300 series stainless steel thin strip and continuous casting method of manufacture thereof

Abstract

This technology belongs to the field of continuous casting technology for steel, and specifically relates to a 300 series stainless steel strip and its continuous casting preparation method. The composition of the stainless steel strip, by mass percentage, is: C 0.01~0.05%; Si 0.30~0.60%; Cr 16.0~18.5%; Mn 0.8~1.6%; Ni 6.0~12.0%; N 0.01~0.05%; Cu 0.2~3.5%; S≤0.005%, P≤0.020%, B≤50ppm, Ce≤100ppm, with the balance being iron and other unavoidable impurities. The preparation method involves: smelting, casting, hot rolling, water cooling, followed by coiling to obtain a hot-rolled strip, holding the hot-rolled strip at a high temperature, and water quenching to obtain the finished 300 series stainless steel strip. This invention utilizes an optimized crystallization roller to obtain high-quality thin strips with tensile strength of 900~1110MPa, yield strength of 670~780MPa, elongation after fracture of 45%~65%, no surface cracks or wrinkles, and a thickness of approximately 0.6mm. The invention features a rationally designed composition, a simple and controllable preparation process, and produces high-performance products suitable for industrial application.

Description

Technical Field

[0001] This technology belongs to the field of steel continuous casting technology, and in particular relates to a 300 series stainless steel strip and its continuous casting preparation method. Background Technology

[0002] 300 series stainless steel is a very common type of stainless steel. Its high nickel and chromium content gives it a fully austenitic structure and excellent corrosion resistance. However, its high price is also a disadvantage, limiting its application to some extent. The production of 300 series stainless steel using thin-strip continuous casting can significantly shorten the production process and reduce costs. Furthermore, rapid solidification results in finer grains in the thin-strip products, improving their processing performance. Companies in Japan, South Korea, and other countries have conducted research on thin-strip continuous casting of 304 stainless steel and achieved some results; however, there are few successful long-term industrial production cases [Ge S, Isac M, Guthrie RI L. Progress of strip casting technology for steel; historical developments[J]. ISIJ international, 2012, 52(12): 2109-2122.]. The industrial production technology of thin-strip continuous casting of 300 series stainless steel still needs further improvement.

[0003] As a near-net-shape continuous casting technology, thin strip continuous casting produces thinner strips, which means lower rolling costs. Reducing the roll gap width can produce even thinner strips, further maximizing its advantages. However, thinner strips require better surface quality, higher casting speeds, and more intense cooling. The surface temperature of the copper roll rises rapidly after contact with the molten steel [Liu L, Liao B, Guo J, et al. 3D numerical simulation on thermalflow coupling field of stainless steel during twin-roll casting[J]. Journal of materials engineering and performance, 2014, 23: 39-48.]. If heat dissipation is insufficient, it will affect the surface quality of the thin strip. Summary of the Invention

[0004] This invention addresses the shortcomings of existing 300 series stainless steel strips and their continuous casting preparation by optimizing the composition, casting process, and hot rolling process to obtain a product with extremely high strength and excellent elongation.

[0005] This invention discloses a 300 series stainless steel strip; the composition of the stainless steel strip, by mass percentage, is: C 0.01~0.05%; Si 0.30~0.60%; Cr 16.0~18.5%; Mn 0.8~1.6%; Ni 6.0~12.0%; N 0.01~0.05%; Cu 0.2~3.5%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm. The balance is iron and other unavoidable impurities.

[0006] Preferably, the present invention provides a 300 series stainless steel strip; the composition of the stainless steel strip, by mass percentage, is: C 0.015~0.025%; Si 0.36~0.48%; Cr 17.5~18.5%; Mn 1.0~1.2%; Ni 7.8~8.5%; N 0.04~0.05%; Cu 0.2~0.4%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm. The balance is iron and other unavoidable impurities.

[0007] As a further preferred embodiment, the present invention provides a 300 series stainless steel strip; the composition of the stainless steel strip, by mass percentage, is: C 0.02~0.023%; Si 0.39~0.45%; Cr 17.7~18.2%; Mn 1.05~1.1%; Ni 8.0~8.03%; N 0.045~0.05%; Cu 0.24~0.35%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm. The balance is iron and other unavoidable impurities.

[0008] As a further preferred embodiment, the present invention provides a 300 series stainless steel strip; the composition of the stainless steel strip, by mass percentage, is: C 0.02%; Si 0.43%; Cr 18.0%; Mn 1.1%; Ni 8.0%; N 0.05%; Cu 0.35%; S≤0.005%, P≤0.020%, B≤50ppm, Ce≤100ppm. The balance is iron and other unavoidable impurities, etc.; or

[0009] The stainless steel strip has the following composition by mass percentage: C 0.021%; Si 0.42%; Cr 18.2%; Mn 1.05%; Ni 8.02%; N 0.046%; Cu 0.36%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm. The balance is iron and other unavoidable impurities; or

[0010] The composition of the stainless steel strip, by mass percentage, is as follows: C 0.02%; Si 0.41%; Cr 18.2%; Mn 1.06%; Ni 8.03%; N 0.048%; Cu 0.31%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm. The balance is iron and other unavoidable impurities.

[0011] The 300 series stainless steel strip of the present invention has an austenitic microstructure.

[0012] The 300 series stainless steel strip obtained by the process of this invention has a room temperature ultimate tensile strength of 900~1110MPa, an optimized tensile strength of 1085~1110MPa, a yield strength of 670~780MPa, preferably 700~780MPa, and an elongation after fracture of 45%~65%, preferably 55%~65%, and has good surface quality.

[0013] In the composition design of the 300 series stainless steel strip described in this invention:

[0014] C: Carbon combines with Cr in stainless steel, reducing its corrosion resistance, but C also helps to improve the strength of the steel, so the carbon content is kept at a low level.

[0015] Si: Silicon works together with Cr 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.

[0016] Cr: Chromium can passivate stainless steel, greatly improving its corrosion resistance, and is an important alloying element in 300 series stainless steel.

[0017] Mn: Manganese is an austenitic stabilizing element and works synergistically with nickel.

[0018] Ni: Nickel is an austenitic stabilizing element that can improve the corrosion resistance of stainless steel and is an important alloying element in 300 series stainless steel.

[0019] Nitrogen is a strong austenite stabilizing element, similar to nickel, but higher nitrogen content can negatively impact product quality; therefore, nitrogen levels must be controlled.

[0020] Cu: Copper can improve the corrosion resistance and ductility of stainless steel.

[0021] B: Trace amounts of boron can promote interfacial heat transfer, which is beneficial for the solidification of thin strips.

[0022] Ce: Trace amounts of cerium can help refine the solidification structure, form heterogeneous nucleation sites, refine grains, and further improve the performance of thin strips.

[0023] This invention discloses a continuous casting method for preparing 300 series stainless steel strips, the specific process flow of which is as follows:

[0024] (1) Smelting: The raw materials are smelted under vacuum according to the following chemical composition: C 0.01~0.05%; Si 0.30~0.60%; Cr 16.0~18.5%; Mn 0.8~1.6%; Ni 6.0~12.0%; N 0.01~0.05%; Cu 0.2~3.5%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm. The balance is iron and other unavoidable impurities.

[0025] (2) Casting: The molten steel obtained from the smelting is cast using twin-roll thin strip casting. The casting temperature is selected as 1490~1540℃, and nitrogen protection is used during casting. The molten steel is poured between copper twin rolls and solidifies to obtain a stainless steel strip with a thickness of 1.0~1.9mm and good surface quality. The crystallization roll speed is selected as 70~100m / min. The cooling rate of the twin rolls is 1000-2000℃ / s.

[0026] (3) Hot rolling: After the cast strip is conveyed out, it is hot rolled 1 to 2 times, then water quenched, and then coiled. The rolling temperature is controlled at 850 to 1050℃, preferably 900 to 1000℃, and the reduction rate is ≤50% to obtain a thin strip with a thickness of 0.5 to 1.3 mm.

[0027] (5) Heat preservation: The obtained cold-rolled strip is kept at 500~900℃, preferably 650~800℃ for 30~120min, preferably 60~60min to relieve stress, and then water-quenched to obtain the finished 300 series stainless steel strip.

[0028] To further improve product quality, this invention, for the first time, employs a cavity-type water channel, replacing the traditional cooling water channel. This significantly increases the cooling water throughput, thereby greatly enhancing the cooling intensity of the crystallizing roller, which is beneficial for improving the quality of the thin strip. Ribs are also incorporated to meet the strength requirements of the twin-roll casting force. The larger cavity hinders rapid cooling water flow; therefore, this invention incorporates a propeller within the cavity to agitate and propel the water flow. The propeller is mechanically driven by internal gears. As the crystallizing roller speed increases, the propeller speed also increases, while eliminating concerns about the problems encountered by motor-driven propellers at high temperatures.

[0029] This invention discloses a continuous casting method for preparing 300 series stainless steel strips, wherein the raw materials include electrolytic chromium, ferromanganese, ferroboron, pure cerium, high-purity nickel, industrial pure iron, ferrochromium nitride, and electrolytic copper.

[0030] Preferably, the continuous casting machine in step 2 is a double vertical roll thin strip continuous casting machine.

[0031] Preferably, the copper roller is made of copper or other copper alloys.

[0032] Preferably, the surface of the copper roller is electroplated with Cr, and the thickness of the Cr plating layer is 0.06~0.12mm.

[0033] In particular, the crystallizing rollers used in the casting process are crystallizing rollers with enhanced cooling intensity.

[0034] Furthermore, the crystallizing roller with enhanced cooling intensity uses cavities that allow water to flow through instead of traditional cooling channels. There are 4 to 12 cavities, evenly distributed, and the cavity thickness accounts for 40% to 60% of the thickness of the crystallizing roller sleeve. The roller surface is supported by ribs, and the thickness of the ribs is 10% to 20% of the cavity width.

[0035] Furthermore, a propeller is installed in each cavity of the crystallizing roller to agitate and propel the water flow. The diameter of the propeller is 50% to 90% of the minimum thickness in the three-dimensional space of the cavity.

[0036] Furthermore, the propeller in the crystallizing roller, which enhances cooling intensity, is driven by an internal gear. The propeller is connected to the internal gear via a shaft, which is fixed to the side of the roller and rotates around the roller shaft as the roller rotates. The gear ring is fixed, thereby driving the internal gear to rotate.

[0037] As a further preferred embodiment, the crystallizing roller 24 is composed of a rotating shaft 1, a main water channel 2, a rotating shaft water channel rib 3, a rotating shaft partition 4, a rotating shaft water groove 5, an inner ring of the roller sleeve 6, a cooling water chamber 7, a roller sleeve surface 8, a propeller 9, a propeller-rotating shaft connection 10, a plug 11, a propeller bearing 12, an internal gear 13, a gear frame 14, a gear frame keyway 15, a rotating shaft keyway 16, a gear ring 17, a roller sleeve rib 18, a flow channel 19, and a gear ring fixing hole 20; wherein the main water channel 2 is arranged concentrically with the rotating shaft 1 inside the rotating shaft 1, and the main water channel 2 penetrates the rotating shaft 1 and has a symmetrical structure;

[0038] The pivot waterway rib 3 is connected to the pivot diaphragm 4; generally, the pivot 1, pivot waterway rib 3, and pivot diaphragm 4 are a whole; in industrial applications, they can be formed into a whole by welding, casting, etc.

[0039] The rotating shaft water channel 5 is located between the distribution water channel (19) and the cooling water chamber (7);

[0040] The inner ring 6 of the roller sleeve is set on the side of the spacer 4 in the cylindrical rotating shaft.

[0041] Each cooling water chamber 7 is formed by the space enclosed by the inner ring 6 of the roller sleeve, the inner wall of the corresponding roller sleeve surface 8, and two roller sleeve ribs 18. In industrial applications, to ensure the uniformity of cooling water and to prevent the cooling uniformity and cooling effect from deteriorating due to the slowdown or stoppage of one or more propellers 9, N small holes can be evenly made on the roller sleeve ribs 18; where N is greater than or equal to 6.

[0042] Propeller 9 is positioned at the center of each chamber.

[0043] The propeller 9 is connected to one end of the propeller shaft 10. The other end of the propeller shaft 10 passes through the propeller bearing 12 and is connected to the internal gear 13. Half of the propeller bearings 12 are located on the side surface C, and the side surface C and the roller sleeve surface 8 form a protrusion on the shaft 1. The propeller bearings 12 located on the side surface C are embedded in the plug 11. The other part of the propeller bearings 12 are fixed to the gear frame support 14.

[0044] The bottom of the gear carrier support 14 is located inside the gear carrier keyway 15; the gear carrier keyway 15 and the shaft keyway 16 are connected by a keying connection.

[0045] The gear ring 17 meshes with the internal gear 13; 17 is fixed externally. 17 does not move with the rotating shaft or does not move at the same frequency as the rotating shaft, thereby driving 13.

[0046] In the 2K-H (NGW) type planetary transmission system composed of three components: ring gear 17, internal gear 13, and gear carrier 14, ring gear 17 is a fixed internal ring gear b, internal gear 13 is a planet gear g, and gear carrier 14 is a planet carrier H. Assuming the existence of a sun gear a, when the speed of the internal ring gear is 0, i.e., n... b When =0, we have

[0047]

[0048] In the formula: —The transmission ratio is as follows: the internal gear ring b is fixed, the sun gear a is the driving gear, and the planet carrier H is the driven gear.

[0049] —— The transmission ratio is as follows: planetary carrier H is fixed, sun gear a is the driving gear, and internal gear ring b is the driven gear.

[0050] —Number of teeth on internal gear ring b

[0051] —Number of teeth on sun gear a

[0052] In this system, the rotational speed of the planetary gear g relative to the planet carrier H is...

[0053]

[0054] In the formula: —The rotational speed of planetary gear g relative to planet carrier H

[0055] —The rotational speed of planetary gear g;

[0056] — Rotational speed of planetary carrier H

[0057] —The transmission ratio in which the planet carrier H is fixed, the planet gear g is the driving force, and the sun gear a is the driven force;

[0058] — Rotation speed of sun gear a

[0059] again:

[0060]

[0061]

[0062] Combining equations (1) to (4), we have:

[0063]

[0064] Among them, the number of teeth b of the internal gear ring Greater than the number of teeth of the planetary gear g That is, the speed of planetary gear g is greater than the speed of planetary carrier H. Therefore, in this design, as the crystallizing roller rotates, the internal gear 13 will rotate at high speed, driving the propeller to push the water flow.

[0065] 1) This invention utilizes a thin-strip continuous casting process to prepare 300-series stainless steel strips, leveraging the advantages of this process to obtain high-performance 300-series stainless steel strips with a shorter process and lower cost. Rapid solidification and the addition of boron (B) and cerium (Ce) in the composition design work together to refine the solidification microstructure. Copper enhances the product's corrosion resistance and antibacterial properties. Rapid solidification overcomes the tendency of copper to segregate, resulting in excellent overall performance.

[0066] 2) This invention features a short process flow and thin strip thickness. To ensure cooling intensity, a crystallizing roller with enhanced cooling capacity is designed. The crystallizing roller uses multiple cooling water chambers instead of cooling water channels, significantly increasing the cooling water flow rate. Ribs are added to improve the structural strength of the crystallizing roller, adapting to the high casting and rolling force requirements of thin strip continuous casting. A propeller is installed in each chamber to alleviate the cooling water flow problem in larger cooling water chambers. The propeller is connected to a gear via a shaft, and its rotation is driven by internal gear mechanical transmission. The propeller speed can increase with the crystallizing roller speed without encountering electrical equipment failure problems due to high temperatures.

[0067] 3) This invention involves only hot rolling and heat preservation steps. Hot rolling welds together defects in the cast strip, and quenching prevents grain coarsening. The lower temperature heat preservation eliminates stress, shortens the process flow while reducing the thickness of the thin strip, and further reduces production costs. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the crystallizing roller with enhanced cooling intensity described in this invention;

[0069] Figure 2 This is a schematic diagram of the crystallizing roller shaft structure;

[0070] Figure 3 for Figure 1 Sectional view of AA;

[0071] Figure 4 for Figure 1 BB section view;

[0072] Figure 5 for Figure 3 CC section view;

[0073] Figure 6 A schematic diagram of the gear carrier and internal gear set;

[0074] Figure 7 This is a schematic diagram of the process flow of the vertical twin-roll thin strip continuous casting unit of the present invention.

[0075] In the diagram: 1: Shaft; 2: Main water channel; 3: Shaft water channel rib; 4: Shaft partition; 5: Shaft water groove; 6: Roller sleeve inner ring; 7: Cooling water chamber; 8: Roller sleeve surface; 9: Propeller; 10: Propeller shaft; 11: Plug; 12: Propeller bearing; 13: Internal gear; 14: Gear frame; 15: Gear frame keyway; 16: Shaft keyway; 17: Gear ring; 18: Roller sleeve rib; 19: Distribution water channel; 20: Gear ring fixing hole; 21: Induction furnace; 22: Tundish; 23: Distribution device; 24: Crystallizing roll; 25: Cooling device; 26: Swing guide plate; 27: Pinch roll; 28: Nitrogen protection area; 29: Online heating area; 30: Roll; 31: Cooling device; 32: Conveyor roll; 33: Flying shear. Detailed Implementation

[0076] The technical route of the present invention is described in detail with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are only some of the embodiments of the inventors' team. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the protection scope of the present invention.

[0077] Regarding the present invention

[0078] Next, using Figure 4The schematic diagram of the vertical twin-roll thin strip continuous casting unit shown illustrates the process flow of this invention.

[0079] The steel is smelted in an induction melting furnace 18 under a protective atmosphere, with the following chemical composition: C 0.01~0.05%; Si 0.30~0.60%; Cr 16.0~18.5%; Mn 0.8~1.6%; Ni 6.0~12.0%; N 0.01~0.04%; Cu 0.2~3.5%; S ≤0.005%; P ≤0.020%; B ≤50ppm; Ce ≤100ppm. The balance is iron and other unavoidable impurities. The steel is then vacuum-melted using electrolytic chromium, ferromanganese, ferroboron, pure cerium, high-purity nickel, industrial pure iron, ferrochromium nitride, and electrolytic copper to obtain molten steel for casting.

[0080] After smelting, the molten steel is cast at a temperature of 1490~1540℃. It is poured into the tundish shown in Figure 19 and flows into the distributor shown in Figure 20, then into the roll gap. The molten steel solidifies to obtain a stainless steel strip with a thickness of 1.0~1.9mm and good surface quality. The crystallizing roll speed is selected as 70~100m / min.

[0081] Figure 4 In the diagram, the crystallizing roller shown in section 4 is the previously described enhanced cooling roller. This roller uses a cooling water chamber instead of a traditional cooling water channel and is equipped with a propeller to assist in driving the water flow, greatly increasing the cooling water flow rate and thus improving the cooling intensity. Its structure is as follows: Figure 1 As shown:

[0082] exist Figure 1 In the diagram, 1 is the rotating shaft, 2 is the main water channel, 3 is the rotating shaft water channel rib, connected to the rotating shaft diaphragm shown in 4. 1, 3, and 4 are cast as a single unit and then machined. 5 is the rotating shaft water groove, and 6 is the inner ring of the roller sleeve. Figure 2 The 18 roller sleeve ribs and 8 roller sleeve surfaces shown constitute the entire crystallizing roller sleeve. The crystallizing roller sleeve is integrally cast and machined, and connected to the shaft by cryogenic injection. 7 is the cooling water chamber. 9 is the propeller, connected to the propeller shaft at 10 via a key. 10 is connected to the internal gear at 13 via a key. 10 is supported by the propeller bearing at 12, and 12 is supported by the plug at 11 and the gear carrier at 14. 15 is the gear carrier keyway, 16 is the shaft keyway, and 14 is connected to the shaft via a key and moves with the shaft. The gear ring at 17 meshes with 13. 17 is externally fixed and does not move with the shaft, thus driving 13.

[0083] exist Figure 2In the schematic diagram of the crystallizing roller shaft structure shown, the entire crystallizing roller shaft is cast and machined. The rotating shaft water channel rib plate shown in Figure 3 connects the rotating shaft and the rotating shaft partition, forming a whole. Cooling water is distributed into the cooling water chamber through the main water channel and the hollowed-out rib plate. The side walls of the rotating shaft partition and the rotating shaft water channel are connected to the roller sleeve.

[0084] The flow of cooling water is assisted by Figure 3 The AA sectional view shown is further explained below:

[0085] exist Figure 3 In the design, the 18-roll sleeve ribs divide the roll into six evenly distributed cavities. The cavity thickness accounts for 40% to 60% of the thickness of the crystallizing roll sleeve. A propeller is positioned at the center of each cavity, as shown by the propeller shaft (Figure 10). The propeller rotates and agitates the water flow in the center of each cavity, with a diameter of 50% to 90% of the cavity thickness. The 18-roll sleeve ribs enhance the structural strength of the crystallizing roll, accommodating larger casting and rolling forces. The rib thickness is 10% to 20% of the cavity width. 2 represents the main water channel at the center of the shaft, which is divided into multiple distribution channels (Figure 19) by the main water channel ribs (Figure 3). Cooling water flows into the cooling water chamber (Figure 7) through the shaft water channel (Figure 5), creating a continuous water flow.

[0086] With the help of Figure 4 The BB cross-sectional view shown further illustrates the structure of the roller sleeve and the rotating shaft.

[0087] like Figure 4 As shown, the 8-roll sleeve roll surface, 18-roll sleeve ribs, and 6-roll sleeve inner ring form a whole, which is obtained by casting and machining. The roll sleeve is installed on the rotating shaft by freezing and driving, as shown in the connection between 4 and 6 in the figure.

[0088] With the help of Figure 5 The CC cross-sectional view shown further illustrates the structure of the cooling water chamber:

[0089] exist Figure 5 In the middle, the 18 roller sleeve ribs divide the inner ring of the 6 roller sleeve into a cooling water chamber as shown in the figure. Water flows through the 7 cooling water chamber to achieve water cooling of the roller surface. The left side of the figure shows the opening for installing the propeller.

[0090] With the help of Figure 6 Explain the structure and motion of the gears:

[0091] Figure 6This is an assembly diagram of the gears on the side of the crystallizing roller. The gear carrier shown in 14 is keyed to the crystallizing roller shaft, thus rotating synchronously with the crystallizing roller. This, in turn, causes the propeller shaft to rotate with the crystallizing roller shaft. The gear carrier gear ring 17 is welded to the gear ring fixing hole 20, and is fixed to the outside through the gear ring fixing hole 20. It does not rotate with the crystallizing roller, but meshes with the internal gear. The internal gear rotates under the combined action of the fixed gear ring and the rotating gear carrier, forming a structure similar to a planetary gear. The internal gear drives the propeller to rotate, assisting in propelling the water flow.

[0092] exist Figure 7 In the process, 24 is the crystallizing roll, 17 is the fixed toothed ring, and 20 is the toothed ring fixing hole for external fixation. After the molten steel rapidly solidifies to form a cast strip, the cast strip is guided to the pinch roll 27 by the swing guide plate 26. During this process, the cooling device 25 sprays water to accelerate cooling and prevent strip breakage. Nitrogen atmosphere protection is used within the dashed box shown in 28 to prevent oxidation. Then, it is fed into the nitrogen-protected area shown in the dashed box 29 for online heating until the temperature rises to 850~1050℃. Hot rolling is performed 1~2 times at the roll shown in 30, with a reduction rate ≤50%, to obtain a hot-rolled thin strip with a thickness of 0.5~1.3mm. It is then fed out by the conveyor roll 32, while being cooled by the cooling device 31 spraying water. Finally, it is sheared and wound.

[0093] After the hot-rolled strip is coiled, the steel coil is held at 500~900℃ for 30~120min in a nitrogen atmosphere to relieve stress, and then water-quenched to obtain the finished 300 series stainless steel thin strip.

[0094] In addition, comparative examples 1 to 4 were obtained by using ingot casting to simulate conventional casting methods, and the processes are as follows:

[0095] (1) Smelting: Select raw materials such as electrolytic chromium, ferromanganese, high-purity nickel, industrial pure iron, ferrochromium nitride, and electrolytic copper according to the composition and smelt them in vacuum to obtain molten steel for casting.

[0096] (2) Ingot casting: Molten steel is poured into a mold and solidified under nitrogen atmosphere protection. After holding at 1200℃ for 360 min, the ingot is obtained by billet cutting.

[0097] (3) Rolling: After the ingot is cut to obtain a steel plate of appropriate thickness, it is rolled. The billet is kept at 850~1050℃ and then hot rolled to obtain a rolled plate. Then it is water cooled, coiled, and heat treated to obtain a 300 series stainless steel plate produced in accordance with the traditional process, as shown in Comparative Examples 1~4.

[0098] The following are Examples 1-6 and Comparative Examples 1-4 of the present invention. It can be seen that the continuous casting method for preparing 300 series stainless steel strips according to the present invention can yield stainless steel strips with excellent mechanical properties. The mechanical properties of 300 series stainless steel strips with conventional composition prepared according to the process of the present invention are significantly better than those obtained by conventional processes. The 300 series stainless steel strips with conventional composition obtained using the process of the present invention can achieve an ultimate tensile strength of 1086 MPa and a maximum elongation of 58%. After adding B and Ce, the maximum elongation increases to 62%, and the ultimate tensile strength can still reach 1105 MPa. In the examples where a crystallizing roller with enhanced cooling strength is not used, the surface quality of the cast strip is slightly worse, and the mechanical properties are also worse than in other examples.

[0099]

[0100]

Claims

1. A continuous casting method for preparing 300 series stainless steel strip, characterized in that, Includes the following steps: (1) Smelting: The raw materials with the following chemical composition are vacuum smelted to obtain molten steel for casting: C 0.01~0.05%; Si 0.30~0.60%; Cr 16.0~18.5%; Mn 0.8~1.6%; Ni 6.0~12.0%; N 0.01~0.05%; Cu 0.2~3.5%; S ≤0.005%; P ≤0.020%; B≤50ppm; Ce≤100ppm, with the balance being iron and other unavoidable impurities. (2) Casting: The molten steel obtained by the smelting is cast using twin-roll thin strip casting. The casting temperature is selected as 1490~1540℃. Nitrogen protection is used during casting. The molten steel is poured between copper twin rolls and solidified to obtain a stainless steel strip with a thickness of 1.0~1.9mm. The crystallization roll speed is selected as 70~100m / min. The cooling rate of the twin rolls is 1000-2000℃ / s. (3) Hot rolling: After the cast strip is conveyed out, it is hot rolled 1 to 2 times, then water quenched, and then coiled. The rolling temperature is controlled at 850 to 1050℃, and the reduction rate is ≤50% to obtain a thin strip with a thickness of 0.5 to 1.3 mm. (5) Heat preservation: The obtained cold-rolled strip is kept at 500~900℃ for 30~120min to relieve stress, and then water-quenched to obtain the finished 300 series stainless steel strip. The crystallizing roller (24) is composed of a rotating shaft (1), a main water channel (2), a rotating shaft water channel rib (3), a rotating shaft partition (4), a rotating shaft water groove (5), an inner ring of the roller sleeve (6), a cooling water chamber (7), a roller sleeve surface (8), a propeller (9), a propeller rotating shaft (10), a plug (11), a propeller bearing (12), an internal gear (13), a gear frame (14), a gear frame keyway (15), a rotating shaft keyway (16), a gear ring (17), a roller sleeve rib (18), a distribution water channel (19), and a gear ring fixing hole (20); wherein the main water channel (2) is arranged concentrically with the rotating shaft (1) inside the rotating shaft (1), and the main water channel (2) passes through the rotating shaft (1) and has a symmetrical structure; The pivot waterway rib (3) is connected to the pivot partition (4); the pivot (1), the pivot waterway rib (3), and the pivot partition (4) are a whole; The rotating shaft water channel (5) is located between the distribution water channel (19) and the cooling water chamber (7); The inner ring (6) of the roller sleeve is set on the side of the cylindrical rotating shaft partition (4); A single cooling water chamber (7) is formed by the space enclosed by the inner ring (6) of the roller sleeve, the inner wall of the corresponding roller sleeve surface (8), and two roller sleeve ribs (18); The propeller (9) is arranged at the center of each chamber; One end of the propeller (9) is connected to the propeller shaft (10); the other end of the propeller shaft (10) passes through the propeller bearing (12) and is connected to the internal gear (13); half of the propeller bearings (12) are set on the side surface C, and the side surface C and the roller surface (8) of the roller sleeve constitute the protrusion on the shaft (1); the propeller bearings (12) set on the side surface C are embedded in the plug (11); the other part of the propeller bearings (12) are fixed on the gear frame (14); The bottom of the gear carrier (14) is located in the gear carrier keyway (15); the gear carrier keyway (15) and the shaft keyway (16) are connected by a keying. The gear ring (17) meshes with the internal gear (13); the gear ring (17) is fixed externally.

2. The continuous casting method for preparing 300 series stainless steel strip according to claim 1, characterized in that: N small holes are evenly opened on the roller sleeve rib (18); the N is greater than or equal to 6.

3. The continuous casting method for preparing 300 series stainless steel strip according to claim 1, characterized in that: The continuous casting machine in step 2 is a double vertical roll thin strip continuous casting machine; The copper roller is made of pure copper or copper alloy; The surface of the copper roller is electroplated with Cr, and the thickness of the Cr plating layer is 0.06~0.12mm.

4. The continuous casting method for preparing 300 series stainless steel strip according to claim 1, characterized in that: The number of cooling water chambers (7) is 4 to 12, evenly distributed, and the cavity thickness accounts for 40% to 60% of the thickness of the crystallizing roller sleeve. The roller surface is supported by ribs, and the thickness of the ribs is 10% to 20% of the cavity width. A propeller is installed in each cavity to agitate and propel the water flow. The diameter of the propeller is 50% to 90% of the minimum thickness in the three-dimensional space of the cavity.

5. The continuous casting method for preparing 300 series stainless steel strip according to claim 1, characterized in that: The composition of the stainless steel strip, by mass percentage, is as follows: C 0.01~0.05%; Si 0.30~0.60%; Cr 16.0~18.5%; Mn 0.8~1.6%; Ni 6.0~12.0%; N 0.01~0.05%; Cu 0.2~3.5%; S ≤0.005%; P ≤0.020%; B ≤50ppm; Ce ≤100ppm; with the balance being iron and other unavoidable impurities.

6. The continuous casting method for preparing 300 series stainless steel strip according to claim 5, characterized in that: The composition of the stainless steel strip, by mass percentage, is as follows: C 0.015~0.025%; Si 0.36~0.48%; Cr 17.5~18.5%; Mn 1.0~1.2%; Ni 7.8~8.5%; N 0.04~0.05%; Cu 0.2~0.4%; S ≤0.005%; P ≤0.020%; B ≤50ppm; Ce ≤100ppm; with the balance being iron and other unavoidable impurities.

7. The continuous casting method for preparing 300 series stainless steel strip according to claim 6, characterized in that: The composition of the stainless steel strip, by mass percentage, is as follows: C 0.02~0.023%; Si 0.39~0.45%; Cr 17.7~18.2%; Mn 1.05~1.1%; Ni 8.0~8.03%; N 0.045~0.05%; Cu 0.24~0.35%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm, with the balance being iron and other unavoidable impurities.

8. The continuous casting method for preparing 300 series stainless steel strip according to claim 7, characterized in that: The composition of the stainless steel strip, by mass percentage, is: C 0.02%; Si 0.43%; Cr 18.0%; Mn 1.1%; Ni 8.0%; N 0.05%; Cu 0.35%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm, with the balance being iron and other unavoidable impurities; or The composition of the stainless steel strip, by mass percentage, is: C 0.021%; Si 0.42%; Cr 18.2%; Mn 1.05%; Ni 8.02%; N 0.046%; Cu 0.36%; S ≤0.005%, P ≤0.020%, B ≤50ppm, Ce ≤100ppm, with the balance being iron and other unavoidable impurities; or The composition of the stainless steel strip, by mass percentage, is as follows: C 0.02%; Si 0.41%; Cr 18.2%; Mn 1.06%; Ni 8.03%; N 0.048%; Cu 0.31%; S ≤0.005%; P ≤0.020%; B ≤50ppm; Ce ≤100ppm, with the balance being iron and other unavoidable impurities.

9. A continuous casting method for preparing 300 series stainless steel strip according to any one of claims 1-8, characterized in that: The obtained 300 series stainless steel strip has an austenitic microstructure. The obtained 300 series stainless steel strip has a room temperature ultimate tensile strength of 900~1110MPa, a yield strength of 670~780MPa, an elongation after fracture of 45%~65%, and no cracks or wrinkles on the surface.

10. The continuous casting method for preparing 300 series stainless steel strip according to claim 9, characterized in that: The obtained 300 series stainless steel strip has an austenitic microstructure. The obtained 300 series stainless steel strip has a room temperature ultimate tensile strength of 1085~1110MPa, a yield strength of 700~780MPa, an elongation after fracture of 55%~65%, and no cracks or wrinkles on the surface.

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