X-ray diffraction peak profile analysis aiming at better understanding of the deformation process and deformed structure of a martensitic steel

Microstructrual characteristics of extra low carbon lath martensite after cold rolling to 85% reduction and equal-channel angular pressing of four passes were studied by means of X-ray diffraction (XRD) peak profile analysis and transmission electron microscopy. The modified Williamson–Hall and Warren–Averbach methodologies were implemented to determine crystallite size distribution, dislocation density and character of prevailing dislocations of the deformed structures. Cold-rolled steel showed lamellar dislocation boundaries which subsequently disappear at large strain by equal-channel angular pressing, turning to a highly and uniformly dislocated structure involving equiaxed ultrafine grains. XRD peak profile analysis revealed that upon further straining of lath martensite; i) crystallite size decreases, ii) dislocation density increases slightly and iii) fraction of screw dislocations increases.