The goal of this study is to specify the optimal factors for the hardening process (tempering temperature, the percentage of nanoparticles, type of base media, nanoparticles type and tempering time) in order to maximize the hardness of medium carbon steel by using Taguchi technique. An (L18) orthogonal array was chosen for the design of the experiment. The optimum process parameters were determined by using signal-to-noise ratio(larger is better) criterion. The important levels of process parameters on hardness were obtained by using analysis of variance which applied with the help of (Minitab17) software to investigate the effect of parameters on the hardness. Percentage of volumetric fractions of nanoparticles with three different levels (0.01, 0.03 and 0.08%) was prepared by dispersing nanoparticles that are (α-Al2O3, TiO2 and Cuo) with base fluids (De-ionized water, salt solution, and engine oil). Medium carbon steel specimens were suffered to hardening and tempering heat treatment process. Tempering temperature was (400℃, 550℃) for (30,45and 60 minutes). Results ended up with a conclusion that tempering temperature (400℃) had the major influence on hardness behavior then type of nanoparticles (TiO2) followed by time tempering (30min) then base media (salt solution) and finally volume fraction of nanoparticles (0.03%).

Nanofluids --- quenching --- hardness --- Taguchi technique.