ESTUDO DO ENVELHECIMENTO APÓS DEFORMAÇÃO EM UM AÇO DUAL PHASE DE BAIXA RESISTÊNCIA MECÂNICA LAMINADO A FRIO
STATIC STRAIN AGING STUDY IN A COLD ROLLED DUAL PHASE STEEL OF LOW MECHANICAL RESISTANCE
Murari, Fabio Dian; Melo, Tulio Magno F. de; Gonzalez, Berenice Mendonça
http://dx.doi.org/10.4322/tmm.00602008
Tecnol. Metal. Mater. Min., vol.6, n2, p.108-112, 2009
Resumo
A cinética de envelhecimento após deformação em aço Dual Phase laminado a frio é estudada por meio de ensaios de tração. Após a etapa de recozimento contínuo, o aço foi pré-deformado de 0,5% em tração e envelhecido no intervalo de temperatura entre 50°C e 185°C, para tempos variando entre 1 minuto e 4.915 minutos. O aço estudado apresenta dois estágios de envelhecimento, o primeiro, entre 50°C e 125°C (para tempos inferiores a 72 minutos) e o segundo entre 125°C (para tempos superiores a 72 minutos) e 185°C. As variações no valor Bake Hardening sugerem, para o primeiro estágio de envelhecimento, um processo controlado pelo ancoramento das deslocações na ferrita devido à formação de clusters e/ou carbonetos de transição, com uma energia de ativação próxima de 70 kJ/mol e obedecendo a uma lei cinética descrita pela equação de Harper com expoente do tempo igual a 0,4. No segundo estágio de envelhecimento, o fenômeno é controlado pelo revenimento da martensita. A energia de ativação correspondente a esse estágio é de cerca de 120 kJ/mol e sua cinética pode ser descrita pela mesma equação, porém com um expoente do tempo igual a 0,5.
Palavras-chave
Aço bifásico, Envelhecimento após deformação, Bake hardening
Abstract
The kinetics of static strain aging in cold rolled Dual Phase steel is studied by means of tensile tests. After the continuous annealing step, the specimens were pre-strained with a tensile strain of 0.5% and then aged in the temperature range of 50°C to 185°C and time intervals ranging from 1 minute to 4,915 minutes. The steel studied showe two strain aging stages: the first one between 50°C and 125°C (for times shorter than 72 minutes) and the second one between 125°C (for times longer than 72 minutes) and 185°C. The changes in the Bake Hardening values suggest, for the first stage, a process controlled by the locking of the dislocations in the ferrite due to the formation of clusters and/ or transition carbides, with an activation energy close to 70 kJ/mol and following a kinetic law described by the Harper equation with a time exponent of 0.4. In the second stage, the phenomenon is controlled by tempering of martensite. The corresponding activation energy is approximately 120 kJ/mol and the kinetics of this stage can be described by the same equation, however with a time expoent of 0.5.
Keywords
Dual phase steels, Static strain aging, Bake hardening
References
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2 SHERMAN, A. M.; ELDIS, G. T.; COHEN, M. The aging and tempering of iron-nickel-carbon martensites. Metallurgical Transactions A, v. 14, n. 6, p. 995-1005, June 1983.
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5 SCHOECK, G. Moving dislocations and solute atoms. Physical Review, v. 102, n. 6, p. 1458-9, 1956.
6 SAMEK, L.; DE MOOR, E.; PENNING, J.; SPEER, J.G.; DE COOMAN, B.C. Static strain aging of microstructural constituents in transformation-induced-plasticity steel. Metallurgical and Materials Transactions A, v. 39, n. 11, p. 2542-54, Nov. 2008.
7 PANDA, A.K.; GANGULY, R.I.; MISRA, S. Studies on kinetics of strain ageing in Nb, Ti, V-Bearing HSLA steels and a dual phase steel. Steel Research, v. 63, n. 3, p. 131-6, 1992.
8 BYUN, Y.S.; KIM, I.S.; KIM, S.J. Yielding and Strain aging behaviors of an Fe-0,07C-1,6Mn dual phase. Transactions ISIJ, v. 24, n. 5, p. 372-8, Sep. 1984.
9 BUONO, V. T. L.; GONZALEZ, B. M.; SILVA, E. M. P.; ANDRADE, M. S. Cinética do envelhecimento após deformação em fios de aços eutetóides. Matéria, v. 2, n. 1, jul. 1997.
10 DE, A.K.; VANDEPUTTE, S.; DE COOMAN, B.C. Kinetics of low temperature precipitation in a ULC-Bake hardening steel. Scripta Materialia, v. 44, n. 4, p. 695-700, Mar. 2001.
11 BAKER, L.J.; PARKER, J.D.; DANIEL, S.R. Mechanism of bake hardening in ultralow carbon steel containing niobium and titanium additions. Materials Science and Technology, v. 18, n. 5, p. 541-7, 2002.
12 WATERSCHOOT, T.; VERBEKEN, K.; DE COOMAN, B.C. Tempering kinetics of the martensitic phase in DP steel. ISIJ International, v. 46, n. 1, p. 138-46, Feb. 2006.
13 CHENG, L.; BRAKMAN, C.M.; KOREVAAR, B.M.; MITTEMEIJER, E.J. The tempering of iron-carbon martensite: dilatometric and calorimetric analysis. Metallurgical Transactions A, v. 19, n. 10, p. 2415-25, Oct. 1988.
14 LEMENT, B.S.; COHEN, M. A dislocation attraction model for the first stage of tempering. Acta Metallurgica, v. 4, p. 469-76, Sep. 1956.
2 SHERMAN, A. M.; ELDIS, G. T.; COHEN, M. The aging and tempering of iron-nickel-carbon martensites. Metallurgical Transactions A, v. 14, n. 6, p. 995-1005, June 1983.
3 BLECK, W.; BRÜHL, S. Bake hardening effects in advanced high strength steels. In: New Developments on Metallurgy and Applications of High Strength Steels. INTERNATIONAL CONFERENCE, 2008, Buenos Aires. [S.n.t.].
4 KRIEGER, M.; JANECEK, M.; ESTRIN, Y. Bake hardening behaviour of two cold rolled dual phase steels subjected to advanced galvanising processing routes. In: INTERNATIONAL CONFERENCE ON THERMO-MECHANICAL PROCESSING OF STEELS, 3., 2008, Padua. Milão: Association Italiana di Metalurgia, 2008
5 SCHOECK, G. Moving dislocations and solute atoms. Physical Review, v. 102, n. 6, p. 1458-9, 1956.
6 SAMEK, L.; DE MOOR, E.; PENNING, J.; SPEER, J.G.; DE COOMAN, B.C. Static strain aging of microstructural constituents in transformation-induced-plasticity steel. Metallurgical and Materials Transactions A, v. 39, n. 11, p. 2542-54, Nov. 2008.
7 PANDA, A.K.; GANGULY, R.I.; MISRA, S. Studies on kinetics of strain ageing in Nb, Ti, V-Bearing HSLA steels and a dual phase steel. Steel Research, v. 63, n. 3, p. 131-6, 1992.
8 BYUN, Y.S.; KIM, I.S.; KIM, S.J. Yielding and Strain aging behaviors of an Fe-0,07C-1,6Mn dual phase. Transactions ISIJ, v. 24, n. 5, p. 372-8, Sep. 1984.
9 BUONO, V. T. L.; GONZALEZ, B. M.; SILVA, E. M. P.; ANDRADE, M. S. Cinética do envelhecimento após deformação em fios de aços eutetóides. Matéria, v. 2, n. 1, jul. 1997.
10 DE, A.K.; VANDEPUTTE, S.; DE COOMAN, B.C. Kinetics of low temperature precipitation in a ULC-Bake hardening steel. Scripta Materialia, v. 44, n. 4, p. 695-700, Mar. 2001.
11 BAKER, L.J.; PARKER, J.D.; DANIEL, S.R. Mechanism of bake hardening in ultralow carbon steel containing niobium and titanium additions. Materials Science and Technology, v. 18, n. 5, p. 541-7, 2002.
12 WATERSCHOOT, T.; VERBEKEN, K.; DE COOMAN, B.C. Tempering kinetics of the martensitic phase in DP steel. ISIJ International, v. 46, n. 1, p. 138-46, Feb. 2006.
13 CHENG, L.; BRAKMAN, C.M.; KOREVAAR, B.M.; MITTEMEIJER, E.J. The tempering of iron-carbon martensite: dilatometric and calorimetric analysis. Metallurgical Transactions A, v. 19, n. 10, p. 2415-25, Oct. 1988.
14 LEMENT, B.S.; COHEN, M. A dislocation attraction model for the first stage of tempering. Acta Metallurgica, v. 4, p. 469-76, Sep. 1956.
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