Effects of welding parameters (especially focus position of the beam and welding speed) on occurrence of defects (such as vertical cracks, root cracks and voids) in electron beam welds of heavy section Cr-Mo steel plates were investigated.
Partial penetration welding in flat position, and 40 to 60 mm penetration depth were employed in this study.
It was concluded that,
(1) Correlations are found to exist at welding speed of 20 cm/min. among the bead shapes in cross sections, patterns of solidification ripple lines in vertical sections and tendency of occurrence of welding defects.
These relations are not clear at 50 cm/min, because defects occurred too frequent at this speed.
(2) Quantitative relations exist, at 20 cm/min. welding speed, between lags of solidication ripple lines in vertical sections and tendency of occurrence of welding defects.
Welding defects are less likely to occur, when lag of solidification (C
1 and C
2) is small and solidification proceeds smoothly forward from the top of the bead to the bottom.
(3) It is desirable to select slow welding speed and below the surface focus position a
b≅0.5 to 0.6 at which a wedge shaped bead is obtained to avoid the above mentioned welding defects.
In this case, the spikes become larger and some measures are required to avoid undesirable effects of spikes.
(4) It is found that formation conditions of vertical cracks and voids, which have been discussed in this report, are very close, and differences of the bead shapes and the lags of solidification ripple lines decide whether voids or vertical cracks occur.
It is more exact, in our opinion, to describe the vertical crack discussed in this report, as a shrinkage cavity which takes the form of a vertical crack.
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