2、 Valve body and welding material analysis
1. Analysis of valve body material composition Carbon steel or low alloy steel is usually used as valve body material of all welded pneumatic ball valve, such as ASTM A105, A694, A350, A516, etc. Its chemical composition has an important impact on the formation of crystal cracks during welding. During welding, impurities such as S and P in the weld will form eutectic with low melting point during crystallization. Among them, sulfur has the greatest impact on the formation of crystal cracks, but its impact is most related to the content of other elements in the steel, such as Mn and S combine to form MnS to remove sulfur, thus inhibiting the harmful effect of S. Mn can also improve the properties, morphology and distribution of sulfide. Therefore, in order to prevent crystal cracks, there are certain requirements for Mn/S value in weld metal. The Mn/sS value is beneficial to prevent crystal cracks, and it is also related to the carbon content. The higher the C content, the higher the Mn/S value is required. The excessive presence of Si, Ni and impurities will also increase the harmful effect of S. Strictly controlling the chemical composition of valve body material procurement and formulating relevant material procurement standards is one of the effective ways to effectively avoid crystal cracks during valve welding.

Effect of solution treatment on the forming of shrink joint