REDUCING RESIDUAL STRESS IN METALLIC ITEMS USING DEEP CRYOGENIC TREATMENT

Residual stresses (RS) in metallic items are generated as a result of plastic deformation caused by applied mechanical loads (impact/work hardening), thermal loads (casting/heat treating) or phase change (austenite to martensite). Residual stress is considered harmful to the longevity of most metallic items. Lower RS correlates to increased wear life, less corrosion and reduced fracture/fatigue initiation rates.

Following austenitizing and quenching, annealing and stress relief are intermediate heat treat processes designed to relieve RS generated during prior homogenization and hardening steps. Deep cryogenic treatment (DCT) is the final thermal treatment that imparts a 20-30% reduction in RS post-DCT - correlating to an average 30% improvement from DCT as seen in common destructive tests such as pin-on-disc, G65 or G81.

X-ray diffraction (XRD) is a highly accurate, non-destructive method of detecting, characterizing and measuring RS that is resident in both surface and subsurface locations - thus a match to the through-core material improvements offered by heat treating and DCT. ASTM E2860 is the known and accepted test standard for measuring RS in metallic items using XRD.