Characteristics of 8T-bolt manufactured by the Yield-Ratio-Control-Steel for Cold Former

A yield-ratio-control-steel(YRCS80, 80gf/mm2-Tensile-Strength) is applied for cold former and manufactured into bolt for automobile. The head and total length of bolt are 14mm and 42mm respectively. The developed bolt satisfied all the required properties, such as hardness and etc. Since the yield ratio of used steel is about 0.5, the steel is started to deform plastically at 40kgf/mm2. The conventional heat-treated steel is AISI1045 and its yield strength is about 60kgf/mm2. Finally, the developed steel is deformed plastically at 20% lower strength than the conventional steel and then the forging load decreased up to 20%. The developed bolt shows the required properties of conventional bolt; hardness distribution (HRC25~30).