Abstract
In order to study whether transient cracks can be re-welded in P/M forging, ring specimens machined from closed-upset 4600-0.37%C preforms with re-sealed cracks but no traces in the circumference were subjected to a squeezing test and an observation of microstructures and fracture surfaces. The factors influencing re-welding of transient cracks were also investigated in tension test of P/M forged Fe and Fe-0.50%C preforms with previously drilled holes of 0.5 or 1 mm diameter, instead of unintentional transient cracks.
It was found that some transient cracks had been re-welded, in consideration of the facts that radial crushing strength of closed-upset specimens with no traces of visible cracks was nearly equal to or larger than that of hot coined ones and the SEM of the fracture surfaces showed a dimple pattern. The drill holes in Fe specimens did not re-welded owing to surface oxidation. Addition of 0.50%C eliminated the deleterious effect of drill holes on the tensile properties. It was also confirmed from the observation of microstructures and fracture surfaces that the drill holes in the specimens had been re-welded. Alloying of carbon in preforms was found to play an important role in re-welding.
