| 摘要 |
PURPOSE:To produce a steel having various levels of high strength and high toughness by subjecting a hypoeutectoid steel having fine crystal grain structure to superplastic working then adjusting the same to a temp. at which alpha:gamma is maintained at an adequate ratio followed by controlled cooling. CONSTITUTION:The hypoeutectoid steel having the fine crystal grain structure is heated to the temp. of, for example, A3 point or above and is then quickly cooled. The cooled steel is subjected to cold working, then to the superplastic working by which the steel is hardened to have martensite structure after heating to and holding at the temp. of A3 point - A3 point + 50 deg.C and is thereafter heated to have the fine two-phase structure. The steel is held at such a temp. at which the ratio of alpha:gamma attains the prescribed value in the alpha+gamma two-phase region (final heating temp.). The gamma is transformed to alpha' (martensite) by the controlled cooling such as quick cooling to form the steel having the fine two-phase structure in which alpha:alpha' is distributed at a desired mixing ratio. The applicable range of the practicable steel as a structural steel is thus expanded. |
