Sub-Surface Microstructural Evolution and Chip Formation During Turning of AF 9628 Steel

Hasbrouck, C. R.; Hankey, Austin S.; Abrahams, Rachel; Lynch, Paul C.

Abstract High-strength low-alloy (HSLA) steels are desired for their high strength-to-weight ratio, relatively low cost, good overall mechanical properties, and relative ease of processing. The development of Eglin steel and AF 9628 has facilitated the current wave of research into next-generation HSLA steels. These alloys are characterized by both high levels of strength and increased levels of ductility and impact toughness over traditional HSLA alloys such as AISI 4340/4330. AF 9628 has proven difficult to machine due to strain hardening while turning. Manual and CNC turning experiments were carried out on AF 9628 cylindrical bars based on current machining practices. In an effort to optimize material removal rate and tool life, quantitative measurements of tool flank wear, surface roughness, hardness, microhardness, and chip thickness were taken. Qualitative observations made on microstructural evolution and chip color and morphology are also discussed.