黄銅の焼鈍脆化現象の結晶粒度依存性について

Abstract

This paper deals with the mechanism of the grain size effect on the susceptibility to the embrittlement of α-brass during annealing. The creep and creep rupture tests were conducted at 300°C on cold rolled specimens of 70-30 brass of different grain size (0.03∼0.50 mm) under different stresses. The results obtained were as follows: (1) Elongation (εc) in ruptured specimens or elongation (ε′) required to embrittle the specimens decreased with grain size (L). The products of L and εc or L and ε′ showed constant values in a wide range of grain size. (2) This can be explained by taking into account the relation that the length of grain boundary sliding (Δs) is nearly proportional to grain size L under a constant elongation: Δs=α·ε·L⁄cosθ, where α is the contribution of grain boundary sliding to the overall elongation, ε is the overall elongation, and θ is the angle between the stressing direction and the sliding direction. (3) Same experiments were conductedon on cold worked aluminium brass which is empirically known to be sensitive to the embrittlement during annealing. The value of L·εc or L·ε′ of the aluminium brass was nearly 1/3 of that of 70-30 brass. (4) The application of these results to the phenomenon of embrittlement encountered in the brass mill gives a satisfactory explanation for the remarkable effect of grain size on this phenomenon.