Efeito do tratamento térmico de solubilização sobre a corrosão por pite de em aço inoxidável austenítico contendo alto de Mn em solução de cloreto

The effect of solution heat treatment on the pitting corrosion resistance of\ud 17Cr-6Mn-5Ni-1.5Cu austenitic stainless steel in 0.6M NaCl aqueous solution was\ud evaluated. UNS S30403 (304L) steel was used as benchmark material. Solution heat\ud treatments (SHT) were conducted at 1010°C, 1040°C, 1070°C and 1100°C. The microstructural\ud characterization revealed the presence of δ-ferrite, especially in the asreceived\ud condition (AR). The SHT decreased the proportion of the ferrite phase. Mnrich\ud precipitates were observed in the as-received condition of 17Cr-6Mn-5Ni-1.5Cu\ud steel, but they were dissolved after the SHT, causing localized Mn enrichment in the\ud austenite. Potentiodynamic tests showed that the pitting potential (Ep) in the 304L\ud steel was not altered significantly after SHT. On the other hand, the value of Ep of\ud the 17Cr-6Mn-5Ni-1.5Cu steel decreased after SHT. This detrimental effect was explained\ud by the formation of Mn enrichment areas due to the solubilization of Mn-rich\ud precipitates, which promoted preferential Cl- adsorption in these regionsCAPESCNP

Effect of austenite grain size on the morphology and kinetics of the bainitic reaction of an austempered ductile iron.

Investigou-se o efeito do tamanho de grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado (FFNA). Foram estudados 3 tamanhos de grão austeníticos, a saber: GG (grão grosseiro), GM (grao mediano); e GR (grao refinado). A condição GR foi obtida pela austenitização rápida de microestruturas martensíticas. A condição GG foi obtida por tratamento de austenitização em duas etapas, de modo a, respectivamente, provocar o crescimento de grão e manter o teor de carbono igual aos das demais condições. Na segunda etapa do tratamento da condição GG ocorreu precipitação de grafita secundária, que acelerou significativamente a taxa de reação bainítica, possibilitando estudar o efeito da.variação na quantidade de interfaces austenita/grafita e austenita/ austenita sobre a cinética e a morfologia da reação bainítica. O refino do grão austenítico acelerou a cinética de reação, aumentou a proporção de ferrita alotriomorfa de contorno de grão, refinou a microestrutura bainítica (ferrita + austenita retida) e melhorou em 14% o limite de escoamento dos FFNA. Finalmente, a predominância de ferrira alotriomorfa na condição mais fina indica que a formação de interfaces incoerentes (mecanismo difusional ao inves de reação displaciva) durante a austenitização rápida da martensita (aquecimento de 100°C/ s).The effect of austenite grain size on the kinetics and the morphology of the bainitic reaction in an austempered ductile iron (ADI) has been investigated, Three austenite grain sizes were produced: GG (coarse grain), GH (medium grain) and GR (fine grain), The GR condition was obtained by the rapid austenitization of martensitic microstructures The secondary graphite precipitation observed in GG condition strongly accelerated the rate of bainite formation and made possible the study of the effect of austenite/graphite interface on the kinetics of this reaction, The austenite grain refinement also accelerated the bainite precipitation, increased the proportion of grain boundary alotriomorphs ferrite, refined the bainitic microstructure and improved by 14% the yield stress of ADI, The predominance of grain boundary alotriomorphs in GR was associated to the structure of austenite/austenite interface formed during the rapid austenitization of the studied ductile iron at heating rates of 100oC/s. It is suggested that the dominant mechanism of austenitization in this condition is a thermally activated one (not a displacive transformation). The different morphologies of the austenite decomposition used the Duhê\'s morphological system

Effect of austenite grain size on the morphology and kinetics of the bainitic reaction of an austempered ductile iron.

Investigou-se o efeito do tamanho de grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado (FFNA). Foram estudados 3 tamanhos de grão austeníticos, a saber: GG (grão grosseiro), GM (grao mediano); e GR (grao refinado). A condição GR foi obtida pela austenitização rápida de microestruturas martensíticas. A condição GG foi obtida por tratamento de austenitização em duas etapas, de modo a, respectivamente, provocar o crescimento de grão e manter o teor de carbono igual aos das demais condições. Na segunda etapa do tratamento da condição GG ocorreu precipitação de grafita secundária, que acelerou significativamente a taxa de reação bainítica, possibilitando estudar o efeito da.variação na quantidade de interfaces austenita/grafita e austenita/ austenita sobre a cinética e a morfologia da reação bainítica. O refino do grão austenítico acelerou a cinética de reação, aumentou a proporção de ferrita alotriomorfa de contorno de grão, refinou a microestrutura bainítica (ferrita + austenita retida) e melhorou em 14% o limite de escoamento dos FFNA. Finalmente, a predominância de ferrira alotriomorfa na condição mais fina indica que a formação de interfaces incoerentes (mecanismo difusional ao inves de reação displaciva) durante a austenitização rápida da martensita (aquecimento de 100°C/ s).The effect of austenite grain size on the kinetics and the morphology of the bainitic reaction in an austempered ductile iron (ADI) has been investigated, Three austenite grain sizes were produced: GG (coarse grain), GH (medium grain) and GR (fine grain), The GR condition was obtained by the rapid austenitization of martensitic microstructures The secondary graphite precipitation observed in GG condition strongly accelerated the rate of bainite formation and made possible the study of the effect of austenite/graphite interface on the kinetics of this reaction, The austenite grain refinement also accelerated the bainite precipitation, increased the proportion of grain boundary alotriomorphs ferrite, refined the bainitic microstructure and improved by 14% the yield stress of ADI, The predominance of grain boundary alotriomorphs in GR was associated to the structure of austenite/austenite interface formed during the rapid austenitization of the studied ductile iron at heating rates of 100oC/s. It is suggested that the dominant mechanism of austenitization in this condition is a thermally activated one (not a displacive transformation). The different morphologies of the austenite decomposition used the Duhê\'s morphological system

Assessment of the Ti-rich corner of the Ti-Si phase diagram using two sublattices to describe the Ti5Si3 phase

Abstract The thermodynamic optimization of Ti-X-Si systems requires that their respective binary systems be constantly updated. The most recent assessments of the Ti-Si phase diagrams used three sublattices to describe the Ti5Si3 phase. The stable version of this phase diagram indicated the presence of Ti(β)+Ti5Si3→Ti3Si and Ti(β)→Ti(α)+Ti3Si reactions in the Ti-rich corner, while the metastable version featured the presence of a Ti(β)→Ti(α)+Ti5Si3 reaction. The present investigation assessed these phase diagrams using two sublattices to describe the Ti5Si3 phase in order to simplify the optimization of Ti-X-Si systems

Simplificação da descrição termodinâmica do sistema Ti-Si

The thermodynamic optimization of ternary or higher order systems containing Ti requires that the Ti-X binary systems are continuously updated. The Ti-Si system has been studied and thermodynamically optimized since de 1950s. The Ti5Si3 phase was initially considered stoichiometric to facilitate the thermodynamic calculations, although experimental results showed that this phase was a non-stoichiometric intermetallic. The most recent optimization of the Ti-Si system described this phase as a non-stoichiometric intermetallic with three sublattices, using the sub-lattice model. The problem of this approach is that it increases considerably the number of variables to be optimized during the calculation of the Ti-Si-X phase diagrams, hindering the convergence of the computational processing. The present work simplifies the optimization of the Ti-Si system, assuming that Ti5Si3 phase is mostly hyper-stoichiometric in relation to Ti. The results showed that this simplification did not significantly affect the phase diagram and the thermodynamic properties calculated for the system

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part II: Thermal stress analysis by FEA

A martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used as a glass roller failed prematurely after six rolling campaigns. A previous fractographic investigation showed that the failure of the roll was caused by thermal stresses associated with microstructural embrittlement of the steel casting. Crack nucleation took place on the internal surface of the roll and the crack propagated by ductile intergranular mode. In the present work, the thermal stresses distribution was investigated by a thermal elastic–plastic model using finite element analysis in order to associate the crack growth with the thermal history of the roll during service. The proposed methodology based on the assessment of thermal stresses by finite element analysis together with coupled thermal–mechanical non-linear modelling and calculations using non-linear elastic–plastic fracture mechanics allowed a better understanding of the stable and unstable growth of a longitudinal crack until the premature failure of the roll during its cooling to room temperature after the sixth campaign. The stable and unstable crack growth and the thermal history of the roll (heating up, glass rolling and cooling operations during the six campaigns of the roll) could be related using the proposed calculation