When a ribbon is cast by heating raw materials to prepare a molten R-T-B-based alloy and supplying the molten alloy to a chill roll to solidify the molten alloy, the temperature of the molten alloy is adjusted in accordance with at least one of the arithmetic mean roughness Ra and the mean spacing of profile irregularities Sm of the surface of the chill roll, thereby controlling the spacing between adjacent R-rich phases in a crystal structure of resulting alloy flakes to a desired value. This makes it possible to inhibit variations in the crystal structure of the resulting alloy flakes that may occur due to wear of the chill roll. In adjusting the temperature of the molten alloy in accordance with at least one of the arithmetic mean roughness Ra and the mean spacing of profile irregularities Sm, it is preferred that the molten alloy temperature be adjusted using the equation: t=7(|Ra||Sm|).sup.0.5/ where t is an amount of adjustment of the molten alloy temperature ( C.); Ra is an amount of change (m) in the arithmetic mean roughness Ra; Sm is an amount of change (m) in the mean spacing of profile irregularities Sm; and is a correlation coefficient.

In a continuous casting device 100 for casting a stainless steel billet 3c, a long nozzle 2 extending into a tundish 101 is provided at a ladle 1. A molten stainless steel 3 is poured through the long nozzle 2 into the tundish 101, and a spout 2a of the long nozzle 2 is immersed into the poured molten stainless steel 3. During pouring, an argon gas 4a is supplied around the molten stainless steel 3 in the tundish 101. Further, continuous casting is performed, in which, while immersing the spout 2a of the long nozzle 2 into the molten stainless steel 3 in the tundish 101, the molten stainless steel 3 is poured from the ladle 1 into the tundish 101 and poured from the tundish 101 into a casting mold 105. During casting, a nitrogen gas 4b is supplied instead of the argon gas 4a around the molten stainless steel 3 inside the tundish 101.

In a continuous casting device 100 for casting a stainless steel billet 3c, a long nozzle 2 extending into a tundish 101 is provided at a ladle 1. A molten stainless steel 3 is poured through the long nozzle 2 into the tundish 101, and a spout 2a of the long nozzle 2 is immersed into the poured molten stainless steel 3. During pouring, an argon gas 4a is supplied around the molten stainless steel 3 in the tundish 101. Further, continuous casting is performed, in which, while immersing the spout 2a of the long nozzle 2 into the molten stainless steel 3 in the tundish 101, the molten stainless steel 3 is poured from the ladle 1 into the tundish 101 and poured from the tundish 101 into a casting mold 105. During casting, a nitrogen gas 4b is supplied instead of the argon gas 4a around the molten stainless steel 3 inside the tundish 101.

Method for directly producing a pickling-free hot-plated sheet strip product from molten steel comprising: obtaining a refined molten steel; thin strip continuous casting: a mixed gas of an inert gas and a reducing gas is used for protection in the billet casting process; hot rolling: the cast strip is levelled at a high temperature so as to improve the sheet shape and rolled to a suitable thickness so as to change the product specification, or provide a mechanical disruption action on the iron oxide skin on the surface of the cast strip; reduction annealing: a sectional reduction method is used to perform sectional reductions with the temperature held within two ranges, i.e., 450-600 C. and 700-1000 C., wherein the reduction is performed within a range of 450-600 C. for 1-5 minutes and within a range of 700-1000 C. for 1-3 minutes to remove the iron oxide skin produced in the previous procedure, the concentration of the reducing gas being not lower than 5%; and hot galvanization: after having been cooled in a protective atmosphere, the strip billet is brought into a zinc bath and hot-plated with zinc and other alloy, and then cooled and coiled. The present invention realizes a highly continuous production of a hot-plated product from molten steel with iron and steel, and hot plating with zinc or an alloy is directly performed without removing elementary iron produced by the reduction, so that the energy consumption in the middle stage can be saved and the recovery of metal reaches close to 100%.

Method for directly producing a pickling-free hot-plated sheet strip product from molten steel comprising: obtaining a refined molten steel; thin strip continuous casting: a mixed gas of an inert gas and a reducing gas is used for protection in the billet casting process; hot rolling: the cast strip is levelled at a high temperature so as to improve the sheet shape and rolled to a suitable thickness so as to change the product specification, or provide a mechanical disruption action on the iron oxide skin on the surface of the cast strip; reduction annealing: a sectional reduction method is used to perform sectional reductions with the temperature held within two ranges, i.e., 450-600 C. and 700-1000 C., wherein the reduction is performed within a range of 450-600 C. for 1-5 minutes and within a range of 700-1000 C. for 1-3 minutes to remove the iron oxide skin produced in the previous procedure, the concentration of the reducing gas being not lower than 5%; and hot galvanization: after having been cooled in a protective atmosphere, the strip billet is brought into a zinc bath and hot-plated with zinc and other alloy, and then cooled and coiled. The present invention realizes a highly continuous production of a hot-plated product from molten steel with iron and steel, and hot plating with zinc or an alloy is directly performed without removing elementary iron produced by the reduction, so that the energy consumption in the middle stage can be saved and the recovery of metal reaches close to 100%.

The present invention provides a metal wire rod composed of iridium or an iridium alloy, wherein the number of crystal grains on any cross-section in a longitudinal direction is 2 to 20 per 0.25 mm.sup.2, and the Vickers hardness at any part is 200 Hv or more and less than 400 Hv. The iridium wire rod is a material which is produced by a -PD method, and has low residual stress and which has a small change in the number of crystal grains and hardness even when heated to a temperature equal to or higher than a recrystallization temperature (1200 C. to 1500 C.). The metal wire rod of the present invention is excellent in oxidative consumption resistance under a high-temperature atmosphere, and mechanical properties.

The present invention provides a metal wire rod composed of iridium or an iridium alloy, wherein the number of crystal grains on any cross-section in a longitudinal direction is 2 to 20 per 0.25 mm.sup.2, and the Vickers hardness at any part is 200 Hv or more and less than 400 Hv. The iridium wire rod is a material which is produced by a -PD method, and has low residual stress and which has a small change in the number of crystal grains and hardness even when heated to a temperature equal to or higher than a recrystallization temperature (1200 C. to 1500 C.). The metal wire rod of the present invention is excellent in oxidative consumption resistance under a high-temperature atmosphere, and mechanical properties.

For continuously casting an ingot of titanium or titanium alloy, molten titanium or titanium alloy is poured into a top opening of a bottomless mold with a circular cross-sectional shape, the solidified molten metal in the mold is pulled downward from the mold, a plurality of plasma torches disposed on an upper side of molten metal in the mold such that their centers are located directly vertically above the molten metal in the mold, are operated to generate plasma arcs that heat the molten metal in the mold, and the plasma torches are moved in a horizontal direction above a melt surface of the molten metal in the mold, along a trajectory located directly vertically above the molten metal in the mold, while keeping a mutual distance between the respective plasma torches such that the plasma torches do not interfere with each other.

Disclosed is an electromagnetic casting method of polycrystalline silicon which is characterized in that polycrystalline silicon is continuously cast by charging silicon raw materials into a bottomless cold mold, melting the silicon raw materials using electromagnetic induction heating, and pulling down the molten silicon to solidify it, wherein the depth of solid-liquid interface before the start of the final solidification process is decreased by reducing a pull down rate of ingot in a final phase of steady-state casting. By adopting the method, the region of precipitation of foreign substances in the finally solidified portion of ingot can be reduced and cracking generation can be prevented upon production of a polycrystalline silicon as a substrate material for a solar cell.

Disclosed is an electromagnetic casting method of polycrystalline silicon which is characterized in that polycrystalline silicon is continuously cast by charging silicon raw materials into a bottomless cold mold, melting the silicon raw materials using electromagnetic induction heating, and pulling down the molten silicon to solidify it, wherein the depth of solid-liquid interface before the start of the final solidification process is decreased by reducing a pull down rate of ingot in a final phase of steady-state casting. By adopting the method, the region of precipitation of foreign substances in the finally solidified portion of ingot can be reduced and cracking generation can be prevented upon production of a polycrystalline silicon as a substrate material for a solar cell.