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[References: 5 tit.]

The high-cyclic fatigue of welded joints of Fe-17Cr-0.8Ti-0.08C steel was investigated by digital image correlation technique. The lapped images of specimen surface were received with optical microscope (50x) and registered by camera to form a panorama. Four stages of deformation evolution are suggested: strain hardening (I), stable necking (II), unstable necking (III), and fatigue crack (IV). Displacement fields in the neck regions were approximated by linear functions to evaluate the mean deformation rate and displacement variance. The basic types of deformation structures and their evolution in base metal, HAZ and in weld are outlined. It is shown that the seam weld keeps some plasticity under fatigue. It was found that fatigue crack is being formed by plastic flow in base metal zone, and its life time is very short. The evolution of mean deformation and its variance are given.