High-Cu-content 200-series stainless steel and continuous casting preparation method of thin strip of high-Cu-content 200-series stainless steel

Abstract

The invention relates to 200-series stainless steel with high Cu content and a thin-strip continuous casting preparation method of the 200-series stainless steel. The 200-series stainless steel with the high Cu content comprises the following components in percentage by mass: 0.1-0.15% of C; 0.30% to 0.50% of Si; 14.0% to 15.0% of Cr; 9.0% to 10.0% of Mn; 1.0 to 2.0 percent of Ni; 0.10% to 0.20% of N; 0.2 to 1.0 percent of Cu; s < = 0.005%, P < = 0.020%; and the balance of iron and other inevitable impurity elements. The preparation method comprises the following steps: selecting the raw materials according to the design components, and smelting to obtain molten steel for casting; molten steel obtained through smelting is cast through double-roller thin-strip continuous casting, a stainless steel cast strip is obtained, the cast strip is subjected to pass hot rolling and then water quenching, and a thin strip is obtained; and carrying out heat preservation treatment on the obtained thin strip to eliminate stress, and then carrying out water quenching to obtain a product. The composition is reasonable in design, the process is simple and controllable, and the obtained product is excellent in performance, thinner in thickness and convenient for industrial application.

Description

Technical Field

[0001] The present technology belongs to the field of steel continuous casting technology, and in particular relates 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 the United Kingdom combined the technology of non-ferrous metal casting and used a twin-roll continuous casting machine to cast metal strips for the first time. The following year, he applied for a patent for a twin-roll continuous casting machine for casting steel, which is considered to be the beginning of thin strip continuous casting. Limited by the development of science and technology, the production process of thin strip continuous casting has been difficult to be well controlled. The thin strip continuous casting process has returned to the attention of steel companies because of its short process, low energy consumption, low cost, good solidification structure, and high tolerance to impurity elements.

[0003] Stainless steel with low nickel content originated in the first half of the 20th century. Due to the lack of nickel resources, people urgently need to reduce the amount of nickel added in stainless steel production to reduce costs and maintain supply. Therefore, 200 series austenitic stainless steel with higher Mn and N content was invented. 200 series austenitic stainless steel has low nickel content, low production cost, excellent performance and good application prospects. At present, 200 series stainless steel is usually prepared by traditional continuous casting combined with a large number of hot rolling processes, and there are few reports on the preparation of 200 series stainless steel strips using twin-roll thin strip continuous casting technology.

[0004] In the prior art, some people have tried to introduce copper into stainless steel to achieve the purpose of improving the elongation of the product; for example, patent CN 103987867A discloses a kind of economical duplex stainless steel and its preparation method, which makes the finished product have good elongation by adding copper element, but does not involve strength data, and at the same time, it uses 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 200 series stainless steel with high Cu content has the following components 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 0.2-1.5%, S ≤0.005%, P ≤0.020%, and the remainder is iron and other inevitable 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 remainder 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 a room temperature ultimate tensile strength of 900-1100 MPa, 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: 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 more reasonable level, such as 0.1~0.15%.

[0012] 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.

[0013] Cr: Chromium can passivate stainless steel and greatly 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 manganese, nitrogen and other elements can not only ensure the corrosion resistance of the product, but also reduce costs and improve the mechanical properties of the product.

[0014] 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.

[0015] Ni: Nickel is an austenite stabilizing element and 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, and the amount thereof is reduced to reduce costs. At the same time, the selected manganese and nitrogen are combined with Cr and a small amount of Ni to ensure that the product has excellent mechanical properties while ensuring corrosion resistance.

[0016] N: Nitrogen is a strong austenite stabilizing element and can replace nickel, but a higher nitrogen content can easily affect product quality, so the nitrogen level must be controlled.

[0017] Cu: Copper can improve the corrosion resistance of stainless steel and increase the ductility of stainless steel.

[0018] The method for preparing the thin strip continuous casting of the 200 series stainless steel with high Cu content has the following specific process flow: Melting: Select various raw materials according to the designed composition, and obtain molten steel for casting through melting; (2) Casting: Use twin-roller thin strip continuous casting to cast the molten steel, the casting temperature is 1480~1530℃, and nitrogen protection is used during casting. The molten steel is poured between the copper twin rollers and solidified to obtain a stainless steel cast strip with a thickness of 0.9~1.5mm and good surface quality. The crystallization roller speed is selected to be 50~90m / min.

[0019] (3) Hot rolling: After the cast strip is delivered, it is hot rolled for 1 to 2 passes, water quenched after rolling, and then coiled. The rolling temperature is controlled at 850 to 1050 ° C, and the reduction rate is ≤ 50% to obtain a thin strip with a thickness of 0.5 to 1.0 mm; (5) Insulation: The obtained thin strip is kept at 500-900°C for 30-120 min to eliminate stress, and water quenched to obtain a finished 200 series stainless steel thin strip.

[0020] 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. When used in industry, vacuum smelting is adopted, and 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.

[0021] Preferably, the continuous casting machine in step 2 is a twin vertical roller thin strip continuous casting machine.

[0022] Preferably, the copper roller is made of red copper or other copper alloys.

[0023] Preferably, the surface of the copper roller is electroplated with Cr with a thickness of 0.06-0.12 mm.

[0024] In particular, during the casting process, a roller surface cooling device is added outside the copper roller to promote the cooling of the roller surface.

[0025] Furthermore, the roller surface cooling device is in an arc shape, buckled on the outside of the roller surface, with a central angle of 90-120°, a thickness of 1 / 5-1 / 2 of the copper roller diameter d, and a width the same as the width of the crystallization roller surface. It is made of copper, and has cooling water flowing inside. 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.

[0026] 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.

[0027] Furthermore, roller brushes are arranged 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.

[0028] Beneficial effects of the present invention:

[0029] 1) The 200 series stainless steel strip prepared by the thin strip continuous casting process of the present invention takes advantage of the characteristics of the thin strip continuous casting process, and obtains a 200 series stainless steel strip with excellent performance with a shorter process and lower cost.

[0030] 2) The 200 series stainless steel strip prepared by the strip continuous casting process of the present invention obtains a two-phase mixed structure of austenite and ferrite due to rapid solidification, thereby improving the strength of the product. At the same time, the designed high-Cu content 200 series stainless steel strip contains a higher Cu in the composition, which improves the ductility of the product and reduces its harm by utilizing the characteristics of strip continuous casting.

[0031] 3) The process flow of the present invention is short and the thickness of the cast strip is thin. In order to ensure the cooling strength, a roller surface cooling device is set up so that the crystallization roller surface can be cooled by both the inner and outer sides, and can be reduced to a lower temperature, thereby improving the cooling strength. The roller surface cooling device utilizes the high lubricity and high thermal conductivity of graphite to cool the moving copper roller without damaging the copper roller. A thin layer of graphite can also be coated on the roller surface to prevent the roller from sticking and improve the surface quality.

[0032] 4) The present invention only has the steps of hot rolling and heat preservation. Hot rolling welds the defects of the cast strip, and quenching prevents grain coarsening. The low temperature heat preservation eliminates stress, shortens the process flow on the basis of reducing the thickness of the thin strip, and further reduces the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It 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.

[0034] Figure 2 It is a schematic diagram of the process flow of the vertical twin-roller thin strip continuous casting unit of the present invention.

[0035] Figure 2Among them, 1 is a ladle, 2 is a tundish, 3 is a crystallizer, 4 is a crystallization roller, 5 is a roller surface cooling device, 6 is a roller brush, 7 is a cooling device, 8 is a swing guide plate, 9 is a pinch roller, 10 is a nitrogen atmosphere protection area, 11 is a nitrogen protection online heating area, 12 is a rolling roller, 13 is a cooling device, 14 is a conveying roller, and 15 is a flying shear.

[0036] Figure 3 This is a physical picture of the product of Example 1. DETAILED DESCRIPTION

[0037] The technical route of the present invention is described in detail in conjunction with 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 all belong to the protection scope of the present invention.

[0038] 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-roller thin strip continuous casting unit shown in the figure introduces the process flow of the present invention Induction melting furnace 1 is used for smelting in protective atmosphere, and 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%, and the balance is iron and other inevitable impurities, and vacuum smelting is performed, and 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.

[0039] After smelting, the molten steel is cast at a casting temperature of 1480-1530°C. After being poured into the tundish shown in 2, it flows into the distributor shown in 3, and then flows into the roll gap. The molten steel solidifies to obtain a stainless steel cast strip with a thickness of 0.9-1.5 mm and good surface quality. The crystallization roll speed is 60 m / min.

[0040] 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 1 As 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 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. According to Figure 1 As shown in (b), it is inserted into the copper substrate in a groove shape, plays a lubricating role between the copper substrate and the copper roller, and 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 6, a roller brush is arranged to clean the roller surface and reduce the wear of the graphite carbon brush, and another roller brush is used to clean the excess graphite on the roller surface.

[0041] After the molten steel rapidly solidifies to form a cast strip, the cast strip is guided to the pinch roller 9 by the swing guide plate 8, and the cooling device 7 is used to spray water to accelerate cooling to avoid strip breakage. Nitrogen atmosphere protection is used in the dotted frame shown in 10 to avoid oxidation. It is then sent to the nitrogen protection area shown in the wire frame 11 for online heating until the temperature reaches the rolling temperature, and hot rolling is carried out at the roller shown in 12 for one pass, with a reduction rate of ≤50%, to obtain a hot-rolled thin strip with a thickness of 0.55 mm, which is then sent out by the conveyor roller 14, and cooled by the cooling device 13 by spraying water, and finally sheared and coiled.

[0042] After the hot rolled strip is coiled, the steel coil is heat treated at a set temperature in a nitrogen atmosphere (the heat treatment conditions are shown in Table 2) to eliminate stress and water quench to obtain a finished 200 series stainless steel thin strip.

[0043] At the same time, mold 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: (1) Melting: Electrolytic chromium, ferromanganese, high purity nickel, industrial pure iron, ferrochromium nitride and electrolytic copper are selected according to the above-mentioned components for vacuum melting. 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] (2) Mold casting: Pour molten steel into a mold under nitrogen atmosphere to solidify, keep it at 1200℃ for 360min, and then cut it into ingots. (3) Rolling: Rough rolling is first performed, and the ingot is kept at 1250°C for 150 min and then hot rolled. The starting rolling temperature is 1205°C and the final rolling temperature is 1156°C to obtain a 7 mm thick hot-rolled plate. Then, finish rolling is performed with the starting rolling temperature at 1050°C and the final rolling temperature at 1006°C to obtain a 0.9 mm thick rolled plate. Subsequently, the ingot is water-cooled and coiled to obtain a 200 series stainless steel plate produced by conventional technology.

[0045] The following are Examples 1 to 5 of the present invention. It can be seen that the thin strip continuous casting method for preparing 200 series stainless steel of the present invention can obtain a stainless steel thin strip with excellent mechanical properties. Figure 3 As shown. The mechanical properties of the 200 series stainless steel strip with traditional composition prepared by the process of the present invention are significantly better than those of the 200 series stainless steel strip prepared by the traditional process. The 200 series stainless steel strip with traditional composition obtained by the process of the present invention can obtain an ultimate tensile strength of 1079MPa and a maximum elongation of 54%. After adding more copper elements, the maximum elongation increases to 60%, and the ultimate tensile strength can also reach 1055MPa; in the embodiment without using the roller surface cooling device, the surface quality of the cast strip is slightly worse, and the mechanical properties are also worse than those of other embodiments.

[0046]

[0047]

Claims

1. A 200 series stainless steel with a high Cu content, characterized in that: The composition of the 200 series stainless steel with high Cu content meets the following requirements in terms of 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 is iron and other inevitable impurity elements.

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%, and the remainder is iron and other inevitable impurities.

3. The 200 series stainless steel with 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. A method for continuously casting a 200 series stainless steel strip having a high Cu content as claimed in any one of claims 1 to 3, characterized in that: The steps include: (1) Melting: Select the raw materials according to the designed composition and obtain molten steel for casting through melting; (2) Casting: Use double-roller thin strip continuous casting to cast the molten steel, the casting temperature is 1480~1530℃, nitrogen protection is used during casting, and the solidification obtains a stainless steel casting strip with a thickness of 0.90~1.50mm and good surface quality. Among them, the crystallization roller speed is selected to be 50~90m / min; (3) Hot rolling: After the cast strip is delivered, it is hot rolled for 1 to 2 passes, water quenched after rolling, and then coiled. The rolling temperature is controlled at 850 to 1050 ° C, and the reduction rate is ≤ 50% to obtain a thin strip with a thickness of 0.5 to 1.0 mm; (4) Insulation: The obtained thin strip is kept at 500-900°C for 30-120 min to eliminate stress, and water quenched to obtain a finished 200 series stainless steel thin strip.

5. The continuous casting method for preparing a 200 series stainless steel thin strip with a high Cu content according to claim 4, characterized in that: A vertical twin-roller thin strip continuous casting machine is used.

6. The continuous casting method for preparing a 200 series stainless steel thin strip with a high Cu content according to claim 4, characterized in that: The copper roller is made of red copper or copper alloy, with chrome plating on the surface. The thickness of the chrome layer is 0.06~0.12mm.

7. The continuous casting method for preparing a 200 series stainless steel thin strip with a high Cu content according to claim 4, characterized in that: 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°, a thickness of 1 / 5-1 / 2 of the copper roller diameter d, and a width the same as the width of the crystallization roller surface. It is made of copper and has cooling water inside. 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.

8. The continuous casting method for preparing a 200 series stainless steel thin strip with a high Cu content according to claim 7, characterized in that: An arc-shaped solid graphite carbon brush is installed on the inner side of the arc of the roller surface cooling device, and 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.

9. The continuous casting method for preparing a 200 series stainless steel thin strip with a high Cu content according to claim 5, characterized in that: Roller brushes are arranged on both sides of the device.

10. The continuous casting method for preparing a 200 series stainless steel thin strip with a high Cu content according to claim 4, 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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