Welding performance concept of metal materials
The weldability of metal materials refers to the ability of metal materials to obtain excellent welded joints under certain conditions including welding methods, welding materials, welding specifications, and welding structure forms. If a metal can get a good weld with ordinary and simple operation in which welding machine process, it is considered that this metal has good welding performance. The weldability of metal materials generally includes two aspects: process weldability and use weldability.
Process weldability: refers to the ability to obtain excellent, defect-free welds under certain welding process conditions. However, it is not an inherent property of metal, but a qualification based on a certain specific welding method and specific process measures adopted. Therefore, the process weldability of metal materials is closely related to the welding process.
Use weldability: refers to the degree to which the welded joint or the entire structure meets the use performance specified in the product technical conditions. The service performance is determined by the working conditions of the welded structure and the technical requirements put forward in the design, usually including mechanical properties, low temperature toughness, brittle fracture resistance, high temperature creep, fatigue performance, endurance strength, corrosion resistance and wear resistance, etc. . For example, the commonly used S30403, S31603 stainless steel can be used in seaside and other environments, and it has excellent corrosion resistance. 16MnDR, 09MnNiDR low temperature steel also has good low temperature toughness properties.
Influencing factors of welding performance of metal materials
Material factors
Materials include base materials and welding materials. Under the same welding conditions, the main factor that determines the weldability of the base metal is its physical properties and chemical composition.
The physical properties include the melting point, thermal conductivity, linear expansion coefficient, density, heat capacity and other factors of the metal, all of which have an impact on thermal cycling, melting, crystallization, phase change and other processes, thereby affecting weldability. Materials with low thermal conductivity such as stainless steel have a large temperature gradient during welding, high residual stress and large deformation. Moreover, due to the long residence time at high temperature, the grains of the heat-affected zone grow, which is detrimental to the joint performance. The austenitic stainless steel has a large linear expansion coefficient, and the deformation and stress of the joint are more serious.
In terms of chemical composition, carbon is the element that has the greatest impact on chemical properties, which means that the carbon content of the material determines its weldability. Most of the other alloying elements in steel are also not conducive to welding, but their degree of influence is generally much smaller than that of carbon. As the carbon content in steel increases, the hardening tendency increases, while the plasticity decreases, and welding cracks are prone to occur. Generally, the sensitivity of metal materials to cracks during welding and the changes in the mechanical properties of the welded joint area are used as the main indicators for evaluating the weldability of materials. Therefore, the higher the carbon content, the worse the weldability. Low-carbon steel and low-alloy steel with a carbon content of less than 0.25% have excellent plasticity and impact toughness, and the plasticity and impact toughness of welded joints after welding are also very good. There is no need for preheating and post-welding heat treatment during welding, and the welding process is easy to control, so it has good weldability.
In addition, the smelting and rolling state, heat treatment state, and structure state of steel can all affect weldability to varying degrees. Improve the weldability of steel through refining, refining or grain refinement and controlled rolling technology. After the strip steel is welded into a pipe, it can also be directly subjected to online bright solution treatment. Hangao Tech (SEKO Machinery) induction heating bright annealing furnace heat treating machine could improve intergranular stress, reducing the hardness.
Welding materials directly participate in a series of chemical metallurgical reactions in the welding process, which determine the composition, structure, performance and defect formation of the weld metal. If the welding material is improperly selected and does not match the base material, not only the joints that meet the requirements of the use cannot be obtained, but also the generation of defects such as cracks and changes in the structure and performance of the material will be introduced. Therefore, the correct selection of welding materials is an important factor to ensure high-quality welded joints.
