Abstract: A method for producing a high fatigue life quenched/tempered steel pipe comprises a quenching treatment of keeping an unquenched starting steel pipe having a composition that comprises, % by mass, C: 0.1 to 0.4%, Si: 0.5 to 1.5%, Mn: 0.3 to 2%, P: at most 0.02%, S: at most 0.01%, Cr: 0.1 to 2%, Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, Al: at most 0.1%, B: 0.0005 to 0.01%, and N: at most 0.01%, with a balance of Fe and inevitable impurities, at 900 to 1100° C. for 10 to 60 seconds and then rapidly cooling it. The cooled pipe is subjected to a tempering treatment of keeping the pipe at 280 to 380° C. for 10 to 60 minutes.

Abstract: A method for producing a high fatigue life quenched/tempered steel pipe comprises a quenching treatment of keeping an unquenched starting steel pipe having a composition that comprises, % by mass, C: 0.1 to 0.4%, Si: 0.5 to 1.5%, Mn: 0.3 to 2%, P: at most 0.02%, S: at most 0.01%, Cr: 0.1 to 2%, Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, Al: at most 0.1%, B: 0.0005 to 0.01%, and N: at most 0.01%, with a balance of Fe and inevitable impurities, at 900 to 1100° C. for 10 to 60 seconds and then rapidly cooling it. The cooled pipe is subjected to a tempering treatment of keeping the pipe at 280 to 380° C. for 10 to 60 minutes.

Abstract: Provided is a steel pipe designed to have a further increased high strength and a further improved fatigue life with suppressing the material cost and the production cost, especially such a steel pipe suitable for machine structure members that are required to be lightweight. The steel pipe is a high fatigue life steel pipe produced according to a process of using a steel plate having a composition that comprises, % by mass, C: 0.1 to 0.4%, Si: 0.5 to 1.5%, Mn: 0.3 to 2%, P: at most 0.02%, S: at most 0.01%, Cr: 0.1 to 2%, Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, Al: at most 0.1%, B: 0.0005 to 0.01%, N: at most 0.01%, and optionally at least one of Ni: at most 0.5%, Ca: at most 0.02%, Mo: at most 0.5%, and V: at most 0.5%, with a balance of Fe and inevitable impurities, and having, on at least one side thereof, a smoothed surface of which the surface roughness Ra in the direction (C direction) perpendicular to the direction to be the longitudinal direction of the steel pipe is at most 0.

Abstract: Provided is a steel pipe suitable for machine structure members that are required to be lightweight, of which the strength is increased and the fatigue life is prolonged with preventing the increase in the material cost and the production cost. The steel pipe is a high fatigue life quenched/tempered steel pipe having a composition comprising, % by mass, C: 0.1 to 0.4%, Si: 0.5 to 1.5%, Mn: 0.3 to 2%, P: at most 0.02%, S: at most 0.01%, Cr: 0.1 to 2%, Ti: 0.01 to 0.1%, Nb: 0.01 to 0.1%, Al: at most 0.1%, B: 0.0005 to 0.01%, N: at most 0.01%, and optionally at least one of Ni: at most 0.5%, Ca: at most 0.02%, Mo: at most 0.5% and V: at most 0.5%, with a balance of Fe and inevitable impurities, in which the mean grain size of the precipitated carbides is at most 0.5 ?m and of which the hardness in the center part of the wall thickness in the cross section perpendicular to the longitudinal direction of the steel pipe is at least 400 HV.

Abstract: A high-strength, high-permeability steel sheet for picture tube band comprises, in mass percent, C: 0.003-0.010%, Si: 0.5-1.0%, Mn: 1.0-2.0%, P: 0.04-0.15%, S: not more than 0.02%, Al: not more than 0.030%, N: not more than 0.004% and the balance of Fe and unavoidable impurities, has a chemical composition satisfying C×Mn×P?2.5×10?4, and has a ferrite crystal grain diameter of 10-100 ?m and a yield stress of 300 N/mm2 or higher, and preferably has a specific permeability ?0.35 in a DC magnetic field of 0.35 Oe of 400 or higher. The steel sheet can be produced by regulating the hot-rolling coiling temperature to 600-700° C. and selecting an appropriate combination of the cold rolling reduction ratio and a final annealing temperature in the range of 750-900° C.

Abstract: A high-strength, high-permeability steel sheet for picture tube band comprises, in mass percent, C: 0.003-0.010%, Si: 0.5-1.0%, Mn: 1.0-2.0%, P: 0.04-0.15%, S: not more than 0.02%, Al: not more than 0.030%, N: not more than 0.004% and the balance of Fe and unavoidable impurities, has a chemical composition satisfying C×Mn×P?2.5×10?4, and has a ferrite crystal grain diameter of 10-100 ?m and a yield stress of 300 N/mm2 or higher, and preferably has a specific permeability ?0.35 in a DC magnetic field of 0.35 Oe of 400 or higher. The steel sheet can be produced by regulating the hot-rolling coiling temperature to 600-700° C. and selecting an appropriate combination of the cold rolling reduction ratio and a final annealing temperature in the range of 750-900° C.

Abstract: The high-temperature relaxation resistance of spring steel is improved by providing a specified composition of the steel, and subjecting that steel composition to a controlled heat treatment. The high-temperature relaxation resistance, which can not be estimated from the mechanical properties (e.g. strength and hardness) of steel materials at an ordinary temperature, is improved by these conditions which the inventors have found out from many experiments. Especially, the temper-softening resistance is enhanced by an increase of the Si content. The density of dislocation is lowered by providing fine carbides (MO.sub.2 C) serving as inhibitors for the migration of dislocation. These are precipitated by a controlled heat treatment without reducing hardness in the tempered state. Consequently, the obtained spring steel can be used operated in a high-temperature environment for a long time without a deterioration in its properties.