There has been adoped in our industries the Unionmelt Walding Process, as a submerged arc Walding, which has two special phenomena and problems to be solved. One is porosity on bead and the other is sulphur cracks grown from Sulphur Bands. These two defectal, we consider, occur mainly, by hydrogen gas, which generates from the dissociation of a bit of moisture contained in flux, caused by arc. 1) When the absorbed hydrogen in deposited metal is more than its solubility limit of solid metal at

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... lting point and its speed of solidification is fairly faster, porosity on bead is formed. 2) When deposited metal comes to have hydrogen in super saturation, Sulphur cracks are easily to start from sulphur band which involved sulphide of low melting point used to be observed in rimmed steel plates. 3) Intergranular crack in welding bead of killed steel plates is as like as one in ice flower structure.