Análise comparativa ao efeito da recuperação por soldagem na resistência a fadiga de um eixo de aço sae 4340 tratado termicamente

Abstract

RESUMO: Os aços de alta resistência e baixa liga são usados em diversas áreas da indústria, suas aplicações contemplam uma enorme gama de equipamentos e componentes. A liga de aço de médio carbono SAE 4340, utilizada no presente trabalho, foi desenvolvida para ter boa combinação de propriedades mecânicas, que normalmente são encontrados em ligas contendo elementos mais nobres, devido a adição de outros elementos de liga em sua composição e de sua boa temperabilidade, além de redução no peso. Neste trabalho, o objeto de estudo é a avaliação do efeito da soldagem pelo processo GMAW em um corpo de prova tratado termicamente em sua resistência a fadiga, utilizando de referência outro corpo de prova apenas tratado termicamente com o intuito de recuperar eixos rompidos por fadiga. Por apresentar excelentes propriedades mecânicas, componentes feitos dessa liga são utilizados em aplicações que, normalmente, estão sujeitas a cargas elevadas em um número elevado de ciclos, logo, também estão sujeitos a fratura por fadiga, evento este que pode significar perdas financeiras ou até mesmo, em alguns casos, riscos de vida. O teor médio de carbono dessa liga implica em condições mais delicadas de soldabilidade, portanto, o processo de solda no corpo foi feito com o eixo na condição de normalizado, para que um resultado apreciável possa ser obtido. Por fim, o corpo soldado passou pelos processos de tratamento térmico, têmpera e revenimento, para que suas propriedades mecânicas fossem avaliadas. Após a extensa análise dos resultados dos ensaios de fadiga por flexão rotativa, observou-se que o método proposto se mostra pouco eficaz, uma vez que a resistência a fadiga da amostra recuperada é de cerca de 40% da amostra sem solda, contudo, o processo pode ser viável em casos específicos. ABSTRACT: High strengths and low alloy steels are used in several industry areas, their applications include a huge range of equipment and components. The medium alloy SAE 4340, used in the present academic work, was developed to have a good mechanical property, which are normally found in alloys containing noble elements, due to the addition of other alloy elements in composition as a good hardenability, besides the weight reduction. The study object of this present academic work will be a fatigue strength limit analysis in a GMAW welded and heat treated specimen using another specimen only heat treated as the reference in order to recover ruptured shafts by fatigue. The parts made of this material have excellent mechanical properties, that’s why, usually, this material are used for structural parts who are under high loads and cycles, when the part suffer in high quantity of cycles, have a chance of rupture by fatigue, that could mean financial issues or even a life threatened. Alloys steel with medium carbon content means delicate weldability, therefore, the specimen was normalized before machining process to ensure a good result. Finally, all the specimen was hardened and quenched for a fatigue mechanical properties analysis. After an extensive analysis of the results of the fatigue tests by rotary bending, it was observed that the proposed method showed little efficiency, since the fatigue resistance of the recovered sample is about 40% of the sample without weld, however, the process can be workable in specific cases.

ABSTRACT: High strengths and low alloy steels are used in several industry areas, their applications include a huge range of equipment and components. The medium alloy SAE 4340, used in the present academic work, was developed to have a good mechanical property, which are normally found in alloys containing noble elements, due to the addition of other alloy elements in composition as a good hardenability, besides the weight reduction. The study object of this present academic work will be a fatigue strength limit analysis in a GMAW welded and heat treated specimen using another specimen only heat treated as the reference in order to recover ruptured shafts by fatigue. The parts made of this material have excellent mechanical properties, that’s why, usually, this material are used for structural parts who are under high loads and cycles, when the part suffer in high quantity of cycles, have a chance of rupture by fatigue, that could mean financial issues or even a life threatened. Alloys steel with medium carbon content means delicate weldability, therefore, the specimen was normalized before machining process to ensure a good result. Finally, all the specimen was hardened and quenched for a fatigue mechanical properties analysis. After an extensive analysis of the results of the fatigue tests by rotary bending, it was observed that the proposed method showed little efficiency, since the fatigue resistance of the recovered sample is about 40% of the sample without weld, however, the process can be workable in specific cases.