# The effect of QPQ treatment on the wear and corrosion resistance of 42CrMo bearing steel

## TL;DR

This study examines how QPQ treatment affects the wear and corrosion resistance of 42CrMo bearing steel by analyzing microstructural changes and performance under different treatment conditions.

## Contribution

The study reveals the optimal QPQ treatment parameters for enhancing wear and corrosion resistance in 42CrMo steel while highlighting the negative effects of excessive treatment.

## Key findings

- QPQ treatment at 620 °C for 120 min produced the thickest compound layer and highest surface hardness.
- The 620 °C × 90 min sample showed the lowest friction coefficient and wear loss.
- Prolonged treatment at 620 °C caused spallation, embrittlement, and porosity, reducing performance.

## Abstract

This study investigates the impact of QPQ (Quench–Polish–Quench) treatment parameters—580 °C and 620 °C, with holding times of 90 min and 120 min—on the microstructure, wear resistance, and corrosion resistance of 42CrMo bearing steel. Microstructural evolution was analyzed by OM, SEM, and XRD, while hardness, friction-wear, and electrochemical tests assessed performance. QPQ treatment produced a three-layer surface structure comprising an oxide film, a compound layer rich in Fe₂₋₃N and Cr₂N, and a diffusion layer. At 620 °C for 120 min, the compound layer reached a thickness of 24.01 μm, with a diffusion depth of 377 μm, and the surface hardness increased to 710.9 HV0.2. The lowest friction coefficient (0.33) and wear loss were observed for the 620 °C × 90 min sample, whereas the highest corrosion resistance occurred for the 580 °C × 120 min sample (Ecorr = − 0.476 V, log10(Icorr) = − 6.242, Rp = 2643 Ω). Temperature exerted a more substantial influence on layer growth and nitrogen diffusion than holding time. However, prolonged treatment at 620 °C resulted in spallation, embrittlement, and porosity, thereby degrading the wear and corrosion performance.