METHOD FOR PRODUCING ALLOY CAST SLAB FOR RARE EARTH SINTERED MAGNET

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Disclosed are : an alloy cast slab for a rare earth sintered magnet, which has high rare earth component yield between before and after pulverization, while having uniform particle size after pulverization; and a method which is capable of commercially producing the alloy at high energy efficiency. The production method comprises : a step (A) for preparing an alloy melt that contains B, Fe and R that is composed of at least one element selected from rare earth metal elements including Y or alternatively contains Fe and at least one element selected from among transition metal elements other than Fe, Si and C, with the balance made up of M; a step (B) for quenching and solidifying the alloy melt to a temperature range of 700-1, 000˚C (inclusive) by a strip casting method using a cooling roll; and a step (C) for heating and maintaining an alloy cast slab, which is separated from the cooling roll by the quenching and solidification of the step (B), within a specific temperature range before the alloy cast slab is cooled to 500˚C or less. By the production method, an alloy cast slab that has a composition containing 27.0-33.0% by mass of R and 0.90-1.30% by mass of boron with the balance made up of M is obtained.