Carbonitride Precipitation In Microalloyed Steel V-nb Thin Slabs Thermomecanically Treated [precipitação De Carbonitretos Em Placas Finas De Aço Microligado V-nb Submetidas A Tratamento Termomecânico]

Abstract

Transmission electron microscopy was used in order to investigate the precipitation of fine carbonitride particles in two thin slabs of vanadium and niobium microalloyed steels during thermomechanical processing. The slabs were solidified in a thin slab casting simulator and subsequently hot rolled from 42 to 12 mm thickness on a laboratory-scale rolling mill. The rolling schedule included 3 roughing passes and 5 finishing passes (with two different temperature regimes for finish rolling), followed by a simulated coiling stage in a tunnel furnace and finally air cooling. TEM results showed interphase precipitation and fine precipitation in austenite whose contributions to yield strength were calculated from the Orowan-Ashby model and compared to an empirical equation which accounts for strengthening effects from the steel's chemical composition and ferrite grain size. The amount of precipitation strengthening was estimated to have reached 130 MPa in one of the slabs, and 146 and 106 MPa, respectively, in the other slab, depending upon the finish rolling temperatures.31173126Honeycombe, R.W.K., (1981) Aços Microestrutura e Propriedades, , Lisboa: Fundação Calouste GulbenkianPriestner, R., Zhou, C., Simulation of microstructural evolution in Nb-Ti micro alloyed steel during hot direct rolling (1995) Ironmaking and Steelmaking, 22 (4), pp. 326-332Kaspar, R., Flüß, P., Laboratory simulation of the direct rolling of steel (1991) Steel Research, 62 (11), pp. 501-506Hansen, S.S., Vander Sande, J.B., Cohen, M., Niobium carbonitride precipitation and austenite recrystallization in hot-rolled micro alloyed steels (1980) Metallurgical Transactions A, 11, pp. 387-402. , MarPalmiere, E.J., Garcia, C.I., DeArdo, A.J., Compositional and microstructural changes which attend reheating and grain coarsening in steels containing Nb (1994) Metallurgical and Materials Transactions A, 25, pp. 277-286. , FebBowden, J.W., Samuel, F.H., Jonas, J.J., Effect of interpass time on austenite grain refinement by means of dynamic recrystallization of austenite (1991) Metallurgical Transactions A, 22, pp. 2947-2957. , DecKaspar, R., Peters, A., Efficient steel processing by disciplined hot forming and microalloying (1998) Steel Research, 69 (4-5), pp. 128-135Kestenbach, H.-J., Gallego, J., On dispersion hardening of microalloyed hot strip steels by carbonitride precipitation in austenite (2001) Scripta Materialia, 44, pp. 791-796Pereloma, E.V., Crawford, B.R., Hodgson, P.D., Strain-induced precipitation behaviour in hot rolled strip steel (2001) Materials Science & Engineering A, 299, pp. 27-37Kestenbach, H.-J., Dispersion hardening by niobium carbonitride precipitation in ferrite (1997) Material Science and Technology, 13, pp. 731-739. , SepItman, A., Cardoso, K.R., Kestenbach, H.-J., Quantitative study of carbonitride precipitation in niobium and titanium micro alloyed hot strip steel (1997) Materials Science and Technology, 13, pp. 47-55. , JanCampos, S.S., Morales, E.V., Kestenbach, H.-J., On strengthening Mechanisms in Commercial Nb-Ti Hot Strip Steels (2001) Metallurgical and Materials Transactions A, 32 A, pp. 1245-1248. , MayPark, J.S., Ajmal, M., Priestner, R., Tensile Properties of Simulated Thin Slab Cast and Direct Rolled Low-carbon Steel Microalloyed with Nb, V and Ti (2000) ISIJ International, 40 (4), pp. 380-385Gentile, F.C., (1999) Desenvolvimento de Protótipo para Simulação do Processo de Lingotamento Continuo de Placas, p. 91. , Campinas: UNICAMP-FEM. Dissertação (Mestrado)Mori, T., (1968) Tetsu to Hagane, 54, p. 763Costae Silva, A.L., Mei, P.R., (1988) Aços e Ligas Especiais. 2 a ed. Sumaré, pp. 213-214. , SP: Eletrometal S. A Metais EspeciaisBoratto, F., Barbosa, R., Yue, S., Jonas, J.J., Effect of chemical composition on the critical temperatures of microalloyed steels (1988) THERMEC-88, pp. 383-390. , The Iron and Steel Institute of Japan, Tokyo, JapanPickering, F.B., (1978) Physical Metallurgy and the Design of Steels, , London: Applied Science Publishers LtdOuchi, C., Sampei, T., Kozasu, I., The effect of hot-rolling condition and chemical-composition on the onset temperature of gamma-alpha-transformation after hot rolling (1982) Trans. ISIJ, 22, pp. 214-222Gladman, T., (1997) The Physical Metallurgy of Microalloyed Steels, pp. 47-56. , The Institute of Materials, LondonDutta, B., Palmiere, E.J., Sellars, C.M., Modelling the Kinetics of strain induced precipitation in Nb microalloyed steels (2001) Acta Materialia, 49, pp. 785-79