Abstract: A carbon substrate is prepared from a molded article of thermosetting resin by heat-treating in an inert atmosphere. The resin is characterized in that the content of Fe, Al, Ni, Co, Cr, and Mg insoluble in the resin is less than 1 ppm each and the content of Ca and Si insoluble in the resin is less than 2 ppm each. The thermosetting resin is further characterized in that the water content is less than 3 wt % and the ratio of the methylene carbon (CH.sub.2) connected to the hydroxyl group (OH) is less than 3% (based on the total carbon number). The carbon substrate prepared in this manner is almost free of defects and voids. It is suitable for use as the substrate of magnetic recording medium. The thermosetting resin may be a powdery or granular one which fluidizes and then cures on heating. A molded article of thermosetting resin is prepared by introducing the resin melt into a mold and curing it with heating under pressure.

Abstract: A carbon substrate manufacturing method includes a hot molding step, a burn-carbonizing step, a hot isostatical pressure treatment step, and a mirror polishing step. In the hot molding step, molding is performed while heating thermosetting resin powders to be a hard carbon substrate after burn-carbonizing, where the thermosetting resin powders are of a particle size 150 .mu.m or more, HPF 80-150 mm, a moisture content 1.0-3.0 weight %, Fe, Ni, Si and Ca respectively 5 ppm or less. In the burn-carbonizing process, a disk shaped resin molded body is filled into a graphite cylinder and burn-carbonized by heating from the external while the condition therefor is maintained in that the disk shaped resin molded body is stacked holding therein a graphite spacer at every one sheet basis or at every plurality of sheet basis and is loaded on its top with a tungsten carbide weight, where the graphite spacer has a heat conductivity 100 kcal/m.hr..degree. C. or less, a bulk density 1.70-1.85, and a flatness degree 10 .mu.