Geometry Optimized Quenching

Quench cracks became a challenge in martensitic  low carbon components. The geometry is simple. Concentration of stresses were neither expected nor indicated by simulation. The crack start area was tracked by the crack surface pattern. Surface observations in SEM combined with micro structure observations revealed grain boundary ferrite in the crack surface of the initiation area. For general understanding, examples from other applications are interesting to consider. For titanium grade 5, grain boundary alpha on prior beta grain boundaries is not accepted for aerospace applications. Ferrite in steel and alpha in titanium is ductile, but the volume of plastic deformation is restricted. On component level, the crack behavior is brittle. The general focus is overcritical surface temperature, vapor phase break and mix of turbulent/lamellar flow. More effective quenching is, in this case, an industrial solution, rather than slower quenching. Ductile, not brittle, material was present at the start area.