A chromium-molybdenum steel container composite corrosion-resistant layer resistant to bromide ion stress corrosion and a preparation process thereof

Abstract

This invention discloses a composite corrosion-resistant layer for chromium-molybdenum steel containers resistant to bromide ion stress corrosion and its preparation process, belonging to the field of pressure vessel manufacturing technology. The preparation process includes: sequentially depositing an ultra-low carbon austenitic stainless steel transition layer, a Ni-Cr-Mo alloy intermediate layer, and a C276 corrosion-resistant layer onto the surface of a chromium-molybdenum steel base layer; performing a first post-weld stress-relieving heat treatment at 670℃~710℃ after depositing the intermediate layer; performing a second post-weld stress-relieving heat treatment at 500℃~630℃ after depositing the C276 layer, the second heat treatment temperature being lower than the first heat treatment temperature; and finally, pickling and passivating the surface of the C276 layer. The linear expansion coefficients of the transition layer, intermediate layer, and C276 layer decrease sequentially, forming a gradient buffer structure. This invention, through the synergistic effect of a three-layer gradient structure design and a dual heat treatment process, eliminates residual stress in the base layer while preventing the precipitation of harmful phases in the C276 layer, significantly improving the stress corrosion cracking resistance of the composite corrosion-resistant layer under low bromide ion media and high stress conditions.

Description

Technical Field

[0001] This invention belongs to the field of pressure vessel manufacturing and metal surface engineering technology, specifically relating to a composite corrosion-resistant layer for stress corrosion resistance of chromium-molybdenum steel containers under high stress in low bromide ion media and its preparation process. It is applicable to the manufacture of corrosion-resistant layers for chromium-molybdenum steel pressure vessels in fields such as petrochemical, coal chemical, pharmaceutical chemical, and bromine production and storage. Background Technology

[0002] Chromium-molybdenum steels (such as 14Cr1Mo and 12Cr2Mo1) are widely used as the main material for hydrogen-containing equipment such as hydrogenation reactors and high-pressure heat exchangers due to their excellent high-temperature strength and hydrogen resistance. However, when such containers are used in contact with bromide ions (Br₂... - When exposed to corrosive media, the inner wall corrosion-resistant layer of the vessel faces a severe risk of stress corrosion cracking (SCC). Bromine ions can destroy the passivation film on the metal surface, forming pits. Stress concentration occurs at the pit locations, and combined with the high internal pressure and temperature stress experienced by the vessel during operation, this ultimately leads to stress corrosion cracking.

[0003] In existing technologies, the inner wall of chromium-molybdenum steel containers is typically protected by overlaying a Hastelloy C276 corrosion-resistant layer. C276 alloy exhibits excellent resistance to pitting corrosion, crevice corrosion, and stress corrosion, making it one of the most widely used corrosion-resistant materials in halide-ion-containing corrosive environments. Chinese patent CN108356397A discloses a wide-band electrode overlay welding method for the corrosion-resistant layer of the inner wall of a large hydrogenation reactor based on residual stress regulation. This method employs a double-layer structure of a transition layer + corrosion-resistant layer, and eliminates residual stress through post-weld heat treatment at 670℃ for 6 hours. However, this technology still has shortcomings: First, it only sets up a two-layer structure of transition layer and corrosion-resistant layer, lacking the design of intermediate stress buffer layer, which makes it difficult to effectively alleviate the interfacial thermal stress caused by the difference in thermal expansion between the chromium-molybdenum steel base layer and C276 corrosion-resistant layer during the welding and subsequent heat treatment process; Second, although the high-temperature heat treatment of 670℃ can meet the stress relief requirements of the base layer, this temperature range has entered the sensitization temperature range of C276 (about 650℃ and above), which will cause harmful intermetallic phases such as μ phase and σ phase to precipitate in the C276 corrosion-resistant layer, reducing its corrosion resistance and toughness, and failing to meet the dual requirements of stress relief of the base layer and maintenance of the corrosion-resistant layer performance.

[0004] Chinese patent CN114192943A proposes a welding method for austenitic stainless steel cladding, employing manual welding of the transition layer combined with submerged arc welding of the corrosion-resistant layer to improve welding efficiency. However, this method primarily targets carbon steel or low-alloy steel substrates for welding austenitic stainless steel cladding. The corrosion-resistant layer material is stainless steel, not a nickel-based alloy, and its resistance to halide ion pitting and stress corrosion is far inferior to that of C276 alloy. Furthermore, it also uses a single post-weld stress-relieving heat treatment process, failing to address the control of the corrosion-resistant layer's sensitization temperature window.

[0005] Chinese patent CN115625446A discloses a welding method for chromium-molybdenum steel and martensitic heat-resistant steel. By depositing an isolation layer at the bevel and performing independent heat treatment, it solves the problem of mismatched temperature windows for stress-relieving heat treatment after welding dissimilar steels. However, this technology targets butt welding between two types of base materials, rather than the stress corrosion protection of a corrosion-resistant layer. Both the isolation layer and the butt welding material are ferritic heat-resistant steel welding materials, which are completely different from the material system of C276 nickel-based corrosion-resistant alloy. Therefore, its technical concept is difficult to transfer to stress corrosion control of nickel-based corrosion-resistant composite structures.

[0006] In addition, the following technical challenges exist when directly surfacing C276 on chromium-molybdenum steel containers: Fe elements in the chromium-molybdenum steel base material will be diluted into the C276 weld overlay, affecting its corrosion resistance; chromium-molybdenum steel has a high carbon content while C276 has an extremely low carbon content. During welding or subsequent high-temperature service, carbon will migrate from the low-alloy steel side to the nickel-based alloy side, forming a chromium-depleted zone at the interface and precipitating chromium carbide, reducing corrosion resistance and interfacial bonding strength; after surfacing C276 on chromium-molybdenum steel containers, solution treatment cannot be performed, limiting the application of conventional techniques for eliminating harmful phases and residual stress through solution treatment.

[0007] In summary, existing technologies lack a systematic solution for stress corrosion cracking of the C276 corrosion-resistant layer in chromium-molybdenum steel containers under bromide ion-containing media and high-stress environments. How to prevent sensitization of the C276 corrosion-resistant layer, reduce its residual tensile stress level, and inhibit interfacial dilution and carbon migration while ensuring the stress-relieving heat treatment requirements of the chromium-molybdenum steel base layer are urgent technical challenges. This invention is proposed based on the aforementioned shortcomings of existing technologies. Summary of the Invention

[0008] In view of the problems mentioned in the background art regarding the existing C276 corrosion-resistant layer preparation technology for chromium-molybdenum steel containers, such as the lack of intermediate stress buffer layer design, C276 sensitization caused by single high-temperature heat treatment, inability to balance stress relief of the base layer and maintenance of corrosion-resistant layer performance, Fe element dilution and carbon migration, and inability to perform solid solution treatment after welding, this invention provides a composite corrosion-resistant layer for chromium-molybdenum steel containers resistant to bromide ion stress corrosion and its preparation process.

[0009] This invention includes the following technical solutions:

[0010] This invention provides a process for preparing a chromium-molybdenum steel container composite corrosion-resistant layer resistant to bromide ion stress corrosion, comprising the following steps:

[0011] S1: The surface of the chromium-molybdenum steel container base to be welded is machined and cleaned to remove surface oxide scale, oil and impurities.

[0012] Preferably, the chromium-molybdenum steel container is a pressure vessel made of 14Cr1MoR, 12Cr2Mo1R, or 12Cr2Mo1VR chromium-molybdenum steel, with a base layer thickness of 20mm to 300mm. The aforementioned grades of chromium-molybdenum steel possess excellent high-temperature strength and hydrogen resistance, making them commonly used main materials for hydrogen-contaminated equipment.

[0013] S2: An ultra-low carbon austenitic stainless steel transition layer is overlaid on the base surface after the treatment of S1, with an overlay thickness of 1.5mm to 4mm, a flatness between overlay passes of ≤2mm, and an interlayer temperature of 100℃ to 200℃.

[0014] The transition layer uses E309L or E309LMo ultra-low carbon austenitic stainless steel welding material. Ultra-low carbon austenitic stainless steel has a low carbon content and good plasticity, which can effectively isolate the chromium-molybdenum steel base layer from the subsequent nickel-based weld overlay layer, and inhibit the dilution of Fe elements into the C276 corrosion-resistant layer and the migration of carbon elements into the nickel-based alloy side.

[0015] Preferably, the welding method for the transition layer is selected from strip welding, electroslag strip welding, shielded metal arc welding, or tungsten inert gas welding. The welding material specifications are a strip thickness of 0.4mm to 0.5mm and a width of 60mm to 75mm, or a welding rod / wire diameter of 2.5mm to 5.0mm. During the welding process, the interpass temperature is 120℃ to 175℃, the overlap between weld passes is 5mm to 15mm, the welding speed is 150mm / min to 350mm / min, and the weld thickness is 2mm to 3mm.

[0016] Preferably, when overlaying the transition layer, the welding current of shielded metal arc welding is 140A to 160A and the arc voltage is 20V to 25V; the welding current of strip electrode overlay welding is 1650A to 1850A and the arc voltage is 28V to 30V; and the welding current of tungsten inert gas welding is 150A to 250A and the arc voltage is 12V to 18V.

[0017] S3: A Ni-Cr-Mo alloy intermediate layer is deposited on the surface of the transition layer, with a deposit thickness of 2mm to 8mm, a flatness between weld passes ≤2mm, and an interlayer temperature ≤120℃. The linear expansion coefficient of the transition layer > the linear expansion coefficient of the intermediate layer > the linear expansion coefficient of the subsequent C276 corrosion-resistant layer.

[0018] The intermediate layer uses ERNiCrMo-3 or ENiCrMo-10 nickel-based alloy welding material. The coefficient of linear expansion of this intermediate layer is between that of an ultra-low carbon austenitic stainless steel transition layer (approximately 16 × 10⁻⁶). -6 / ℃~17×10 -6 / ℃) and C276 corrosion-resistant layer (approximately 11×10) -6 / ℃~12×10 -6Between / ℃, a gradient transition of the coefficient of linear expansion is formed, which helps to alleviate the interfacial thermal stress caused by the difference in thermal expansion of each layer of material during the welding and subsequent heat treatment process, and reduces the level of residual tensile stress at the interface.

[0019] Preferably, the welding method for the intermediate layer is selected from strip welding, electroslag strip welding, shielded metal arc welding, or tungsten inert gas welding. The welding material specifications are a strip thickness of 0.4mm to 0.5mm and a width of 60mm to 75mm, or a welding rod / wire diameter of 2.0mm to 4.0mm. During the welding process, the interpass temperature is ≤100℃, the overlap between weld passes is 5mm to 15mm, the welding speed is 150mm / min to 350mm / min, and the weld thickness is 3mm to 6mm.

[0020] Preferably, when welding the intermediate layer, the welding current of shielded metal arc welding is 130A to 180A and the arc voltage is 22V to 28V; the welding current of strip welding is 1600A to 1900A and the arc voltage is 26V to 32V; and the welding current of tungsten inert gas welding is 140A to 240A and the arc voltage is 12V to 18V.

[0021] S4: Perform the first post-weld stress relief heat treatment on the chromium-molybdenum steel container after the intermediate layer has been welded. The heat treatment temperature is 670℃~710℃, the holding time is 3h~10h, the heating rate and cooling rate above 400℃ are 15℃ / h~90℃ / h independently, and the furnace is cooled to below 400℃ and then air cooled.

[0022] The first post-weld stress-relieving heat treatment is performed before the C276 corrosion-resistant layer is welded. Its purpose is to fully eliminate the residual welding stress in the chromium-molybdenum steel base layer and intermediate layer, ensuring the inherent safety of the base layer. Since the C276 corrosion-resistant layer has not yet been welded at this time, the high-temperature heat treatment will not cause harmful phase precipitation damage to the C276 corrosion-resistant layer.

[0023] Preferably, the temperature of the first post-weld stress-relieving heat treatment is 680℃~700℃, the holding time is 4h~8h, and the heating rate and cooling rate above 400℃ are independently 50℃ / h~55℃ / h. The heat treatment is carried out in a bogie-type heating furnace or a pit-type heat treatment furnace, and a protective atmosphere is introduced into the inner wall of the container during the heat treatment process to prevent oxidation.

[0024] S5: A C276 corrosion-resistant layer is deposited on the surface of the intermediate layer, with a deposit thickness of 1mm to 4mm, a flatness between deposited passes of ≤1.5mm, and an interpass temperature of ≤100℃. The C276 corrosion-resistant layer uses ENiCrMo-4 nickel-based alloy welding material.

[0025] The C276 corrosion-resistant layer is a surface functional layer that comes into direct contact with bromide-containing corrosive media. Its excellent resistance to pitting corrosion, crevice corrosion, and stress corrosion provides a protective barrier against bromide ion erosion for containers.

[0026] Preferably, the welding method for the C276 corrosion-resistant layer is selected from strip welding, electroslag strip welding, shielded metal arc welding, or tungsten inert gas welding. The welding material specifications are strip thickness of 0.4mm to 0.5mm × width of 60mm to 75mm, or welding rod / wire diameter of 2.0mm to 4.0mm. During the welding process, the interpass temperature is ≤100℃, the overlap between weld passes is 5mm to 15mm, the welding speed is 150mm / min to 350mm / min, and the weld thickness is 1.5mm to 3mm.

[0027] S6: Perform a second post-weld stress relief heat treatment on the chromium-molybdenum steel container with the C276 corrosion-resistant layer completed by welding. The heat treatment temperature is 500℃~630℃, the holding time is 1.5h~4h, the heating rate and cooling rate above 400℃ are independently 15℃ / h~90℃ / h, the furnace is cooled to below 300℃ and then air-cooled. The temperature of the second post-weld stress relief heat treatment is lower than the temperature of the first post-weld stress relief heat treatment.

[0028] The second post-weld stress-relieving heat treatment is performed after the C276 corrosion-resistant layer is welded. Its temperature range is lower than the sensitization temperature of C276 (approximately 650°C). This effectively eliminates residual stress in the C276 weld overlay while preventing the precipitation of harmful phases (μ phase, σ phase, etc.), overcoming the technical challenge of performance degradation of the C276 corrosion-resistant layer caused by traditional single high-temperature heat treatment. The second heat treatment temperature is lower than the first heat treatment temperature, ensuring that the adverse effects of high-temperature heat treatment on the C276 layer are completely avoided.

[0029] Preferably, the temperature of the second post-weld stress-relieving heat treatment is 520℃~620℃, the holding time is 2h~3h, and the heating rate and cooling rate above 400℃ are independently 50℃ / h~55℃ / h. The temperature of the second post-weld stress-relieving heat treatment is at least 50℃ lower than the temperature of the first post-weld stress-relieving heat treatment.

[0030] S7: The surface of the C276 corrosion-resistant layer is subjected to acid pickling and passivation treatment to form a passivation film on the surface of the C276 corrosion-resistant layer.

[0031] Pickling and passivation can remove the oxide layer and surface contaminants that may form on the surface of the C276 corrosion-resistant layer during high-temperature heat treatment, while generating a uniform and dense chromium-rich passivation film on the surface, further improving the pitting corrosion resistance and stress corrosion resistance of the C276 corrosion-resistant layer in bromide-containing media.

[0032] Preferably, the pickling and passivation treatment uses a mixed pickling solution containing nitric acid and hydrofluoric acid, wherein the mass fraction of nitric acid is 10%–25% and the mass fraction of hydrofluoric acid is 1%–5%, the pickling temperature is 20℃–60℃, and the pickling time is 10 min–60 min. After pickling, the surface is rinsed with deionized water 2–5 times and then dried with hot air at 50℃–100℃. After the pickling and passivation treatment, a chromium-rich passivation film with a thickness of 1 nm–10 nm is formed on the surface of the C276 corrosion-resistant layer.

[0033] This invention also provides a chromium-molybdenum steel container composite corrosion-resistant layer resistant to bromide ion stress corrosion prepared by the above-described preparation process, wherein the composite corrosion-resistant layer consists of the following layers sequentially from the surface of the chromium-molybdenum steel container base layer outward:

[0034] The ultra-low carbon austenitic stainless steel transition layer is directly metallurgically bonded to the base layer, with a thickness of 1.5mm to 4mm and a coefficient of linear expansion of 16×10⁻⁶. -6 / ℃~17×10 -6 / ℃;

[0035] A Ni-Cr-Mo alloy intermediate layer, directly metallurgically bonded to the transition layer, has a thickness of 2mm to 8mm and a coefficient of linear expansion of 13×10⁻⁶. -6 / ℃~14×10 -6 / ℃;

[0036] The C276 corrosion-resistant layer, directly metallurgically bonded to the intermediate layer, has a thickness of 1mm to 4mm and a coefficient of linear expansion of 11×10⁻⁶. -6 / ℃~12×10 -6 / ℃;

[0037] The surface of the C276 corrosion-resistant layer has a chromium-rich passivation film formed by acid pickling and passivation treatment, and the linear expansion coefficient of the transition layer is greater than that of the intermediate layer and the linear expansion coefficient of the C276 corrosion-resistant layer.

[0038] Preferably, the thickness of the transition layer is 2mm to 3mm, and the material is E309L or E309LMo ultra-low carbon austenitic stainless steel; the thickness of the intermediate layer is 3mm to 6mm, and the material is ERNiCrMo-3 or ENiCrMo-10 nickel-based alloy; the thickness of the C276 corrosion-resistant layer is 1.5mm to 3mm, and the material is ENiCrMo-4 nickel-based alloy.

[0039] This invention also provides the application of the aforementioned bromide ion stress corrosion resistant composite corrosion-resistant layer for chromium-molybdenum steel containers in chromium-molybdenum steel pressure vessels used in petrochemical, coal chemical, pharmaceutical chemical, or bromine production and storage processes involving media containing bromide ions. The composite corrosion-resistant layer is applied to the inner wall of the chromium-molybdenum steel container via welding, enabling the container to exhibit excellent resistance to stress corrosion cracking under low bromide ion media and high-stress service conditions.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) By setting an ultra-low carbon austenitic stainless steel transition layer, the present invention effectively isolates the Fe element in the chromium-molybdenum steel base layer from diluting to the C276 corrosion-resistant layer and inhibits the migration of carbon elements from the chromium-molybdenum steel side to the nickel-based alloy side, thus avoiding the formation of a chromium-depleted zone at the interface and the precipitation of chromium carbide, and ensuring the corrosion resistance and interface bonding strength of the C276 corrosion-resistant layer.

[0042] (2) In this invention, a Ni-Cr-Mo alloy intermediate layer is introduced between the transition layer and the C276 corrosion-resistant layer. The linear expansion coefficient of this intermediate layer is between that of the transition layer and the C276 corrosion-resistant layer, forming a coefficient of 16-17×10. -6 / ℃→13-14×10 -6 / ℃→11-12×10 -6 The gradient transition structure of " / ℃" effectively alleviates the interfacial thermal stress caused by the difference in thermal expansion of each layer of material during the welding and subsequent heat treatment process, and reduces the level of residual tensile stress at the interface.

[0043] (3) This invention proposes a combined post-weld stress-relieving heat treatment system of "high temperature first, then low temperature". The first high-temperature heat treatment (670℃~710℃) is carried out before the C276 corrosion-resistant layer is welded, which fully eliminates the residual stress of the chromium-molybdenum steel base layer. The second low-temperature heat treatment (500℃~630℃) is carried out after the C276 corrosion-resistant layer is welded. The temperature is lower than the sensitization temperature range of C276, which avoids the precipitation of harmful phases and effectively eliminates the residual stress of the C276 weld layer. The two work together to meet the dual requirements of stress relief of the base layer and maintenance of the corrosion-resistant layer performance.

[0044] (4) Through the synergistic combination of the second low-temperature heat treatment and the gradient design of the linear expansion coefficient of the intermediate layer, the intermediate layer reduces the interfacial thermal stress in terms of structure, and the low-temperature heat treatment further eliminates the residual stress of welding in terms of process. The two work together to systematically reduce the residual tensile stress level of the C276 corrosion-resistant layer, which significantly weakens the synergistic cracking effect of tensile stress and bromide pitting corrosion.

[0045] (5) The present invention removes the oxide layer that may be formed during high-temperature treatment by pickling and passivating the surface of the C276 corrosion-resistant layer, and at the same time generates a uniform and dense chromium-rich passivation film on the surface, which further improves the anti-pitting corrosion and anti-stress corrosion performance of the corrosion-resistant layer in bromide ion-containing media.

[0046] (6) This invention overcomes the technical limitation that C276 chromium-molybdenum steel containers cannot be solution treated after welding. By combining heat treatment processes, it achieves effective control of residual stress and avoidance of harmful phases without solution treatment, and is suitable for on-site manufacturing of large containers.

[0047] (7) The method of the present invention is applicable to pressure vessels made of various grades of chromium-molybdenum steel such as 14Cr1MoR, 12Cr2Mo1R, and 12Cr2Mo1VR. The welding method is compatible with various processes such as strip welding, electroslag strip welding, shielded metal arc welding and tungsten inert gas welding. It has good versatility and application value. Attached Figure Description

[0048] Figure 1 This is a cross-sectional metallographic diagram of the composite corrosion-resistant layer obtained in Example 1 of the present invention, wherein: 1-chromium-molybdenum steel base layer, 2-ultra-low carbon austenitic stainless steel transition layer, 3-Ni-Cr-Mo alloy intermediate layer, 4-C276 corrosion-resistant layer;

[0049] Figure 2 Wherein 2a is a photograph of the surface morphology of the C276 corrosion-resistant layer before pickling and passivation treatment in Example 1 of the present invention; 2b is a photograph of the surface morphology of the C276 corrosion-resistant layer after pickling and passivation treatment in Example 1 of the present invention.

[0050] Figure 3 2a is a photograph of the surface morphology of the C276 corrosion-resistant layer in the welded state of Comparative Example 1 after operation under actual working conditions containing bromide ions; 2b is a photograph of the surface morphology of the C276 corrosion-resistant layer after low-temperature welding stress relief heat treatment in Example 1 of the present invention after operation under the same working conditions.

[0051] Figure 4 This is a schematic diagram of the temperature curves of the first and second post-weld stress relief heat treatments of the present invention, wherein curve a is the first heat treatment (690℃×8h), curve b is the second heat treatment (520℃×2h), and curve c is the second heat treatment (610℃×3h). Detailed Implementation

[0052] The technical solution of the present invention will be described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments. All equivalent substitutions or modifications known to those skilled in the art based on the technical solution of this application shall be deemed to fall within the scope of protection of the present invention.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for descriptive purposes only and is not intended to limit the scope of the invention.

[0054] In this invention, the term "low-bromine ion medium" refers to a corrosive medium environment with a bromide ion mass concentration below 5000 ppm. "High stress" refers to a stress state where the sum of the residual tensile stress and the working stress on the surface of the C276 corrosion-resistant layer during container pressure bearing or service is greater than or equal to 30% of the yield strength of the corrosion-resistant layer material. "Weld bead flatness" refers to the surface height difference between adjacent weld beads after welding, measured using a ruler and feeler gauge. "Sensitization temperature range" refers to the temperature range within which harmful intermetallic phases such as μ-phase and σ-phase precipitate at grain boundaries and within the grains when the C276 alloy is held at approximately 650℃ to 1100℃. "Furnace cooling" refers to the process where the heating power is turned off after heat treatment, allowing the workpiece to cool naturally within the furnace.

[0055] Unless otherwise specified, the chromium-molybdenum steel base layer, welding materials, and testing methods used in the various embodiments and comparative examples of this invention are all conventional choices in the art, and are specifically described below:

[0056] The chromium-molybdenum steel base layer is made of 12Cr2Mo1R steel plate, supplied in normalized + tempered condition, with a thickness of 30mm to 100mm, and its chemical composition meets the requirements of GB / T 713.2 standard.

[0057] The transition layer welding material is E309L ultra-low carbon austenitic stainless steel strip, with a specification of 0.4mm×75mm. Its chemical composition (mass fraction) is: C≤0.030%, Si≤0.90%, Mn 1.0%~2.5%, Cr 22.0%~25.0%, Ni 12.0%~14.0%, S≤0.020%, P≤0.030%, with the balance being Fe and unavoidable impurities.

[0058] The intermediate layer welding material uses ERNiCrMo-3 nickel-based alloy strip electrode with a specification of 0.5mm×60mm. Its chemical composition (mass fraction) is: C≤0.030%, Si≤0.50%, Mn≤0.50%, Cr 20.0%~23.0%, Ni≥58.0%, Mo 8.0%~10.0%, Nb+Ta 3.0%~4.5%, Fe≤5.0%, S≤0.015%, P≤0.020%, with the balance being unavoidable impurities.

[0059] The C276 corrosion-resistant coating welding material uses ENiCrMo-4 nickel-based alloy strip electrode with specifications of 0.5mm×60mm. Its chemical composition (mass fraction) is as follows: C≤0.010%, Si≤0.08%, Mn≤1.0%, Cr 14.5%~16.5%, Ni balance, Mo 15.0%~17.0%, W 3.0%~4.5%, Fe 4.0%~7.0%, Co≤2.5%, S≤0.010%, P≤0.020%, with the balance being unavoidable impurities.

[0060] The strip welding equipment is equipped with a magnetic control device with a magnetic control current of 3.0A to 4.5A. For electroslag strip welding, the flux should be dried at 300℃ to 400℃ for 2 to 4 hours before use. For tungsten inert gas (TIG) welding, the shielding gas is argon with a purity ≥99.99%, and the gas flow rate is 8L / min to 15L / min.

[0061] Post-weld stress relief heat treatment is carried out in a bogie-type heating furnace, with no fewer than three thermocouples arranged inside the furnace to monitor temperature uniformity, and the temperature control accuracy is ±5℃.

[0062] The pickling and passivation treatment uses a pickling solution prepared from nitric acid (65%–68% by mass), hydrofluoric acid (40%–55% by mass) and deionized water.

[0063] Penetrant testing shall be conducted in accordance with NB / T 47013.5-2015, with a sensitivity level of Class I.

[0064] Hardness testing shall be conducted in accordance with GB / T 4340.1, with a test force of HV10 (98.07N) and a holding time of 10s to 15s. At least 5 points shall be tested for each sample and the average value shall be taken.

[0065] Intergranular corrosion tests were conducted according to ASTM G28 A method (ferric sulfate-sulfuric acid method). The samples were immersed in boiling solution for 120 hours, and the corrosion rate (mm / year) was calculated by the weight loss method.

[0066] The residual stress test was performed by X-ray diffraction according to GB / T 7704, using Cr target Kα rays, and the diffraction plane was (311).

[0067] The stress corrosion cracking susceptibility test was conducted in accordance with ASTM G36. The specimen was a U-shaped bending specimen (bending radius R=5mm). After loading, it was immersed in a boiling magnesium chloride solution (mass fraction of about 42%) with added NaBr to a Br⁻ concentration of 1000ppm. The cracking time (h) was recorded.

[0068] The present invention will be further illustrated below through specific embodiments and comparative examples.

[0069] Example 1:

[0070] This embodiment describes the preparation of a composite corrosion-resistant layer on the inner wall of a 12Cr2Mo1R steel container cylinder, with the cross-sectional structure shown below. Figure 1 As shown, the specific steps are as follows:

[0071] S1: Base layer preparation. The inner wall surface of the 12Cr2Mo1R steel container to be welded is mechanically ground to remove oxide scale, oil, and impurities, ensuring a surface roughness Ra ≤ 6.3μm and a metallic luster. The base layer surface to be welded is then subjected to 100% magnetic particle testing. After confirming the absence of defects, subsequent welding is carried out.

[0072] S2: Welded transition layer. An electroslag strip welding method is used, employing E309L strip electrodes (0.4mm × 75mm) and a matching sintering flux to deposit an ultra-low carbon austenitic stainless steel transition layer onto the base layer surface. Figure 1 The location is marked as 2. The welding current is 1600A–1800A, the arc voltage is 26V–30V, the welding speed is 150mm / min–200mm / min, the overlap is 8mm–12mm, and the interpass temperature is controlled at 120℃–175℃. After welding, the transition layer thickness is 2.5mm–3mm, and the measured flatness between weld passes is ≤1.2mm.

[0073] S3: Intermediate Layer Welding. An electroslag strip welding method is used, employing an ERNiCrMo-3 strip (0.5mm × 60mm) with a matching sintering flux to deposit a Ni-Cr-Mo alloy intermediate layer onto the transition layer surface. Figure 1 The location is marked as 3. The welding current is 1700A–1900A, the arc voltage is 28V–32V, the welding speed is 150mm / min–200mm / min, the overlap is 8mm–12mm, and the interpass temperature is controlled at ≤100℃. After welding, the intermediate layer thickness is 3mm–3.5mm, and the measured flatness between weld passes is ≤1.0mm.

[0074] S4: First Post-Weld Stress Relief Heat Treatment. The cylinder sections with the completed transition and intermediate layers are loaded into a bogie-type furnace for the first post-weld stress relief heat treatment, and the temperature curve is shown below. Figure 4 As shown in curve a. The heat treatment regime is as follows: heat to 690±10℃ at a heating rate of ≤55℃ / h, hold for 8 hours, then furnace cool to below 400℃ at a cooling rate of ≤55℃ / h, followed by air cooling to room temperature. The heating and cooling rates are controlled above 400℃ during the heat treatment process.

[0075] S5: C276 corrosion-resistant layer overlay. An electroslag strip overlay method is used, employing an ENiCrMo-4 strip (0.5mm × 60mm) with a matching sintering flux to overlay a C276 corrosion-resistant layer on the intermediate layer surface. Figure 1The location is marked as 4. The welding current is 1700A~1850A, the arc voltage is 26V~30V, the welding speed is 150mm / min~200mm / min, the overlap is 8mm~12mm, and the interpass temperature is controlled at ≤100℃. After welding, the C276 corrosion-resistant layer thickness is 2.5mm~3mm, and the measured flatness between weld passes is ≤0.8mm.

[0076] S6: Second Post-Weld Stress Relief Heat Treatment. The cylinder sections with the C276 corrosion-resistant layer welded on are loaded into a bogie-type heating furnace for the second post-weld stress relief heat treatment. The temperature curve is shown below. Figure 4 As shown in curve b. The heat treatment regime is 520±10℃×2h: heat to 520±10℃ at a heating rate of ≤55℃ / h, hold for 2h, then furnace cool to below 300℃ at a cooling rate of ≤55℃ / h, followed by air cooling to room temperature. The heating and cooling rates are controlled above 400℃.

[0077] S7: Pickling and Passivation Treatment. Preparation of the pickling solution: Mix nitric acid (68% by mass) and hydrofluoric acid (40% by mass) at a volume ratio of 5:1, then dilute with deionized water to achieve a nitric acid mass fraction of 15% and a hydrofluoric acid mass fraction of 3%. Immerse the surface of the C276 corrosion-resistant layer in the pickling solution at a temperature of 40℃±5℃ for 30 minutes. After pickling, rinse three times with deionized water and dry with hot air at 80℃±5℃ to form a chromium-rich passivation film on the surface of the C276 corrosion-resistant layer. The surface morphology of the C276 corrosion-resistant layer before pickling is as follows. Figure 2 As shown in Figure a, the surface morphology after pickling is as follows: Figure 2 As shown in b, the surface is bright and uniform after pickling, with no oxide scale residue.

[0078] S8: Quality Inspection. A quality inspection is performed on the composite corrosion-resistant layer after all steps have been completed, including penetrant testing, hardness testing, intergranular corrosion testing, residual stress testing, and stress corrosion cracking susceptibility testing. The test results are shown in Table 1.

[0079] Example 2:

[0080] The difference between this embodiment and Embodiment 1 is that the temperature of the second post-weld stress-relieving heat treatment in S6 is 610±10℃×3h, and its temperature curve is as follows. Figure 4 The curve is shown in Figure c. The remaining steps and parameters are exactly the same as in Example 1. Specifically, the temperature is increased to 610±10℃ at a heating rate of ≤55℃ / h, held for 3h, and then furnace cooled to below 300℃ at a cooling rate of ≤55℃ / h, followed by air cooling to room temperature. The test results are shown in Table 1.

[0081] Comparative Example 1:

[0082] This comparative example follows the method described in the embodiment of Chinese Patent CN108356397A, employing only a single high-temperature post-weld stress-relieving heat treatment process, without an intermediate layer, and without a second low-temperature heat treatment or pickling passivation treatment. The specific steps are as follows:

[0083] After pretreatment of the 12Cr2Mo1R steel base surface, a transition layer (welding material 22.11.L, thickness approximately 3.5mm) was welded using a strip electrode welding method, followed by a corrosion-resistant layer (welding material 19.9LNb, thickness approximately 3.2mm). After both layers were welded, a single post-weld stress-relieving heat treatment was performed at 690±10℃ for 8 hours, with a heating / cooling rate of 50℃ / h to 55℃ / h above 400℃. No intermediate layer was used, and no second low-temperature heat treatment or pickling / passivation treatment was performed. The test results are shown in Table 1. The surface morphology of the C276 corrosion-resistant layer obtained in Comparative Example 1 after operation under actual bromide ion-containing conditions is as follows: Figure 3 As shown in Figure a, obvious pitting and microcracks are present on the surface.

[0084] Comparative Example 2:

[0085] The difference between this comparative example and Example 1 is that the S3 intermediate layer is not set; that is, the C276 corrosion-resistant layer is directly welded onto the surface of the transition layer. Meanwhile, the S6 second post-weld stress-relieving heat treatment temperature remains 520±10℃×2h. The remaining steps and parameters are the same as in Example 1. The test results are shown in Table 1.

[0086] Comparative Example 3:

[0087] The difference between this comparative example and Example 1 is that the temperature of the second post-weld stress-relieving heat treatment in S6 was increased to 690±10℃×8h (the same temperature as in S4), meaning that a high-temperature stress-relieving treatment was used on the C276 corrosion-resistant layer. The remaining steps and parameters were the same as in Example 1. The test results are shown in Table 1.

[0088] Comparative Example 4:

[0089] The difference between this comparative example and Example 1 is as follows: After the S2 transition layer is welded, the S3 intermediate layer is not welded; instead, a C276 corrosion-resistant layer is directly welded onto the surface of the transition layer. The first post-weld stress-relieving heat treatment (S4) is performed after the C276 corrosion-resistant layer is welded (i.e., S4 and S5 are sequentially interchanged), with a heat treatment regime of 690±10℃×8h. The second low-temperature heat treatment (S6) is not performed. The remaining steps and parameters are the same as in Example 1. The test results are shown in Table 1.

[0090] Experimental example:

[0091] I. Performance Testing of Composite Corrosion-Resistant Layer

[0092] The performance of the composite corrosion-resistant layer samples prepared in Examples 1, 2 and 1-4 was tested, and the test results are summarized in Table 1.

[0093] Table 1. Performance test results of composite corrosion-resistant layers in Examples 1-2 and Comparative Examples 1-4

[0094] serial number weld overlay structure Heat treatment system PT testing Hardness HV10 Intergranular corrosion rate (mm / year) Residual stress (MPa) SCC cracking time (h) Example 1 Three layers (with a middle layer) 690℃×8h + 520℃×2h qualified 222、228、231、226、224 5.3、5.7、5.5 +33、+31、+29 252、240、234 Example 2 Three layers (with a middle layer) 690℃×8h + 610℃×3h qualified 226、230、233、228、225 6.3、6.7、6.4 +29、+27、+28 222、216、222 Comparative Example 1 Double-layered (without a middle layer) 690℃×8h (welded state) qualified 227、232、234、229、226 4.3、4.6、4.5 +183、+186、+181 74、68、70 Comparative Example 2 Double-layered (without a middle layer) 690℃×8h + 520℃×2h qualified 225、229、231、226、224 5.7、6.1、5.8 +127、+123、+125 122、118、120 Comparative Example 3 Three layers (with a middle layer) 690℃×8h + 690℃×8h qualified 243、248、251、244、246 12.4、13.0、12.6 +32、+29、+31 98、94、100 Comparative Example 4 Double-layered (without a middle layer) 690℃×8h (sequential exchange, C276 sensitization) qualified 246、250、253、247、249 13.6、14.1、13.8 +176、+180、+177 50、46、48

[0095] Note: Hardness HV10 is the measured value at 5 measuring points; intergranular corrosion rate is the measured value at 3 parallel samples; residual stress is the measured value at 3 measuring points; "+" indicates tensile stress; SCC cracking time is the measured value at 3 parallel samples.

[0096] Results analysis:

[0097] 1. Penetration testing

[0098] The penetration test results of Examples 1, 2 and Comparative Examples 1-4 are all qualified, indicating that there are no defects such as cracks, pores, cold shuts, or delamination on the surface and near the surface of each weld overlay.

[0099] 2. Hardness test

[0100] The measured hardness values ​​for Example 1 were 222–231 HV10, for Example 2 225–233 HV10, for Comparative Example 1 226–234 HV10, and for Comparative Example 2 224–231 HV10. The similar hardness ranges of the four examples indicate that the low-temperature heat treatment at 520℃ for 2 hours or 610℃ for 3 hours did not cause significant strengthening or softening of the C276 corrosion-resistant layer, and no large-scale precipitation of harmful phases occurred. The measured hardness values ​​for Comparative Example 3 were 243–251 HV10, and for Comparative Example 4 246–253 HV10, showing a significant increase in hardness. This indicates that the high-temperature heat treatment at 690℃ for 8 hours led to the precipitation of hard and brittle intermetallic phases such as μ-phase and σ-phase in the C276 corrosion-resistant layer, thus increasing the hardness.

[0101] 3. Intergranular corrosion test

[0102] The corrosion rate of Example 1 was 5.3–5.7 mm / year, and that of Example 2 was 6.3–6.7 mm / year, approximately half that of Comparative Example 3 (12.4–13.0 mm / year) and Comparative Example 4 (13.6–14.1 mm / year), respectively. This indicates that low-temperature heat treatment can significantly reduce the intergranular corrosion susceptibility of the C276 corrosion-resistant layer compared to high-temperature heat treatment. Comparative Example 1 had a corrosion rate of 4.3–4.6 mm / year, lower than the examples, but its residual stress was as high as +181–+186 MPa, indicating an extremely high risk of stress corrosion cracking.

[0103] 4. Residual stress test

[0104] The measured residual stress values ​​for Example 1 were +29 to +33 MPa, for Example 2 +27 to +29 MPa, and for Comparative Example 3 +29 to +32 MPa, all showing relatively low residual stress levels. However, Comparative Example 3 exhibited a high intergranular corrosion rate of 12.4 to 13.0 mm / year, indicating severe degradation in corrosion resistance. The measured residual stress value for Comparative Example 2 was +123 to +127 MPa, higher than that of Examples 1 and 2, suggesting that the stress buffering effect of the intermediate layer contributed to reducing residual stress. Comparative Example 1 (+181 to +186 MPa) and Comparative Example 4 (+176 to +180 MPa) showed the highest residual stress levels.

[0105] 5. Stress corrosion cracking susceptibility test

[0106] The cracking time of Example 1 was 234–252 h, and that of Example 2 was 216–222 h, significantly better than that of Comparative Example 1 (68–74 h), Comparative Example 3 (94–100 h), and Comparative Example 4 (46–50 h). Although Comparative Example 1 had a lower corrosion rate, its high residual stress led to rapid cracking in a stress corrosion environment. Although Comparative Example 3 had lower residual stress, the high-temperature heat treatment caused the precipitation of harmful phases, significantly reducing its corrosion resistance. Comparative Example 4 had the shortest cracking time due to high residual stress and sensitization of C276. The surface morphology of the C276 corrosion-resistant layer obtained in Example 1 after operation under actual bromide-containing conditions is as follows: Figure 3 As shown in b, the surface is uniform and intact, without obvious pitting or cracking. The surface morphology of Comparative Example 1 after operation is as follows. Figure 3 As shown in Figure a, obvious pitting and microcracks are present on the surface.

[0107] The above results show that the present invention achieves synergistic optimization of residual stress and corrosion resistance through a systematic approach of "gradient buffering of linear expansion coefficient in intermediate layer + first high-temperature heat treatment + second low-temperature heat treatment", and its resistance to stress corrosion cracking is significantly better than that of the prior art.

[0108] In summary, the chromium-molybdenum steel container composite corrosion-resistant layer and its preparation process provided by this invention can be widely used in the manufacture of chromium-molybdenum steel pressure vessels exposed to bromide-containing corrosive media in fields such as petrochemicals, coal chemicals, pharmaceutical chemicals, and bromine production and storage. The processes in each step of this invention are mature, and the required equipment and materials are all commonly used in the field and commercially available welding materials, demonstrating good industrial applicability and promotional value.

[0109] It should be noted that the above embodiments are merely preferred embodiments of the present invention, used to explain the technical principles and application effects of the present invention, and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions, modifications, or improvements made based on the technical concept of the present invention within the spirit and principles of the present invention should be included within the scope of protection of the present invention. In practical applications, those skilled in the art can make adaptive adjustments to the relevant parameters according to the specific test materials, working conditions, and accuracy requirements, all of which fall within the scope of protection of the present invention.

Claims

1. A process for preparing a composite corrosion-resistant layer for chromium-molybdenum steel containers resistant to bromide ion stress corrosion, characterized in that, Includes the following steps: S1: The surface of the chromium-molybdenum steel container base to be welded is machined and cleaned to remove surface oxide scale, oil and impurities; S2: An ultra-low carbon austenitic stainless steel transition layer is overlaid on the base surface after the treatment of S1, with an overlay thickness of 1.5mm to 4mm, a flatness between overlay passes of ≤2mm, and an interlayer temperature of 100℃ to 200℃. S3: A Ni-Cr-Mo alloy intermediate layer is deposited on the surface of the transition layer, with a deposit thickness of 2mm to 8mm, a flatness between weld passes of ≤2mm, and an interlayer temperature of ≤120℃; the linear expansion coefficient of the transition layer is greater than that of the intermediate layer, which is greater than that of the subsequent C276 corrosion-resistant layer. S4: Perform the first post-weld stress relief heat treatment on the chromium-molybdenum steel container after the intermediate layer has been welded. The heat treatment temperature is 670℃~710℃, the holding time is 3h~10h, the heating rate and cooling rate above 400℃ are 15℃ / h~90℃ / h independently, and the furnace is cooled to below 400℃ and then air-cooled. S5: A C276 corrosion-resistant layer is deposited on the surface of the intermediate layer, with a deposit thickness of 1mm to 4mm, a flatness between deposit passes of ≤1.5mm, and an interlayer temperature of ≤100℃; S6: The chromium-molybdenum steel container with the C276 corrosion-resistant layer after welding is subjected to a second post-weld stress relief heat treatment. The heat treatment temperature is 500℃~630℃, the holding time is 1.5h~4h, the heating rate and cooling rate above 400℃ are independently 15℃ / h~90℃ / h, the furnace is cooled to below 300℃ and then air-cooled. The temperature of the second post-weld stress relief heat treatment is lower than the temperature of the first post-weld stress relief heat treatment. S7: The surface of the C276 corrosion-resistant layer is subjected to pickling and passivation treatment to form a passivation film on the surface of the C276 corrosion-resistant layer.

2. The preparation process according to claim 1, characterized in that, In S2, the transition layer uses E309L or E309LMo ultra-low carbon austenitic stainless steel welding material. The welding method is selected from strip welding, electroslag strip welding, shielded metal arc welding or tungsten inert gas welding. The welding material specifications are strip thickness of 0.4mm to 0.5mm × width of 60mm to 75mm, or welding rod / wire diameter of 2.5mm to 5.0mm. During the welding process, the interpass temperature is 120℃ to 175℃, the overlap between weld passes is 5mm to 15mm, the welding speed is 150mm / min to 350mm / min, and the weld thickness is 2mm to 3mm.

3. The preparation process according to claim 1, characterized in that, In S3, the intermediate layer uses ERNiCrMo-3 or ENiCrMo-10 nickel-based alloy welding material. The welding method is selected from strip welding, electroslag strip welding, shielded metal arc welding or tungsten inert gas welding. The welding material specifications are strip thickness of 0.4mm to 0.5mm × width of 60mm to 75mm, or welding rod / wire diameter of 2.0mm to 4.0mm. During the welding process, the interpass temperature is ≤100℃, the overlap between weld passes is 5mm to 15mm, the welding speed is 150mm / min to 350mm / min, and the weld thickness is 3mm to 6mm.

4. The preparation process according to claim 1, characterized in that, In S5, the C276 corrosion-resistant layer uses ENiCrMo-4 nickel-based alloy welding material. The welding method is selected from strip welding, electroslag strip welding, shielded metal arc welding or tungsten inert gas welding. The welding material specifications are strip thickness of 0.4mm to 0.5mm × width of 60mm to 75mm, or welding rod / wire diameter of 2.0mm to 4.0mm. During the welding process, the interpass temperature is ≤100℃, the overlap between weld passes is 5mm to 15mm, the welding speed is 150mm / min to 350mm / min, and the weld thickness is 1.5mm to 3mm.

5. The preparation process according to claim 1, characterized in that, When the transition layer is overlaid in S2, the welding current is 140A to 160A and the arc voltage is 20V to 25V for shielded metal arc welding; or the welding current is 1650A to 1850A and the arc voltage is 28V to 30V for strip welding; or the welding current is 150A to 250A and the arc voltage is 12V to 18V for tungsten inert gas welding.

6. The preparation process according to claim 1, characterized in that, When overlaying the intermediate layer in S3, the welding current is 130A to 180A and the arc voltage is 22V to 28V for shielded metal arc welding; or the welding current is 1600A to 1900A and the arc voltage is 26V to 32V for strip welding; or the welding current is 140A to 240A and the arc voltage is 12V to 18V for tungsten inert gas welding.

7. The preparation process according to claim 1, characterized in that, In S4, the temperature of the first post-weld stress-relieving heat treatment is 680℃~700℃, the holding time is 4h~8h, the heating rate and cooling rate above 400℃ are independently 50℃ / h~55℃ / h, and the furnace is cooled to below 400℃ and then air-cooled; and the heat treatment is carried out in a bogie-type heating furnace or a pit-type heat treatment furnace, and a protective atmosphere is introduced into the inner wall of the container during the heat treatment process to prevent oxidation.

8. The preparation process according to claim 1, characterized in that, In S6, the temperature of the second post-weld stress relief heat treatment is 520℃~620℃, the holding time is 2h~3h, the heating rate and cooling rate above 400℃ are independently 50℃ / h~55℃ / h, and the furnace is cooled to below 300℃ and then air-cooled; the temperature of the second post-weld stress relief heat treatment is at least 50℃ lower than the temperature of the first post-weld stress relief heat treatment.

9. The preparation process according to claim 1, characterized in that, In S7, the pickling and passivation treatment uses a mixed pickling solution containing nitric acid and hydrofluoric acid, wherein the mass fraction of nitric acid is 10% to 25% and the mass fraction of hydrofluoric acid is 1% to 5%, the pickling temperature is 20℃ to 60℃, and the pickling time is 10 min to 60 min; after pickling, it is rinsed with deionized water 2 to 5 times and dried with hot air at a temperature of 50℃ to 100℃; after the pickling and passivation treatment, a chromium-rich passivation film with a thickness of 1 nm to 10 nm is formed on the surface of the C276 corrosion-resistant layer.

10. A composite corrosion-resistant coating for chromium-molybdenum steel containers resistant to bromide ion stress corrosion, characterized in that, The composite corrosion-resistant layer, prepared by the preparation process described in any one of claims 1 to 9, comprises the following layers sequentially from the surface of the chromium-molybdenum steel container base layer outward: An ultra-low carbon austenitic stainless steel transition layer, directly metallurgically bonded to the base layer, has a thickness of 1.5mm to 4mm and a coefficient of linear expansion of 16×10⁻⁶. -6 / ℃~17×10 -6 / ℃; A Ni-Cr-Mo alloy intermediate layer, directly metallurgically bonded to the transition layer, has a thickness of 2mm to 8mm and a coefficient of linear expansion of 13×10⁻⁶. -6 / ℃~14×10 -6 / ℃; The C276 corrosion-resistant layer, directly metallurgically bonded to the intermediate layer, has a thickness of 1mm to 4mm and a coefficient of linear expansion of 11×10⁻⁶. -6 / ℃~12×10 -6 / ℃; The surface of the C276 corrosion-resistant layer has a chromium-rich passivation film formed by pickling and passivation treatment. The linear expansion coefficient of the transition layer is greater than that of the intermediate layer, which is greater than that of the C276 corrosion-resistant layer. The surface C276 corrosion-resistant layer of the composite corrosion-resistant layer has lower stress corrosion cracking sensitivity under low bromide ion medium and high stress service conditions than the welded C276 corrosion-resistant layer.

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