Austenitizing Temperature and Cooling Rate Effects on the Martensitic Transformation in a Microalloyed-Steel

Abstract

The effects of the austenitizing temperature and the cooling rate upon the kinetic of athermal martensitic transformation in a microalloyed steel were evaluated. Considering the studied steel, the knowledge about these effects on the martensitic transformation has a great relevance for naval manufacturers and steel researchers. In this study, computational simulation was performed aiming to evaluate the phase's stability. Specimens were submitted to quenching simulations in a dilatometer, considering four different austenitizing temperatures and four cooling rates. The results shown that the austenite chemical composition was not significantly affected by the austenitizing temperatures. Both the austenitic grain size and the cooling rate affected the martensitic transformation kinetics. The larger the austenitic grain size, the higher the Ms. The austenitic grain growth promoted a decrease in the required chemical energy to compensate the free energy increase associated with the lattice strain and the creation of new interfaces, leading to a lower austenite undercooling. An extrinsic effect of the cooling rate on the Ms was observed. For lower cooling rates, the carbide precipitation modified que austenite chemical composition, changing its stability and increasing Ms. A predictability equation, correlating the M S with the austenite grain size and the steel cooling rate, was proposed.

Effect of Step Quenching Heat Treatments on the Kinetics of Ferrite Formation and Quenching & Partitioning Modeling for a Commercial C-Mn-Si Steel

“…A significant decrease in M s temperature was observed as the step time increased. One factor that strongly influences this temperature is the austenite carbon content 34,35 , so that the higher the austenite carbon content, the lower its M s temperature. Thus, the decrease in M s temperature with the increase of step time, indicates the occurrence of carbon partition for austenite due to ferrite formation in the step stage.…”

“…However, the carbon partition for austenite due to the ferrite formation in an intercritical annealing, can lead to a non-homogeneous austenite carbon profile, as discussed by Tan et al 6 and Santofimia et al 36 , influencing the retained austenite morphology and the occurrence of the TRIP effect during deformation 39 . The M s temperature determination after the SQ treatment is necessary to guarantee great agreement between the thermodynamic predictions and the real Q&P heat treatments, since this M s value can be considered an indirect measurement of the austenite carbon content prior to the partial quenching in a Q&P cycle 35 .…”

“…Solving the equation system formed by Equation 6, Equation 7and Equation 8, the martensite and austenite carbon concentrations are known after the end of carbon diffusion during the partitioning stage. Therefore, carbon enriched austenite has, at the partitioning end, a lower M s temperature (to be mathematically determined by empirical equations available in technical literature 35 ). Thus, the final quenching up to room temperature can lead to the formation of a certain secondary martensite fraction, and can also be calculated by Equation 8.…”

Avaliação da formulação de reativos à base de ácido pícrico visando a revelação do grão austenítico prévio em diferentes tipos de aços

“…A melhor condição de ataque foi com 1,5mL de HCl (60 segundos). Esse aço pode ser classificado como um aço de alta resistência baixa liga, comumente empregado na indústria naval [17]. Ele possui adições de Cr e Mo que são bons formadores de carbonetos.…”

The Effect of Cooling Conditions on Martensite Transformation Temperature and Hardness of 15% Cr Chromium Cast Iron

“…The issue of the effect of cooling rate on T Ms in the process of quenching carbide-containing steels was discussed in a number of publications. Authors of [22] have found that in the case of low-alloy high-strength steels, lower values of T Ms corresponded to higher specimen cooling rates. They assumed that at lower values of the cooling rate, precipitation of chromium and molybdenum carbides become possible.…”