Cryogenic cooling is a new emerging cooling application in machining processes. Quantitative understanding of the effects of cryogenic cooling on the machining performance is important for continued applications. This study focuses on cryogenic machining of hard-to-machine material, AISI 52100, particularly with an analysis of cooling-induced chip morphology, chip hardness and the effect of workpiece hardness, etc., as these measures reflect the material's thermo-mechanical behavior during the plastic deformation. AISI 52100 steel, with different initial hardness values, is selected as the work material for orthogonal cutting under dry and cryogenic cooling conditions, and the results are compared. The findings of this study show that cryogenic cooling affects the chip formation process, and the associated hardness produced on the machined surface.