| 摘要 |
PROBLEM TO BE SOLVED: To obtain machinability equal to that of Pb-contg. free cutting brass and to reutilize cutting chips by allowing the brass to have a specified compsn. contg. Cu, Si, P and Mg, and the balance Zn. SOLUTION: This super-free cutting brass is composed of, by weight, 69 to 80% Cu, 2 to 4% Si, 0.02 to 0.1% P and 0.02 to 0.1% Mg, and the balance Zn. In brass containing only Cu, Si and Zn by the amounts identical to those in the above compsn., when temp. increases from 250 to 550 deg.C at a 100 deg.C step, a brittle phase is formed on the grain boundaries, and curly continuous cutting chips are formed at the time of cutting. Moreover, its corrosion resistance is deteriorated, and, e.g. in the case of being contacted with salt water, red rust and moreover patina are generated. In the case this brass contains P and Mg by the above amounts, however, the cutting chips are made finer to a degree identical to that of Pb-contg. free cutting brass, and moreover, in the case it is contacted with salt water, the brass of this invention is only discolored in the shape of slightly white spots.
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