Observation of the Performance of Low Hydrogen Electrodes

Abstract

The superiority of the service performance of the joints welded with low hydrogen electrodes is well proved by various weldability tests. However, this type of electrodes are highly sensitive to the operating condition during the welding process and such sensitivity is limiting or preventing an extensive employment of the low hydrogen electrodes.The authors have made an investigation about the effect of welding procedure in relation with the blow hole which develops in the weldment, and also its effect on the fracture of welded joint, and then reached to the following conclusions.1. The home made low hydrogen electrodes, comparison with imported ones, are far surpassed in the quality for the prevention of blow hole.2. Both home made and imported ones showed only a slight difference in regard to three grades classified under AWS standard, but according to the size of diameter of electrodes the extent of devolopment of blow holes differed very noticeably.3. The extent of the development of blow holes is lowered as the welding current grows higher, but this tendency does not follow the same course when the current became excee dingly high.4. The development of blow holes is noticeable at the start of the bead, but if an arc striking was given prior to the start of the welding, or the tapered end type electrodes. were employed, we discovered, it acted very effectively for the prevention of blow holes.5. When we classified extent of the development of blow holes, according to the grades specified in JIS, and viewing the result of the tension and fatigue tests of the welded joints, it appears that there was hardly any defference between the grades 34 and grades 12. but with the grades 56, the performance of the joint is degraded, yet still it showed about the same record that showed by that of ilmenite type electrodes.6. We made study of the notch toughness of the welded joints stressed under the cyclic load by using the specimens containing artificial notch (V and key-hole notchs), then it was observed that such effect was noticeable in case of sharp notch even under the stress less than fatigue limit, but on the other hand, in case of round notch like the shape of a blow hole the effect was not so highly noticeable.7. Viewing from what we stated above, we may say that when low hydrogen electrodes are employed, it is necessary to limit the development of blow- holes to the minimum extent by carring out the welding under the suitable process, nevertheless, it appears that to limit the extent of the utilization of this type of electrodes which possess highly superior weldability, just simply in fear of the development of blow holes by no means in an adequate measure.