Microstructural characterization of a maraging steel submitted for surface treatment of plasma nitriding

Abstract

The naval weapon systems, land, and air are produced by industries using knowledge, technologies, and materials available to the producing countries. Calls sensitive technologies are those that, if used by states for military purposes, can generate a significant imbalance in the use of force in conflicts. For this reason, these technologies since their earliest stages of maturity, national states suffer some kind of protection. The ultra-high-strength steels, such as maraging steel, fall into this class of materials; it is therefore of fundamental importance to the field of production and manufacturing processes involved with this type of steel. A major impact of developments in the 1960s was that of maraging steel (martensite aging). Martensitic steels are low-carbon, high-alloy, in which high mechanical strength is achieved by aging in the martensitic state and not, as in conventional steels. Unlike many high-strength steels, maraging steels have a little dimensional distortion in heat treatment, good weldability, and a good combination of strength and toughness, which facilitates its use. Maraging steels are alloys Ni-Co-Mo-Ti ultra-high-strength and wide application ranging from nuclear arms industry and to aircraft components, pressure vessels, and the sports industry. Maraging steels are of fundamental interest in nuclear and aerospace industries due to their high mechanical strength combined with excellent toughness, highly desirable features especially for weight reduction, and increased safety. In addition, maraging steels have good weldability fundamental property in the production of components. These steels have been proposed to replace the stainless steel 300M or 4340 in parts of the Brazilian satellite launch vehicle (SLV). Another factor of interest is the possibility of associating good structural steels with these processes for surface treatment, providing diverse characteristics: corrosion protection, increased surface hardness, and wear resistance as well as improved fatigue properties. Thermochemical processes such as plasma nitriding have proven effective for these purposes. However, these treatments introduce changes in the microstructure of the steel in question, since it acts as a heat treatment cycle because of the dwell time at the temperatures used during the process. Surface treatments to conventional structures such as aircraft landing gear, for example, still need to replace an efficient technique for the treatment of hard chrome, which while improving the wear properties, considerably reduces fatigue life. This work aims to study the mechanical properties of a 300 maraging steel subjected to surface treatment by plasma nitriding. To achieve a conclusive result and be able to correlate the mechanical properties and microstructure will be performed: a) microstructural characterization by optical microscopy, scanning electron and X-ray diffraction, and b) mechanical characterization through tensile tests to evaluate the influence treatment on the mechanical strength and the ductility of the steel. (AU)