Machinability and chip morphology evolution of hardened stainless steel using liquid nitrogen cryogenic

The impeller material FV520B-hardened stainless steel is a typical difficult-to-machine material. During the cutting process, the force and thermal load are large, and the chip breaking is difficult, resulting in poor processing quality and serious tool wear. Low temperature cooling can improve the machinability of materials by significantly reducing the temperature of the cutting zone. It is an important development direction of clean cutting in the future. In this paper, the effects of low temperature cooling (18 ~  − 196℃) on cutting machinability and chip morphology evolution of FV520B were systematically studied from macroscopic and microscopic aspects by setting triaxial milling and orthogonal turning experiments respectively based on low-temperature jet formed by mixing liquid nitrogen and compressed air. The experimental results show that liquid nitrogen cryogenic cutting can significantly improve the machinability of material FV520B and promote the formation of serrated chips. Under the condition of cutting speed of 80 m/min, axial cutting depth of 1 mm and feed per tooth of 0.25 mm/r, the cutting force, cutting vibration, and surface roughness of FV520B at − 100℃ are reduced by 30%, 62%, and 18% respectively compared with those at 18℃. When the cutting speed is 80 m/min, the axial cutting depth is 1 mm, and the feed per tooth is 0.1 mm/z, the tool life at − 100℃ is 43% higher than that at 18℃. With the increase of cutting speed and the decrease of jet temperature, the serration degree, pitch, and shear angle of chips increase and the deformation coefficient of chips decreases.