Daido Tokushuko Kabushiki Kaisha

Toshimitsu Fujii

Sadayuki Nakamura

Kenji Isokawa

A steel shaft material having desirable cuttability and induction hardenability even in the form of milled stock without being subjected to any heat treatment, such as annealing, and a method for manufacturing the same. A steel ingot is prepared containing 0.38 to 0.45 wt. % of carbon, 0.15 wt % or less of silicon, 0.3 to 1.0 wt % of manganese, 0.0005 to 0.0030 wt % of boron, 0.01 to 0.05 wt % of titanium, 0.01 to 0.06 wt % of aluminum, 0.010 wt % or less of nitrogen, optionally at least one of chromium in an amount of 0.3 wt % or less and molybdenum in an amount of 0.10 wt % or less, and optionally at least one of 0.005 to 0.30 wt % of sulfur, 0.0002 to 0.005 wt % of calcium, 0.005 to 0.30 wt % of lead and 0.005 to 0.10 wt % of tellurium, and the remainder being iron and unavoidable impurities. After the ingot is heated to 1,100.degree. C. or less, the ingot is milled at a finishing temperature of 950.degree. C. or below and an area reduction rate of 70% or higher, and then cooled in the atmosphere. The steel material of the present invention has a microstructure formed of ferrite and lamellar pearlite (the amount which remains bainite being %5 or less) and having a ferrite grain size number of 6 or higher, as determined by JISG0552, a HRB hardness of 80 to 90, as determined by JISZ2245, and a DM-T decarbonized depth of 0.20 mm or less, as determined by JISG0558.

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Tokai, Japan

Toshimitsu Fujii