| 摘要 |
PROBLEM TO BE SOLVED: To provide an electrical resistance welded steel tube with excellent fatigue-resistant characteristics, which is suitably used for an automotive drive system component, and to provide a method for manufacturing the same.SOLUTION: A steel strip having a composition including, by mass, C: 0.41-0.55%, Si: 0.01-0.5%, Mn: 1.0-2.0%, Al: 0.05% or less, P: 0.02% or less, S: 0.01% or less, Cr: 1.0% or less, Cu: 1.0% or less, and Ni: 1.0% or less, and satisfying 2Cu+1.52Ni+1.1Cr≥1.0 is made into an electrical resistance welded steel tube. The electrical resistance welded steel tube is further heated and soaked at a temperature of an Actransformation point or higher, and subjected to diameter reduction rolling at a cumulative diameter reduction rate: 35-70% and a rolling end temperature: >800°C and ≤950°C. According to this, an electrical resistance welded steel tube with excellent fatigue-resistant characteristics is obtained. This steel tube has a width of white layer of 40 μm or less and a uniform hardness distribution such that the absolute value of hardness difference &Dgr;HV between the hardness of the white layer and the hardness of a base metal portion at a Vickers hardness HV 0.5 after high-frequency quenching is 25 points or less. |
