Weldability concept Paste silver solderability is an indication of the material's adaptability to the welding process. It is used to measure the ease with which a material can obtain a good joint under certain welding conditions and whether the joint can operate reliably under the conditions of use. Weldability includes both process weldability and weldability. Process weldability refers to the ability to obtain excellent, dense, defect-free welded joints under certain welding process conditions. It is not inherent in the properties of the metal itself, but is based on a soldering method of the creamy silver solder and the specific process measures employed. Therefore, the process weldability of metal materials is closely related to the welding process. For fusion welding, it is generally necessary to undergo a heat transfer process and a metallurgical reaction process, and thus the process weldability can be classified into "heat weldability" and "metallurgical weldability". Thermal weldability refers to the degree of influence of welding thermal cycle on the microstructure performance and defects of the heat affected zone. Used to assess the sensitivity of the metal being soldered to heat, such as crystal growth, changes in tissue properties, etc. It is mainly related to the material to be welded and the welding process. Metallurgical weldability refers to the degree of influence of physical and chemical changes on weld performance and defects under certain metallurgical process conditions. It includes the effects of oxidation, reduction, nitridation, evaporation, hydrogen, oxygen, and nitrogen dissolution of alloying elements on the formation of pores, inclusions, cracks, etc., to assess the sensitivity of the material to be metallurgical defects. The use of creamy silver solderability refers to the extent to which the welded joint or the entire structure satisfies the performance specifications specified in the product specifications. The performance of use depends on the working conditions of the welded structure and the technical requirements set forth in the design. It usually includes conventional mechanical properties, low temperature toughness, brittle fracture resistance, high temperature creep, fatigue properties, durability, corrosion resistance and wear resistance. In theory, any two metals or alloys that can form a solid solution or a eutectic with each other in a molten state can be welded in principle. That is to say, it has the so-called principle weldability, also called physical weldability. However, this principle of weldability only provides a theoretical basis for the material to achieve welding, and does not mean that the material can be obtained with any welding method, and can obtain high-quality welded joints that meet the performance requirements. The same metals or alloys have the principle of weldability, but their weldability under different welding process conditions shows great differences. For example, when oxy-acetylene flame welding is used between aluminum alloy 2A16, cracks or severely reduced strength and plasticity are liable to occur, and it is difficult to obtain a high-quality welded joint. However, when using argon arc welding, the effect is very good. It shows that the adaptability of 2A16 aluminum alloy to gas welding is poor, and the adaptability to argon arc welding is better. Therefore, the weldability of metallic materials is not only related to the inherent properties of the material itself, but also to many welding process conditions. The same material has different weldability under different welding process conditions. Moreover, with the development and improvement of new welding methods, welding materials or welding processes, some metal materials with poor weldability will also become materials with good weldability. 1.1.2 Factors affecting weldability Weldability is a process property of metallic materials. In addition to the nature of the material itself, it is also affected by process conditions, structural conditions and conditions of use. (1) Paste silver solder material factor Materials include base metals and solder materials. Under the same welding conditions, the main factor determining the weldability of the base metal is its physical and chemical properties. Physical properties, such as the melting point, thermal conductivity, linear expansion coefficient, density, heat capacity and other factors of the metal, have an effect on the processes of thermal cycling, melting, crystallization, phase transformation, etc., thereby affecting the weldability. Pure copper has high thermal conductivity, heat loss during welding is rapid, the temperature rise is wide, the groove is not easy to melt, and it needs to be heated more strongly during welding. If the heat source power is insufficient, a defect of insufficient penetration will occur. For materials with high thermal conductivity such as copper and aluminum, the molten pool crystallizes quickly and is prone to generate pores. Titanium, stainless steel and other materials with low thermal conductivity have large temperature gradient during welding, high residual stress and large deformation. Moreover, due to the long residence time of the high temperature, the grain growth in the heat-affected zone is unfavorable to the joint performance. Aluminum and austenitic stainless steel have large linear expansion coefficients and joint deformation and stress. The density of aluminum and its alloys is small. When welding, bubbles and non-metallic inclusions in the molten pool are not easy to float and escape, and pores and slag are left in the weld. In terms of chemical properties, it mainly depends on the affinity of metal and oxygen. Such as aluminum, titanium and their alloys are very chemically active. It is easily oxidized under high temperature welding. Some metals are sensitive to gases such as hydrogen and nitrogen. When welding, they must be reliably protected, such as inert gas shielded or vacuum welded. Otherwise welding is difficult to achieve. If it is a dissimilar metal soldering, only the metal whose physical and chemical properties and crystal structure are close to each other is easier to achieve soldering. For the welding of steel, the main factor affecting the weldability is the chemical composition contained. The most influential elements are carbon, sulfur, phosphorus, hydrogen, oxygen and nitrogen, which are prone to defects in the welding process and reduce the performance of the joint. Other alloying elements such as manganese, silicon, chromium, nickel, aluminum, titanium, vanadium, niobium, copper, boron, etc. all increase the hardening tendency and crack sensitivity of the welded joint to varying degrees. Therefore, the weldability of the steel always deteriorates as the carbon content and the alloying element content increase. In addition, the smelting and rolling state, the heat treatment state, and the state of the steel of the steel affect the weldability to varying degrees. Therefore, in recent years, various CF steels (anti-cracking steel), Z-direction steel (anti-layered tearing steel), TMCP steel (controlled rolling steel), etc. have been developed and developed, which are refined or refined by refining, or refining grains and controlled rolling. Processes and other means to improve the weldability of steel. The welding material directly participates in a series of chemical metallurgical reactions in the welding process, which determines the composition, structure and properties of the weld metal. And the formation of defects. If the welding material is selected improperly, it does not match the base metal. Not only can the joint that meets the requirements for use be obtained, but also defects such as cracks and changes in the structural properties can be caused. Therefore, the correct selection of welding materials is also an important metallurgical condition for obtaining high quality welded joints. (2) Paste silver solder process factors Process factors include welding methods, welding process parameters, welding sequence, preheating, post-heating, and post-weld heat treatment. The welding method has a great influence on the weldability, mainly in the two aspects of heat source characteristics and protection conditions. Different welding methods have great differences in heat source, power density, maximum heating temperature and the like. Metals welded under different heat sources will exhibit different weldability. For example, the electroslag welding power is very large, but the energy density is very low, the maximum heating temperature is not high, the heating is slow during welding, and the high temperature residence time is long. The grain in the heat-affected zone is coarsened and the impact toughness is significantly reduced. It must be treated by normalizing to improve. In contrast, electron beam welding, laser welding and other methods have little power, but the energy density is high and the heating is rapid. The high temperature residence time is short, the heat affected zone is narrow, and there is no danger of grain growth. Adjusting the welding process parameters, taking preheating multi-layer welding and controlling the interlayer temperature and other process measures, can adjust and control the welding thermal cycle, which can change the weldability of the metal. For example, when welding some high-strength steels with a tendency to harden, the material itself has a certain cold cracking sensitivity. When the process is not properly selected, the welded joint may produce cold cracks or reduce the plasticity and toughness of the joint. If you choose the right filler material, reasonable welding heat cycle, and take pre-weld preheating or post-weld heat treatment. It is entirely possible to obtain a welded joint that has no crack defects and meets the performance requirements. (3) Structural factors Mainly refers to the design of the welded structure and welded joints, such as the shape, size, thickness, joint groove form, weld arrangement and its cross-sectional shape and other factors on the weldability. Its effects are mainly manifested in the heat transfer and the state of force. Different plate thicknesses, different joint forms or groove shapes have different heat transfer directions and heat transfer speeds, which affect the crystal orientation and grain growth of the molten pool. The shape of the structure, the thickness of the plate and the arrangement of the welds determine the stiffness and restraint of the joint and affect the stress state of the joint. Poor crystal morphology, severe stress concentration and excessive welding stress are the basic conditions for forming weld cracks. It is an important measure to improve the weldability in the design to reduce the rigidity of the joint, reduce the cross weld, avoid the excessive density of the weld and reduce the various factors causing the stress concentration. (4) Conditions of use Refers to the working temperature, load conditions and working medium during the service of the welded structure. These working environments and operating conditions require that the welded structure have corresponding performance properties. For example, welded structures operating at low temperatures must have brittle fracture resistance; structures operating at high temperatures must have creep resistance; structures operating under alternating load have good fatigue resistance; in acids, bases or salts Welded containers for media work should have high corrosion resistance and so on. In short, the harsher the conditions of use, the higher the quality requirements for welded joints, and the less stringent the weldability of the material. 1.1.3 Research methods for metal weldability Welding engineers often encounter new materials, new structures or new processes. Before the formal production, it is usually necessary to carry out the welding research work to ensure that the new materials, structures or processes are used to obtain high quality welded joints. The basic method of the study is to analyze the post-test, that is, to make the necessary weldability test based on the theoretical analysis of weldability. Weldability analysis can avoid the blindness of the test, and the weldability test can verify the results of the theoretical analysis. (1) Weldability analysis Weldability analysis is to use the theoretical knowledge and practical experience of modern welding science and technology to make judgments or predictions about the difficulty of welding metal materials, estimate the technical problems that may occur in the welding process, analyze the causes of problems and find solutions to problems. The usual analysis is to examine the adaptability of the material to welding from the two aspects of process weldability and weldability. The former is to solve the problem that the material can not be welded, and the latter is to solve the problem that can not be used after welding. The power transmission line steel poles are mainly used in 10KV, 35KV, 110KV and 220KV transmission lines. Power Transmission Steel Pole,Steel Transmission Pole,Steel Distribution Poles,Power Transmission Steel Poles Jiangsu Baojuhe Science and Technology Co.,Ltd. , https://www.galvanizedsteelpole.com