CLADDING TECHNOLOGY SHANXI CO., LTD45Cr4NiMoV Roller Overlay Welding Electrode Process and Properties
Literature Overview
This 2006 paper published in the Journal of Wuhan University of Technology (Traffic Science and Engineering Edition) by Wang Xuanguo and Wu Yongyu from the School of Materials Science and Engineering at Wuhan University of Technology investigates the overlay welding process and properties of a 45Cr4NiMoV alloy on metallurgical rollers using a purpose-developed welding electrode. Supported by the Hubei Provincial Natural Science Foundation (grant 2002AB017), this work addresses a significant industrial need: the restoration and enhancement of worn or damaged metallurgical rollers used in hot rolling mills, where extreme temperatures, mechanical loads, and abrasive conditions demand overlay materials with exceptional hardness, wear resistance, and thermal stability.
Core Technical Content
The 45Cr4NiMoV alloy is a high-carbon, high-chromium martensitic steel with additional nickel, molybdenum, and vanadium alloying elements that provide enhanced hardenability, temper stability, and wear resistance. The overlay is intended to restore the surface hardness of rollers that have been worn down during hot rolling operations, where the roller surface is subjected to temperatures exceeding 900 degrees Celsius, contact pressures in the range of several gigapascals, and continuous abrasive contact with hot steel strip.
Electrode and Process Design
The welding electrode developed for this application is a low-hydrogen, heavy-coated electrode with a 45Cr4NiMoV alloy core. The coating composition is designed to provide adequate arc stability, slag coverage, and alloying element transfer to the weld deposit. The overlay is typically applied in multiple passes, with each pass designed to achieve a specific hardness and microstructure profile.
| Parameter | Specification | Rationale |
|---|---|---|
| Electrode core composition | 45Cr4NiMoV (C 0.42 to 0.48%, Cr 3.5 to 4.5%, Ni 1.0 to 1.5%, Mo 0.4 to 0.6%, V 0.2 to 0.3%) | Ensures adequate hardenability and wear resistance |
| Electrode coating type | Low-hydrogen, heavy coating | Provides arc stability and minimizes hydrogen-induced cracking |
| Electrode diameter (mm) | 4.0 to 5.0 | Balances deposition rate and arc control |
| Welding current (A) | 180 to 280 | Sufficient to achieve full penetration and good fusion |
| Preheat temperature (degrees C) | 200 to 300 | Reduces cooling rate and minimizes cracking risk |
| Post-weld heat treatment | Temper at 540 to 580 degrees C | Achieves target hardness of 45 to 55 HRC |
The overlay weld deposit, after tempering, achieves a hardness in the range of 45 to 55 HRC, which is significantly higher than the base roller steel (typically 30 to 38 HRC). The microstructure of the tempered overlay consists primarily of tempered martensite with dispersed carbide particles, including M7C3, M23C6, and MC-type vanadium carbides. These carbides are responsible for the excellent wear resistance of the overlay and contribute to its thermal stability at elevated operating temperatures.
Microstructural Analysis
The untempered overlay weld deposit exhibits a fully martensitic microstructure due to the high carbon and alloy content, which provides a very high cooling rate and suppresses the formation of softer phases such as pearlite or ferrite. The martensite is relatively fine-grained due to the rapid solidification and subsequent transformation during cooling. After tempering at 540 to 580 degrees Celsius, the martensite transforms to tempered martensite with secondary carbide precipitation, which provides a favorable combination of hardness and toughness.
| Condition | Hardness (HRC) | Microstructure | Wear Resistance |
|---|---|---|---|
| As-welded | 58 to 65 | Un tempered martensite with retained austenite | High hardness but low toughness; susceptible to cracking |
| Tempered at 540 degrees C | 45 to 50 | Tempered martensite with fine carbides | Good balance of hardness and toughness |
| Tempered at 580 degrees C | 40 to 45 | Tempered martensite with coarser carbides | Reduced hardness but improved toughness |
The tempering temperature of 540 to 580 degrees Celsius is selected to balance hardness and toughness while maintaining sufficient wear resistance for hot rolling service. The authors report that the overlay exhibits excellent resistance to thermal fatigue cracking, which is a common failure mode in hot rolling rollers subjected to repeated thermal cycling.
Engineering Practice Integration
The overlay welding of metallurgical rollers is a well-established practice in the steel industry, and the development of purpose-specific welding electrodes is critical to achieving consistent and reliable results. The 45Cr4NiMoV overlay described in this paper is particularly suitable for finishing mill rolls and intermediate rolls in hot strip mills, where the combination of high temperature, high pressure, and abrasive contact with hot steel strip demands a surface layer with exceptional thermal stability and wear resistance.
In production practice, the overlay is typically applied in a ring pattern around the roller circumference, with the overlap between adjacent weld beads carefully controlled to ensure uniform coverage and avoid areas of incomplete coverage or excessive buildup. The total overlay thickness is typically 3 to 5 millimeters, with the final surface ground to the required dimensional tolerance and surface finish. The quality of the overlay is verified through hardness testing, ultrasonic testing for subsurface defects, and, in some cases, dye penetrant testing for surface cracks.
Key Questions and Reflections
A key question that arises from this study is the long-term durability of the overlay under actual hot rolling conditions. The overlay hardness and microstructure are characterized under laboratory conditions, but the actual service environment involves complex thermal and mechanical loading that may cause progressive degradation of the overlay properties. Thermal cycling can lead to temper embrittlement in high-alloy martensitic steels, and the repeated thermal shock of hot strip contact can initiate thermal fatigue cracks at the overlay surface or at the overlay-substrate interface. The authors' recommendation of a tempering temperature in the range of 540 to 580 degrees Celsius is reasonable, but I would emphasize the importance of avoiding the temper embrittlement temperature range of 370 to 520 degrees Celsius, where prolonged exposure can significantly reduce the toughness of the overlay.
Another important consideration is the compatibility of the overlay with the base roller steel. The thermal expansion mismatch between the overlay and the base material can generate residual stresses at the interface, which may contribute to delamination or cracking under cyclic loading. The preheat temperature of 200 to 300 degrees Celsius helps to reduce the thermal gradient and minimize these residual stresses, but post-weld stress relief may also be necessary for critical applications.
Summary
This paper presents a well-developed overlay welding solution for metallurgical rollers using a purpose-designed 45Cr4NiMoV welding electrode, with detailed process parameters and microstructural characterization that demonstrate the effectiveness of the approach. The tempered martensitic microstructure with dispersed carbide precipitates provides the required combination of hardness, wear resistance, and thermal stability for hot rolling service. For engineers involved in roller maintenance and restoration, the key message is that the success of the overlay depends on careful control of the welding process, appropriate heat treatment, and rigorous quality verification to ensure that the overlay meets the demanding requirements of hot rolling operations.