Abstract: A steel has a predetermined chemical composition with a balance being Fe and incidental impurities, wherein a sum of Cu content and Ni content is 0.15 mass % or more, and a crystal grain size after forming into a stabilizer shape and quenching is in a range of 7.5 to 10.5 in prior austenite crystal grain size number. Thus, a highly durable stabilizer steel that has a tensile strength of 1200 MPa or more and excellent normal-temperature and low-temperature toughness and is used in an environmentally friendly manufacturing process at lower cost can be realized.

Abstract: A steel, having a high corrosion resistance and low-temperature toughness, for a vehicle suspension spring part, the steel includes 0.21 to 0.35% by mass of C, more than 0.6% by mass but 1.5% by mass or less of Si, 1 to 3% by mass of Mn, 0.3 to 0.8% by mass of Cr, 0.005 to 0.080% by mass of sol. Al, 0.005 to 0.060% by mass of Ti, 0.005 to 0.060% by mass of Nb, not more than 150 ppm of N, not more than 0.035% by mass of P, not more than 0.035% by mass of S, 0.01 to 1.00% by mass of Cu, and 0.01 to 1.00% by mass of Ni, the balance being Fe and unavoidable impurities, with Ti+Nb?0.07% by mass, wherein crystal grains of the steel after hardening have a prior austenite grain size number of 7.5 to 10.5, and the steel having a tensile strength of not less than 1,300 MPa.

Abstract: A low carbon resulfurized free cutting steel consisting of 0.04 to 0.15% of C, more than 0.10% and 0.70% or less of Si, 0.85 to 1.50% of Mn, 0.040 to 0.120% of P, 0.250% or more and less than 0.400% of S, less than 0.005% of Al, more than 0.0020% and 0.0120% or less of O, and more than 0.0070% and 0.0150% or less of N, all by mass percentage, and the balance of Fe and inevitable impurities, and satisfying a formula (1) and a formula (2), as follows: 0.15%?Si %+2×P %?(5×Al %+10×O %+3×N %)?0.75%??(1), and ([Mn %]5)/15<S %<([Mn %]5)/2??(2).

Abstract: Steel, excellent in corrosion resistance and low-temperature toughness, for a vehicle suspension spring part, includes 0.15 to 0.35% by mass of C, more than 0.6% by mass but 1.5% by mass or less of Si, 1 to 3% by mass of Mn, 0.3 to 0.8% by mass of Cr, 0.005 to 0.080% by mass of sol. Al, 0.005 to 0.060% by mass of Ti, 0.005 to 0.060% by mass of Nb, not more than 150 ppm of N, not more than 0.035% by mass of P, not more than 0.035% by mass of S, 0.01 to 1.00% by mass of Cu, and 0.01 to 1.00% by mass of Ni, the balance consisting of Fe and unavoidable impurities, with Ti+Nb?0.07% by mass. The steel has a tensile strength of not less than 1,300 MPa.

Abstract: According to one embodiment, a high-strength stabilizer steel for vehicles having excellent corrosion resistance and low-temperature toughness, containing 0.07 to 0.20% C, more than 0.6% and 1.5% or less Si, 1 to 3% Mn, 0.1 to 1.0% Cr, 0.005 to 0.080% sAl, 0.005 to 0.060% Ti, 0.005 to 0.060% Nb, 0.070% or less Ti+Nb, 150 ppm or less N, 0.035% or less P, 0.035% or less S, 0.01 to 1.00% Cu, 0.01 to 1.00% Ni, the remainder being Fe, and unavoidable impurities, wherein a structure before molding a stabilizer is any one of a bainite, a martensite, and a mixed structure of bainite/martensite and an original austenitic crystal grain size number after a heat treatment of the stabilizer is Gh 9 or more.

Abstract: A low carbon free cutting steel can be obtained by allowing the steel to contain 0.02 to 0.15 mass % of C, 0.05 to 1.8 mass % of Mn, 0.20 to 0.49 mass % of S, more than 0.01 mass % and not more than 0.03 mass % of O, 0.3 to 2.3% of Cr, and the balance consisting of Fe and inevitable impurities, the Cr/S ratio falling within a range of between 2 and 6.

Abstract: According to one embodiment, a high-strength stabilizer steel for vehicles having excellent corrosion resistance and low-temperature toughness, containing 0.07 to 0.20% C, more than 0.6% and 1.5% or less Si, 1 to 3% Mn, 0.1 to 1.0% Cr, 0.005 to 0.080% sAl, 0.005 to 0.060% Ti, 0.005 to 0.060% Nb, 0.070% or less Ti+Nb, 150 ppm or less N, 0.035% or less P, 0.035% or less S, 0.01 to 1.00% Cu, 0.01 to 1.00% Ni, the remainder being Fe, and unavoidable impurities, wherein a structure before molding a stabilizer is any one of a bainite, a martensite, and a mixed structure of bainite/martensite and an original austenitic crystal grain size number after a heat treatment of the stabilizer is Gh 9 or more.