PURPOSE:To suit the hardness and toughness of a welding part and handle part by welding a handle part made of alloy steel corresponding to JISSUP 10 to the edge part made of high speed steel, and making concurrent quenching in a N2 gas atmosphere or a vacuum condition of 10-2-10-3Torr. CONSTITUTION:An edge part 1, made of high speed steel and a helical flute 4 is formed on its outer periphery, is welded with a handle part 2, made of JISSUP 10 alloy steel and a tang 5 is provided to its end part, on a welding surface 3 by friction welding or flush-butting welding. Next, the edge part 1 and handle part 2 are charged in a N2 gas atmosphere furnace or a vacuum furnace of vacuum 10-2-10-3Torr, and temperature is gradually risen from about 600 deg.C to about 1200 deg.C. After that, when they are moved to a cooling chamber and cooled to about 60 deg.C or below, suitable hardness and toughness can be given to a mixing part and its vicinity with C having nonuniform density in a high speed steel side in the vicinity of a welding part 3 diffused and coarse needle-like structure improved.
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