Comparison of surfacing methods

Search on Baidu: As an economical and rapid process method for modifying material surfaces, surfacing is being increasingly used in the manufacturing and repair of parts across various industrial sectors. To maximize the effectiveness of the surfacing layer, it is desirable that the surfacing method employed result in minimal dilution of the base material, a high deposition rate, and excellent properties of the surfacing layer – in other words, a surfacing technique that is high-quality, efficient, and features a low dilution rate. Basic Information Chinese Name: Cladding Welding Pinyin: duī hàn Zhuyin: ㄉㄨㄟ ㄏㄢˋ Table of Contents 1. Introduction 2. Overview 3. Cold Welding Cladding 4. Application Areas 5. Electroslag Cladding 6. Repair Applications 7. Cladding Methods 8. Arc Cladding Collapse Edit This Section: Introduction Duī hàn is a welding method in which metal is melted using welding or gas welding techniques and then applied to tools or machine parts. It is usually used to repair worn and chipped parts. English: Overlay welding. Fold to view this section’s overview. Fold to see applications. There are many surfacing methods used in production; the dilution rate and deposition rate of several of these methods are shown in the table below. Comparison of folding characteristics, surfacing methods, dilution rate (%), and deposition rate (kg/h): Submerged arc surfacing – single wire: 30–60, 4.5–11.3; multi-wire: 15–25, 11.3–27.2. Series arc surfacing: 10–25, 11.3–15.9. Single-pole surfacing: 10–20, 12–36; multi-pole surfacing: 8–15, 22–68. Plasma arc surfacing with automatic powder feeding: 5–15, 0.5–6.8; manual wire feeding: 5–15, 0.5–3.6; automatic wire feeding: 5–15, 0.5–3.6. Dual-wire surfacing: 5–15, 13–27. Metal inert gas welding: Self-shielded arc welding: 10–40, 0.9–5.4; 15–40, 2.3–11.3. Electroslag welding with a pole: 10–14, 15–75. As can be seen from Table 3, pole-based surfacing methods have a higher deposition rate, while plasma arc surfacing results in a lower dilution rate. Based on this, researchers have further developed advanced pole-based surfacing and plasma arc surfacing techniques that are both efficient and have low dilution rates. Folding. Edit this section: Cold welding and surfacing. The cold welding and surfacing technique utilizes the principle of high-frequency electric spark discharge to perform heatless surfacing on workpieces, thereby repairing surface defects and wear on metal components while preserving their integrity. Additionally, its strengthening capabilities can be employed to enhance the workpiece’s properties, such as wear resistance, heat resistance, and corrosion resistance. Cold welding surfacing equipment enables the repair of metal parts without deformation or annealing, offering high welding strength and wear resistance. Metallographic, tensile, and hardness tests can be conducted, and the metallurgical bonding between the welding material and the base material ensures the strength of the weld. It is commonly used for the repair of pinholes, pores, burrs, flash, dents, scratches, chipped corners, collapsed corners, sand holes, cracks, wear, indentations, manufacturing errors, defects in production, and welding defects, as well as for the strengthening of mechanical surfaces. Folding. Edit this section: Application areas. Folding. Mold manufacturing. Roughening the surface of plastic molds to enhance their aesthetics and service life; surfacing repair of parting lines on plastic molds for helmets; surface hardening of runner cones in aluminum alloy die-casting molds; repair and strengthening of molds with dimensional deviations, wear, scratches, etc. Repair of folded plastic and rubber as well as plastic and rubber machinery components; correction, repair, and maintenance of molds used for rubber and plastic parts when they are out of specification or worn out. Foldable aerospace applications include the repair or restoration of aircraft engine components, turbines, and turboshafts; surface strengthening repairs for rocket nozzles; repair of aircraft skin components; strengthening or repair of satellite casings; local carburizing to enhance titanium alloy parts; local carburizing to strengthen iron-based superalloy parts; application of corrosion-resistant coatings such as Al on the surface of magnesium alloys; patching of local defects in magnesium alloy parts; and local surfacing repairs for nickel-based/cobalt-based superalloy blade components, such as wear on the damping surfaces of blade crowns and blade tips, as well as ablation of guide vanes. Folding manufacturing and repair: In the automotive manufacturing and repair industry, it is used for filling gaps and repairing components such as cams, crankshafts, pistons, cylinders, brake discs, impellers, wheel hubs, clutches, friction plates, and exhaust valves; it is also used to correct defects in the surface welds of vehicle bodies. Repair of electrical components on foldable ships, such as electric cranks, shaft sleeves, bearing shells, and resistors; welding of the connections between the wheels of electric railway locomotives and the track; manufacturing and welding of conductive rollers in electroplating plants, as well as copper and aluminum electrodes for metal oxidation treatment. Folding machinery industry: correcting workpieces with dimensional deviations and repairing machine tool guides, various shafts, cams, hydraulic press plungers, cylinder walls, journal bearings, rolling mills, gears, pulleys, mandrels for spring shaping, plug gauges, ring gauges, various types of rollers, rods, columns, locks, bearings, etc. Folded casting industry: Repair of defects such as sand holes and pores in iron, copper, and aluminum castings, as well as repair of worn aluminum molds. Fold Edit Section​ Electroslag cladding Background: The inner surfaces of hydrogenation reactors, primary synthesis towers in the petrochemical industry, coal liquefaction reactors, as well as thick-walled pressure vessels in nuclear power plants, all require large-area cladding with stainless steel linings that can resist high temperatures and corrosion caused by oxygen and hydrogen sulfide. In the 1970s, SAW technology was widely adopted both domestically and internationally in this field. The width of the strip has also evolved from narrow strips to wide strips of 60mm, 90mm, 120mm, and 150mm. This technology has made significant progress over flux-cored wire submerged arc welding in terms of dilution rate and deposition rate. However, as pressure vessels are becoming increasingly large and operating under higher parameters, there is a growing need for surfacing technologies that are of better quality and greater efficiency. In the early 1970s, Germany was the first to develop the electrode-based electroslag welding technique, which was later further improved by countries such as Japan, the United States, and the former Soviet Union. Thanks to its advantages such as higher production efficiency, lower dilution rate, and good weld morphology compared to electrode-based submerged arc welding, this technique has seen rapid development and wide application both domestically and internationally. A key aspect of foldable content: Electroslag welding with electrodes utilizes the resistive heat of the conductive slag to melt the welding material and the base material; apart from the initial stage, an arc must be generated throughout the entire welding process. To achieve a stable electroslag welding process, there are several key technical aspects: a folded welding power supply. During electroslag welding, the stability of the slag pool has a significant impact on the quality of the weld; voltage fluctuations are the most critical factor affecting the stability of the slag pool. Therefore, it is necessary to minimize voltage fluctuations during the welding process, which requires the use of a DC power supply with constant voltage characteristics. In addition, the power supply should have a low voltage and high current output, high control precision, strong capability to compensate for voltage fluctuations in the power network, and reliable protection features. The rated current of the power supply varies depending on the bandwidth used; generally, for a 60mm×0.5mm strip, the rated current is 1500A, 2000A for 90mm×0.5mm, and 2500A for 120mm×0.5mm. Folded flux. Another necessary condition for achieving a stable electroslag process is that the flux must have good electrical conductivity. The conductivity of electroslag surfacing fluxes generally needs to reach 2–3 Ω⁻¹cm⁻¹, which is 4–5 times that of ordinary submerged arc welding fluxes. The electroslag welding fluxes used domestically and internationally are mostly sintered type. The conductivity of the flux depends on the amount of chlorides (such as NaF, CaF2, Na3AIF6, etc.) present in its composition. When the mass fraction of chlorides is less than 40%, the surfacing process is an arc process; within the range of 40% to 50%, it is roughly a combination of arc and electroslag processes; when the chloride content exceeds 50%, a purely electroslag process can be achieved. CaF2 is both a good conductive material and a major slag-forming agent; therefore, it is usually the main component of electroslag surfacing fluxes. In addition to electrical conductivity, flux must also have good surfacing process properties (slag removal, shaping, wettability) and good metallurgical characteristics (low loss of alloying elements, minimal increase in undesirable elements), as well as an appropriate particle size (generally finer than that of SAW flux). To meet the above requirements, there are many types of fluxes that have been used in production, such as the foreign-made FJ-1 (Japan), EST122 (Germany), Sandvik37S (United States); and domestically produced ones like SJ15, SHD202, and so on. Folded magnetic control device: For broad-band electrodes (electrode width greater than 60 mm) used in electroslag surfacing, the magnetic contraction effect causes undercutting in the surfaced layer. As the electrode width increases, the surfacing current also rises, thereby exacerbating the undercutting phenomenon. Therefore, it is necessary to employ an external magnetic field to prevent undercutting from occurring (magnetic control method). As shown in the figure. At the same time, the positions of the magnetic poles must be arranged appropriately, and a suitable magnitude of excitation current must be selected. Both excessively strong and excessively weak external magnetic fields can affect the formation of the surfacing weld bead (Figure 2). The magnetron currents of the two poles should be adjustable separately. For example, for workpieces in a flat welding position that are not preheated, when the strip size is 60mm×0.5mm, the control currents for the north and south poles of the magnetron device are 1.5A and 3.5A respectively; for a strip size of 90mm×0.5mm, these values are 3A and 3.5A respectively. Folding process parameters: Using appropriate surfacing process parameters is an effective way to ensure stability during the electroslag surfacing process and to obtain high-quality welds. The most important process parameters affecting the quality of strip electrode electroslag surfacing are welding voltage, current, and welding speed; followed by factors such as the length of the strip electrode protruding outside, the thickness of the flux layer, the overlap between weld beads, and the welding position. ① Precise control of the welding voltage is of great significance for strip electrode electroslag cladding; when the voltage is too low, there is a tendency for the strip electrode to adhere to the base material. When the voltage is too high, arcing increases significantly, the molten pool becomes unstable, and spatter also increases. It is recommended to choose a welding voltage in the range of 20–30 V. ② The welding current also has a significant impact on the quality of strip electrode electroslag cladding. As the welding current increases, the penetration depth, width, and deposit height of the weld bead all increase as well; the dilution rate decreases slightly. However, if the current is too high, spatter will increase. Different welding currents should be selected for electrodes of varying widths; for example, for electrodes with dimensions of φ75mm×0.4mm, a current in the range of 1000–1300A is preferred. ③ As the welding speed increases, the weld bead width and height decrease, while the penetration depth and dilution rate increase. Excessively high welding speeds can lead to an increased occurrence of arcs. To maintain a certain dilution rate and ensure the properties of the weld overlay, the welding speed is generally controlled at 15–17 cm/min. ④ During slag welding with a stepped process, the inclination of the base material affects the dilution rate and the shape of the weld bead; it is generally recommended to use a horizontal position or a slight upward slope of 1º–2º for welding. ⑤ The recommended values for some other parameters are: the length of the electrode protrusion is 25–35 mm, the thickness of the flux is 25–35 mm, and the overlap amount of the weld bead is 5–10 mm. Applications of folded processes: Pulsed electrode electroslag welding and pulsed electrode submerged arc welding have the following advantages over other methods: 1) High deposition efficiency – at moderate current levels, it is 50% higher than that of submerged arc welding; 2) The penetration depth is shallow and uniform, with a low dilution rate of the base material, which can generally be kept below 10%. This is half that of submerged arc welding, and single-layer welding is sufficient to meet the required performance standards. 3) The surfacing layer is well-formed, with few defects such as slag inclusions; its surface quality is excellent, and the surface unevenness is less than 0.5 mm (greater than 1 mm in submerged arc surfacing). Therefore, no mechanical processing of the surface is required, resulting in material and time savings. 4) In the strip electrode, the burnout of alloying elements and the increase in detrimental elements are minimal, and the plasticity and toughness of the surfacing layer are higher than those of the submerged arc welding process. 5) Due to the narrow carbon diffusion layer and small width of the martensite bands in the weld fusion zone, the properties of the weld fusion zone are superior to those obtained by strip electrode submerged arc surfacing. It is precisely because of the aforementioned advantages of pole-type electroslag cladding that it is widely used both domestically and internationally for large-scale cladding of the inner surfaces in hydrogenation control reactors, thermal wall exchangers in gas engineering, and pressure vessels in nuclear power plant equipment. Due to certain characteristics of electroslag strip cladding, it also has a limited range of applications: Electroslag strip cladding involves a high heat input, so it is generally used for cladding thick-walled workpieces with a thickness of 50–200 mm. The minimum recommended diameter and wall thickness for such workpieces are shown in Table 1. Table 1 Recommended minimum dimensions for electrodes suitable for electrode-slag welding with poles: Minimum diameter, wall thickness, minimum base thickness, minimum curved surface diameter – outer surface, inner surface. 60×0.5, 40, 250, 450; 90×0.5, 80, 500, 900. Fold to edit this section. Repair applications: Wang Ruijun and Huang Xiaoou from the Surface Technology Research Institute of the Chinese Academy of Agricultural Mechanization Sciences. Fold. Abstract: As a fundamental industry of the national economy, the power industry has always been a key focus for development. This paper describes the successful repair of shaft diameter wear defects in the sealing section of a turbine generator rotor using the electric spark surfacing process, which subsequently withstood two and a half years of operational testing. In addition, the repair of the sealing surface of the steam turbine casing and the worn surface of the main circulating shaft in the heat network has also been completed. To date, this process has been used to successfully repair nearly twenty rotors of related types as well as dozens of related components, yielding significant economic and social benefits. Foldable keywords: electric spark surfacing, power plants, wear, repair Foldable introduction: As a fundamental industry in the national economy, the power industry has always been a key focus for development. The past two decades have been the period of fastest development and greatest achievements in China’s power sector history. By 1998, China’s installed power capacity had reached 277,289 MW, with annual electricity generation amounting to 1.1576 trillion kilowatt-hours. There were 68 large-scale thermal power plants in the country (with an installed capacity of over 1,000 MW). As the number of voltage levels increases and the capacity and parameters of individual units keep rising, the maintenance and repair of these units become increasingly complex and important. As the core component of a turbine generator set, the generator rotor features high operating precision and fast speed, but its manufacturing cost is high. Once damaged, it will directly lead to a decrease in the overall output power of the unit or even its complete shutdown. Various repair methods such as thermal spraying, TIG welding, pick and place machines, and brush plating have been employed, but the actual practical results of these repairs were not satisfactory. In this paper, the DZ-1400 type electrical spark surfacing equipment (abbreviated as ESD), developed and produced by the Surface Engineering Technology Institute of the Chinese Academy of Agricultural Mechanization Sciences, was used to carry out on-site repair of the shaft diameters of the worn seal sections of generator rotors. Satisfactory results and successful experience were achieved; nearly twenty worn rotor shaft diameters have been repaired to date, with the longest operating time after repair exceeding two and a half years. Practice has shown that the electric spark surfacing process plays an important role in the repair of power plant components, bringing significant economic and social benefits. Wear of the folding axis diameter: 0.125 mm. Once the shaft diameter becomes worn or scratched, it becomes difficult to maintain balanced oil pressure within the sealing layer; this leads to hydrogen leakage. The sealing layer between the shaft diameter and the bearing is completely compromised, hindering the high-speed rotation of the rotor. In severe cases, this can render the unit inoperable. Figure 1 is a schematic diagram showing the wear of the rotor shaft diameter. 3. Comparison of electric spark surfacing and related processes~ To ensure high-speed operation of the rotor as well as effective cooling, a three-layer sealing system composed of hydrogen, oil, and water is used between the rotor shaft and the bearings. During operation, the clearance between the shaft diameter and the bearing shells is maintained at 0.075. The electric spark surfacing process differs from processes such as welding, spraying, or element infiltration. Simply put, it is a process that lies between those two; it has some characteristics of processes such as welding, while also offering unique advantages such as low heat input and strong metallurgical bonding between the weld layer and the base material. In certain applications with special requirements, the electric spark surfacing process compensates for the shortcomings of other processes (its working principle is described in another paper). Table 1 compares the electric spark surfacing process with other processes. Fold test results ⒊1 Sample preparation: Using a common material corresponding to the rotor shaft diameter of 50mm×10mm, 35CrMoA was selected as the base material for the sample. An Inconel superalloy rod with dimensions of 25mm×6.0mm was used as the surfacing electrode; its chemical composition is shown in Table 2. ⒊The selection of the 2 surfacing electrode materials is based on the factory’s requirements: the surfacing layer should have the same hardness as the base material, and it must possess self-lubricating and self-polishing properties, resistance to cavitation, as well as a high alloy content. Turning method, brush plating method, spark surfacing method. Advantages: 1. High machining precision; 1. Suitable for on-site processing; 2. Low cost; 1. Maintains the original design dimensions; 1. Suitable for on-site processing; 2. High efficiency; 1. On-site construction; 2. Short cycle time; 3. Maintains original dimensions; 4. High bonding strength; 5. Minimal residual stress. Disadvantages: 1. Reduction in shaft diameter; 2. Need to re-fit bearings, poor part interchangeability. ⒊ Long cycle time, high costs, and difficulties in on-site processing. 1. Low bonding strength. 2. Limited coating thickness. 3. The copper coating has poor wear resistance and is prone to galvanic corrosion. ⒈The interlayer porosity of the patches is high; 2. The bonding strength is low – resulting in lower efficiency. Table 2: Composition of surfacing electrodes: Ni, Cr, Fe, Mo, Mn, Si, Other – 70, 14, 4.5, —, 7.8, 0.5. Bar 2. Experimental analysis: Oxides on the surface of the specimens were removed using sandpaper and copper wire brushes; thereafter, any oil or grease on the surface was cleaned off using a acetone solution. Securely connect the specimen substrate to the ground wire of the spark welding machine, then perform surfacing on the specimen surface; the surfacing thickness should be 1 mm. 3000), it can be seen that: after electric spark surfacing, the cross-section of the surfaced layer is obtained using wire cutting, and metallographic specimens are prepared. Figure 5 is a metallographic cross-sectional photo of the surfacing layer: (1) The surfacing layer has no welding defects such as pores, oxide inclusions, or cracks. ⑵The grains in the surfacing layer and the base metal transition layer are fine, with no tendency to grow. ⑶The microstructure of the surfacing layer consists of extremely fine columnar grains, indicating that this layer possesses good corrosion and wear resistance. |Surfacing layer | Substrate | Through the measurement of the microhardness of the substrate, it can be seen that the average hardness of the surfacing layer and the heat-affected zone is HV220, which is very close to the hardness of the substrate. T heat-affected zone Tm. This not only demonstrates that electric spark surfacing can produce a surfacing layer with good metallurgical bonding to the base material, but also shows that the heat-affected zone resulting from surfacing is extremely narrow, and the residual welding stresses are negligible. Figure 6 shows the map of the surfacing layer; Figure 5 presents the energy spectrum analysis of the Ni and Cr elements in the surfacing layer. Measurements indicate that the thickness of the heat-affected zone resulting from electric spark surfacing is only 10.3. As shown in Figure m), the hardness of the surfacing layer is consistent with that of the base material. The above analysis results meet the requirements of the power plant regarding the repair of the motor rotor shaft diameter. Figures 7 and 8 show the diameter of the repaired generator rotor shaft. Tests have shown that when Inconel alloy is cladded using the electric spark cladding process, a metallurgical bond is formed between the cladding layer and the base material, with no welding defects. The heat-affected zone after welding is extremely narrow; when the cladding layer reaches 1 mm, the heat-affected zone is only 0.01 mm. In the past two years, the electric spark deposition cladding process has been used to successfully address the issues of repair and surface strengthening of critical components in power plants, such as the repair of erosion on the sealing surfaces of turbine cylinders and the repair of worn surfaces on the shafts of heat network circulation pumps. Figures 9 and 10 are the working photos of the repairs carried out using the electric spark surfacing process, respectively. Folding conclusions 1. The electric spark surfacing layer is metallurgically bonded to the base metal; the heat-affected zone of the surfacing is extremely narrow, and residual stresses are negligible. ⒉ The electrical spark surfacing process can be used to repair damaged critical components in power plants; it allows for operation online and is a simple process. Minimal machining is required after patch welding, reducing downtime. ⒊ The electric spark surfacing process holds broad application prospects in power plants, offering significant economic and social benefits. References: Electric Power Reliability Management Center, Handbook of Large-Scale Power Plants, 1998; Perspectives on Welding Technologies in Power Plants, Collection of Papers Presented at the 60th Anniversary Academic Conference of the Chinese Society for Electrical Engineering; Williams A.D., Humphries J.L., Selected Papers from the 15th International Thermal Spraying Conference (ITSC’98). Cladding Methods: The Mianxie Xing Cement Plant used manual arc welding to clad the rolls of its double-roll crushers, achieving a service life of 10 months and the ability to crush 150,000 tons of clinker. The key points for surfacing welding are as follows: (1) Selection of electrodes: D-65, D-667, and 506 electrodes should be used. Before surfacing welding, these electrodes must be dried according to the instructions provided, and then stored in an insulated box for later use. (Using welding material of grade 506 will cause severe spalling.) The material to be used for surfacing as a base layer should be a welding material of grade 100S-G or higher. (2) Roller surface treatment: Roller surface repair can be carried out through two methods – local direct welding repairs or complete removal of the surface followed by overall welding repairs; in other words, it involves two separate processes. For uneven wear along the roll width, as well as uneven wear caused by patterns and hard particles, and overall wear of the roll surface, local repair methods involving direct welding can be employed. After 5–6 such direct weldings, the base material is subjected to repeated high compressive stresses, causing the welding microcracks to continue expanding; this results in the formation of a fatigue layer of a certain thickness on the surface of the grinding roll. At this point, if wear-resistant repair welding rods are used for further welding, interlayer delamination is likely to occur. Therefore, it is necessary to thoroughly remove the fatigue layer from the roll surface before applying a wear-resistant layer. Xiexing Cement Plant repairs the roller surface by completely removing it and then welding it back in place. Whether through direct welding or by removing the entire section and then welding it back, the roundness error of the grinding rollers as well as the diameter difference between the two rollers must not be excessive; otherwise, it will cause horizontal vibration in the roller press and an increased uneven load on the grinding rollers. To remove the fatigue layer from the roller surface, carbon arc gouging can be used; the fatigue layer must be completely removed so that the base material of the roller is exposed. Before surfacing, the electrode should be dried in accordance with the electrode usage instructions, the workpiece should be preheated, and slow cooling should be applied after welding. ⑶A DC welding machine with a power of 10 kVA or more, or an AC welding machine with a power of 20 kVA or more, should be selected. When using a DC welder, it must be connected in reverse (with the electrode connected to the positive pole). During surfacing, an AC welding machine is required to have an no-load voltage of ≥70V, with the current should be kept around 200A. If the no-load voltage is below 70V, the current should be increased until the electrode and the base material are fully fused. The ratio of weld bead width to height should be 3:1. Only in this way can it truly bond firmly with the base material, forming the desired wear-resistant structure. ⑷Welding sequence and thickness: After preheating the roll surface, 1–3 layers should be welded using 506 welding rod first in order to round out the roll. Then, several layers of D-667 are weld-on evenly to achieve the desired thickness. After the D-667 weld layer has been deposited, another layer of D-65 is applied, with a deposition thickness of 3–5 mm; after the D-65 weld layer is in place, another layer of D-65 is used to create a lattice pattern. (The occurrence of roll surface wear requires both the pressure necessary to crush the material and relative sliding. The pressure is determined by the properties of the material and is usually difficult to change. It is easier to reduce the relative sliding between the material and the roller surface during extrusion by using patterns on the roller surface. The herringbone pattern used in early domestic applications could prevent the circumferential sliding of the material, but it did not restrict its axial sliding during the extrusion process; especially when extruding materials with small particles, wear was more severe. In comparison, a roller surface with a diamond pattern and hard particles in the middle exhibits the best wear resistance. ) The side length of the diamond-patterned design is 4–5 cm, the width of the weld seam is about 1 cm, and the height is around 4 mm. The thickness of each wear-resistant layer should be kept as uniform as possible, so that the extrusion roller remains circular throughout its use. ⑸During surfacing, three shifts are required, with no downtime for the workers while the welding process continues, so as to maintain a high temperature in the welded part for an extended period. Foldable edit section: Principle of arc surfacing. The plasma arc surfacing technology for wear-resistant materials makes use of the high temperature and high current density characteristics of plasma arcs. High-hardness particles are evenly brazed into the surfacing layer metal, with little to no melting of these particles, thereby forming a composite surfacing layer. This composite layer is composed of two or more different materials that possess distinct properties on a macroscopic scale. One type of particle is the carbide-based hard particle that provides the main wear resistance in the surfacing layer; such particles typically include cast tungsten carbide, chromium carbide, boron carbide, and sintered tungsten carbide. In principle, various carbides, borides, and even diamond, which has an even higher hardness, can be used as components of such composite surfacing layers. In industrial applications both domestically and internationally, the hard particles most commonly used in plasma arc surfacing are cast tungsten carbide, which has an eutectic composition and a hardness of 250–300. The other component of the surfacing layer is the base metal, also known as the matrix metal, which serves as the foundation of the surfacing layer. It is generally believed that the bond between the hard particles and the matrix metal is a brazing bond, while the bond between the surfacing layer and the base material is a metallurgical bond. A key advantage of using plasma arc surfacing technology is that it results in a composite surfacing layer with stable and reliable quality. Recent advancements in this technology enable the creation of surfacing layers free from defects such as pores, cracks, carbide degradation, and melting. The carbide particles are evenly distributed within the surfacing layer. Surfaces coated with wear-resistant materials exhibit high wear resistance; under conditions of severe wear, the wear resistance of composite surfacing layers is particularly outstanding, allowing them to extend the service life of surfaces made of iron, cobalt, or nickel-based alloys by several times or even more. These composite surfacing layers also have high bond strength. Since the bond between the surfacing layer and the surface of the workpiece being protected is metallurgical, they can meet very high strength requirements. Compared to composite wear-resistant coatings obtained through thermal spraying, the bond strength of surfacing layers is 3–8 times greater. Composite surfacing layers can also meet certain impact resistance requirements. For example, in limestone crushers used in cement production, the hammers are subjected to significant impact forces during operation, which leads to a short service life when made of high-manganese steel. Coating these hammers with high-carbon, high-chromium alloys may cause the coating to crack and peel off. However, using composite wear-resistant surfacing layers can prevent this problem and significantly improve wear resistance. This technology enables higher levels of automated production, reduces the workload on workers, improves working conditions, and increases productivity.