Abstract
Relations between occurrence of vertical cracking defects, solidification structures and solidification patterns, bead shapes and welding conditions were investigated in flat position electron beam welding of heavy section 0.17C steel and 2 1/4 Cr-1 Mo low alloy steel plates. Penetration depths up to 80 mm were investigated. Models of welding phenomena were proposed to explain occurrence of the vertical cracks. It was concluded that, (1) 21/4 Cr-1 Mo steel was more liable to cause vertical cracks than 0.17 C steel. It was possible, however, to obtain a weld bead composed of stable type I (most stable) and type II (stable) solidification structures by selecting a proper welding condition.(2) The proper welding condition should be selected to satisfy the following requirements, (i) slow welding speed (in this experiment 0.2 m/min.)(ii) narrow bead width(iii) formation of a wedge-shaped bead (small value of "bead form factor")Oscillation of the electron beam in the X (in the line of welding) direction was effective to broaden the range of selection of welding conditions.(3) The degree of lag of solidification front was reduced by selecting a slow welding speed and parameters to form a wedge-shaped bead. This reduction of lag seemed to be one of main reasons that prevented the formation of type III (unstable structure with segregation) and type IV (vertical crick) solidification structures.
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