Cracknell A., Petch N.J. Frictional Forces on Dislocation Arrays at the ower Yield Point in Iron

Article. Acta Metallurgica, Vol. 3, March 1955, pp. 186-189.
The equation, which relates the lower yield point of polycrystalline iron with the grain diameter l, has been confirmed. Here k* and t are constants and it is suggested that Q depends in part upon the frictional forces exerted by solute atoms and precipitates on the dislocation arrays that propagate
the yield. In agreement, it is found that t increases when the solute atom concentration is increased by nitriding or by sub-critical quenching and there is a further increase on ageing, followed by a decrease on over-ageing. A linear relationship is calculated between t0 and the concentration of carbon + nitrogen in solution, and this is confirmed by experimental measurements.