Zhuojin Pipe Fitting Co., LtdAlloy Overlay Welding Technology for Roughing Mill Rolls
Literature Overview
The paper by Sun Guanquan and Ge Haitao (1990), published in Angang Technology (No. 4, pp. 50-54), presents a comprehensive study of alloy overlay welding technology applied to roughing mill rolls. The authors, affiliated with Angang Second Roughing Mill, conducted systematic experiments to optimize the overlay welding process parameters and demonstrated significant improvements in roll life and economic performance. The classification codes TG333.17 and TG455 indicate relevance to both metal forming and welding processes, reflecting the dual nature of the problem: the overlay layer must provide wear resistance for the rolling process while maintaining the mechanical integrity of the roll.
Core Technical Content
Roughing mill rolls are subjected to severe wear conditions during the rolling of steel billets, with the wear rate directly affecting production efficiency and cost. The paper reports that the international advanced level of roll consumption is 0.03 kg per ton of billet, the domestic advanced level is 0.04–0.06 kg per ton, and the domestic general level is 0.08–0.09 kg per ton. The authors' objective was to reduce roll consumption by applying alloy overlay welding technology, and they achieved a roll consumption of 0.04–0.06 kg per ton, representing a significant improvement.
Overlay Welding Process Parameters
| Parameter | Specification | Technical Rationale |
|---|---|---|
| Base material | High-carbon chromium bearing steel | Provides core strength and toughness |
| Overlay material | Alloy steel with high carbon and alloy content | Provides wear resistance and hardness |
| Overlay thickness | 8–15 mm | Sufficient for wear resistance; avoids excessive dilution |
| Weld layer thickness | 3–5 mm per pass | Controls dilution rate and ensures uniform composition |
| Post-weld heat treatment temperature | 800–850 °C | Normalizes the microstructure and relieves residual stresses |
| Post-weld heat treatment time | 2–4 hours | Ensures complete stress relief and microstructural homogenization |
| Optimal roll diameter | Determined by experiments | Balances wear resistance and mechanical integrity |
The overlay material selection is critical for achieving the desired wear resistance. The alloy composition typically includes high carbon (1.5–2.5%) and alloy elements such as chromium, molybdenum, and vanadium, which form hard carbides that provide wear resistance. The hardness of the overlay layer should be in the range of 55–65 HRC to provide adequate wear resistance without being so hard that it becomes brittle and prone to cracking.
Experimental Approach and Optimization
The authors conducted a series of experiments to optimize the overlay welding process parameters, including the weld layer thickness, the optimal roll diameter, and the post-weld heat treatment temperature and time. The experimental approach followed a systematic methodology: first, the base parameters were established based on theoretical considerations and literature review; second, a series of welding trials were conducted with varying parameters; third, the overlay layers were characterized through hardness testing, microstructural analysis, and wear testing; and fourth, the optimal parameters were selected based on the test results.
The post-weld heat treatment is a critical step in the overlay welding process, as it serves to normalize the microstructure of the overlay layer and relieve the residual stresses generated during welding. The heat treatment temperature of 800–850 °C is in the austenitizing range for the overlay material, which allows for the dissolution of carbides and their subsequent precipitation during cooling. This results in a fine, uniform distribution of carbides that provides excellent wear resistance.
Engineering Practice Insights
The application of alloy overlay welding to roughing mill rolls offers significant economic benefits. The paper reports that the roll life is improved by a factor of three, the roll consumption is reduced by 30%, and the capital tied up in rolls is reduced by 30%. The economic benefit is estimated at 800,000–1,000,000 yuan, which represents a substantial return on investment for the overlay welding technology.
From a practical standpoint, the overlay welding of rolls requires careful consideration of several factors. First, the roll must be properly prepared for welding, including cleaning, preheating, and the removal of any existing defects. Second, the welding sequence must be planned to minimize distortion, as distortion can affect the dimensional accuracy of the roll and lead to rolling defects. Third, the post-weld heat treatment must be carefully controlled to avoid excessive grain growth or decarburization, which can reduce the wear resistance of the overlay layer.
The maintenance of overlay-welded rolls during service also requires attention. The overlay layer can be damaged by improper handling, such as dropping the roll or allowing it to come into contact with other hard surfaces. In addition, the overlay layer can be worn through during extended service, and periodic inspection is necessary to detect wear before it becomes critical.
Key Questions and Reflections
The paper raises several important questions that extend beyond the specific overlay welding procedure. First, what is the effect of the overlay layer on the rolling process itself? The hardness and surface finish of the overlay layer can affect the rolling force, the surface quality of the rolled product, and the roll-to-billet contact conditions. Second, what is the long-term performance of the overlay layer under repeated thermal cycling during rolling? The thermal cycling can generate stresses at the overlay-base interface that may lead to cracking and delamination.
Third, the paper does not discuss the comparison between overlay welding and other roll surface treatment methods, such as induction hardening, nitriding, or laser cladding. Each of these methods has its own advantages and disadvantages, and the selection of the most appropriate method depends on the specific requirements of the rolling operation. The overlay welding approach offers the advantage of allowing the repair of worn rolls without complete replacement, but it may not be suitable for all rolling applications.
Study Insights and Implications
This literature provides a comprehensive case study in the application of alloy overlay welding to roughing mill rolls, demonstrating the technical feasibility and economic benefits of this approach. The systematic experimental methodology used to optimize the welding process parameters and the quantitative reporting of economic benefits make this paper a valuable reference for engineers involved in roll maintenance and improvement. The emphasis on post-weld heat treatment as a critical step in the overlay welding process highlights the importance of understanding the metallurgical aspects of the technology. For engineers in the steel industry, this paper underscores the potential of overlay welding as a cost-effective method for extending the service life of critical rolling mill components.