The black heart malleable cast iron according to the present embodiment comprises a matrix of ferrite and lump graphite included in the matrix, the black heart malleable cast iron comprising 50 ppm or more and 100 ppm or less of boron, and 65 ppm or more and 200 ppm or less of nitrogen in a mass ratio, wherein a grain size of the matrix is 8.0 or more and 10.0 or less in terms of grain size number, numerically determined by comparison between a metallographic photograph and a standard grain size chart.

A graphite steel available as a material for mechanical parts of industrial machines or automobiles, and more particularly, a steel wire for graphitization heat treatment and a graphite steel and methods of manufacturing the same. The graphite steel includes, in percent by weight (wt %), 0.6 to 0.9% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less of phosphorus (P), 0.03% or less of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.01 to 0.02% of titanium (Ti), 0.0005 to 0.002% of boron (B), 0.003 to 0.015% of nitrogen (N), 0.005% or less of oxygen (O), and the remainder of iron (Fe) and inevitable impurities, and satisfying Equation (1) below: wherein graphite grains are distributed in a ferrite base as a microstructure and a graphitization rate is 100%, (1) −0.003<[N]−[Ti]/3.43−[B]/0.77<0.003, wherein in Equation (1), [Ti], [N], and [B] are wt % of titanium, nitrogen, and boron, respectively.

The present disclosure discloses a method for producing high strength hot rolled steel. The method includes casting a steel slab of a composition, comprising in weight %: carbon (C) of about 0.45 wt. %-1.2 wt. %, manganese (Mn) of about 0.0-1.0 wt. %, silicon (Si) of about 0.0-0.5 wt. %, niobium (Nb) up-to 0.03 wt. %, sulphur (S) up-to 0.05 wt. % of S, phosphorous (P) up-to 0.05 wt. %, nitrogen (N) 0.002 wt. %-0.012 wt. % and balance being Iron (Fe) optionally along with incidental elements. The method also involves, heating, hot rolling, cooling, coiling the steel and retaining the steel at an ambient temperature to produce high strength hot rolled steel with 75-95% spheroid microstructure and 5-25% pearlite microstructure.

A high rigid spheroidal graphite cast iron, comprising: more than 3.0% to less than 3.6% of C, 1.5 to 3.0% of Si, 1.0% or less of Mn, 1.0% or less of Cu, less than 0.03% of P, 0.02% to 0.07% of Mg, residual Fe and inevitable impurities, as represented by mass %, wherein a carbon equivalent (a CE value) calculated by the mathematical expression (1): CE=C %+Si %/3 in terms of C and Si contents is 3.6 to 4.3%, the Young's modulus is 170 GPa or more, the tensile strength is 550 MPa or more, and the impact value is 12 J/cm.sup.2 or more.

A steel sheet has a composition containing, in mass %, from 0.60 to 1.25% of C, 0.50% or less of Si, from 0.30 to 1.20% of Mn, 0.030% or less of P, 0.030% or less of S, from 0.30 to 1.50% of Cr, from 0.10 to 0.50% of Nb, from 0 to 0.50% of Ti, from 0 to 0.50% of Mo, from 0 to 0.50% of V, from 0 to 2.00% of Ni, the balance being Fe with unavoidable impurities. A ferrite phase as a metal matrix has dispersed therein cementite particles and NiTi based carbide particles. A number density (cross section parallel to rolling and thickness directions) of the carbide particles having a circle equivalent diameter of 0.5 m or more is from 3,000 to 9,000 per mm.sup.2 and a number density of voids having a circle equivalent diameter of 1.0 m or more is 1,250 per mm.sup.2 or less.

The present invention relates to a particulate inoculant for treating liquid cast-iron, comprising, on the one hand, support particles made of a fusible material in the liquid cast-iron, and on the other hand, surface particles made of a material that promotes the germination and the growth of graphite, disposed and distributed in a discontinuous manner at the surface of the support particles, the surface particles presenting a grain size distribution such that their diameter d50 is smaller than or equal to one-tenth of the diameter d50 of the support particles.

The invention relates to ferritic cast iron comprising spheroidal graphite, containing, in % by mass, from 3.4 to 3.8% of carbon (C) from 1.5 to 2.1% of silicon (Si) not more than 0.25% of manganese (Mn) not more than 0.05% of sulfur (S) up to 0.6% of usual accompanying elements balance iron (Fe)

In order to achieve a notched impact energy of at least 20 J at a temperature of 10 C. in the case of such a ferritic cast iron comprising spheroidal graphite, the invention proposes that the accompanying elements chromium (Cr), vanadium (V), niobium (Nb) and titanium (Ti) in total be limited to 0.05% by mass. This results in a graphite nodule count of less than or equal to 160/mm.sup.2 in this cast iron. The invention further relates to the use of such a cast iron for cold-sensitive components, in particular in ships or wind power plants.

A high rigid spheroidal graphite cast iron, comprising: more than 3.0% to less than 3.6% of C, 1.5 to 3.0% of Si, 1.0% or less of Mn, 1.0% or less of Cu, less than 0.03% of P, 0.02% to 0.07% of Mg, residual Fe and inevitable impurities, as represented by mass %, wherein a carbon equivalent (a CE value) calculated by the mathematical expression (1): CE=C %+Si %/3 in terms of C and Si contents is 3.6 to 4.3%, the Young's modulus is 170 GPa or more, the tensile strength is 550 MPa or more, and the impact value is 12 J/cm.sup.2 or more.

The present invention relates to a graphite steel having excellent machinability, and a manufacturing method therefor, and more specifically, to a calcium-containing graphite steel having machinability superior to that of normal free-cutting steel and a manufacturing method therefor.

The present disclosure relates to a graphite steel wire rod for TV PEM nut parts, a graphite steel, and a manufacturing and cutting method therefor, and more particularly, to a cutting method for manufacturing industrial parts, a graphite steel wire rod, a graphite steel wire rod, a graphite steel, and a manufacturing method therefor.