Alloy coating suitable for low alloy steel and preparation method thereof

Abstract

The invention discloses an alloy coating suitable for low alloy steel and a preparation method of the alloy coating. The alloy coating comprises the following elements in percentage by weight: 6.3-12.3% of Cr and Filt. , 3.1%, Mult; 4.3%, Colt; 1%, Mnlt; 0.5%, Silt; the alloy comprises the following components in percentage by weight: 0.5% of C, 0.62%-2.55% of W and the balance of nickel. The alloy coating suitable for the low-alloy steel is prepared from various components according to the specific proportion, the Fe-Ni compound, the WC, the W2C, the Cr-Fe compound and the like are generated through the reaction among the elements in the components, the thin alloy coating is formed on the surface of the low-alloy steel, the corrosion resistance and the wear resistance of the coating are improved, and meanwhile the bonding strength of the coating and the low-alloy steel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal material surface modification, in particular to an alloy coating suitable for low alloy steel and a preparation method thereof. Background Art

[0002] Low alloy steel is a type of steel that adds a small amount of alloying elements such as chromium, nickel, molybdenum, and vanadium to iron-based materials. It has high strength, good toughness and ductility. Due to its good comprehensive performance and high cost performance, low alloy steel is widely used in industrial fields such as bridges, vehicles, ships, buildings, pressure vessels, and special equipment. However, in harsh corrosive and high wear environments, the welded joints of low alloy steel often face the problem of insufficient wear resistance and corrosion resistance, which seriously affects its service life.

[0003] In the welding process of low alloy steel, high current welding is usually used to ensure the strength of the joint. This high heat input causes the grains of the weld and heat affected zone to coarsen significantly (the size can reach 70-90μm), and reduces the hardness, strength and toughness of this area, becoming a weak point in the structure. Due to the differences in metallographic structure and element distribution between the joint and the parent material, the joint is more prone to micro cracks, which aggravates the wear. The joint area of ​​low alloy steel, especially the weld and heat affected zone, is often lower in hardness than the parent material due to uneven alloy elements and organizational structure, and has poor wear resistance. In high friction and high stress environments (such as fluid scouring in pipeline transportation systems or continuous friction of structural parts), the joint area is more susceptible to wear. This wear not only weakens the integrity of the material surface, but also induces stress concentration, leading to crack propagation, thereby shortening the service life of the component. In many industrial environments, low alloy steel joints are often exposed to corrosive media (such as water, acid, alkali and salt), especially in harsh environments such as oil and gas pipelines and marine facilities. The stress concentration and grain coarsening caused by welding make the corrosion resistance of the joint area lower than that of the parent material. In sulfur- or chlorine-containing media, pitting and crevice corrosion are prone to occur in the joint area, which may even cause leakage risks. In addition, in a humid environment, galvanic corrosion is prone to form at the joint, which accelerates the corrosion process and further reduces the corrosion resistance of the joint. The parent material, weld and heat-affected zone in the welded joint area differ in chemical composition and crystal phase structure, so the electrochemical properties are uneven. In a humid or corrosive environment, the weld and heat-affected zone often become the anode of the electrochemical corrosion reaction, forming galvanic corrosion with the parent material, accelerating the damage of the welded joint and significantly shortening the service life of low-alloy steel in harsh environments.

[0004] At present, the common methods to improve the wear resistance and corrosion resistance of low alloy steel joints include surface coating, heat treatment, etc. However, these methods have some limitations, such as the coating process is difficult to ensure the close bonding between the coating and the substrate, the heat treatment is difficult to evenly cover the complex joint area, and the wear resistance and corrosion resistance are also limited. Therefore, these traditional methods are difficult to achieve the demand for long-term service in a high wear and high corrosion environment.

[0005] In order to solve the problem of insufficient wear resistance and corrosion resistance at low alloy steel joints, it is urgent to develop an efficient and low-cost improvement solution to improve the service life and reliability of low alloy steel joints. This can not only improve the comprehensive performance of low alloy steel, but also provide a more economical and effective solution for related industrial fields. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide an alloy coating suitable for low-alloy steel and a preparation method thereof, which can improve the uniformity of the wide-range structure of the welding transition and the bonding strength with the low-alloy steel while improving the corrosion resistance and wear resistance of the coating.

[0007] To achieve the above-mentioned purpose, the first aspect of the present invention provides an alloy coating suitable for low alloy steel, wherein the element composition in the alloy coating includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

[0008] Furthermore, the alloy coating is made by heat treating cladding material powder, and the element composition in the cladding material powder includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

[0009] Furthermore, the element composition of the low alloy steel includes, by weight percentage, C 0.16%-0.2%, Si<0.55%, P<0.045%, Mn 1.00%-1.60%, and the balance is iron.

[0010] A second aspect of the present invention provides a method for preparing an alloy coating suitable for low alloy steel, comprising the following steps:

[0011] 1) Deoxidation treatment is performed on the surface of the low alloy steel to be treated;

[0012] 2) Using a laser cladding process to perform laser cladding on the surface of the low alloy steel after oxidation treatment, so as to form an alloy coating as described in any one of claims 1 to 3 on the surface of the low alloy steel.

[0013] Furthermore, the process parameters of laser cladding include a laser power of 1500-2000W, a scanning speed of laser cladding of 300-500mm / min, a spot diameter of laser cladding of 2-4mm, and a thickness of the cladding coating of 1-2mm.

[0014] Further, the deoxidation treatment is performed on the surface to be treated of the low alloy steel, including:

[0015] Deoxidize the surface of the low alloy steel plate and weld the plate by laser welding;

[0016] After welding is completed, let the weldment cool to room temperature;

[0017] Deoxidation treatment is performed on the weld joints of the weldment.

[0018] Furthermore, the element composition of the low alloy steel includes, by weight percentage, C 0.16%-0.2%, Si<0.55%, P<0.045%, Mn 1.00%-1.60%, and the balance is iron.

[0019] Furthermore, the alloy coating is made by heat treating cladding material powder, and the element composition in the cladding material powder includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

[0020] Furthermore, the average particle size of the cladding material powder is 120-250 meshes.

[0021] A third aspect of the present invention provides a low alloy steel weld joint, the alloy coating is formed on the surface of the low alloy steel weld joint by the above-mentioned preparation method.

[0022] The present invention prepares an alloy coating suitable for low alloy steel by preparing various components according to a specific ratio, utilizes the reaction between elements in the components to generate Fe-Ni compounds, WC, W2C and Cr-Fe compounds, etc., to form a thinner alloy coating on the surface of the low alloy steel, thereby improving the corrosion resistance and wear resistance of the coating while improving the bonding strength with the low alloy steel.

[0023] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 The metallographic structure of the comparative example 1-1 in which the low alloy steel plate is laser welded comprises (a) a weld zone and (b) a heat affected zone;

[0026] Figure 2 This is a SEM and EDS comparison diagram of Example 2-1 of the present invention;

[0027] Figure 3 This is a SEM and EDS comparison diagram of Example 2-2 of the present invention;

[0028] Figure 4 is the XRD pattern of Example 2-1 of the present invention;

[0029] Figure 5 This is the XRD pattern of Example 2-2 of the present invention. DETAILED DESCRIPTION

[0030] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the present invention will be more comprehensive and complete and fully convey the concept of the example embodiments to those skilled in the art.

[0031] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0032] A first aspect of the present invention provides an alloy coating suitable for low alloy steel, wherein the element composition of the alloy coating includes, by weight percentage, Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

[0033] In this embodiment, an alloy coating suitable for low alloy steel is prepared by various components according to a specific ratio. The elements in the components react to generate Fe-Ni compounds, WC, W2C and Cr-Fe compounds, etc., to form a thinner alloy coating on the surface of the low alloy steel. WC and W2C have high hardness and wear resistance, which play a role in improving the wear resistance of the low alloy steel surface. Fe-Ni compounds and Cr-Fe compounds play a role in improving the corrosion resistance of the low alloy steel surface due to their own high standard electrode potential and the dense protective film generated. Under the joint action of Fe-Ni compounds, WC, W2C and Cr-Fe compounds, the corrosion resistance and wear resistance of the coating are improved while the bonding strength with the low alloy steel is improved.

[0034] In one embodiment of the present invention, the alloy coating is made by heat treatment of cladding material powder, and the element composition of the cladding material powder includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

[0035] In one embodiment of the present invention, the element composition of the low alloy steel includes C 0.16%-0.2%, Si<0.55%, P<0.045%, Mn 1.00%-1.60%, and the balance is iron.

[0036] A second aspect of the present invention provides a method for preparing an alloy coating suitable for low alloy steel, comprising the following steps:

[0037] 1) Deoxidation treatment is performed on the surface of the low alloy steel to be treated;

[0038] 2) Using a laser cladding process to perform laser cladding on the surface of the low alloy steel after oxidation treatment, so as to form an alloy coating as described in any one of claims 1 to 3 on the surface of the low alloy steel.

[0039] In one embodiment of the present invention, the process parameters of laser cladding include a laser power of 1500-2000W, a scanning speed of laser cladding of 300-500mm / min, a spot diameter of laser cladding of 2-4mm, and a thickness of the cladding coating of 1-2mm.

[0040] In one embodiment of the present invention, performing deoxidation treatment on the surface to be treated of low alloy steel includes:

[0041] Deoxidize the surface of the low alloy steel plate and weld the plate by laser welding;

[0042] After welding is completed, let the weldment cool to room temperature;

[0043] Deoxidation treatment is performed on the weld joints of the weldment.

[0044] In one embodiment of the present invention, the laser welding process parameters include a laser power of 3450W-5300W and a laser scanning speed of 0.015m / min-0.025m / min. In this embodiment, a welded joint is obtained by laser welding, which has a fast welding speed and a large depth. At the same time, the high-intensity short-time pulse also enables the grains in the molten pool of the welded joint to be refined to a certain extent, and the quality of the welded joint is excellent. At the same time, through the optimized welding process parameters, the uniformity of the wide-area structure of the welding transition zone is improved, and the galvanic corrosion intensity of the welding street is reduced.

[0045] In one embodiment of the present invention, the element composition of the low alloy steel includes C 0.16%-0.2%, Si<0.55%, P<0.045%, Mn 1.00%-1.60%, and the balance is iron.

[0046] In one embodiment of the present invention, the alloy coating is made by heat treatment of cladding material powder, and the element composition in the cladding material powder includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel. The laser cladding material is prepared by weighing intermediate powders of nickel, chromium, molybdenum, iron, manganese, and silicon and mixing them in a high-speed mixer for 6 hours.

[0047] In one embodiment of the present invention, the average particle size of the cladding material powder is 120-250 meshes.

[0048] A third aspect of the present invention provides a low alloy steel weld joint, the alloy coating is formed on the surface of the low alloy steel weld joint by the above-mentioned preparation method.

[0049] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0050] Comparative Example 1-1

[0051] Low alloy steel (Q345 steel) was welded by laser with a laser power of 4050w and a welding speed of 0.015m / min to obtain a weldment without coating.

[0052] The obtained plates were wire cut, one part was subjected to salt spray corrosion test to obtain weight loss rate; one part was subjected to wear resistance test for 1 hour; one part was subjected to structure observation and hardness test; one part was subjected to galvanic corrosion performance test; the results are shown in Data Table 1.

[0053] The microstructure morphology of Comparative Example 1 was analyzed, and the results were as follows Figure 1 As shown, Figure 1 The microstructure morphology of the weld zone and heat-affected zone is composed of a small amount of bainite and martensite.

[0054] Comparative Example 1-2

[0055] Q345 steel is laser welded with a laser power of 3450W and a speed of 0.015m / min

[0056] The same measurement method as that of Comparative Example 1-1 was adopted, and the results are shown in Data Table 1.

[0057] Comparative Examples 1-3

[0058] Q345 steel is laser welded with a laser power of 5300W and a speed of 0.025m / min

[0059] The same measurement method as that of Comparative Example 1-1 was adopted, and the results are shown in Data Table 1.

[0060] Comparative Examples 1-4

[0061] Q345 steel is laser welded with a laser power of 4500W and a speed of 0.025m / min

[0062] The same measurement method as that of Comparative Example 1-1 was adopted, and the results are shown in Data Table 1.

[0063] Embodiment 2-1 of the present invention

[0064] Using a better welding joint, nickel-based powder with an average particle size of about 120-250 mesh, 30% WC and other components by volume, the cladding material powder elements include Cr 12.3%, Fe 2.19%, Mo3.36%, Co 0.23%, Mn 0.45%, Si 0.12%, C 2.55%, W 30.96%, and the balance is nickel. Mix in a high-speed mixer for 6 hours. Preheat before laser cladding, the preheating temperature is 300℃, and the cladding material is clad on the surface of the substrate. During the cladding process, the laser power is 1500-2000w, the scanning speed of laser cladding is 300-500mm / min, the spot diameter of laser cladding is 2-3mm, and the coating thickness is 1mm.

[0065] The prepared coating was tested. Salt spray corrosion was carried out, and a neutral salt spray test was carried out in a salt spray test chamber for 72 hours; the wear resistance of the coating was tested in a relatively dry environment, using a reciprocating friction tester with a load of 5N, a stroke of 20mm, a frequency of 1Hz, and a time of 1h; the hardness was measured using a hardness tester; the galvanic corrosion performance was measured using a galvanic corrosion equipment, and the specific data was obtained in Table 2.

[0066] Figure 2 For comparison of the cross-section and surface SEM morphology of Example 2-1, on the cross-section, a good metallurgical bond is formed between the coating and the substrate, with a relatively obvious fusion line, and the coating has no defects such as holes and cracks. At the same time, the distribution of WC ceramic particles is relatively uniform, and there is no deposition, agglomeration, etc. It can be seen from the surface morphology that the coating has good forming performance and has no obvious defects such as pores and cracks.

[0067] Figure 4 For the XRD spectrum of comparative example 2-1, the coating contains Fe-Ni compounds, WC, W2C and Cr-Fe compounds, etc. Among them, the peak intensity of the nickel-iron compound is much higher than the peaks of other phases, indicating that the nickel-iron compound mainly exists in the form of intermetallic compounds in the coating, and the nickel-iron compound mainly exists in the form of Fe3Ni2.

[0068] Embodiment 2-2 of the present invention

[0069] The average particle size is about 20-250 mesh, the volume fraction of WC and other components is 10%, and the cladding material powder elements include Cr 6.3%, Fe 3.1%, Mo 2.57%, Co 0.15%, Mn 0.33%, Si0.45%, C 0.63%, W 9.63% by weight, and the balance is nickel.

[0070] The same experimental operation as in Example 2-1 was subsequently performed. Specific data are shown in Table 2.

[0071] Figure 3 The cross-section and surface SEM morphology of comparative example 2-1 show that the coating and the substrate form a good metallurgical bond on the cross-section, with a relatively obvious fusion line, and the coating has no defects such as holes and cracks. At the same time, the distribution of WC ceramic particles is relatively uniform, without deposition, agglomeration, etc. The surface SEM shows that the coating has good forming performance, and there are no obvious defects such as pores and cracks.

[0072] Figure 5 For comparison of the XRD patterns of Example 2-1, the coatings all contain Fe-Ni compounds, WC, W2C, and Cr-Fe compounds, etc. Among them, the peak intensity of Ni3Fe nickel-iron compound is much higher than the peaks of other phases, indicating that it mainly exists in the coating in the form of intermetallic compounds, and some WC particles are slightly decomposed into secondary carbides W2C at high temperatures.

[0073] Table 1 Comparative Examples 1-n Related Data

[0074]

[0075] Table 2 Related data of comparative example 2-n

[0076]

[0077] It can be seen from the specific data shown in Table 1 and Table 2 that the four groups of comparative examples in Table 1 have poor wear resistance and corrosion resistance because no alloy coating is formed at the weld joint, and cannot meet the demand for long-term service in a high-wear and high-corrosion environment. The two groups of embodiments of the present invention in Table 2 adopt nickel-based cladding material coatings at the weld joints with excellent performance. After laser cladding, the hardness and corrosion resistance and wear resistance are greatly improved compared with the substrate. The weld joints clad with the two coatings are not corroded. Among them, the cladding coating with a component ratio of WC of 30wt.% has better hardness, and the service life of the Q345 steel welded joints is greatly extended.

[0078] The present invention adopts a laser welding method with better joint performance to fundamentally reduce the influence of high current, high heat input, and long-time heat input on the performance of the welded joint. In addition, the preferred low laser power and high welding speed process parameters reduce the temperature difference and temperature diffusion time between the weld zone and the heat-affected zone during the welding of the Q345 base material, obtain a more uniform weld transition zone structure, reduce the galvanic corrosion sensitivity of the weld transition zone, and also avoid the problem of local peeling of the coating caused by the uneven bonding force between the surface protective coating and the substrate due to the uneven microstructure of the weld transition zone. In addition, laser cladding technology is adopted at the weld joint, and matching cladding materials are used to evenly and thickly apply the coating and metallurgically combine it with the substrate, thereby enhancing the hardness and corrosion resistance of the wide-area structure of the weld joint and its surroundings. Therefore, the present invention not only reduces the galvanic corrosion tendency of the weld joint itself caused by the uneven microstructure, and improves the corrosion resistance of the weld transition zone; it also reduces the uneven bonding between the coating and the substrate caused by the uneven microstructure, thereby causing local peeling of the coating; the bonding between the coating and the substrate is improved from two aspects: the uniformity of the microstructure in the weld transition zone and the metallurgical bonding of the laser-clad nickel-based coating and the Q345 substrate, and the corrosion and wear resistance of the coating are synergistically improved from two aspects: the optimization of the welding process and the optimization of the coating ratio.

[0079] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0080] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. An alloy coating suitable for low alloy steel, characterized in that: The element composition of the alloy coating includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C0.62%-2.55%, W 9.6%-31% by weight percentage, and the balance is nickel.

2. The alloy coating according to claim 1, characterized in that The alloy coating is made by heat treatment of cladding material powder, and the element composition of the cladding material powder includes Cr6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C 0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

3. The alloy coating according to claim 1, characterized in that The element composition of the low alloy steel includes C 0.16%-0.2%, Si<0.55%, P<0.045%, Mn 1.00%-1.60% by weight, and the balance is iron.

4. A method for preparing an alloy coating suitable for low alloy steel, characterized in that: The steps include: 1) Deoxidation treatment is performed on the surface of the low alloy steel to be treated; 2) Using a laser cladding process to perform laser cladding on the surface of the low alloy steel after oxidation treatment, so as to form an alloy coating as described in any one of claims 1 to 3 on the surface of the low alloy steel.

5. The method for preparing the alloy coating according to claim 4, characterized in that: The process parameters of laser cladding include laser power of 1500-2000W, scanning speed of laser cladding of 300-500mm / min, spot diameter of laser cladding of 2-4mm, and thickness of cladding coating of 1-2mm.

6. The method for preparing the alloy coating according to claim 4, characterized in that: Deoxidation treatment of low alloy steel surfaces includes: Deoxidize the surface of the low alloy steel plate and weld the plate by laser welding; After welding is completed, let the weldment cool to room temperature; Deoxidation treatment is performed on the weld joints of the weldment.

7. The method for preparing an alloy coating according to any one of claims 4 to 6, characterized in that: The element composition of the low alloy steel includes C 0.16%-0.2%, Si<0.55%, P<0.045%, Mn 1.00%-1.60% by weight, and the balance is iron.

8. The method for preparing the alloy coating according to claim 4, characterized in that: The alloy coating is made by heat treatment of cladding material powder, and the element composition of the cladding material powder includes Cr 6.3%-12.3%, Fe<3.1%, Mo<4.3%, Co<1%, Mn<0.5%, Si<0.5%, C0.62%-2.55%, W 9.6%-31%, and the balance is nickel.

9. The method for preparing the alloy coating according to claim 8, characterized in that: The average particle size of the cladding material powder is 120-250 meshes.

10. A low alloy steel welded joint, characterized in that: The alloy coating is formed on its surface by the preparation method as claimed in claim 4.

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