The nitrogen contents of Fe-Cr and Fe-Ni weld metals deposited in the atmosphere of nitrogen, air or nitrogen oxygen gas mixture's were systematically determined. Some of them were compared with the solubility of nitrogen in the alloys concerned. The extent of porosity was also investigated. The main results are summarized as follows: 1. The nitrogen contents were shown as a function of the concentration of chromium or nickel. 2. The nitrogen content of the Fe-Cr weld metals made in a nitrogen atmosphere increases continuously with the chromium content, but in an air atmosphere it exhibits a minimum at about 1 % chromium, thereafter increasing with the chromium content as well as in a nitrogen atmosphere. 3. The enhancement of nitrogen absorption by the coexistence of oxygen with nitrogen in welding atmospheres does not take place in high chromium steel welds. 4. At low contents, nickel scents to increase somewhat the nitrogen content of the Fe-Ni weld metals. And at higher contents it gradually reduces the nitrogen absorption. 5. The blowholes in the weld metals seem to be reduced by increasing the chromium content of the electrode wires.
The authors have studied the mechanism of bead formation, taking note of the discontinuous bead, particularly "humping bead" at high current and high speed welding. Following facts are clarified. 1. In high current and high speed welding, the difference of temperature between the front part and the rear part of the molten pool is much greater than that in ordinary welding and this temperature difference causes strong surface-tension-stream directing from the front to the rear part of the pool resulting in the discontinuity of the bead. 2. The authors have investigated some methods to prevent the formation of the discontinuous bead at high speed welding. The basic conceptions are as follows: a. Gravity control of the stream b. Decrease of temperature difference between the front and the rear part of the molten pool c. Decrease of surface tension of the molten pool These methods aim to repress the strong stream from the front to the rear of the molten pool.For example, by elongating wire extension the arc takes the form of so-called "rotating arc", which heats the molten pool uhconcentratively different from concentrative heating of spray arc and acts to prevent discontinuity of the bead. Fig. 5 shows the critical relation to get continuous bead at high speed welding. This curve is applicable to every diameter of wire. 3. The authors analized "melting efficiency" (see equ. 4) of the bead and clarified the relation between "melting efficiency and bead character". The results show that the welding speed at maximum melting efficiency is the limit to form the continuous bead.
The characteristics of the anode drop were studies through measuring only the arc voltage of the constricted TIG arc burned between tungsten electrode (cathode) and base metal (anode) of various materials of different heat conductivities. To study the cathode drop, we estimated the temperature distribution along the electrode by measuring the radiation energy from the pure and 2% thoriated tungsten electrode surface. The following facts were made clear; (1) The anode drop is influenced by the temperature of the anode. It decreases when anode is heated to high temperature. For material of higher thermal conductivity, the anode drop is higher for given current.It decreases as the current increase tending to zero. (2) When the cathode is heated high by some other method (Joule's heating), the cathode drop decreases to low value and results in a negative cathode power. (3) Cathode drop is affected by the work function of the substance added to the cathode. The amount of the change of cathode drop predominates over the amount of the change of work function. Therefore the cathode power is affected remarkably by a small change of work function of material added to cathode.
Of the metallurgical factors influencing the notch toughness of submerged-arc weld heat-affected zone, study was made on the effect of pre-treatment of base metal on notch toughness of coarse grained heat-affected zone, especially for steel containing strong carbide or nitride forming elements. Also the effect of cooling rate and microstructure on the notch toughness of duplicated weld heat-affected zone was investigated with maximum heating temperature 1350°C. Notch toughness of duplicated weld heat-affected zone in solution-treated steel is lower in general. In steels containing niobium, vanadium and titanium, notch toughness of duplicated weld heat-affected zone is higher in rapidly cooled cycles, when the base metal is normalized or quenched, both followed by spheroidizing treatment. Austenite grain size in heat-affected zone is smaller, comparing to that of steel free from such elements. However, the effect was hardly observed in duplicated weld heat-affected zone cooled with slower rate of cooling, 7°C/sec at 540°C. In ferritic steels such as Steel AtoH, slower the cooling rate of duplicated weld heat-affected zone, the lower the notch toughness greatly. While low alloy high tensile steel such as Steel ItoL, cooling rate dependency of notch toughness is smaller, i.e., low alloy high strength steel with higher hardenability has superior notch toughness in weld heat-affected zone in case of large heat input welding. According to the results for quenched and tempered Steel I highest notch toughness is obtained, when the weld heat-affected zone is cooled, keeping up with the Cf' time of CCT diagram. Especially the peak of notch toughness is brought by mixed structure of lower bainite and martensite.