| 摘要 |
<p>PROBLEM TO BE SOLVED: To make ferritic grain size very small, overcome brittleness, demerit of P, and obtain solid solution strengthening capability, merit of P, by caliber- rolling a steel containing a specified quantity of P at a specified temperature. SOLUTION: Steel containing 0.04-0.2 mass% P is caliber-rolled in the temperature range of 400 deg.C or more but not higher than Ac3, and muti-pass groove roll rolling is preferred. The steel having the structure of carbide and ferrite grains of 2μm or less as the entire C cross section contains 20% or less in volume of C(carbon) of carbide containing cementite as a chemical component. The steel is composed of 0.8 or less Si, 0.05-3 Mn, and 0.1 or less Al in mass% and the balance substantially of Fe. It is a round bar of 3.5 mm in diameter and 25 mm in gauge length, and the yield point through the room-temperature tensile test at the rate of deflection of 0.5 mm/min is 500 MPa or more, and the strength is 550 MPa or more. The Charpy impact value in the temperature range of room temperature to 78 K is 250 J or more.</p> |
