In heat treatment industries, quench medium is used to increase the cooling rate of heat-treated materials, thus altering their microstructure and properties. Several conventional quench medium, such as salt bath system, petroleum-based oil, and polymers are commonly used, depend on the cooling rate needed for the process. Most of those quench medium, however, are harmful for environment due to their high chemical reactivity, mostly non-reusable and dangerous post-usage product. A recent approach to address this problem is by using nanofluid as quench medium. Nanofluids are colloids obtained by combining high thermal conductivity solid nanoparticles with base fluids, such as water, ethylene glycol, or oil. Water-based nanofluids with carbon nanoparticles are promising candidate as quench medium because of their reusable components, relatively inert element, non-toxic waste, and adjustable quench severity. Carbon nanoparticles are chosen due to their enhanced thermal properties and high thermal conductivity of 1.7 W/mK at 25°C, comparing to other nanoparticle materials with higher cost, such as Al2O3, CuO and TiO2. In this study, ordinary charcoals were comminuted and sieved repeatedly to obtain carbon powder. Furthermore, the powder was milled to get nano-sized carbon particles. The dimension of carbon particles were roughly μm size after sieving, measured by Field Emission Scanning Electron Microscope (SEM). Composition and crystallinity of carbon particle were characterized using Electron Diffraction X-ray Spectroscopy (EDS) and showed a pure carbon x-ray spectrum. Carbon nanoparticles with variation from 0.06 wt% to 0.14 wt% were mixed with 100 ml water as the base fluid to create nanofluid.