Desarrollo de recubrimientos nano-estructurados a base de sales fundidas para aplicaciones en componentes y piezas industriales de alto rendimiento

Abstract

Tool, machinery and structural steels are the type of Fe-C alloy, which is the material most used in the manufacture of tools, machine parts and equipment for the construction, in addition to work elements that allow various industrial activities in which high-strength and durability is required due to the corrosion and wear effects. In this sense, there are common steels that are useful for different manufacturing applications to improve their working efficiency and lifetime through the study of the mechanical behavior when they are subjected to a heat treatment and thermochemical process to be viable operationally and they can meet the requirements of the engineering industry. For this reason, the need to improve the materials used daily in the engineering industry, construction, agriculture, chemical, food, among others, so in this research three types of AISI carbon steels (D2, cold work tooling, H13, hot work tooling and 1045 structural materials) were subjected to a heat treatment followed by a thermochemical nitriding process using two different salt mixtures: NaCNO + Na2CO3 or NaNO3 + KNO3 in order to improve their wear resistance and corrosion protection. Additionally, two heat treatments such as quenching and tempering were combined for a better performance. Furthermore, the nitriding times used in this research varied from 60-120 min in terms of two temperatures 600 and 650 °C. The nitrided products were structurally characterized by using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), while the nitride hardness surface was determined by Vicker test (Hv). Additionally, the evaluation of corrosion resistance was performed by electrochemical techniques; anodic polarization-DC current and electrochemical impedance spectroscopy, EIS, AC current. The results indicate that the application of a suitable thermochemical treatment for a tool and structural steels can significantly increase the lifetime of the steel-materials. The best nitriding time was found to be 120 min, in which different thicknesses of the nitrided layer was obtained: 52 m in D2 steel, 44 m for H13 steel and 21 m in 1045 steel. The X-ray analysis of the nitrided products showed that it is possible to produce hard compounds on the surface of nitrided steels. Furthermore, the SEM images showed that some steel samples are composed by two layers, an oxide layer followed by a nitride coating. In some cases the results of the analysis, showed that the nitrided layer is not observed on steels, an oxide compounds of hematite, magnetite and cohenite were formed at high temperatures. Finally, the corrosion tests indicated that the nitriding layer is useful to decrease the corrosion rate providing corrosion resistance of the industrial steels.