A method for overlaying a surface isolation layer on stainless steel castings without allowance and stainless steel castings

Abstract

This invention provides a method for welding a surface isolation layer on a stainless steel casting with no allowance, and the stainless steel casting itself. The method includes: cleaning the surface of the casting pump casing to be welded and confirming the inner and outer diameters of the surface; dividing the isolation layer to be welded into layers vertically, from bottom to top, denoted as layer to layer; and using a welding torch to weld layers to the surface from bottom to top sequentially, wherein each layer covers the surface to be welded, and the inner diameter of each layer is smaller than the inner diameter of the surface to be welded by a first preset length, the outer diameter of each layer is larger than the outer diameter of the surface to be welded by a first preset length, the inner diameter of each layer is smaller than the inner diameter of the layer by a second preset length, and the outer diameter of each layer is larger than the outer diameter of the layer by a second preset length. This invention employs an inverted trapezoidal isolation layer structure, and solves the problem of no dimensional allowance in the inner and outer diameters of the casting pump casing by adjusting and controlling the welding dimensions of each layer.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and particularly relates to a method for overlaying a surface isolation layer on a stainless steel casting without allowance, and the stainless steel casting itself. Background Technology

[0002] The welding of the primary-side coolant outlet pipe and the stainless steel casting pump casing to the steam generator of the CAP1400 and CAP1000 pressurized water reactors of the third-generation nuclear power plants is a critical manufacturing process. The casting pump casing is made of ferritic stainless steel casting SA351CF8A. The design structure requires the welding of a stainless steel 309 isolation layer at the suction end of the casting pump casing, with a weld thickness of 35mm. There is no machining allowance in the inner and outer diameter directions of the weld surface. After welding, the isolation layer must be subjected to five types of inspection: dimensional inspection (DT), visual inspection (VT), liquid penetration inspection (PT), ultrasonic inspection (UT), and radiographic inspection (RT). The isolation layer and the base material (casting) within a 13mm range must not have any defects exceeding the standard.

[0003] Due to the inherent structural characteristics of castings, compared to forgings, their structure is less dense and has obvious defects such as porosity, shrinkage cavities, and impurities. When stainless steel ER309L is welded onto their surface, defects such as porosity, hot cracks, and slag inclusions are more likely to occur. Since it is made of stainless steel casting, the base material is not easy to repair, and there is no design allowance for the inner and outer diameters of the weld overlay surface. During the weld overlay process, the base material is prone to surface defects due to thermal shrinkage.

[0004] In the heavy industry, cold wire tungsten inert gas (TIG) welding or manual TIG welding is commonly used for the surfacing of the isolation layer of cast pump casings. This method has low welding efficiency and requires a high level of skill from personnel, making it unsuitable for large-scale surfacing operations like those involving cast pump casings. In the nuclear power industry, cold wire TIG welding is used. Cold wire welding itself is inefficient. Before surfacing, in order to address the issue of no machining allowance in the inner and outer diameter directions of the cast pump casing base material, arc-extinguishing plates (rings) are welded to the inner and outer ends of the base material. The final machining dimensions are ensured by directly surfacing the arc-extinguishing plates. This method has significant drawbacks and quality risks. For example, the isolation layer, especially the area where the arc-extinguishing plate is processed and removed, has numerous defects shown by PT and radiographic testing, requiring rework with long rework cycles. Based on industry experience, during welding process experiments, the stainless steel isolation layer ER309L on the side of the representative cast pump casing showed dense cracks around the entire ring. The cracks were concentrated in the heat-affected zone of the welding layer, requiring grinding to a depth of over 8mm before removal. The defect was caused by an unreasonable air baffle ring fixing process, leading to heat and stress cracking of the isolation layer during welding. Furthermore, the industry's existing isolation layer welding process does not meet the requirements for welding cast pump casings, failing to consider the material characteristics of the castings and the lack of machining allowance in the structure. If similar defects appear in the isolation layer welding of subsequent pump casing products, it will have a significant impact on the weld quality and manufacturing cost. Summary of the Invention

[0005] The purpose of this invention is to provide a method for welding an isolation layer on the surface of stainless steel castings with no allowance. The method adopts an inverted trapezoidal isolation layer structure and solves the problem of no dimensional allowance in the inner and outer diameters of the casting pump casing by adjusting and controlling the welding size of each layer.

[0006] This invention is achieved through the following technical solution: A method for overlaying a surface isolation layer on a stainless steel casting with no allowance includes the following steps: Clean the surface of the casting pump casing to be welded and confirm the inner and outer diameters of the surface to be welded; The isolation layer to be welded is divided into layers vertically, from bottom to top, denoted as follows: Layer to layer; Use a welding torch to sequentially weld from bottom to top on the surface to be welded. Layer to Layer, wherein The layer covers the surface to be welded, and the The inner diameter of the layer is smaller than the inner diameter of the surface to be welded by a first preset length. The outer diameter of the layer is larger than the outer diameter of the surface to be welded by a first preset length. The inner diameter of the layer is smaller than The inner diameter of the layer is the second preset length. The outer diameter of the layer is greater than The outer diameter of the layer has a second preset length. .

[0007] Furthermore, the welding torch is used to sequentially deposit welds from bottom to top on the surface to be welded. Layer to Prior to the layer step, the method includes: An outer baffle ring and an inner baffle ring are respectively installed on the outer and inner side walls of the suction port of the casting pump casing, and the outer baffle ring and the inner baffle ring are respectively at a preset distance from the surface to be welded. The welding torch is used to sequentially weld from bottom to top on the surface to be welded. Layer to Following the layer step, the method includes: Remove the outer and inner air baffle rings.

[0008] Furthermore, the welding torch is used to sequentially deposit welds from bottom to top on the surface to be welded. Layer to The steps of layering include: weld overlay Layer: The welding method used is GTAW, the welding material is ER309L, the welding wire specification is φ0.9mm, the welding current is 250-285A, the hot wire current is 40-80A, the polarity is DC positive, the welding voltage is 11-13V, the welding speed is 11-12cm / min, the tungsten electrode size is cerium-tungsten or lanthanum-tungsten, the tungsten electrode size is φ4mm, and the wire feed speed is 4-6m / min. 。; The present invention also provides a stainless steel casting, which is prepared by the above-mentioned method of overlaying a surface isolation layer on a stainless steel casting without allowance.

[0009] The present invention also provides a stainless steel casting, including a cast pump housing, wherein the cast pump housing is provided with a suction port, and the end face of the suction port away from the cast pump housing is a surface to be welded. An isolation layer is provided on the surface to be welded, and the isolation layer includes multiple weld overlay layers from bottom to top. The inner diameter of the bottommost weld overlay layer is smaller than the inner diameter of the surface to be welded by a first preset length, and its outer diameter is larger than the outer diameter of the surface to be welded by a first preset length. In two adjacent weld overlay layers, the inner diameter of the upper weld overlay layer is smaller than the inner diameter of the lower weld overlay layer by a second preset length, and the outer diameter of the upper weld overlay layer is larger than the outer diameter of the lower weld overlay layer by a second preset length.

[0010] Compared to existing technologies, the advantages of this invention are: welding is performed sequentially from bottom to top on the surface to be welded. Layer to layer, The layer covers the surface to be welded and extends outward by a first preset length. Layer ratio The layer extends outward by a second preset length, making the overall isolation layer present an inverted trapezoidal weld overlay structure. This can completely solve the problem of no dimensional allowance in the inner and outer diameters of the cast pump casing, and also solve the problem of the final processing dimensions not meeting the requirements caused by the traditional trapezoidal weld overlay structure. Attached Figure Description

[0011] Figure 1 This is a flowchart of the steps of the method for welding a surface isolation layer on a stainless steel casting with no allowance according to the present invention; Figure 2 This is a schematic diagram of the welding structure in the surface isolation layer welding method for stainless steel castings with no allowance according to the present invention; Figure 3 A schematic diagram of the baffle ring structure in the invention of a method for overlaying a surface isolation layer on stainless steel castings with no allowance. In the diagram, 1-cast pump casing, 2-isolation layer, 3-outer baffle ring. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0013] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0014] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0015] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0016] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0017] Please see Figure 1 and Figure 2 , Figure 1 This is a flowchart illustrating the steps of the method for welding a surface isolation layer on a stainless steel casting without allowance according to the present invention. Figure 2This is a schematic diagram of the welding structure in the method for welding a surface isolation layer on a stainless steel casting without allowance according to the present invention. The present invention provides a method for welding a surface isolation layer on a stainless steel casting without allowance, comprising the following steps: S1. Clean the surface of the casting pump casing to be welded and confirm the inner and outer diameters of the surface to be welded; S2. The isolation layer to be welded is divided into layers vertically, from bottom to top, denoted as follows: Layer to layer; S3. Using a welding torch, weld sequentially from bottom to top on the surface to be welded. Layer to Layer, in which, The layer covers the surface to be welded, and The inner diameter of the layer is smaller than the inner diameter of the surface to be welded by a first preset length. The outer diameter of the layer is larger than the outer diameter of the surface to be welded by a first preset length. The inner diameter of the layer is smaller than The inner diameter of the layer is the second preset length. The outer diameter of the layer is greater than The outer diameter of the layer has a second preset length. .

[0018] In step S1 above, the surface of the pump casing to be welded is cleaned before welding. Liquid penetration testing (PT), ultrasonic testing (UT), and radiographic testing (RT) should be performed on the surface to be welded and within 13mm below it, according to weld requirements. Areas beyond 13mm should be protected with high-temperature tape. All pump casing isolation layer welding must be sealed off from wind, and extensive grinding work is prohibited around the weld. The protection of the pump casing base material must be carefully maintained throughout the entire process. The inner and outer diameters of the surface to be welded must be confirmed to determine the dimensions of each subsequent weld layer.

[0019] In step S2 above, the isolation layer to be welded is divided vertically from bottom to top into three parts. Layer to Each layer has a thickness of h, which is used to prepare for welding. The thickness h of each layer can be designed according to the actual situation, such as approximately 1.6 mm per layer.

[0020] In step S3 above, the first preset length is within 0.5mm, and the second preset length is between 0.5mm and 1mm. Therefore, during the welding process, the first layer... The first layer of weld overlay should cover an area within 0.5mm of the inner and outer diameters of the weld overlay surface. The weld overlay area should not exceed 0.5mm of the inner or outer diameter of the surface to be welded to avoid cracks and incomplete fusion. Subsequent... In the layer, The inner diameter of the layer is smaller than The inner diameter of the layer is 0.5mm-1mm. The outer diameter of the layer is greater than The outer diameter of the layer is 0.5mm-1mm, that is, the first... Layer ratio The layer is expanded 0.5-1mm both inside and out. During the welding process, oxides and other inclusions are removed promptly, paying particular attention to the accumulated oxides in the molten pool / tungsten electrode area, which must be ground away. The final isolation layer has an overall inverted trapezoidal weld structure, ensuring that the weld width of the isolation layer is greater than the weldable surface of the casting pump casing, preventing depressions that do not meet machining dimensional requirements during subsequent processing. After the isolation layer is processed and ground, it undergoes liquid penetrant testing (PT), ultrasonic testing (UT), and radiographic testing (RT).

[0021] Furthermore, in step S3, welding is performed sequentially from bottom to top on the surface to be welded using a welding torch. Layer to The steps of layering include: S31, weld overlay Layer: The welding method used is GTAW, the welding material is ER309L, the welding wire specification is φ0.9mm, the welding current is 250-285A, the hot wire current is 40-80A, the polarity is DC positive, the welding voltage is 11-13V, the welding speed is 11-12cm / min, the tungsten electrode size is cerium-tungsten or lanthanum-tungsten, the tungsten electrode size is φ4mm, and the wire feed speed is 5m / min. .

[0022] In step S31 above, GTAW (Gas Tungsten Arc Welding) is used. This welding method produces aesthetically pleasing and high-quality welds with fewer porosities and slag inclusions. Furthermore, the heat input is controllable, resulting in minimal deformation, making it suitable for thin plates and precision parts. Before the actual welding, the welding program is edited, and the welding parameters are entered. Details of the welding parameters are shown in Table 1 below (Note: If using a rotary platform, adjust the angular velocity accordingly). No preheating or heat treatment is required.

[0023] Table 1 Welding parameters for the isolation layer

[0024] Specifically, if the total thickness of the isolation layer is 31mm, it is welded in three stages.

[0025] In stage 1 of the surfacing process, an 8mm surfacing layer is deposited at the upper-middle speed. In this embodiment, the welding speed is 11.5cm / min, and the wire feed is 5m / min. The first layer of surfacing overlaps the inner and outer diameters of the surfacing surface by no more than 0.5mm. That is, the surfacing range of the first layer does not exceed 0.5mm of the inner and outer diameters of the surface to be surfacing. If it exceeds 0.5mm, cracks and incomplete fusion are likely to occur. Subsequent layers expand 0.5-1mm inward and outward for each layer. Each layer is observed and self-inspected and cleaned, and oxides and other inclusions are removed in a timely manner. Special attention should be paid to observing the oxides accumulated in the molten pool / tungsten electrode position, which must be ground off. Stage 1 surfacing layer is subjected to penetrant testing and ultrasonic testing. Stage 2 of welding: In this stage, weld 10mm thick, with each layer expanding 0.5-1mm both inside and out. The welding parameters are slightly lowered in this stage, such as the welding speed at 11.2cm / min and the wire feed at 4.8m / min. Pay attention to the weld bead arrangement, with an overlap of 0.5d (d is the weld bead width) between beads. That is, the tungsten electrode should be aligned with the previous fusion line. Too much or too little overlap will result in uneven thickness and incomplete fusion defects. After stage 2 is completed, perform penetrant testing and ultrasonic testing. Stage 3 of welding: In this stage, a 13mm weld is made up, including a 3mm stop and a 2mm process allowance. The control of this stage is the same as that of stage 2. The first three layers of welding parameters were adjusted to allow for faster wire feeding, rapid welding, and quick filling. Each pass was cleaned and inspected to isolate impurities and porosity inherent in the base casting material. Through parameter adjustments in the first three layers and cleaning between passes, the overall quality of the isolation layer was effectively ensured. Furthermore, while improving welding efficiency through hot-wire oscillation welding, reasonable welding parameter matching (welding heat input and wire feed rate) was selected (see Tables 1 and 2) to control the weld pool temperature, reduce the high-temperature residence time of the molten metal, and prevent hot cracking. Simultaneously, the welding efficiency was high, and visual inspection, dimensional checks, penetrant testing, ultrasonic testing, and radiographic testing of the weld ensured first-pass quality. The weld's bending toughness and tensile strength were ≥550 MPa, fully meeting design requirements.

[0026] Table 2 Welding parameters

[0027] The method of surfacing isolation layer on the surface of stainless steel castings with no allowance according to the present invention can effectively ensure the quality of the surfacing weld on the surface of the casting material. The weld performance fully meets the design specifications, as shown in Table 3. This method solves the problem of surfacing welding of casting materials in the industry.

[0028] Table 3 Mechanical properties of welds

[0029] Furthermore, welding is performed sequentially from bottom to top on the surface to be welded using a welding torch. Layer to Before the layer steps, the method includes: S3a. Install an outer baffle ring and an inner baffle ring on the outer and inner side walls of the pump casing inlet of the casting, respectively, and the outer baffle ring and the inner baffle ring are respectively at a preset distance from the surface to be welded. Use a welding torch to deposit welds from bottom to top on the surface to be welded. Layer to Following the layer steps, the method includes: S3b, Remove the outer and inner air baffle rings.

[0030] In step S3a above, the arc-extinguishing plate in the traditional trapezoidal weld overlay structure is replaced with an outer gas-blocking ring and an inner gas-blocking ring. These rings are not welded to the cast pump casing; they are mechanically fixed 5-15mm below the surface to be welded, sealing the gap area. They serve only as gas protection. Compared to a structure without gas-blocking rings, the gas flow is buffered by the rings and then flows back, better ensuring the molten pool of the inner and outer isolation layers is in a protective gas atmosphere. This controls the weld quality of the inner and outer isolation layers. Simultaneously, the mechanical connection avoids cracking in the weld joint area due to weld tensile stress, ensuring the weld overlay quality of the isolation layer. Furthermore, the outer and inner gas-blocking rings are stainless steel rings, each consisting of two semi-circular modules connected by riveting, thus mechanically fixing them to the inner and outer walls of the cast pump casing. The entire ring is sealed with high-temperature tape.

[0031] This invention also provides a stainless steel casting prepared using the aforementioned method for depositing a surface isolation layer on a stainless steel casting. This stainless steel casting, prepared using the aforementioned method for depositing a surface isolation layer on a stainless steel casting, possesses all the technical effects of the aforementioned method, and will not be elaborated further.

[0032] This invention also provides a stainless steel casting, including a cast pump housing. The cast pump housing has a suction port, and the end face of the suction port away from the cast pump housing is the surface to be welded. An isolation layer is provided on the surface to be welded. The isolation layer comprises multiple weld overlay layers from bottom to top. The inner diameter of the lowest weld overlay layer is smaller than the inner diameter of the surface to be welded by a first preset length, and its outer diameter is larger than the outer diameter of the surface to be welded by a first preset length. In two adjacent weld overlay layers, the inner diameter of the upper weld overlay layer is smaller than the inner diameter of the lower weld overlay layer by a second preset length, and the outer diameter of the upper weld overlay layer is larger than the outer diameter of the lower weld overlay layer by a second preset length. The isolation layer as a whole presents an inverted trapezoidal weld overlay structure, solving the problem of no dimensional allowance in the inner and outer diameters of the cast pump housing, and also solving the problem of unmet final machining dimensions caused by traditional trapezoidal weld overlay structures.

[0033] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for overlaying a surface isolation layer on a stainless steel casting with no allowance, characterized in that, Includes the following steps: Clean the surface of the casting pump casing to be welded and confirm the inner and outer diameters of the surface to be welded; The isolation layer to be welded is divided into layers vertically, from bottom to top, denoted as follows: Layer to layer; Use a welding torch to sequentially weld from bottom to top on the surface to be welded. Layer to Layer, wherein The layer covers the surface to be welded, and the The inner diameter of the layer is smaller than the inner diameter of the surface to be welded by a first preset length. The outer diameter of the layer is larger than the outer diameter of the surface to be welded by a first preset length. The inner diameter of the layer is smaller than The inner diameter of the layer is the second preset length. The outer diameter of the layer is greater than The outer diameter of the layer has a second preset length. .

2. The method for overlaying a surface isolation layer on a stainless steel casting with no allowance according to claim 1, characterized in that, The welding torch is used to sequentially weld from bottom to top on the surface to be welded. Layer to Prior to the layer step, the method includes: An outer baffle ring and an inner baffle ring are respectively installed on the outer and inner side walls of the suction port of the casting pump casing, and the outer baffle ring and the inner baffle ring are respectively at a preset distance from the surface to be welded. The welding torch is used to sequentially weld from bottom to top on the surface to be welded. Layer to Following the layer step, the method includes: Remove the outer and inner air baffle rings.

3. The method for overlaying a surface isolation layer on a stainless steel casting with no allowance according to claim 1, characterized in that, The welding torch is used to sequentially weld from bottom to top on the surface to be welded. Layer to The steps of layering include: weld overlay Layer: The welding method used is GTAW, the welding material is ER309L, the welding wire specification is φ0.9mm, the welding current is 250-285A, the hot wire current is 40-80A, the polarity is DC positive, the welding voltage is 11-13V, the welding speed is 11-12cm / min, the tungsten electrode size is cerium-tungsten or lanthanum-tungsten, the tungsten electrode size is φ4mm, and the wire feed speed is 4-6m / min. .

4. A stainless steel casting, characterized in that, The surface isolation layer of the stainless steel casting is prepared by the welding method according to any one of claims 1-3.

5. A stainless steel casting, comprising a cast pump housing, wherein the cast pump housing is provided with a suction port, characterized in that, The end face of the suction port away from the casting pump casing is the surface to be welded. An isolation layer is provided on the surface to be welded. The isolation layer includes multiple weld overlay layers from bottom to top. The inner diameter of the bottommost weld overlay layer is smaller than the inner diameter of the surface to be welded by a first preset length, and its outer diameter is larger than the outer diameter of the surface to be welded by a first preset length. Among two adjacent weld overlay layers, the inner diameter of the upper weld overlay layer is smaller than the inner diameter of the lower weld overlay layer by a second preset length, and the outer diameter of the upper weld overlay layer is larger than the outer diameter of the lower weld overlay layer by a second preset length.

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