jacketed kettleWhy do cracks occur? What are the reasons? Let's take a look at the electric heating sandwich pot and analyze the reasons as follows:

During the production process of this stainless steel sandwich pot equipment, the hemispherical head flaps are formed by cold working without stress relief treatment, resulting in significant residual stress within the flaps. Additionally, the hemispherical head flaps have a high degree of constraint due to their shape during welding. After the molten pool cools down, the metal shrinks, and its external dimensions are fixed and difficult to contract with, resulting in tensile stress perpendicular to the weld seam and heat affected zone.

During the welding process of the sandwich pot, manual arc welding is used to weld the stainless steel inside the pot. The welding rod used is A102, which has a composition similar to that of 1Cr18Ni9TI and can be used as a welding rod for welding between 1Cr18Ni9TI stainless steel plates. Due to the large temperature gradient between the base metal and the fusion zone, as well as between the heat affected zone and the fusion zone during the welding process; As a result, stainless steel is sensitized and heated, and the diffusion rate of carbon to the grain boundary is faster than that of chromium, and it is broken out in the form of carbides (Cr23C6) at the grain boundary. The chromium content in the broken carbides (Cr23C6) is much higher than the average chromium content in the steel. Therefore, in the grain boundary and its adjacent areas (weld and heat affected zone), a chromium depleted zone along the grain boundary is formed due to the aggregation and precipitation of chromium carbides at the grain boundary.