Fine grain rare earth alloy cast strip, preparation method thereof, and a rotary cooling roll device

Abstract

An alloy cast strip includes grains having R2Fe14B-type compound as main phase, where R denotes a rare earth element, Fe denotes iron, and B denotes boron. The grains include non-columnar grains having an aspect ratio in a range from 0.3 to 2 and columnar grains having an aspect ratio equal to or larger than 3. A ratio of an area of the non-columnar grains to a total area of the grains is equal to or larger than 60% and a ratio of a number of the non-columnar grains to a total number of the grains is equal to or larger than 75%. A ratio of an area of the columnar grains to the total area of the grains is equal to or smaller than 15% and a ratio of a number of the columnar grains to the total number of the grains is equal to or smaller than 10%.

What is claimed is: 
     
         1 . An alloy cast strip comprising grains having R 2 Fe 14 B-type compound as main phase, wherein:
 R denotes a rare earth element, Fe denotes iron, and B denotes boron;   the grains include non-columnar grains having an aspect ratio in a range from 0.3 to 2 and columnar grains having an aspect ratio equal to or larger than 3;   a ratio of an area of the non-columnar grains to a total area of the grains is equal to or larger than 60% and a ratio of a number of the non-columnar grains to a total number of the grains is equal to or larger than 75%; and   a ratio of an area of the columnar grains to the total area of the grains is equal to or smaller than 15% and a ratio of a number of the columnar grains to the total number of the grains is equal to or smaller than 10%.   
     
     
         2 . The alloy cast strip according to  claim 1 , wherein one of the grains includes:
 an R 2 Fe 14 B-type main phase; and   rare-earth-rich phases including:
 in-grain rare-earth-rich phases embedded in the one of the grains, a spacing between neighboring ones of the in-grain rare-earth-rich phases is in the range of 0.5-3.5 μm; and 
 boundary rare-earth-rich phases distributed at a boundary of the one of the grains. 
   
     
     
         3 . The alloy cast strip according to  claim 2 , wherein the rare-earth-rich phases do not extend from a first surface of the alloy cast strip to a second surface of the alloy cast strip, the first surface and the second surface being opposite to each other. 
     
     
         4 . The alloy cast strip according to  claim 2 , wherein the boundary rare-earth-rich phases are distributed in an irregularly closed configuration along a temperature gradient direction cross section. 
     
     
         5 . The alloy cast strip according to  claim 1 , further comprising:
 an additive element T, the additive element T including at least one of Co, Ni, Cu, Mn, Cr, Ga, V, Ti, Al, Zr, Nb, or Sn;   wherein R includes at least one of La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Sc, or Y.   
     
     
         6 . The alloy cast strip according to  claim 5 , wherein a mass ratio of B in the alloy cast strip is 0.85% to 1.1%. 
     
     
         7 . The alloy cast strip according to  claim 1 , wherein equivalent circle diameters of the grains are in a range from 2.5 to 65 μm in a cross section along a temperature gradient direction. 
     
     
         8 . The alloy cast strip according to  claim 7 , wherein a ratio of an area of one or more of the grains that have an equivalent circle diameter of 10 to 50 μm to a total area of the grains is equal to or larger than 80%. 
     
     
         9 . The alloy cast strip according to  claim 8 , wherein a ratio of an area of one or more of the grains that have an equivalent circle diameter of 15 to 45 μm to the total area of the grains is equal to or larger than 50%. 
     
     
         10 . The alloy cast strip according to  claim 7 , wherein, in the cross section along the temperature gradient direction, an average equivalent circle diameter of one or more of the grains that are in a range of 100 μm to a first surface of the alloy cast strip is in a range from 6 to 25 μm, and an average equivalent circle diameter of one or more of the grains in a range of 100 μm to a second surface of the alloy cast strip is in a range from 35 to 65 μm, the first surface and the second surface being opposite to each other. 
     
     
         11 . The alloy cast strip according to  claim 1 , wherein a ratio of an area of one or more of the grains that have a heterogeneous nucleation center to a total area of the alloy cast strip is equal to or smaller than 5%. 
     
     
         12 . The alloy cast strip according to  claim 1 , wherein the grains do not extend from a first surface of the alloy cast strip to a second surface of the alloy cast strip, the first surface and the second surface being opposite to each other.