1995 Volume 35 Issue 1 Pages 86-91
A dispersion of precipitates introduces a threshold stress which opposes deformation. The effect of precipitate shape on dispersion strengthening at elevated temperature has been examined. Three kinds of Mod. 9Cr-1Mo steels without Nb(C, N), with spherical Nb(C, N) and with complex Nb(C, N)+V(N, C) "V-wing" were designed to have the same microstructures except for the shape of precipitates. The threshold stresses were measured by tensile and creep tests at 600°C. Two sorts of effects have been observed. The first is that complex precipitates restrain dislocation from climbing even in a condition in which dislocation climbs over a spherical precipitate. Mobile dislocations are considerably trapped at the concavity of the V-wings during deformation. The second effect is that the probability of dislocation trapping at V-wing is larger than that at spherical Nb(C, N). These trapping effects play important roles in the strenghening effect of precipitate.