A method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting

Abstract

The invention belongs to the technical field of steel production, and discloses a method for reducing the probability of occurrence of twin-roll cast weathering steel cracks. The chemical composition of the molten steel in the invention includes, by mass percentage, C: ≤0.03-0.009*Si-0.01*Si*Mn-0.0015*Mn-0.013*Cu; Mn: 0.4-1.0%; Si: 0.2-0.4%; Cu: 0.25-0.4%; Cr: 0.3-0.5%; P: 0.07-0.18%; S: ≤0.003%; O: 0.004-0.008%; H≤0.0005%. By optimizing the chemical composition and casting and rolling process of weathering steel, the crack determination rate of twin-roll thin strip cast weathering steel is reduced to no more than 1.0%.

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and in particular relates to a method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting. Background Art

[0002] Weathering steel has the characteristics and significant advantages of being green, environmentally friendly and long-lasting. It is not only suitable for a variety of climates and environments, but also has the characteristics of high strength, high toughness, weldability, fire resistance and wear resistance. It is widely used in the manufacture of containers, vehicles, buildings, bridges, pipelines, machinery and other industries.

[0003] Hot-rolled weathering steel accounts for more than 90% of all weathering steel products. At present, the production technology and equipment routes of hot-rolled weathering steel include conventional hot rolling, thin slab continuous casting and rolling, and twin-roller thin strip casting and rolling. The crack problem has always been one of the key issues faced by weathering steel production.

[0004] Patent document 201811587434.0 discloses the "Production Method of Weathering Steel Q355NHD", which belongs to the category of conventional hot rolling and suppresses the occurrence of cracks in the corners of weathering steel ingots.

[0005] The document "Analysis and Improvement of Causes of Center Cracks in SPA-H Steel Plate" also belongs to the category of conventional hot rolling. It believes that the central eccentricity, looseness and MnS inclusions enriched in the center of the ingot are the root causes of the cracks. The cracks are prevented by reducing the S content to below 80ppm, controlling the superheat at around 25°C, optimizing the electromagnetic stirring process, optimizing the dynamic light reduction process and other measures.

[0006] The document "Research on the Quality of Hot-rolled Container Plate Continuous Casting Billets" belongs to the category of thin slab continuous casting and rolling. It believes that C is in the range of peritectic reaction and the excessive heat flux density of the crystallizer is the cause of cracks. Cracks can be prevented by reducing the C content to below 0.06% and reducing the continuous casting speed.

[0007] The document "Study on the Heating Process in a Roller-Heat Heating Furnace for SPA-H Container Plate Continuous Casting" also belongs to the category of thin slab continuous casting and rolling. It believes that copper brittleness is the cause of cracks, and that cracks can be prevented by adding a certain amount of Ni or Si.

[0008] The twin-roll thin strip technology belongs to the category of sub-rapid solidification. The peritectic point in the phase diagram shifts significantly to the left, and cracks are very likely to occur when the carbon content is too high. Patent document 200910048141.X discloses "A weathering steel and its manufacturing method" and patent document 201410591781.6 discloses "A weathering steel hot-rolled thin strip without P segregation and its manufacturing method" belong to this category. The carbon content of this method falls within the sub-peritectic steel range, and the steel strip is prone to cracks.

[0009] The twin-roll thin strip technology belongs to the category of sub-rapid solidification. The segregation tendency of the Cu element is small. Without adding Ni or adding less Ni, the cracks caused by Cu are eliminated. Patent document 201710888181.X disclosed "A weathering steel and its production method" and patent document 201910130658.7 disclosed "A low-cost weathering steel and its production method" belong to this category, but the problem of weathering steel cracks has not been completely solved. Summary of the invention

[0010] The purpose of the present invention is to provide a method for reducing the probability of cracks in the production of weathering steel by twin-roll casting and rolling. The method significantly reduces the probability of cracks in the production of weathering steel by twin-roll casting and rolling by optimizing the chemical composition and casting and rolling process of weathering steel, significantly improves the qualified rate of weathering steel, and ensures that the twin-roll casting and rolling technology route is used to produce weathering steel in an industrialized and economical manner.

[0011] To achieve the purpose of the present invention, the present invention adopts the following technical solution:

[0012] According to a first aspect of the present invention, a method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting is disclosed, the method comprising the following steps:

[0013] (1) Smelting to obtain molten steel, the molten steel composition is as follows:

[0014] Si: 0.20-0.40%;

[0015] Mn: 0.40-1.0%;

[0016] Cu: 0.25-0.40%

[0017] C: 0.03-0.009*Si-0.01*Si*Mn-0.0015*Mn-0.013*Cu;

[0018] Cr: 0.3-0.5%

[0019] P: 0.07-0.18%;

[0020] S: ≤0.003%;

[0021] The balance is Fe and unavoidable impurities;

[0022] (2) the molten steel obtained in step (1) is subjected to thin strip continuous casting by a twin-roll casting device under the protection of inert gas to obtain a cast strip, and a roller brush is used to clean the surface of the casting roll, wherein the roller brush torque is controlled to be ≥250 lb·in, the roller brush speed is controlled to be 400±20 rpm, the O content of the tundish is controlled to be 0.004-0.008%, the H content of the tundish is controlled to be ≤0.0005%, and the thickness of the cast strip is controlled to be 1.85-2.5 mm;

[0023] (3) The cast strip obtained in step (2) is put into a hot box, wherein the hot box includes a No. 1 hot box, a No. 2 hot box, and a No. 3 hot box, wherein the inert gas flow rate of the No. 1 hot box is controlled to be ≥ 600m 3 / h, the hot box looper quantity is controlled at 20-40%;

[0024] (4) hot rolling the cast strip obtained in step (3) into a thin strip through one pass, wherein the reduction ratio of the hot rolling is controlled to be ≥22%.

[0025] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in step (2), the roller brush torque is controlled to be 250 to 300 lb·in.

[0026] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in the step (2), the speed of the roller brush is controlled to be 400-420 rpm.

[0027] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in the step (2), the O content in the tundish is controlled to be 0.0046-0.0073%.

[0028] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in the step (2), the H content of the tundish is controlled to be ≤0.00042%.

[0029] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in the step (2), the thickness of the cast strip is 1.9 to 2.4 mm.

[0030] According to the method for reducing the crack occurrence probability of weathering steel produced by twin-roll casting of the present invention, preferably, in step (3), the inert gas flow rate of the No. 1 hot box is 700-1020m 3 / h.

[0031] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in the step (3), the amount of hot box looper is controlled to be 25-38%.

[0032] According to the method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting of the present invention, preferably, in the step (3), the reduction ratio of hot rolling is controlled to be ≥25.8%.

[0033] According to a second aspect of the present invention, a weathering steel is disclosed. The production process of the weathering steel adopts the above-mentioned method for crack control, wherein the crack detection rate of the weathering steel is not higher than 1.0%.

[0034] Technical concept

[0035] The present invention believes that the leftward shift of the peritectic point leads to an early solid-state phase transformation from δ ferrite to →γ austenite, which causes insufficient strength of the solidified shell and makes it difficult to resist phase transformation shrinkage, resulting in cracks. The present invention effectively avoids this phenomenon by optimizing the composition. Si, Mn, Cu, and S shift the peritectic point of the phase diagram to the left. Under the condition of meeting the weathering steel standards or customer requirements, the Si, Mn, and Cu contents are controlled, and the C content is further limited to offset the effect of the leftward shift of the peritectic point.

[0036] According to the above concept, the control of Si, Mn, Cu, C and S in the present invention is as follows:

[0037] Si: 0.20-0.40%;

[0038] Mn: 0.40-1.0%;

[0039] Cu: 0.25-0.40%;

[0040] C: 0.03-0.009*Si-0.01*Si*Mn-0.0015*Mn-0.013*Cu;

[0041] S: ≤0.003%.

[0042] The present invention believes that when the density of P combined with the solidified metal surface is higher than a certain level, it will hinder the solidification of the metal and easily form a closed liquid film. When the tensile stress on the casting strip is too large, the grains on both sides of the closed liquid film are pulled apart, forming a crack source. The strength of the shell is too low, and the crack source expands to form cracks. Since P is an important weathering element, it is impossible to remove it. The negative effects of P need to be eliminated by other means:

[0043] (1) The present invention limits the thickness of the casting strip to 1.85-2.5 mm, ensuring that a certain amount of liquid core is retained when the casting strip passes through the hot box, thereby reducing the probability of the occurrence of a closed liquid film and the probability of the formation of a crack source.

[0044] (2) The present invention limits the thickness of the casting strip to 1.85 to 2.5 mm, increases the thickness of the casting strip, reduces the casting strip temperature, increases the strength of the billet shell, and inhibits the expansion of the crack source.

[0045] (3) The present invention limits the inert gas flow rate of the No. 1 hot box to ≥ 600m 3 / h, reducing the temperature of the casting strip when passing through the hot box looper, increasing the strength of the billet shell and inhibiting the expansion of the crack source.

[0046] (4) The present invention limits the amount of hot box loopers to 20-40%, thereby reducing the tensile stress on the casting belt when passing through the hot box and inhibiting the formation of crack sources.

[0047] The present invention believes that low-frequency vibration during casting and rolling may cause cracks: the present invention limits the O content of the tundish to 0.004-0.008%, which can effectively inhibit the occurrence of low-frequency vibration.

[0048] The present invention believes that H accumulates between the casting rolls and the casting belt, seriously affecting the interface heat transfer, causing uneven solidification and forming cracks: the present invention limits the H content of the tundish to ≤ 0.0005%.

[0049] The thickness of the oxide film on the casting roll in the twin-roll casting process significantly affects the interfacial heat transfer between the molten steel and the casting roll. If the oxide film is too thin, too thick or uneven, it will inhibit the interfacial heat transfer and cause cracks: the present invention limits the roller brush torque to ≥250lb·in and the roller brush speed to 400±20rpm, which can ensure a uniform and appropriate oxide film and inhibit the occurrence of cracks.

[0050] The present invention believes that sufficient hot rolling reduction can weld some cracks: the present invention limits the hot rolling reduction to ≥ 22%.

[0051] Beneficial technical effects

[0052] Compared with the prior art, the technical features and beneficial technical effects of the present invention are at least:

[0053] Under existing production conditions, the present invention analyzes and studies the specific causes of weathering steel cracks, and reduces the crack detection rate of twin-roll thin strip cast weathering steel to no more than 1.0% by optimizing the chemical composition and casting process without adding existing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] 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.

[0055] Figure 1 Schematic diagram of the production process for manufacturing thin-gauge weathering steel according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Example 1

[0060] (1) Molten steel smelting: Electric furnace steelmaking, VD vacuum furnace degassing, LF furnace refining are adopted to obtain molten steel with qualified composition, which is as follows by weight: C: 0.0162%; Si: 0.25%; Mn: 0.85%; Cu: 0.31%; Cr: 0.38%; P: 0.080%; S: 0.0020%; the remainder is iron and unavoidable impurity elements.

[0061] (2) The content of O and H in the tundish is 0.0073% and 0.00036% respectively.

[0062] (3) Thin strip continuous casting: The strip thickness is 1.9 mm, and the inert gas flow rate of the No. 1 hot box is 1020 m 3 / h, the hot box looper amount is controlled at 38%, the roller brush torque is 250-270lb·in, and the roller brush speed is 410-420rpm.

[0063] (4) Hot rolling: The cast strip was hot rolled in one pass at a reduction of 25.8% to form a hot rolled thin strip with a thickness of 1.41 mm.

[0064] Under this process parameter, the probability of steel strip cracks is 0%.

[0065] Example 2

[0066] (1) Molten steel smelting: Electric furnace steelmaking, VD vacuum furnace degassing, LF furnace refining are adopted to obtain molten steel with qualified composition, which is as follows by weight: C: 0.022%; Si: 0.31%; Mn: 0.55%; Cu: 0.32%; Cr: 0.40%; P: 0.12%; S: 0.0022%; the remainder is iron and unavoidable impurity elements.

[0067] (2) The content of O and H in the tundish is 0.0062% for O and 0.00042% for H.

[0068] (3) Thin strip continuous casting: The strip thickness is 2.2 mm, and the inert gas flow rate of the No. 1 hot box is 700 m 3 / h, the hot box looper amount is controlled at 28%, the roller brush torque is 278-300lb·in, and the roller brush speed is 400-410rpm.

[0069] (4) Hot rolling: The cast strip was hot rolled in one pass at a reduction of 33.2% to form a hot rolled thin strip with a thickness of 1.47 mm.

[0070] Under this process parameter, the probability of steel strip cracks is 0%.

[0071] Example 3

[0072] (1) Molten steel smelting: Electric furnace steelmaking, VD vacuum furnace degassing, LF furnace refining, to obtain molten steel with qualified composition, by weight percentage: C: 0.0194%; Si: 0.32%; Mn: 0.72%; Cu: 0.28%; Cr: 0.35%; P: 0.092%; S: 0.0015%; the remainder is iron and unavoidable impurity elements.

[0073] (2) The content of O and H in the tundish is 0.0046% and 0.00025% respectively.

[0074] (3) Thin strip continuous casting: The strip thickness is 2.4 mm, and the inert gas flow rate of the No. 1 hot box is 850 m 3 / h, the hot box looper amount is controlled at 25%, the roller brush torque is 272-295lb·in, and the roller brush speed is 400-410rpm.

[0075] (4) Hot rolling: The cast strip was hot rolled in one pass at a reduction of 45% to form a hot rolled thin strip with a thickness of 1.32 mm.

[0076] Under this process parameter, the probability of steel strip cracks is 0%.

[0077] 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 probability of cracks occurring in weathering steel produced by twin-roll casting, characterized in that: The method comprises the following steps: (1) Smelting to obtain molten steel, the molten steel composition is as follows: Si: 0.20-0.40%; Mn: 0.55-1.0%; Cu: 0.25-0.32%; C: 0.03-0.009*Si-0.01*Si*Mn-0.0015*Mn-0.013*Cu; Cr：0.3-0.4％； P：0.07-0.18％； S：≤0.003％； The balance is Fe and unavoidable impurities; (2) the molten steel obtained in step (1) is subjected to thin strip continuous casting by a twin-roll casting device under the protection of inert gas to obtain a cast strip, and a roller brush is used to clean the surface of the casting roll, wherein the roller brush torque is controlled to be ≥250 lb·in, the roller brush speed is controlled to be 400±20 rpm, the O content of the tundish is controlled to be 0.004-0.008%, the H content of the tundish is controlled to be ≤0.0005%, and the thickness of the cast strip is controlled to be 1.85-2.4 mm; (3) The cast strip obtained in step (2) is put into a hot box, wherein the hot box includes a No. 1 hot box, a No. 2 hot box, and a No. 3 hot box, wherein the inert gas flow rate of the No. 1 hot box is controlled to be ≥ 600m 3 / h, the hot box looper quantity is controlled at 20-40%; (4) hot rolling the cast strip obtained in step (3) into a thin strip through one pass, wherein the reduction ratio of the hot rolling is controlled to be 22 to 45%.

2. The method for reducing the probability of cracks in producing weathering steel by twin-roll casting according to claim 1, characterized in that: In the step (2), the roller brush torque is controlled to be 250 to 300 lb·in.

3. The method for reducing the probability of cracks in producing weathering steel by twin-roll casting according to claim 1, characterized in that: In the step (2), the rotation speed of the roller brush is controlled to be 400-420 rpm.

4. The method for reducing the probability of cracks in producing weathering steel by twin-roll casting according to claim 1, characterized in that: In the step (2), the O content of the tundish is controlled to be 0.0046-0.0073%.

5. The method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting according to claim 1, characterized in that: In the step (2), the H content of the tundish is controlled to be ≤ 0.00042%.

6. The method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting according to claim 1, characterized in that: In the step (2), the thickness of the cast strip is 1.9 to 2.4 mm.

7. The method for reducing the probability of cracks in producing weathering steel by twin-roll casting according to claim 1, characterized in that: In step (3), the inert gas flow rate of the No. 1 hot box is 700-1020m 3 / h.

8. The method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting according to claim 1, characterized in that: In the step (3), the amount of hot box looper is controlled to be 25-38%.

9. The method for reducing the probability of cracks occurring in weathering steel produced by twin-roll casting according to claim 1, characterized in that: In the step (3), the reduction ratio of hot rolling is controlled to be 25.8 to 45%.

10. A weathering steel, characterized in that: The production process of the weathering steel adopts the method according to any one of claims 1 to 9 to perform crack control, wherein the crack detection rate of the weathering steel is not higher than 1.0%.

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