Method for solving welding stress concentration of duplex stainless steel

Abstract

The invention relates to the field of welding pressure containers and welding structural parts, and provides a method for solving the problem of welding stress concentration of duplex stainless steel, and the method for solving the welding stress concentration of the duplex stainless steel is used for carrying out ultrasonic impact treatment on a steel welding seam of the duplex stainless steel. Compared with the prior art, the method for solving the welding stress concentration of the duplex stainless steel has the advantages that the duplex stainless steel welding seam is subjected to ultrasonic impact treatment, and a ferrite phase in the welding seam bears strain and forms dislocation in ferrite, so that the original thermodynamic equilibrium of two phases in an alloy is destroyed; a strip-shaped ferrite and austenite refined layer which is 50-100 microns thick and parallel to the surface orientation can be formed on the surface of the weld joint subjected to ultrasonic impact treatment, the surface tensile stress of the duplex stainless steel is changed into pressure stress, the stress concentration on the surface of the weld joint can be effectively relieved, and the spot corrosion resistance of the material is improved; the method is simple to operate and can be applied to large-scale structural members.

Description

Technical Field

[0001] The invention relates to the field of welded pressure vessels and welded structural parts, and in particular to a method for solving the welding stress concentration of duplex stainless steel. Background Art

[0002] Duplex stainless steel contains ferrite and austenite phases in almost the same proportion, combining the advantages of ferrite and austenite steels, and thus has good mechanical properties and corrosion resistance. To ensure the comprehensive performance of duplex stainless steel, on the one hand, it is required to ensure a balanced two-phase structure, and on the other hand, it is necessary to control harmful precipitation phases. However, during the welding process, repeated thermal cycles will reduce the performance of the joint, especially the pitting corrosion resistance and impact toughness. In addition, during the welding process, due to uneven heating, cooling, phase change and constraints, transient thermal stress and residual stress are generated at the welded joint, causing welding deformation, often prone to welding cracks, resulting in a serious reduction in the strength and fatigue life of the welded structure, and also causing accelerated corrosion in a corrosive environment.

[0003] The structure of duplex stainless steel is ferrite and austenite. Conventional medium-temperature heat treatment stress relief methods cannot avoid the appearance of σ phase during ferrite heat treatment. High-temperature solution treatment is only applicable to small "quasi-solid" parts, not to asymmetric parts, thin-walled parts, slender parts and large parts.

[0004] The patent application number CN201310241030.7 in the prior art discloses the processing technology of large duplex stainless steel impellers, including casting, deformation protection before heat treatment, solution treatment, casting cleaning and rough grinding, component re-inspection, mechanical property inspection, RT ray flaw detection, cleaning defects, welding and rough grinding, rough machining, finishing, stress relief heat treatment, semi-finishing, fine grinding, fine machining and balance test deweighting. Although the patent has a small work hardening effect, small dimensional deformation, good impeller processing dimensional accuracy, and high surface finish, for large structural parts with large size and thin wall, large deformation is easy to occur during welding, and due to the limitation of workpiece size, conventional low temperature aging cannot be used for stress relief treatment; this not only affects the structural stability of the product, but also may cause pitting corrosion caused by stress concentration in seawater.

[0005] Especially when welding large seawater desalination evaporators and condensers, there is a large welding residual stress, deformation of structural parts, and decreased corrosion resistance. There is an urgent need for a method to solve the stress concentration of duplex stainless steel welding. A convenient stress reduction method is needed to solve the problem of stress concentration of duplex stainless steel welding, stabilize the structure of large equipment, and improve the pitting corrosion resistance.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to propose a method for solving the stress concentration of duplex stainless steel welding, so as to solve the problem in the prior art that large structural parts with large size and thin wall are prone to large deformation during welding, and due to the limitation of workpiece size, conventional low-temperature aging cannot be used for stress relief treatment; this not only affects the structural stability of the product, but also may cause pitting corrosion in seawater caused by stress concentration.

[0008] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0009] A method for solving the stress concentration of duplex stainless steel welding is provided. The method for solving the stress concentration of duplex stainless steel welding is to perform ultrasonic impact treatment on the duplex stainless steel weld.

[0010] The method for solving the stress concentration of duplex stainless steel welding described in the present invention is to perform ultrasonic impact treatment on the duplex stainless steel weld, so that the ferrite phase inside the weld bears strain and forms dislocations inside the ferrite, thereby destroying the original thermodynamic equilibrium of the two phases in the alloy. During subsequent welding, the ferrite to austenite phase transformation reaction is induced and promoted at a higher temperature, and the new austenite phase is formed at the ferrite grain boundary and grows along its interface, and the volume content of austenite in the alloy increases. In addition, a layer of strip ferrite and austenite refinement layer with a thickness of 50 to 100 um and parallel surface orientation will be formed on the weld surface of the weld after ultrasonic impact treatment, and the tensile stress on the surface of the duplex stainless steel is changed to compressive stress, which can effectively alleviate the stress concentration on the weld surface and improve the material's resistance to pitting corrosion. At the same time, under the action of surface pressure stress, the welding deformation of the duplex steel material can be effectively alleviated.

[0011] Furthermore, the method for solving the stress concentration of duplex stainless steel welding uses an ultrasonic processing system to perform ultrasonic impact treatment on the duplex stainless steel weld. The ultrasonic processing system includes an ultrasonic controller, an ultrasonic vibrator and an ultrasonic impact head. The ultrasonic controller is connected to the ultrasonic vibrator, and the ultrasonic impact head is installed on the ultrasonic vibrator.

[0012] Furthermore, the method for solving the duplex stainless steel welding stress concentration comprises the following steps:

[0013] S1, connecting the ultrasonic vibrator to the ultrasonic controller;

[0014] S2, installing the ultrasonic impact head on the ultrasonic vibrator;

[0015] S3, setting the ultrasonic frequency of the ultrasonic vibrator to 10-20KHZ and the power to 500-800W on the ultrasonic controller;

[0016] S4. Use an ultrasonic impact head to perform ultrasonic impact treatment on the weld and heat-affected zone.

[0017] Furthermore, in step S3, the moving speed of the ultrasonic impact head is 60-200 mm / min.

[0018] Furthermore, the diameter of the ultrasonic impact head is d, and d satisfies 2.5-5 mm.

[0019] Furthermore, in step S3, the maximum output amplitude of the ultrasonic wave is 30 um.

[0020] Furthermore, the heat affected zone is 2 to 3 times the thickness of the weld.

[0021] Furthermore, the ultrasonic frequency of the ultrasonic vibrator is set to 15KHZ and the power is set to 650W on the ultrasonic controller.

[0022] Furthermore, the ultrasonic frequency of the ultrasonic vibrator is set to 10KHZ and the power is set to 800W on the ultrasonic controller.

[0023] Furthermore, the ultrasonic frequency of the ultrasonic vibrator is set to 20KHZ and the power is set to 500W on the ultrasonic controller.

[0024] Compared with the prior art, the method for solving the stress concentration of duplex stainless steel welding described in the present invention has the following beneficial effects:

[0025] 1) The method for solving the stress concentration of duplex stainless steel welding described in the present invention can be used for stress elimination of duplex stainless steel and welded structural parts after welding. The duplex stainless steel weld is subjected to ultrasonic impact treatment, and the ferrite phase inside the weld bears strain and forms dislocations inside the ferrite, thereby destroying the original thermodynamic equilibrium of the two phases in the alloy. During subsequent welding, the ferrite to austenite phase transformation reaction is induced and promoted at a higher temperature, and the newly formed austenite phase is formed at the ferrite grain boundary and grows along the interface, and the volume content of austenite in the alloy increases, thereby converting the tensile stress on the weld surface into compressive stress.

[0026] 2) The method for solving the stress concentration of duplex stainless steel welding described in the present invention forms a thin layer of strip ferrite and austenite with a thickness of 50 to 100 um and parallel to the surface orientation on the weld surface after ultrasonic impact treatment, and changes the tensile stress on the surface of the duplex stainless steel into compressive stress, which can effectively alleviate the stress concentration on the weld surface and improve the material's resistance to pitting corrosion.

[0027] 3) The method for solving the stress concentration of duplex stainless steel welding described in the present invention can effectively alleviate the welding deformation of the weld under the action of surface pressure stress, thereby ensuring the structural stability of the product.

[0028] 4) The method for solving the stress concentration problem of duplex stainless steel welding described in the present invention is simple to operate, applicable to large duplex stainless steel workpieces, and provides strong technical support for the manufacture of large structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic structural diagram of an ultrasonic system for a method for solving stress concentration in duplex stainless steel welding according to an embodiment of the present invention;

[0030] Figure 2 This is a morphology diagram of a weld cross section after being processed using a method for solving stress concentration in duplex stainless steel welding according to an embodiment of the present invention;

[0031] Figure 3 This is a schematic structural diagram of an application product of a method for solving stress concentration in duplex stainless steel welding according to an embodiment of the present invention.

[0032] Description of reference numerals:

[0033] 1. Ultrasonic controller; 2. Ultrasonic vibrator; 3. Ultrasonic impact head; 4. Welding seam. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The descriptions of "first", "second", etc. mentioned in the embodiments of the present invention are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0035] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0036] Example 1

[0037] The present invention is directed to large structural parts, such as large seawater desalination evaporators and condensers, such as Figure 3As shown in the figure, the material is S32205 duplex stainless steel, which is favored for its excellent corrosion resistance and mechanical properties. However, this type of component is large in size and thin in wall, which is prone to large deformation during welding. Due to the limitation of workpiece size, conventional low-temperature aging cannot be used for stress relief treatment. This not only affects the structural stability of the product, but also may cause pitting corrosion caused by stress concentration in seawater.

[0038] In order to solve the above technical problems, this embodiment proposes a method for solving the stress concentration of duplex stainless steel welding. The method for solving the stress concentration of duplex stainless steel welding performs ultrasonic impact treatment on the duplex stainless steel weld 4.

[0039] This embodiment proposes a method for solving the stress concentration of duplex stainless steel welding. The method is simple to operate and is suitable for large duplex stainless steel workpieces. The duplex stainless steel weld 4 is subjected to ultrasonic impact treatment to change the stress state on the surface of the weld 4 by physical means, which not only converts the tensile stress on the surface of the weld 4 into compressive stress, but also unexpectedly finds that under the action of the surface compressive stress, the welding deformation of the weld 4 can be effectively alleviated to ensure the structural stability of the product; at the same time, the weld 4 treated with ultrasonic impact will form a layer of strip ferrite and austenite refinement layer with a thickness of 50 to 100 um and parallel to the surface orientation on the surface of the weld 4, which greatly improves the material's resistance to pitting corrosion.

[0040] The purpose of the present invention is to solve the problem of stress concentration in duplex stainless steel welding in a convenient way, control the thermal deformation of duplex stainless steel welding, and improve the pitting corrosion resistance of duplex stainless steel.

[0041] The core of the present invention is to perform stress relief treatment on the duplex stainless steel weld 4 through designed process parameters, and to transform the tensile stress on the surface of the duplex stainless steel into compressive stress through physical methods.

[0042] Specifically, the method for solving the stress concentration of duplex stainless steel welding uses an ultrasonic treatment system to perform ultrasonic impact treatment on the duplex stainless steel weld 4, such as Figure 1 As shown, the ultrasonic processing system includes an ultrasonic controller 1, an ultrasonic vibrator 2 and an ultrasonic impact head 3, wherein the ultrasonic controller 1 is used to set and control the frequency and power of the ultrasonic wave; the ultrasonic vibrator 2 receives the signal of the ultrasonic controller 1 and generates vibration; the ultrasonic controller 1 is connected to the ultrasonic vibrator 2, and the ultrasonic impact head 3 is installed on the ultrasonic vibrator 2 to directly perform impact treatment on the weld 4.

[0043] Specifically, the method for solving the duplex stainless steel welding stress concentration comprises the following steps:

[0044] S1, connecting the ultrasonic vibrator 2 to the ultrasonic controller 1;

[0045] S2, installing the ultrasonic impact head 3 on the ultrasonic vibrator 2;

[0046] S3, setting the ultrasonic frequency of the ultrasonic vibrator 2 to 10-20KHZ and the power to 500-800W on the ultrasonic controller 1;

[0047] S4. Use the ultrasonic impact head 3 to perform ultrasonic impact treatment on the weld 4 and the heat-affected zone.

[0048] Specifically, in step S3, the moving speed of the ultrasonic impact head 3 is 60-200 mm / min.

[0049] More specifically, in this embodiment, the moving speed of the ultrasonic impact head 3 is 130 mm / min.

[0050] Specifically, the diameter of the ultrasonic impact head 3 is d, and d satisfies 2.5-5 mm. The specific selection can be adjusted according to the size of the weld 4 and the impact effect.

[0051] More specifically, in this embodiment, the diameter d of the ultrasonic impact head 3 is 3.5 mm.

[0052] Specifically, in step S3, the maximum output amplitude of the ultrasonic wave is 30 um.

[0053] Specifically, the heat affected zone is 2 to 3 times the thickness of the weld 4, ensuring that the treatment effect covers the entire critical area.

[0054] More specifically, in this embodiment, the heat affected zone is 2.5 times the thickness of the weld 4 .

[0055] Specifically, in this embodiment, the ultrasonic frequency of the ultrasonic vibrator 2 is set to 15KHZ and the power is set to 650W on the ultrasonic controller 1.

[0056] The present invention provides a convenient and effective method for solving the welding stress concentration of large duplex stainless steel structural parts. Through ultrasonic impact treatment, not only the stress state of the weld 4 is changed, but also the corrosion resistance of the material is improved, and the welding deformation is effectively controlled, providing strong technical support for the manufacture of large structural parts.

[0057] Example 2

[0058] In this embodiment, different from Embodiment 1, specifically, the ultrasonic frequency of the ultrasonic vibrator 2 is set to 10KHZ and the power is set to 800W on the ultrasonic controller 1; the moving speed of the ultrasonic impact head 3 is 60mm / min; the diameter d of the ultrasonic impact head 3 is 5mm; and the heat affected zone is twice the thickness of the weld 4.

[0059] Example 3

[0060] In this embodiment, different from Embodiment 1, specifically, the ultrasonic frequency of the ultrasonic vibrator 2 is set to 20KHZ and the power is set to 500W on the ultrasonic controller 1; the moving speed of the ultrasonic impact head 3 is 200mm / min; the diameter d of the ultrasonic impact head 3 is 2.5mm; and the heat affected zone is 3 times the thickness of the weld 4.

[0061] Comparative Example 1

[0062] In this comparative example, unlike Example 1, no treatment is performed on the duplex stainless steel weld 4 .

[0063] Performance Testing

[0064] The same large-scale seawater desalination evaporator and condenser product was treated using the methods of Examples 1 to 3 and Comparative Example 1. Figure 3 As shown, the material of the large-scale seawater desalination evaporator and condenser product is S32205 duplex stainless steel. The treated products are subjected to 4-point corrosion rate tests of the welds. The test standard is: GB / T17897: 6% FeCl3 solution, stable at 25±1°C. The results are shown in Table 1. The morphology of the welds treated in Example 1 is characterized. The results are shown in Table 1. Figure 2 .

[0065] Table 1 Pitting corrosion rate of welds in Examples 1 to 3 and Comparative Example 1

[0066] <![CDATA[Weld point corrosion rate (g*m 2 / h)]]> Example 1 0.01 Example 2 0.02 Example 3 0.03 Comparative Example 1 2.0

[0067] It can be seen from Table 1 that, through pitting corrosion resistance testing, the corrosion rate of the duplex stainless steel welds (and heat affected) treated by ultrasonic impact in Examples 1 to 3 of the present invention is greatly reduced, which greatly improves the pitting corrosion resistance of the material.

[0068] from Figure 2 It can be seen that after the ultrasonic impact treatment, a thinning layer of strip ferrite and austenite with a thickness of 50 to 100 um and oriented parallel to the surface is formed on the surface of the weld 4 .

[0069] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for solving the stress concentration of duplex stainless steel welding, characterized in that: The method for solving the duplex stainless steel welding stress concentration is to perform ultrasonic impact treatment on the duplex stainless steel weld (4).

2. A method for solving duplex stainless steel welding stress concentration according to claim 1, characterized in that: The method for solving the stress concentration of duplex stainless steel welding uses an ultrasonic treatment system to perform ultrasonic impact treatment on a duplex stainless steel weld (4). The ultrasonic treatment system comprises an ultrasonic controller (1), an ultrasonic vibrator (2) and an ultrasonic impact head (3). The ultrasonic controller (1) is connected to the ultrasonic vibrator (2), and the ultrasonic impact head (3) is installed on the ultrasonic vibrator (2).

3. A method for solving duplex stainless steel welding stress concentration according to claim 2, characterized in that: The method for solving the duplex stainless steel welding stress concentration comprises the following steps: S1, connecting the ultrasonic vibrator (2) to the ultrasonic controller (1); S2, installing the ultrasonic impact head (3) on the ultrasonic vibrator (2); S3, setting the ultrasonic frequency of the ultrasonic vibrator (2) to 10-20 kHz and the power to 500-800 W on the ultrasonic controller (1); S4. Use an ultrasonic impact head (3) to perform ultrasonic impact treatment on the weld (4) and the heat-affected zone.

4. A method for solving duplex stainless steel welding stress concentration according to claim 3, characterized in that: In step S3, the moving speed of the ultrasonic impact head (3) is 60-200 mm / min.

5. A method for solving duplex stainless steel welding stress concentration according to claim 3, characterized in that: The diameter of the ultrasonic impact head (3) is d, and d satisfies 2.5-5 mm.

6. A method for solving duplex stainless steel welding stress concentration according to claim 3, characterized in that: In step S3, the maximum output amplitude of the ultrasonic wave is 30 um.

7. A method for solving duplex stainless steel welding stress concentration according to claim 3, characterized in that: The heat affected zone is 2 to 3 times the thickness of the weld (4).

8. The method for solving the stress concentration of duplex stainless steel welding according to claim 3, characterized in that: The ultrasonic frequency of the ultrasonic vibrator (2) is set to 15KHZ and the power to 650W on the ultrasonic controller (1).

9. A method for solving duplex stainless steel welding stress concentration according to claim 3, characterized in that: The ultrasonic frequency of the ultrasonic vibrator (2) is set to 10KHZ and the power to 800W on the ultrasonic controller (1).

10. A method for solving duplex stainless steel welding stress concentration according to claim 3, characterized in that: The ultrasonic frequency of the ultrasonic vibrator (2) is set to 20KHZ and the power to 500W on the ultrasonic controller (1).

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