What is a welded joint

【Summary Description】 Welded joint What is a welded joint Joints connected by welding are called welded joints. Welded joints include welds, fusion zones and heat affected zones: 1 weld area: joint metal and filler metal melting, and at a faster rate of cooling and solidification after formation. Weld tissue is from the liquid metal crystallization of the cast tissue, coarse grain, composition segregation, tissue is not dense. However, due to the small welding pool, fast cooling, strict chemical composition control, carbon, sulfur, phosphorus are low, but also through the alloy to adjust the chemical composition of the weld, so that it contains a certain amount of alloying elements, therefore, the performance of the weld metal problem is not big, can meet the performance requirements, especially the strength is easy to achieve. 2 Fusion zone: the transition between the melting zone and the non-melting zone. The chemical composition of the fusion zone is uneven, and the organization is coarse, which is often a coarse overheated organization or a coarse hardened organization. Its performance is often the worst in welded joints. The overheating zone (or quenching zone) in the fusion zone and the heat-affected zone is the weakest part of the mechanical properties of the welded joint, will seriously affect the quality of welded joints. 3 heat affected zone: the area where the microstructure and properties are changed by the high temperature heating of the weld zone. The heat affected zone of low carbon steel can be divided into overheating zone, normalizing zone and partial transformation zone. (1) The area above the maximum heating temperature of the overheating zone has coarse grains and even overheated tissue, which is called the overheating zone. The plasticity and toughness of the superheated zone are obviously reduced, which is the worst part of the mechanical properties in the heat affected zone. (2) In the area where the highest heating temperature in the normalizing zone is from Ac3 to ℃, the normalizing structure with fine grains is obtained by air cooling after welding, which is called the normalizing zone. The mechanical properties of the normalizing zone are better. (3) part of the phase change zone the highest heating temperature from Ac1 to Ac3 area, only part of the tissue phase change, called part of the phase change zone. The grain in this area is not uniform and the performance is poor. In the installation of welding, welding welding method is applied more. The welded joint is an uneven body formed by the local heating of the base metal by the high temperature heat source while melting and solidifying with the molten filler metal. According to the different organization and performance of each part, the welded joint can be divided into three parts. As shown in Figure 2-l, The area where melting and solidification occurs in the weld is called the weld, which is composed of molten base metal and filler metal. The area where the matrix metal is heated (but not melted) during welding 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 one hub of the fusion zone is very narrow, with a width of 0.1~0.4mm.

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