To provide steel for mechanical structure having an excellent balance among strength, elongation and toughness surpassing that of maraging steel and also to provide an application product thereof.
The steel for mechanical structure with excellent strength, ductility and toughness is characterized in that: its steel composition consists of, by mass, >0.30 to 0.5% C, ≤1.0% Si, ≤1.5% Mn, ≤0.025% Al, 0.3 to 0.5% Mo, 0.0005 to 0.01% B and the balance Fe with inevitable impurities; and its structure at a volume ratio of ≥90% consists of martensite structure whose constituent blocks are ≤1.5μm in size; and the ratio of solid solution B is ≥0.0005% and the solid solution B is present on old austenite grain boundaries in an amount ≥1.5 times that in old austenite grains.
KUROSAWA NOBUTAKA
HAYASHI TORU
KIMURA HIDETO
TOYOOKA TAKAAKI
HASE KAZUKUNI
YAMADA KATSUMI
Kazuhiro Mori