Tecnologia em Metalurgia, Materiais e Mineração
https://tecnologiammm.com.br/article/doi/10.4322/2176-1523.0844
Tecnologia em Metalurgia, Materiais e Mineração
Artigo Original

MECANISMOS DE NITRETAÇÃO SOB PLASMA DO AÇO INOXIDÁVEL MARTENSÍTICO AISI 420 NITRETADO A ALTA E BAIXA TEMPERATURA

ON THE MECHANISMS OF PLASMA NITRIDING OF MARTENSITIC STAINLESS STEEL AISI 420 AT LOW AND HIGH TEMPERATURE

Pinedo, Carlos Eduardo; Magnabosco, Rodrigo

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Resumo

Este trabalho apresenta o mecanismo de formação da camada nitretada sob plasma em baixa e alta temperatura para o aço inoxidável martensítico AISI 420, suas características morfológicas, cinéticas e de endurecimento. Na nitretação sob plasma a alta temperatura (HTPN) a termodinâmica desempenha o papel mais importante no mecanismo de nitretação e, neste caso, a elevada interação entre Cr-N controla o crescimento caracterizado pela intensa precipitação de nitretos de cromo na zona de difusão. No entanto, na nitretação sob plasma a baixa temperatura (LTPN) a restrição cinética supera as necessidades termodinâmicas e o mecanismo de formação da camada nitretada é alterado, suprimindo a precipitação de nitretos de cromo e formando martensita revenida expandida (α’N) com a precipitação simultânea de nitretos de ferro. Os diferentes mecanismos operantes a alta e a baixa temperatura também modificam a capacidade e as características de endurecimento superficial, bem como a resistência à corrosão e a dureza original do substrato.

Palavras-chave

Nitretação sob plasma, Aço inoxidável martensítico, Martensita expandida, Endurecimento.

Abstract

In the present work a discussion on the nitriding mechanism as a function of temperature, as a balance between thermodynamic and kinetics aspects is presented. After High Temperature Plasma Nitriding (HTPN) thermodynamics plays the most important role on nitriding mechanism and high interaction characteristic between Cr-N controls the case growth with intensive chromium nitrides precipitation. However, at Low Temperature Plasma Nitriding (LTPN) kinetics restriction overcomes thermodynamics needs and the nitrided case mechanism is changed, no chromium nitrides precipitation occurs and the nitrided case growths with expanded tempered martensite (α’N) formation and iron nitrides precipitation. These different nitriding mechanisms operating at low and high temperature modify the hardening effect, the corrosion resistance and the core hardness.

Keywords

Plasma nitriding, Martensitic stainless steel, Expanded martensite, Hardening.

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