Corrosion Behavior of Annealed 20MnCr5 Steel

TL;DR

This study shows how different annealing treatments affect the corrosion resistance of 20MnCr5 steel in salt solutions.

Contribution

The study introduces a correlation diagram to statistically assess the interplay between microstructural features and corrosion behavior.

Findings

Corrosion resistance depends on the balance of grain size, morphology, and phase distribution.

Normalization leads to better corrosion resistance with equiaxed grains and moderate phase ratios.

Grain refinement alone does not guarantee improved corrosion performance without morphological uniformity.

Abstract

This study investigated the influence of various annealing treatments on the microstructure and corrosion behavior of 20MnCr5 steel in a 3.5% NaCl solution. A combination of microstructural analysis, hardness testing, and electrochemical techniques was used to comprehensively characterize each condition. To enhance data interpretability, a correlation analysis was performed and visualized through a correlation diagram, enabling statistical assessment of the relationships between grain features, phase distribution, mechanical properties, and corrosion indicators. The results demonstrated that corrosion resistance in 20MnCr5 steel is not governed by a single parameter but by the interplay between grain size, morphology, and phase balance. Excessive pearlite content or coarse, irregular grains were consistently associated with higher corrosion rates and lower electrochemical stability. In contrast, a moderate phase ratio and equiaxed grain structure, achieved through normalization, resulted in better corrosion resistance, confirmed by the highest polarization resistance and lowest corrosion current density values among all samples. Although increased grain refinement improved the hardness, it did not always correlate with a better corrosion performance, especially when morphological uniformity was lacking. This highlights the importance of balancing mechanical and corrosion properties through carefully controlled thermal processing.

Figures