This study presents an experimental investigation of chip micro-hardness under Minimum Quantity Lubrication (MQL) conditions using castor oil. The experiments were conducted by varying cutting speed (100–170 m/min) and feed rate (0.16–0.24 mm/rev), while keeping the depth of cut constant. Micro-hardness measurements were obtained using a Shimadzu micro-hardness tester at different regions of the saw-tooth chip, namely the tooth, middle, and bottom. The results show that chip micro-hardness values ranged between 47.2 and 49.4 HRC. It was observed that micro-hardness increases with increasing feed rate, while cutting speed showed a comparatively smaller effect. The highest hardness value was obtained at low cutting speed and high feed rate. This behavior is attributed to increased plastic deformation, higher cutting temperatures, and strain hardening at elevated feed rates. The findings indicate that cutting parameters significantly influence chip micro-hardness, which in turn affects machining performance and surface integrity.