| 摘要 |
<p>A high-strength steel sheet adapted for deep drawing, which contains 0.04-0.25 mass % of carbon and 0.3-3.0 mass % of at least one of silicon and aluminum, contains ferrite as the principal phase (the phase having the highest volume fraction), has a composite structure containing at least 3 vol.% of austenite, bainite and martensite, and satisfies the following conditions: Vg/C = 40-140 (wherein Vg is the volume fraction (vol.%) of austenite before working and C is the content (mass %) of carbon in the steel as a whole), Vp/Vs </= 0.8 (wherein Vp is the volume fraction of austenite in plane-strain tensile deformation and Vs is the volume fraction of austenite in shrink flange deformation), and 220 < Vg ä300(2750Cg+600)/(HfVf+HbVb+HmVm)-1ü < 990 (wherein Cg is the carbon concentration in austenite; Hf is the hardness of ferrite; Vf is the volume fraction thereof; Hb is the hardness of bainite; Vb is the volume fraction thereof; Hm is the hardness of martensite before working; and Vm is the volume fraction thereof). This sheet is produced by specifying the inlet side temperature of rough rolling (hot rolling), intercritical annealing condition in the continuous annealing step after cold rolling, cooling condition, and bainitic transformation condition. <IMAGE></p> |
