Wear is an important cause of invalidation of industrial equipment, especially with the rapid development of chemical, energy and transportation industries, the invalidation caused by wear is more serious in the fields of the modern chemical industry, cement, and smelting. With the development of surface engineering technology, the surfacing welding technology of large-area composite wear-resistant plate is just for solving the above problems to be popularized and used, our company developed the new technology of surface ARC SURFACING WELDING WEAR-RESISTANT PLATE. It is a new type of wear-resisting composite steel plate made of ordinary steel plate by using a new type of open-arc surfacing welding wear-resisting welding wire.
ADVANTAGES OF COMPOSITE WEAR-RESISTANT STEEL PLATE
HIGH WEAR RESISTANCE
The chemical composition of the wear-resistant layer contains 3-5% carbon and 20-40% chromium, the volume fraction of carbide in the microstructure is more than 50 %, the macro-hardness is HRC55-65, and the micro-hardness of carbide is HV1400-1800. The microhardness is HV800-1200 higher than that of the quartz of sand. The wear resistance of composite steel plate is 5-6 times of heat-treated wear-resistant steel, 5 times of stainless steel, 5-6 times of High Manganese Steel and 11 times of Q345(16Mn). In surfacing welding of wear-resistant plates, a special process method is used to control the direction of carbide growth so that the direction of carbide growth is perpendicular to the direction of abrasive flow, even compared with the casting alloy with the same composition and hardness The wear resistance of the coating is much higher than that of the coating prepared by spray welding and thermal spraying. It is suitable for the dust concentration, not more than 3 Kg/M3 Dust Abrasive wear under the working conditions of air velocity not more than 25M/S.
Good Impact Resistance
The base plate of wear-resistant Composite Steel Plate is made of low carbon steel or low alloy steel, which shows the advantage of Bimetal, the wear-resistant layer can resist the wear of medium, and the base plate can bear the load of the medium, so it has good impact resistance. It can bear the impact and wear under the working condition of high drop hopper in the material conveying system.
The wear-resistant composite steel plate can be cut, leveling, drilling, bending and crimping, made of a flat plate, Arc Plate, cone plate, cylinder, and other shapes. The composite plate can be made into various forms of engineering structures or parts by the way of tailor-welding. The Composite Plate can also be heated and pressed into a complex shape by a mold. The wear-resistant composite steel plate can be fixed on the equipment by means of bolts or welding, which is convenient for replacement and maintenance.
The wear-resistant composite steel plate has a high manufacturing cost, but it can greatly extend the service life of the parts and reduce the maintenance cost and shutdown loss. High Utilization Rate of the equipment means high production efficiency and enterprise economic benefit. Its performance-to-price ratio is about 2-4 times higher than that of ordinary materials. The more the material is treated, the more serious the wear is and the more the running rate is affected, the more obvious the economic benefit is produced by using a wear-resistant composite steel plates.
Selection of base material and wear-resistant welding wire
Chosen of the base material
According to market research and analysis, Q235 steel has better comprehensive properties due to its moderate carbon content compared with other structural steel materials. Strength, plasticity, and weldability are relatively good, so using Q235 carbon structural steel as the base material of the composite wear-resistant plate, it’s chemical composition as shown in Table 1:
Table 1 Q235 mechanical properties and chemical composition (mass fraction)(%)
As the yield strength and tensile strength of the four Q235 sheets of steel are the same, the chemical composition is slightly different. Considering the cost, we choose Q235A as the base material of the composite wear-resistant plate.
SELECTION OF WEAR-RESISTANT WELDING WIRE
Through many many tests, we select the wear-resistant welding wire WED-100 open-arc surfacing welding wire. The chemical composition of the deposited metal is shown in Table 2 The deposited metal is a CR-FE-C type high chromium alloy with a chromium content of 22 ~ 27 and a carbon content of 3.0 ~ 5.0. A Cr7C3 carbide with a volume fraction of more than 50% can be formed in the surfacing layer (as shown in Fig. 1) Carbide is the hardest and most wear-resistant phase in the alloy structure (the microhardness of carbide is HV 1300 ~ 1800) In the course of wear, the pressing and friction of abrasive particles are strongly hindered. At the same time, the eutectic structure and carbides have proper strength combination, which makes the carbides not easy to fall off, which is equivalent to embedding high-hardness particles on the Matrix with certain strength The direction of carbide growth is perpendicular to the plate surface, so the whole surfacing layer has excellent abrasive wear resistance. The average micro-hardness of the surfacing layer can reach 60-63HRC.
Table 2 Chemical composition of deposited metal (%)
Selection Of Process Parameters
According to the working condition of the surfacing layer, mainly the requirement of hardness, and considering the thickness of the base plate, the height of surfacing, and the efficiency of surfacing. After many tests, the optimum process parameters of open-arc surfacing welding wire for different thickness of plate and different thickness of welding layer, such as 4 mm surfacing welding on 8mm Q235 steel plate, are determined as follows: The diameter of welding wire is 2.8 mm, welding current is 300A, welding voltage 30V, welding speed 120mm/Min, welding gun swing 40mm, welding wire diameter 3.2 mm, welding current 320A, welding voltage 32V, welding speed 12mm/Min, welding gun swing 40mm. Because of the difference of welding machine (or welding wire diameter), base material and build-up welding layer thickness, the best welding parameters and specifications will also have great difference.
Before hardfacing welding, the open arc surfacing welding wire is passed through the wire feed wheel and conductive nozzle, a welding torch is connected with positive of the welding power source, the base material is connected with negative of the welding power source. The ARC begins to form between the wire and the base plate and enters the steady welding process. In the course of hardfacing welding, the swing width of welding torch should be more than 4 times of the diameter of welding wire, so as to avoid excessive swing width resulting in excessive penetration on both sides of Weld Bead, excessive swing width resulting in bad forming. Hardfacing process of vulnerable parts, such as conductive nozzle, wire wheel should be replaced in time, otherwise it will lead to wire feeding is not smooth, and break arc. The length of welding wire should be moderate, can not be too long or too short (general 25mm), too long will lead to uneven weld bead, affect the formation of the weld, too short will lead to broken arc, affect the quality of continuous welding and wear-resistant plate.
In the actual production process, in order to improve the welding efficiency, we adopt the technology of double-heads hardfacing welding wear-resistant plates. Using this method and using two surfacing welding machines, at the same time can greatly improve the production efficiency and reduce the cost for the Q235 steel plate of 1500mmX3500mm, when 2.8 mm welding wire is used and 4mm thickness is welded, only 6 to 7 hours are needed. The whole plate can be welded by one person, and the water cooling technology is also used in the welding process. That is to improve the cooling rate, but also improve the wear plate hardness and wear resistance.
Selection of Welding Speed
From view of welding forming, when welding speed is too small, the line energy is too large and more metal is melted, which makes the molten metal flow to both sides of the weld and affects the weld forming at the same time, it is easy to cause the non-fusion defect between edge part and base material. When welding speed is too high, it will make the middle of the surfacing layer concave or the thickness uneven. With the increase of welding current, welding speed also increases slightly. In addition, welding speed also affects the thickness of the surfacing layer. Therefore, in the actual surfacing welding, we should consider various factors to select the welding speed.
RELEASE OF WELDING STRESS IN SURFACING LAYER
Due to the effect of welding thermal stress, there are many cracks on the surface of the cladding steel plate. These cracks can release welding stress and reduce the deformation of the base plate. The cracks in the surfacing layer shall be small, dispersed, disorderly, not deep into the motherboard, and perpendicular to the length of the weld bead. This kind of crack is the result of stress release in the welding process, which helps to improve the toughness of the composite wear-resistant plate and prevent the wear-resistant layer from falling off. In addition, the high chromium wear-resistant hardfacing plate has good machinability, and the fine wire-like stress-releasing cracks on its surface, can avoid the flaking and peeling of the wear-resistant composite steel plate during the processing.
LEVELING OF COMPOSITE STEEL PLATE
The Composite Steel Plate after surfacing welding will have more serious deformation generally, the thinner the base plate, the more serious the deformation. Surfacing welding, in order to prevent the deformation of the base plate, generally in the base plate around the use of a pressure plate or pressure bar compaction. However, under the action of welding thermal stress, the mother plate can produce shrinkage displacement. When the deformation is serious, the shrinkage displacement can reach 5% ~ 8% of the length of the motherboard. When the pressure plate is released after welding, the composite steel plate will produce a warping deformation. After research and experiment, the composite wear-resistant plate can be leveled by the plate bending machine, the deforming wear-resistant plate can be made through the action of the plate bending machine, and the deformation of the base plate can be gradually reduced and finally disappeared through the drawing of the base plate by the Bending Machine. The plate with large size and severe deformation needs to be stretched several times before it can be leveled and its efficiency is slow. With this method, the unevenness of the composite steel plate can not exceed 5mm/M2, and it can meet the requirements of types of equipment and parts such as lining plate, clay groove, hopper, sieve plate, etc.
Hardfacing hardness test
Using Q235 as the base plate, using the same welding wire WED-100 and the same technology, the large area (larger than 4.5 m 2) of surfacing welding layer with different thickness δ2 on the base plate with different thickness δ1 was tested. Samples of each type of hardfacing plate are then tested, and the average surface hardness is shown in Table 3:
|Surface hardness HRC||60.4||60.6||62.1||63.7||61.2||62.4||62.3||63|
Table 3 hardness of wear-resistant plates of various specifications
From the above results, it can be seen that the surface hardness of the wear-resistant plate varies slightly with the thickness of the substrate, the analysis is mainly caused by the detection error, but the hardness increases significantly with the increase of the thickness of the hardfacing layer, when the thickness of the hardfacing layer is more than 4 mm, no matter what the thickness of the substrate, its surface hardness is more than 60HRC, which meets the design requirements of wear-resistant plate and the use requirements of wear-resistant plate.
Compared with other process methods, the process is simple and convenient, the dilution of the surfacing layer is low, the deposition efficiency is high, the whole deformation of the plate is small, and the hardness of the surfacing surface is high strong wear resistance, good reprocessing performance. The wear-resistant plate products produced by this technology are widely used in different industries because of their advanced performance indexes, stable product quality, low production cost, and strong adaptability. Has a strong market competitiveness, has been more and more wear-resistant plate production enterprises to adopt, with good social and economic benefits.
#composite wear-resistant plate #HIGH WEAR RESISTANCE #wear-resistant welding wire #