A method for reducing the crack incidence in the production of medium carbon high strength steel

Abstract

The present invention relates to a method for reducing the crack incidence rate of medium-carbon high-strength steel and the medium-carbon high-strength steel obtained by controlling the production of the method. The present invention reduces the crack incidence rate of the steel coil surface when the medium-carbon high-strength steel is produced by the twin-roll casting process by adjusting the chemical composition of the molten steel, the roller brush torque, the vibration amplitude, the surface roughness of the casting roller, the thickness of the casting strip and the hot rolling reduction rate. The method mainly includes: the Mn content in the chemical composition of the molten steel is ≥0.60%, and the Mn / Si value range is required to be 2.8-5.2; the surface roughness of the casting roller is 6-16μm, the roller brush torque is 150-250lb·in, the vibration amplitude is ≤50lb·in, the thickness of the casting strip is 1.9-2.5mm, and the hot rolling reduction rate is ≥20%. By adopting one or more of the above control means, the crack incidence rate of the steel coil surface when the medium-carbon high-strength steel is produced by the twin-roll casting process can be effectively reduced, and the product qualification rate and benefit level can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and relates to a method for reducing the crack incidence rate of medium-carbon high-strength steel in production, and specifically relates to a method for reducing the crack incidence rate of steel coil surface in a twin-roll casting production process. Background Art

[0002] As the fields of engineering machinery, agricultural machinery and transport trucks develop towards lightweight, high-quality and energy-saving, the demand for thin-gauge, high-strength steel is increasing. High-strength steel with medium carbon composition system has less alloy content and low alloy cost, so its production cost is low compared with high-strength steel with low carbon composition system, which can reduce the manufacturing cost of end customers.

[0003] In the traditional continuous casting process, the thickness of the ingot is large (generally 200-280mm), and there is protective slag during the casting process, so surface cracks are not easy to appear on the surface of the ingot. In the twin-roll casting process, the thickness of the cast strip cast by two counter-rotating casting rollers is small (generally less than 3mm), and there is no protective slag during the casting process, so crack defects are easy to appear on the surface of the cast strip. Compared with low-carbon steel, medium-carbon steel has slow heat transfer efficiency and is more likely to have crack defects on the surface of the ingot during the continuous casting process, so the control requirements for process parameters in the continuous casting process are more stringent. Summary of the invention

[0004] The purpose of the present invention is to provide a method for reducing the crack incidence rate of medium carbon high strength steel based on the twin-roll casting process. The method adopts a completely different idea from the prior art and does not require the addition of additional equipment. It can effectively reduce the crack incidence rate of medium carbon high strength steel based on the twin-roll casting process and significantly improve the product qualification rate of hot-rolled medium carbon high strength steel.

[0005] According to the present invention, the method can effectively reduce the crack incidence of medium carbon high strength steel based on the twin-roll casting process by controlling one or more of the chemical composition of molten steel, roller brush torque, vibration amplitude, casting roller surface roughness, cast strip thickness and hot rolling reduction rate.

[0006] More specifically, the present invention adopts the following technical solutions:

[0007] According to a first aspect of the present invention, a method for reducing the crack incidence in the production of medium carbon high strength steel is disclosed, the method comprising the following steps:

[0008] (1) Using electric furnace smelting to obtain molten steel;

[0009] (2) the molten steel obtained in step (1) is continuously casted into a thin strip through two counter-rotating casting rolls to obtain a cast strip, and a roller brush is used to clean the surface of the casting rolls;

[0010] (3) hot-rolling the cast strip obtained in step (2) into a hot-rolled thin strip through one pass, cooling it through gas mist, and coiling it to obtain a hot-rolled coil.

[0011] The method for reducing the crack incidence rate of medium carbon high strength steel production further adopts one or more of the following control measures:

[0012] (a) controlling the Mn content of the molten steel in step (1) to be ≥ 0.60%;

[0013] (b) controlling the Mn / Si value of the molten steel in step (1) to be in the range of 2.8 to 5.2;

[0014] (c) controlling the roller brush torque in step (2) to be 150 to 250 lb·in;

[0015] (d) controlling the vibration amplitude of the roller brush in step (2) to be ≤50 lb·in;

[0016] (e) controlling the surface roughness of the casting roll in step (2) to be 6 to 16 μm;

[0017] (f) controlling the thickness of the cast strip obtained in step (2) to be 1.9-2.5 mm;

[0018] (g) Controlling the reduction ratio of one hot rolling pass in step (3) to be ≥20%.

[0019] According to the method for reducing the crack incidence in the production of medium carbon high strength steel of the present invention, preferably, the method further comprises in step (1), designing the composition of molten steel according to the performance requirements of the product produced by the twin roll casting process.

[0020] According to the method for reducing the crack incidence rate in producing medium carbon high strength steel of the present invention, preferably, the control means (a) further comprises: controlling the Mn content to be ≥ 0.65%.

[0021] According to the method for reducing the crack incidence in the production of medium carbon high strength steel of the present invention, preferably, the control means (b) further comprises: controlling the Mn / Si value to be in the range of 3.25 to 4.54.

[0022] According to the method for reducing the crack incidence rate in the production of medium carbon high strength steel of the present invention, preferably, the control means (c) further comprises: controlling the roller brush torque to be 160-230 lb·in.

[0023] According to the method for reducing the crack incidence rate in the production of medium carbon high strength steel of the present invention, preferably, the control means (d) further comprises: controlling the vibration amplitude of the roller brush to be 15 to 45 lb·in.

[0024] According to the method for reducing the crack incidence in the production of medium carbon high strength steel of the present invention, preferably, the control means (e) further comprises: controlling the surface roughness of the casting roll to be 8-14 μm.

[0025] According to the method for reducing the crack incidence in the production of medium carbon high strength steel of the present invention, preferably, the control means (f) further comprises: controlling the thickness of the cast strip to be 1.95-2.2 mm.

[0026] According to the method for reducing the crack incidence rate in the production of medium carbon high strength steel of the present invention, preferably, the control means (g) further comprises: controlling the reduction rate of hot rolling to 30-55%.

[0027] According to a second aspect of the present invention, a medium carbon high strength steel is disclosed. The production method of the medium carbon high strength steel is controlled by the aforementioned method for reducing the crack incidence rate of the medium carbon high strength steel, wherein the crack detection rate of the medium carbon high strength steel is not higher than 1.2%.

[0028] Invention Concept

[0029] In the process of producing medium carbon high strength steel by twin roll casting, MnO and SiO are formed on the surface of the casting roll. 2 The oxide film has a MnO content of more than 90%. The thickness and uniformity of the oxide film will affect the heat transfer efficiency and uniformity during the casting process, and thus affect the incidence of cracks on the surface of the cast strip. According to the inventor's research, the following process parameters will have a significant impact on the crack defects on the surface of the cast strip:

[0030] Molten steel composition: Mn content affects the speed of oxide film formation. Increasing the Mn content in the composition will promote the formation of oxide film and evenly cover the surface of the casting roll, improving the uniformity of heat transfer. The Mn / Si value affects the material form of the oxide film. In a certain form of the oxide film, the heat transfer efficiency of the casting roll surface is the best, so there is an appropriate range of Mn / Si values.

[0031] Roller brush torque and / or vibration amplitude: Roller brush torque affects the thickness of the oxide film on the surface of the casting roll. There is an optimal value for the thickness of the oxide film. Too thick or too thin will affect the heat transfer efficiency of the casting roll surface and affect the incidence of surface cracks. The roller brush will vibrate during rotation. If the vibration amplitude is too large, the oxide film on the surface of the casting roll will be unevenly distributed, resulting in uneven solidification during continuous casting and crack defects on the surface of the cast strip. Therefore, the vibration amplitude of the roller brush should be as small as possible.

[0032] Surface roughness of casting roll: Reducing the surface roughness of casting roll is beneficial to promoting the oxide film to evenly cover the surface of casting roll and improve the uniformity of heat transfer. However, if the surface roughness of casting roll is too low, it will deteriorate the wettability of the interface between molten steel and casting roll and reduce the heat transfer efficiency.

[0033] Strip thickness: Increasing the strip thickness can improve solidification quality and reduce the incidence of cracks.

[0034] Hot rolling reduction rate: Increasing the hot rolling reduction rate can weld surface crack defects to a certain extent.

[0035] By adjusting the above main process parameters, the incidence of surface cracks in steel coils when producing medium-carbon high-strength steel using the twin-roll casting process can be effectively reduced, thereby improving product qualification rate and efficiency.

[0036] Beneficial technical effects

[0037] Compared with the prior art, the beneficial technical effects of the present invention include at least:

[0038] The present invention analyzes and studies the specific causes of cracks under existing production conditions, and effectively reduces the crack problem of medium carbon high strength steel by adjusting the chemical composition of molten steel, roller brush torque, vibration amplitude, casting roller surface roughness, casting strip thickness and hot rolling reduction rate without adding equipment. The method of the present invention is easy to operate, has a low process improvement cost, and can significantly improve the product qualification rate and benefit level. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments are briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0040] Figure 1 The figure is a schematic diagram of the process and equipment for producing medium carbon high strength steel according to the method of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one of ordinary skill in the art to which the present invention belongs.

[0043] The following are embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments that can be obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] 355MPa grade medium carbon high strength steel, the chemical composition design Mn content is 0.65%, Mn / Si value is 3.25, the molten steel with qualified smelting composition is continuously cast by two counter-rotating casting rollers, the surface roughness of the casting roller is 10μm, and the roller brush cleans the oxide film on the surface of the casting roller. The roller brush torque setting value is 160lb·in, the vibration amplitude is 20lb·in, the thickness of the cast strip is 1.95mm, and the cast strip is hot rolled in one pass at a reduction rate of 30%, cooled by gas mist, and coiled to obtain the hot rolled coil.

[0046] Under the control of this process parameter, the crack incidence rate of the product is 0.8%.

[0047] Example 2

[0048] 550MPa grade medium carbon high strength steel, the chemical composition design Mn content is 1.50%, Mn / Si value is 3.75, the molten steel with qualified smelting composition is continuously cast by two counter-rotating casting rollers, the surface roughness of the casting roller is 14μm, and the roller brush cleans the oxide film on the surface of the casting roller. The roller brush torque setting value is 230lb·in, the vibration amplitude is 45lb·in, the cast strip thickness is 2.0mm, the cast strip is hot rolled in one pass at a reduction rate of 45%, and is cooled by gas mist and coiled to obtain a hot-rolled coil.

[0049] Under the control of this process parameter, the crack incidence rate of the product is 0.5%.

[0050] Example 3

[0051] 700MPa grade medium carbon high strength steel, the chemical composition design Mn content is 2.0%, Mn / Si value is 4.54, the molten steel with qualified smelting composition is continuously cast by two counter-rotating casting rollers, the surface roughness of the casting roller is 8μm, and the roller brush cleans the oxide film on the surface of the casting roller. The roller brush torque setting value is 180lb·in, the vibration amplitude is 15lb·in, the thickness of the cast strip is 2.2mm, and the cast strip is hot rolled in one pass at a reduction rate of 55%, cooled by gas mist, and coiled to obtain a hot-rolled coil.

[0052] Under the control of this process parameter, the product crack incidence rate is 0.3%.

[0053] The above description is only a specific implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing the crack incidence in the production of medium carbon high strength steel, characterized in that: The method comprises the following steps: (1) Using electric furnace smelting to obtain molten steel; (2) the molten steel obtained in step (1) is continuously casted into a thin strip through two counter-rotating casting rolls to obtain a cast strip, and a roller brush is used to clean the surface of the casting rolls; (3) hot-rolling the cast strip obtained in step (2) into a hot-rolled thin strip through one pass, cooling it through gas mist, and coiling it to obtain a hot-rolled coil. The method for reducing the crack incidence rate of medium carbon high strength steel in production adopts the following control means: (a) controlling the Mn content of the molten steel in step (1) to be 0.60-2.00%; (b) controlling the Mn / Si value of the molten steel in step (1) to be in the range of 2.8 to 5.2; (c) controlling the roller brush torque in step (2) to be 150 to 250 lb·in; (d) controlling the vibration amplitude of the roller brush in step (2) to be ≤50 lb·in; (e) controlling the surface roughness of the casting roll in step (2) to be 6 to 16 μm; (f) controlling the thickness of the cast strip obtained in step (2) to be 1.9-2.5 mm; (g) Controlling the reduction ratio of one hot rolling pass in step (3) to be ≥20%.

2. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: In step (1), the composition of molten steel is designed according to the performance requirements of the product produced by the twin-roll casting process.

3. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (a): Control the Mn content to 0.65-2.00%.

4. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (b): Control the Mn / Si value in the range of 3.25 to 4.

54.

5. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (c): Control the roller brush torque to be 160 to 230 lb·in.

6. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (d): Control the vibration amplitude of the roller brush to 15 to 45 lb·in.

7. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (e): Control the surface roughness of the casting roll to 8 to 14 μm.

8. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (f): Control the thickness of the cast strip to be 1.95-2.2 mm.

9. The method for reducing the crack incidence in the production of medium carbon high strength steel according to claim 1, characterized in that: Control means (g): Control the hot rolling reduction ratio to 30 to 55%.

10. A medium carbon high strength steel, characterized in that: The method for producing medium carbon high strength steel is controlled by the method for reducing the crack incidence rate of medium carbon high strength steel according to any one of claims 1 to 9, wherein the crack incidence rate of the medium carbon high strength steel is not higher than 1.2%.

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