Austenite formation from a steel microstructure containing martensite/austenite and bainite bands

Austenite formation from a steel microstructure containing martensite/austenite and bainite bands

Blog Article

In many commercial steel processing routes, steel microstructures are reverted to an austenitic condition prior to the final processing steps.Understanding the PERFORMANCE+TONGKAT ALI microstructure development during austenitization is crucial for improving the performance and reliability of the microstructure that forms from austenite.In this work, austenite formation in a high-C steel (0.85 wt%) from a microstructure containing martensite/austenite and bainite bands is investigated.It is shown that austenite formation from bainite results in a refined austenite grain structure, and the martensite matrix thus obtained on quenching has a homogeneous distribution of carbides with a relatively low fraction of retained austenite (24%).

On the other hand, a coarser austenite microstructure is obtained when austenite forms from a mixture of martensite and retained austenite.The reason for the coarse austenite grains is argued to be a memory effect, which is substantiated by in situ X-ray diffraction analysis.After quenching, an inhomogeneous carbide distribution and a higher retained austenite fraction (30%) Slim are observed in the regions that were initially martensite/austenite.The global microstructure, hence, has a bimodal size distribution of prior austenite grains and carbide-dense bands.The causes for these heterogeneities are discussed with the help of interrupted quench experiments, equilibrium phase calculations, and DICTRA simulations.