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Optimization of the Continuous Galvanizing Heat Treatment Process in Ultra-High Strength Dual Phase Steels Using a Multivariate Model

1
Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (CINVESTAV), Unidad Saltillo, Zona Industrial, Ramos Arizpe C.P. 25903, Mexico
2
Instituto Tecnológico de Saltillo. Blvd, Venustiano Carranza #2400, Col. Tecnológico, Saltillo C.P. 25280, Mexico
3
Facultad de Sistemas, Universidad Autónoma de Coahuila, Ciudad Universitaria, Carretera a México Km 13, Arteaga, Coahuila, Mexico
4
International Zinc Association, 2530 Meridian Parkway, Durham, NC 27713, USA
*
Author to whom correspondence should be addressed.
Metals 2019, 9(6), 703; https://doi.org/10.3390/met9060703
Received: 26 April 2019 / Accepted: 4 May 2019 / Published: 21 June 2019
(This article belongs to the Special Issue Numerical Modelling and Simulation of Metal Processing)
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Abstract

The main process variables to produce galvanized dual phase (DP) steel sheets in continuous galvanizing lines are time and temperature of intercritical austenitizing (tIA and TIA), cooling rate (CR1) after intercritical austenitizing, holding time at the galvanizing temperature (tG) and finally the cooling rate (CR2) to room temperature. In this research work, the effects of CR1, tG and CR2 on the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) of cold rolled low carbon steel were investigated by applying an experimental central composite design and a multivariate regression model. A multi-objective optimization and the Pareto Front were used for the optimization of the continuous galvanizing heat treatments. Typical thermal cycles applied for the production of continuous galvanized AHSS-DP strips were simulated in a quenching dilatometer using miniature tensile specimens. The experimental results of UTS, YS and EL were used to fit the multivariate regression model for the prediction of these mechanical properties from the processing parameters (CR1, tG and CR2). In general, the results show that the proposed multivariate model correctly predicts the mechanical properties of UTS, YS and %EL for DP steels processed under continuous galvanizing conditions. Furthermore, it is demonstrated that the phase transformations that take place during the optimized tG (galvanizing time) play a dominant role in determining the values of the mechanical properties of the DP steel. The production of hot-dip galvanized DP steels with a minimum tensile strength of 1100 MPa is possible by applying the proposed methodology. The results provide important scientific and technological knowledge about the annealing/galvanizing thermal cycle effects on the microstructure and mechanical properties of DP steels. View Full-Text
Keywords: dual phase steel; hot dip galvanizing line; multivariate analysis; multi-objective optimization; dilatometry dual phase steel; hot dip galvanizing line; multivariate analysis; multi-objective optimization; dilatometry
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Costa, P.; Altamirano, G.; Salinas, A.; González-González, D.S.; Goodwin, F. Optimization of the Continuous Galvanizing Heat Treatment Process in Ultra-High Strength Dual Phase Steels Using a Multivariate Model. Metals 2019, 9, 703.

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