Search Results

Applying the Heat Tinting Technique the microestrutural characterization of a 300M steel (medium carbon steel) was accomplished. The steel was austenitized for 20 min to 900°C, followed by holding at 400°C (in the bainitic temperature), with maintenance time of the material in the temperature of 1min, 5min and 30min, aiming at the formation of a multiphase structure. Through the metallographic analysis it is verified that, with the use of this technique, it is possible the determination of the volume fraction of the present phases in the 300M steel, especially in the identification and quantification of the retained austenite.

In this work five methods of heat treatments are investigated in order to obtained convenient volume fractions of ferrite, bainite, martensite and retained austenite, starting with a low carbon steel and seeking the distinction of the phases, through optical microscopy. Specific chemical etching is improved. The results in tensile and fatigue tests were accomplished and the results were related with the microstructural parameters. The results show that the mechanical properties are closely related with the phases, grains size and the phases morphology.

The dual-phase are produced by intercritical heat treatment and, getting a microstructure composed, basically, by ferrite and martensite, are detached by introduce typical characteristcs like high tensile strength, good ductility and conformability high rate of work-hardening and low yield stress. In the present work was studied the tensile behaviour of dual-phase steel in several conditions of tempering, with the purpose to investigate the ferrite - martensite interaction. The influence of different temperatures, used on the heat treatment, about the mechanical properties was related with microstructural parameters, like volumetric fraction, microhardness and phase morphology. The results showed that tempering caused reductions on martensitic volumetric fraction and phases microhardness, changing the dual-phase steels morphology. Furthermore, the elevation of tempering temperature occasioned a decreased on tensile strength levels and an increased on ductility.