| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tension cold-rolled steel sheet having ultrafine granular structure and especially excellent in the balance of strength-elongation and stretch-flanging in the mechanical characteristics. SOLUTION: This steel has a composition containing especially C, Si, Mn, Ni, Ti, and Nb in the respective quantities satisfying the following formulas (1), (2), (3) and the balance Fe with inevitable impurities in the steel components, and has the structure of≥65 vol% ferrite having≤35μm average crystal grain diameter and limits to <3 vol% structure partial ratio except bainite phase and/or tempered martensite phase, in the remaining structure except the ferrite phase. 637.5+4930äTi<SP>*</SP>+(48/93)×[%Nb]}≥A<SB>1</SB>: (1), A<SB>3</SB>≤860: (2), [%Mn]+[%Ni]≥1.3: (3). Wherein, Ti<SP>*</SP>=[%Ti]-(48/32)×[%S]-(48/14)×[%N], A<SB>1</SB>: presumed value (°C) of A<SB>1</SB>transformation point obtained with a calculating equation, A<SB>3</SB>: presumed value (°C) of A<SB>3</SB>transformation point obtained with a calculating equation. COPYRIGHT: (C)2004,JPO&NCIPI
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