Using various mixed gases of CO2-O2, CO2-N2 and N2-H2 systems, gas-shielded metal arc welding AISI Type 304 stainless steel was studied as compared with A or A-O2 shielded metal arc (MIG) of welding. The experimental results were as follows : (1) With reduction of oxidizing property, i.e. decrease of oxygen in CO2-O2 system and increase of nitrogen in CO2-N2 system, manganese and silicon contents of weld metal increased gradually, but molybdenum and nickel contents remained almost constant. Chromium content also was unchangeable above 70% CO2 of CO2-O2 system. (2) Carbon content decreased as increase of oxygen in CO2-O2 system. (3) With increase of hydrogen content in N2-H2 system, manganese, silicon and molybdenum contents increased gradually, chromium content remained unvaried, and nickel content showed a decreasing tendency. (4) A remarkable porosity was recognized in the radiograph of the weld metal obtained using the supplied gas above 60-80% N2 in CO2 -N2 system, but not in that of the weld metal obtained gas containing even 100% O2 in CO2-O2 system. (5) Microscopic cavities were sometimes recognized in the weld metal obtained using N2 _H2 and A-O2 systems. (6) According to the results of corrosion tests of single pass weld metal with Strauss and 10% HF+3% NaF reagents, the corrosion resistance of weld metals by CO2-O2 or CO2 N2 systems up to 30% O2 or N2 is better than or equal to those of weld metals by A or A-O2 arc welding and base metal. (7) In tension tests of joints obtained by CO2, CO2+28% O2 and CO2+30% N2, all specimens broke at base metal, but the joint specimens by A at fusion line. (8) All weld metals by supplied gases described in (7) were always excellent in tensile strength compared with the base metal, but were inferior to the latter in elongasion, reduction of area and corrosion resistance. (9) Intercrystalline-corrosion and intercrystalline-corrosion bend tests showed that the effect of heat treatment or heating cycle was more serious than that of selection of process or shielding gas in welding stainless steel. The intercrystalline-corrosion cracking was sensitized by annealing at 600°C, decreased remarkably by that at 950°C and was prevented completely by solution treatment at 1050°C. (10) When the CO2 N2 system was adopted, the nitrogen content of weld metal increased and the amount of ferrite of weld metal decreased with addition of nitrogen in supplied gas.
In this paper, we investigated the all position welding process by CO2 gas arc welding and a new multiple-electrodes automatic arc welding process which coupled CO2 gas arc welding with Submerged arc welding. The former intends to apply automatic arc welding to all positions of fillet and butt weld for welding construction, and the latter does to form welds equal to base metal by controlling deposited metal metallurgically on the process of welding for high notch toughness quenched and tempered steel, and moreover of improvement and high efficiency of workability of welding.
A physico-chemical study has been made on the chemical reactions between slags and metals in the welding processes by five series of electrodes containing Ni, Cr, Mo, W and V in the coatings as alloying elements, and the following results were obtained. (1) Equilibrium index K'Ni is independent of slag-basicity BL and the relation between K'Ni and BL is represented by the following equation; log K'Ni (Ni Addition)=-2.586 (2) K'Cr decreases with increasing BL and the relation between K'cr and BL is represented by the following equation; log K'cr (Cr Addition)=-0.08OBL-2.903 (3) K'Mo, K'W and K'v increase with increasing BL and the relations between the equilibrium indexes and BL are represented by the following equations, respectively; log K'Mo (Mo Addition)=+0.262BL-3.111 log K'W (W Addition)=+0.277BL-2.532 log K'V (V Addition)=+0.218BL-1.427 (4) The activity coefficients yMmon of various oxides in weld slags are represented by the following equations; where yMmOn=1, when BL→0; log yNiO=0 log yCr2O3=+0.080BL log yMoO2=-0.262BL log yWO2=-0.277BL log yV2O3=-0.218BL (5)The feasibility of the oxidization which is effected by FeO in slag against the elements in liquid steel during welding is approximately analogous to that of the oxidization by oxygen gas against the elements in pure state. (6)The values of a log yMmOn/∂BL increase with decreasing values of 2Z/R2 ; where Z is the valency of a cation, and R is the summation of the radii of the cation and an oxygen ion.
In the previous papers (1) (2), fatigue strength was investigated on butt weld joint containing a notch, in case where this notch line was perpendicular or parallel to loading direction. This paper deals with butt welded specimen containing an oblique notch line in order to study the combined effect of normal and shear stresses on fatigue fracture. As the result, a reasonable, stress criterion could be proposed for specimens used.