The amount of charged hydrogen and its effect on ductility in three kinds of ultra high strength low alloy TRIP-aided steels with different matrix structure were investigated. These TRIP-aided steels, especially the TRIP-aided steels with bainitic ferrite matrix, were charged hydrogen more than the conventional tempered martensitic steel. This was principally associated with retained austenite trapped so much hydrogen in solute. Hydrogen embrittlement was considerably suppressed in the

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... d steels, especially in the TRIP-aided steel with annealed martensite matrix. It was considered that the scanty hydrogen embrittlement of the steel was caused by trapping of much hydrogen into retained austenite, uniform fine structure, TRIP effect of retained austenite and appearance of quasi-dimple fracture.