Volume 6, Issue 9 (October 2009)
The Effect of Core and Carburized Surface Microstructural Stability on Residual Stress Evolution during Tempering
It is a well-known fact that compressive residual stresses are developed during the quenching process of carburized parts. The main purpose of this work is related to the tempering effects on as-quenched compressive residual stresses of commercial carburized samples. The work was carried out by using SAE 4120 RH steel samples with different diameters (15 and 38 mm), which led to different cooling rates with a direct effect on the nucleus microstructure. The carburized surface microstructure was considered similar. The 15 mm bars nucleus microstructures were predominantly martensitic but bainitic in the larger samples. The as-quenched surface compressive residual stress was lower in the smaller diameter samples. The compressive residual stress reduction due to increasing tempering temperature was continuous for the larger diameter work piece. The smaller diameter samples had different behaviors in two regions; the compressive stress for lower tempering temperatures was reduced, while values were enhanced over higher temperatures.