| 摘要 |
<p>A mild high carbon steel sheet characterized by having a chemical composition containing C: 0.20% to 0.50%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.02% or less, sol.Al: 0.08% or less, N: 0.02% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and a microstructure composed of ferrite and cementite, wherein each of the average grain size ds of the above-described ferrite in the region from the surface of the steel sheet to the position at one-quarter of the sheet thickness and the average grain size dc of the above-described ferrite in the region from the position at one-quarter of the sheet thickness of the steel sheet to the sheet thickness center is 20 to 40 µm, 0.80 ‰¤ ds/dc ‰¤ 1.20 is satisfied, the average grain size of the above-described cementite is 1.0 µm or more, the spheroidizing ratio is 90% or more, and 90% or more of cementite, on a ratio of the number of grains basis, is present inside ferrite grains.</p> |
