EFEITO DO GRÃO ULTRAFINO NO COMPORTAMENTO MECÂNICO DO AÇO Nb-Ti DE LAMINADO A MORNO
THE ULTRAFINE GRAIN SIZE EFFECT ON MECHANICAL BEHAVIOR OF A Nb-Ti STEEL PROCESSED BY WARM ROLLING
Duarte, Dayanna Moreira; Faria, Erick Ribeiro de; Balancin, Oscar; Santos, Dagoberto Brandão
http://dx.doi.org/10.4322/tmm.00504003
Tecnol. Metal. Mater., vol.5, n4, p.204-209, 2009
Resumo
Quando deformados plasticamente, os aços baixo carbono microligados apresentam um interessante comportamento. O alongamento uniforme, por exemplo, aumenta com a redução do tamanho de grão ferrítico, enquanto se reduz a razão elástica. O objetivo deste trabalho é acompanhar a evolução microestrutural ao longo do processamento térmico e mecânico para interpretar o desempenho mecânico de um aço microligado baixo carbono (0,11C-1,41Mn-0,028-Nb-0,012Ti) de grão ferrítico ultrafino, obtido por meio de tratamentos térmicos de têmpera, laminação a morno e recozimentos intercrítico e subcrítico. Para isso, verifica-se a evolução do tamanho de grão ferrítico e avalia-se o comportamento mecânico por meio de testes de tração e impacto. A resistência mecânica do aço recozido a 550°C mostra um acréscimo de 25%, comparada com o aço na condição de fornecimento. Para o aço recozido a 800°C, há aumento na resistência mecânica e na energia absorvida no ensaio de impacto.
Palavras-chave
Grão ultrafino, Recozimento intercrítico, Laminação a morno, Cementita
Abstract
The grain size refining is the unique mechanism capable of to increase both mechanical strength and toughness. In this way the refining of ferritic grain is a very attractive processing. The steel with an ultra-fine ferritic grain structure shows the better relationship between mechanical strength, ductility and toughness, while the low carbon content enhances good welding characteristics. The objective of this work is to investigate the behavior of work hardening of a micro alloyed low carbon-manganese (0.11C-1.41Mn-0.028Nb-0.012Ti) steel with ultra-fine ferritic grain structure produced through thermal treatment, warm rolling, followed by sub and intercritical annealing. After quenching in ice brine, the samples was processed by warm rolling and annealing. The mechanical behavior of the steel was estimated using tensile and impact tests. The mechanical strength obtained after all processing have shown a 15% increasing when compared with results from the steel in as hot rolling industrial condition.
Keywords
Ultra-fine grain, Sub critical annealing, Warm rolling, Cementite
Referências
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10 SONG, R.; PONGE, D.; RAABE, D.; KASPAR, R. Microstructure and crystallographic texture of an ultrafine grained C-Mn steel and their evolution during warm deformation and annealing. Acta Materialia, v. 53, n. 3, p. 845-58, 2005.
11 SANTOS, D.B.; BRUZUSZEK, R.K.; RODRIGUES, P.C.M.; PERELOMA, E.V. Formation of ultra-fine ferrite microstructure in warm rolled and annealed C-Mn steel. Materials Science and Engineering A, v. 346, n. 1-2, p. 189-95, 2003.
12 SILVA, H.R.; LOURENÇO, G.G.; BRAGA, L.H.R.; RODRIGUES, P.C.M.; SANTOS, D.B. Encruamento e tenacidade do aço Nb-Ti de grão ultrafino. In: CONGRESSO ANUAL DA ABM, 62, 2007, Vitória-ES. Anais… São Paulo: ABM, 2007. 1 CD-ROM. p. 3351-9.
13 HUMPHREYS, F.J.; HATHERLY, M. Recrystallization and related annealing phenomena. UK: Pergamon, 1995.
14 HAWKINS, D.N.; SHUTTLEWORTH, A.A. The effect of warm rolling on the structure and properties of low-carbon steel. Journal of Mechanical Working Technology, v. 2, n. 4, p. 333-45, Feb.1979.
15 KIMURA, Y.; INOUE, T.; YIN, F.; TSUZAKI, K. Inverse temperature dependence of toughness in ultrafine grainstructure steel. Science, v. 320, n. 5879, p. 1057-60, May 2008.
2 HORVATH, D.C.; FEKETE, J.R. Opportunities and challenges for increased usage of advanced strength steels in automotive applications. In: INTERNATIONAL CONFERENCE ON ADVANCED HIGH STRENGTH SHEET STEELS FOR AUTOMOTIVE APPLICATIONS, 2004, Winter Park, Colorado. Warrendade, PA: AIST, 2004. p. 3-10.
3 DeARDO, A.J. New challenges in the thermomechanical processing of HSLA steels. Materials Science Forum, v. 426-32, p. 49-56, 2003.
4 VALIEV, R.Z.; KORZNIKOV, V.A.; MULYUKOV. R.R. Structure and properties of ultra-fine-grained materials produced by severe plastic deformation. Materials Science Engineering A, v. 168, n. 2, p. 141-8, 1993.
5 RINTARO, U.; TSUJIB, N.; MINAMINOB, Y.; KOIZUMI, Y. Effect of rolling reduction on ultrafine grained structure and mechanical properties of low-carbon steel thermomechanically processed from martensite starting structure. Science & Technology-Advanced Materials, v. 5, n. 1-2, p. 153-62, Jan.-Mar. 2004.
6 SAITO, Y.; UTSUNOMIYA, H.; TSUJI, N.; SAKAI, T. Novel ultra-high straining process for bulk materials-development of the accumulative roll-bonding (ARB) process. Acta Materialia, v. 47, n. 2, p. 579-83, 1999.
7 NAGAI, K. Ultrafine-grained ferrite with dispersed cementite particles. Journal of Materials Processing Technology, v. 117, n. 3, p. 329-32, Nov. 2001.
8 OHMORI, A.; TORIZUKA, S.; NAGAI, K. Strain-hardening due to dispersed cementite for low carbon ultrafinegrained steels. ISIJ International, v. 44, n. 6, p. 1063-70, 2004.
9 SONG, R.; PONGE, D.; RAABE, D. Mechanical properties of an ultrafine grained C-Mn steel processed by warm deformation and annealing. Acta Materialia, v. 53, n. 18, p. 4881-92, 2005.
10 SONG, R.; PONGE, D.; RAABE, D.; KASPAR, R. Microstructure and crystallographic texture of an ultrafine grained C-Mn steel and their evolution during warm deformation and annealing. Acta Materialia, v. 53, n. 3, p. 845-58, 2005.
11 SANTOS, D.B.; BRUZUSZEK, R.K.; RODRIGUES, P.C.M.; PERELOMA, E.V. Formation of ultra-fine ferrite microstructure in warm rolled and annealed C-Mn steel. Materials Science and Engineering A, v. 346, n. 1-2, p. 189-95, 2003.
12 SILVA, H.R.; LOURENÇO, G.G.; BRAGA, L.H.R.; RODRIGUES, P.C.M.; SANTOS, D.B. Encruamento e tenacidade do aço Nb-Ti de grão ultrafino. In: CONGRESSO ANUAL DA ABM, 62, 2007, Vitória-ES. Anais… São Paulo: ABM, 2007. 1 CD-ROM. p. 3351-9.
13 HUMPHREYS, F.J.; HATHERLY, M. Recrystallization and related annealing phenomena. UK: Pergamon, 1995.
14 HAWKINS, D.N.; SHUTTLEWORTH, A.A. The effect of warm rolling on the structure and properties of low-carbon steel. Journal of Mechanical Working Technology, v. 2, n. 4, p. 333-45, Feb.1979.
15 KIMURA, Y.; INOUE, T.; YIN, F.; TSUZAKI, K. Inverse temperature dependence of toughness in ultrafine grainstructure steel. Science, v. 320, n. 5879, p. 1057-60, May 2008.
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