Wear-Resistant Overlay Welding of 45Cr4NiMoV Roll Shafts Using Custom Electrodes

Literature Overview

This 2006 study by Wang Xuanguo and Wu Yongyu from Wuhan University of Technology, published in the "Journal of Wuhan University of Technology (Traffic Science and Engineering)," investigates the development and application of a custom wear-resistant overlay welding electrode for the repair of 45Cr4NiMoV steel roll shafts. The research was supported by the Hubei Provincial Natural Science Foundation (Grant 2002AB017). Roll shafts are critical components in steel rolling mills, and their surface wear directly impacts product quality and production efficiency. The ability to restore worn roll shafts through overlay welding is a cost-effective alternative to replacement, and this study addresses the consumable development and process optimization required for this application.

Core Technical Findings

Electrode Development and Microstructure

The custom-developed roll shaft overlay welding electrode produces a deposited metal microstructure consisting of a martensite matrix with a small amount of carbides. This microstructural composition is well-suited for the wear conditions experienced by roll shafts, which are subjected to a combination of:

• Sliding wear: Between the roll shaft and the bearing or guide ring.
• Impact loading: From the rolling forces transmitted through the shaft.
• Thermal cycling: From the hot rolling process environment.

The martensite matrix provides high hardness and strength, while the carbide particles contribute to wear resistance. The combination of these phases is a classic approach to achieving wear resistance in overlay weld metals.

Hardness and Wear Performance

The overlay layer achieved an average hardness of approximately HRC 52, which meets the hardness requirement of the 45Cr4NiMoV roll shaft material. More importantly, the wear resistance of the overlay layer was measured to be 127.5 times greater than that of the base 45Cr4NiMoV steel. This extraordinary improvement in wear resistance is the primary justification for the overlay welding repair approach.

Crack Prevention Through Transition Layer

A key finding of the study is that the use of a transition layer between the base material and the final overlay layer effectively prevents cracking during the overlay welding process. This is a critical process insight because 45Cr4NiMoV is a high-carbon, high-alloy steel with a high hardenability and susceptibility to cracking during welding. The transition layer serves to:

• Reduce the dilution level between the base material and the overlay metal.
• Provide a more favorable carbon equivalent for crack resistance.
• Act as a buffer against the high cooling rates that can produce brittle microstructures in the dilution zone.

Process Analysis

Overlay Welding Sequence

The overlay welding process for roll shaft repair typically follows this sequence:

1. Surface preparation: Grinding or machining to remove the worn surface and any surface contamination.
2. Preheating: Heating the roll shaft to 200–300°C to minimize cracking risk in the base material.
3. Transition layer deposition: Applying a crack-resistant transition layer using a suitable electrode.
4. Overlay layer deposition: Applying the wear-resistant overlay layer using the custom-developed electrode.
5. Post-weld heat treatment: Tempering to reduce residual stresses and optimize hardness.

Process Parameters

The process parameters for roll shaft overlay welding must be carefully controlled to achieve the desired microstructure and properties:

• Current type: DCEN (direct current electrode negative) for stable arc and deep penetration.
• Deposition rate: Moderate to ensure adequate fusion and avoid excessive dilution.
• Interpass temperature: Maintained below 200°C to prevent softening of the previously deposited layers.
• Number of passes: Typically 2–3 passes for the transition layer and 2–4 passes for the overlay layer, depending on the required overlay thickness.

Engineering Practice Integration

This study has direct relevance to several industrial applications:

• Roll shaft repair: Restoring worn roll shafts in hot rolling mills, cold rolling mills, and tube mills.
• Roll neck repair: Where the bearing journals of rolls require dimensional restoration and surface hardening.
• Roll surface repair: Where the working surface of a roll requires restoration after wear or damage.
• Other high-wear steel components: The approach can be extended to other high-carbon, high-alloy steel components that require wear-resistant overlay repair.

The 127.5-fold improvement in wear resistance is a compelling economic argument for overlay welding repair over replacement. For critical production equipment such as rolling mills, even modest improvements in component life can result in significant cost savings and reduced downtime.

Key Reflections and Insights

One of the most important insights from this study is the demonstration that a custom-developed electrode can achieve wear resistance far exceeding that of the base material. This highlights the importance of consumable selection in overlay welding applications—using a standard electrode designed for general-purpose welding would not achieve the same level of performance improvement.

The use of a transition layer to prevent cracking is a practical solution to a common problem in overlay welding of high-carbon, high-alloy steels. Engineers should adopt this approach as a standard practice when overlay welding components made of materials with high carbon equivalents or high hardenability.

The wear resistance improvement of 127.5 times is remarkable and suggests that the microstructural design of the overlay metal—specifically the combination of martensite and carbides—is highly effective for the wear conditions experienced by roll shafts. This finding supports the use of martensitic overlay alloys for applications involving sliding and abrasive wear.

The study also underscores the importance of process optimization in overlay welding. The combination of proper consumable selection, transition layer usage, and controlled process parameters is essential for achieving reliable, high-performance overlay welds. Engineers should not rely on consumable selection alone but should develop comprehensive welding procedures that address all aspects of the process.

This study provides a valuable reference for engineers developing overlay welding procedures for roll shaft repair and similar applications, and the documented process parameters and performance results serve as a useful benchmark for similar projects.