Avaliação da influência da viscosidade de óleos minerais e sintéticos como meio de têmpera na microestrutura do aço SAE 1045

Abstract

With the constant search for improvement of metallurgical materials, especially at surface engineering, the study of ways to change the carbon steel alloys mechanical properties, for applications submitted of wear, have received great attention. In this scenario, there are several ways of improving wear resistance added to tenacity in components for industrial application. Tempering, a heat treatment by abrupt cooling from the austenitic temperature, is a low-cost and quite versatile tool, so that for each cooling environment used, a different microstructural result can be obtained. When it comes to oil quenching, a fluid property that has great influence on the steel metallographic transformation is viscosity, which enables a range of commercial oils possibilities, in addition to competitive prices. The present work is an investigation of the influence of this property on the microstructural transformation and hardening of SAE 1045 steel, as well as a verification of how the formation of vapor films can affect the hardening process during cooling. For this purpose, experimental procedures were used to obtain the viscosity of the oils, microstructure observation and acquisition of Vickers microhardness. The results showed that, for all oils, the hardening of the surface was higher than in the core. It was also found that there was no great variation of Vickers microhardness from one sample to another, as well as the microstructural composition, indicating that the viscosity interferes more intensely when there is a big difference of this magnitude from one oil to another. Finally, the presence of vapor film during tempering caused Vickers microhardness variation along the defined profile (nucleus - surface) and more intense bainitic transformation than martensitic ones.