Abstract AISI D6 tool steel and AISI 304 stainless steel are among the most widely used material in the industry. However, this application field can still be expanded through the coatings deposition. In this regard, the objective of this work was to evaluate the impact of coatings application by cathodic cage technique using Hastelloy’s cathodic cage, on corrosion resistance of these steels. Two treatment temperatures were compared. The samples were characterized by Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-Ray Diffraction with the application of the Rietveld routine and corrosion test. The results showed the formation of multiphase layers that contributed to corrosion potentials reduction for treatments at 400 °C, being more effective when applied on AISI D6. It was observed that the corrosion resistance is influenced by the temperature, which was attributed to the precipitation of chromium nitride and iron oxide at 450 ºC.

RESUMO A necessidade cada vez maior de transportar grandes quantidades de petróleo e gás em ambientes agressivos fez surgir uma demanda por aços de alta resistência e baixa liga (ARBL) de classificação API (American Petroleum Institute). O principal método de falha é, sem dúvida, as trincas induzidas por hidrogênio (TIH), dessa forma há uma necessidade de buscar alternativas metalúrgicas para diminuir a susceptibilidade desses materiais a esse fenômeno e algumas dessas soluções é a laminação a morno e nitretação a plasma. O presente estudo tem como objetivo avaliar a influência da laminação a morno na microestrutura e formação da camada nitretada em aço API 5L X70, para isso, amostras do aço em questão foram submetidas a laminação a morno com 49,4 % de redução com temperatura inicial de 863 °C e final de 689 °C, posteriormente, foi realizado nitretação a plasma convencional e com auxílio de gaiola catódica usando como parâmetros: 450 °C, com fluxo de gás 75 % H2 - 25 % N2 e 25 % H2 - 75 % N2, pressão 2,5 Torr. Para a caracterização, foram realizados microscopia ótica, ensaio de microdureza Vickers e difração de raios-X. Os resultados obtidos mostram que a microestrutura apresentou um menor bandeamento, em relação à microestrutura do material como recebido, através de uma maior distribuição de perlita causada pela laminação a morno. A nitretação formou uma fina camada de compostos de dureza superficial de até 670,0 HV (HV 0.05) formadas por nitretos do tipo ε (Fe3N) e γ’ (Fe4N). Estas características são importantes no combate às trincas induzidas por hidrogênio, e sugerem que a combinação dessas duas técnicas pode ser promissora.

ABSTRACT The increasing need to transport large quantities of oil and gas in aggressive environments has led to a demand for high strength and low alloy steels (HSLA) of API (American Petroleum Institute) grade. No doubt, the main failure method of these steels is hydrogen-induced cracking (HIC), so there is a need to look for metallurgical alternatives to reduce the susceptibility of these materials to this phenomenon and some of these solutions is the warm rolling and plasma nitriding. The present study aims on evaluating the influence of the warm rolling on the microstructure and formation of the nitrided layer in API 5L X70 steel. For this, samples of the steel in question were submitted to controlled warm rolling with 49.4% reduction with initial temperature 863 °C and final temperature 689 °C, posteriorly, conventional plasma nitriding and using cathodic cage in parameters were performed: 450 °C, with a gas flow of 75% H2 - 25% N2 and 25% H2 - 75% N2, pressure 2.5 Torr. For the characterization, optical microscopy, Vickers microhardness test and X-ray diffraction were performed. The obtained results show that the microstructure presented a lower banding, in relation of the material as received, through a higher distribution of perlite caused by the warm rolling. The nitriding formed a thin layer of compounds of superficial hardness of up to 670.0 HV (HV 0.05) formed by nitrides of type (Fe3N) and γ '(Fe4N). These characteristics are important in the fight against hydrogen-induced cracking, and suggest that the combination of these two techniques may be promising.