The fusion welded joint is formed by local heating of high temperature heat source. The welded joint consists of weld metal, fusion zone, heat affected zone and base metal.
After melting, the connecting metal and the filler metal cool and solidify at a faster speed. The weld structure is as-cast structure of liquid metal crystallization, with coarse grains, segregation of components and loose structure.
Due to the small welding pool, fast cooling, strict control of chemical composition, low carbon, sulfur and phosphorus, the chemical composition of the weld is adjusted by alloying to make it contain certain alloying elements, and the performance of the weld metal is not serious, which can meet the performance requirements, especially the strength is easy to achieve.
Extended data:
Transition between melting zone and non-melting zone. The chemical composition of the fusion zone is uneven and the structure is coarse, which is often coarse overheated structure or coarse hardened structure. Its performance is often the worst among welded joints. The overheating zone (or quenching zone) in the fusion zone and heat affected zone is the weak part with the worst mechanical properties in the welded joint.
The area where melting and solidification occur in welding is called weld, which is composed of molten base metal and filler metal. In the welding process, due to the influence of heat (but not melting), the area where the metallographic structure and mechanical properties of the base metal change is called the heat affected zone. The fusion zone is the junction of the weld metal and the heat affected zone in the welded joint, and the fusion zone is very narrow, with a width of 0.1~ 0.4 mm.
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