Effect of Boron in Cold Rolled DP Steels; Fundamentals of Metallurgy & General Property Map

Abstract

Dual-phase (DP) steels with their dual phase microstructures (hard martensite and soft ferrite) are used in many industrial applications, especially in the automotive industry, thanks to their desired mechanical properties and formability. These properties are directly related to their phase distribution in microstructure obtained as a result of the production conditions. The most important step of the production of cold rolled DP steels is the annealing process. In this study, the effect of boron alloying with line scale heat treatment cycle on the microstructure and mechanical properties of cold rolled DP steel was investigated. For this purpose, mechanical test, formability and weldability tests were carried out. The materials were characterized by optical microscopy (OM) and scanning electron microscopy (SEM/EBSD) studies. According to the results, alloying with boron delays the formation of ferrite and pearlite/bainite during the cooling process and increases the martensite formation rate. Boron alloyed cold rolled DP steel shows improved yield and tensile strength without significant loss of elongation. On the other hand, alloying with boron does not have a detrimental effect on the weld properties.

Keywords

• boron alloying
• inter-critical annealing
• dp steels
• microstructure
• mechanical testing