Behavior of Hydrogen in Arc Welding (Report 2) : Sources of Hydrogen in a Shielded Metal Arc Welding

概要

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Studies are made to determine the contribution of every source to hydrogen in a shielded arc weld metal. Evaporation of water from electrode coating is found to occur at two stages ; one is the evaporation of moisture at temperatures of up to 200℃ and the other is that of bound water with a peak temperature at 750℃. The latter is more harmful to hydrogen dissolution into weld metal. By assuming that dissolution of hydrogen into arc melting metal obeys Sieverts' law, an equation for distinguishing the effect of humidity in ambient atmosphere from that of moisture absorbed into coating is derived theoretically. Coefficients involved in the equation are then determined experimentally. The following formula is proposed which can predict the diffusible hydrogen content in weld metal, [H]_D, from a material constant related with bound water in coating, A, moisture absorbed into coating, a, and partial vapor pressure in ambient atmosphere, b. [H]_D=(A+12a+0.64b)^<1/2>-1.8 Practical means for controlling the diffusible hydrogen content can be suggested from this formula.
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