ELECTRIC RESISTANCE WELDED STEEL PIPE FOR HIGH-STRENGTH THIN HOLLOW STABILIZER AND MANUFACTURING METHOD THEREFOR

A method for manufacturing an electric resistance welded steel tube for high-strength thin hollow stabilizers is provided. A steel with a chemical composition including, in mass%, C: 0.20 to 0.40%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0%, Al: 0.01 to 0.10%, Cr: 0.01 to 1.0%, Ti: 0.01 to 0.05%, B: 0.0005 to 0.0050%, Ca: 0.0001 to 0.0050%, and N: not more than 0.010% is heated to a temperature of 1000 to 1300°C, hot rolled under conditions where the rolling finish temperature is 750 to 950°C, cooled, coiled into a coil at 500 to 650°C, and skin pass rolled with a rolling reduction ratio of not less than 0.3%. The resultant hot rolled sheet is electric resistance welded into an electric resistance welded steel tube, which is then reheated to a temperature of 800 to 1100°C and hot stretch-reducing rolled under conditions where the rolling finish temperature is not more than 850°C and the cumulative diameter reduction is not more than 75%. Consequently, a thin electric resistance welded steel tube is produced which has a depth of a decarburized layer in wall thickness direction on the tube inner surface of not more than 120 µm from the surface, has a surface roughness Ra of the tube inner surface of 0.01 to 5.0 µm, and has a YR of not less than 65%. This thin product tube, after quenching and tempering treatment, has a hardness expressed in Vickers hardness of not less than 450 HV and exhibits excellent fatigue resistance.