Kiyokazu Ogawa, and Eiichi Takeuchi
The treatment of carbo-nitriding are generally performed at a high temperature over the transformation point, but in our experiment we investigated the wearing of steel treated at a low temperature below Al point. As related to the previous reports, the steel of test pieces, carbo-nitriding salt, and wearing condition were the same as before, and the sliding wear, using lublicant, of steel which was treated for 20 min, 40 min, and 60 min at the temperatures 700°, 650° and 600°, respectively, were per-formed. The results of experiment are as follows: the steel treated at low temperature below the transformation point has superior wearing resistance compared with that treated at high temperature. Next, we performed various experiments in order to make clear the reason for this. (i) Treating carbo-nitriding at low temperature,nitrogen acts on steel actively, so we experimented by dibutyl adipate, which does not act on nitrogen, whether the nitrogen contained in steel acts on the lubricant oil, and changes the orientation of oil on steel surface. We did not recognize its effect. (ii) In the structure of the hardened layer treated at low temperature, globular and fine Fe3C are enclosed by the nitride of low hardness. (iii) The hardened layer, produced by the treatment at low temperature is very thin, but its true hardness is very high. (iv) It can be assumed that the internal stress of steel is small, owing to the low temperature treatment, and the deformation caused by the heat treatment is hardly recognized. Summarizing these results, the wearing resistance of steel treated at low temperature appears to be reliable mainly(ii),(iii),(iv) and we believe that it is the ideal one for the parts of the complicated form and light load wearing.
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