In this investigation the variation of gas content in the electron beam(EB) weld metal for structural high strength steels was made clear, and moreover the effects of welding condition and chemical composition on the occurring characteristics for weld defects were studied by using twenty different structural steels of 40 to 80 kg/mm2 in strength. The remarkable conclusions are as follows:
(1) The oxygen and nitrogen contents in the EB weld metal for high strength steels did not show a distinct variation as compared with those for respective base metal in spite of the change of weld heat input.
(2) The weld defects observed in weld metal are mainly porosity-defects, and they were divided into two main classes, that is, "Root porosity" occurred in the bottom of weld penetration and "A-porosity" in the middle part of weld penetration.
(3) Root porosity tends to be increased with an increase of weld heat input or with a decrease of ab parameter up to ab=0.75. Meanwhile the amount of A-porosity occurred in weld metal is the most in case of ab=1.1 in general.
(4) A-porosity tends to be decreased with an increase of weld heat input and it is increased with an increase of oxygen or nitrogen content in steel.
(5) The allowable limit for oxygen and nitrogen contents in these steels against A-porosity is recommended to be less than 60-70 ppm in case of 15KJ/cm weld heat input, respectively. However the limit is raised with an increase of weld heat input.
