The carbonization of cellulose fiber fabric comprises an initial stage of heat treatment up to 250 C. to 350 C., with a relatively high mean temperature rise speed of 10 C./min to 60 C./min, an intermediate stage up to 350 C. to 500 C. with a lower mean temperature rise speed of 2 C./min to 10 C./min, and a final stage up to 500 C. to 750 C. with a mean temperature rise speed that is again raised to 5 C./min to 40 C./min.