Method for producing austenitic stainless steel round billet by using full-arc continuous casting machine

Abstract

The invention belongs to the technical field of metallurgy, and particularly provides a method for producing an austenitic stainless steel round billet by using a full-arc continuous casting machine, which comprises the following steps of: 1) preparing molten steel, injecting the molten steel into a tundish from a steel ladle through a long nozzle, and injecting the molten steel in the tundish into a crystallizer through a submersed nozzle; 2) initially setting the molten steel in a crystallizer; (3) the casting blank obtained after initial setting is subjected to blank drawing; (4) the casting blank obtained after blank drawing enters an arc-shaped roller way area to be subjected to secondary cooling; (5) the casting blank obtained after secondary cooling is straightened through a withdrawal and straightening machine, and round blank casting is completed; the problem that in the prior art, a full-arc-shaped continuous casting machine is not adopted for casting austenitic stainless steel round billets with the diameter ranging from 500 mm to 800 mm is solved. According to the method, the austenitic stainless steel round billet with the diameter of 500-800 mm is cast and produced through the full-arc continuous casting machine, and it is guaranteed that the quality of the produced round billet meets the standard.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology, and particularly relates to a method for producing austenitic stainless steel round billets by using a fully arc-shaped continuous casting machine. Background Art

[0002] At present, most domestic large-section stainless steel round billets are produced by vertical continuous casting machines, and the investment cost of vertical continuous casting machines is relatively large. There are also some steel plants that use fully arc-shaped continuous casting to produce small-section stainless steel round billets. There are not many straight-arc continuous casting methods for large-section stainless steel round billets. Most of the time, due to unreasonable formulation of key process parameters, the quality of the produced billets is difficult to guarantee. The quality problems are mainly central porosity and segregation of the billets, and the roundness of the billets does not meet the requirements.

[0003] Chinese patent document with publication number CN104525880A discloses a method for manufacturing extra-large-section round billets. The method includes the following steps: 1) Pouring: Pouring molten steel from a ladle into a tundish; 2) Crystallization: Pouring the molten steel in the tundish into a mold to obtain an incompletely solidified billet. Among them, the performance of the mold powder is as follows: alkalinity 0.2-0.5, melting temperature 980-1130 °C, viscosity at 1300 °C is 12-18.0 Pa·S; Set the mold electromagnetic stirring as follows: current 400-500 A, frequency 3.0-4.0 Hz; 3) Drawing: Drawing speed: 0.08-0.13 m / min; 4) Secondary cooling: The upper area of the secondary cooling uses full-water strong cooling, and the lower area of the secondary cooling uses gas-water atomization weak cooling. The comprehensive specific water volume: 0.25-0.35 L / kg steel; 5) Continuously straightening the billet after secondary cooling, and controlling the straightening strain rate at 0.08%-0.13%. This document is based on a fully arc-shaped alloy steel continuous casting machine with an arc radius of 16.5 meters to achieve batch production of round billets with a diameter of 900 mm or more, and cannot achieve the casting of round billets with a diameter of 500 mm - 800 mm, and cannot ensure good internal quality of the casting and avoid defects such as central porosity and central segregation inside. Summary of the Invention

[0004] The method for producing austenitic stainless steel round billets by using a fully arc-shaped continuous casting machine provided by the present invention aims to overcome the problem that there is no use of a fully arc-shaped continuous casting machine to cast austenitic stainless steel round billets with a diameter of 500 mm - 800 mm in the prior art.

[0005] For this reason, the present invention provides a method for producing austenitic stainless steel round billets by using a fully arc-shaped continuous casting machine, including the following steps:

[0006] 1) Prepare molten steel, pour the molten steel from the ladle into the tundish through a long nozzle, and the molten steel in the tundish is poured into the mold through a submerged nozzle;

[0007] 2) The molten steel starts to solidify in the mold;

[0008] 3) Withdraw the cast slab after initial setting;

[0009] 4) The cast slab after withdrawal enters the curved roller table area for secondary cooling;

[0010] 5) The cast slab after secondary cooling is straightened by a straightening machine to complete the casting of round billets.

[0011] Preferably, the casting machine radius of the full-curved continuous casting machine is 14.5 - 15.5 meters.

[0012] Preferably, the liquidus temperature of the molten steel is 1460 - 1470 °C, and the tundish temperature is 1485 ± 2 °C.

[0013] Preferably, the submerged nozzle adopts an integral four-split side-up inclination of 1.5° structure.

[0014] Preferably, the insertion depth of the submerged nozzle is 80 mm - 100 mm.

[0015] Preferably, the mold taper is 1.20 - 1.24%.

[0016] Preferably, the water flow velocity in the water gap of the mold is 6.5 m / s - 8.5 m / s, and the temperature difference of the mold cooling water is 5 °C - 8 °C.

[0017] Preferably, the liquid level control in the mold adopts an electromagnetic or cesium source type liquid level automatic control system, and the liquid level fluctuation in the mold is stabilized at ±3 mm.

[0018] Preferably, the argon blowing requires blowing argon gas throughout the molten steel casting process, and the argon gas flow rate is 48 - 52 L / min.

[0019] Preferably, the roll gap shrinkage in the curved roller table area is 0.10 - 0.12 mm / m.

[0020] Advantages of the present invention:

[0021] 1. The method for producing austenitic stainless steel round billets using the full-curved continuous casting machine provided by the present invention can produce round billets with a diameter of 500 mm - 800 mm, ensuring the compliance of the quality of the produced round billets.

[0022] 2. The method for producing austenitic stainless steel round billets using the full-curved continuous casting machine provided by the present invention requires the molten steel to meet the quality standards, which can reduce the probability of central porosity and segregation of the cast slab.

[0023] 3. The method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine provided by the present invention has a liquidus temperature of the molten steel of 1460 - 1470 °C and the tundish temperature is controlled at 1485 °C ± 2 °C, which can avoid central porosity and shrinkage cavities in the produced billets.

[0024] 4. The method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine provided by the present invention adopts an electromagnetic or cesium source type liquid level automatic control system for controlling the liquid level in the mold, and the liquid level fluctuation in the mold is stabilized within ± 3 mm to prevent slag entrainment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described in detail below with reference to the accompanying drawings.

[0026] Figure 1 It is a schematic flow chart of the method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The principles and features of the present invention will be described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. For those not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are adopted. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0028] Example 1:

[0029] As Figure 1 shown, a method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine includes the following steps:

[0030] 1) Prepare the molten steel, and inject the molten steel from the ladle into the tundish through a long nozzle. The molten steel in the tundish is injected into the mold through a submerged nozzle; the molten steel is qualified molten steel.

[0031] 2) The molten steel starts to solidify in the mold.

[0032] 3) Withdraw the solidified billet.

[0033] 4) The withdrawn billet enters the arc roller table area for secondary cooling.

[0034] 5) The billet after secondary cooling is straightened by a straightening machine to complete the casting of the round billet.

[0035] Specifically, the molten steel is required to be of qualified quality, which can reduce the probability of central porosity and segregation in the billets. Among them, the requirements for qualified molten steel are: the content of S (sulfur) in the molten steel meets the standard, and the inclusions in the molten steel meet the standard; through the method of the present invention, austenitic stainless steel round billets with a diameter of 500 mm - 800 mm can be produced, ensuring the compliance of the quality of the produced round billets.

[0036] Preferably, the casting machine radius of the full-arc continuous casting machine is 14.5 - 15.5 meters.

[0037] Specifically, by using a full-arc continuous casting machine with a casting machine radius of 14.5 - 15.5 meters for casting, round billets with a diameter of 500 mm - 800 mm can be produced.

[0038] Preferably, the casting machine radius of the full-arc continuous casting machine is 15 meters.

[0039] Specifically, by using a full-arc continuous casting machine with a casting machine radius of 15 meters for casting, the cost performance is higher. Compared with a vertical continuous casting machine, the investment is greatly reduced. Compared with a straight-arc continuous casting machine, it can effectively avoid cracks in the bending area and the test of high-temperature austenitic stainless steel bending on the equipment.

[0040] Preferably, the soft blowing time of the molten steel refining is more than 20 minutes, the total Ar time is more than 40 minutes, and the total calming time is more than 20 minutes; where Ar is argon.

[0041] Specifically, the quality of the molten steel is made to meet the standards through refining. Only when the quality of the molten steel refining meets the standards can qualified continuous casting billets be produced.

[0042] Example 2:

[0043] Based on Example 1, the molten steel composition includes components with the following mass percentages: 0.07% - 0.09% C, 0.9% - 1.1% Si, 1.8% - 2.2% Mn, 0.033% - 0.037% P, 0.02% - 0.04% S, 17% - 19% Cr, 7% - 9% Ni, 0.4% - 0.6% Mo, 0.5% - 0.7% Cu, 0.09% - 0.11% N, 14.285% - 14.294% trace elements and inclusions, and the balance is Fe.

[0044] Specifically, C is carbon, Si is silicon, Mn is manganese, P is phosphorus, S is sulfur, Cr is chromium, Ni is nickel, Mo is molybdenum, Cu is copper, N is nitrogen, and Fe is iron; the composition of the molten steel determines the performance of the later products. Only by strictly controlling the composition of the molten steel can it be possible to produce qualified continuous casting billets. The performance of the later products can be guaranteed. In particular, the content of S in the molten steel should be strictly controlled to prevent the occurrence of MnS segregation. Only by controlling the impurity elements can the probability of central porosity and segregation of the continuous casting billets be reduced.

[0045] Preferably, the molten steel composition includes components with the following mass percentages: 0.08% C, 1.0% Si, 2.0% Mn, 0.035% P, 0.03% S, 18% Cr, 8% Ni, 0.5% Mo, 0.6% Cu, 0.1% N, 14.289% trace elements and inclusions, and the balance is Fe; the trace elements include components with the following mass percentages: 0.25% Pb (lead), 0.35% Sn (tin), 0.3% As (arsenic), 0.035% Sb (antimony), 0.004% Bi (bismuth), 13.3% W (tungsten), 0.05% Nb (niobium).

[0046] Specifically, the molten steel composition of the present invention contains only 0.03% S to prevent the segregation of MnS; since the purity of the molten steel directly affects the internal quality of the continuous casting billet, by strictly controlling the trace elements and inclusions in the finished product, the purity of the molten steel is guaranteed to ensure the internal quality of the continuous casting billet.

[0047] Preferably, the liquidus temperature of the molten steel is 1460 - 1470 °C, and the tundish temperature is controlled at 1485 °±2 °C.

[0048] Specifically, calculate the liquidus temperature according to the steel grade composition to ensure the steel temperature on the turntable. By controlling the tundish temperature, the center porosity and shrinkage cavity of the produced continuous casting billet are avoided.

[0049] Preferably, the liquidus temperature of the molten steel is 1465 °C, and the superheat of the tundish is 15 °C - 25 °C.

[0050] Specifically, calculate the liquidus temperature to be 1465 ° according to the molten steel composition to ensure that the steel temperature on the turntable is 1555 °. Control the superheat of the tundish at about 15 ° - 25 °. If conditions permit, the superheat of the tundish can be lower, controlled at about 20 °. The tundish temperature is controlled at about 1485 °±2 °C. It is necessary to strictly control the superheat of the molten steel in the tundish, otherwise the produced continuous casting billet is particularly prone to center porosity and shrinkage cavity. According to the liquidus temperature of the casting steel grade, select a reasonable mold powder to ensure that the melting point of the mold powder matches the liquidus.

[0051] Example 3:

[0052] On the basis of Example 2, the submerged entry nozzle adopts an integral four-split side-upward inclined 1.5° structure.

[0053] Specifically, the integral structure ensures the strength and stability of the submerged nozzle, which is not prone to deformation or damage during the pouring process and can stably supply molten steel to the mold. The four-split side-upward inclination of 1.5° structure enables the molten steel to flow into the mold evenly and smoothly, contributing to maintaining the stability of the mold liquid level and reducing the liquid level fluctuation. Excessive liquid level fluctuation will cause the powder to be entrained into the molten steel, forming inclusion defects, and may also affect the uniform growth of the billet shell. A stable liquid level is conducive to obtaining a slab with good surface quality. Since the molten steel flows evenly and smoothly, the temperature distribution in the mold is also more uniform, providing good conditions for the solidification of the slab, facilitating the uniform solidification of the slab, reducing defects such as segregation and porosity inside the slab, and improving the internal quality of the slab.

[0054] Preferably, the insertion depth of the submerged nozzle is 80 mm - 100 mm.

[0055] Specifically, the insertion depth of 80 mm - 100 mm helps to maintain the stability of the mold liquid level. The liquid level fluctuation can be controlled within a small range, and the liquid level fluctuation can be ±3 mm. A stable liquid level is conducive to the uniform spreading and melting of the powder on the liquid surface, forming a uniform slag film, which plays a good role in lubrication and heat preservation and reduces the generation of surface defects of the slab.

[0056] Example 4:

[0057] On the basis of Example 3, the taper of the mold is 1.20 - 1.24%.

[0058] Specifically, the mold taper of 1.20 - 1.24% accelerates the solidification speed of the slab, improves production efficiency, and the uniform contact also ensures the uniform surface temperature of the slab, reduces temperature fluctuations, and prevents the generation of defects such as surface cracks.

[0059] Preferably, when producing a round billet with a diameter of 500 mm, the mold taper is 1.22%.

[0060] Specifically, this mold taper can better cast a round billet with a diameter of 500 mm.

[0061] Preferably, the water flow velocity in the water gap of the mold is 6.5 m / s - 8.5 m / s, and the temperature difference of the cooling water in the mold is 5°C - 8°C.

[0062] Specifically, the control of the water flow velocity and the cooling water temperature difference in the mold directly determines the thickness and temperature of the billet shell after it exits the mold, which has a great impact on the secondary cooling water distribution at the rear. Ensuring good solidification quality of the slab, controlling the uniformity of the cooling water temperature difference, and avoiding excessive temperature difference in local areas of the mold, which may lead to uneven temperature gradient on the surface of the slab, and further preventing problems such as local overheating resulting in cracks or excessive cooling causing too fast solidification and generating defects.

[0063] Preferably, the liquid level in the mold is controlled by an electromagnetic or cesium source type automatic liquid level control system, and the liquid level fluctuation in the mold is stabilized within ±3 mm.

[0064] Specifically, the electromagnetic or cesium source type automatic liquid level control system can accurately measure the position change of the liquid level, with high measurement accuracy and high sensitivity. It can effectively control the liquid level fluctuation in the mold within ±3 mm, making the molten steel flow evenly and smoothly, and the temperature distribution in the mold more uniform, providing good conditions for the solidification of the billet, facilitating the uniform solidification of the billet, reducing defects such as segregation and shrinkage porosity inside the billet, and improving the internal quality of the billet. At the same time, it also helps to prevent defects such as longitudinal cracks on the surface of the billet, because the stable liquid level and uniform heat flow distribution can make the thickness of the initial solidified shell more uniform, reducing stress concentration and crack initiation caused by uneven shell thickness.

[0065] Preferably, for round billets with a diameter of 500 mm - 600 mm, the mold length is 780 mm; for round billets with a diameter of 700 mm - 800 mm, the mold length is 700 mm.

[0066] Specifically, this mold length can ensure good solidification quality of the billet at a certain casting speed, thereby increasing the casting speed, increasing the billet output per unit time, and improving production efficiency.

[0067] Preferably, the starting casting speed is 0.05 m / min, and the casting speed is increased from 0.05 m / min to the target casting speed within 250 s after the start of pouring, and the target casting speed is within 0.28 m / min.

[0068] Specifically, this casting speed can increase the production capacity of the continuous caster, improve production efficiency, and reduce production costs.

[0069] Preferably, the mold adopts hydraulic vibration, and the hydraulic vibration adopts non-sinusoidal vibration, A (amplitude) = 1.5 + 1.5 * V (casting speed), f (vibration frequency) = 80 + 20 * V (casting speed), and the skew rate is 20%.

[0070] Specifically, the hydraulic vibration with these parameters can form uniform and regular oscillation marks on the surface of the billet, which is conducive to the infiltration of the mold powder, improving the lubrication conditions between the mold and the billet, reducing the adhesion and scratches on the surface of the billet, and improving the surface finish of the billet. At the same time, this vibration can promote the uniform solidification of the molten steel in the mold, making the liquid-solid interface at the solidification front more stable, reducing internal cracks, shrinkage cavities and other defects caused by uneven solidification, and improving the internal quality of the billet.

[0071] Preferably, the mold adopts a slotted copper tube, the water gap width is 6 mm, the depth is 14 mm, and it is evenly arranged in one circle, and the water jacket adopts a precision-machined water jacket.

[0072] Specifically, this structure ensures the water passage area, enhances the heat transfer effect, and optimizes the fluid flow.

[0073] Example 5:

[0074] Based on Example 4, during the process of pouring molten steel, argon gas is blown throughout the process, and the argon gas flow rate is 48 - 52 L / min.

[0075] Specifically, blowing argon gas throughout the casting process ensures normal argon blowing at the long nozzle, tundish, and submerged entry nozzle, which can purify the molten steel, homogenize the composition and temperature, protect the molten steel from oxidation, facilitate the formation and growth of equiaxed crystals, increase the equiaxed crystal ratio, reduce the proportion of columnar crystals, lower the risk of defects such as center segregation and center porosity in the slab, and improve the internal quality of the slab.

[0076] Preferably, the argon gas flow rate is 50 L / min.

[0077] Specifically, strictly controlling the argon gas flow rate at 50 L / min, an excessive argon gas flow rate may cause slag entrainment, while a too small flow rate may cause oxidation of the molten steel.

[0078] Preferably, the roll gap shrinkage in the curved roller table area is 0.10 - 0.12 mm / m.

[0079] Specifically, a roll gap shrinkage of 0.10 - 0.12 mm / m can reduce internal cracks and surface quality problems of the slab caused by bulging, promote the liquid phase flow inside the slab, make the solidification structure more dense, reduce internal defects such as porosity and shrinkage cavity, improve the internal quality and density of the slab, and thereby enhance the mechanical properties of the steel.

[0080] Preferably, the roll gap shrinkage in the curved roller table area is 0.11 mm / m.

[0081] Specifically, according to the high-temperature characteristics of the steel, fully considering the solidification shrinkage in the secondary cooling zone, the final shrinkage roll gap is determined. The roll gap shrinkage is implemented at the end of the movable section, and the shrinkage amount is executed according to 0.11 mm / m, resulting in the best slab quality.

[0082] Preferably, the secondary cooling zone is divided into Cooling Zone I, Cooling Zone II, and Cooling Zone III. The cooling method in Cooling Zone I is water cooling, and the cooling methods in Cooling Zone II and Cooling Zone III are both gas-water cooling. The specific water ratio in Cooling Zone I is 0.9 L / Kg, the specific water ratio in Cooling Zone II is 1.01 L / Kg, and the specific water ratio in Cooling Zone III is 1.02 L / Kg.

[0083] Specifically, to ensure uniform spray cooling and the roundness of the continuous casting billet, the secondary cooling zone is divided into three cooling zones. Cooling zone I is the mold foot roll zone, where two rows of nozzles are arranged, with 8 pure water cooling nozzles in each row. Cooling zones II and III each have four rows, with 4 gas-water cooling nozzles in each row, and the nozzles in each row are arranged in a rotating and staggered manner. An air-cooling zone is set after cooling zone III, and the air-cooling zone is equipped with a heat preservation cover to slowly cool the continuous casting billet.

[0084] Preferably, the fully arc continuous casting machine adopts electromagnetic stirring, and the electromagnetic stirring adopts three-stage electromagnetic stirring, which is mold electromagnetic stirring, secondary cooling electromagnetic stirring, and final electromagnetic stirring.

[0085] Specifically, electromagnetic stirring promotes the homogenization of the composition in the molten steel and reduces defects such as central segregation. The mold electromagnetic stirring adopts 300A / 2HZ, the secondary cooling electromagnetic stirring adopts 150A / 5HZ, and the final electromagnetic stirring adopts 380A / 3HZ.

[0086] The final electromagnetic stirring moving technology is adopted, so that when the drawing speed changes, the electromagnetic stirring coil can move up and down along the direction of the continuous casting billet to ensure a reasonable stirring position.

[0087] Preferably, the depth of the residual molten steel in the tundish during casting is not less than 300mm.

[0088] Specifically, a depth of not less than 300mm ensures that the molten steel has sufficient residence time and good flow state in the tundish, which is beneficial to the floating of inclusions.

[0089] Preferably, side guiding rollers are set in the straightener area to prevent the continuous casting billet from running off track.

[0090] Preferably, the straightener adopts displacement control, and according to the theoretical calculation of the bulging and solidification shrinkage of the continuous casting billet, the roll gap is continuously shrunk.

[0091] Specifically, it is to avoid central porosity and shrinkage cavity due to insufficient pressure, or to avoid flattening of the continuous casting billet due to excessive pressure. After the continuous casting billet is taken offline, it enters the slow cooling pit to slowly cool the continuous casting billet.

[0092] In the description of the present invention, it should be understood that if there are terms such as "front", "inside", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation to the present invention.

[0093] The above examples are only illustrative of the present invention and do not constitute a limitation to the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine, characterized in that: It includes the following steps: 1) Prepare molten steel, inject the molten steel from the ladle into the tundish through a long nozzle, and the molten steel in the tundish is injected into the mold through a submerged nozzle; 2) The molten steel starts to solidify in the mold; 3) Withdraw the solidified slab; 4) The withdrawn slab enters the curved roller table area for secondary cooling; 5) The slab after secondary cooling is straightened by a straightening machine to complete the casting of round billets.

2. The method for producing austenitic stainless steel round billets using a fully arc continuous casting machine as claimed in claim 1, wherein: The casting radius of the fully curved continuous casting machine is 14.5 - 15.5 meters.

3. The method for producing austenitic stainless steel round billets using a fully arc continuous casting machine according to claim 1, characterized in that: The liquidus temperature of the molten steel is 1460 - 1470 °C, and the tundish temperature is 1485 ± 2 °C.

4. The method for producing austenitic stainless steel round billets by using a fully arc continuous casting machine according to claim 1, characterized in that: The submerged nozzle adopts an integral four-split side-up inclination of 1.5° structure.

5. The method for producing austenitic stainless steel round billets by using a fully-arc continuous casting machine according to claim 4, characterized in that: The insertion depth of the submerged nozzle is 80 mm - 100 mm.

6. The method for producing austenitic stainless steel round billets by using a fully arc-shaped continuous casting machine as claimed in claim 1, characterized in that: The taper of the mold is 1.20 - 1.24%.

7. The method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine according to claim 1, characterized in that: The water flow velocity in the water gap of the mold is 6.5 m / s - 8.5 m / s, and the temperature difference of the mold cooling water is 5 °C - 8 °C.

8. The method for producing austenitic stainless steel round billets by using a fully arc-shaped continuous casting machine as claimed in claim 1, wherein: The liquid level control in the mold adopts an electromagnetic or cesium source type liquid level automatic control system, and the liquid level fluctuation in the mold is stabilized at ±3 mm.

9. The method for producing austenitic stainless steel round billets by using a fully arc continuous casting machine according to claim 1, characterized in that: Regarding argon blowing, argon gas is blown throughout the molten steel casting process, and the argon gas flow rate is 48 - 52 L / min.

10. The method for producing austenitic stainless steel round billets using a fully arc-shaped continuous casting machine as claimed in claim 1, wherein: The roll gap shrinkage in the curved roller table area is 0.10 - 0.12 mm / m.

Images