Super duplex stainless steels (SDSS) have high corrosion resistance because of their high contents of chromium, nickel, molybdenum and nitrogen but low wear resistance. To improve the wear resistance of these steels without affecting their corrosion resistance, samples of SDSS were treated by plasma ion nitriding at temperatures ranging from 350 °C to 570 °C for two hours. This thermochemical treatment resulted in the formation of different types of nitrides that affected the microhardness, the microwear behaviour and the corrosion resistance of the metal surface. The microwear resistance decreased at 400 °C because different nitrides formed on the surface, thereby increasing the hardness and volume wear resistance of the steel. The test results showed that the alloys that were nitrided at 400 °C and 450 °C exhibited the highest corrosion resistance to a solution medium containing chloride ions.

O objetivo deste trabalho é a construção de um dispositivo para a realização de ensaios de micro desgaste abrasivo por esfera fixa. O contato abrasivo é realizado por uma esfera de aço AISI 52100, a qual é presa num eixo que gira com grande precisão, com ajuda de um motor, em relação a uma amostra plana que se manterá estacionária. A carga normal de ensaio é aplicada através de ajustes de peso no suporte pivotado do corpo de prova, a qual pode ser variada a cada ensaio realizado. Este dispositivo foi utilizado para a determinação da resistência ao desgaste abrasivo e da eficácia de tratamentos de superfície utilizados em peças que sofrem este tipo de solicitação em serviço, além de utilizá-lo para estudar novos produtos desenvolvidos para o aumento de resistência ao desgaste de superfícies. Foi avaliada a resistência ao microdesgaste abrasivo de aço AISI 420 temperado e revenido. Observou-se que o aumento da dureza do material tratado aumentou a resistência ao desgaste abrasivo quando comparado com o material sem tratamento térmico.Palavras-chave: desgaste microabrasivo, esfera fixa, aço AISI 420, configuração experimental. ABSTRACTThe abrasive microwear testing has been the subject of a significant amount of research in recent years, when its potential to evaluate the behaviour of thin coating became relevant. The aim of this work is to build a apparatus for abrasive microwear testing by rotating sphere. The abrasive contact is performed by a AISI 52100 steel ball which rotates, with great accuracy with the help of an electric motor, in relation to a flat sample that will remain stationary. The normal load is applied by weight adjustments in the support of the test specimen, which can be varied for each performed test. This device was used to determine the abrasive wear resistance and effectiveness of surface treatments used in parts that undergo this kind of requirement in service, and also for studying new products developed for increasing the wear resistance of surfaces. The microwear resistance of the quenched and tempered AISI 420 steel was evaluated. It was observed that increasing the hardness of the treated material produced an increased wear resistance when compared with untreated material Keywords: microabrasive wear, rotating sphere, stainless steel AISI 420, experimental setup. INTRODUÇÃOA palavra tribologia, derivada do grego, significa estudo do atrito, sendo a ciência e tecnologia que estuda a Matéria, v.20, n.2, pp. 304 -315, 2015.

In an attempt to improve a surface of super-duplex stainless steel was carried out ion plasma nitriding. The super-duplex stainless steel was nitriding by plasma process during 2 hours at the 350 -570 o C. As can be seen, the thermochemical treatment influenced the microhardness superficial due to kind of nitride formed. The microwear resistance decreased at 400 o C due to formation different nitrides in surface, causing an increase in hardness and wear volume resistance.

The P20 steel, mainly used in plastic molds, was thermochemical treated by ion plasma nitriding, solid and gas carburization.In this work, the solid and gas carburization were carried out at 925ºC in four different times. The ion plasma nitriding was performed at 520ºC in three different times. It was observed that the thermochemical treatment increases the microwear resistance of the studied material. The gas carburizing treatment produced a bigger surface microhardness. Longer times of treatment increase effectiveness of thickness layer in all cases. The solid carburization produced larger thickness layer than gas carburization and ion nitriding.