| 摘要 |
PROBLEM TO BE SOLVED: To provide a stock steel sheet which is suitable to the steel sheet for link-plate of a chain, and is excellent in punching workability and bendability. SOLUTION: The steel sheet has chemical composition containing, by mass%, of 0.25-0.6% C,≤2% Si,≤2% Mn,≤2% Cr,≤0.02% P,≤0.02% S, 0.05-0.5% V and further, if necessary, one or more kinds of≤2% Mo or further,≤0.1% Nb,≤0.1% Ti and the balance Fe with inevitable impurities. Wherein, Mn+Cr is≥1.5%, and the sheet thickness is 3.5-15 mm. The hardness H<SB>M</SB>the center part of the sheet thickness direction is 180-350HV. When the difference between H<SB>M</SB>and hardness H<SB>X</SB>of depth position Xμm from the surface is defined asΔH=H<SB>M</SB>-H<SB>X</SB>, and the surface layer hardnesses (HV) at the 20μm, 100μm and 500μm depths from the surface are fefined as respective H<SB>20</SB>, H<SB>100</SB>and H<SB>500</SB>, the steel sheet has softened layer on the surface layer part, so that the differences between the hardness of the center part at the sheet thickness direction and the hardness of the surface layer part at the respective depth position, that is,ΔH<SB>20</SB>=H<SB>M</SB>-H<SB>20</SB>,ΔH<SB>100</SB>=H<SB>M</SB>-H<SB>100</SB>andΔH<SB>500</SB>=H<SB>M</SB>-H<SB>500</SB>, satisfy (1)ΔH<SB>20</SB>≥50, (2) 20≤ΔH<SB>100</SB>≤100 and (3) H<SB>500</SB>≤20. COPYRIGHT: (C)2011,JPO&INPIT
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