A method for continuously casting and preparing 200 series stainless steel with high Cu content and its thin strip

Abstract

The present invention relates to a 200 series stainless steel with a high Cu content and a thin strip continuous casting method for preparing the same. The composition of the 200 series stainless steel with a high Cu content satisfies the following composition by mass percentage: C 0.1-0.15%; Si 0.30-0.50%; Cr 14.0-15.0%; Mn 9.0-10.0%; Ni 1.0-2.0%; N 0.10-0.20%; Cu 0.2-1.0%; S ≤0.005%, P ≤0.020%; the remainder being iron and other unavoidable impurity elements. The preparation method comprises: selecting raw materials according to the designed composition, smelting to obtain molten steel for casting; casting the molten steel using twin-roll thin strip continuous casting to obtain a stainless steel cast strip; hot-rolling the cast strip and then water quenching it to obtain a thin strip; heat-insulating the obtained thin strip to eliminate stress, and then water quenching it to obtain the product. The components of the present invention are reasonably designed, the process is simple and controllable, the obtained product has excellent performance and thinner thickness, and is convenient for industrial application.

Description

Technical Field

[0001] The present invention relates to the field of steel continuous casting technology, and in particular to a 200 series stainless steel with a high Cu content and a thin strip continuous casting preparation method thereof. Background Art

[0002] In 1856, Bessemer of England, combining nonferrous metal casting techniques, first cast thin metal strip using a twin-roll continuous caster. The following year, he patented a twin-roll continuous caster for steel casting, marking the beginning of thin strip casting. Limited by technological advancements, the production process of thin strip casting has been difficult to control. However, due to its short process flow, low energy consumption, low cost, excellent solidification structure, and high tolerance to impurities, the thin strip casting process has regained the attention of steel companies.

[0003] Low-nickel stainless steel originated in the first half of the 20th century. Due to the scarcity of nickel resources, there was an urgent need to reduce the amount of nickel added in stainless steel production to reduce costs and maintain supply. Consequently, 200 series austenitic stainless steels with higher Mn and N contents were invented. 200 series austenitic stainless steels have low nickel usage and low production costs, while offering excellent performance and promising application prospects. Currently, 200 series stainless steels are typically produced through traditional continuous casting combined with extensive hot rolling processes. Few studies have been reported on the production of 200 series stainless steel strips using twin-roll thin strip casting technology.

[0004] In the prior art, some have attempted to introduce copper into stainless steel to increase the product's elongation. For example, patent CN 103987867A discloses an economical duplex stainless steel and a method for preparing the same. The addition of copper results in a finished product with good elongation, but does not involve strength data. Furthermore, the patent utilizes a large amount of Cr and a small amount of Mn. Summary of the Invention

[0005] In view of the problems existing in the existing stainless steel production, the present invention provides a 200 series stainless steel with a high Cu content and a thin strip continuous casting preparation method thereof.

[0006] The high-Cu-content 200 series stainless steel comprises the following components by mass percentage: C 0.1-0.15%; Si 0.30-0.50%; Cr 14.0-15.0%; Mn 9.0-10.0%; Ni 1.0-2.0%; N 0.10-0.20%; Cu 0.2-1.5%; S ≤0.005%, P ≤0.020%, with the remainder being iron and other unavoidable impurities.

[0007] Preferably, the composition of the stainless steel strip is as follows by mass percentage: C 0.1-0.12%; Si 0.35-0.45%; Cr 14.3-14.5%; Mn 9.5-9.8%; Ni 1.1-1.3%; N 0.14-0.15%; Cu 0.2-1.5%; S ≤0.005%, P ≤0.020%, and the balance is iron and other inevitable impurities.

[0008] In industrial applications, in order to obtain a product with higher strength, the Cu content can be optimized to 0.23~0.85wt%.

[0009] The microstructure of the 200 series stainless steel thin strip with high Cu content of the present invention is a mixed structure of austenite and delta ferrite.

[0010] The 200 series stainless steel thin strip with high Cu content obtained by the process of the present invention has an ultimate tensile strength of 900-1100 MPa at room temperature, a yield strength of 670-780 MPa, an elongation after fracture of 45%-65%, and good surface quality.

[0011] In the composition design of the 200 series stainless steel strip with high Cu content described in the present invention, the roles played by appropriate amounts of various elements are as follows:

[0012] C: Carbon will combine with the Cr element in stainless steel to reduce corrosion resistance, but C also helps to improve the strength of steel, so the carbon content is controlled at a relatively reasonable level, such as 0.1~0.15%.

[0013] Si: Silicon and Cr work together to improve the corrosion resistance of stainless steel, but silicon will increase the grain coarsening tendency of steel and increase brittleness, so it is controlled at a low level.

[0014] Cr: Chromium can passivate stainless steel and significantly improve its corrosion resistance. However, compared with other 200 series stainless steels, the present invention reduces the amount of Cr and optimizes the Cr content to 14-14.5%. This is because the addition of appropriate amounts of elements such as manganese and nitrogen not only ensures the corrosion resistance of the product, but also reduces costs and improves the mechanical properties of the product.

[0015] Mn: Manganese is an austenite stabilizing element. It can not only replace nickel, but also play a synergistic role with appropriate amounts of Cr, N, etc.

[0016] Ni: Nickel is an austenite stabilizing element that can improve the corrosion resistance of stainless steel. In the present invention, appropriate amounts of Mn and N are used to replace part of Ni, reducing their usage to reduce costs. At the same time, the selected manganese and nitrogen are combined with Cr and a small amount of Ni to ensure the corrosion resistance of the product while also having excellent mechanical properties.

[0017] N: Nitrogen is a strong austenite stabilizing element and can replace nickel. However, a higher nitrogen content can easily affect product quality, so the nitrogen level must be controlled.

[0018] Cu: Copper can improve the corrosion resistance of stainless steel and increase the ductility of stainless steel.

[0019] The specific process flow of the thin strip continuous casting preparation method of the 200 series stainless steel with high Cu content is as follows:

[0020] Melting: Select raw materials according to the designed composition, and obtain molten steel for casting through melting;

[0021] (2) Casting: The molten steel is cast using twin-roll thin strip casting at a temperature of 1480-1530°C under nitrogen protection. The molten steel is poured between twin copper rollers and solidified to form a stainless steel strip with a thickness of 0.9-1.5 mm and good surface quality. The crystallization roller speed is 50-90 m / min.

[0022] (3) Hot rolling: After the cast strip is delivered, it is hot rolled for 1~2 passes, water quenched after rolling, and then coiled. The rolling temperature is controlled at 850~1050℃, and the reduction rate is ≤50%, obtaining a thin strip with a thickness of 0.5~1.0mm;

[0023] (5) Insulation: The obtained thin strip is kept at 500~900℃ for 30~120min to eliminate stress, and water quenched to obtain the finished 200 series stainless steel thin strip.

[0024] The raw materials used in step (1) of the present invention include: electrolytic chromium, ferromanganese, high-purity nickel, industrial pure iron, ferrochromium nitride, and electrolytic copper. In industrial applications, vacuum melting is used to first add electrolytic chromium, high-purity nickel, and industrial pure iron for melting, and then add ferrochromium nitride, ferromanganese, and electrolytic copper to obtain molten steel for casting.

[0025] Preferably, the continuous casting machine in step 2 is a twin vertical roller thin strip continuous casting machine.

[0026] Preferably, the copper roller is made of red copper or other copper alloys.

[0027] Preferably, the surface of the copper roller is electroplated with Cr with a thickness of 0.06-0.12 mm.

[0028] In particular, during the casting process, a roller surface cooling device is added outside the copper roller to promote roller surface cooling.

[0029] Furthermore, the roller surface cooling device is arc-shaped and buckled onto the outside of the roller surface, with a central angle of 90-120 degrees. Its thickness is 1 / 5-1 / 2 of the copper roller diameter d, and its width is the same as the width of the crystallization roller surface. It is made of copper and has cooling water flowing through it. The diameter of the cooling water channel is 1 / 3-1 / 2 of the device thickness. When the roller surface is rolling, the roller surface cooling device does not move with the roller surface.

[0030] Furthermore, an arc-shaped solid graphite carbon brush is added to the inner side of the arc of the roller surface cooling device. The thickness of the arc-shaped solid graphite carbon brush is 1 / 10 to 1 / 3 of the thickness of the roller surface cooling device, which reduces friction resistance and ensures the heat transfer rate. At the same time, a thin layer of graphite is evenly coated on the roller surface, which is beneficial to heat transfer, prevents roller sticking, and improves the surface quality of the thin strip.

[0031] Furthermore, roller brushes are provided on both sides of the roller surface cooling device to clean the roller surface, reduce the wear of the roller surface cooling device, and reduce the excessive adhesion of graphite.

[0032] Beneficial effects of the present invention:

[0033] 1) The present invention uses a thin strip continuous casting process to prepare a 200 series stainless steel thin strip, which gives full play to the characteristics of the thin strip continuous casting process, uses a shorter process and lowers the cost to obtain a 200 series stainless steel thin strip with excellent performance.

[0034] 2) The 200 series stainless steel strip produced using the strip casting process in this invention achieves rapid solidification, resulting in a dual-phase structure of austenite and ferrite, enhancing product strength. Furthermore, the high copper content of the designed high-Cu 200 series stainless steel strip enhances product ductility, leveraging the advantages of strip casting to mitigate its harmful effects.

[0035] 3) This invention features a short process flow and thin cast strip. To ensure cooling intensity, a roll surface cooling device is installed. This allows the crystallization roll surface to be cooled both internally and externally, lowering the temperature and improving cooling intensity. This device utilizes graphite's high lubricity and high thermal conductivity to cool the moving copper roll without damaging it. A thin layer of graphite can also be applied to the roll surface to prevent sticking and improve surface quality.

[0036] 4) The present invention involves only hot rolling and holding steps. Hot rolling welds cast strip defects, and quenching prevents grain coarsening. Holding at a lower temperature eliminates stress, shortens the process flow while reducing strip thickness, and further reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the roller surface cooling device of the present invention. Figure 1 (a) is the arc, water channel and graphite carbon brush structure of the device. The graphite carbon brush is arranged according to Figure 1 (b) is inserted into the copper base and can be replaced after wear. Figure 1 (c) is a schematic diagram of the three-dimensional structure of the device.

[0038] Figure 2 It is a schematic diagram of the process flow of the vertical twin-roll thin strip continuous casting unit of the present invention.

[0039] Figure 2 Among them, 1 is the ladle, 2 is the tundish, 3 is the crystallizer, 4 is the crystallization roller, 5 is the roller surface cooling device, 6 is the roller brush, 7 is the cooling device, 8 is the swing guide plate, 9 is the pinch roller, 10 is the nitrogen atmosphere protection area, 11 is the nitrogen protection online heating area, 12 is the rolling roller, 13 is the cooling device, 14 is the conveying roller, and 15 is the flying shear.

[0040] Figure 3 This is a physical picture of the product of Example 1. DETAILED DESCRIPTION

[0041] The technical route of the present invention is described in detail with reference to the drawings in the embodiments of the present invention. The following embodiments are only some embodiments of the inventor's team. Other embodiments obtained based on the embodiments of the present invention by those skilled in the art without making any creative work shall all fall within the scope of protection of the present invention.

[0042] Figure 1 This is a schematic diagram of the roller surface cooling device of the present invention. Figure 2 The process flow diagram of the vertical twin-roll thin strip continuous casting unit shown in FIG.

[0043] Melting is performed in an induction melting furnace 1 under a protective atmosphere. Electrolytic chromium, ferromanganese, high-purity nickel, industrial pure iron, ferrochromium nitride, and electrolytic copper are selected according to the chemical composition of C 0.1-0.15%; Si 0.30-0.50%; Cr14.0-15.0%; Mn 9.0-10.0%; Ni 1.0-2.0%; N 0.10-0.20%; Cu 0.2-1.5%; S ≤0.005%, P ≤0.020%, with the balance being iron and other inevitable impurities. Vacuum melting is performed. Electrolytic chromium, high-purity nickel, and industrial pure iron are first added for melting, and then ferrochromium nitride, ferromanganese, and electrolytic copper are added to obtain molten steel for casting.

[0044] After smelting, the molten steel is cast at a temperature of 1480-1530°C. It is poured into the tundish (2) and then into the distributor (3). It then flows into the roll gap. The molten steel solidifies, resulting in a stainless steel cast strip with a thickness of 0.9-1.5 mm and good surface quality. The crystallization rolls rotate at a speed of 60 m / min.

[0045] As shown in the figure, a roller surface cooling device 5 is used on the outer side of the copper roller shown in 4 to cool the roller surface. Figure 1As shown, Figure 1 (a) is a schematic diagram of the copper arc, water channel and graphite carbon brush structure of the device. The central angle of the copper arc roller surface cooling device is 90°, the thickness is 1 / 3 of the copper roller diameter d, and the width is the same as the width of the crystallization roller surface. Cooling water flows inside, and the diameter of the cooling water channel is 1 / 2 of the device thickness. The graphite carbon brush is a solid graphite block with a thickness of 1 / 8 of the device thickness, which reduces friction resistance and ensures heat transfer rate. At the same time, a thin layer of graphite is evenly coated on the roller surface, which is beneficial to heat transfer, prevents sticking to the roller, and improves the surface quality of the thin strip. Figure 1 As shown in (b), it is inserted into the copper base in a groove shape and acts as a lubricant between the copper base and the copper roller. It can be replaced after wear. Figure 1 (c) is a schematic diagram of the three-dimensional structure of the roller surface cooling device. Figure 2 As shown in Figure 6, a roller brush is arranged to clean the roller surface and reduce the wear of the graphite carbon brush. The other roller brush is used to clean the excess graphite on the roller surface.

[0046] After the molten steel rapidly solidifies to form a cast strip, it is guided to pinch rolls 9 by a swinging guide plate 8. Cooling is accelerated by a water spray from a cooling device 7 to prevent strip breakage. A nitrogen atmosphere is used within the dotted box 10 to prevent oxidation. The strip is then fed into the nitrogen-protected area shown in the wire frame 11 for online heating until the temperature reaches the rolling temperature. Hot rolling is then performed in one pass at the rolling rolls 12, with a reduction of ≤50%, to obtain a 0.55 mm thick hot-rolled strip. The strip is then fed out by conveyor rolls 14 and cooled by a water spray from a cooling device 13. Finally, it is sheared and coiled.

[0047] After the hot-rolled strip is coiled, the steel coil is heat treated at a set temperature under a nitrogen atmosphere (heat treatment conditions are shown in Table 2) to eliminate stress and water quench to obtain a finished 200 series stainless steel thin strip.

[0048] At the same time, die casting was used to simulate a conventional casting method as a comparative example (i.e., comparative examples 1-4 of the present invention), and the process was as follows:

[0049] (1) Melting: Electrolytic chromium, ferromanganese, high-purity nickel, industrial pure iron, ferrochromium nitride, and electrolytic copper are selected according to the above composition and vacuum smelted. Electrolytic chromium, high-purity nickel, and industrial pure iron are first added for smelting, and then ferrochromium nitride, ferromanganese, and electrolytic copper are added to obtain molten steel for casting.

[0050] (2) Mold casting: Pour molten steel into the mold under nitrogen atmosphere to solidify, keep it at 1200℃ for 360min, and then open the mold to obtain the ingot

[0051] (3) Rolling: Rough rolling is first performed, and the ingot is kept at 1250℃ for 150min and then hot rolled. The starting rolling temperature is 1205℃ and the final rolling temperature is 1156℃ to obtain a 7mm thick hot rolled plate. Then, finish rolling is performed with the starting rolling temperature at 1050℃ and the final rolling temperature at 1006℃ to obtain a 0.9mm thick rolled plate. Then, the ingot is water-cooled and coiled to obtain a 200 series stainless steel plate produced by the traditional process.

[0052] The following are Examples 1 to 5 of the present invention. It can be seen that the thin strip continuous casting method of 200 series stainless steel of the present invention can obtain a stainless steel strip with excellent mechanical properties. Figure 3 As shown in the figure, the mechanical properties of the conventional 200 series stainless steel strip prepared using the process of the present invention are significantly superior to those of the conventional 200 series stainless steel strip. The conventional 200 series stainless steel strip produced using the process of the present invention can achieve an ultimate tensile strength of 1079 MPa and a maximum elongation of 54%. With the addition of a larger amount of copper, the maximum elongation increases to 60%, and the ultimate tensile strength reaches 1055 MPa. In the embodiment without the roller surface cooling device, the surface quality of the cast strip is slightly inferior, and the mechanical properties are also inferior to those of the other embodiments.

[0053]

[0054]

Claims

1. A 200 series stainless steel with a high Cu content, characterized by: The composition of the 200 series stainless steel with a high Cu content satisfies the following in percentage by mass: C 0.1-0.15%; Si 0.30-0.50%; Cr 14.0-15.0%; Mn 9.0-10.0%; Ni 1.0-2.0%; N 0.10-0.20%; Cu 0.2-1.0%; S ≤0.005%, P ≤0.020%; the balance being iron and other unavoidable impurity elements; The 200 series stainless steel with high Cu content is prepared by the following steps: (1) Melting: Select raw materials according to the designed composition and obtain molten steel for casting through melting; (2) Casting: The molten steel is cast using twin-roll thin strip continuous casting. The casting temperature is 1480-1530°C. Nitrogen protection is used during casting. The solidification results in a stainless steel cast strip with a thickness of 0.90-1.50 mm and good surface quality. The crystallization roller speed is 50-90 m / min. A roller surface cooling device is added to promote roller surface cooling; the roller surface cooling device is arc-shaped, buckled on the outside of the roller surface, with a central angle of 90-120 degrees, a thickness of 1 / 5-1 / 2 of the copper roller diameter d, and the same width as the crystallization roller surface width. It is made of copper and has cooling water flowing through it. The diameter of the cooling water channel is 1 / 3-1 / 2 of the device thickness. When the roller surface is rolling, the roller surface cooling device does not move with the roller surface; An arc-shaped solid graphite carbon brush is installed on the inner side of the arc of the roller surface cooling device. The thickness of the arc-shaped solid graphite carbon brush is 1 / 10~1 / 3 of the thickness of the roller surface cooling device. (3) Hot rolling: After the cast strip is delivered, it is hot rolled for 1~2 passes, water quenched after rolling, and then coiled. The rolling temperature is controlled at 850~1050℃, and the reduction rate is ≤50%, obtaining a thin strip with a thickness of 0.5~1.0mm; (4) Insulation: The obtained thin strip is kept at 500~900℃ for 30~120min to eliminate stress, and water quenched to obtain the finished 200 series stainless steel thin strip.

2. The 200 series stainless steel with a high Cu content according to claim 1, characterized in that: The composition of the 200 series stainless steel with a high Cu content meets the following requirements in terms of mass percentage: C 0.1-0.12%; Si 0.35-0.45%; Cr 14.3-14.5%; Mn 9.5-9.8%; Ni 1.1-1.3%; N 0.14-0.15%; Cu 0.2-1.5%; S ≤0.005%, P ≤0.020%, with the remainder being iron and other unavoidable impurities.

3. The 200 series stainless steel with a high Cu content according to claim 1, characterized in that: The microstructure of the 200 series stainless steel with a high Cu content is a mixed structure of austenite and delta ferrite.

4. The 200 series stainless steel with a high Cu content according to claim 1, characterized in that: A vertical twin-roll thin strip continuous caster is used.

5. The 200 series stainless steel with a high Cu content according to claim 1, characterized in that: The copper roller is made of red copper or copper alloy, with a chrome-plated surface and a chrome layer thickness of 0.06~0.12mm.

6. The 200 series stainless steel with a high Cu content according to claim 1, characterized in that: Roller brushes are set on both sides of the device.

7. The 200 series stainless steel with a high Cu content according to claim 1, characterized in that: The room temperature ultimate tensile strength of the obtained continuous casting thin strip is 900~1100MPa, the yield strength is 670~780MPa, and the elongation after fracture is 45%~65%.

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