Abstract: There is provided a robot device including: a head portion coupled to a trunk; four leg portions on a front left, a front right, a rear left, and a rear right coupled to the trunk; a first indirect portion that tilts the head portion left and right; and a second joint portion that rotates, with respect to the trunk, one of the leg portions on the rear left and the rear right to a front side, and the other to a rear side. It is possible to faithfully reproduce the movement of the four-legged animal by providing the first joint portion and the second joint portion.

Abstract: In a first process of a method of gas carburizing, a steel treatment object in a carburizing atmosphere containing carburizing gas is heated to an initial set temperature which is not higher than a peritectic point at which ? iron and a liquid phase transform into ? iron and not less than a eutectic point at which the liquid phase transforms into ? iron and cementite, such that the surface carbon concentration thereof does not exceed a solid solubility limit. In a second process following the first process, the carburizing temperature is gradually decreased from the initial set temperature such that the surface carbon concentration of the treatment object increases without exceeding the solid solubility limit, and such that the carburized depth of the treatment object increases.

Abstract: In a first process of a method of gas carburizing, a steel treatment object in a carburizing atmosphere containing carburizing gas is heated to an initial set temperature which is not higher than a peritectic point at which ? iron and a liquid phase transform into ? iron and not less than a eutectic point at which the liquid phase transforms into ? iron and cementite, such that the surface carbon concentration thereof does not exceed a solid solubility limit. In a second process following the first process, the carburizing temperature is gradually decreased from the initial set temperature such that the surface carbon concentration of the treatment object increases without exceeding the solid solubility limit, and such that the carburized depth of the treatment object increases.