Heat treatment of material particularly quenching requires a high thermal conductivity quench medium. Hardenability of material, dimension, and geometry of the component are considerate on choosing quench medium. The cooling rate of quenching affects the properties and microstructures by creating specific phase transformation to occur. Enhancing the quench medium by accelerating the cooling rate can be attained by the addition of nanoparticle which has higher thermal conductivity. This nanoparticle-added medium is commonly termed as nanofluid. Commercial and laboratory grade of TiO2 was used as the nanoparticle to distilled water as the nanofluid base to acquired higher conductivity on the heat treatment process. In this experiment, a top-down method was done to obtain TiO2 particles by grounding using a planetary ball mill for 15 hours at 500 rpm. Nanofluid quench medium was mixed with TiO2 in various concentration of 1%, 5% and 10% with a volume of 100 ml each. Samples of AISI 1045 or JIS S45C carbon steel were used to obtain different cooling rate on a different type of TiO2 particles. Samples were heat treated by austenizing at 1000°C for 1 hour, followed by rapid quenching in nanofluid quench medium with the addition of agitation as quenching variable. Observation of particle morphology and size, material composition, and the change of surface ere measured by Field-Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). Initial characterization showed that the TiO2 particle size was at 150 nm range, and roughly free from any impurities. Martensite microstructures have the most significant area and the amount at laboratory-grade TiO2 in 0.2 wt% composition, followed by commercial-grade at 0.3 wt% composition.

Quenching is performed as part of steel heat-treatment to enhance mechanical properties, by rapid cooling. Factors that affect the selection of quench medium are hardenability of material, geometry, and dimensions of the component. In recent developments, nanofluids are used to improve heat transfer capacity. In this research, nanofluids were synthesized using the two-step method. Milling of particles was done using a high energy ball mill for 15 hours at 500 rpm. Observation of particle size, material composition, and morphology of particle, and surface changes of the particle were measured by Field-Emission Scanning Electron Microscope (FE- SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). Water-based nanofluids with a volume of 100ml were produced using the two-step method, with carbon concentrations of 0.1%, and 0.5% and Sodium Dodecylbenzene Sulfonate concentrations of 0%, 1%, 3%, and 5%. Samples of S45C steels were austenized at 1000°C for 60 minutes. Hardness testing results correspond to the severity of the quenching mediums, with peak hardness of 845 HV for 0.1% Carbon with 1% SDBS, and 878 HV for 0.5% carbon with 3% SDBS. Hardness testing results show a significant improvement over results without SDBS addition. Excess surfactant addition yields a lower hardness due to the re-agglomeration of particles.

Quenching takes an important part in the heat treatment process that controls the microstructure, thus enhance its mechanical properties. The heat treatment process starts with heating at an elevated temperature, holding time then rapid cooling to room temperature. It requires a medium with a good thermal conductivity that can be achieved by the addition of nanoparticles to the quench medium, referred to as nanofluids. In this research, carbon particles were prepared by the top-down method, where the reduction of carbon particle was done by planetary ball-mill for 15 hours at 500 rpm. Cetyl Trimethyl Ammonium Bromide is utilized as a cationic surfactant in order to reduce agglomeration at suspended particles thus increase quenching efficiency. Field-Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive X-Ray Spectroscopy (EDX) were used to observe the composition of material, particle size and particle morphology, and the change of the surface. Initial characterization by FE-SEM showed that the particle size after milling was averaged roughly at 15 µm, therefore, it was still not in the nanometer range. However, EDS result confirmed that the powder used in this research were 99% carbon. Carbon microparticles were added as the particle to distilled water as the microfluid base. Water-based carbon microfluid with a volume of 100 ml was produced by the two-step method, by mixing carbon microparticles at 0.1 wt%, and 0.5 wt% in various concentration of cationic surfactant of 1 wt%, 3 wt%, and 5wt % respectively. Samples of AISI 1045 or JIS S45C carbon steels were heat treated by austenizing at 1000°C in a heating furnace, followed by rapid quenching in microfluid as the medium quench resulting on cooling rate diagram. Mechanical properties and microstructures of the quenched samples will be observed by conducting hardness examination and metallography observation to analyze the effect of various carbon and surfactant concentration used in the water-based carbon microfluid quench medium.