Chain parts and other steel articles are provided with hard, wear-resistant carbide coatings by tumbling them in a heated retort with a particulate mix which includes a source of vanadium andor niobium. The arc-generating device is mounted in the housing to generate an electric arc. Upon receipt of control code data via a user input unit, a processor unit of the mobile terminal enables establishing of a communications link with the control terminal with reference to a call data code portion of the control code data, and terminates automatically the communications link after a duration corresponding to a termination control code portion of the control code data.