Grain-size dependence of the mechanical properties of an age-hardening Fe-1 % Cu-alloy

The contribution of grain size and precipitation hardening to the yield stress and other mechanical properties was investigated. An alloy of iron with 1 % copper was prepared as supersaturated solid solution with grain sizes between 12 and 140 μm. By ageingat 500 and 600° C different precipitation hardening conditions were produced. For small particle sizes an additive behaviour of grain-boundary and precipitation hardening was found (particle radiusr < 50 Å). For large particle sizes the yield stress is independent of grain size (r > 150 Å). A transition is found for intermediate particle sizes with grain size dependence for small and independence for large grain sizes (50 Å <r < 150 Å). The effect of grain boundaries and particles on the formation and motion of dislocations is used to explain this behaviour.