non-graphitizable carbon 

https://doi.org/10.1351/goldbook.N04194
A non-graphitic carbon which cannot be transformed into graphitic carbon solely by high-temperature treatment up to 3300 K under atmospheric pressure or lower pressure.
Note:
The term non-graphitizable is limited to the result of heat treatment without additional influence of foreign matter or neutron radiation. Non-graphitizable carbon can be transformed into graphitic carbon by a high-temperature process via intermediate dissolution in foreign matter and precipitation under high pressure or by radiation damage.
Source:
PAC, 1995, 67, 473. (Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)) on page 498 [Terms] [Paper]