Eventos Anais de eventos
COBEM 2017
24th ABCM International Congress of Mechanical Engineering
Effects of prior heat treatment on AISI 420 steel low-temperature plasma nitrocarburizing
Submission Author:
Cristiano Scheuer , RS
Co-Authors:
Adriano David dos Anjos, Rodrigo Perito Cardoso, Silvio Francisco Brunatto, Cristiano Scheuer
Presenter: Cristiano Scheuer
doi://10.26678/ABCM.COBEM2017.COB17-0342
Abstract
Plasma surface thermochemical treatments have been applied to a large extent on tools and industrial components to improve their surface properties. Several methods for plasma diffusion process, such nitriding, carburizing, nitrocarburizing, etc., have been developed as primary surface hardening process. Nitrocarburizing is one of the most applied methods for improving performance engineering materials. It involves the nitrogen and carbon introduction into the component surface, to produce a compound layer with mixed -Fe2-3(N,C) phases and a interstitial solid solution of nitrogen and carbon. Such nitrocarburized generated phases are known to be valuable to the tribological properties due to the inherently high internal stresses arising in the lattice parameter. However, on stainless steels treatment, chromium carbides/nitrides precipitation can occur when treatments were carried out at high temperature or for excessive time, resulting in a depletion of stainless steel corrosion resistance. For martensitic stainless steels, special attention should be credited on choice of heat pretreatment conditions, once materials microstructure and defect density, resulting of heat treatment, affect the carbon/nitrogen diffusion and carbide/nitride precipitation kinetics. Thus, this research aims to investigate the effect of heat pretreatment in growth kinetics and mechanical properties of nitrocarburized layer produced on AISI 420 steel. Thereunto, plasma nitrocarburizing treatments were carried out using DC-pulsed power supply in a 71% N2 + 18% H2 + 10% Ar + 1% CH4 gas mixture, at temperatures of 300 to 450 °C, and times of 2 to 12 h for annealed, as-quenched and tempered AISI 420 steel. The applied peak voltage, gas flow rate and pressure were kept constant at 600 V, 3.32 × 10−6 Nm3 s−1 and 400 Pa, respectively. The treated samples were characterized by optical microscopy, X-ray diffractometry and microhardness measurements. Results demonstrate that the nitrocarburized layer growth kinetics depends on the samples prior heat treatment. Plotting layer thickness data on an Arrhenius plot, two slopes can be observed, indicating different activation energies for high and low temperatures treatments. Finality, XRD data show that chromium nitride/carbide precipitation occurs for temperatures above 400 °C, as illustrated by the micrographs.
Keywords
martensitic stainless steel, low temperature plasma nitrocarburizing, expanded martensite, prior heat treatment, process kinetics.
