Stress-induced transformation in a carburized steel—Experiments and analysis

Abstract

Stress-induced transformation of austenite to martensite was studied experimentally and numerically to gain an understanding of the increase in transformation strain with increasing tensile both and decreasing temperature. In addition, the anisotropy of the transformation strains was determined both experimentally and numerically. The material chosen for the study was a carburized 4320 steel with 35% retained austenite content. Monotonic and cyclic experiments were conducted in the range from -60 to 150°C. At 22°C, the volumetric transformation strain reached 0.006 at fracture in the uniaxial tensile test and 0.004 in the torsion test. Numerical calculations of the volumetric transformation strain and the anisotropy of the transformation strains were obtained with a modified Eshelby model where planes favorably oriented gradually transformed as stress was applied. The analysis predicted the experimentally observed transformation strains under both uniaxial and torsional loadings. The model also predicted the anisotropy of the transformation strains that was observed in experiments.