چكيده به لاتين
The automotive industry has shown significant growth in recent decades, involving many branches of engineering, including metallurgy, in the problems and issues observed in the industry. One of the major challenges in the automotive industry that has always been studied and researched is to increase occupant safety and at the same time reduce vehicle fuel consumption, which is largely related to the body material of the vehicle. Therefore, achieving both components simultaneously in designing of car body has become very important in recent years. To achieve the mentioned objectives in this study, the effect of quench and partitioning (Q&P) heat treatment process parameters on the microstructure and tensile properties of a δ-TRIP steel from the Fe-Al-Mn-C medium carbon steel family with a chemical composition of Fe-4.84Al-1.09Mn-0.47C-0.36Si has been investigated under variable conditions. The prototypes used in this research are in the form of hot rolled cast that are austenitized at two temperatures of 850 and 900 ° C for 1200 seconds during four different heat treatment paths and then partially quenched at 150 ° C in oil bath for 20 seconds and finally partitioned at 350 and 430 ° C, which are above the Ms temperature of this alloy, for 100, 500, 1000, 1600 and 2000 seconds. Microstructure of samples was investigated by (OM), (SEM), and (EBSD). These studies showed that the microstructure of these samples contained delta ferrite phase, martensite, and austenite. The fuzzy fraction of retained austenite and the amount of carbon in austenite were calculated using the X-ray diffraction pattern (XRD). Also, the tensile and hardness tests were applied to obtain the optimal conditions of tensile properties. And then, yield strength, final strength, percentage of total elongation, toughness, and hardness of the samples were calculated. The results of the tensile test shows that increasing partitioning time and temperature and austenitization temperature causes more carbon to escape from the martensite and infiltrate into the retained austenite and increase the austenite stability. In addition, it was found that after various heat treatments, a relatively large increase in the percentage of elongation occurs, which leads to an increase in toughness. Comparison of the data obtained from samples with the prototype shows that the strength and elongation percentage have increased in a way that in some heat treatment paths strength increases about 27% and in some other samples elongation increases about 100% compared to the prototype. Also, in some samples that have the optimal level of strength and ductility, the increase in strength is about 7-11% and the increase in elongation is about 70-85% compared to the prototype. All these data indicate an increase in the toughness and safety factor of this alloy for use in the automotive body.
