Obtention of a multiphasic steel from A 0.084%C, 1.44% Mn and 0.81%Si steel

A 0.084%C-1.44%Mn-0.84%Si steel is studied in order to produce a multiphase steel by means of an appropriate fabrication process that permits to induce this multiphase microstructure starting with the typical chemical composition of a welding electrode. Moreover, this fabrication process must be easy to use by siderurgical industry. The effect of two initial microstructures were studied: a ferriticperlitic (F/P) and a ferritic-martensitic (F/M). After producing these two microstructures, the steels were 70% cold rolled, with 1 mm final thickness, after which, an annealing treatment at 800°C for 600 s was carried out. Then the samples were cooled at three cooling rates: normalized, oil quenching and water quenching. The metallographic analysis was carried out using optical microscopy, scanning electronic microscopy and atomic force microscopy, revealing a ferrite-retained austenite-bainite and martensite multiphase microstructure. The retained austenite was confirmed by means of X-ray diffraction. Also, it was concluded that the grain size is lower in the case of a ferritic-martensitic microstructure. From these results it is possible to conclude that from a commercial chemical composition of the steel, a multiphase microstructure can be obtained, that constitutes the initial stage in the fabrication of a TRIP aided steel.