Heat-treatment-free repair method for steel casting

Abstract

According to the heat-treatment-free repairing method for the steel casting, the welding material matched with the steel casting is utilized, high-temperature tempering treatment can be conducted on a heat affected zone through heat generated by a follow-up welding bead under the condition of no postweld heat treatment, the residual stress of a welded joint is reduced, the welded joint has the good tempered structure morphology, and the welding quality is improved. And the joint performance is equivalent to that of the same material after-weld heat treatment, and the method has universality for steel castings with the carbon equivalent being not higher than 0.6.

Description

Technical Field

[0001] The present disclosure relates to the technical field of repairing steel castings without post-weld heat treatment, and in particular, to a method for repairing steel castings. Background Art

[0002] When local parts of thick-walled equipment components fail, the more economical solution is to repair these parts rather than replace them, considering the value of the equipment itself, its distribution location, and environmental restrictions. Many important equipment such as power station valves, pumps, and high and medium pressure outer cylinders are made of cast low-alloy steel. However, the manufacturing process performance of castings is poor, and during operation, the body often fails at the stress concentration location, resulting in excessive defects. Grinding to the maximum depth may not eliminate the defects, and welding repair is required.

[0003] According to the conventional standard processing procedures, in order to ensure the good metallurgical and mechanical properties of the welded joints, it is essential to perform overall or partial post-weld heat treatment on these repaired parts. However, due to the limitations of environmental conditions, material aging and the conditions of the parts themselves, the conventional patching repair process may lead to irreversible consequences such as the failure to implement the heat treatment process normally, the expansion of defects in the non-repaired area or the deformation of the sealing surface affecting assembly, making it impossible to carry out the repair normally, and the tempering weld repair technology needs to be used.

[0004] Therefore, it is necessary to provide a new tempering weld repair technology to solve the problem of local failure of thick-walled equipment components, and to effectively avoid the adverse effects of conventional patching and repair processes, thus providing a strong guarantee for the reliable operation of the equipment. Summary of the invention

[0005] The purpose of the present invention is to provide a new steel casting repair technology, which can achieve high-temperature tempering heat treatment of the affected area and weld of the steel casting through welding without high-temperature tempering heat treatment, so as to solve the problem of local failure of thick-walled equipment components, and can effectively avoid the adverse effects of conventional patching and repair processes to obtain qualified organization and performance.

[0006] In order to achieve the above object, the present disclosure provides a method for repairing a steel casting, the method comprising the following steps: S1. Pre-treating the area to be repaired of the steel casting sample; S2, using a first welding material to perform a first welding on the area to be repaired by a manual arc welding method to obtain a first layer of primer; S3, grinding the first base layer to remove the surface welding slag, and then performing a second welding on the base layer by manual arc welding using a second welding material to obtain a second transition layer; S4, grinding the second transition layer to remove the surface welding slag, and then using a third welding material to fill the area to be repaired on the surface of the second transition layer to obtain a third filling layer; S5, welding a fourth welding material on the third filling layer to obtain a fourth covering layer, and grinding the fourth covering layer; The steel casting sample is a steel casting with a carbon equivalent not higher than 0.6; The first welding material, the second welding material, the third welding material and the fourth welding material are all welding materials of the same material matching the steel casting.

[0007] Optionally, in step S1, the pretreatment includes machining and polishing the area to be repaired of the steel casting sample to make the area to be repaired present a metallic luster, and preheating the area to be repaired at 120-150°C by flame heating.

[0008] Optionally, in step S2, the first welding material includes a welding rod with a diameter of 2.5 mm, and the parameters of the first welding include: an interlayer temperature of 150-250°C, a welding speed of 20-25 cm / min, a current of 84-86A, a voltage of 16-18V, and an overlap between welds of 45-50%.

[0009] Optionally, the thickness of the first primer layer is not greater than the diameter of the welding material.

[0010] Optionally, in step S3, the second welding material includes a welding rod with a diameter of 3.2 mm, and the parameters of the second welding include: an interlayer temperature of 150-250°C, a welding speed of 20-25 cm / min, a current of 108-112A, a voltage of 18-20V, and an overlap between welds of 45-50%.

[0011] Optionally, the thickness of the second transition layer is not greater than the diameter of the welding material; the distance between the weld toe of the second transition layer and the weld toe of the first base layer is 3-5 mm.

[0012] The weld toe defined in the present disclosure refers to the junction between the weld surface and the base material, which is the junction position between the edge of the weld pool after solidification and the base material. It is used in the present disclosure to accurately describe the relative position relationship between each welding layer.

[0013] Optionally, in step S4, the distance between the weld toe of the third filling layer and the weld toe of the first primer layer is not less than 3 mm.

[0014] Optionally, the thickness of the third filling layer is not greater than the diameter of the third welding material.

[0015] Optionally, in step S5, the distance between the weld toe of the fourth cover layer and the weld toe of the first base layer is not less than 3 mm.

[0016] Optionally, the thickness of the fourth covering layer is not greater than the diameter of the fourth welding material.

[0017] Through the above technical scheme, the present disclosure provides a method for repairing steel castings. The method uses the same welding material as the steel castings to repair steel castings with a carbon equivalent of not more than 0.6. The method can perform high-temperature tempering heat treatment on the heat-affected zone and weld of the repaired area without post-weld heat treatment, thereby reducing the residual stress of the welded joint, making it have a better tempering microstructure morphology, and having joint performance equivalent to that of the same material after post-weld heat treatment.

[0018] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings: Figure 1 Schematic diagram of the first layer of base layer and the second layer of transition layer; Figure 2 This is a schematic diagram of the third filling layer; Figure 3 This is a schematic diagram of the fourth cover layer; Figure 4 This is the SEM image of the steel casting repaired in Example 1; Figure 5 These are the hardness values ​​of the welded joints at different positions and states of the steel castings repaired in the examples. DETAILED DESCRIPTION

[0020] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0021] The present invention provides a method for repairing a steel casting, the method comprising the following steps: S1. Pre-treating the area to be repaired of the steel casting sample; S2, using a first welding material to perform a first welding on the area to be repaired by a manual arc welding method to obtain a first layer of primer; S3, grinding the first base layer to remove the surface welding slag, and then performing a second welding on the base layer by manual arc welding using a second welding material to obtain a second transition layer; S4, grinding the second transition layer to remove the surface welding slag, and then using a third welding material to fill the area to be repaired on the surface of the second transition layer to obtain a third filling layer; S5, welding a fourth welding material on the third filling layer to obtain a fourth covering layer, and grinding the fourth covering layer; The steel casting sample is a steel casting with a carbon equivalent not higher than 0.6; The first welding material, the second welding material, the third welding material and the fourth welding material are all welding materials of the same material matching the steel casting.

[0022] The steel casting repair method provided by the present invention can ensure the quality and stability of the repaired part through step-by-step welding and processing. The base layer, transition layer, filling layer and cover layer are arranged in sequence to make the structure of the repaired part more solid. Each layer uses welding materials of the same material and specification as the original steel casting, which can ensure the consistency of the repaired position with the original steel casting, thereby improving the overall performance and reliability after repair. In addition, the method is universal for steel castings with a carbon equivalent of not more than 0.6.

[0023] The welding materials of the same material and specification provided in the present disclosure refer to welding materials with the same key characteristics such as chemical composition, mechanical properties and metallographic structure of the deposited metal. Only in this way can it be ensured that during the welding process, from the microstructure of the weld to the macroscopic mechanical performance, a high degree of adaptability and consistency can be achieved with the parent material, thereby ensuring the stability and reliability of the welding quality.

[0024] In addition, the method provided by the present invention uses a manual arc welding method to weld the base layer and the transition layer. The equipment is simple, easy to operate, and has a low cost. In addition, the repair progress can be adjusted by changing conditions such as the current.

[0025] Optionally, the pretreatment includes machining and polishing the area to be repaired of the cast steel sample to make the area to be repaired present a metallic luster, and preheating the area to be repaired at 120-150°C by flame heating. The preheating temperature varies for different types of steel and can be adjusted according to actual needs.

[0026] The present invention uses mechanical processing and grinding to make the shape and size of the area to be repaired more regular and remove impurities, providing a good foundation for subsequent welding work; through preheating, the welding area is kept at a certain temperature during the welding process, thereby reducing the cooling rate, reducing the risk of cracks and rework due to welding defects, and reducing the repair cost.

[0027] Optionally, in step S2, the first welding material includes a welding rod with a diameter of 2.5 mm, and the parameters of the first welding include: an interlayer temperature of 150-250°C, a welding speed of 20-25 cm / min, a current of 84-86A, a voltage of 16-18V, and an overlap between welds of 45-50%.

[0028] Optionally, the thickness of the first primer layer is not greater than the diameter of the welding material.

[0029] Optionally, in step S3, the second welding material includes a welding rod with a diameter of 3.2 mm, and the parameters of the second welding include: an interlayer temperature of 150-250°C, a welding speed of 20-25 cm / min, a current of 108-112A, a voltage of 18-20V, and an overlap between welds of 45-50%.

[0030] Optionally, the thickness of the second transition layer is not greater than the diameter of the welding material; the distance between the weld toe of the second transition layer and the weld toe of the first base layer is 3-5 mm.

[0031] Optionally, in step S4, the distance between the weld toe of the third filling layer and the weld toe of the first base layer is not less than 3 mm; and the thickness of the third filling layer is not higher than the diameter of the third welding material.

[0032] Optionally, in step S5, the distance between the weld toe of the fourth capping layer and the weld toe of the first base layer is not less than 3 mm; and the thickness of the fourth capping layer is not higher than the diameter of the fourth welding material.

[0033] The present disclosure further optimizes the welding process parameters. At the above welding temperature, the welding material and the cast steel sample are fully fused to form a solid weld joint. The above parameter combination of welding speed, current and voltage is a relatively reasonable welding parameter obtained by the inventor of the present application after a large number of creative experiments. The selection of these parameters can make the arc burn stably during the welding process, the welding material melt evenly, and the weld is well formed.

[0034] The present invention further regulates that the single layer thickness of the first base layer, the second transition layer, the third filling layer, and the fourth cover layer is not higher than the diameter of the selected welding material; and the distance between the weld toe of the second transition layer and the weld toe of the first base layer is 3-5mm; optionally, the weld toes of the third filling layer and the fourth cover layer are each independently not less than 3mm from the weld toe of the first base layer.

[0035] The present invention can effectively avoid the unclear effect of the tempering weld bead caused by unreasonable weld layer thickness during welding by further controlling the thickness of each weld layer. Reasonable weld toe size control helps to improve the tempering weld bead effect in the heat affected zone near the weld toe of the weld joint.

[0036] The present invention is further described in detail below by way of examples.

[0037] Example 1 In this embodiment, defective areas of steel castings are repaired, and the material analysis of the selected steel castings is as follows: the hardenability of the steel castings to be repaired is analyzed by carbon equivalent, and Table 1 lists some steel castings that can be exempted from heat treatment by the method provided in this embodiment.

[0038] Table 1 Chemical elements of different steel castings / %

[0039] In the field of material welding and processing, carbon equivalent (CE) is a key indicator for measuring the welding performance of steel castings, and its calculation formula is: CE=[C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15]×100%. After a large number of experimental studies, it was found that the tempering weld bead technology proposed in this embodiment has unique advantages, which can make the steel castings shown in Table 1 free of heat treatment and effectively improve their performance and processing efficiency. However, in the process of screening and adaptability testing of commonly used steel castings, it was found that the steel castings such as WC9, C5, C12, C12A, CA15 in the ASTM A 217 series have high carbon equivalent (CE) and great hardening tendency due to their own characteristics, which leads to a series of problems such as welding cracks and tissue hardening when using the tempering weld bead technology provided in this embodiment, and it is impossible to achieve the ideal repair and processing effect, so it is not suitable to adopt this method. Through rigorous experimental verification and comprehensive consideration of multiple factors such as the feasibility of welding process and the stability of repair quality, it was finally determined that the method provided in this embodiment is only applicable to steel castings with a carbon equivalent (CE) not higher than 0.6, thereby ensuring the reliability and effectiveness of the technical implementation and providing accurate and targeted solutions for the field of steel casting repair.

[0040] This embodiment takes ASTM A217 WC6 steel repair as an example, and the repair process is as follows: S1. Remove defects of the steel casting A217 WC6 to be repaired by machining and grinding. After the defects are eliminated, grind the surface near the area to be repaired to a metallic luster; preheat the area to be repaired by flame heating at a preheating temperature of 150°C; S2. Use manual arc welding (SMAW) to weld the first layer of weld in the area to be repaired (the welding material is R30 electrode matching the cast steel, with a specification of Φ2.5mm), to obtain the first layer of base layer, the thickness of the base layer is 2.2-2.5mm, the interlayer temperature between the first layer of base layer and the area to be repaired of the cast steel sample is controlled to be 220℃, the welding speed is 22cm / min; the current is 85A, the voltage is 16V; the overlap between welds is 45%; S3. After the first layer of base layer is welded, grind it to make the surface smooth and remove the surface welding slag (grinding amount ≤ 0.5mm); use a Φ3.2mm welding rod to weld the second transition layer on the first layer of base layer. The schematic diagram of the first layer of base layer and the second layer of transition layer is as follows Figure 1 As shown, the thickness of the second transition layer is 3.0 mm, the distance between the weld toe of the second transition layer and the first base layer is 3-5 mm, the interlayer temperature is controlled to be 200 ° C, the welding speed is 24 cm / min, the current is 110 A, the voltage is 18 V, and the overlap between welds is 45%; S4. Use a Φ3.2mm electrode to fill the weld on the second transition layer to obtain a third filling layer. The schematic diagram of the third filling layer is as follows: Figure 2 As shown, the distance between the weld toe of the third filling layer and the first base layer is 2.8 mm, and the weld thickness of each layer is 3.0 mm.

[0041] S5. Use a Φ3.2mm welding rod to weld the last weld on the basis of the third filling layer to obtain the fourth cover layer. Grind the fourth cover layer to obtain the repaired steel casting. The schematic diagram of the fourth cover layer and the repair welding layer is shown in FIG. Figure 3 As shown, the distance between the weld toes of the fourth cover layer and the first base layer is 3.2 mm, and the weld thickness of the fourth cover layer is 3.0 mm.

[0042] The welding consumables are welding consumables of the same material and specification that match the steel casting.

[0043] Comparative Example 1 This comparative example uses conventional high temperature tempering heat treatment technology (compared with Example 1, including post-weld heat treatment, the process is 650°C*1.5h) to repair the defects of the same steel casting as Example 1. The test results are shown in Table 4 and Figure 5 shown.

[0044] Test Example 1 This test example evaluates the process of the steel castings repaired in Example 1 and Comparative Example 1, and compares them with the joints in the normal post-weld heat treatment state. Figure 4 As shown ( Figure 4(a is the base material, b is the fine grain area, c is the coarse grain area, d is the fusion line, and e is the weld). The metallographic structures of each region show a high degree of consistency: the weld is mainly composed of tempered bainite, and contains a small amount of ferrite; the coarse grain area of ​​the heat affected zone presents a tempered bainite structure; the base material stably presents a combination of ferrite and bainite. The weld is well fused with the base material, and no cracks, hardened martensite structure, or overheated structure are found. The performance results are shown in Tables 4 and Figure 5 As shown in the figure, it can be intuitively seen that the mechanical properties are almost the same: whether it is tensile, impact, bending test, or hardness test, the results obtained are all higher than the performance index requirements set for A217 WC6 welded joints in the standard. Further in-depth exploration of the microhardness distribution, after multi-point sampling and testing at the 1.5mm position on the joint surface and the middle position of the joint, it was found that the hardness value fluctuated very little and the difference was not significant. The tempered weld bead has a significant improvement in the heat affected zone and weld hardness of the welded joint.

[0045] Table 4 A217 WC6 steel welded joint properties

[0046] The steel casting repaired in Example 1 of the present disclosure without high-temperature tempering heat treatment can use the heat generated by the subsequent weld to perform high-temperature tempering treatment on the heat-affected zone, thereby softening the structure of the heat-affected zone, eliminating residual stress, and improving toughness, thereby ensuring the performance of different positions of the steel casting. The method provided by the present disclosure is universal for steel castings with a carbon equivalent of not more than 0.6, and can be repaired uniformly using the repair method provided by the present disclosure, eliminating the post-weld heat treatment step.

[0047] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0048] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for repairing a steel casting, characterized in that: The method comprises the following steps: S1. Pre-treating the area to be repaired of the steel casting sample; S2, using a first welding material to perform a first welding on the area to be repaired by a manual arc welding method to obtain a first layer of primer; S3, grinding the first base layer to remove the surface welding slag, and then performing a second welding on the base layer by manual arc welding using a second welding material to obtain a second transition layer; S4, grinding the second transition layer to remove the surface welding slag, and then using a third welding material to fill the area to be repaired on the surface of the second transition layer to obtain a third filling layer; S5, welding a fourth welding material on the third filling layer to obtain a fourth covering layer, and grinding the fourth covering layer; The steel casting sample is a steel casting with a carbon equivalent not higher than 0.6; The first welding material, the second welding material, the third welding material and the fourth welding material are all welding materials of the same material matching the steel casting.

2. The method according to claim 1, wherein: The pretreatment includes machining and grinding the area to be repaired of the steel casting sample to make the area to be repaired present a metallic luster, and preheating the area to be repaired to 120-150°C.

3. The method according to claim 1, wherein: In step S2, the first welding material includes a welding rod with a diameter of 2.5 mm, and the parameters of the first welding include: an interlayer temperature of 150-250°C, a welding speed of 20-25 cm / min, a current of 84-86A, a voltage of 16-18V, and an overlap between welds of 45-50%.

4. The method according to claim 3, wherein: The thickness of the first base layer is not greater than the diameter of the first welding material.

5. The method according to claim 1, wherein: In step S3, the second welding material includes a welding rod with a diameter of 3.2 mm, and the parameters of the second welding include: interlayer temperature of 150-250°C, welding speed of 20-25 cm / min, current of 108-112A, voltage of 18-20V, and overlap between welds of 45-50%.

6. The method according to claim 5, wherein: The thickness of the second transition layer is not greater than the diameter of the second welding material; The distance between the weld toe of the second transition layer and the weld toe of the first primer layer is 3-5 mm.

7. The method according to claim 1, wherein: In step S4, the distance between the weld toe of the third filling layer and the weld toe of the first primer layer is not less than 3 mm.

8. The method according to claim 7, wherein: The thickness of the third filling layer is not greater than the diameter of the third welding material.

9. The method according to claim 1, wherein: In step S5, the distance between the weld toe of the fourth cover layer and the weld toe of the first primer layer is not less than 3 mm.

10. The method according to claim 9, wherein: The thickness of the fourth capping layer is not greater than the diameter of the fourth welding material.

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