This study concerned the influence of the material strength, ductility and impact energy and the relationship of the broken section profile vs. ductile transition brittle where the steel material was treated under different tempering temperature and hardness. Generally after the steel materials, 10B35 coil wire materials which was generally applied to form screws, was treated by quenching and tempering, its hardness ranged from HRC30 to HRC45. The results showed that the elongation rate beyond 20.4% would be proportional to the impact energy with linear relation, but with reverse proportion to the hardness value. The brittle-tough point of the hardness was set around HRC37 after heat treatment in order to balance the strength and the toughness. In addition, the coil wire materials were analyzed from broken section materials showing good toughness; this represented that the area of the cross section radiation layer due to ductile fracture would largely increase. On the contrary, the wire material test fragment with bad toughness represented that the area of the shear layer due to brittle fracture would largely increase as well. As to that material, if its hardness was greater than or equal to HRC37, that material would have an excellent turning danger from transition. At the same time, when the tempering temperature of the wire steel material was set under 4600C and its corresponding central hardness was about HRC37, the distance between two cementite phase layers suddenly increased. This result leaded to the reason why the wire material test fragment was turned into brittleness from ductility. Therefore, when the fastener was manufactured under tempering treatment, avoiding the tempering brittleness temperature range was necessary.
