Effect Of Thermomechanical Process And Precipitation On Mechanical Properties Of Microalloyed Steels

Abstract:

The aim of this research work is to study the effect of thermomechanical process on microstructure and properties of structural microalloyed steels, as well as to study of precipitation of carbonitrides because is an important phenomenon influencing the microstructure of microalloyed steels and their corresponding mechanical properties. This is very important for the thermomechanical treatment to be applied to achieved the desired mechanical strength.Processing parameters are considered such as finishing rolling temperature, rolling reduction, cooling rate and their effect on microstructure and mechanical properties of experimental microalloyed steels has been studied by tensile and charpy impact test and optical microscopy. Microalloyed steel with was produced by casting in an electrical induction oven of 25 Kg. capacity. Carbon content in steel was less than 0.1 %. Steel was processed thermomechanically; reheated to 1250 °C and hot rolled on a laboratory mill to a 13.0 mm thick plate with a finish rolling temperature of 950ºC and a thickness reduction of 80%. It has been found that tensile and impact properties of microalloyed steels are improved by controlled rolling. The cause of such improvement in mechanical properties of steel is correlated with changes in microstructure, i.e. ferrite grain refinement. Furthermore low carbon content in steel cause improvement in toughness and weldability. This work shows what precipitates are present in steel, the type of precipitates and their morphology. Particles of precipitates of NbC were found by transmission electron microscopy.

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