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The focus of this study was to determine the residual stress and retained austenite profiles for carbonitrided and nitrocarburized SAE 1010 plain carbon steel and to relate these profiles to one another and to the distortion resulting from heat treatment. Navy C-ring specimens were used for the purpose of this study and X-ray diffraction techniques were used to measure both residual stress and retained austenite. The findings from this research are then applied to a manufacturing application involving the surface hardening of a thin shelled, plain carbon steel automotive component.

Steels such as SAE 8620 and PS-18 are typically used in the carburized condition for powertrain applications in the automotive industry. Such steels always contain retained austenite to varying degrees in both the ashardened and tempered microstructures. As well as retained austenite, heat treatment can produce residual stresses, which lead to both size and shape distortions. The intent of this study was to investigate the effects of initial microstructure, composition, and heat treatment on the amount of residual stress, retained austenite, and distortion in carburized SAE 8620 and PS-18 steels. A specially designed specimen, the Navy C-ring, was used to evaluate distortion. X-ray diffraction techniques were used to determine the residual stress and the amount of retained austenite.

The fatigue performance of fillet-welded transverse attachments was compared for several procedure variants for both FCAW and SAW on ½ in. steel plates. Measurements of weld toe shape on adjacent pieces of weld indicated that smoother weld toes, as evidenced by larger weld toe radius, were correlated to improved fatigue performance for both processes. Fatigue tests conducted on 59 and 109 ksi yield strength plates did not show an effect of plate strength. Weld procedures designed to provide smooth toes, such as reduced parameter FCAW beads at horizontal weld toes and flat position FCAW at higher heat inputs, were shown to provide fatigue performances near post-weld improved fillets.