Shot blasting treatment method for improving corrosion resistance of 2205 duplex stainless steel welded joint

Abstract

The invention discloses a shot blasting treatment method for improving corrosion resistance of a 2205 duplex stainless steel welded joint, and belongs to the technical field of metal surface strengthening. The method comprises the following steps that the surface of a 2205 duplex stainless steel plate to be welded is pretreated, and assembling is conducted in a butt joint mode; then welding by adopting an argon tungsten-arc welding method; and then shot blasting treatment is carried out, and a welded joint is cleaned. According to the method, the surface of a material is impacted by high-speed shots, residual compressive stress is introduced to the surface layer, permeation and diffusion of a corrosive medium are effectively hindered, the probability of occurrence of local corrosion is reduced, and crack initiation is effectively inhibited; meanwhile, grains on the surface of the material are refined through impact of the projectile, a compact microstructure is formed, and permeation of a hydrogen sulfide corrosion medium is greatly hindered. According to the surface structure optimization, the welded joint subjected to shot blasting treatment shows higher stability in the aspect of sulfide stress corrosion resistance, and excellent sulfide stress corrosion cracking resistance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of metal surface strengthening technology, specifically, it relates to a shot peening method for improving the corrosion resistance of 2205 duplex stainless steel welded joints. The invention aims to improve the corrosion resistance of 2205 duplex stainless steel welded joints, and its method is particularly suitable for welded components serving in harsh marine corrosive environments. Background Technology

[0002] 2205 duplex stainless steel (DSS) possesses excellent corrosion resistance and good mechanical properties, and has been used as an engineering alloy for many years, finding wide application in many industrial fields, especially in corrosive environments. The ratio of ferrite to austenite phases and the passivation film on the surface of duplex stainless steel welded joints determine their corrosion resistance. In the field of welding manufacturing, welded joints, due to the residual tensile stress formed during thermal cycling, have long been a weak point in equipment structures under corrosive environments. Especially in acidic environments containing hydrogen sulfide, they are highly susceptible to sulfide stress corrosion cracking, leading to sudden brittle failure and seriously threatening safe production. Traditionally, integral heat treatment processes are used to eliminate residual stress to address this problem. However, this method has drawbacks such as long processing cycles, high energy consumption, and potential for workpiece deformation or deterioration of material mechanical properties. On the other hand, while some surface mechanical treatment techniques can improve the stress state to some extent, their effects are often limited to the macroscopic stress level, making it difficult to simultaneously achieve synergistic optimization of the deep compressive stress field and microstructure at the material surface. This limitation of existing technologies results in insufficient barrier capacity of treated welded joints against corrosive media, especially small molecule media like hydrogen sulfide that can induce hydrogen-induced cracking. This fails to fundamentally and effectively inhibit the synergistic effect of corrosive media penetration and crack initiation, resulting in a significant bottleneck in improving their stress corrosion resistance. Therefore, there is an urgent need for an efficient surface strengthening method that can deeply optimize surface stress and microstructure, thereby significantly improving the long-term stability of welded joints in harsh corrosive environments. Summary of the Invention

[0003] The purpose of this invention is to provide a shot peening method for improving the corrosion resistance of 2205 duplex stainless steel welded joints. By optimizing the shot peening process parameters, the surface condition and residual stress distribution of the welded joint are effectively improved, thereby significantly enhancing its corrosion resistance. At the same time, this method has the advantages of simple operation, low cost, and environmental friendliness.

[0004] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a shot peening treatment method for improving the corrosion resistance of welded joints of 2205 duplex stainless steel, characterized by comprising the following steps: Step 1: Pre-treat the surface of the 2205 duplex stainless steel plate to be welded, and assemble it in the form of a butt joint; Step 2: Then, weld using tungsten inert gas (TIG) welding. Step 3: Then, shot peening is performed to clean the welded joint. Further specified, the thickness of the stainless steel plate is 1.5mm-2mm.

[0005] Further specifying the pretreatment steps, the following steps are performed: mechanical grinding, chemical cleaning until the surface is clean, and drying. Specific operations are as follows: Clean the area within 20mm on both sides of the bevel. First, use a dedicated grinding wheel to grind the surface, then wipe it with solvents such as alcohol / acetone to ensure the removal of surface oil and water.

[0006] Further specify the welding parameters: base current 30A, pulse current 90A, voltage 7V-8V, pulse frequency 2.5Hz, duty cycle 45%, welding speed 19cm / min, welding wire ER2209 Φ1.2 mm, wire feed speed 1.0m / min, and shielding gas 99.9%Ar.

[0007] Furthermore, the shot peening medium is 304 stainless steel with a radius of 0.5 mm to 0.8 mm.

[0008] Further specifying, the shot peening operating frequency is 20 kHz-25 kHz.

[0009] Further specified, the shot peening height is 8 mm-12 mm.

[0010] Furthermore, the shot peening time is specified as 30-60 minutes.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes high-speed shot blasting to impact the metal surface, thereby improving the residual stress state and enhancing the corrosion resistance of welded joints. The high-speed shot impact introduces residual compressive stress into the material surface, effectively hindering the penetration and diffusion of corrosive media, reducing the probability of localized corrosion, and effectively suppressing crack initiation. Simultaneously, the shot impact refines the surface grains, forming a dense microstructure that significantly impedes the penetration of hydrogen sulfide corrosive media. This optimized surface structure results in welded joints treated with shot peening exhibiting stronger stability against sulfide stress corrosion cracking and achieving excellent resistance to sulfide stress corrosion cracking.

[0012] The method of this invention has the advantages of significantly improving corrosion resistance, optimizing surface residual stress distribution, simple operation and low cost, environmental friendliness, strong applicability and comprehensive performance improvement. It can effectively solve the problems existing in the prior art and has important practical application value and broad market prospects.

[0013] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0014] Figure 1 The morphology of the un-shot-peened welded joint after a 10X inspection following a hydrogen sulfide stress corrosion test. Figure 2 The morphology of the welded joint was examined at 10X after a hydrogen sulfide stress corrosion test 50 minutes after shot peening. Figure 3 The morphology of the un-shot-peened welded joint after a hydrogen sulfide stress corrosion test at 50X. Figure 4 The morphology of the welded joint was examined at 50X after a shot peening time of 50 minutes and a hydrogen sulfide stress corrosion test. Detailed Implementation

[0015] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0016] Example 1: The shot peening method used in this embodiment to improve the corrosion resistance of 2205 duplex stainless steel welded joints is achieved through the following steps: Step 1: Pre-treat the surface of the 2205 duplex stainless steel plate to be welded: The material used is 2205 duplex stainless steel plate (1.5mm thick). Before welding, the area within 20mm on both sides of the bevel is cleaned. First, a special grinding wheel is used to grind the surface of the workpiece to remove impurities such as oil, rust, and oxide scale. Then, acetone is used to wipe the surface to ensure that the welded joint is clean and dry.

[0017] Step 2: The welding method is tungsten inert gas welding (GTAW). After welding, X-ray inspection showed no defects.

[0018] Welding parameters: base current 30A, pulse current 90A, voltage 7-8V, pulse frequency 2.5Hz, duty cycle 45%, welding speed 19cm / min, welding wire ER2209 Φ1.2 mm, wire feed speed 1.0m / min, shielding gas 99.9%Ar.

[0019] Step 3: Shot peening of welded joints Place the 2205 duplex stainless steel welded joint on the shot peening equipment's worktable. Adjust the nozzle position and spray direction to match the selected shot peening parameters. Based on the material properties of 2205 duplex stainless steel and the specific conditions of the welded joint, select appropriate shot peening media, shot peening frequency, shot peening height, and shot peening time. The shot peening media used is 304 stainless steel with a radius of 0.5 mm; the shot peening frequency is 20 kHz; the shot peening height is 10 mm; and the shot peening time is 30-60 minutes. During the shot peening process, maintain the stability of the welded joint to avoid affecting the shot peening effect due to vibration or other factors. Simultaneously, carefully observe the shot peening condition on the welded joint surface to ensure uniform shot peening. After shot peening, clean the welded joint to remove residual steel shot and metal debris generated during the shot peening process. The cleaned welded joint surface should be free of obvious defects such as cracks or pits, and exhibit a uniform shot peening texture.

[0020] The following experiments were used to verify the effectiveness of the invention: (1) Resistance to pitting corrosion To compare the pitting corrosion resistance of welded joints before and after shot peening in a chlorine environment, the experiment was conducted according to ASTM G48, "Standard Method for Testing Stainless Steel and its Alloys for Pitting and Cracking Corrosion Resistance using Ferric Chloride Solution." The test was performed in a ferric chloride solution with a mass fraction of approximately 6 wt%. The weight before corrosion was recorded. The samples were then immersed in beakers placed in a 25°C constant temperature water bath for 72 hours, and the weight after pitting was recorded. Pitting corrosion tests were performed on stainless steel welded samples and samples after shot peening according to ASTM G48. The results are shown in Table 1. The results demonstrate that the invented shot peening method can slow down the corrosion rate of welded joints in corrosive media.

[0021] Table 1. Results of pitting corrosion experiments

[0022] (2) Resistance to hydrogen sulfide stress corrosion cracking: 2205 duplex stainless steel has a uniform internal structure and strong intercrystalline bonding, which effectively resists corrosion cracking caused by sulfide environments under stress. Therefore, the 2205 duplex stainless steel base material itself has good resistance to hydrogen sulfide stress corrosion and exhibits stable performance in acidic environments. However, the welded joint will generate large and unevenly distributed residual stress and uneven microstructure during the manufacturing process, leading to a decrease in its stress corrosion resistance. Especially under sulfide stress environments, cracks often form at the welded joint location, resulting in failure.

[0023] To investigate the resistance of the 2205 duplex stainless steel welded joint to hydrogen sulfide stress corrosion cracking after shot peening, hydrogen sulfide stress corrosion cracking (SSC) tests were conducted on the prepared welded joint and the welded joint after shot peening. The test was conducted according to NACE TM0177-2016, "Laboratory tests on metals for resistance to sulfide stress cracking and stress corrosion cracking in hydrogen sulfide environments." The samples were placed in a simulated hydrogen sulfide environment, and then a constant stress was applied to the samples using a four-point bending loading device. This method assesses the cracking susceptibility of the welded joint in a hydrogen sulfide environment by simulating the synergistic effect of the corrosive medium and continuous mechanical force. After the sulfide stress corrosion cracking test, the tensile surface was examined under a 10X magnifying glass. Figure 1 The morphology of the un-shot-peened welded joint after hydrogen sulfide stress corrosion test was examined at 10X, and a crack with a length of about 6 mm was visible. Figure 2 The weld joint was examined at 10X after a hydrogen sulfide stress corrosion test following shot peening for 50 minutes; no cracks were observed. The longitudinal section of the specimen was then examined. Figure 3 After a hydrogen sulfide stress corrosion test on an un-shot-peened welded joint, a 50X inspection revealed corrosion pits on the surface, with cracks extending inward from the pits. Figure 4 A 50X inspection was performed on the welded joint after shot peening for 50 minutes following a hydrogen sulfide stress corrosion test. Corrosion pits were observed on the surface, but no cracks were formed. This indicates that the welded joint treated with shot peening exhibited improved resistance to hydrogen sulfide stress corrosion cracking.

[0024] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A shot peening treatment method for improving the corrosion resistance of 2205 duplex stainless steel welded joints, characterized in that, Includes the following steps: Step 1: Pre-treat the surface of the 2205 duplex stainless steel plate to be welded, and assemble it in the form of a butt joint; Step 2: Then, weld using tungsten inert gas (TIG) welding. Step 3: Then, shot peening is performed to clean the welded joint.

2. The method according to claim 1, characterized in that, The thickness of the stainless steel plate is 1.5mm-2mm.

3. The method according to claim 1, characterized in that, The pretreatment steps are as follows: mechanical grinding, chemical cleaning until the surface is clean, and drying.

4. The method according to claim 1, characterized in that, Welding parameters: base current 30A, pulse current 90A, voltage 7V-8V, pulse frequency 2.5Hz, duty cycle 45%, welding speed 19cm / min, welding wire ER2209 Φ1.2 mm, wire feed speed 1.0m / min, shielding gas 99.9%Ar.

5. The method according to claim 1, characterized in that, The shot peening medium is 304 stainless steel with a radius of 0.5mm-0.8mm.

6. The method according to claim 1, characterized in that, The shot peening operating frequency is 20kHz-25kHz.

7. The method according to claim 1, characterized in that, The shot peening height is 8mm-12mm.

8. The method according to claim 1, characterized in that, The shot peening time is 30-60 minutes.

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