Abstract: This paper analysies the difference of standards and specifications in the world on the working methods of V-notch and surface roughness of the Charpy V-notch impact specimens, elects convention four working methods of V-notch: grinding, milling, broaching, electrospark process, measures separately the impact energy, lateral expansion, and the percentage of shear fracture at variant temperature of testing on the four groups impact specimens, draws the ductile-brittle transition' curves of two metallic materials (16Mn, 3.5Ni) on the four working methods of V-notch. This paper indicates: in the upper section of the curve of ductile-brittle transition, the effect of the working methods on impact toughness is small (<100%): with decrease of temperature, the effect of working methods (surface roughness) on impact toughness increase, in order for the impact test to conform to the requirements of standards and specifications, specially, for the impact test at low temperature, the surface roughness (Ra) or the working methods of V-notch should specify specially (RaC1.6pm).

Key words: 表面粗糙度, 电火花, 拉削, 冷脆转变, 磨削, 切割, 铣削