Microstructural evolution mechanisms in rolled 17-4PH steel processed by ultrasonic surface rolling process

摘要: Abstract The surface of rolled 17-4 precipitation-hardening steel was subjected to the ultrasonic rolling process technique at room temperature. Microstructural evolution mechanisms and its intrinsic relation with processing history, namely formation heat treatment, were systematically analyzed via high-resolution transmission electron microscopy. results indicated that a gradient nanocrystalline structure layer generated surface, where amorphous transitional microstructure formed on topmost layer. paramount role dislocation activities in nanocrystallization investigated detail. It found precipitates also surrounded sheared by dislocations into smaller size, which then dissolved matrix. Meanwhile, phase transformation from martensite δ-ferrite occurred processed superlattice elemental redistribution or/and realignment phenomena appeared. reason for these high grain boundary density provided “short circuit diffusion” channels, raised number enrichment sites enhanced diffusion kinetics, acted as fast paths, thus accelerating atomic diffusion.