Ynoshin Imai and Hikotar Imai
Using 0.01∼0.05%B added to 3 plain carbon steels (0.2∼0.3%C) and one Mn-steel (0.3%C, 1.5%Mn), several experiments were made and the following results were obtained:
(1) For identification of Iron-Boride(Fe2B) from the cementite, Na2O2 is very useful as etching reagent,in which Iron-Boride colours brown or dark grey, while cementite remains white. (2) No effect of Boron on the A1 and A3 transformation temperatures is observable within the range of Boron-content in the present experiment. (3) The hardenability of Boron-treated steels was estimated by the gradient-quench. (4) From the change of hardness and the behaviour of precipitation of the supersaturated nitride on tempering,it is shown that the rate of precipitation of supersaturated nitride accelerated at the range of 200∼300°C with addition of Boron.
It is considered that marked increase of hardenability by addition of a small amount of Boron is due to the acceleration of precipitation of supersaturated nitride.
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