Stress Corrosion Behavior of AISI 4340 in High-Speed Hard Milling Using MQL

Stress corrosion is one of the main factors affecting the long-term reliability of mechanical components. This research investigates the stress corrosion behavior of AISI 4340 steel during high-speed hard milling (HSHM) using minimum quantity lubrication. Accordingly, the effect of roughness, texture, microhardness, residual stresses, chemical composition, and corrosion resistance was studied. Experiments were conducted across five levels of cutting speeds ranging from 300 to 600 m/min. Chemical analysis also revealed the presence of carbon, oxygen, and chlorine on the surface at the cutting speed of 450 m/min, while these elements were absent at 600 m/min, leaving only austenite and ferrite phases. Residual stress measurements indicated a transition from tensile stresses at lower speeds to compressive stresses at 600 m/min, indicating mitigation of negative thermal effects in HSHM. Electrochemical tests demonstrated a significant increase (up to 1.32 times) in the electrochemical resistance of the surface at a cutting speed of 600 m/min. This improvement is attributed to the presence of compressive residual stresses and reduced abnormal surface phases, thereby improving the stress corrosion resistance. This research underscores the necessity for detailed investigations into the effects of machining processes on stress corrosion behavior, providing valuable insights for manufacturing industries.