Study on Deep Drawing Behavior of the Interstitial Free Steel in Correlation With the Microstructure

Abstract

The objective of this paper was to present results obtained about the behaviour of the IF steel associated with high deformation. To evaluate the deep drawing aptitude, samples were subjected to tensile test, n and r values determination, hole expansion and Erichsen tests. The results were correlated with a microstructural study. Through thermodynamic simulation, the phase transformation temperature (Tg®a) and the precipitates formation were estimated. The Tg®a value was also determined by dilatometry test. The failure of the material during deep drawing or stamping process is evidenced through the formation of cracks in areas with critical angles changes. It was relevant to understand the mechanisms of fracture nucleation and propagation of the IF steel. A fractography study was carried out and was possible to verify the presence of cavitation mechanism as results of the superplastic flow at high deformation conditions, promoting necking and fracture after a high plastic deformation achieved.

Thermal characterization by dilatometry tests of a ferritic-bainitic (FB) steel for automotive application

“…The methodology is in complete agreement with [6,7]. The microstructure of all the samples were characterized and the results of present phases obtained, were correlated with a thermodynamic simulation applying the software FactSage 8.1 [8]. In this case, the cooling of the ferrite-bainite steel was simulated in the range between 400 °C to 1200 °C, at equilibrium conditions.…”

“…A study of equilibrium conditions on DP-590 steel was carried out by Fact Sage 8.1 software. This software is an important tool that allows to predict thermodynamics properties of materials [8].…”

“…Fig 8. Microstructure aspect with ferrite and pearlite presence observed in the specimen cooled at 0.03 °C/s.…”

“…Therefore, the cooling rate controls the kinetic of  →  solid state phase transformation, the final microstructure, and the mechanical properties of the steel sheet. Dilatometry tests were extensively used to increase the knowledge on the thermal process impact on the steel microstructure and were considered as an important tool for many researchers [3][4][5][6][7][8]. In this study, dilatometry tests provided information of the phase transformation temperatures during heating and under different cooling rate conditions of the steel.…”