Abstract: A steel sheet has a chemical composition containing, by mass %, C: 0.20% or more and 0.40% or less, Si: more than 1.0% and 3.0% or less, Mn: 1.5% or more and 3.5% or less, P: 0.002% or more and 0.010% or less, S: 0.0002% or more and 0.0020% or less, sol. Al: 0.40% or less (not including 0%), and N: 0.0100% or less, with the balance being Fe and incidental impurities; and a steel microstructure containing, in area fraction, tempered martensite: 45% or more and 83% or less, bainite: 15% or more and 53% or less, and retained austenite: 2% or more. Carbides in the tempered martensite have an average particle size of 0.40 ?m or less, an average amount of C in the retained austenite is 0.5% by mass or more, and a tensile strength is 1,470 MPa or more.

Abstract: A steel sheet has a certain chemical composition and a steel microstructure containing, in area fraction, martensite: 40% or more and 78% or less, bainite: 20% or more and 58% or less, and retained austenite: 2% or more. Carbides in tempered martensite in the martensite have an average particle size of 0.40 ?m or less, an average amount of C in the retained austenite is 0.5% by mass or more, a Si concentration in a region within 100 ?m in a thickness direction from a surface of the steel sheet is 1.3% by mass or less, and a tensile strength is 1,470 MPa or more.

Abstract: A tightening apparatus for a dental implant includes a torque wrench and a slip detection device. The torque wrench includes a tightening part engageable with an abutment of the implant and a tightening torque detector for detecting tightening torques generated when the abutment is screwed to the fixture. The slip detection device includes a slip determiner and an indicator. The slip determiner samples an amount or rate of change of the torques detected by the torque detector in every predetermined period, to sequentially compare the amount or rate of change of the torques in a prior predetermined period with that in a subsequent predetermined period, and to determine whether or not the latter amount or rate is smaller than the former amount or rate. The indicator activates when the slip determiner determines that the latter amount or rate of change is smaller than the former amount or rate of change.