A wire rod of a Cu—Zn—Si based alloy obtained by up-drawing continuous casting is provided; the amount of Cu is within a range of 75.0 mass% or more and 76.9 mass% or less, the amount of Si is within a range of 2.6 mass% or more and 3.1 mass% or less, the amount of Zr is within a range of 0.003 mass% or more and 0.20 mass% or less, the amount of P is within a range of 0.02 mass% or more and 0.15 mass% or less, the balance is composed of Zn and inevitable impurities, and the number density of a Zr—P compound containing Zr and P is within a range of 1500 pieces/mm.sup.2 or more and 7000 pieces/mm.sup.2 or less.

A continuously casting method including arranging temperature measuring elements according to specified conditions, selecting as evaluation targets for temperatures of copper plates on a wide face of mold values measured by the temperature measuring elements arranged closer to a center in a width direction of a cast slab than short sides of the cast slab under continuous casting at levels of 50 mm or more lower in a slab withdrawal direction than a meniscus of a molten steel in a mold, and adjusting a casting condition such that a standard deviation of the values measured over the width direction of the copper plates on the wide face of mold at a same level in the slab withdrawal direction is 20° C. or lower.

A horizontal continuous casting apparatus includes a fluid supply pipe for supplying a lubricating fluid to the hollow portion of the mold, which is arranged on one end side of the mold; and, a cooling water cavity for accommodating cooling water cooling an inner peripheral surface of the hollow portion of the mold, which is formed outside the inner peripheral surface, wherein the inner peripheral surface and the inner bottom surface of the cooling water cavity facing the inner peripheral surface form parallel surfaces with each other, and a cooling wall of the mold between the inner peripheral surface and the inner bottom surface is formed so that the heat flux value per unit area from the molten aluminum alloy to the cooling water is 10×10.sup.5 W/m.sup.2 or more.

Continuous casting mold is provided having a mold copper plate having plural separate portions filled with foreign metal formed by filling concave grooves formed on the inner wall surface of the mold copper plate and having a diameter of 2 mm to 20 mm in the inner wall surface at least in the region from a meniscus to a position located 20 mm or more lower than the meniscus with the foreign metal whose thermal conductivity is 80% or less or 125% or more of the mold copper plate, the ratio of the Vickers hardness HVc of the mold copper plate to the Vickers hardness HVm of the filling metal satisfies expression (1), and the ratio of the thermal expansion coefficient αc of the mold copper plate and the thermal expansion coefficient αm of the filling metal satisfies expression (2).

0.3 HVc/HVm≦2.3   (1),

0.7≦αc/αm≦3.5   (2)

Continuous casting mold is provided having a mold copper plate having plural separate portions filled with foreign metal formed by filling concave grooves formed on the inner wall surface of the mold copper plate and having a diameter of 2 mm to 20 mm in the inner wall surface at least in the region from a meniscus to a position located 20 mm or more lower than the meniscus with the foreign metal whose thermal conductivity is 80% or less or 125% or more of the mold copper plate, the ratio of the Vickers hardness HVc of the mold copper plate to the Vickers hardness HVm of the filling metal satisfies expression (1), and the ratio of the thermal expansion coefficient αc of the mold copper plate and the thermal expansion coefficient αm of the filling metal satisfies expression (2).

0.3 HVc/HVm≦2.3   (1),

0.7≦αc/αm≦3.5   (2)

Provided are lean duplex stainless steel having a dual-phase structure of an austenite phase and a ferrite phase, and a method for producing the lean duplex stainless steel. The lean duplex stainless steel, as a ferrite-austenite stainless steel, has the preferred stacking fault energy (SFE) value of the austenite phase, expressed by the formula 2 below, of 19-37 and critical strain value range, within which the strain-induced martensite phases occurs, of 0.1−0.25. Formula 2: SFE=25.7+1.59×Ni/[K(Ni)−K(Ni)×V(γ)+V(γ)]+0.795×Cu/[K(Cu)−K(Cu)×V(γ)+V(γ)]−0.85×Cr/[K(Cr)−K(Cr)×V(γ)+V(γ)]+0.001×(Cr/[K(Cr)−K(Cr)×V(γ)+V(γ)]).sup.2+38.2×(N/[K(N)−K(N)×V(γ)+V(γ)]).sup.0.5−2.8×Si/[K(Si)−K(Si)×V(γ)+V(γ)]−1.34×Mn/[K(Mn)−K(Mn)×V(γ)+V(γ)]+0.06×(Mn/[K(Mn)−K(Mn)×V(γ)+V(γ)]).sup.2. Ni, Cu, Cr, N, Si and Mn indicate the overall content (wt. %) of the respective constituent element, and K(x) is the distribution index of respective constituent element (x) and is expressed by the formula 3 below, and V(γ) is the component ratio of austenite (in the 0.45-0.75 range). Formula 3: K(x)=[amount of element x in ferrite phase]/[amount of element x in austenite phase]

Provided are lean duplex stainless steel having a dual-phase structure of an austenite phase and a ferrite phase, and a method for producing the lean duplex stainless steel. The lean duplex stainless steel, as a ferrite-austenite stainless steel, has the preferred stacking fault energy (SFE) value of the austenite phase, expressed by the formula 2 below, of 19-37 and critical strain value range, within which the strain-induced martensite phases occurs, of 0.1−0.25. Formula 2: SFE=25.7+1.59×Ni/[K(Ni)−K(Ni)×V(γ)+V(γ)]+0.795×Cu/[K(Cu)−K(Cu)×V(γ)+V(γ)]−0.85×Cr/[K(Cr)−K(Cr)×V(γ)+V(γ)]+0.001×(Cr/[K(Cr)−K(Cr)×V(γ)+V(γ)]).sup.2+38.2×(N/[K(N)−K(N)×V(γ)+V(γ)]).sup.0.5−2.8×Si/[K(Si)−K(Si)×V(γ)+V(γ)]−1.34×Mn/[K(Mn)−K(Mn)×V(γ)+V(γ)]+0.06×(Mn/[K(Mn)−K(Mn)×V(γ)+V(γ)]).sup.2. Ni, Cu, Cr, N, Si and Mn indicate the overall content (wt. %) of the respective constituent element, and K(x) is the distribution index of respective constituent element (x) and is expressed by the formula 3 below, and V(γ) is the component ratio of austenite (in the 0.45-0.75 range). Formula 3: K(x)=[amount of element x in ferrite phase]/[amount of element x in austenite phase]

A method of casting a metal ingot with a microstructure that facilitates further working, such as hot and cold rolling. The metal is cast in a direct chill casting mold, or the equivalent, that directs a spray of coolant liquid onto the outer surface of the ingot to achieve rapid cooling. The coolant is removed from the surface at a location where the emerging embryonic ingot is still not completely solid, such that the latent heat of solidification and the sensible heat of the molten core raises the temperature of the adjacent solid shell to a convergence temperature that is above a transition temperature for in-situ homogenization of the metal. A further conventional homogenization step is then not required. The invention also relates to the heat-treatment of such ingots prior to hot working.

A method of casting a metal ingot with a microstructure that facilitates further working, such as hot and cold rolling. The metal is cast in a direct chill casting mold, or the equivalent, that directs a spray of coolant liquid onto the outer surface of the ingot to achieve rapid cooling. The coolant is removed from the surface at a location where the emerging embryonic ingot is still not completely solid, such that the latent heat of solidification and the sensible heat of the molten core raises the temperature of the adjacent solid shell to a convergence temperature that is above a transition temperature for in-situ homogenization of the metal. A further conventional homogenization step is then not required. The invention also relates to the heat-treatment of such ingots prior to hot working.

In production of a reactive metal using a melting furnace for producing metal having a hearth, ingots can be efficiently produced by efficiently cooling the ingots extracted from the mold provided in the melting furnace. In addition, an apparatus structure in which multiple ingots can be produced with high efficiency and high quality from one hearth, is provided. A melting furnace for producing metal is provided, the furnace has a hearth for having molten metal formed by melting raw material, a mold in which the molten metal is poured, an extracting jig which is provided below the mold for extracting ingot cooled and solidified downwardly, a cooling member for cooling the ingot extracted downwardly of the mold, and an outer case for keeping the hearth, the mold, the extracting jig, and the cooling member separated from the air, wherein at least one mold and extracting jig are provided in the outer case, and the cooling member is provided between the outer case and the ingot, or between the multiple ingots.