Effect of annealing on grain size and flaring limit of seamless SUS 304 stainless microtubes

Abstract

Size effects make traditional macroforming generally ineffective for microforming. Although the microtube is one of the most important microparts, the effect of grain size on material behavior has seldom been studied. In this study, seamless SUS 304 stainless microtubes were annealed to investigate their grain growth and to analyze their mechanical properties, including yielding stress and strain-hardening coefficient, by conducting a tensile test. A nano-indentation system, Triboindenter, was employed to measure the reduced modulus and hardness of grain. A flaring system was developed to investigate the relationship between flaring limit and T/D (thickness/average grain size) ratio. The method of fabricating a conical micropunch is also described. The optimal T/D ratio, which enhances the flaring limit, is 9.9.

Keywords:

• microflaring
• grain size effect

Acknowledgments

The authors would like to thank the National Science Council of the Republic of China, Taiwan, for financially supporting this research under Contract No. NSC97-2221-E-150-030.