The effect of carbon content in iron on the stability of γ′ and ε phases in the Lehrer diagram was investigated by the thermodynamic equilibrium calculation using CALPHAD method. The low alloy steels with different carbon content of 0.1 mass%, 0.45 mass% and 1.0 mass% were adopted for gas nitriding, and their nitrided phases were identified. The ε- phase is stabilized at lower nitriding temperature and with lower nitriding potential as the increase of the carbon content, while the γ′-phase is unstabilized there. The phases in the gas nitride layer of the steels showed a good agreement with the calculation result of 0.1%C containing steel. Decarburization during the nitriding may be responsible for the insensitive with carbon content of the steels.

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Laser bending is a forming process exploiting thermal stress introduced by laser scanning, and the process parameters include laser power, beam diameter, scanning speed and repetition number of scans. In this study, AZ31 magnesium alloy sheets were successfully bent by the laser irradiation, irrespective of the smaller temperature gradient originating from their high thermal conductivity, low melting point and low formability, although high laser power and low travelling speed result in the formation of cracks in the upper side of the sheets. It was found, furthermore, that crack-free laser bending is possible if laser absorbent is painted and the bottom side is cooled, because larger temperature gradient between both sides of the sheets can be achieved.

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