High-Temperature Wear Behavior of 42CrMo Continuous Casting Roll Overlay Hardfacing Layer

Literature Overview

This study by Cheng Jianguo and colleagues from Baowu Heavy Industry Co., Ltd. investigates the high-temperature wear characteristics of a 414N hardfacing alloy deposited on 42CrMo continuous casting rolls at temperatures of 400°C, 500°C, and 600°C. The research was supported by the Anhui Provincial Key Research and Development Program (1804a09020067) and published in the journal Materials Protection (Vol. 54, No. 7, 2021, pp. 37-43). The work is particularly relevant to engineers working in continuous casting technology, where roll surface integrity directly affects product quality and equipment availability.

Core Technical Findings

The study employed a high-temperature wear testing machine to evaluate wear performance, supplemented by SEM/EDX and XRD characterization to understand the mechanisms governing wear behavior at elevated temperatures. The key quantitative results demonstrate a dramatic deterioration in wear resistance as temperature increases beyond 400°C.

At 400°C, the 414N hardfacing layer exhibits a relatively balanced combination of wear mechanisms, with oxidative wear and debris wear being the primary contributors, accompanied by a small amount of oxide spalling. However, when the temperature rises to 500°C and 600°C, the mechanism shifts decisively toward oxidative wear and oxide spalling, indicating that the protective oxide layer becomes increasingly unstable and mechanically weak at higher temperatures.

Analysis of Oxide Layer Phase Composition

A critical finding from this study concerns the phase composition of the oxide scale formed on the hardfacing surface during high-temperature wear. The oxide layers at all three temperatures consist of three phases: α'-Fe, cubic-structured (Fe,Cr)₂O₃, and hexagonal-structured (Fe,Cr)₂O₃. This triphasic oxide composition is consistent with the Cr-bearing steel hardfacing alloy system, where chromium plays a dual role in both hardening the matrix and modifying the oxidation behavior.

The most significant observation is what happens at temperatures at or above 500°C: the bright white oxides in the wear tracks are substantially reduced, and the chromium content in the dark-colored oxides decreases markedly. This indicates that at elevated temperatures, chromium is preferentially depleted from the oxide scale, leaving behind a more iron-rich, less protective oxide layer. The loss of chromium from the oxide scale is a critical degradation mechanism, as chromium oxide phases (particularly Cr₂O₃) are known for their superior adherence, lower diffusion coefficients, and protective qualities compared to iron oxide phases.

Engineering Practice Integration

From an engineering perspective, this research has direct implications for the design and operation of continuous casting rolls in steel production. The 42CrMo substrate is a standard quenched-and-tempered alloy steel used for casting rolls due to its good toughness and fatigue resistance. The 414N hardfacing alloy provides the necessary surface hardness and wear resistance for contact with hot billets.

The practical takeaway is clear: the 414N overlay performs acceptably at temperatures up to approximately 400°C, but its wear life degrades significantly at higher temperatures. For applications where roll surface temperatures may reach 500°C or above—such as in certain hot rolling finishing mill configurations or specific casting configurations—alternative hardfacing alloys with higher chromium content or different carbide-forming elements should be considered. This finding reinforces the principle that hardfacing alloy selection must be based not only on room-temperature hardness but also on high-temperature oxidation resistance and oxide scale stability.

Key Questions and Reflections

Several important questions arise from this study that merit further investigation:

• What is the precise temperature threshold at which chromium depletion in the oxide scale begins to accelerate? The transition between 400°C and 500°C appears to be critical, but a more granular temperature study (e.g., at 450°C) could clarify the onset mechanism.
• Could the addition of other alloying elements (such as aluminum, titanium, or silicon) to the hardfacing alloy improve high-temperature oxidation resistance and extend the effective service temperature range?
• How does the wear rate correlate with actual field service life in continuous casting operations? Laboratory wear tests, while valuable for comparative purposes, may not fully replicate the complex thermal and mechanical loading conditions encountered in production.

The study effectively demonstrates that the phase composition and chromium content of the oxide scale are the dominant factors determining the wear mechanism and wear rate of the hardfacing layer at elevated temperatures. This insight is valuable for engineers seeking to optimize hardfacing alloy selections for high-temperature applications.

Summary and Implications

This research provides essential quantitative data on the temperature-dependent wear behavior of 414N hardfacing alloys on 42CrMo continuous casting rolls. The finding that wear depth increases by a factor of 2.1 to 2.5 between 400°C and 500-600°C, coupled with the mechanistic explanation involving chromium depletion from the oxide scale, offers engineers a clear decision framework for hardfacing alloy selection in high-temperature rolling and casting applications. The study underscores the importance of considering not just the base alloy properties but also the dynamic behavior of oxide scales under thermal cycling and mechanical loading conditions.