Microstructure Evolution at Different Cooling Rates of Low Carbon Microalloyed Steels

Abstract

Abstract:In low carbon microalloyed steels (C  0.1%), the content of V, Nb and Ti affects the phases transformation kinetic during cooling in the rolling process. The final microstructure determines the required mechanical properties such as high formability, high toughness and adequate strength. For this reason it is relevant to identify and determine the volume fraction of the ferrite, bainite and martensite present in the structure. The microalloying elements: V, Nb and Ti promote carbides precipitation during cooling. The precipitates control the grain size refinement during hot rolling process and the mechanical properties of the steel. In this sense it is necessary to increase the knowledge on the microstructure evolution at different cooling rates. In this paper, the results obtained on two low carbon microalloyed steels (with C contents between 0.11%-0.06%) are reported. An integrated methodology including dilatometry in combination with microscopy techniques was applied. By EBSD (Electron Backscatter Diffraction) technique and microhardness measurements, the structural study was completed. Through a thermodynamic simulation using Fact Sage the type of precipitates in the studied steels structure at the temperature range between 950 °C and 450 °C, were predicted. The information on the evolution of the steel structure at rolling process conditions is relevant to consider changes in processing conditions.

Characterization of hot forged P285NH steel by metallurgical investigation and reliability analysis

“…The requirements about mechanical properties are focused in high strength combined with high toughness or high formability. These mechanical properties are achieved through an appropriate processing and a precise ratio of specific phases [2]. For this reason it is relevant to increase the knowledge about γ !…”

“…The steel behavior strongly depends on the proportion and distribution of phases [3]. Other microstructural aspects like the grain size refinement, dislocations or precipitations produce increments in strength and toughness [2,3]. The austenite grain size and cooling rate play a major role in determining the transformation kinetics and resulting microstructure.…”

Estudio del Comportamiento Termomecánico de Aceros Especiales Sometidos a Velocidades de Enfriamiento Elevadas para Lograr Ultra Alta Resistencia

“…Asimismo, se puede obtener una estrucutura de grano ultrafino, que será de gran utilidad en cuestiones de seguridad, ya que el sistema podrá absorber una elevada energía de impacto ante un eventual accidente de tránsito (Weng, 2009). La distribución y el porcentaje de fases presentes, así como su naturaleza cristalográfica, son también parámetros fundamentales que juegan un rol importante sobre las propiedades del acero (Brandaleze et. al, 2017).…”