Explanations are given on the features as well as on the apparatus of the FN process, a new submerged-arc welding process, which authors have developed. Discussions from the merallurgical view-point are are also given on some experimental data that support the unique features of this process. Results are given of the welded joint test in which this process was applied for a mild steel and a 60kg/mm2-level high tensile strength steel (quenched and tempered steel). Test results are summarized as follows : 1. The apparatus of this process can be easily adapted to the conventional submerged-arc welding machine, and the welding procedures of this prccess are as easy as those of conventional proccess. 2. The toughness of welded metal deposited by this process showed a superior value to any other conventional process using fused flux in the market. 3. The cracking resistance of welded metal is very strong. No hot cracking has been observed, which we often experienced in the middle of pear-shaped bead section in the conventional process. This means the welding conditions applicable from the view-point of cracking resistance become broad. It has also been experienced that crater cracks have become remarkably few. 4. The width of softened part in the heat affected zone becomes less than half of that of the coventional process. The fracture at the softened part has not been observed at all in the welded joint tensile test, which has been one of the problems in the welded joint test of the quenched and tempered steel by the conventional processes. 5. It has been found that the width of brittle part in the heat affected zone is smaller and the degree of brittleness is less than that of the conventional processes in the quenched and tempered steel. 6. The rate of deposition in this process can be increased by 30 to 40% in comparison with that of the conventional process, and thus we can save the number of welding layers. 7. One feature of this process is that the width of bead and the height of reinforcement are larger than those of the conventional process although the depth of penetration is smaller. 8. It has also been found that the welding strain in this process is smaller than that of the conventional process. It may be concluded that this process is more economical than the conventional ones.
To study the corrosion resistance of weld heat-affected zone in a type 304 stainless steel the author used synthetic specimens given thermal cycles with, current heating. Zero to twenty thermal cycles were given at various peak temperatures. Then the relationship between the corrosion resistance and the behaviour of carbide was investigated on all of the specimens given thermal cycles. The following results were obtained. (1) In the specimens given thermal cycles at the peak temperatures 650° and 800°C, the susceptibility. for corrosion increased with the number of thermal cycles. (2) In the specimens given thermal cycles at the peak temperatures 650°and 800°C, the corrosion on grain boundaries was observed as a local etching around the carbide particles. (3) In the observation of carbon extraction replica of the specimens given thermal cycles at the peak temperatures 650°and 800°C, carbide particles were observed, precipitating on grain boundaries as isolated dendritic particles. In the specimens given thermal cycles at the peak temperatures 500°, 1000°and 1200°C no carbide particles were observed.
In order to obtain the melting surface of slagcovered welding electrode, strong impact was horizontally exerted upon the welding rod in the course of welding. The molten droplet hanging at the tip of electrode was thrown away, and the resulting convex or concave melting surface during welding was observed and measured. In addition to this, specific melting rate (S.M.R.), and mean diameter of droplet (d50), as defined in the previous paper, were measured with five types of electrode at various welding currents and polarities. The results obtained were as follows. (1) The melting surface of each electrode changes from convex to concave as welding current increases, and the more concave it becomes, the higher is the specific melting rate of the electrode, excluding D4316 type electrode. The changes in melting. surface with current are remarkable in case of D4316, being the highest in S.M.R., and in case of D4313 being, the lowest. (2) The specific melting rate is not affected by the changes in welding current, mean diameter of droplet, or electrode tip pattern. (3) Difference in specific melting rate, d 50 or electrode tip pattern, with the polarity of welding current, is rather small compared with that which. occurs with the flux type of electrode, and there is no definite rule on, the effect. (4) Small indentations always . were observed on the melting surface except pt in the case of very small, current, which might prove direct action of the arc accompanying the indirect action on the bare surface of melting during welding (5) A new mechanism for detachment of droplet from the tip of welding electrode is proposed, . which is based on the rotation of the dorplet around the melting surface of electorode, motivated by the interaction between surface tension of droplet and repulsive force of the arc.