Samples of ductile cast irons alloyed with Cu, Cu-Ni and Cu-Ni-Mo were austempered, borided and boro-austempered and characterized for hardness and micro-adhesive wear behavior. The kinetics of layer formation was also studied. The boriding method used was molten borax bath, in periods of 2 and 4 hours at temperatures of 850, 900 and 950 ºC. The direct austempering treatment was performed immediately following the boriding treatment (from 850, 900 and 950 ºC) using molten salt baths at temperatures of 240, 300 and 360 ºC for 4 hours (boro-austempering treatment). For comparative purposes, the conventional austempering treatment was also conducted. Optical microscopy, scanning electron microscopy, Brinell hardness measurements (on the substrate) and Vickers (on the layers) were performed, along with micro-adhesive wear tests. The boriding treatment resulted in the formation of high hardness layers, in the range of 1450 to 1750 HV, with high wear resistance. The wear resistance of borided and boro-austempered samples were increased by 40 times when compared to as cast or austempered samples, indicating the high efficiency of this type of treatment in increasing the wear resistance of this material.

Os aços inoxidáveis endurecíveis por precipitação foram desenvolvidos a partir de 1945, em decorrência das necessidades da indústria aeroespacial em termos da disponibilidade de aços com resistência mecânica e à corrosão, em temperaturas mais elevadas, superiores às dos aços inoxidáveis tradicionais, aliadas à facilidade de soldagem. Esses aços apresentam microestruturas martensíticas do tipo substitucional, endurecidas posteriormente por precipitados. Nesse trabalho, foram produzidos dois aços com composições alternativas usando o Nb como formador de precipitados, bem como um aço PH13-8Mo para efeito de comparação, em termos de resistências mecânica e à corrosão. O Aço 1 apresentou resistência à corrosão semelhante à do aço PH13-8Mo e o Aço 2 apresentou resistência mecânica próxima à do aço PH13-8Mo.

Precipitate-hardened stainless steel was developed in 1945 as a consequence of the aerospace industry’s need for a high-strength steel that would be resistant to corrosion at high temperatures, and easily welded exceeding the properties of conventional stainless steel. This steel possesses substitutional martensitic microstructures that can afterwards be hardened by precipitation. For this research, two types of steel with alternative compositions were produced by using Nb as a precipitate producer, and PH13-8Mo steel for comparison purposes in terms of mechanical and corrosive resistance. Steel 1 showed corrosive resistance similar to PH13-8Mo and Steel 2 presented mechanical resistance close to that of PH13-8Mo.

A dureza e, conseqüentemente, a resistência ao desgaste dos aços inoxidáveis austeníticos podem ser acentuadamente aumentadas, sem perdas na resistência à corrosão, com a produção de camadas superficiais pelo tratamento de nitrocementação por plasma. Nesse trabalho, foram nitrocementadas por plasma, na temperatura de 450°C, amostras do aço AISI 316L. As camadas obtidas foram caracterizadas por meio de ensaios micrográficos, de microdureza e de microdesgaste. A camada produzida constituiu-se de duas regiões, sendo a mais externa constituída de nitrocarbonetos de cromo e, abaixo dela, verificou-se a presença de austenita expandida, rica em nitrogênio, com dureza próxima a 850HV. A espessura média total da camada foi de, aproximadamente, 40µm. Sua resistência ao desgaste foi muito superior à do substrato.

Hardness and consequently wear resistance of austenitic stainless steel can be highly increased, without losing corrosion resistance, by plasma nitrocarburizing surface treatment. In this re-search, an AISI 316L stainless steel was plasma nitrocarburized at 450°C, and the obtained layers were characterized by optical microscopy, microhardness and micro-wear tests. It was verified that the layer is composed of chromium nitrides precipitates and beneath them, a nitrogen rich expanded austenite, with hardness around 850HV. The total average thickness of the layer was about 40µm and presented good uniformity. The wear resistance of the layer was much higher than that of the substrate.