Cold Welding Overlay Process for 100m3 Blast Furnace Bell Surface

Literature Overview

This paper, authored by Yang Wenkui of Shandong Metallurgical Machinery Factory and published in the journal Welding (1997, Issue 5), documents a significant process innovation in the overlay welding of blast furnace bells. The 100 m³ blast furnace bell is a critical component that must withstand extreme thermal cycling, abrasive wear from descending burden materials, and corrosive high-temperature gas environments. The author reports the successful development of a cold welding overlay process that eliminates the conventional requirement for preheating the bell to 500°C prior to welding, thereby overcoming longstanding limitations in productivity, cost, and defect control.

Core Technical Challenge and Traditional Approach

The blast furnace bell operates under severe conditions where the surface is continuously subjected to abrasion from descending ore, coke, and flux, as well as thermal degradation from furnace gas at temperatures exceeding 1000°C. To extend service life, a high-temperature resistant wear-resistant overlay layer must be deposited on the bell surface. Historically, the industry practice required preheating the entire bell assembly to approximately 500°C before applying the overlay weld, maintaining this temperature throughout the welding operation. This hot welding approach was necessitated by the high carbon equivalent of the bell material and the susceptibility of the heat-affected zone to cold cracking.

The conventional hot welding process suffered from several critical deficiencies:

• Preheating to 500°C required substantial fuel consumption and extended setup time, making operations extremely inconvenient on site.
• Welding speed was inherently limited due to the need to maintain thermal input consistency across the heated surface.
• Significant material and energy waste occurred during the prolonged preheating and post-weld stress relief stages.
• Post-weld low-temperature stress relief treatment was mandatory to prevent cracking, adding further cost and schedule burden.
• Despite all these measures, surface cracking could not be completely eliminated, resulting in quality failures and rework.

Development of the Cold Welding Process

Through repeated trial and error in production practice, the author's team systematically explored alternative process parameters that would allow overlay welding without preheating. The fundamental strategy involved selecting appropriate filler metal compositions with lower carbon equivalent, higher hydrogen resistance, and improved ductility in the weld metal, combined with optimized heat input control to manage the thermal gradient and residual stress distribution.

Key process parameters and design decisions likely include:

The selection of filler metal is the cornerstone of this process innovation. By choosing a weld metal with reduced carbon content and appropriate alloying additions, the weld deposit can accommodate the rapid thermal cycling inherent in cold welding without generating excessive residual stresses or brittle phases in the heat-affected zone. The lower hydrogen solubility characteristics of the selected filler metal also contribute to crack resistance even in the absence of preheating.

Engineering Practice and Process Control Considerations

From a practical standpoint, the transition from hot welding to cold welding for blast furnace bell overlay represents a paradigm shift in maintenance welding philosophy. Several critical control points must be addressed:

1. Surface preparation: The base metal surface must be thoroughly cleaned of scale, oxide, and contamination to ensure proper weld fusion and minimize hydrogen pickup.
2. Welding sequence design: A systematic welding sequence that balances thermal input across the bell geometry is essential to prevent localized distortion and residual stress concentration.
3. Heat input management: Since preheating is eliminated, the welding parameters must be carefully calibrated to achieve adequate penetration without excessive thermal cycling that could induce cracking.
4. Deposition layer integrity: The overlay layer must maintain its metallurgical integrity without post-weld heat treatment, requiring a filler metal that forms beneficial phases in the as-welded condition.

Key Questions and Reflections

This paper raises important questions about the applicability of cold welding overlay processes to other heavy equipment components with similar thermal and mechanical demands. The success of this approach for blast furnace bells suggests that with appropriate filler metal selection and process parameter optimization, many overlay welding applications that traditionally require extensive preheating could potentially be simplified. The author's emphasis on practical, field-proven results rather than purely laboratory-based development is commendable and reflects the engineering pragmatism required in industrial settings.

The elimination of post-weld stress relief treatment is particularly noteworthy, as residual stress management is often the most challenging aspect of overlay welding on thick-section steel components. This achievement implies that the selected process parameters and filler metal combination effectively manage the thermal and mechanical stresses through metallurgical design rather than thermal post-processing.

Summary

The cold welding overlay process developed for 100 m³ blast furnace bells represents a valuable engineering innovation that addresses real production challenges through systematic process optimization. By eliminating preheating requirements and post-weld stress relief while simultaneously reducing surface cracking, this approach demonstrates that intelligent filler metal selection and parameter control can overcome the limitations of conventional hot welding practices. The paper provides a practical framework for engineers seeking to improve overlay welding efficiency on large, thick-section steel components operating in high-temperature, abrasive environments.