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Title

EFFECT OF COIL COOLING CONDITIONS ON THE OCCURRENCE OF THICKNESS OSCILLATION DURING COLD ROLLING OF A CR-MO ALLOY DP STEEL

Authorship

Bahia, Jean Viana; Santos, Antônio Adel dos; Buono, Vicente Tadeu Lopes; Barbosa, Ronaldo Antonio Neves Marques

Bahia, Jean Viana

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Santos, Antônio Adel dos

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Buono, Vicente Tadeu Lopes

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Barbosa, Ronaldo Antonio Neves Marques

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DOI

10.5151/9785-9785-32227

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Abstract

During cold rolling of Cr-Mo alloyed DP steel, considerable oscillation of thickness may occur. The literature points out that such occurrence is due to non-uniform cooling of the coil after the hot rolling process. Since the austenite transformation in this steel continues after coiling, the microstructure and, consequently, mechanical properties are very susceptible to natural variations in cooling rates associated with distinct positions of the coil. The influence of coil cooling conditions on thickness oscillation during cold rolling was evaluated in this work by using both industrial experiments and dilatometer tests. It was verified that an industrial coil presented large variation of mechanical properties associated with its heterogeneous microstructure. Consequently, thickness oscillation occurred during cold rolling. Dilatometer tests simulating hot run-out table and coil cooling showed that the austenite transformation is very slow under small cooling rates that occur after coiling. Thus, the slow transformation rate makes the coil very susceptible to environmental conditions around it during its natural cooling and is responsible for variation in mechanical properties of the coil. To ensure the formation of a more homogeneous microstructure in the whole coil, it is necessary either to make use of technologies that improves the cooling uniformity or to adjust the steel alloy design. The latter alternative has been done with relative success by using conceptions with lower amounts of Cr and Mo.

Keywords

thickness oscillation, Cold rolling, Cr-Mo DP steels, coil cooling.