Effect of post-oxidation times in the nitrocarburizing process on the wear behavior of an AISI 4140 steel

Taşkoparan Yılmaz Ü., Erkan A., Akar N., Kilicli V.

MATERIALPRUEFUNG/MATERIALS TESTING, vol.00, no.00, 2024 (SCI-Expanded)

  • Publication Type: Article / Article
  • Volume: 00 Issue: 00
  • Publication Date: 2024
  • Doi Number: 10.1515/mt-2024-0062
  • Journal Name: MATERIALPRUEFUNG/MATERIALS TESTING
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Compendex
  • Ankara Haci Bayram Veli University Affiliated: Yes

Abstract

Abstract This study investigates the influence of post-oxidation duration on the wear performance and microstructural features of AISI 4140 steel subjected to nitrocarburizing followed by post-oxidation. For this aim, the quenched and tempered AISI 4140 samples were nitrocarburized (NC) and post-oxidized (PO) at various times (45–180 min) under low vacuum. Microstructural features were investigated using optical microscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectrum analysis (EDS), X-ray diffraction (XRD) analysis, and microhardness test. Wear behavior was evaluated using a ball-on-disk tribometer. Experimental results showed that the structures consisting of nitride layer (ε-Fe2–3N) and γ′-Fe4N + iron oxide (Fe3O4) were obtained at the top surfaces of the samples. Increasing post-oxidation times resulted in a notable enhancement in the thickness of the Fe3O4 layer. The growing Fe3O4 layer has induced the closing of micro porosities for further post-oxidizing times, leading to decreased surface roughness of the samples. It was determined that the post-oxidation times have no significant effect on the hardness profiles of NC + PO samples. The highest (0.375) and lowest (0.276) mean coefficient of friction was obtained in the post-oxidation times of 150 and 180 min, respectively. The best wear rate was obtained in the post-oxidized sample for 150 min.