Análise da usinabilidade de ferros fundidos nodulares austemperados como função dos tratamentos térmicos e microestruturas

• Autor(a) principal: Werlang Filho, Armindo
• Data de Publicação: 2015
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da PUC_RS
• Texto Completo: http://tede2.pucrs.br/tede2/handle/tede/6049
• topic: ENGENHARIA DE MATERIAIS; METAIS - USINAGEM; METAIS - TRATAMENTO TÉRMICO; USINAGEM; FERRO FUNDIDO; ENGENHARIAS

The objective of this work is to analyze the influence of annealing and austempering heat treatments on the machinability with constant pressure of an austempered ductile cast iron. The results were correlated to microstructural formation and mechanical properties. It was used the turning process varying the depth of cut, the speed of cut, the angle of tool and the use of cut fluid. The samples (18 initially annealed) were heated at 910°C for 90 minutes for austenitization and cooled in salt bath in one-step at temperatures 300°C, 360°C and 420°C for 30, 60 and 90 minutes. Other 16 samples (8 previously annealed) were austempered in two-step process at 245oC and 300oC for 5 and 30 minutes, respectively. The samples were analyzed initially by optical microscopy and mechanical tests (Brinell hardness and Vickers microhardness), and after were machined in an universal lathe for machinability tests. The mechanical lathe was instrumented in relation to active power and cutting time, and the machinability evaluation was made with reference to cutting force, cutting pressure and material removal index criteria. The samples austempered at 300oC for 30 minutes (with annealing) showed the best machinability, impact resistance and lowest hardness in the one-step process. However, the samples in the same temperature and time (with annealing) showed the worst machinability, highest hardness and lowest impact resistance. The two-step austempering was performed in 8 samples that showed the best machinability and 8 samples that showed the worst machinability in one-step process. In these samples, the machinability test were performed with and without fluid cut and cut angle of 90o and 60o. The results showed the highest performance for the condition austempered at 300oC for 30 minute in two-step process, with previous annealing, when machined with fluid cut and angle of tool of 60o. The microstructure was composed by ausferrite, graphite and retained austenite.