| 摘要 |
PURPOSE:To make controlling of titled values possible relatively and easily by quenching and tempering Ni-contg. steel and controlling old austenite grain sizes and the amount of austenite measured under specific conditions. CONSTITUTION:Steel contg. 7.5-10.0wt% Ni is quenched once or more to the prestructure of martensite and lower bainite and is tempered once or more to uniformly form fine austenite. These austenites are extremely stable. In this way, old austenite grain sizes (dr) and the amount of austenite (reff) measured after a 5% distortion is given at -196 deg.C are controlled. The threshold COD value deltac of a fatigue notched COD test at -162--196 deg.C is controlled by controlling the grain sizes (dr) and (reff), and the Ni-concg. low-temp. steel of the desired deltac value is obtained by adequately controlling (reff) and (dr). |
