Ozone corrosion resistant high strength pipe and method of manufacturing same

Abstract

A tube having a corrosion-resistant layer and a base layer in the thickness direction is disclosed. The corrosion-resistant layer is located at least on the inner wall of the tube. The corrosion-resistant layer further contains the following chemical elements in wt% in addition to Fe and inevitable impurities: 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%; and N: 0.02 - 0.20%, and Cr, Mo and N satisfy the inequality: Cr + 3.3 × Mo + 16 × N ≥ 25%. Accordingly, a method for manufacturing the tube is further disclosed, including: (1) preparing a corrosion-resistant layer slab and a base layer slab; (2) assembling the corrosion-resistant layer slab and the base layer slab to obtain a clad slab; (3) heating and rolling: heating the clad slab at a temperature of 1100 - 1200 °C, then performing multi-pass rolling, where the total reduction ratio is 90% or more, and performing the final rolling at a temperature of 900 °C or more; (4) coiling: after water cooling, controlling the coiling to be performed at a temperature of 500 - 650 °C to obtain a hot-rolled coil; (5) performing surface treatment on the hot-rolled coil; and (6) manufacturing the tube.

Description

[Technical field]

[0001] Technical Field FIELD OF THE DISCLOSURE The present disclosure relates to tubing and methods of manufacture thereof, and more particularly to ozone corrosion resistant high strength tubing and methods of manufacture thereof. [Background technology]

[0002] background As is well known, ozone is typically used in current water supply facilities to disinfect and sterilize water sources to ensure water quality. In practical application, the pipeline between the ozone generator and the ozone injection device in the water supply facility typically comes into direct contact with ozone gas. The pre-ozone contact tank and the water outlet pipe of the ozone contact tank also come into contact with the water in which ozone is dissolved. If these equipment and pipelines are not specially treated, they are highly susceptible to ozone corrosion. Therefore, in order to prevent these equipment and pipelines from being corroded by ozone as much as possible, the equipment and pipelines are currently generally produced and manufactured using carbon steel materials and 316 stainless steel materials.

[0003] However, compared with carbon steel materials, the strength of 316 stainless steel structure is low, and under the same operating conditions, a larger thickness is required, which results in an increase in the amount of material used. At the same time, welding, machining, etc. with 316 stainless steel are more difficult. In addition, 316 stainless steel itself contains more valuable metal elements such as Cr, Ni, and Mo, which results in an increase in the use cost during production, manufacturing, and installation. During the use of 316L stainless steel with traditional composition, localized material corrosion occurs, mainly due to insufficient overall corrosion ability in ozone environment.

[0004] Therefore, carbon steel pipes are also generally manufactured from carbon steel materials, and such carbon steel pipes can be used as water outlet pipes behind the valves of the pre-ozone contact tank and the ozone contact tank, and the water transported in the pipeline contains a small amount of residual ozone. In order to improve the corrosion resistance of the inner wall of the pipeline, a measure of applying a special ozone-resistant fluorocarbon coating on the inner wall is generally adopted. However, due to problems such as damage and peeling of the coating on the inner wall of the pipeline, the carbon steel pipes are still inevitably corroded by ozone during long-term use and operation, resulting in water pollution, and even leakage and rupture of the pipeline.

[0005] On this basis, in consideration of the above defects and shortcomings in the prior art, the present disclosure intends to provide a new pipe having excellent ozone corrosion resistance as well as good mechanical properties and economic efficiency, which shows great economic and social benefits. Summary of the Invention [Means for solving the problem]

[0006] Summary of the Invention One of the objectives of the present disclosure is to provide a pipe which not only has excellent ozone corrosion resistance, but also has good mechanical properties and high economic efficiency, can solve the essential problems of 316 stainless steel or carbon steel used in water supply facilities in ozone corrosive medium environments, meet the increasing requirements for corrosion resistance and mechanical properties of pipelines and equipment used by water supply facilities in ozone corrosive medium environments, and greatly improve the applicability, safety and durability of these pipelines and equipment while avoiding secondary pollution to water, and has great economic and social benefits.

[0007] In order to achieve the above object, the present disclosure provides a pipe having a corrosion-resistant layer and a base layer in a thickness direction, the corrosion-resistant layer being located at least on an inner wall of the pipe, and the corrosion-resistant layer contains the following chemical elements in addition to Fe and unavoidable impurities: 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%; and N: 0.02-0.20%; Further comprising, in weight percent: where Cr, Mo and N satisfy the following inequality: Cr+3.3×Mo+16×N≧25% To provide a tube that satisfies the above.

[0008] Preferably, the corrosion resistant layer comprises the following chemical elements: 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%; and N: 0.02-0.20%; The balance is Fe and unavoidable impurities; In mass percent, Here, Cr, Mo and N satisfy the following inequality: Cr+3.3×Mo+16×N≧25%.

[0009] In order to ensure the ozone corrosion resistance of the tube, the ozone corrosion resistance of the corrosion resistant layer must first be ensured.

[0010] In the current water supply facility, the pipeline between the ozone generator and the ozone injection device transports 100% ozone gas as a medium or contacts with 100% ozone gas. The flanges, blind sheets, outlet pipes, and other equipment in the preliminary-ozone contact tank and the ozone contact tank transport water containing 1mg / L~3mg / L of dissolved ozone as a medium or contacts with 100% ozone gas, and the water also contains Cl up to 5ppm. - The main corrosive medium is ozone, and the operating temperature ranges from 0 to 40°C.

[0011] Based on the above operating conditions of pipelines and facilities used by water supply facilities in the current ozone corrosive media environment, the inventors have conducted many studies on the chemical element composition of the corrosion-resistant layer, and carried out an optimized design to ensure the ozone corrosion resistance of the corrosion-resistant layer.

[0012] In the present disclosure, the design principle of the chemical elements in the corrosion-resistant layer is as follows.

[0013] C: In the corrosion-resistant layer according to the present disclosure, C is a strong austenite-forming element, which can replace nickel to a certain extent, promote austenite formation, stabilize the austenite structure, and at the same time increase the strength of stainless steel. However, it should be noted that the content of C should not be too high. When the carbon content is too high, the combination of carbon and chromium forms chromium-rich carbides at the grain boundaries, causing intergranular corrosion. Therefore, in order to achieve the beneficial effect of C, in the corrosion-resistant layer according to the present disclosure, the mass percentage of C is controlled to satisfy 0 < C ≤ 0.08%.

[0014] In some preferred embodiments, in order to obtain better technical effects, the mass percentage of C is preferably controlled to be between 0.005% and 0.030%.

[0015] Si: In the corrosion-resistant layer according to the present disclosure, Si is mainly used for deoxidation in the smelting process, and therefore a certain amount of silicon is generally contained. However, it should also be noted that the content of Si should not be too high. When the content of Si is too high, the solubility of nitrogen decreases. Therefore, in the corrosion-resistant layer according to the present disclosure, the mass percentage of Si is controlled to satisfy 0 < Si ≤ 0.75%.

[0016] In some preferred embodiments, in order to obtain better technical effects, the mass percentage of Si is preferably controlled to be between 0.3% and 0.6%, more preferably between 0.4% and 0.6%.

[0017] Mn: In the corrosion-resistant layer according to the present disclosure, Mn is a strong austenite structure stabilizing element and can increase the solubility of nitrogen in steel. However, manganese has a negative effect on the corrosion resistance of austenitic stainless steel at the same time. Therefore, by balancing the beneficial and adverse effects of Mn, the mass percentage of Mn is controlled to satisfy 0 < Mn ≦ 2.0% in the corrosion-resistant layer according to the present disclosure.

[0018] In some preferred embodiments, in order to obtain better technical effects, the mass percentage of Mn is preferably controlled to be between 0.5% and 1.5%, more preferably between 1.10% and 1.25%.

[0019] Ni: In the corrosion-resistant layer according to the present disclosure, Ni is the most important element for forming and stabilizing the austenite phase, and the addition of an appropriate amount of Ni can ensure the formation of an austenite structure at room temperature. However, nickel is expensive, and in order to ensure a relatively low cost, the mass percentage of Ni is controlled to be between 10.00% and 14.00% in the corrosion-resistant layer according to the present disclosure.

[0020] In some preferred embodiments, in order to obtain better technical effects, the mass percentage of Ni is preferably controlled to be between 12.00% and 14.00%.

[0021] Cr: In the corrosion-resistant layer according to the present disclosure, Cr is the guarantee for obtaining the stainless steel and corrosion resistance of stainless steel, and generally the minimum chromium content for obtaining corrosion resistance is 10.5%. Since chromium is an element that significantly improves corrosion resistance, in order to ensure good corrosion resistance, the content of chromium in the steel of the present disclosure is controlled to be 16.0% or more. However, chromium is the main ferrite forming element, and if the content of chromium is too high, it is difficult to ensure an austenite structure in the cladding at room temperature. Therefore, in the corrosion-resistant layer according to the present disclosure, the mass percentage of Cr is controlled to be between 16.00% and 18.00%.

[0022] In some preferred embodiments, the mass percentage of Cr is preferably controlled to be between 16.50% and 17.50% in order to obtain better technical effect.

[0023] Mo: In the corrosion-resistant layer according to the present disclosure, Mo is an important element for improving corrosion resistance, and its mechanism is to stabilize the passive film and promote the enrichment of chromium in the passive film. Molybdenum can also synergize with nitrogen to further improve pitting corrosion 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 as well. If the content of molybdenum is too high, the cost of the alloy will increase. In order to ensure a relatively low cost, in the corrosion-resistant layer according to the present disclosure, the mass percentage of Mo is controlled to be between 2.00% and 3.00%.

[0024] In some preferred embodiments, the mass percentage of Mo is preferably controlled to be between 2.50% and 3.00% to obtain better technical effect.

[0025] N: In the corrosion-resistant layer according to the present disclosure, N is a very powerful element to form, stabilize and expand the austenite field, and the addition of an appropriate amount of N can effectively increase the pitting corrosion resistance of stainless steel. However, if the content of nitrogen is too high, the risk of the formation of nitrogen-containing intermetallic phases increases, and at the same time, the difficulty of smelting and hot processing increases, making production difficult. Therefore, in the corrosion-resistant layer according to the present disclosure, the mass percentage of N is controlled to be between 0.02% and 0.20%.

[0026] In some preferred embodiments, the mass percentage of N is preferably controlled to be between 0.05% and 0.15% to obtain better technical effect.

[0027] Therefore, it should be noted that in the corrosion-resistant layer according to the present disclosure, while controlling the mass percentage of one chemical element, it is also preferable to control the elements Cr, Mo and N to satisfy the following inequality: Cr+3.3×Mo+16×N≧25%, where each element represents the content in mass percentage of the corresponding element. Such control can further ensure that the corrosion-resistant layer exhibits excellent corrosion resistance in an ozone environment.

[0028] Preferably, the chemical elements of the corrosion resistant layer are, in mass percent: C: 0.005-0.030%; 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%; and Cr+3.3×Mo+16×N≧26% At least one of the following is satisfied.

[0029] Preferably, in the corrosion resistant layer, the unavoidable impurities include: S≦0.030%; and P≦0.045%.

[0030] In the corrosion-resistant layer of the tube according to the present disclosure, both P and S are unavoidable impurity elements, and in order to ensure the quality of the steel, the lower the content of impurity elements in the steel, the better, if conditions permit.

[0031] S: In the corrosion-resistant layer according to the present disclosure, S is a harmful impurity element. Therefore, the mass percentage of S in the corrosion-resistant layer needs to be strictly controlled, and is controlled to satisfy S≦0.030%. Preferably, the mass percentage of S can be controlled to be 0-0.005%.

[0032] P: In the corrosion-resistant layer according to the present disclosure, P is a harmful impurity element. Therefore, the mass percentage of P in the corrosion-resistant layer needs to be strictly controlled, and is controlled to satisfy: P≦0.045%. Preferably, the mass percentage of P can be controlled to be 0-0.035%.

[0033] Preferably, the single-layer corrosion-resistant layer has a thickness of 0.5% to 20% of the total thickness of the tube, and the chemical elements of the base layer are, in mass percent: 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%; and N ≤ 0.006%; The balance is Fe and unavoidable impurities. It is.

[0034] Preferably, the base layer comprises: 0 <B≦0.0003%; 0 <Ni≦0.20%; 0 <Cr≦0.20%;および 0 <Mo≦0.10% The present invention further includes at least one of the following:

[0035] In the above technical solution of the present disclosure, it is preferable to further add elements B, Ni, Cr and Mo to the base layer in order to further optimize the quality of the base layer steel.

[0036] Preferably, the chemical elements of the substrate are, in mass percent: 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%; and Nb: 0.005-0.015% At least one of the following is satisfied.

[0037] In the present disclosure, to ensure good mechanical properties of the tube according to the present disclosure, the chemical element composition of the base carbon steel is selected to ensure both high strength and good workability.

[0038] Therefore, in the present disclosure, the design principles of each chemical element in the base carbon steel are as follows:

[0039] C: In the base layer of the present disclosure, C is an austenite stabilizing element, which can function as a solid solution strengthening of the steel and can significantly increase the strength of the steel. However, it should be noted that the content of C in the steel should not be too high. If the content of C in the steel is too high, not only is the weldability and toughness of the material disadvantageous, but hard phase structures such as pearlite and martensite-austenite islands tend to increase, which adversely affects the corrosion resistance of the steel. Therefore, considering the balance of strength and toughness of the steel plate and the requirements of corrosion resistance of carbon steel materials, in the base layer steel according to the present disclosure, the mass percentage of C is controlled to be between 0.01% and 0.20%.

[0040] In the present disclosure, the amount of C added is controlled to be 0.01-0.20%, which can not only ensure that the steel plate can obtain a certain degree of hardness and strength under the condition of air cooling after rolling, but also avoid the deterioration of the weldability of the base steel. Especially for highly corrosion-resistant clad plates (corrosion-resistant layer slab + base slab) with a corrosion-resistant layer thickness accounting for 0.5%-20% of the total thickness, the carbon content of the base steel should be controlled to be within the above range.

[0041] In order to obtain better technical effect, the mass percentage of C is preferably controlled to be between 0.01% and 0.18%.

[0042] Si: In the base layer of the present disclosure, adding Si to steel can effectively improve the purity and deoxidation of steel. Although Si can play a role in the solid solution strengthening of steel, Si does not contribute to the weldability of the material; in the present disclosure, the silicon content in the base carbon steel is controlled to be 0.5% or less, which does not have any effect on the corrosion resistance of the corrosion-resistant layer, and the base carbon steel has good weldability. Therefore, in the base layer according to the present disclosure, the mass percentage of Si is controlled to be between 0.10% and 0.50%.

[0043] In order to obtain a better technical effect, the mass percentage of Si is preferably controlled to be between 0.10% and 0.30%.

[0044] Mn: In the base layer according to the present disclosure, adding an appropriate amount of Mn to the steel can delay the pearlite transformation, reduce the critical cooling rate, and improve the hardenability of the steel; at the same time, Mn also has the function of solid solution strengthening, and is the main solid solution strengthening element in steel. However, it should be noted that Mn should not be added excessively. If the content of Mn in the steel is too high, segregation bands and martensite structures tend to occur, which has an adverse effect on the toughness of the steel, and the segregation bands also reduce the corrosion resistance of the steel. The amount of Mn to be added mainly depends on the strength grade of the steel. Generally, the manganese content of low carbon micro-alloy steel does not exceed 2.0%. In this case, the Mn contained in the base carbon steel does not have an adverse effect on the corrosion-resistant layer. Based on this, in the base layer according to the present disclosure, the mass percentage of Mn is controlled to be between 0.50% and 2.00%.

[0045] In order to obtain better technical effect, the mass percentage of Mn is preferably controlled to be between 0.50% and 1.50%.

[0046] Al: In the substrate according to the present disclosure, Al is a strong deoxidizing element. To ensure that the content of oxygen in the steel is as low as possible, the mass percentage of Al is controlled to be between 0.02% and 0.04%. Excess Al after deoxidation can combine with N in the steel to form AlN precipitates, thus improving the strength of the steel and refining the austenite grain size of the steel during heat treatment. To obtain a better technical effect, the mass percentage of Al is preferably controlled to be between 0.02% and 0.03%.

[0047] Ti: In the base layer according to the present disclosure, Ti is a strong carbide-forming element, and adding a small amount of Ti to the steel is beneficial to immobilize N in the steel, and the TiN formed by the combination of Ti and N can prevent the matrix austenite grains of the base layer from growing excessively when the base slab is heated, and refine the original austenite grain size. In addition, Ti can combine with carbon and sulfur in the steel to form TiC, TiS, Ti4C2S2, etc., which can exist in the form of inclusions and second phase particles. These carbonitride precipitates of Ti can also prevent grain growth in the heat-affected zone during welding, and improve the weldability of the base layer carbon steel. Based on this, in the base layer according to the present disclosure, the mass percentage of Ti is controlled to be between 0.005% and 0.018%.

[0048] In order to obtain a better technical effect, the mass percentage of Ti is preferably controlled to be between 0.005% and 0.015%.

[0049] Nb: In the base layer of the present disclosure, Nb is a strong carbide-forming element, and a small amount of Nb is added to the steel mainly to increase the recrystallization temperature to match the high final rolling temperature of the clad plate formed by the base layer slab and the corrosion-resistant layer slab in the subsequent rolling process, so that the grains of the base layer are refined in the recrystallized and non-recrystallized zones after rolling, which is beneficial to improving the low-temperature impact toughness of the base layer. Based on this, in the base layer according to the present disclosure, the mass percentage of Nb is controlled to be between 0.005% and 0.020%.

[0050] In order to obtain a better technical effect, the mass percentage of Nb is preferably controlled to be between 0.005% and 0.015%.

[0051] N: In the base layer of the present disclosure, N can form second-phase particles with titanium and aluminum to refine the particles and improve the strength. However, if the mass percentage of N is too high, the amount of TiN formed is too large, and the particles are too coarse, which affects the plasticity of the clad base material of the present disclosure. Based on this, in the base layer according to the present disclosure, the mass percentage of N is controlled such that N ≤ 0.006%.

[0052] B: In the present disclosure, B can greatly improve the hardenability of steel. Considering the air cooling after rolling of a highly corrosion-resistant clad plate (corrosion-resistant layer slab + base layer slab), especially for highly corrosion-resistant steel plates and strips where the thickness of the corrosion-resistant layer is in the range of 0.5% to 5% of the total thickness, it is required to obtain as much ferrite + pearlite structure as possible and inhibit the formation of bainite. Therefore, in the present disclosure, it is required to control the addition amount of B in the base layer to satisfy 0 < B ≤ 0.0003%.

[0053] Ni: In the present disclosure, Ni is an element for stabilizing austenite and plays a role in improving the strength of steel. Furthermore, adding an appropriate amount of Ni to steel, especially quenched and tempered steel, can greatly improve the low-temperature impact toughness of the steel. Based on this, in the base layer according to the present disclosure, an appropriate amount of Ni can be added, and the addition amount of Ni is controlled to satisfy 0 < Ni ≤ 0.20%.

[0054] Cr: In the present disclosure, the segregation tendency of Cr is smaller than that of Mn. When the Mn content of the base carbon steel is high and obvious segregation bands and striped patterns exist in the steel, the Mn content can be appropriately reduced, and the deficiency can be replaced by Cr. Second, adding an appropriate amount of Cr to the matrix carbon steel is also beneficial for suppressing the diffusion of Cr in the corrosion-resistant layer into the base layer. Based on this, in the base layer according to the present disclosure, Cr satisfying 0 < Cr ≤ 0.20% can be added.

[0055] Mo: In the present disclosure, Mo can significantly refine particles and improve the strength and toughness of steel. Furthermore, Mo can also reduce the temper brittleness of steel, and at the same time, extremely fine carbides can precipitate during tempering, which significantly strengthens the steel matrix. Additionally, the addition of Mo also contributes to suppressing the self-tempering brittleness that easily occurs in the steel plate during air cooling. Based on this, in the base layer according to the present disclosure, an appropriate amount of Mo can be added, and the addition amount of Mo is controlled to satisfy 0 < Mo ≦ 0.10%.

[0056] Preferably, in the base layer, inevitable impurities include: S ≦ 0.010%; and P ≦ 0.015%.

[0057] In the above technical solution of the present disclosure, both P and S belong to inevitable impurity elements in the base layer, and S combines with Mn in the steel to form plastic inclusions of manganese sulfide, which is not particularly favorable for the transverse plasticity and toughness of the steel. Therefore, the content of S in the base layer should be as low as possible. Furthermore, P is also a harmful element in the steel, which significantly impairs the plasticity and toughness of the steel plate.

[0058] Regarding the present disclosure, both P and S are inevitable impurity elements, so the lower the content, the better. Considering the actual steelmaking level of the steelworks, in the base layer of the present disclosure, S and P are controlled to satisfy S ≦ 0.010%; and P ≦ 0.015%.

[0059] Preferably, the single-layer corrosion-resistant layer has a thickness that occupies 0.5% - 20% of the total thickness of the pipe.

[0060] In the present disclosure, according to the operating conditions, the selection of the thickness of the corrosion-resistant layer plays a major role in obtaining good corrosion resistance, mechanical properties and formability of the tube. If the corrosion-resistant layer is too thick, the mechanical properties and production cost of the material will be affected; but if the corrosion-resistant layer is too thin, the corrosion resistance and service life of the material will decrease. For this reason, in the present disclosure, the corrosion-resistant layer has a controlled thickness, preferably occupying 0.5%-20% of the total thickness of the clad slab, more preferably 2.5%-10% of the total thickness of the tube.

[0061] Preferably, the substrate has a ferrite+pearlite or ferrite+pearlite+bainite microstructure; and the corrosion resistant layer has an austenite microstructure.

[0062] Preferably, the pipe has a yield strength of ≧435 MPa, a tensile strength of ≧590 MPa, an elongation of ≧30%, preferably ≧32%, and a uniform corrosion rate of the corrosion resistant layer in an ozone environment of ≦0.05 mm / year.

[0063] Accordingly, another object of the present disclosure is to provide a method for manufacturing the above-mentioned tube, which is simple and feasible, can efficiently prepare the above-mentioned tube, and can break the limitation of the thickness of the corrosion-resistant layer, and can control the thickness of the corrosion-resistant layer within the range of 0.5% to 20% of the total thickness of the tube.

[0064] In order to achieve the above object, the present disclosure provides a method for manufacturing the above-mentioned tube, comprising the steps of: (1) preparing a corrosion-resistant layer slab and a base layer slab; (2) assembling the corrosion-resistant layer slab and the base layer slab to obtain a clad slab, wherein the single-layer corrosion-resistant layer preferably has a thickness of 0.5%-20% of the total thickness of the clad slab, more preferably 2.5%-10% of the total thickness of the clad slab; (3) heating and rolling: heating the clad slab at a temperature of 1100-1200°C, and then performing multi-pass rolling within the austenite recrystallization and non-recrystallization temperature ranges of the base layer slab and the corrosion-resistant layer slab, where the total reduction is 90% or more, and final rolling is performed at a temperature of 900°C or more; (4) Coiling process: After water cooling, coil winding is controlled to be performed at a temperature of 500 to 650°C to obtain a hot-rolled coil; (5) subjecting the hot rolled coil to a surface treatment; and (6) A process for manufacturing pipes.

[0065] In this disclosure, based on the rational design of chemical composition, the inventors have designed a novel manufacturing method in an optimized manner through extensive research, and the ozone corrosion resistant high strength tube can be efficiently prepared by this method.

[0066] In the manufacturing method according to the present disclosure, the corrosion-resistant layer slab and the base layer slab can be prepared by smelting and casting according to the chemical composition design, and then the corrosion-resistant layer slab and the base layer slab are assembled to obtain a highly corrosion-resistant clad plate (corrosion-resistant layer plate + base plate). The obtained highly corrosion-resistant clad plate is then heated, rolled and coiled to obtain a hot-rolled coil having a clad interlayer structure, and the hot-rolled coil is subjected to surface treatment and then to tube manufacturing, thus obtaining a tube according to the present disclosure.

[0067] In the present disclosure, the inventors design the heating and rolling process in step (3) in an optimized manner to ensure that a transition layer structure with a certain thickness can be formed between the corrosion-resistant layer and the base layer of the highly corrosion-resistant clad plate by processes such as heating and rolling, thus realizing a perfect metallurgical combination of the corrosion-resistant layer and the base layer, thereby improving the applicability and economic efficiency of the material while ensuring the ozone corrosion resistance and mechanical properties.

[0068] In step (2) of the manufacturing method according to the present invention, the prepared corrosion-resistant layer slab and base layer slab may be pretreated, the periphery of the joining surfaces of the slabs are welded and sealed, and the welded and sealed joining surfaces are vacuum treated to complete the assembly of the slabs.

[0069] Accordingly, in step (5), the hot rolled coil is subjected to surface treatment, which may be achieved by pickling or mechanical descaling. Furthermore, in the tube manufacturing process in step (6), a conventional spiral welding method or a longitudinal welding method may be adopted for forming and welding. The welding method may be selected from submerged arc welding, metal gas arc welding, tungsten inert gas welding, plasma arc welding, welding rod arc welding, high frequency welding, or laser welding.

[0070] In the manufacturing method according to the present disclosure, the temperature at which the final rolling is carried out in step (3) is preferably controlled to be in the range of 920 to 1000°C.

[0071] Preferably, in the manufacturing method according to the present disclosure, preheating is further included between step (2) and step (3), where the preheating is carried out at a temperature of 1150 to 1250°C.

[0072] In the manufacturing method according to the present disclosure, it can also be determined whether to carry out a pre-heating process between step (2) and step (3) according to the performance requirements of the final product. In the pre-heating process, the clad slab obtained by assembling the slabs can be heated at a temperature of 1150-1250°C, so that a uniform austenitized structure can be obtained in the corrosion-resistant layer on the surface of the clad slab, and the carbides that may have existed before can be completely dissolved as much as possible, and at the same time, the compounds of alloying elements such as niobium and titanium in the carbon steel can be completely or partially dissolved; the elements of the corrosion-resistant layer and the carbon steel base layer diffuse at the interface to form a stable transition layer, and then slowly cool down to room temperature.

[0073] Preferably, in the manufacturing method according to the present disclosure, cold rolling and annealing are further included between steps (5) and (6).

[0074] In the manufacturing method according to the present disclosure, if the target product before tube manufacturing is a cold-rolled coil instead of a hot-rolled coil in practical use, a cold rolling and annealing step can be further added between step (5) and step (6), which can be achieved by cold rolling to a target thickness and then annealing. Preferably, the annealing is carried out at a temperature of 900-1000°C.

[0075] Therefore, in the present disclosure, an ozone corrosion-resistant layer is formed by rolling process on the surface of the base layer of carbon steel plate through the composition design and ratio design of the corrosion-resistant layer and the base layer, and a plate / strip with ozone corrosion resistance, good mechanical properties and high economic efficiency is finally formed, which is further processed into a pipe for use in pipelines and equipment for water supply facilities in ozone corrosive medium environment.

[0076] It should be noted that design challenges in this disclosure include: 1) The composition design of the corrosion-resistant layer and the base layer must satisfy the overall properties of the material. The composition of the corrosion-resistant layer must be designed according to the characteristics of ozone corrosion and meet the requirements of corrosion resistance under working conditions. For the composition design of the carbon steel of the base layer, in addition to meeting the requirements of mechanical properties, it is also necessary to consider that when the carbon content of the transition layer at the junction between the corrosion-resistant layer and the base layer is high, there is a lack of stabilizing elements, and there is an obvious decarbonization layer on one side of the carbon steel at the junction of the interface, and the structure of the carbon steel base material is uneven, so that after processing, there is a tendency to surface defects, and the mechanical properties also cannot meet the standards. 2) The ratio of the corrosion-resistant layer to the matrix metal and the difference in material properties make the heating, rolling, and heat treatment processes difficult to control. For example, uneven temperature during the heating process can cause deformation and blistering, making it impossible to bond with the base layer. For example, it can separate from the matrix during rolling and crack, and it is difficult to ensure thickness uniformity. 3) For pipelines and equipment for water supply facilities in ozone corrosive medium environment, such as ozone generators, ozone injection equipment, and pipelines between pre-ozone contact tanks and water outlet pipes of ozone contact tanks, if the initial cladding is not complete and the bonding quality is poor, the continuity and uniformity of the corrosion-resistant layer of the final product cannot be guaranteed after subsequent processing steps such as pickling, pipe making and forming, welding, etc. This poses significant risks to the applicability, safety and durability of the equipment and pipelines.

[0077] In the present disclosure, the present inventors have successfully overcome the above difficulties through rational design and have been able to prepare an ozone corrosion resistant high strength tube according to the present disclosure.

[0078] Compared with the prior art, the ozone corrosion resistant high strength tube and its manufacturing method according to the present disclosure have shown the following advantages and beneficial effects: In this disclosure, the inventors consider the operating conditions of pipelines and equipment for water supply facilities in the current ozone corrosive medium environment. Through the composition design and ratio design of the corrosion-resistant layer and base layer, the corrosion-resistant layer and base layer are combined and assembled, and then subjected to appropriate heating, rolling and coiling processes, and pipe manufacturing processes, to obtain a pipe with ozone corrosion resistance, good mechanical properties, and high economic efficiency. The pipe has a yield strength of ≧435 MPa, a tensile strength of ≧590 MPa, an elongation of ≧30%, and a uniform corrosion rate of ≦0.05 mm / year of the corrosion-resistant layer in ozone environment.

[0079] In the present disclosure, a transition layer structure with a certain thickness is formed between the corrosion-resistant layer and the base layer by processes such as heating, rolling, etc., and a perfect metallurgical bond between the corrosion-resistant layer and the base layer is achieved, thus improving the applicability and economic efficiency of the material while ensuring the ozone corrosion resistance and mechanical properties.

[0080] By using the pipe manufactured by the above composition design and process control method, the essential troubles of 316 stainless steel or carbon steel used by water supply facilities in ozone corrosive medium environment can be solved; the pipe can be used as pipelines and equipment used in water supply facilities in ozone corrosive medium environment, such as ozone generator, ozone injection device, and pipeline between preliminary-ozone contact tank and outlet pipe of ozone contact tank, and can meet the requirements for ozone corrosion resistance and mechanical properties of these pipelines and equipment, greatly improve the applicability, safety and durability of these pipelines and equipment, and avoid secondary pollution to water, showing great economic and social benefits.

[0081] Compared with the 316 stainless steel pipes used as the pipeline between the ozone generator, the ozone injection device, and the pre-ozone contact tank and the outlet pipe of the ozone contact tank in the water supply facility, the pipes according to the present disclosure exhibit higher strength, simpler welding and machining, better corrosion resistance, and higher economic efficiency.Compared with the carbon steel pipes used in the water outlet pipes behind the valves of the pre-ozone contact tank and the ozone contact tank, the pipes according to the present disclosure can omit the process of applying a corrosion-resistant coating to the pipes, while exhibiting corrosion resistance and durability that the carbon steel pipes cannot match, and are more energy-saving, environmentally friendly, and maintenance-free. [Brief description of the drawings]

[0082] [Figure 1] FIG. 1 is a schematic diagram of an interlayer structure of a tube according to one embodiment of the present disclosure; [Diagram 2]FIG. 2 is a schematic diagram of an interlayer structure of a tube according to another embodiment of the present disclosure; [Diagram 3] FIG. 3 is a photograph of the microstructure of the bonding interface between the base layer and the corrosion-resistant layer of the tube in Example 5; and [Figure 4] FIG. 4 is a photograph of the microstructure of the substrate of the tube in Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] Detailed Description The tube and its manufacturing method according to the present disclosure will be further described and illustrated with reference to the accompanying drawings and specific embodiments, which are not intended to unduly limit the technical solutions of the present disclosure.

[0084] Examples 1 to 6 and Comparative Example 1 Table 1 lists the chemical elements in the corrosion resistant layers of the tubes in Examples 1-6 and Comparative Example 1 in mass percent.

[0085] [Table 1]

[0086] Table 2 lists the chemical elements in the substrate layers of the tubes in Examples 1-6 and Comparative Example 1 in mass percent.

[0087] [Table 2]

[0088] The tubes in Examples 1 to 6 and Comparative Example 1 of the present disclosure were manufactured by the following process: (1) According to the chemical compositions shown in Tables 1 and 2, smelting and casting were carried out to prepare corrosion-resistant layer slabs and base layer slabs, respectively. (2) The corrosion-resistant layer slab and the base layer slab are assembled to obtain a clad slab: the thickness of the corrosion-resistant layer is controlled to be 0.5%-20% of the total thickness of the clad slab, the corrosion-resistant layer slab and the base layer slab are subjected to pre-treatment, the periphery of the bonding surface of the slab is welded and sealed, and the welded and sealed bonding surface is vacuum treated; whether to carry out a pre-heating process is determined according to the performance requirements of the final product after the slab is assembled, and if pre-heating is required, the pre-heating temperature is controlled to be 1150-1250°C. (3) Heating and rolling: the clad slab is heated at a temperature of 1100-1200°C, then multi-pass rolling is carried out within the temperature range of austenite recrystallization and non-recrystallization of the base layer slab and the corrosion-resistant layer slab, the total reduction is controlled to be 90% or more, and the final rolling is carried out at a temperature of 900°C or more, preferably the final rolling is carried out at a temperature between 920°C and 1000°C. (4) Coiling: After water cooling, the coil winding was controlled to be performed at a temperature of 500 to 650°C to obtain a hot-rolled coil. (5) Pickling or mechanical descaling was adopted to perform surface treatment on the hot-rolled coil; when the target product is cold-rolled coil, cold rolling and annealing process was further carried out, followed by annealing to the target thickness after cold rolling. (6) Tube manufacturing: Spiral welding method or longitudinal welding method was adopted for forming and welding; and the tube manufacturing was carried out by a welding method selected from submerged arc welding, metal gas arc welding, tungsten inert gas welding, plasma arc welding, welding rod arc welding, high frequency welding or laser welding.

[0089] It should be noted that in the present disclosure, the tubes in Examples 1 to 6 of the present disclosure were all manufactured using the process of steps (1)-(6) above, and the chemical compositions and related process parameters all satisfied the control requirements of the design specifications of the present disclosure.

[0090] Table 3 lists the specific process parameters for the tubes in Examples 1-6 and Comparative Example 1 in the steps of the manufacturing process described above.

[0091] [Table 3]

[0092] It should be noted that according to the process parameters shown in Table 3 above, in Examples 1 and 3, after step (5) of performing surface treatment on the hot-rolled coil, cold rolling and annealing are further carried out, thereby obtaining a cold-rolled plate; and in Example 2, Example 4, Example 5, Example 6 and Comparative Example 1, a hot-rolled plate is obtained after step (5).

[0093] Therefore, the plates prepared according to the Examples and Comparative Examples can be further used to prepare corresponding tubes in the tube manufacturing process in step (6).

[0094] The tubes in Examples 1-6 and Comparative Example 1 prepared by the above process were sampled respectively, and the microstructures of the sample tubes in Examples 1-6 and Comparative Example 1 were further observed, and after observing the microstructures of the tubes, the sample tubes in Examples 1-6 and Comparative Example 1 were further subjected to mechanical property tests and ozone corrosion resistance tests, and the test results are shown in Table 4 below.

[0095] The relevant performance test methods were as follows: Mechanical property test: According to GB / T 6396-2008 Clad steel plate-Mechanical and technological test, the yield strength, tensile strength and elongation of the sample pipes in Examples 1-6 and Comparative Example 1 were obtained.

[0096] Ozone corrosion resistance test: Using "Coupon testing method for specific application scenarios", a test coupon was installed on the water outlet pipe of the reserve-ozone contact tank of the water supply facility; and after 3 months, the test coupon was taken out to observe the surface state of the corrosion-resistant layer to check whether there was any corrosion phenomenon, thereby obtaining the ozone corrosion resistance of the sample pipe in Examples 1-6 and Comparative Example 1.

[0097] Table 4 shows the test results of the microstructure, mechanical properties and ozone corrosion resistance of the tubes in Examples 1 to 6 and Comparative Example 1.

[0098] [Table 4]

[0099] In combination with Table 4 above, it can be seen that in the present disclosure, the pipes in Examples 1 to 6 exhibited a yield strength of 435 MPa to 516 MPa, a tensile strength of 590 MPa to 650 MPa, and an elongation of 30.0% to 40.0%, and exhibited excellent ozone corrosion resistance, and none of the corrosion-resistant layers were corroded after 3 months in an ozone environment; on the other hand, the final corrosion layer in Comparative Example 1 was slightly corroded due to the composition design of the corrosion-resistant layer not satisfying the design requirements of the present disclosure.

[0100] As can be seen from the above examples, a pipe with good mechanical properties and ozone corrosion resistance can be obtained by appropriate material selection, composition design, rolling and heat treatment process and pipe manufacturing, which can solve the essential problems of 316 stainless steel or carbon steel currently used by water supply facilities in ozone corrosive medium environment, meet the increasing requirements for corrosion resistance and mechanical properties of pipelines and equipment used by water supply facilities in ozone corrosive medium environment, and have great economic and social benefits.

[0101] FIG. 1 is a schematic diagram of an interlayer structure of a tube according to one embodiment of the present disclosure.

[0102] As shown in FIG. 1, in this embodiment, a tube according to the present disclosure may include two corrosion-resistant layers located on the inner and outer surfaces of the tube, and a base layer located between the two corrosion-resistant layers.

[0103] FIG. 2 is a schematic diagram of an interlayer structure of a tube according to another embodiment of the present disclosure.

[0104] As shown in FIG. 2, in this embodiment, a tube according to the present disclosure may include a corrosion resistant layer located on an inner surface of the tube, and a base layer located on an outer surface of the tube.

[0105] FIG. 3 is a photograph of the microstructure of the bonding interface between the base layer and the corrosion-resistant layer of the tube in Example 5.

[0106] As shown in FIG. 3, in Example 5, the microstructure of the substrate of the tube was ferrite-pearlite-bainite; the microstructure of the corrosion-resistant layer was austenite; therefore, the elements of the corrosion-resistant layer and substrate diffused at the bonding interface to form a stable transition layer with a diffusion distance of 50-100 μm.

[0107] FIG. 4 is a photograph of the microstructure of the substrate of the tube in Example 5.

[0108] As shown in FIG. 4, in Example 5, the microstructure of the tube substrate was ferrite-pearlite-bainite.

[0109] It should be noted that the prior art part in the protection scope of the present disclosure is not limited to the embodiments described in the documents of the present disclosure, and all prior art that is not inconsistent with the solution of the present disclosure may be included in the protection scope of the present disclosure, including but not limited to prior patent documents, prior publications, prior public uses, etc. Furthermore, the combination of features of the present disclosure is not limited to the combinations described in the claims or specific embodiments, and all features described in the present disclosure can be freely combined or combined in any manner as long as they are not inconsistent with each other.

[0110] It should also be noted that the above embodiments are merely specific embodiments of the present disclosure. Obviously, the present disclosure is not limited to the above embodiments, and similar modifications or variations made accordingly may be directly derived from the disclosure content of the present disclosure or may be easily conceived by those skilled in the art from the disclosure content of the present disclosure, and fall within the protection scope of the present disclosure.

Claims

1. A pipe having a corrosion resistant layer and a base layer through its thickness, the corrosion resistant layer being located at least on an inner wall of the pipe, and the corrosion resistant layer containing, in addition to Fe and unavoidable impurities, the following chemical elements: 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%; and N: 0.02-0.20%; Further comprising, in weight percent: where Cr, Mo and N satisfy the following inequality: Cr + 3.3 × Mo + 16 × N ≥ 25% Satisfying, tube.

2. The chemical elements of the corrosion resistant layer, in mass percent: 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%; and N: 0.02-0.20%; The balance is Fe and unavoidable impurities; where Cr, Mo and N satisfy the following inequality: Cr + 3.3 × Mo + 16 × N ≧ 25% The tube of claim 1 , wherein

3. The chemical elements of the corrosion resistant layer, in mass percent: 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%; and Cr+3.3×Mo+16×N≧26% The tube according to claim 2 , which satisfies at least one of the above.

4. 3. The tube of claim 1 or 2, wherein in the corrosion resistant layer, unavoidable impurities include: S≦0.030%; and P≦0.045%.

5. The single-layer corrosion-resistant layer has a thickness of 0.5% to 20% of the total thickness of the pipe, and the chemical elements of the base layer are, in mass percent: 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%; and N≦0.006%; The balance is Fe and unavoidable impurities.

3. The tube of claim 1 or 2,

6. Substrate: 0＜B≦0.0003%; 0<Ni≦0.20%; 0<Cr≦0.20%; and 0<Mo≦0.10% The tube of claim 5 further comprising at least one of:

7. The chemical elements of the substrate, in mass percent: 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%; and Nb: 0.005-0.015% The tube according to claim 5 , which satisfies at least one of the above.

8. 6. The tube of claim 5, wherein in the substrate, unavoidable impurities include: S≦0.010%; and P≦0.015%.

9. 3. A tube according to claim 1 or 2, wherein the single anti-corrosion layer has a thickness which accounts for 0.5% to 20% of the total thickness of the tube.

10. 3. The tube of claim 1 or 2, wherein the base layer has a ferrite+pearlite or ferrite+pearlite+bainite microstructure; and the corrosion resistant layer has an austenitic microstructure.

11. 3. The pipe of claim 1 or 2 having a yield strength of ≧435 MPa, a tensile strength of ≧590 MPa, an elongation of ≧30%, and a uniform corrosion rate of the corrosion resistant layer in an ozone environment of ≦0.05 mm / year.

12. A method for manufacturing a tube according to any one of claims 1 to 11, comprising the steps of: (1) preparing a corrosion-resistant layer slab and a base layer slab; (2) assembling the corrosion-resistant layer slab and the base layer slab to obtain a clad slab, wherein the single-layer corrosion-resistant layer preferably has a thickness of 0.5% to 20% of the total thickness of the clad slab, more preferably 2.5% to 10% of the total thickness of the clad slab; (3) heating and rolling: heating the clad slab at a temperature of 1100-1200°C, then carrying out multi-pass rolling, in which the total reduction is 90% or more, and final rolling is carried out at a temperature of 900°C or more; (4) Coiling process: After water cooling, coil winding is controlled to be performed at a temperature of 500 to 650°C to obtain a hot-rolled coil; (5) subjecting the hot rolled coil to a surface treatment; and (6) Pipe manufacturing process A method comprising:

13. The method according to claim 12, wherein in step (3), the final rolling is carried out at a temperature of 920 to 1000°C.

14. 13. The method of claim 12, further comprising a preheating step between steps (2) and (3), wherein the preheating is at a temperature of 1150 to 1250°C.

15. 13. The method of claim 12, further comprising cold rolling and annealing between steps (5) and (6), wherein the annealing is preferably performed at a temperature of 900-1000°C.

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