This paper represents the effect of workpiece hardness obtained of different heat treatments of steel (AISI X 210 Cr 12) on surface roughness quality during turning operation. Three different levels of hardness for specimen’s material, typically (18, 48 and 59 HRC). Taguchiʹs L27 orthogonal array design was used (3-levels and 4-factors) to study the analysis of variance (ANOVA) and signal to noise ratio. In this study, cutting speed, feed rate, depth of cut and hardness of workpiece material were selected as process parameters, while surface roughness (Ra), metal removal rate (MRR) and roundness error were selected as quality responses. The results obtained from the S/N and (ANOVA) indicated that feed rate was the most significant parameter on surface roughness followed by cutting speed. Cutting speed was the most significant parameter on roundness followed by hardness while the most significant parameter on MRR was cutting speed followed by depth of cut. The increase in hardness improves surface roughness and increase roundness error.