METHOD FOR PRODUCING RARE EARTH BASED ALLOY PIECE

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When casting an ingot by heating a starting material to form a molten R-T-B based alloy and by solidifying the molten alloy as a result of supplying same to a rapid cooling roll, it is possible to inhibit the variation in the crystalline structure of the obtained alloy piece due to the rapid cooling roll wearing down by adjusting the temperature of the molten alloy in accordance with the arithmetic average roughness (Ra) of the surface of the rapid cooling roll and/or the average interval (Sm) between concaves and convexes, and by controlling the R-rich phase interval in the crystalline structure of the obtained alloy piece to a target value. When adjusting the temperature of the molten alloy in accordance with the arithmetic average roughness (Ra) and/or the average interval (Sm) between concaves and convexes, it is preferred that the temperature of the molten alloy is adjusted in accordance with the equation Δt=-7×(|ΔRa|×|ΔSm|)0.5/α, wherein Δt represents the degree (°C) by which the temperature of the molten alloy is adjusted, ΔRa represents the amount (μm) by which the arithmetic average roughness (Ra) changes, ΔSm represents the amount (μm) by which the average interval (Sm) between the concaves and convexes changes, and α represents a coefficient of correlation.