By using a reconstruction program recently developed by the present authors, the parent austenite grain structure is reconstructed from the crystal orientation map of bainite structure. Local austenite orientation can be reconstructed from non-ausformed bainite structure with errors of 1.7° and 1.0° at spatial resolutions of 5 and 20 μ m respectively. The angle of errors is further reduced to be less than 0.5° when an analysis area is extended to a whole austenite grain. Application of the reconstruction program to the bainite structure transformed from deformed austenite has clarified that the variation in grain shape and deformation texture of parent austenite can be well reconstructed.
A Mn ± C steel with an as quenched martensite microstructure expected to be used as a high strength steel for automobile parts. However, the fatigue strength of the steel is relatively low in spite of its high tensile strength. Such low fatigue strength is attributed to a low elastic limit caused by mobile dislocations in the as quenched martensite structure. Shot peening improves the fatigue life markedly below 10 7 cycles but has little effect at 10 7 cycles. These results are explained by the fact that the initiation site of the fatigue crack changes from the surface of the as quenched specimen to the interior of the shot peened specimen.MST/5163
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