Abstract: The present invention relates to a system for and a method of manufacturing a linear gear (rack gear), in which a forming roll and a guide roll are used to form gear teeth in a sequential manner so as not to require a high load, thereby enabling to easily manufacture the rack gear. A system for manufacturing a rack gear according to the invention includes a forming roll having a convexo-concave portion formed on a part of the surface contacting with a linear bar, a guide roll adapted to roll while facing the forming roll, and at least one support member for supporting the linear bar so as to allow the linear bar to linearly move.

Abstract: A steel having an improved tensile strength includes a first layer formed of an ultra-low carbon steel; and a second layer that is formed in contact with the first layer, includes a first surface opposite to the first layer, is formed of a solid solution obtained by solid-solving nitrogen in the ultra-low carbon steel, and has a structure substantially the same as a structure of the first layer.

Abstract: Provided is a method for nitriding a metal in a salt bath by using a non-cyanide salt and a nitrided metal manufactured using the same. The method includes the steps of: immerging at least one salt selected from the group consisting of KNO3, KNO2, Ca(NO3)2, NaNO3 and NaNO2 into the salt bath; melting the salt by heating and maintaining the molten salt at a predetermined temperature; and submerging the metal in the salt bath. Nitriding in non-cyanide salts, such as potassium nitrate (KNO3), potassium nitrite (KNO2), sodium nitrate (NaNO3), sodium nitrite (NaNO2), calcium nitrate (Ca(NO3)2) and their mixtures, is capable of solving an environmental pollution problem and reducing a cost. Also, the method is capable of increasing nitrided depth of the metal two to six times compared to conventional nitriding methods. As a result, the method can be carried out in various application fields.