In low chromium-high carbon steels, the magnetic transformation below 200° takes place in two steps, which were previously attributed to existence of two carbides, i. e., cementite and α-double carbide by one of the present writers. By annealing and slow cooling the specimens, the change takes place in one step. This trans-formation temperature in well annealed specimens, gradually decreases, as the chromium content increases. The corrosibility of the carbide existing in low chromium steels by boiling picrate solution gradually decreases, as the chromium content increases. From these facts it is concluded that the chromium dissolves in cementite forming a θ-solid solution, and the α-carbide is not a double carbide. β-carbide previously proposed by one of the present writers is also the θ-phase dissolving much chromium and not a double carbide.
The corrosibility of carbides by several etching reagents, and the X-ray spectrum of carbides in many alloys of this system were investigated. In this system there exist two other carbides, η-and ε-phases, besides θ-phase, above described. The η-and ε-phases are solid solutions dissolving iron in trigonal and cubic carbides, Cr
7C
3 and Cr
4C, respe-ctively and not double carbide, confirming the view of Westgren, etc.
From these results a constitutional diagram at the room temperature showing the fields in which several phases exist was constructed, that of Westgren etc. being somewhat modified.
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