The role of grain size in static and cyclic deformation behaviour of a laser reversion annealed metastable austenitic steel

Different grain sizes were created in a metastable 17Cr-7Mn-7Ni steel by martensite-to-austenite reversion at different temperatures using a laser beam. Two fully reverted material states obtained at 990 degrees C and 780 degrees C exhibited average grain sizes of 7.7 and 2.7 mu m, respectively. The third microstructure (610 degrees C) consisted of grains at different stages of recrystallization and deformed austenite. A hot-pressed, coarse-grained counterpart was studied for reference. The yield and tensile strengths increased with refined grain size, maintaining reasonable elongation except for the heterogeneous microstructure. Total strain-controlled fatigue tests revealed increasing initial stress amplitudes but decreasing cyclic hardening and fatigue-induced alpha'-martensite formation with decreasing grain size. Fatigue life was slightly improved for the 2.7-mu m grain size. Contrary, the heterogeneous microstructure yielded an inferior lifetime, especially at high strain amplitudes. Examinations of the cyclically deformed microstructure showed that the characteristic deformation band structure was less pronounced in refined grains.