The Pr-Fe-B ternary system has been investigated by means of X-ray diffraction and differential thermal analysis. The room temperature section of this ternary system with B≤48 at.%, the Pr-Fe binary phase diagram, the vertical section of the Pr-Fe-B ternary system with 6 at.% of boron (Pr<60 at.%) and several vertical sections of pseudo-binary systems Fe—Pr2Fe14B—Pr, Pr2 Fe17—Pr2Fe14B—Pr2Fe7B6 and Fe-Pr2Fe7B6, which are related to the phase Pr2Fe14B, have been determined. The hard magnetic phase Pr2Fe14B is the product of peritectic reaction of L + γ- Fe Pr2Fe14B. It melts noncongruently at 1145℃ and the corresponding liquidus point is about 1298℃. Eutectic reactions between Pr2Fe14B and Pr, Pr2Fe14B and Pr2Fe17, and Pr2Fe14B and Pr2Fe7B6 take place at 676℃, 1085℃ and 1100℃ respectively.

The phase diagram of Nd-Fe-B ternary system ( B ≤50 at%) has been investigated by means of X-ray diffraction, thermal analysis and magnetic measurement. (ⅰ) The phase diagram of Nd-Fe binary system has been redetermined. (ⅱ) A new permanent magnet is composed of three phases: major phase Nd2Fe14B, minor phase Nd and Nd8Fe27B24. (ⅲ) The highest sintering temperature must not be higher than 1100℃ and the post-heat treatment temperature is at about 600℃ for the powder metallurgy. (ⅳ) The structures of Nd2Fe14B and Nd8Fe27B24 compound as well as the homogeneous phase region of Nd2-Fe24B have been investigated. (ⅴ) The thermostability of Nd2Fe14B compound has been discussed and the powder metallurgical process explained.