Creep strengthening and weakening mechanisms by martensite lath in high Cr ferritic heat-resistant steel

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In this study, we clarified creep strengthening and weakening mechanisms by martensite lath structure in high Cr ferritic heat resistant steel. Firstly, the interaction of dislocations and lath boundaries were observed with in-situ tensile test in high-voltage transmission electron microscope. Then, lath structure coarsening behavior during creep deformation was evaluated by the crystal orientation analysis. From these results, we concluded that lath structure is a dominant factor of creep strength in high Cr ferritic heat resistant steel. In addition, in order to understand the mechanism of improvement of lath structure stability by precipitates formed on grain boundary, the size and the density of precipitates on each grain boundary were estimated using the microstructural observation. Those parameters of precipitates obviously depended on the grain boundary character.