The influences of microstructrue on plane strain fracture toughness,blunt notch toughness and tensile ductility have been investigated for the quenched and low temperature tempered 30CrMnSiA steel.The results showed that the plane strain fractture toughness was contorlled by the micro-structural variatins in the small local zone (1 to 2 times the crack tip opening displacements #delta#)_c at critical condition) ahead of the crack tip.and the micro-plasticity ahead of the sharp crack tip could be reflected by the thickness - length ratio of martensite lath (d_L,d_P).The tensile ductility and blunt notch toughness were dominated by austenite grain size or amrtensite packet diameter.In the case of ductile rupture,retained austenite and other non-martensite structures decreased the fractrue toughness.but it was beneficial to blunt notch impact toughness.
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