A metal piece having at least two areas of lower mechanical strength than the body of the piece, said pieces being respectively arranged on one side and the other of a longitudinal central section (PM) of said piece and alternatively located in two locations separated longitudinally along the piece, the areas of lower mechanical strength than the body of the piece being formed by local control of the stamping temperature during a stamping process of the piece, notably a process comprising steps including heating the piece to a temperature range suitable for obtaining an austenitic stage, then stamping this piece in a stamping tool suitable for defining different temperatures in the different areas of the stamped piece, for example by virtue of the voids formed in the stamping tool or by local reheating of the stamping tool.