SEM STUDY OF HIGH-CHROMIUM MARTENSITIC STEEL LCF FRACTURE

Low cycle fatigue of high-chromium 13X11H2B2M Phi stainless steel has been studied after cyclic tests at room temperature with the frequency of loading, 0.45Hz and amplitude, +/- 1mm. The samples were v-notched with the dimensions delta x2 delta x50, where delta=3mm. The peculiarities of fatigue crack propagation and influence of heat treatment, sizes of grains and laths, and disposition of microcrack and microstructure elements of the steel were studied. Next, the main effect on propagation direction is caused by the shape of grains and laths. It turned apparent that main microcrack is composed of individual micro-components with the lengths correlating with the dimensions of grains and martensitic laths. During growth crack propagation direction changes from lath to lath; however, general trend remains unchanged. The results of tests indicate that speed of fatigue failure rises when the frequency and amplitude of loading increases. The work includes x-ray characterization of the steel, statistical distribution curve for angles between the main direction of macrocrack propagation and micro-components, and explanation of micro- and macrocrack propagation alteration is given.