Abstract
Welding defects such as porosity, spike and solidification crack have sometimes occurred in deep penetration electron beam welds. These defects are attributed to the complicated welding phenomena, i.e. the interaction between electron beam and metal, the molten metal flow and its solidification. In this report, the formation mechanism of a longitudinal crack and the molten metal behavior in electron beam welding have been investigated.The results obtained are as follows.(1) Longitudinal crack sensitive regions could be classified into two types according to the formation mechanism.(2) The longitudinal crack occurred in the high welding speed range was caused by the lack of molten metal at the narrow rear solidification wall.(3) In the low welding speed range, remarcable concave of solidification line in the backward direction of the welding, which means the occurrence of the local delay of the solidification, was recognized for just or upper focussing condition. The longitudinal crack was apt to occur in this delayed portion.(4) The delayed solidification was resulted from remelting or secondary melting effect of the solidified wall by the stagnated molten metal in a beam cavity.
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