Prilipko E. Process of underwater wet flux-cored wire welding with external electromagnetic effect

In this thesis, basing on the results of investigation of physical-metallurgical features of effect of external electromagnetic field on weld pool in flux-cored wire underwater welding, the specialized equipment has been developed and technological recommendations were issued for underwater mechanized welding with external electromagnetic effect, which improve the weld metal quality and widen the technological capabilities of this method of welding at depths of up to 50 m. The efficiency of effect of external electromagnetic field on the process of weld metal degassing was proved. The content of diffusive hydrogen in welds is 2-3 times reduced to concentrations of 11-12 cm3/100 g. Validity of statement about possibility decrease in weld metal susceptibility to pore formation on the basis of theoretical investigations was shown experimentally. At magnetic field intensity of 10-15 mT the total volume of pores in weld section is 5-8 times decreased as compared with the initial conditions, moreover, the amount of large pores of more than 16 m diameter is decreased to a larger extent. The increase in level of strength by 40-50 Mpa and simultaneously in ductility (by 66%, by 33 %) is attained in the range of 10-20 mT values of magnetic inductance. Pilot-industrial samples of inductor and unit of control of external magnetic field were designed and manufactured. Pilot-industrial checking of technological recommendations was made and their efficiency in welding of elements of underwater structures of low-carbon and low-alloy steels was shown providing the level of mechanical properties according to the requirements "Specifications on underwater welding" ANSI/AWS D3.6. Key words: wet underwater welding, external electromagnetic influence, weld metal, gas saturation, pores, structure, mechanical properties.