Effects of carbon and nitrogen concentrations on precipitation sequence during tempering of martensitic steels investigated by advanced experimental methods and modeling - Groupe de physique des matériaux
Communication Dans Un Congrès Année : 2024

Effects of carbon and nitrogen concentrations on precipitation sequence during tempering of martensitic steels investigated by advanced experimental methods and modeling

Résumé

Advanced characterization techniques and modeling are used to get new insight on the microstructural evolutions occurring during the tempering of low-alloyed steels with initial martensitic microstructure. Tempering temperatures from 150°C to 600°C, are considered to make vary the metallurgical phenomena activated, form carbon segregation to defects to precipitation of different types of carbides (transition, cementite, alloyed). A large range of carbon compositions, from 0.1 to 0.7 wt.% are investigated, with the same main experimental technique: in situ HEXRD at synchrotron beamlines, with complementary post mortem fine-scale characterizations by TEM and 3D-APT. In the middle of this range (~0.3wt.%), the usual sequence is observed: successive precipitation of transition and cementite carbides. New observations concern the carbon concentrations outside this range. For high carbon concentrations (~0.6wt.%), the same sequence occurs but the martensite/ferrite matrix remains highly supersaturated in carbon compared to equilibrium, for a long time and even after the precipitation of cementite. For low carbon concentrations (~0.1wt.%) most of the carbon starts to segregate at defects (dislocations, lath boundaries). This enters in competition with the transition carbides which are almost fully hindered, whereas cementite precipitates afterwards. Two previous models from literature are combined to predict the concomitant kinetics of carbon segregation and precipitation. Segregation puts the transition carbides at a disadvantage with cementite and for this reason, the latter precipitates earlier than usually reported. The effects of nitrogen enrichment (up to ~0.4 wt.%N, context of carbonitriding thermochemical treatments) in austenite domain of stability (before the martensitic quench) are also investigated. In low-alloyed steel considered (23MnCrMo5), nitrides are formed upon enrichment (CrN, MnSiN2). This has a strong impact on the precipitation sequence, compared to model systems previously investigated (Fe-N, Fe-C-N).

Domaines

Matériaux
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Dates et versions

hal-04766623 , version 1 (05-11-2024)

Identifiants

Citer

J. Teixeira, M. Salazar, J. Macchi, S. Gaudez, G. Geandier, et al.. Effects of carbon and nitrogen concentrations on precipitation sequence during tempering of martensitic steels investigated by advanced experimental methods and modeling. IFHTSE 2024 - the 29th International Federation for Heat Treatment and Surface Engineering World Congress, Sep 2024, Cleveland, United States. pp.327-331, ⟨10.31399/asm.cp.ifhtse2024p0327⟩. ⟨hal-04766623⟩
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