ANÁLISE DE PRECIPITADOS POR MICROSCOPIA ELETRÔNICA DE VARREDURA E DE TRANSMISSÃO EM UM AÇO AO BORO
PRECIPITATES ANALYSIS BY SCANNING ELECTRON AND TRANSMISSION MICROSCOPY IN A BORON STEEL
Suski, Cassio Aurélio; Oliveira, Carlos Augusto S. de
http://dx.doi.org/10.4322/tmm.2013.045
Tecnol. Metal. Mater. Min., vol.10, n4, p.336-345, 2013
Resumo
Foi estudada a precipitação de carbonetos em aço baixo carbono ao boro austenitizado a 870°C, 1.050°C e 1.200°C e temperado em óleo através de microscopia eletrônica de varredura (MEV) e de transmissão (MET). Foram avaliados os sítios de nucleação e tamanho dos precipitados, além da microestrutura obtida. A análise dos precipitados por MET foi realizada através da réplica de carbono e filmes finos. Foi observada a presença de cementita, Fe3C, e de borocarbonetos, M23(C,B)6, em todas as condições experimentais. A cementita apresentou tamanhos aproximadamente iguais em todas as temperaturas de austenitização, fato atribuído a solubilização e reprecipitação durante o resfriamento de têmpera. Observou-se a presença de borocarbonetos em todas as temperaturas de austenitização, sendo que na temperatura de 870°C a precipitação foi mais grosseira. Esta distribuição de tamanhos foi atribuída a não solubilização e coalescimento dos borocarbonetos à 870°C e a solubilização e reprecipitação durante o resfriamento de têmpera nas outras duas temperaturas. Percebeu-se ainda, uma menor precipitação de borocarbonetos no contorno de grão a 1.050°C quando comparada a 1.200°C.
Palavras-chave
Aço baixo carbono ao boro, Precipitação, Têmpera
Abstract
We studied the carbides precipitation of low carbon steel with boron austenitized at 870°C, 1,050°C and 1,200°C, oil-hardened by scanning electron microscopy (SEM) and transmission (TEM). We evaluated the nucleation sites and size of the precipitates, in addition to the microstructure obtained. The precipitates by TEM analysis was performed using the replica and carbon thin films. It was observed the presence of cementite, Fe3C, and borocarbides, M23(C,B)6 at all test conditions. The cementite showed approximately equal sizes in all austenitizing temperatures, which was attributed to solubilization and reprecipitation during cooling tempering. It was observed the presence of borocarbides in all austenitizing temperatures, and at a temperature of 870°C the precipitation was coarser. This size distribution was not attributed to solubilization and coarsening of borocarbides to 870°C and the solubilization and reprecipitation during cooling tempering the other two temperatures. There was also a lesser precipitation in the grain boundary borocarbides to 1,050°C compared to 1,200°C.
Keywords
Low carbon steel with boron, Precipitation, Quench
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