It was recalled that the small coherent body-centered cubic precipitates of Cu that formed during fast-neutron irradiation of ferritic steels were an important feature of the irradiation hardening that occurred during service. The usual explanation of the hardening due to Cu precipitates was given in terms of the Russell-Brown modulus hardening model, in which precipitates were treated as soft spots in the Fe. In the present work, the core structure and energy of a <111> screw dislocation were calculated as it approached a row of precipitates. The results indicated that the hardening observed in experiments was due to the effect of the screw dislocation core upon the body-centered cubic Cu structure

rather than being due to elastic interaction. This was a new precipitate strengthening effect. The increase in the flow stress was estimated from the interaction energy between the dislocation and the precipitate row, and the resultant values for precipitates of the size and spacing found in irradiated reactor pressure-vessel steels were close to those found experimentally.

Computer Simulation of the Core Structure of the <111> Screw Dislocation in α-Iron Containing Copper Precipitates - II. Dislocation-Precipitate Interaction and the Strengthening Effect. T.Harry, D.J.Bacon: Acta Materialia, 2002, 50[1], 209-22