EFEITO DA TAXA DE RESFRIAMENTO NA OCORRÊNCIA DE AUSTENITA RETIDA EM UM AÇO PARA ELETRODOS DE SOLDA
INFLUENCE OF COOLING RATE ON THE OCORRENCE OF RETAINED AUSTENITE IN A STEEL FOR WELDING ELECTRODES
Ferreira, Helder Carvalho; Boratto, Francisco José Martins; Buono, Vicente Tadeu L.
http://dx.doi.org/10.4322/2176-1523.0813
Tecnol. Metal. Mater. Min., vol.12, n1, p.58-64, 2015
Resumo
A influência da taxa de resfriamento na ocorrência de austenita retida em um aço de baixo teor de carbono ligado ao Si e Mn, utilizado na fabricação de eletrodos de solda, é medida aqui através da combinação de seccionamento de corpo de prova Jominy com o método de medição de austenita retida através da difração de raios-X. Foi observado que a quantidade de austenita retida aumenta de zero, quando a taxa de resfriamento é menor do que 0,8°C/s e a estrutura é majoritariamente ferrítica, para um valor máximo de 6%, no ponto em que a quantidade de bainita também é máxima. Essa informação passa a guiar assim o projeto do ciclo de resfriamento pós-laminação de fio máquina para eletrodos de solda. O conhecimento da proporcionalidade da austenita retida com a presença de fases duras passa a permitir o uso da difração de raios-X como exame liberatório de fio máquina neste tipo de aço, assim como na simplificação de ciclo de tratamento térmico antes da trefilação.
Palavras-chave
Eletrodo, Austenita retida, Taxa de resfriamento.
Abstract
The effect of cooling rate on the occurrence of retained austenite in a low carbon Si-Mn steel, used for welding electrodes, is measured here by combining the sectioning of Jominy test samples with the measurement of retained austenite by X-ray diffraction. It was observed that the amount of retained austenite increases from zero, as the cooling rate is less than 0.8°C/s, and the structure is mostly ferrite, to a maximum of 6%, where the quantity of bainite is also maximum. This information guides the post-rolling cooling cycle when welding grade is been rolled. The hard phases proportionality with the amount of retained austenite allows, then, the use of X-ray diffraction as an end of the line equipment for quality control, and also permits simplification of heat treatment before wire drawing.
Keywords
Electrode, Retained austenite, Cooling rate.
Referências
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6 American Society for Testing and Materials. ASTM A255-2: Standard test methods for determining hardenability of steel. West Conshohocken: ASTM; 2002.
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2 Kandpal BC, Chutani A, Harsimran AG, Sadanna C. A review on Jominy test and determination of effect of alloying elements on hardenability of steel using Jominy end quench test. International Journal of Advances in Engineering & Technology. 2011;1(3):65-71.
3 Cullity BD, Stock SR. Elements of X-ray diffraction. 3. ed. New Jersey: Prentice Hall; 2001.
4 Michette AG, Pfauntsch SJ. Laser plasma x-ray line spectra fitted using the Pearson VII function. Journal of Applied Physics D: Applied Physics. 2000;33(10):1186-1190. http://dx.doi.org/10.1088/0022-3727/33/10/308.
5 Dmitrieva O, Ponge D, Inden G, Millan J, Choi P, Sietsma J, et al. Chemical gradients across phase boundaries between martensite and austenite in steel studied by atom probe tomography and simulation. Acta Materialia. 2011;59(1):364-374. http://dx.doi.org/10.1016/j.actamat.2010.09.042.
6 American Society for Testing and Materials. ASTM A255-2: Standard test methods for determining hardenability of steel. West Conshohocken: ASTM; 2002.
7 American Society for Testing and Materials. ASTM E975-95: X-ray determination of retained austenite in steel with near randon crystallographic orientation. Philadelphia: ASTM; 1995.
8 Billo EJ. Excel for scientists and engineers. New York: John Wiley and Sons; 2007. Nonlinear regression using the solver; p. 313-339. http://dx.doi.org/10.1002/9780470126714.ch14.
9 Roberts CS. Effect of carbon on the volume fraction and lattice parameters of retained austenite and martensite. Journal of Metals Transactions AIME. 1953;197:203-204.
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