ESTUDO COMPARATIVO DA TRANSFORMAÇÃO AUSTENITA-FERRITA EM DOIS AÇOS IF COM DIFERENTES COMPOSIÇÕES QUÍMICAS
COMPARATIVE STUDY ABOUT AUSTENITE-FERRITA TRANSFORMATION IN TWO IF STEELS WITH DIFFERENT CHEMICAL COMPOSITIONS
Ana Luiza Soares Cezário, Geraldo Lúcio de Faria
Resumo
Os aços IF são livres de elementos intersticiais na matriz ferrítica. Esses elementos são controlados no processo de refino na aciaria a partir da aplicação de técnicas de desgaseificação a vácuo e adição de elementos estabilizantes. Durante a fabricação e em algumas aplicações específicas dos aços IF, como por exemplo em soldagem onde a transformação de fase γ → α e o efeito dos elementos de liga na sua cinética têm forte influência na microestrutura final. Neste contexto, este trabalho caracterizou microestruturalmente e comparou as cinéticas de transformação de fases de dois tipos de aços IF com composições químicas diferentes, sendo um deles estabilizado ao Ti (IF-Ti) e outro estabilizado ao Ti e ao Nb (IF-TiNb) com adição de Mn. Concluiu-se que o aço IF-TiNb no estado de entrega possui uma microestrutura mais refinada devido à presença do Nb e seu papel de refinador de grão na laminação controlada do aço. Verificou-se que as temperaturas críticas Ar3 e Ar1 do aço IF-TiNb são menores do que as temperaturas medidas para o aço IF-Ti. Atribui-se este efeito à diferença no teor de Mn entre os aços estudados, que parece potencializar o refino de grão na etapa final de resfriamento da chapa de aço laminada.
Palavras-chave
Abstract
The IF steels are free of interstitial elements in the ferritic matrix. These elements are controlled in the refining process in the steel plant through the application of vacuum degassing techniques and the addition of stabilizing elements. During the manufacture and in some specific applications of the IF steels, as for example in welding where the phase transformation γ → α and the effect of the alloying elements on their kinetics have strong influence on the final microstructure. In this context, this work characterized microstructurally and compared the phase transformation kinetics of two types of IF steels with different chemical compositions, one being stabilized to Ti (IF-Ti) and the other stabilized to Ti and Nb (IF-TiNb) with addition of Mn. It was concluded that the IF-TiNb steel in the delivery state has a more refined microstructure due to the presence of Nb and its role as a grain refiner in the controlled rolling of the steel. It was found that the critical temperatures Ar3 and Ar1 of the IF-TiNb steel are lower than the measured temperatures for the IF-Ti steel. This effect is attributed to the difference in Mn content between the studied steels, which seems to potentiate the grain refining in the final stage of cooling of the rolled steel sheet.
Keywords
Referências
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