CRESCIMENTO ANORMAL DO GRÃO AUSTENÍTICO E SUA INFLUÊNCIA NA FRAÇÃO VOLUMÉTRICA DE AUSTENITA RETIDA APÓS A TÊMPERA DE UM AÇO ABNT 5135
INFLUENCE OF ABNORMAL AUSTENITE GRAIN GRAIN GROWTH IN QUENCHED ABNT 5135 STEEL
Ferreira, Camila de Brito; Modenesi, Paulo José; Santos, Dagoberto Brandão
http://dx.doi.org/10.4322/2176-1523.0682
Tecnol. Metal. Mater. Min., vol.12, n1, p.50-57, 2015
Resumo
O tamanho de grão nos aços é bastante importante nos tratamentos térmicos de têmpera. A temperatura e tempo de austenitização maiores levam ao aumento dos grãos austeníticos. Por sua vez, após a têmpera de um aço baixa liga, a microestrutura é constituída por martensita e uma fração de austenita retida, dependente de vários fatores, inclusive do tamanho de grão austenítico. Neste trabalho, estudou-se a influência do tamanho de grão austenítico sobre a fração volumétrica de austenita retida, após a têmpera de um aço ABNT 5135. Foram medidas as áreas dos grãos da austenita bem como a quantificação de austenita retida por difração de raios-X. As temperaturas de Mi e Mf foram determinadas por equação empírica e experimentalmente por análise térmica diferencial. Também foram feitos testes de microdureza Vickers. Foi mostrado que o aumento do grão austenítico promove uma maior fração volumétrica de austenita retida após a têmpera em água, diferentemente do que é relatado na literatura, quando se comenta que a temperabilidade do aço aumenta com o tamanho de grão austenítico.
Palavras-chave
Austenita retida, Grão austenítico, Têmpera, Crescimento de grão.
Abstract
Grain size in the steels is a relevant aspect in quenching and tempering heat treatments. It is known that high austenitizing temperature and long time provide an increase in austenitic grain sizes. Likewise, after hardening of low alloy steel, the microstructure consists of martensite and a volume fraction of retained austenite. This paper evaluates the influence of austenite grain size on the volume fraction of retained austenite measured by metallographic analyses and X-ray diffraction. The Mi and Mf temperatures were calculated using an empirical equation and experimentally determined by differential thermal analysis. The mechanical behavior of the steel was evaluated by Vickers microhardness testing. Differently from other results published in the literature that steel hardenability increases with the austenite grain size, it was observed that the increase in austenite grain promotes greater volume fraction of retained austenite after water quenching.
Keywords
Martensite, Retained austenite, Athermal martensite, Grain growth.
Referências
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4 Lai GY, Wood WE, Clark RA, Zackay VF, Parker ER. The effect of austenitizing temperature on the microstructure and mechanical properties of as-quenched 4340 steel. Metallurgical Transactions. 1974;5(7):1663-1670. http://dx.doi.org/10.1007/BF02646340.
5 Mohanty GO. On the stabilization of retained austenite: mechanism and kinetics. Materials Science and Engineering. 1995;32(3):267-278. http://dx.doi.org/10.1016/0921-5107(95)03017-4.
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10 Guimarães JRC, Rios PR. Martensite start temperature and the austenite grain-size. Journal of Materials Science. 2010;45(4):1074-1077. http://dx.doi.org/10.1007/s10853-009-4044-0.
11 Guimarães JRC. Athermal martensite: Genesis of microstructure and transformations curves. Materials Science and Engineering A. 2008;476(1-2):106-111. http://dx.doi.org/10.1016/j.msea.2007.04.068.
12 Bhadeshia HKDH, Christian JW. Bainite in steels. Metallurgical Transactions. A, Physical Metallurgy and Materials Science. 1990;21(3):767-797. http://dx.doi.org/10.1007/BF02656561.
13 Cohen M. Martensitic nucleation - revisited. Materials Transactions, JIM. 1992;33(3):178-183.
14 Fisher JG. Application of nucleation theory to isothermal martensite. Acta Metallurgica. 1953;1(1):32-35. http://dx.doi.org/10.1016/0001-6160(53)90007-8.
15 Lee S-J, van Tyne CJ. A kinetics model for martensite transformation in plain carbon and low-alloyed steels. Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science. 2012;43(2):422-427. http://dx.doi.org/10.1007/s11661-011-0872-z.
16 Liu Y-J, Li Y-M, Huang B-Y. Influence of austenitizing temperature on apparent morphologies as-quenched microstructure of steels. Journal Central South University of Technology. 2006;13(2):122-129. http://dx.doi.org/10.1007/s11771-006-0142-1.
17 Guimarães JRC, Rios PR. Unified description of martensite microstructure and kinetics. Journal of Materials Science. 2009;44(4):998-1005. http://dx.doi.org/10.1007/s10853-008-3218-5.
18 Ajus C, Tavares SSM, Silva MR, Corte RRA. Magnetic properties and retained austenite quantification in SAE 4340 steel. Revista Materia. 2009;14(3):993-999. http://dx.doi.org/10.1590/S1517-70762009000300011.
19 Rodrigues TFM, Viana VDC, Modenesi PJ, Santos DB. Quantificação de austenita por meio da difração de raios-x em um aço inoxidável supermatensítico. In: Associação Brasileira de Metalurgia, Materiais e Mineração. Anais do 66° Congresso da ABM; 2011; São Paulo, Brasil. São Paulo: ABM; 2011. p. 1780-1791.
20 Bernal C, Couto AB, Breviglieri ST, Cavalheiro ÉTG. Influência de alguns parâmetros experimentais nos resultados de análises calorimétricas diferenciais. Quimica Nova. 2002;25(5):849-855. http://dx.doi.org/10.1590/S0100-40422002000500023.
21 Andrews KW. Empirical formulae for the calculation of some transformation temperatures. Journal of the Iron and Steel Institute. 1965;203:721-727.
22 Kashchenco MP, Chaschina VG. Critical grain size in the γ→α martensite transformation. Thermodynamic analysis with regard to spatial scales characteristic of martensite nucleation. Physical Mesomechanics. 2010;13(3-4):189-194. http://dx.doi.org/10.1016/j.physme.2010.07.012.
23 Van Bohemen SMC, Sietsma J. Martensite formation in partially and fully austenitic plain carbon steels. Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science. 2009;40(5):1059-1068. http://dx.doi.org/10.1007/s11661-009-9796-2.
2 Totten GE. Steel heat treatment – metallurgy and technologies. New York: CRC Taylor & Francis; 2007. Chapter 6. p. 384-390.
3 Guimarães JRC. Conceituação, cinética e morfologia da transformação martensítica em aços. Revista Latinoamericana de Metalurgia e Materiales. 1981;1(1):3-9.
4 Lai GY, Wood WE, Clark RA, Zackay VF, Parker ER. The effect of austenitizing temperature on the microstructure and mechanical properties of as-quenched 4340 steel. Metallurgical Transactions. 1974;5(7):1663-1670. http://dx.doi.org/10.1007/BF02646340.
5 Mohanty GO. On the stabilization of retained austenite: mechanism and kinetics. Materials Science and Engineering. 1995;32(3):267-278. http://dx.doi.org/10.1016/0921-5107(95)03017-4.
6 Matlock DK, Alogab KA, Richards MD, Speer JG. Surface processing to improve the fatigue resistance of advanced bar steels for automotive applications. Materials Research. 2005;8(4):453-459. http://dx.doi.org/10.1590/S1516-14392005000400017.
7 Lee S-J, Lee Y-K. Effect of austenite grain size on martensitic transformation of a low alloy steel. Materials Science Forum. 2005;475-479:3169-3172. http://dx.doi.org/10.4028/www.scientific.net/MSF.475-479.3169.
8 Yang H-S, Bhadeshia HKDH. Austenite grain size and the martensite-start temperature. Scripta Materialia. 2008;60(7):493-495. http://dx.doi.org/10.1016/j.scriptamat.2008.11.043.
9 García-Junceda A, Capdevila C, Caballero FG, Garcia de Andrés C. Dependence of martensite start temperature on fine austenite grain size. Scripta Materialia. 2008;58(2):134-137. http://dx.doi.org/10.1016/j.scriptamat.2007.09.017.
10 Guimarães JRC, Rios PR. Martensite start temperature and the austenite grain-size. Journal of Materials Science. 2010;45(4):1074-1077. http://dx.doi.org/10.1007/s10853-009-4044-0.
11 Guimarães JRC. Athermal martensite: Genesis of microstructure and transformations curves. Materials Science and Engineering A. 2008;476(1-2):106-111. http://dx.doi.org/10.1016/j.msea.2007.04.068.
12 Bhadeshia HKDH, Christian JW. Bainite in steels. Metallurgical Transactions. A, Physical Metallurgy and Materials Science. 1990;21(3):767-797. http://dx.doi.org/10.1007/BF02656561.
13 Cohen M. Martensitic nucleation - revisited. Materials Transactions, JIM. 1992;33(3):178-183.
14 Fisher JG. Application of nucleation theory to isothermal martensite. Acta Metallurgica. 1953;1(1):32-35. http://dx.doi.org/10.1016/0001-6160(53)90007-8.
15 Lee S-J, van Tyne CJ. A kinetics model for martensite transformation in plain carbon and low-alloyed steels. Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science. 2012;43(2):422-427. http://dx.doi.org/10.1007/s11661-011-0872-z.
16 Liu Y-J, Li Y-M, Huang B-Y. Influence of austenitizing temperature on apparent morphologies as-quenched microstructure of steels. Journal Central South University of Technology. 2006;13(2):122-129. http://dx.doi.org/10.1007/s11771-006-0142-1.
17 Guimarães JRC, Rios PR. Unified description of martensite microstructure and kinetics. Journal of Materials Science. 2009;44(4):998-1005. http://dx.doi.org/10.1007/s10853-008-3218-5.
18 Ajus C, Tavares SSM, Silva MR, Corte RRA. Magnetic properties and retained austenite quantification in SAE 4340 steel. Revista Materia. 2009;14(3):993-999. http://dx.doi.org/10.1590/S1517-70762009000300011.
19 Rodrigues TFM, Viana VDC, Modenesi PJ, Santos DB. Quantificação de austenita por meio da difração de raios-x em um aço inoxidável supermatensítico. In: Associação Brasileira de Metalurgia, Materiais e Mineração. Anais do 66° Congresso da ABM; 2011; São Paulo, Brasil. São Paulo: ABM; 2011. p. 1780-1791.
20 Bernal C, Couto AB, Breviglieri ST, Cavalheiro ÉTG. Influência de alguns parâmetros experimentais nos resultados de análises calorimétricas diferenciais. Quimica Nova. 2002;25(5):849-855. http://dx.doi.org/10.1590/S0100-40422002000500023.
21 Andrews KW. Empirical formulae for the calculation of some transformation temperatures. Journal of the Iron and Steel Institute. 1965;203:721-727.
22 Kashchenco MP, Chaschina VG. Critical grain size in the γ→α martensite transformation. Thermodynamic analysis with regard to spatial scales characteristic of martensite nucleation. Physical Mesomechanics. 2010;13(3-4):189-194. http://dx.doi.org/10.1016/j.physme.2010.07.012.
23 Van Bohemen SMC, Sietsma J. Martensite formation in partially and fully austenitic plain carbon steels. Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science. 2009;40(5):1059-1068. http://dx.doi.org/10.1007/s11661-009-9796-2.
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