There are three kinds of segregation phenomena in the butt welding machine during the welding process: 1. microsegregation; 2. regional segregation; 3. lamellar segregation. The following editors introduce you:
When the molten pool is crystallized at one time, the crystallized center metal is pure first, and the later crystallized part contains other alloying elements and impurities slightly higher, and the crystallized part, that is, the outer end and leading edge of the crystal, contains other alloying elements and impurities. The phenomenon of uneven chemical composition distribution within a columnar grain and between grains is called microsegregation.
During the primary crystallization of the molten pool, due to the continuous growth and progress of columnar crystals, impurities will be "rushed" to the center of the molten pool, so that the impurity content in the center of the molten pool is more than other parts. This phenomenon is called regional segregation.
The shape of the weld section has a great influence on the distribution of regional segregation. For narrow and deep welds, the boundary of each columnar crystal is at the center of the weld, so there are more impurities in the center of the weld. Such a weld seam is prone to thermal cracking at its center. For wide and shallow welds, impurities accumulate in the upper part of the weld, which has a high resistance to thermal cracking.
During the crystallization of the molten pool, the latent heat of crystallization must be continuously released. When the latent heat of crystallization reaches a certain value, the crystallization of the molten pool will temporarily stop. In the future, with the heat dissipation of the molten pool, the crystallization restarts, forming periodic crystals. With the periodic fluctuation of the impurity concentration in the liquid metal at the leading edge of the crystal, periodic segregation is called layered segregation. Layered segregation concentrates some harmful elements, so defects often appear in layered segregation. Stomata caused by layered segregation.
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