A hot-rolled steel sheet includes a specific chemical composition, and includes a microstructure represented by, in vol %: retained austenite: 2% to 30%; ferrite: 20% to 85%; bainite: 10% to 60%; pearlite: 5% or less; and martensite: 10% or less. A proportion of grains having an intragranular misorientation of 5° to 14° in all grains is 5% to 50% by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more.

Disclosed are a high-strength steel bar and a production method therefor. The high-strength steel bar comprises, by mass percentage, the following chemical components: C: 0.15-0.32%, Si+Mn: 0.5-1.9%, Mn+Cr+Mo+Ni: 1.1-2.1%, V: 0.02-0.8%, at least one of Nb, Ti and Al: 0.01-0.3%, and the balance of Fe and inevitable impurities; wherein Mn=(2.5-3.5)Si, and a carbon equivalent satisfies Ceq=C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15≤0.56%.

A hot-rolled steel sheet for a heavy-wall, high-strength line pipe, the steel sheet having a chemical composition including, in mass %, C: 0.02 to 0.20%, Mn: 0.80 to 2.10%, Si: 0.01 to 0.50%, P: 0.034% or less, S: 0.0050% or less, Nb: 0.01 to 0.15%, Ti: 0.001 to 0.030%, and Al: 0.001 to 0.080%, the balance being Fe and incidental impurities, the steel sheet having a microstructure in which a main phase is a continuous cooling transformation structure and in which {001}.sub.α grains in a plane whose normal direction is the sheet width direction constitute an area fraction of 10% or less and have a combined size of 10 μm or less, wherein the steel sheet has a tensile strength of 520 MPa or greater, and, in a drop weight tear test, a temperature at which a percent ductile fracture reaches 85% is −25° C. or lower.

There is provided a steel sheet including an inner layer and a hard layer formed on one or both surfaces of the inner layer, wherein each content of C and Mn in the hard layer is more than each content of C and Mn in the inner layer, a thickness of the hard layer is 20 μm or more and a total of the thickness of the hard layer is ⅖ or less of the entire sheet thickness, an average micro-Vickers hardness of the hard layer is 400 HV or more and less than 800 HV, an average micro-Vickers hardness of the inner layer is 350 HV or more and is 50 HV or more smaller than a hardness of the hard layer, and a screw dislocation density of the inner layer is 2.0×10.sup.13 m/m.sup.3 or more.

The invention consists of a gray cast iron comprising carbon, silicon, vanadium, manganese, nickel, chromium, molybdenum, copper, sulfur, phosphorous, tin and titanium, wherein: the percentage by weight of carbon is from 3.70 to 3.90%; the percentage by weight of silicon is from 1.30 to 2.10%; the percentage by weight of vanadium is from 0.10 to 0.15%; the percentage by weight of manganese is from 0.60 to 0.90%; the percentage by weight of nickel is from 0.05 to 0.50%; the percentage by weight of chromium is from 0.20 to 0.35%; the percentage by weight of molybdenum is no more than 0.10%; the percentage by weight of copper is no more than 0.35%; the percentage by weight of sulfur is less than 0.10%; the percentage by weight of phosphorous is less than 0.10%; the percentage by weight of tin is less than 0.10%; the percentage by weight of titanium is no more than 0.01%; the remainder by weight being iron.

A method for treating a Yankee cylinder, where the Yankee cylinder has a cylinder shell made of steel with a ferritic-pearlitic structure. In the disclosed method, the outer surface of the cylinder shell is heat-treated with a laser beam and hardened as a result.

A steel sheet has a chemical composition with a steel structure containing, by volume fraction, soft ferrite: 0-30%, retained austenite: 3-40%, fresh martensite: 0-30%, pearlite and cementite: 0-10%, and a remainder including hard ferrite. In the steel sheet, a number proportion of retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, and a soft layer having a thickness of 1-100 μm is present. In the soft layer, a volume fraction of ferrite grains having an aspect ratio of less than 3.0 is 50% or more, and a volume fraction of retained austenite is 50% or more of the volume fraction of the retained austenite of the inside of the steel sheet. A peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 μm to 5 μm or less from the surface.

A diesel engine piston is cast in one piece and consists of almost fully pearlitic cast iron with spheroidal graphite as the piston material. Such a piston is used for “light vehicle” diesel engines, “heavy duty” diesel engines and “large bore” diesel engines.

A spheroidal graphite cast iron having a chemical composition of: C: 3.0% to 4.0%, Si: 2.0% to 2.4%, Cu: 0.20% to 0.50%, Mn: 0.15% to 0.35%, S: 0.005% to 0.030%, Mg: 0.03% to 0.06%, each by mass, and the balance being Fe and inevitable impurities, where Mn and Cu are contained at 0.45% to 0.75% in total; and a structure in which a ferrite layer encloses spheroidal graphite crystallized out in a matrix of pearlite. Part of the pearlite is extended from the matrix side to the spheroidal graphite side to divide the ferrite layer at one or more areas.

A wire rod and a steel wire for a high stress suspension spring for motorcycles, wherein decarbonization and low-temperature structure occurrence are easily suppressed when the wire rod and the steel wire are cooled down; and a manufacturing method therefor. A steel wire for a high strength spring includes, in percent by weight (wt %), 0.55 to 0.65% of carbon (C), 0.5 to 0.9% of silicon (Si), 0.3 to 0.8% of manganese (Mn), 0.3 to 0.6% of chromium (Cr), 0.015% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of aluminum (Al), 0.005% or less of nitrogen (N), and the remainder of iron (Fe) and inevitable impurities, satisfies Formula (1) below, and comprises 90% or more of a tempered martensite structure. In Formula (1), C, Mn, Cr, and Si denote contents (wt %) of the corresponding elements, respectively. (1) 0.77≤C+(⅙)*Mn+(⅕)*Cr+( 1/24)*Si≤0.83.