This steel material for bearings includes prescribed components in the steel, the oxide inclusions in the steel that have a minor axis of 1 m or greater satisfying the following conditions (1) and (2). (1) The average composition contains specific respective amounts of CaO, Al.sub.2O.sub.3, SiO.sub.2, and TiO.sub.2, and CaO+Al.sub.2O.sub.3+SiO.sub.2+TiO.sub.260%. (2) The proportion of oxide inclusions in which TiN occurs at the interface of the oxide inclusions and the steel is 30% or more of the total of the oxide inclusions.

A vanadium alloyed steel that includes carbon and vanadium and has a steel microstructure with coherent interphase precipitates that have vanadium. A method for producing a vanadium alloyed steel that includes providing a starting steel; heating the starting steel to at least partially austenitise the starting steel; and holding the temperature at 650 C.200 C. for about 25 minutes or less.

Disclosed are: a cold forging wire rod and a steel part in which the microstructure is controlled through the alloy composition and manufacturing method, thus enabling cost reduction and enhancing delayed fracture resistance; and a method for manufacturing same. The steel part having improved delayed fracture resistance according to an embodiment of the present invention contains, in weight percent, 0.18-0.25% of C, 0.30-0.50% of Si, 0.35-0.50% of Mn, more than 0% and no more than 0.03% of P, more than 0% and no more than 0.03% of S, 0.45-0.60% of Cr, 0.015-0.03% of Ti, 0.001-0.004% of B, with the remainder comprising Fe and inevitable impurities, and may include at least 90% by volume of auto-tempered martensite.

Disclosed are: a cold forging wire rod and a steel part in which the microstructure is controlled through the alloy composition and manufacturing method, thus enabling cost reduction and enhancing delayed fracture resistance; and a method for manufacturing same. The steel part having improved delayed fracture resistance according to an embodiment of the present invention contains, in weight percent, 0.18-0.25% of C, 0.30-0.50% of Si, 0.35-0.50% of Mn, more than 0% and no more than 0.03% of P, more than 0% and no more than 0.03% of S, 0.45-0.60% of Cr, 0.015-0.03% of Ti, 0.001-0.004% of B, with the remainder comprising Fe and inevitable impurities, and may include at least 90% by volume of auto-tempered martensite.

The present disclosure relates to a steel comprising 0.8 wt % to 0.87 wt % C; 1.5 wt % to 2.3 wt % Si; 0.5 wt % to 1.3 wt % Ni; a grain refining agent, selected from the group consisting of 0.08 wt % to 0.25 wt % V, 0.015 wt % to 0.04 wt % Nb, and a combination thereof; and the balance being Fe and inevitable impurities. The present disclosure further relates to a screwdriver bit made of the steel, and a method for processing the steel.

The present disclosure relates to a steel comprising 0.8 wt % to 0.87 wt % C; 1.5 wt % to 2.3 wt % Si; 0.5 wt % to 1.3 wt % Ni; a grain refining agent, selected from the group consisting of 0.08 wt % to 0.25 wt % V, 0.015 wt % to 0.04 wt % Nb, and a combination thereof; and the balance being Fe and inevitable impurities. The present disclosure further relates to a screwdriver bit made of the steel, and a method for processing the steel.

A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and an AlN precipitation parameter.

A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and an AlN precipitation parameter.

A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and a TiC precipitation parameter.

A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and a TiC precipitation parameter.