Microstructure and Properties of Two Medium Chromium Cladding Alloys

Literature Overview

This study by Lei Sheng and colleagues from Anhui Jianzhu University, published in Hot Working Technology in 2019, investigates the optimization of the XU524-A type welding wire composition to develop a novel Fe-Cr-C cladding alloy wire for improved high-temperature wear resistance in rolling mill roll applications. The research employed automatic submerged arc welding (SAW) for cladding trials and conducted comprehensive microstructural, hardness, and wear resistance testing.

Core Technical Findings

The authors optimized the composition of the XU524-A welding wire by adjusting the Fe-Cr-C system to create a new cladding alloy wire. Cladding trials were performed on the surface layer of rolling mill rolls using an automatic submerged arc welder. The resulting cladding layers from both the original XU524-A wire and the optimized wire were examined through metallographic analysis, microhardness testing, and high-temperature wear resistance evaluation.

The study found that both cladding alloy wires produced cladding layers with good fusion to the base material and no defects. The new wire produced a cladding layer with higher microhardness than the XU524-A wire. Notably, the surface hardness of the cladding layer reached its peak at a tempering temperature of 400 degrees Celsius. The wear resistance of the new wire's cladding alloy exceeded that of the standard XU524-A wire.

Metallurgical Analysis

The improvement in microhardness and wear resistance can be attributed to the optimized carbon and chromium content in the new wire composition. In Fe-Cr-C systems, the formation of chromium carbides (such as M7C3 and M23C6) provides significant hardening and wear resistance. The peak hardness at 400 degrees Celsius suggests that tempering at this temperature optimally balances the precipitation of fine carbides against the softening effects of higher-temperature tempering.

Engineering Practice Considerations

For rolling mill roll repair operations, the selection of cladding wire is critical to achieving extended service life between regrinding cycles. The study's findings have direct practical implications:

1. The optimized wire offers enhanced wear resistance, potentially extending roll service intervals and reducing downtime.
2. The 400-degree-Celsius tempering peak provides a clear post-weld heat treatment target for maximizing hardness in service.
3. The good fusion and absence of defects in both wires confirm that the SAW cladding process is reliable for roll repair applications.

Engineers should note that the wear resistance improvement, while confirmed in laboratory testing, must be validated under actual rolling mill operating conditions. Factors such as rolling temperature, material being rolled, and rolling speed all influence the actual wear behavior of the cladding layer in service.

Study Insights and Reflections

The optimization of Fe-Cr-C cladding alloys remains a challenging task due to the complex interplay between carbon content, chromium content, cooling rate, and resulting microstructure. The study demonstrates a systematic approach to wire composition optimization, which is valuable for engineers developing proprietary cladding materials. The finding that peak hardness occurs at 400 degrees Celsius during tempering is particularly useful for post-weld heat treatment planning.

One limitation of the study is the absence of quantitative wear resistance data and the specific compositions of the two wires. For engineers seeking to replicate or adapt these results, additional information on the exact chemical composition and the wear testing methodology would be essential. Nevertheless, the research provides a solid foundation for further development of medium chromium cladding alloys for industrial roll applications.