The electrolytic polishing method was applied to the surface preparation of the light metal alloys to be spot welded, that is, the test pieces, treated by the electrolytic polishing method were spot-welded. The results were compared with those obtained in the case in which the test pieces were treated by other surface preparation methods.
In the first half of this research, welding tests were made on two high tensile alloy steels with 0.32%C. 2.98%Ni, 1.31%Cr, 0.46% Mo and 0.42%C, 1.18%Mn, 1.60%Cr, 0.26%Mo under con-current heating at various temperatures, i. e., from the martensite formation range to the A1. And the relation between the cracks and the hardness and micro-structure in the zone adjacent to-the weld was surveyed systematically. Thus it was conformed that the formation of cracks in the heat-affected zone could be perfectry avoided by the so-called hot welding. In order to attain this object in a shorter heating time, suitable temperature ranges are to be adopted. Ni-Cr-Mo steel can be successfully welded with about 20 minute holding at 300-C to 400-C after depositing. Hearing to about 650-C may be also suitable but requires a considerably long time. Mn-Cr-Mo steel is to be held at about 650°C to 675°C and about 300°C to 400°C for about 40 and 10 minutes after welding respectively. The above-mentioned phenomena can be explained in the light of the so-called S-curves usually dealt with in physical metallurgy. But in welding a zone immediately adjacent to the weld is heated up to the solidus, and thus the maximum heating temperature is much higher than in the case of usual physical metallurgy. Therefore there may be appreciable differences between the two cases (e.g. incubation periods before transformation begins may be longer in welding). Secondly, to compare with the prevention of the formation of the hardened zone by the so-called hot welding, the post-heating procedure, which tempering the martensite softens the hardened zone induced by welding, was carried out systematically. The last results show that post-heating immediately below the Al can safely and sufficiently soften the hardened zone in a very short time. Namely, compared with the hot welding, the same degree of softening can be obtained with about one-sixtieth time holding in post-heating.
In the case of cast iron welding, it is favorable to use a cast iron rod of preferable chemical composition to promote graphitization of weld metal. And when ledeburite is formed in weld, it is necessary to change it by heating at proper temperature. In this research, determination was intended of the characteristics of cast ast iron welding rod having such chemical composition as to promote graphitization of weld metal. In stead of a usual welding process, cast specimens of various compositions, having been cast in a copper mold as shown in Fig. 2, were used in the experiment. The specimens were 10mm in dia, and 50mm in length. The macrostructure of the rods were examined at the cross section 20mm from the lower end. From the results of the above experiments, the proper chemical composition of rod was determined as shown in Fig. 3. The chemical composition of original cast iron is shown in Table 1 and the amount of alloying material added (pure A' and ferrosilicon) are shown in Table 2. Ledeburile in the cast rod of proper composition was found thoroughly graphitized by heating at 850°-950°C for a few minutes.