Effect of Multi-walled Carbon Nanotube and Polyethylene Glycol Addition in Nanofluid Quench Medium for Steel Heat Treatment Application

In the steel heat treatment industry, quenching is a critical stage for enhancing the characteristics of steel. However, the lack of adherence to appropriate procedures, especially in quenchant selection, can lead to cracks or distortion. Quenchant selection is based on the required cooling rate for the specific steel being quenched. Cooling rate of the quenchant is primarily determined by the thermal conductivity of the fluid. This conductivity can be modified by dispersing stabilized solid particles, typically in the nano-scale range, thus forming a nanofluid. It is important to note that a higher conductivity will increase the heat transfer characteristic and vice versa, hence, cooling rate can be controlled by adjusting the amount of the dispersed particle. In this study, the dispersed particle and surfactant used was multi-walled carbon nanotube (MWCNT) and polyethylene glycol (PEG), respectively. The concentrations of the dispersed particle were 0.1, 0.3, and 0.5 weight%. Furthermore, the surfactant was added at 3 - 30% on each particle variation. The results showed that the highest thermal conductivity of 0.68 W/mK was achieved at 0.5% MWCNT and 5% PEG. This translated into better steel properties, as it led to a hardness of 48 in Hardness Rockwell C-scale (HRC) compared with the water-quenching technique. A higher percentage of PEG surfactant decreases the thermal conductivity of the quenching medium and steel hardness. This decrease was attributed to the high viscosity of the medium. In conclusion, adjusting the particle and surfactant concentration allows for the optimal quenching medium, offering enhanced steel properties.