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.