| Piercing punches have been made from ausformed AISI H13 and M2 steels, and their service performance has been tested in actual nut manufacturing process. Ausformed H13 punches show increased service life by a factor of about 3 when compared with conventional M2 punches. This life improvement, which mainly results from reduced possibility of fracture at punch body, is primarily due to the increase of strangth by ausforming without deterioration of toughness. Metallographic observations indicate that, in ausformed H13 punches, the subsurface cracks initiated and propagated parallel to the worn surface, whereas, in conventional M2 punches, the cracks run inward from the surface. The life of ausformed M2 punches is about 2.5 times as long as that of conventional M2 ones. This result is associated with uniform dispersion of small carbides. |
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