DENKI-SEIKO

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95 kinds of alloyed steels which were specially prepared were nitrided using NH₃ gas at 500°C for varying hours of time (25hrs, 50hrs, 100hrs), and also at 525°, 550° and 600° for 50 hours. The influences of the various elements such as Al, Cr, Mo, Ni and C on the properties of the case parts of these hardened specimens were systematically studied, when these elements were alloyed singly and two or three together.
The study was made chiefly by Vicker's hardness tester and a microscope, and the weight increase of the specimens due to the nitridiug was also measured. By X-ray analysis the new hard phase ε' was found in the hardened case of Fe-Al and Fe-Al-Cr alloys or “Nitralloy, ” and the strong distorsion of the space lattice in the Fe-Cr alloys which were nitrided at 500°C for 2 hours was confirmed.
From these results, the mechanism of nitrogen case hardening of steels containing, Al or Cr was discussed, and further it was explained form the structural diagrams of the Fe-Cr-N and the Fe-Al-N alloys.

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