R-T-B based alloy powder, compound for anisotropic bonded magnet and anisotropic bonded magnet

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The present invention provides R-T-B based alloy powders, wherein R represents at least one rare earth element, and T represents at least one element selected from the group consisting of ferrum and cobalt. The R-T-B based alloy powders have main phase grains, grain boundary phases and additive phases. The main phase grains are composed of R2T14B and have an average grain size of 200 nm or more and 500 nm or less. The grain boundary phases are richer in R than the main phase grains. With respect to any cross section of the R-T-B based alloy powders, the coverage of the main phase grains defined by equation 1 with the grain boundary phases with a roundness defined by equation 2 being 0.1 or more and 0.6 or less, is 10% or more and 40% or less. coverage ≡ ∑ i ⁢ ⁢ l i ∑ j ⁢ ⁢ L j ⁢ ⁢ l i ⁢ : ⁢ ⁢ Circumference ⁢ ⁢ of ⁢ ⁢ each ⁢ ⁢ grain boundary ⁢ ⁢ phase ⁢ ⁢ L j ⁢ : ⁢ ⁢ Circumference ⁢ ⁢ of ⁢ ⁢ each ⁢ ⁢ main phase ⁢ ⁢ grain 〈 equation ⁢ ⁢ 1 〉 Roundness = 4 ⁢ ⁢ π ⁢ ⁢ A ⁢ / ⁢ L 2 〈 equation ⁢ ⁢ 2 〉 A represents the area of the cross section of the grain boundary phase, and L represents the circumference of the cross section of the grain boundary phase.