0.010%, [N] ≤ 0.0040%; (5) Round billet continuous casting process: The tundish uses a carbon-free, low-silicon covering agent, a slag retaining wall and a slag retaining weir, the tundish baking temperature is ≥1300°C, the baking time is ≥3h, the tundish uses magnesium refractory materials, an aluminum-carbon upper nozzle, an aluminum-carbon stopper rod and an immersed nozzle; the tundish molten steel temperature is 1527-1537°C; the protective slag uses a special protective slag for medium-carbon high-silicon steel; the mass number of oxygen and nitrogen content in the tundish molten steel is controlled to be T[O]≤20ppm, [N]≤40ppm; The composition and mass percentage of the special protective slag for medium carbon high silicon steel are: SiO2: 30.0-35.0%, CaO: 22.0-28.0%, MgO: 0.5-1.5%, Al2O3: 3.0-5.0%, Na2O: 10.0-12.0%, F: 3.0-5.0%, C: 12.5-15.5%, the melting point is 1000-1100°C, and the viscosity is 1.60-2.20 poise; Low pulling speed is used for casting, the pulling speed is ≤0.4m / min, the water distribution of the crystallizer adopts the slow cooling mode, and the water volume of the crystallizer is 1500-1600L / min; the secondary cooling zone adopts the cooling mode of weak front and strong back, the water volume ratio of the front and rear sections of the secondary cooling is 1:1.4-1.6, and the total water volume is 0.14-0.16L / kg; The N content in the medium-carbon high-silicon steel round billet is ≤40ppm, and the S content is ≤0.003%.

2. The method for producing a medium-carbon high-silicon steel round billet without surface cracks according to claim 1, characterized in that: In the converter smelting process, the converter steel is tapped using a front and rear double-block process, the front block uses a slag blocking plug, and the rear block uses a slide plate and a slag blocking mark to block the slag, and the lower slag thickness is ≤30mm.

3. The method for producing a medium-carbon high-silicon steel round billet without surface cracks according to claim 1 or 2, characterized in that: The specification of the medium carbon high silicon steel round billet is φ200-600mm.

4. The method for producing a medium carbon high silicon steel round billet without surface cracks according to claim 1 or 2, characterized in that: The medium carbon high silicon steel round billet has no surface cracks.

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