Research materials and methods Armco iron was used as an initial material. Nitrogen content in the samples was determined with the “Leco" method. In order to decarbonise and anneal Armco iron samples that were used in the tests, annealing was conducted in the temperature of 1,200°C in dry hydrogen atmosphere over a period of 30 h. After this process, the samples possessed grain with the average surface of ca. 0.10 mm2, and the magnetic coercion force was 0.30-0.50 Oe (24-40 A/m), 1 Oe = 80 A/m. The magnetic coercion force was measured with the aid of a precise coercion meter manufactured by Foerster company and using a special internal probe (inside the tube) that covered volume below 1 urn3. In order to maintain the continuity of “in situ" investigations, the sample was aged in the coercion meter tube in a special grip, where the required ageing temperature was maintained with the aid of thermostated oil (Fig. 2). The morphology of the precipitations of nitrides after specified ageing times was observed with the JEM 120 electron transmission microscope manufactured by JEOL with accelerating voltage of 120 kV and with the HREM Philips 301 microscope with accelerating voltage of l00 kV. Fig. 1. Coercive force steps in the a[...]
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