Efeito do tempo de estocagem após resfriamento na redução de área na estricção e no teor de hidrogênio em fio-máquina de aço alto carbono

• Ano de defesa: 2008
• Autor(a) principal: Carlos Jose Carneiro Filho
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Redução de área; Dessorção de hidrogênio; Aço alto carbono; Engenharia metalúrgica; Metalurgia física
• Link de acesso: http://hdl.handle.net/1843/MAPO-7R5N3M

In this study it was determined the reduction of area ( Z% ) variation in tensile test with stock time of a high carbon steel wire rod for prestressed concrete, after the process of rolling and controlled cooling. The objective is to determine the necessary minimum time that the wire rod must remain in stock so that the wire rod could be drawn with guaranteethat the effect of hydrogen in the ductility does not compromise the wire drawing process.Samples of the 11mm diameter wire rod of the steel produced without vacuum degassing have been removed after the process of controlled cooling and storage at room temperature for times varying between 0 and 960 hours. The hydrogen content was measured for each storage time. The value after controlled cooling was 1.85ppm, and decreased with the storage time, it stabilized between 0.55 and 0.60 ppm after 216 hours.The reduction of area in the tensile test after controlled cooling was 20%, it increased with storage time, and kept constant between 37% and 38% after 216 hours. It was also determined the variation of the hydrogen content and reduction of area in the tensile test with time for samples removed from wire rod with vacuum degassing storage in the same conditions of the samples without vacuum degassing. For the samples with vacuum degassing, the hydrogen content and reduction of area in the tensile test after controlledcooling was 0.95ppm and 29%, for 288 hours of storage time or higher than this time the value was between 0.55 ppm and 0.65ppm, 42% and 43%, respectively.The analysis of these results, through the adjustment of the values of the hydrogen concentration versus time, showed that the responsible process for the increase in the reduction of area in the tensile test with time of storage at room temperature is the desorption of hydrogen, imprisoned in steel defects as dislocations and Fe/Fe3C interfaces.This work allowed us to conclude that is possible to produce high carbon steel wire rod for prestressed concrete without vacuum degassing increasing storage time at room temperature from 72 hours to 144 hours, thus allowing to achieve the specified reduction of area of 30% as requested by costumers.