In the cooling stage of solution treatment, fine plate-like M3B2precipitated at grain boundaries, the quantity increasing with increasing boron content in the alloy. When boron content reached 310 ppm, the precipitation of M3B2during cooling mainly concentrated on the surfaces of lump-like M3B2at grain boundaries. In the process of standard heat treatment, the quantity of granular M3B2increased with increasing boron content. Boron could suppress the segregation of plate-like MC at grain boundaries. Granular M3B2precipitated homogeneously in a disperse form. It was discovered that it could precipitate on the surfaces of blocky-like M3B2and plate-like MC when the boron content reached 310 ppm. Blocky-like and granular M3B2in the alloy were composed of tungsten, titanium, chromium, iron, etc. with a general formula MxM'3-xB2; here, in addition to some granular M3B2with x = 2, x was normally larger than 2.