| 摘要 |
<p>A steel for mechanical structure with an excellent balance of strength, elongation and toughness surpassing that of maraging steel; and an application product thereof. There is provided a steel for mechanical structure excelling in strength, ductility and toughness characterized in that its component formulation is composed of, by mass percentage, more than 0.30 to 0.5% C, 1.0% or less Si, 1.5% or less Mn, 0.025% or less Al, 0.3 to 0.5% Mo, 0.0005 to 0.01% B and the balance Fe and unavoidable impurities, and that the structure thereof at a volume ratio of 90% or greater consists of martensite structure whose constituent blocks are 1.5 Vm or less in size, and that the ratio of solid solution B is 0.0005% or greater and is present on old austenite grain boundaries in an amount of at least 1.5 times that within old austenite grains.</p> |
