The author studied the weldability of an electrode core, with the intention of determining whether the quality of an electrode could be determined by summing up the weldability of its core and flux. The most important factors of the core weldability seems to be the size of molten-metal drops, stillness of molten-metal pool and melting speed of the core at the welding operation. The author found that there was another important factor apart from the ones already discussed generally, namely chemical constituents such as C, Si, Mn, etc, and the non-metallic inclusions, which seriously affect the core weldabilitY, as a result of investigations of the manufacturing process and trial-making of various cores. It is desirable that the inclusions should be less than 0.01% (analysed by the acid dissolving method) for pure iron and standard mild steel core. Many difficulties are expected in the steel making process, especially under such bad conditions as in our country, but efforts should be made to decrease the inclusions as much as possible even under these conditions for obtaining a core of good quality. Next, the author made some studies on a core containing more Si than the above-mentioned two types, and found the core could not show so good a weldability as the two types. The immediate cause of the bad weldability seems to be existence of CO gas produced when the inclusions are reduced by C included in the core and parent metals at a very high temperature of the welding arc.
In this report, first of all, many small ingots made of Mn-Cr steels and Mn-Cr-Ti steels were prepared by.melting in the Tammann crucible in a high frequency furnace. Then, the measurement of their hardnesses and the estimation of their magnetic properties were made and the following results were obtained. (A) The unstable austenite field in the ternary equilibrium diagram of Fe-Mn-Cr was estimated, especially the location of the boundary line between unstable and stable austenite fields was determined. And the location of the line determined by the authors was not different considerably from the one reported by Hans Legat. (B) An addition of titanium to Mn-Cr Steels displaced the above mentioned boundary line to the lower manganese and chromium content. In other words, the stable austenite field was enlarged with titanium. Next, many kinds of Mn-Cr and Mn-Cr-Ti and other steel rods were manufactured tentatively and coated electrodes were made of these rods. Rectangular special specimens were welded with them. Then, we compared the cracks which occurred in the deposited beads, and measuredthe hardnesses of weld metals and found the following facts. (C) The coated electrode made of the core steel, whose composition existed in the unstab'e austenite fleid, was apt to cause weld metal cracks in welding alloy steels, but the one made of core steel containing more manganese and chromium, whose composition existed in the stable austenite field and at some distance from the boundary line, gave a weld metal in which cracks do not occur. (D) An addition of about one percent of nickel to a Mn-Cr steel core, whose micro-structure was supposed to be an unstable austenite from the contents of manganese and chromium, prevented the occurrence of cracks in the weld metals. From further experiments in this research, we suppose as follows. (E) Judging from the effect of titanium addition on the mechanical properties of Mn-Cr steels and the fact that an addition of manganese to the coating of the unstable austenitic Mn-Cr steel electrode lowers the hardness of the weld metal, an addition of titanium to the core or of manganese to the coating may be able to-prevent the weld metal cracks.