Microstructural Change Induced by Fine Particle Peening and Its Effect on Elemental Diffusion

Abstract

Investigation of microstructural changes in pure commercial-grade iron caused by fine particle peening (FPP) treatment was undertaken by detailed observation using field emission-scanning electron microscopy (FE-SEM) and measurement of the X-ray diffraction peak full width at half maximum (FWHM). The effect of pre-FPP treatment on the oxygen diffusion process within iron is also discussed. FPP treatment produced stratification patterns with many dislocations and grain boundaries on the treated surface. This unique microstructure strongly affected the diffusion capacity, so that thicker oxygen-concentrated layers were observed on pre-FPP/oxygen diffusion-treated surfaces.

Surface-hardened Layer Properties of Newly Developed Case-hardening Steel

“…In general, the hardness in a surface-hardened layer of the carburized steels is enhanced by the following microstructural changes developed by FPP: (i) Formation of a white layer and increases in the dislocation density in the matrix and untransformed retained austenite because of severe plastic deformation; [10][11][12][17][18][19]24) (ii) Increase in the volume fraction of hard martensite because of the strain-induced martensite transformation of the retained austenite. [25][26][27][28][29][30][31][32] The relationship between the maximum Vickers hardness and the maximum volume fraction of strain-induced martensite in the TM and SNCM420 steels is shown in Fig.…”