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Dislocation structure in the HAZ of the HSS steel after shot peening
Kruml, Tomáš ; Buirette, C. ; Degallaix, G. ; Polák, Jaroslav
The welds of a high strength C-Mn microalloyed steel with ferritic-bainitic microstructure were shot peened in order to improve the fatigue resistance. Since the weakest point was the heat affected zone (HAZ), the dislocation structure in two depth off the zone was investigated before and after shot peening. No specific dislocation arrangement was found neither in the initial state nor after shot peening and the arrangement can be characterised as random. The dislocation density was elevated in the initial state due to bainitic transformation. The shot peening resulted in appreciable increase of the dislocation density with a very strong gradient. The results were discussed in terms of the effect of surface hard layer induced by shot peening on the fatigue life of the weld and on the initiation and growth of fatigue crack in HAZ.
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