The Effect of Bake Hardening on Quenched and Partitioned AISI 420 Stainless Steel

Bake hardening (BH) is a static strain aging phenomenon, where the yield strength of steel increases during industrial paint baking. In this study, the effect of standard BH treatment on the mechanical properties of a quenched and partitioned (Q&P) AISI 420 stainless steel is investigated. The parameters for the Q&P treatment are selected based on numerical simulations, dilatometry, X-ray diffraction, and tensile tests, and the results are compared to conventional quenching and tempering (Q&T) treatment. It is shown that, in comparison with Q&T, Q&P can slightly increase the strength of the steel without sacrificing elongation. Heat-treated samples are then subjected to a paint baking treatment with and without prestrain. It is indicated that the mechanical properties of the heat-treated steel are not affected by paint baking without prestrain, whereas after a 2% prestrain the yield strength is drastically increased up to 1800 MPa, resulting in BH index exceeding 100 MPa. However, this increase in yield strength is instantly followed by necking and reduced post-uniform elongation. The results suggest that the effect of industrial paint baking is a considerable practical aspect in the design of Q&P components if the steel is subjected to deformation before painting.