PURPOSE: A high strength wheel rim having good processability is manufactured from a strip-shaped thin steel sheet by bending the sheet to a loop, welding after butting the joint parts, heating the product to above the A1 transformation point and cooling at a limited cooling rate to a specified temp.
CONSTITUTION: A strip-shaped thin steel sheet comprising a high tensile steel contg. by weight 0.02W0.2%C, 0.4W2.5% Mn, and 0.01W0.15% Al is formed to a loop by bending. The joints of the bent members are butted and welded; the whole body of the welded member is heated to above the A1 transformation point. After cooling, the cooled member is formed to a final shape to obtain a wheel rim. The cooling rate CV(°C/sec) from the A1 transformation point in the cooling stage to 200°C is controlled within a range defined by the formula.
KATOU TOSHIYUKI
TOSAKA AKIO
MATSUMOTO YOSHIHIRO
NISHIDA MINORU
