良成形性 600MPa 級熱延高強度薄鋼板の疲労損傷に及ぼす強化機構の影響

概要

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Low cycle fatigue damage of two types of formable hot-rolled high strength sheet steels for automobile use with different static strengthening mechanisms of 600MPa class in tensile strength ; 0.9% Si-1.2% Mn dual phase and 0.04% Nb added precipitation hardened steel was studied by the X-ray differaction, SEM and TEM methods, the following results were obtained. (1) Si-Mn dual phase steel (DP) with low yield ratio shows higher cyclic stress than Nb containing precipitation hardened steel with high yield to tensile strength ratio. (2) Nb containing steel shows monotonuous cyclic softening which provides a decrease in the X-ray half value breadth resulting from sub-boundaries due to the rearrangement of dislocations. (3) DP steel offers initial cyclic hardening followed by cyclic softening with an initial increase followed by a decrease in the X-ray half value breadth, this resulting from fine cell-structures in the ferrite matrix. (4) DP steel seems to show high resistance to a fatal crack due to the effect of microstructures of soft ferrite and fine martensite.
社団法人日本鉄鋼協会の論文
1990-03-01