Nitrogen effects on the kinetics and microstructural evolutions during tempering of a low alloyed steel

The role of nitrogen on microstructural evolutions during tempering in multiconstituent low alloyed steels has been fewly studied in literature whereas it is of importance for controlling the carbonitriding process used in the automotive industry. In this project, the tempering kinetics of a nitrogen enriched multiconstituent steel (23MnCrMo5) will be examined in details by means of in situ high-energy synchrotron X-ray diffraction. Three main aspects of tempering will be analyzed: firstly, the identification of the formed precipitates (carbides, nitrides and carbonitrides); secondly, the sequence of precipitation as well as their nucleation, growth and coarsening kinetics during continuous heating and isothermal tempering; thirdly, the evolution of the retained austenite that depends too on tempering conditions. In addition to phase fractions, cell parameters that are correlated to chemical composition and internal stresses will be determined as well as dislocation recovery kinetics.