A high-strength pipe resistant to ozone corrosion and a manufacturing method thereof

Abstract

The invention discloses an ozone corrosion resistant high-strength pipeline, which has a corrosion-resistant layer and a base layer in the thickness direction, wherein the corrosion-resistant layer is at least located on the inner wall of the pipeline, and the corrosion-resistant layer contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages: 0<C≤0.08%; 0<Si≤0.75%; 0<Mn≤2.0%; Ni: 10.00~14.00%; Cr: 16.00~18.00%; Mo: 2.00~3.00%; N: 0.02~0.20%; and satisfies: Cr+3.3×Mo+16×N≥25%. Correspondingly, the present invention also discloses a method for manufacturing the above-mentioned pipeline, which comprises the following steps: (1) preparing a corrosion-resistant layer slab and a base slab; (2) assembling the slabs; (3) heating and rolling: the heating temperature is 1100-1200°C, and then the base slab and the corrosion-resistant layer slab are rolled in multiple passes within the austenite recrystallization and non-recrystallization temperature range of the base slab and the corrosion-resistant layer slab, with the total reduction rate not less than 70% and the final rolling temperature not less than 900°C; (4) coiling: after water cooling, the coiling temperature is controlled to be 500-650°C; (5) surface treatment of the hot rolled coil; and (6) pipe making.

Description

Technical Field

[0001] The invention relates to a pipeline and a manufacturing method thereof, in particular to a corrosion-resistant pipeline and a manufacturing method thereof. Background Art

[0002] As we all know, in current water supply plants, ozone is usually used to disinfect and sterilize water sources to ensure water quality. In actual application, the pipes between the ozone generators and the ozone dosing device of the water supply plant are usually directly in contact with ozone gas, and the outlet pipes of the pre-ozone contact tank and the ozone contact tank are also in contact with water dissolved with ozone. If these equipment and pipes are not specially treated, they are very easy to be corroded by ozone. Therefore, in order to prevent these equipment and pipes from being corroded by ozone as much as possible, carbon steel materials and 316 stainless steel materials are usually used for production and manufacturing.

[0003] However, compared with carbon steel materials, the strength of 316 stainless steel structures is lower. Under the same operating conditions, the required thickness is larger, which will lead to an increase in material usage. At the same time, welding and machining of 316 stainless steel materials are more difficult. 316 stainless steel itself contains more precious metal elements such as Cr, Ni, Mo, etc., which will lead to higher usage costs during production, manufacturing, and installation. Conventional 316L stainless steel will also experience local material corrosion during use, the main reason being insufficient comprehensive corrosion resistance in an ozone environment.

[0004] Therefore, carbon steel is often used to make carbon steel pipes. Such carbon steel pipes can be used as outlet pipes after valves in pre-ozone contact tanks and ozone contact tanks. The water transported inside contains a small amount of residual ozone. In order to enhance the corrosion resistance of the inner wall of the pipe, it is generally adopted to apply a special ozone-resistant fluorocarbon coating on the inner wall. However, since the coating applied on the inner wall of the pipe still has problems such as coating damage and peeling, in the long-term use and operation process, the carbon steel pipe is still inevitably corroded by ozone, resulting in water pollution, and even pipeline leakage and burst.

[0005] Based on this, in view of the deficiencies and defects in the above-mentioned prior art, the present invention hopes to obtain a new ozone corrosion-resistant high-strength pipe, which not only has excellent ozone corrosion resistance, but also has good mechanical properties and economy, and has great economic and social benefits. Summary of the invention

[0006] One of the purposes of the present invention is to provide a high-strength pipe resistant to ozone corrosion. The high-strength pipe resistant to ozone corrosion not only has excellent ozone corrosion resistance, but also has good mechanical properties and high economy. It can solve the essential pain points of 316 stainless steel or carbon steel currently used in water supply plants in ozone corrosive medium environments, meet the ever-increasing demand for pipeline equipment used in water supply plants in ozone corrosive medium environments for pipeline corrosion resistance and mechanical properties, greatly improve the applicability, safety and durability of these pipeline equipment, while avoiding secondary pollution of water quality, and has great economic and social benefits.

[0007] In order to achieve the above object, the present invention provides an ozone corrosion resistant high-strength pipeline, which has a corrosion-resistant layer and a base layer in the thickness direction, wherein the corrosion-resistant layer is at least located on the inner wall of the pipeline, wherein the corrosion-resistant layer contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0008] 0<C≤0.08%;

[0009] 0<Si≤0.75%;

[0010] 0<Mn≤2.0%;

[0011] Ni: 10.00~14.00%;

[0012] Cr: 16.00~18.00%;

[0013] Mo: 2.00~3.00%;

[0014] N: 0.02~0.20%;

[0015] And it satisfies: Cr+3.3×Mo+16×N≥25%.

[0016] Furthermore, in the ozone corrosion resistant high-strength pipeline of the present invention, the mass percentage of each chemical element in the corrosion resistant layer is:

[0017] 0<C≤0.08%;

[0018] 0<Si≤0.75%;

[0019] 0<Mn≤2.0%;

[0020] Ni: 10.00~14.00%;

[0021] Cr: 16.00~18.00%;

[0022] Mo: 2.00~3.00%;

[0023] N: 0.02~0.20%;

[0024] The balance is Fe and other unavoidable impurities;

[0025] The mass percentage of each chemical element also satisfies: Cr+3.3×Mo+16×N≥25%.

[0026] In the ozone corrosion resistant high-strength pipeline of the present invention, in order to ensure the ozone corrosion resistance of the pipeline, the ozone corrosion resistance of the corrosion-resistant layer must be ensured first.

[0027] In the current water supply plant, the pipes between ozone generators and ozone dosing devices will transport or contact the medium of 100% ozone gas; while the flanges, baffles, outlet pipes and other facilities of the pre-ozone contact tank and ozone contact tank will transport or contact the medium of water with an ozone dissolved content of 1mg / L to 3mg / L, which may also contain up to 5ppm of Cl - The main corrosive medium is ozone, and the working temperature is 0-40℃.

[0028] Based on the above-mentioned operating conditions of the pipeline equipment of the current water supply plant in the ozone corrosive medium environment, the inventors have conducted a lot of research and optimized the chemical element composition of the corrosion-resistant layer to ensure the ozone corrosion resistance of the corrosion-resistant layer.

[0029] In the present invention, the design principle of the chemical elements of the corrosion resistant layer is as follows:

[0030] C: In the corrosion-resistant layer of the present invention, C is a strong austenite-forming element, which can replace nickel to a certain extent, promote austenite formation, stabilize austenite structure, and improve the strength of stainless steel. However, it should be noted that the C content should not be too high. When the carbon content is too high, carbon and chromium will form chromium-rich carbides at the grain boundaries, leading to intergranular corrosion. Therefore, in order to give full play to the beneficial effects of the C element, in the corrosion-resistant layer of the present invention, the mass percentage of the C element is controlled to meet 0<C≤0.08%.

[0031] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the C element may be further preferably controlled between 0.005-0.03%.

[0032] Si: In the corrosion-resistant layer of the present invention, the Si element is mainly used for deoxidation during the smelting process, so it generally contains a certain amount of silicon. However, it should be noted that the Si element content should not be too high. When the silicon content is too high, the solubility of nitrogen will be reduced. Therefore, in the corrosion-resistant layer of the present invention, the mass percentage of the Si element is controlled to meet 0<Si≤0.75%.

[0033] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of Si element may be further preferably controlled between 0.3% and 0.6%.

[0034] Mn: In the corrosion-resistant layer of the present invention, the Mn element is a strong austenite structure stabilizing element and can improve the solubility of nitrogen in steel. However, manganese also has a negative impact on the corrosion resistance of austenitic stainless steel. Therefore, considering the beneficial effects and adverse effects of the Mn element, in the corrosion-resistant layer of the present invention, the mass percentage of the Mn element is controlled to meet 0<Mn≤2.0%.

[0035] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Mn element may be further preferably controlled between 0.5 and 1.5%.

[0036] Ni: In the corrosion-resistant layer of the present invention, Ni is the most important element for forming and stabilizing the austenite phase. Adding an appropriate amount of Ni element can ensure the formation of austenite structure of steel at room temperature. However, nickel is expensive. In order to ensure a relatively low cost, in the corrosion-resistant layer of the present invention, the mass percentage of Ni element is controlled between 10.00 and 14.00%.

[0037] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Ni element may be further preferably controlled between 12.00 and 14.00%.

[0038] Cr: In the corrosion-resistant layer of the present invention, Cr is the guarantee for obtaining the stainlessness and corrosion resistance of stainless steel. Generally, the minimum chromium content for obtaining corrosion resistance is 10.5%. Since chromium is an element that significantly enhances corrosion resistance, in order to ensure good corrosion resistance, the chromium content in the steel of the present invention is controlled to be above 16.0%. However, chromium is the main ferrite-forming element, and too high a chromium content will make it difficult to ensure that the coating obtains austenite at room temperature. Therefore, in the corrosion-resistant layer of the present invention, the mass percentage of the Cr element is controlled between 16.00 and 18.00%.

[0039] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Cr element may be further preferably controlled between 16.50 and 17.50%.

[0040] Mo: In the corrosion-resistant layer of the present invention, Mo is an important element for improving corrosion resistance. Its mechanism is to stabilize the passivation film and promote the enrichment of chromium in the passivation film. Mo can also work synergistically with nitrogen to further improve pitting resistance. Therefore, the main function of adding molybdenum is to improve corrosion resistance. It should be noted that the content of Mo should not be too high. Too high a content of Mo will increase the cost of the alloy. In order to ensure a relatively low cost, in the corrosion-resistant layer of the present invention, the mass percentage of Mo is controlled between 2.00 and 3.00%.

[0041] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the Mo element may be further preferably controlled between 2.50 and 3.00%.

[0042] N: In the corrosion-resistant layer of the present invention, N is a very strong element for forming, stabilizing and expanding the austenite zone. Adding an appropriate amount of N element can effectively improve the pitting corrosion resistance of stainless steel. However, when the nitrogen content is too high, the risk of forming nitrogen-containing intermetallic phases will increase, and the difficulty of smelting and hot working will increase, resulting in difficulty in production. Therefore, in the corrosion-resistant layer of the present invention, the mass percentage of N element is controlled between 0.02 and 0.20%.

[0043] Of course, in some preferred implementations, in order to obtain better implementation effects, the mass percentage of the N element may be further preferably controlled between 0.05 and 0.15%.

[0044] Accordingly, it should be noted that in the corrosion-resistant layer of the ozone-resistant high-strength pipeline of the present invention, while controlling the mass percentage of a single chemical element, the Cr element, the Mo element and the N element are further controlled to satisfy: Cr+3.3×Mo+16×N≥25%. Each element in the formula is substituted into the mass percentage of the corresponding element. Through such control, it can be further ensured that the corrosion-resistant layer has a fairly excellent corrosion resistance in an ozone environment.

[0045] Furthermore, in the ozone corrosion resistant high-strength pipeline of the present invention, the mass percentage of each chemical element in the corrosion-resistant layer satisfies at least one of the following items:

[0046] C: 0.005~0.03%;

[0047] Si: 0.3-0.6%;

[0048] Mn: 0.5-1.5%;

[0049] Ni: 12.00~14.00%;

[0050] Cr: 16.50~17.50%;

[0051] Mo: 2.50~3.00%;

[0052] N: 0.05~0.15%;

[0053] Cr+3.3×Mo+16×N≥26%.

[0054] Furthermore, in the ozone corrosion resistant high-strength pipeline described in the present invention, in the corrosion-resistant layer, among other inevitable impurities, S≤0.030%; P≤0.045%.

[0055] In the corrosion-resistant layer of the ozone-resistant high-strength pipeline of the present invention, P and S are both inevitable impurity elements. In order to ensure the quality of the steel, the lower the content of impurity elements in the steel, the better, provided that conditions permit.

[0056] S: In the corrosion-resistant layer of the present invention, the S element is a harmful impurity element, so the mass percentage of the S element in the corrosion-resistant layer needs to be strictly controlled to control the S element to meet: S≤0.030%. Of course, it is more preferred to control the S element to between 0-0.005%.

[0057] P: In the corrosion-resistant layer of the present invention, the P element is a harmful impurity element, so the mass percentage of the P element in the corrosion-resistant layer needs to be strictly controlled to control the P element to meet: P≤0.045%. Of course, it is more preferred to control the P element to between 0-0.035%.

[0058] Furthermore, in the ozone corrosion resistant high-strength pipeline of the present invention, when the thickness of the single-layer corrosion-resistant layer accounts for 0.5-20% of the total thickness of the pipeline, the mass percentage of each chemical element in the base layer is:

[0059] C: 0.01~0.20%;

[0060] Si: 0.10~0.50%;

[0061] Mn: 0.50~2.00%;

[0062] Al: 0.02~0.04%;

[0063] Ti: 0.005~0.018%;

[0064] Nb: 0.005~0.020%;

[0065] N≤0.006%;

[0066] The balance is Fe and unavoidable impurities.

[0067] Furthermore, in the ozone corrosion resistant high-strength pipeline of the present invention, the base layer also includes at least one of the following items:

[0068] 0<B≤0.0003%;

[0069] 0<Ni≤0.20%;

[0070] 0<Cr≤0.20%;

[0071] 0<Mo≤0.10%.

[0072] In the above technical solution of the present invention, in order to further optimize the quality of the base steel, B element, Ni element, Cr element and Mo element may be further added to the base.

[0073] Furthermore, in the ozone corrosion resistant high-strength pipeline of the present invention, the mass percentage of each chemical element of the base layer satisfies at least one of the following items:

[0074] C: 0.01~0.18%;

[0075] Si: 0.10~0.30%;

[0076] Mn: 0.50~1.50%;

[0077] Al: 0.02-0.03%;

[0078] Ti: 0.005~0.015%;

[0079] Nb: 0.005~0.015%.

[0080] In the present invention, in order to ensure that the ozone corrosion resistant high-strength pipeline of the present invention obtains good mechanical properties, the chemical element composition of the base carbon steel is selected to ensure both high strength and good machinability.

[0081] Therefore, in the present invention, the design principles of each chemical element of the base carbon steel are as follows:

[0082] C: In the base layer described in the present invention, C is an austenite stabilizing element, which can play a role of solid solution strengthening in steel and can significantly improve the strength of the steel. However, it should be noted that the C content in the steel should not be too high. When the C content in the steel is too high, it is not only not conducive to the welding performance and toughness of the material, but also easy to increase the pearlite structure and hard phase structures such as Mahō Island, which has an adverse effect on the corrosion resistance of the steel. Therefore, considering the strength and toughness matching of the steel plate and the requirements for the corrosion resistance of the carbon steel material, in the base steel described in the present invention, the mass percentage of the C element is controlled between 0.01 and 0.20%.

[0083] In the present invention, the addition amount of C is controlled to be 0.01-0.20%, which can not only ensure that the steel plate can obtain a certain hardness and strength under air cooling after rolling, but also avoid deteriorating the welding performance of the base steel. Especially for high corrosion-resistant composite plates (corrosion-resistant layer slab + base slab) with a corrosion-resistant layer thickness of 0.5% to 20% of the total thickness, the carbon content of the base steel is required to be controlled within the above range.

[0084] Of course, in order to obtain a better implementation effect, the mass percentage of the C element can also be further controlled between 0.01 and 0.18%.

[0085] Si: In the base layer described in the present invention, adding Si element to the steel can effectively improve the purity and deoxidation of the steel. Si element can play a role in solid solution strengthening in steel, but Si element is not conducive to the welding performance of the material; in the present invention, the silicon content of the base carbon steel is controlled to be less than or equal to 0.5%, which will not have any effect on the corrosion resistance of the corrosion-resistant layer, and the base carbon steel has good welding performance. Therefore, in the base layer described in the present invention, the mass percentage of Si element is controlled to be between 0.10 and 0.50%.

[0086] Of course, in order to obtain a better implementation effect, the mass percentage of Si element can be further controlled between 0.10 and 0.30%.

[0087] Mn: In the base layer described in the present invention, adding an appropriate amount of Mn element to the steel can delay the pearlite transformation, reduce the critical cooling rate, and improve the hardenability of the steel; at the same time, the Mn element also has the effect of solid solution strengthening, and it is the main solid solution strengthening element in steel. However, it should be noted that the Mn element should not be added too much. When the Mn content in the steel is too high, segregation bands and martensitic structures are likely to appear, which have an adverse effect on the toughness of the steel, and the appearance of segregation bands will also reduce the corrosion resistance of the steel. The amount of Mn added mainly depends on the strength level of the steel. Generally, the manganese content in low-carbon microalloy steel does not exceed 2.0%. At this time, the Mn element contained in the base carbon steel will not have an adverse effect on the corrosion-resistant layer. Based on this, in the base layer described in the present invention, the mass percentage of the Mn element is controlled between 0.50 and 2.00%.

[0088] Of course, in order to obtain a better implementation effect, the mass percentage of the Mn element can also be further controlled between 0.50 and 1.50%.

[0089] Al: In the base layer described in the present invention, Al is a strong deoxidizing element. In order to ensure that the oxygen content in the steel is as low as possible, the mass percentage of the Al element is controlled between 0.02 and 0.04%. The excess Al after deoxidation and the N element in the steel can combine to form AlN precipitates, thereby improving the strength of the steel and refining the elemental austenite grain size of the steel during heat treatment. Of course, in order to obtain a better implementation effect, the mass percentage of the Al element can also be further controlled between 0.02 and 0.03%.

[0090] Ti: In the base layer of the present invention, Ti is a strong carbide-forming element. Adding a small amount of Ti to the steel is beneficial to fix the N in the steel. The TiN formed by the combination of Ti and N can prevent the matrix austenite grains from growing too much when the base blank of the base layer is heated, and refine the original austenite grain size. In addition, Ti can also be combined with carbon and sulfur in the steel to form TiC, TiS, Ti 4 C 2 S 2 They can exist in the form of inclusions and second phase particles. These carbonitride precipitates of Ti can also prevent the grain growth of the heat-affected zone during welding, and improve the welding performance of the base carbon steel. Based on this, in the base of the present invention, the mass percentage of the Ti element is controlled between 0.005 and 0.018%.

[0091] Of course, in order to obtain a better implementation effect, the mass percentage of the Ti element can be further controlled between 0.005 and 0.015%.

[0092] Nb: In the base layer described in the present invention, Nb is a strong carbide-forming element. A small amount of niobium is added to the steel mainly to increase the recrystallization temperature, so as to match the higher final rolling temperature of the composite plate formed by the base slab and the corrosion-resistant layer slab in the subsequent rolling process, so that the base layer has grain refinement after the rolling in the recrystallization and non-recrystallization zones, which is beneficial to the improvement of the low-temperature impact toughness of the base layer. Based on this, in the base layer described in the present invention, the mass percentage of the Nb element is controlled between 0.005 and 0.020%.

[0093] Of course, in order to obtain a better implementation effect, the mass percentage of the Nb element can also be further controlled between 0.005 and 0.015%.

[0094] N: In the base layer of the present invention, N element can generate second phase particles with titanium and aluminum, refine the grains, and improve the strength. However, when the mass percentage of N element is too high, the amount of TiN generated is too large and the particles are too coarse, which will affect the plasticity of the composite material substrate of the present invention. Based on this, in the base layer of the present invention, the mass percentage of N element is controlled to N≤0.006%.

[0095] B: In the present invention, B can greatly improve the hardenability of steel. For the air cooling after rolling of the high corrosion-resistant composite plate (corrosion-resistant layer slab + base slab), it is required to obtain ferrite + pearlite structure as much as possible and inhibit the formation of bainite, especially for high corrosion-resistant plate and strip steel with a corrosion-resistant layer thickness in the range of 0.5%-5% of the total thickness. Therefore, in the present invention, it is required to control the addition amount of B element in the base to meet 0<B≤0.0003%.

[0096] Ni: In the present invention, Ni is an element that stabilizes austenite, and has a certain effect on improving the strength of steel. In addition, adding a proper amount of Ni to steel, especially adding a proper amount of Ni to quenched and tempered steel, can greatly improve the low-temperature impact toughness of steel. Based on this, in the base layer described in the present invention, a proper amount of Ni can be added, and the addition amount of Ni element is controlled to satisfy 0<Ni≤0.20%.

[0097] Cr: In the present invention, the segregation tendency of Cr is smaller than that of Mn. When the Mn content of the base carbon steel is high and there are obvious segregation bands and banded structures in the steel, the Mn content can be appropriately reduced and the insufficient part can be replaced by Cr. Secondly, adding an appropriate amount of Cr element to the base carbon steel is also beneficial to inhibiting the diffusion of Cr in the corrosion-resistant layer to the base. Based on this, in the base layer described in the present invention, 0<Cr≤0.20% of Cr element can be added.

[0098] Mo: In the present invention, the Mo element can significantly refine the grains and improve the strength and toughness of the steel. In addition, Mo can also reduce the temper brittleness of the steel, and at the same time, very fine carbides can be precipitated during tempering, which significantly strengthens the steel matrix. In addition, the addition of the Mo element is also beneficial to suppress the self-tempering brittleness that is easily generated during the air cooling process of the steel plate. Based on this, in the base layer described in the present invention, an appropriate amount of Mo can be added, and the amount of Mo added is controlled to satisfy 0<Mo≤0.10%.

[0099] Furthermore, in the ozone corrosion resistant high-strength pipeline described in the present invention, in the base layer, other unavoidable impurities include: S≤0.010%; P≤0.015%.

[0100] In the above technical solution of the present invention, P and S are both inevitable impurity elements in the base layer. S will combine with Mn in steel to form plastic inclusions such as manganese sulfide, which is particularly detrimental to the transverse plasticity and toughness of the steel. Therefore, the content of S in the base layer should be as low as possible. In addition, P is also a harmful element in steel, which will seriously damage the plasticity and toughness of the steel plate.

[0101] For the present invention, S and P are both inevitable impurity elements and should be as low as possible. Considering the actual steelmaking level of the steel plant, in the base layer described in the present invention, the S and P elements are controlled to meet the following conditions: S≤0.010%; P≤0.015%.

[0102] Furthermore, in the ozone corrosion resistant high-strength pipeline described in the present invention, the thickness of the single-layer corrosion-resistant layer accounts for 0.5-20% of the total thickness of the pipeline.

[0103] In the present invention, according to the use conditions, the selection of the thickness of the corrosion-resistant layer plays a vital role in obtaining good corrosion resistance, mechanical properties, and forming properties of the ozone-resistant high-strength pipeline of the present invention. If the corrosion-resistant layer is too thick, it will affect the mechanical properties and production cost of the material; and if the corrosion-resistant layer is too thin, it will reduce the corrosion resistance and service life of the material. For this reason, in the present invention, it is preferred to control the thickness of the corrosion-resistant layer to 0.5%-20% of the total thickness of the pipeline.

[0104] Furthermore, in the ozone corrosion resistant high-strength pipeline described in the present invention, the microstructure of the base layer is ferrite+pearlite or ferrite+pearlite+bainite; the microstructure of the corrosion-resistant layer is austenite.

[0105] Furthermore, in the ozone corrosion-resistant high-strength pipeline described in the present invention, the yield strength of the pipeline is ≥435MPa, the tensile strength is ≥590MPa, the elongation is ≥32%, and the uniform corrosion rate of the corrosion-resistant layer in an ozone environment is ≤0.05mm / year.

[0106] Correspondingly, another object of the present invention is to provide a method for manufacturing the above-mentioned ozone-resistant high-strength pipeline. The manufacturing method is simple and feasible, and can effectively prepare the above-mentioned ozone-resistant high-strength pipeline of the present invention, and can break the limitation of the thickness of the corrosion-resistant layer, and control the thickness of the corrosion-resistant layer within the range of 0.5-20% of the total thickness of the pipeline.

[0107] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned ozone corrosion resistant high-strength pipeline, which comprises the steps of:

[0108] (1) preparing a corrosion-resistant layer slab and a base slab;

[0109] (2) Assembly;

[0110] (3) Heating and rolling: The heating temperature is 1100-1200°C, and then multiple rolling is performed within the austenite recrystallization and non-recrystallization temperature range of the base slab and the corrosion-resistant layer slab, with the total reduction rate not less than 90% and the final rolling temperature not less than 900°C;

[0111] (4) Coiling: After water cooling, the coiling temperature is controlled to be 500-650°C;

[0112] (5) Surface treatment of hot rolled coil;

[0113] (6) Pipe making.

[0114] In the present invention, based on a reasonable chemical composition design, the inventor has optimized and designed a new manufacturing process through a lot of research. The manufacturing method of the ozone-resistant high-strength pipe can effectively prepare the above-mentioned ozone-resistant high-strength pipe of the present invention.

[0115] In the above manufacturing method of the present invention, the corrosion-resistant layer slab and the base slab can be prepared by smelting and casting according to the chemical composition design, and then the two can be assembled to obtain a high-corrosion-resistant composite plate (corrosion-resistant layer plate + base plate). The obtained high-corrosion-resistant composite plate is further heated, rolled, and coiled to obtain a hot-rolled coil with a composite interlayer structure. The hot-rolled coil is surface-treated and then pipe-made to obtain the ozone-resistant high-strength pipe of the present invention.

[0116] In the present invention, the inventors have optimized the heating and rolling process of step (3) to ensure that a transition layer structure of a certain thickness can be formed between the corrosion-resistant layer and the base layer of the high-corrosion-resistant composite plate through heating, rolling and other processes, thereby achieving complete metallurgical bonding between the corrosion-resistant layer and the base layer, thereby ensuring ozone corrosion resistance and mechanical properties while improving the applicability and economy of the material.

[0117] In step (2) of the manufacturing method of the present invention, the prepared corrosion-resistant layer slab and base slab can be pretreated, and the slab bonding surfaces can be welded and sealed on all sides, and the bonding surfaces after welding and sealing can be vacuumed to complete the assembly.

[0118] Accordingly, in the hot rolled coil surface treatment of step (5), pickling or mechanical descaling can be adopted. In addition, in the pipe making process of step (6), conventional spiral welded pipe or straight seam welded pipe can be adopted for forming and welding, and the welding method can be selected from submerged arc welding, metal arc welding, tungsten inert gas welding, plasma arc welding, arc welding, high frequency welding or laser welding.

[0119] Furthermore, in the manufacturing method of the present invention, in step (3), the final rolling temperature is controlled to be 920-1000°C.

[0120] Furthermore, in the manufacturing method of the present invention, a preheating step (2a) is further included between step (2) and step (3): the preheating temperature is 1150-1250°C.

[0121] In the manufacturing method of the present invention, it can be determined whether to select a preheating process between step (2) and step (3) according to the performance requirements of the finished product. In the preheating process, the composite slab obtained by assembling can be heated at a temperature of 1150-1250°C so that the corrosion-resistant layer on the surface of the composite slab can obtain a uniform austenitized structure, and the carbides that may have existed originally can be completely dissolved as much as possible, and the compounds of alloy elements such as niobium and titanium in the carbon steel can be completely or partially dissolved; the corrosion-resistant layer and the carbon steel base layer elements diffuse at the interface to form a stable transition layer, and then slowly cool to room temperature.

[0122] Furthermore, in the manufacturing method of the present invention, cold rolling and annealing are also included between step (5) and step (6).

[0123] In the manufacturing method of the present invention, if in actual use, the target product before pipe making is a cold-rolled coil rather than a hot-rolled coil, a cold rolling and annealing step can be further added between step (5) and step (6), and the pipe can be cold rolled to a target thickness and then annealed.

[0124] It can be seen that in the present invention, the inventors designed the corrosion-resistant layer and the base layer components, and designed the ratio of the two, and formed an ozone-resistant corrosion-resistant layer on the surface of the base carbon steel plate through a rolling process, and finally formed a plate strip with ozone corrosion resistance, good mechanical properties and high economy, which was then processed into pipes for use in water supply plants as pipeline equipment in ozone-corrosive medium environments.

[0125] It should be noted that during the design process of this application, the difficulties include:

[0126] 1) The design of the corrosion-resistant layer and base composition needs to meet the comprehensive performance of the material. The corrosion-resistant layer needs to be designed according to the characteristics of ozone corrosion to meet the corrosion resistance requirements under the use conditions. In addition to considering the mechanical performance requirements, the design of the base carbon steel composition must also consider that when the carbon content of the transition layer is high, there is a lack of stabilizing elements, and there will be an obvious decarburization layer on the carbon steel side of the interface. The carbon steel substrate structure is uneven, and surface defects are easily generated after processing, and the mechanical properties are difficult to meet.

[0127] 2) The difference in the ratio of the corrosion-resistant layer to the base metal and the material properties will make the heating process, rolling process, and heat treatment process difficult to control. For example, the uneven temperature during the heating process will cause deformation and bulging, resulting in the inability to combine with the base layer. For example, it is easy to separate from the base and crack during the rolling process, and the uniformity of thickness is difficult to ensure.

[0128] 3) For pipes and equipment used in water supply plants in ozone corrosive media environments, such as pipes between ozone generators, ozone dosing devices, pre-ozone contact tanks, and outlet pipes of ozone contact tanks, if the early composite is not completed and the bonding quality is poor, then after subsequent pickling, pipe forming, welding and other processing, the continuity and uniformity of the corrosion-resistant layer of the finished product cannot be guaranteed, which will cause huge hidden dangers to the applicability, safety, and durability of the equipment and pipes.

[0129] In the present invention, the inventors have successfully overcome the above difficulties through reasonable design, and prepared the ozone corrosion-resistant high-strength pipeline of the present invention.

[0130] Compared with the prior art, the ozone corrosion resistant high-strength pipeline and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0131] In the present invention, the inventors have taken into account the operating conditions of the pipeline equipment of the current water supply plant in an ozone corrosive medium environment, and have designed the components of the corrosion-resistant layer and the base layer, and designed the ratio of the two. The corrosion-resistant layer and the base layer are combined to form a blank, and appropriate heating, rolling, and coiling processes are applied. In combination with the pipe making process, an ozone-resistant high-strength pipeline with resistance to ozone corrosion, good mechanical properties and high economy can be obtained, wherein the yield strength is ≥435MPa, the tensile strength is ≥590MPa, the elongation is ≥32%, and the uniform corrosion rate of the corrosion-resistant layer in an ozone environment is ≤0.05mm / year.

[0132] In the present invention, a transition layer structure of a certain thickness is formed between the corrosion-resistant layer and the base layer through heating, rolling and other processes, thereby achieving complete metallurgical bonding between the corrosion-resistant layer and the base layer, so as to improve the applicability and economy of the material while ensuring ozone corrosion resistance and mechanical properties.

[0133] The ozone corrosion-resistant high-strength pipe manufactured using the above-mentioned component design and process control method can solve the essential pain points of 316 stainless steel or carbon steel used in water supply plants in ozone corrosive medium environments; the ozone corrosion-resistant high-strength pipe can be used for pipes and equipment used in water supply plants in ozone corrosive medium environments, such as pipes between ozone generators, ozone dosing devices, pre-ozone contact tanks, and water outlet pipes of ozone contact tanks. It can meet the requirements of these pipes and equipment for ozone corrosion resistance and mechanical properties, greatly improve the applicability, safety, and durability of these pipe equipment, while avoiding secondary pollution of water quality, and has great economic and social benefits.

[0134] Compared with the 316 stainless steel pipes currently used in the ozone generator inter-pipeline, ozone dosing device, pre-ozone contact tank and ozone contact tank outlet pipes of the water supply plant, the ozone corrosion resistant high-strength pipe of the present invention has higher strength, simpler welding and machining, better corrosion resistance, and higher economy. Compared with the carbon steel pipe currently used in the valve outlet pipe of the pre-ozone contact tank and the ozone contact tank, the ozone corrosion resistant high-strength pipe of the present invention can exempt the pipeline corrosion-resistant coating process, and at the same time has corrosion resistance and durability that carbon steel pipes cannot achieve, and is more energy-saving, environmentally friendly, and maintenance-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0135] Figure 1 This is a schematic diagram of the interlayer structure of the ozone corrosion resistant high-strength pipeline in one embodiment of the present invention.

[0136] Figure 2 This is a schematic diagram of the interlayer structure of the ozone corrosion resistant high-strength pipeline in another embodiment of the present invention.

[0137] Figure 3 This is a microstructure photograph of the interface between the base layer and the corrosion-resistant layer of the ozone-resistant high-strength pipeline of Example 5.

[0138] Figure 4 This is a photo of the base microstructure of the ozone corrosion resistant high-strength pipeline of Example 5. DETAILED DESCRIPTION

[0139] The ozone corrosion-resistant high-strength pipeline and the manufacturing method thereof described in the present invention will be further explained and illustrated below in conjunction with the drawings in the specification and specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0140] Examples 1-6 and Comparative Example 1

[0141] Table 1 lists the mass percentages of chemical elements in the corrosion-resistant layers of the ozone-resistant high-strength pipes of Examples 1-6 and the comparative pipe of Comparative Example 1.

[0142] Table 1. (wt%, the balance is Fe and other inevitable impurities except P and S)

[0143]

[0144] Note: In the above Table 1, the mass percentage of each element in the formula Cr+3.3×Mo+16×N is substituted into the corresponding element.

[0145] Table 2 lists the mass percentages of various chemical elements in the base layer of the ozone corrosion resistant high-strength pipes of Examples 1-6 and the comparative pipe of Comparative Example 1.

[0146] Table 2. (wt%, the balance is Fe and other inevitable impurities except P and S)

[0147]

[0148] The ozone corrosion resistant high-strength pipes of Examples 1-6 of the present invention and the comparative pipe of Comparative Example 1 are prepared by the following steps:

[0149] (1) Smelting and casting according to the chemical compositions shown in Table 1 and Table 2 to prepare the corrosion-resistant layer slab and the base slab respectively.

[0150] (2) Assembly: The thickness of the corrosion-resistant layer is controlled to be 0.5%-20% of the total thickness of the blank, the corrosion-resistant layer and the base plate are pre-treated, and the bonding surface of the plate is welded and sealed all around, and the bonding surface after welding and sealing is vacuumed; after assembly, determine whether to select the preheating process according to the performance requirements of the finished product. If preheating is required, the preheating temperature is controlled to be 1150-1250°C.

[0151] (3) Heating and rolling: The composite slab is heated at a temperature of 1100-1200°C, and then rolled multiple times within the austenite recrystallization and non-recrystallization temperature range of the base slab and the corrosion-resistant layer slab, with the total reduction ratio being no less than 70%, the final rolling temperature being no less than 900°C, and the optimal final rolling temperature being between 920-1000°C.

[0152] (4) Coiling: After water cooling, the coiling temperature is controlled at 500-650°C.

[0153] (5) The hot rolled coil is treated by pickling or mechanical dephosphorization. If the target product is a cold rolled coil, it is further subjected to cold rolling and annealing processes, and annealing is performed after cold rolling to the target thickness.

[0154] (6) Pipe making: spiral welded pipe or straight seam welded pipe is used for forming and welding; the welding method can be selected from submerged arc welding, metal arc welding, tungsten inert gas welding, plasma arc welding, arc welding, high frequency welding or laser welding.

[0155] It should be noted that in the present invention, the ozone corrosion-resistant high-strength pipes of Examples 1-6 described in the present invention are all prepared by the process flow of the above steps (1) to (6), and their chemical composition and related process parameters meet the control requirements of the design specifications of the present invention.

[0156] Table 3 lists the specific process parameters of the ozone corrosion resistant high-strength pipes of Examples 1-6 and the comparative pipe of Comparative Example 1 in the step flow of the above-mentioned manufacturing method.

[0157] Table 3.

[0158]

[0159] It should be noted that, according to the process parameters shown in Table 3 above, after the hot-rolled coil surface treatment in step (5) is carried out in Example 1 and Example 3, cold rolling and annealing are further carried out to obtain cold-rolled sheets; while in Example 2, Example 4, Example 5, Example 6 and Comparative Example 1, hot-rolled sheets are obtained through step (5).

[0160] Accordingly, the plates prepared according to the embodiments and comparative examples can be further used in the pipe making process of step (6) to prepare corresponding ozone corrosion-resistant high-strength pipes.

[0161] The finished products of Examples 1-6, ozone corrosion resistant high-strength pipes and the comparative pipes of Comparative Example 1, prepared by the above process, were sampled respectively, and the microstructures of the sample pipes of Examples 1-6 and Comparative Example 1 were further observed. After the microstructures of the pipes of each example were obtained by observation, the sample pipes of Examples 1-6 and Comparative Example 1 were further tested for mechanical properties and ozone corrosion resistance. The test results are listed in Table 4 below.

[0162] The relevant performance testing methods are as follows:

[0163] Mechanical property test: The test was conducted according to GB / T 6396-2008 composite steel plate mechanical and process property test method, thereby obtaining the yield strength, tensile strength and elongation of the sample pipes of Examples 1-6 and Comparative Example 1.

[0164] Ozone corrosion resistance test: The test sample was hung in the outlet pipe of the pre-ozone contact tank of the water supply plant. After 3 months, the surface condition of the corrosion-resistant layer was observed to see if there was any corrosion. Thus, the ozone corrosion resistance of the sample pipes of Examples 1-6 and Comparative Example 1 can be obtained.

[0165] Table 4 lists the test results of the microstructure, mechanical properties and ozone corrosion resistance of the ozone corrosion resistant high-strength pipes of Examples 1-6 and the comparative steel plate of Comparative Example 1.

[0166] Table 4.

[0167]

[0168] It can be seen from Table 4 that in the present invention, the yield strength of the ozone corrosion-resistant high-strength pipes of Examples 1-6 is between 435-516 MPa, the tensile strength is between 590-650 MPa, and the elongation is between 32.0-40.0%. Examples 1-6 have excellent ozone corrosion resistance, and the corrosion-resistant layer did not corrode in an ozone environment for 3 months. However, since the composition design of the corrosion-resistant layer of Comparative Example 1 does not meet the design requirements of the present invention, its final corrosion-resistant layer has slight corrosion.

[0169] It can be seen from the above embodiments that the present invention can obtain an ozone-resistant high-strength pipeline with good mechanical properties and ozone corrosion resistance through appropriate material selection, component design, rolling and heat treatment processes and in conjunction with pipe making. It can solve the essential pain points of 316 stainless steel or carbon steel currently used in water supply plants in ozone-corrosive medium environments, meet the ever-increasing demand for pipeline corrosion resistance and mechanical properties of pipeline equipment used in water supply plants in ozone-corrosive medium environments, and have great economic and social benefits.

[0170] Figure 1 This is a schematic diagram of the interlayer structure of the ozone corrosion resistant high-strength pipeline in one embodiment of the present invention.

[0171] like Figure 1 As shown, in this embodiment, the ozone corrosion resistant high-strength pipeline of the present invention may include: two corrosion-resistant layers located on the inner surface and the outer surface of the pipeline and a base layer located in the middle.

[0172] Figure 2 This is a schematic diagram of the interlayer structure of the ozone corrosion resistant high-strength pipeline in another embodiment of the present invention.

[0173] like Figure 2 As shown, in this embodiment, the ozone corrosion resistant high-strength pipeline of the present invention may include: a corrosion-resistant layer located on the inner surface of the pipeline and a base layer located on the outer surface of the pipeline.

[0174] Figure 3 This is a microstructure photograph of the interface between the base layer and the corrosion-resistant layer of the ozone-resistant high-strength pipeline of Example 5.

[0175] like Figure 3 As shown, in Example 5, the microstructure of the base layer of the ozone-resistant high-strength pipeline is ferrite-pearlite-bainite; the microstructure of the corrosion-resistant layer is austenite; accordingly, the elements of the corrosion-resistant layer and the base layer diffuse at the bonding interface to form a stable transition layer, and the diffusion distance is between 50 and 100 um.

[0176] Figure 4 This is a photo of the base microstructure of the ozone corrosion resistant high-strength pipeline of Example 5.

[0177] like Figure 4 As shown, in Example 5, the microstructure of the base layer of the ozone corrosion resistant high-strength pipe is ferrite-pearlite-bainite.

[0178] It should be noted that the existing technologies in the protection scope of the present invention are not limited to the embodiments given in the present application documents. All existing technologies that do not contradict the solutions of the present invention, including but not limited to prior patent documents, prior public publications, prior public uses, etc., can be included in the protection scope of the present invention. In addition, the combination of various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0179] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A high-strength pipe resistant to ozone corrosion, characterized in that: It has a corrosion-resistant layer and a base layer in the thickness direction, wherein the corrosion-resistant layer is at least located on the inner wall of the pipeline, and the thickness of the single-layer corrosion-resistant layer accounts for 0.5%-20% of the total thickness of the pipeline, and the mass percentage of each chemical element in the corrosion-resistant layer is: 0＜C≤0.08％； 0<Si≤0.75%; 0<Mn≤2.0%; Ni: 10.00~14.00%; Cr：16.00～18.00％； Mo: 2.00~3.00%; N：0.02～0.20％； And meet the following requirements: Cr+3.3×Mo+16×N≥25%; The balance is Fe and other unavoidable impurities; The mass percentage of each chemical element in the base layer is: C：0.01～0.20％； Si: 0.10~0.50%; Mn: 0.50~2.00%; Al：0.02～0.04％； Ti: 0.005~0.018%; Nb: 0.005~0.020%; N≤0.006％； The balance is Fe and inevitable impurities.

2. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: The mass percentage of each chemical element in the corrosion-resistant layer satisfies at least one of the following items: C：0.005～0.03％； Si: 0.3-0.6%; Mn: 0.5-1.5%; Ni: 12.00~14.00%; Cr：16.50～17.50％； Mo: 2.50~3.00%; N：0.05～0.15％； Cr+3.3×Mo+16×N≥26%.

3. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: In the corrosion-resistant layer, among other inevitable impurities, S≤0.030%; P≤0.045%.

4. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: The base layer also includes at least one of the following: 0＜B≤0.0003％； 0<Ni≤0.20%; 0＜Cr≤0.20％； 0<Mo≤0.10%.

5. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: The mass percentage of each chemical element of the base layer satisfies at least one of the following items: C：0.01～0.18％； Si: 0.10~0.30%; Mn: 0.50~1.50%; Al：0.02～0.03％； Ti: 0.005~0.015%; Nb: 0.005~0.015%.

6. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: In the base layer, unavoidable impurities include: S≤0.010%; P≤0.015%.

7. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: The microstructure of the base layer is ferrite+pearlite or ferrite+pearlite+bainite; the microstructure of the corrosion-resistant layer is austenite.

8. The ozone corrosion resistant high-strength pipeline according to claim 1, characterized in that: The yield strength of the pipeline is ≥435MPa, the tensile strength is ≥590MPa, the elongation is ≥32%, and the uniform corrosion rate of the corrosion-resistant layer in an ozone environment is ≤0.05mm / year.

9. The method for manufacturing an ozone corrosion resistant high-strength pipeline according to any one of claims 1 to 8, characterized in that: Includes steps: (1) preparing a corrosion-resistant layer slab and a base slab; (2) Assembly; (3) Heating and rolling: The heating temperature is 1100-1200°C, and then the base slab and the corrosion-resistant layer slab are rolled in multiple passes within the austenite recrystallization and non-recrystallization temperature range, with the total reduction rate not less than 90% and the final rolling temperature not less than 900°C; (4) Coiling: After water cooling, the coiling temperature is controlled to be 500-650°C; (5) Surface treatment of hot rolled coil; (6) Pipe making.

10. The manufacturing method according to claim 9, characterized in that: In step (3), the final rolling temperature is controlled to be 920-1000°C.

11. The manufacturing method according to claim 9, characterized in that: Between step (2) and step (3), there is also a step (2a) of preheating: the preheating temperature is 1150-1250°C.

12. The manufacturing method according to claim 9, characterized in that: Cold rolling and annealing are also included between step (5) and step (6).

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