A massive castings defects are examined in this doctoral thesis, specialise in steels passing through peritectic transformation. There are typical types of defects at massive steel castings, as contrasted to „ordinary“ internal and surface ones. For massive steel castings are typical defects under feeders like conchoidal fractures, segregations, microporesities, reoxidation products. Combination of Al and Zr is an ordinary final deoxidation of EOP and LF steel for castings in ŽĎAS a.s. foundry. The aim of Al + Zr combination was to both deep deoxidation by Al (decrease of bubbles risk) and denitrification by Zr (decrease of conchoidal fractures). This theses refute premission mentioned above and verified persisting risk of defects under massive feeders, even though Al + Zr deoxidation is used. A final deoxidation by increased amount of Al was examinated, in combination with other deoxidation agents. Castings had 11 [cm] maximal modulus, and occurence of conchoidal fracture, reoxidation products and primary austenite grain size was evaluated. A selected optimal final deoxidations (Al, Al+Ti, Al+Zr) as a result from experiment described above, were evaluated on castings with 15 [cm] maximal modulus. The result of experiment is, that is not possible to repeatedly produce massive steel casting using EOP metallurgical equipment without defects under feeders, despite of deoxidation and pouring temperature optimalization. The defect indications look like conchoidal fracture, but there are microporesity and impurities instead. Finally, castings with maximal modulus 15 [cm] were produced using so called secondary metallurgy (LF, VD). Secondary metallurgy allowed to both significant decrease of sulfur and degassing of melted metal. Only this metallurgical procedure guarantees production of heavy steel castings without typical defects under massive feeders

Orientador: Carlos Alberto Cimini Júnior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T13:05:51Z (GMT). No. of bitstreams: 1 Nascimento_NataliciodeMedeiros_M.pdf: 37176226 bytes, checksum: 4fbe964ff4a98beca09e3f5d3f4dffc6 (MD5) Previous issue date: 2013 / Resumo: A soldagem por atrito com pino não consumível (SAPNC), tem se mostrado muito útil na possível solução de limitações apresentadas por outros processos de soldagem, gerando juntas soldadas com menor nível de tensão residual e menor distorção final, permitindo soldar ligas metálicas não soldáveis por outros processos e apresentando a vantagem de não necessitar de material consumível. Porém, para uma possível aplicação prática desta tecnologia, se torna importante o conhecimento de parâmetros de resistência mecânica, resistência à fadiga e resistência à fratura da junta soldada. Dentro deste contexto, este trabalho procurou avaliar experimentalmente a medida da tenacidade à fratura de juntas de aço inoxidável supermartensítico via SAPNC por meio de ensaios padronizados de CTOD (Crack Tip Opening Displacement) de acordo com a norma BS 7448. Para isto, foi necessária a preparação de corpos de prova de tamanho padronizado em função da espessura da chapa. As chapas utilizadas foram usinadas com espessura de 17,7±0,2mm e posteriormente unidas por soldagem SAPNC, sendo a partir destas retirados corpos de prova de ensaio de flexão de três pontos. Procedendo-se a aplicação de uma carga senoidal sobre a amostra obtida, foram produzidas os pré-trincamentos necessários ao ensaio. Destes, se obtiveram resultados que, mostram que a soldagem deste material produz juntas com valores CTOD abaixo daqueles apresentadas pelo material de base, fragilizando acentuadamente a junta soldada somente na chamada região de avanço. Além disso, o modo de fratura se mostrou dúctil, com a geometria do trincamento sendo fortemente influenciada pelas alterações microestruturais geradas pelo processo / Abstract: The friction welding with non-consumable pin (SAPNC), has proved very useful in the solution of possible limitations presented by other welding processes, generating welded joints with lower residual stress and lower distortion, allowing welding of alloys not weldable by other processes and having the advantage of requiring no consumables. However, for a possible practical application of this technology, it becomes important to know the mechanical strength, fatigue strength and resistance to fracture of the welded joint. Within this context, this study sought to experimentally measure the fracture toughness of supermartensitic stainless steel joints made via SAPNC through standardized CTOD (Crack Tip Opening Displacement) tests in accordance with BS 7448 standard. For this was necessary to prepare specimens of standardized size as a function of plate thickness. The plates used were machined with a thickness of 17.7 ± 0.2 mm and subsequently joined by SAPNC welding being removed from these three point bending assay specimens. Proceeding applying a sinusoidal load on the obtained samples were produced precracks needed for testing. From these, were obtained results that show that the welding of this material produces joints with CTOD values below those presented by the base material, markedly weakening the welded joint only in the region called advancing side. Furthermore, the fracture mode showed being ductile, and the geometry of the cracking being strongly influenced by the microstructural changes generated by the process / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

A massive castings defects are examined in this doctoral thesis, specialise in steels passing through peritectic transformation. There are typical types of defects at massive steel castings, as contrasted to „ordinary“ internal and surface ones. For massive steel castings are typical defects under feeders like conchoidal fractures, segregations, microporesities, reoxidation products. Combination of Al and Zr is an ordinary final deoxidation of EOP and LF steel for castings in ŽĎAS a.s. foundry. The aim of Al + Zr combination was to both deep deoxidation by Al (decrease of bubbles risk) and denitrification by Zr (decrease of conchoidal fractures). This theses refute premission mentioned above and verified persisting risk of defects under massive feeders, even though Al + Zr deoxidation is used. A final deoxidation by increased amount of Al was examinated, in combination with other deoxidation agents. Castings had 11 [cm] maximal modulus, and occurence of conchoidal fracture, reoxidation products and primary austenite grain size was evaluated. A selected optimal final deoxidations (Al, Al+Ti, Al+Zr) as a result from experiment described above, were evaluated on castings with 15 [cm] maximal modulus. The result of experiment is, that is not possible to repeatedly produce massive steel casting using EOP metallurgical equipment without defects under feeders, despite of deoxidation and pouring temperature optimalization. The defect indications look like conchoidal fracture, but there are microporesity and impurities instead. Finally, castings with maximal modulus 15 [cm] were produced using so called secondary metallurgy (LF, VD). Secondary metallurgy allowed to both significant decrease of sulfur and degassing of melted metal. Only this metallurgical procedure guarantees production of heavy steel castings without typical defects under massive feeders