Ustinov A. . Devеlоpment of weldinq material and technoloqy of manual underwater wet weldinq of low alloy steels. .

. The Thesis is devoted to the decision of a problem of decrease of metal cooling speed at underwater wet welding by development of welding materials and the technology, allowing to increase plastic properties and to reduce the cracking susceptibility of metal at using by the covered electrodes for welding low alloy steels, having C.E.? 0,45 % . Subject of research are processes that flow in metal and in welding materials at heating and cooling for underwater wet welding. Object of research are temperature field of base metal, influence of welding parameters and isolation of the heated up surfaces from water on thermal cycle of heat effected zone (HEZ), fusion of coating electrodes and base metal, formation of weld metal and welding slag, influence of cooling rate on property of underwater welded joints from low alloy steels. Research methods include thermal cycle recoding by loop oscillogragh, temperature field study by mathematical simulation with computers use., laboratory test and naturally condition underwater test of welding materials and technology, metallographic analysis, Vickers hardness test and bend test of underwater welded joints. It was defined, that thermal isolation of the heated up surfaces from water reduces cooling rete of HEZ metal more considerably then increase of running energy. . The combined thermal isolation consisting from isolated welding slag and adjoining layers of ciloxane-pitch rubber is developed. The two-layer heavy- coated electrodes are used. The such thermal isolation reduces cooling rete of HEZ metal in an interval temperature 800...500 oC in 1,4...2,0 time. Underwater welded joints get high plastic properties. HEZ metal of low alloy steels, having C.E.? 0,45 % is insusceptibility to the cracking at underwater wet welding by electrodes with low carbon wire. Result of that work ensured the economical effect in Petrozavodsk repair-experimental base of fleet..