Bonding pipe joints, where two or more parts use a combination of welded joints, or refers to two or more parts connected by welding joints, including welds, fusion zone and heat affected zone.

Welded joints zone

After fitting the metal and filler metal melts faster speed Youyi formed after cooling and solidification. Weld from the cast structure of the liquid metal crystals, coarse grains, segregation, the organization is not dense. However, due to the small weld pool, fast cooling, strict control of the chemical composition, carbon, sulfur, phosphorus are low, but also by adjusting the chemical composition of the weld alloying, it contains a certain amount of alloying elements, so the performance of the weld metal not a big problem, meet the performance requirements, particularly strength easy reach.

Fusion zone

Melting zone and a transition portion between the non-melting zone. Chemical composition of fusion zone unevenly thick tissue is often coarse thick hardened tissue or overheating tissue. The performance of the welded joints are often the worst. Fusion zone and the heat affected zone of the overheated zone (or quench zone) is the worst of the mechanical properties of welded joints of the weak parts, will seriously affect the quality of welded joints.

Heat affected zone

Heated high-temperature weld zone microstructure and properties caused by changes in the region. Low-carbon steel heat-affected zone can be divided into overheated areas, and part of the phase transition region normalizing area.

(1) the maximum heating temperature superheat zone area above 1100 ℃, coarse grains, and even overheating tissue, called the superheat region. Ductility and toughness decreased significantly overheated zone, the heat affected zone is the worst part of the mechanical properties.

(2) The maximum heating temperature from normalizing zone area Ac3 to 1100 ℃, the air-cooled welding grains get smaller after normalizing organization called normalizing area. Better mechanical properties of the normalizing zone.

(3) part of the maximum heating temperature phase transition region to region from Ac1 Ac3, only part of the organization phase transition, called partial phase transition area. This area grain uneven performance is also poor. During the installation welding, welding welding method more often. The high temperature heat welded joint is locally heated matrix metal and the filler uniform body of molten metal while solidifying the molten form. Depending on the microstructure and properties of the various parts of welded joints can be divided into three parts.