Nitriding in low carbon steels using non-toxic salt baths

Abstract

Resumo O objetivo deste artigo é desenvolver um método de nitretação em banhos de sais atóxicos, utilizando nitrato de potássio (KNO3) e nitrito de sódio (NaNO2), bem como, avaliar a dureza e o aspecto visual da camada superficial de um aço com 0,2% de carbono, vislumbrando uma alternativa que busca redução no impacto ambiental, gerado pelo processo convencional de nitretação em banho de sal, contendo cianeto e cianato. Também, estudou-se meios que reduzam os óxidos não aderentes, gerados durante o processo de nitretação. Os resultados indicam que os sais KNO3 e NaNO2 atuam na formação de uma camada nitrada, evidenciada pela mudança microestrutural e pelo aumento da dureza da camada, em relação ao material sem tratamento. Porém, dependendo das proporções entre sal atóxico e sal redutor de óxido, tem-se melhor acabamento superficial, o que contribui para o meio ambiente, pois evita a geração de resíduos na base de cianeto e cianato. Palavras-chave: Aço baixo carbono. Nitretação. Banho de sal atóxico. Abstract The objective of this article is to develop a method of nitriding in non-toxic salt baths, using potassium nitrate (KNO3) and sodium nitrite (NaNO2), as well as to evaluate the hardness and the visual aspect of the surface layer of a steel with 0.2% carbon, seeking for an alternative to reduce the environmental impact caused by the conventional process of nitriding in salt bath containing cyanide and cyanate. It was also studied some means that can reduce the non-adherent oxides generated during the nitriding process. The results indicate that the salts KNO3 and NaNO2 act in the formation of a nitrated layer, evidenced by a microstructural change and the increase of the layer hardness, in relation to the material without any treatment. However, depending on the proportions between non-toxic salt and oxide-reducing salt, there is a better surface finishing, which contributes to the environment, as it avoids the generation of cyanide and cyanate-based residues. Keywords: Low carbon steel. Nitriding. Non-toxic salt bath.

Corrosion Resistance Enhancement for Low Carbon Steel by Gas Phase Coating

“…Zn coatings have excellent resistance to corrosion and the possibility for economic competitiveness [25]- [29]. On the other hand, adding nitrogen gas to steel through the nitriding process leads to improving the surface properties, such as increasing the corrosion resistance by the formation of nitriding layers [30]- [31]. This work is aimed at protecting low carbon steel from corrosive ingredients present in the working environment and enhancing the corrosion resistance through the deposition of the layers of coating of N and Zn using the gas-phase method.…”