Ref.: MmeCa09-033
Apresentador: Giovani Gonçalves Ribamar
Autores (Instituição): Ribamar, G.G.(Universidade de São Paulo); Nishikawa, A.S.(TATA steel group); Escobar, J.D.(Universidade de São Paulo); Oliveira, J.P.(Universidade Nova de Lisboa); Diaz, J.A.(Universidade do Estado de São Paulo - Campus de São João da Boa Vista); Goldenstein, H.(Universidade de São Paulo);
Resumo:
The study of tempering phenomena has a long-standing history, with microstructural characterization being conducted through a range of techniques, from conventional methods like optical microscopy to advanced approaches such as atom probe tomography (APT). While the tempering mechanisms in many steels are well-established, a novel alloying combination has reshaped our understanding of the impact of temperature and time on these phenomena. Silicon, employed as a cementite precipitation inhibitor in martensite, introduces a delay that facilitates carbon diffusion from supersaturated martensite to retained austenite. This delay, observed during isothermal heat treatments in steels previously quenched between the martensite start and finish temperatures, serves to thermally and mechanically stabilize retained austenite, giving rise to what is commonly known as the Quenching and Partitioning (Q&P) heat treatment. This treatment holds promise for a variety of steels, including Transformed Induced Plasticity (TRIP) steels, where retained austenite can be stabilized for subsequent transformation into martensite via deformation, or for achieving a higher degree of stabilization where austenite transformation is undesirable. The altered kinetics of cementite precipitation due to silicon alloying significantly influences the energy required for tempering phenomena. Understanding these changes is crucial for designing more effective Q&P heat treatments. This study presents a comprehensive analysis of the Gibbs's energy involved in tempering phenomena, employing diverse methods such as dilatometry behavior, in-situ synchrotron X-ray diffraction, APT, scanning electron microscopy, and electron backscatter diffraction. A comparative assessment with low-silicon steels highlights the elevated values associated with higher silicon alloying.