Cold Welding Process for Surfacing of 100m³ Blast Furnace Charging Bell

Literature Overview

This 1997 study by Yang Wenkui from Shandong Metallurgical Machinery Factory addresses a persistent industrial challenge in blast furnace maintenance: the surfacing of wear-resistant, high-temperature-resistant layers on the surface of 100 m³ blast furnace charging bells. The paper documents a transition from conventional hot welding (requiring preheating to 500°C) to a cold welding approach that eliminates the need for post-weld heat treatment. Published in the journal Welding, this work represents an important field-driven innovation in heavy equipment repair welding technology.

Core Technical Problem and Background

The blast furnace charging bell operates under extreme conditions—high temperatures, abrasive material impact, and cyclic thermal loading. The base material is typically a thick carbon steel casting or plate assembly. The conventional hot welding approach involved:

Preheating the entire bell to 500°C and maintaining temperature during welding
Slow deposition rates due to thermal management constraints
Mandatory low-temperature stress relief treatment after welding
Persistent surface cracking even under optimized hot welding conditions
Significant operational inconvenience and material waste

These limitations made the hot welding process economically unsustainable and technically unreliable for production-scale charging bell manufacturing.

Cold Welding Process Development

Process Parameters and Methodology

The cold welding approach eliminates preheating entirely and removes the need for post-weld heat treatment. Key process considerations include:

Parameter	Hot Welding (Conventional)	Cold Welding (Improved)
Preheat temperature	500°C	None (ambient)
Interpass temperature control	Required	Not required
Post-weld stress relief	Required	Not required
Deposition rate	Low	Higher
Surface cracking tendency	Moderate to high	Reduced
Operational convenience	Poor	Significantly improved

Metallurgical Considerations

The cold welding process on a thick carbon steel substrate presents significant challenges regarding hydrogen-induced cracking and residual stress accumulation. The success of this approach likely depends on several factors:

Weld consumable selection: Low-hydrogen or specialized surfacing electrodes that resist cold cracking, possibly with specific dilution characteristics to achieve the desired wear-resistant composition.
Heat input management: Controlled arc energy to minimize the thermal gradient while avoiding excessive residual stresses.
Layer design: Multi-pass surfacing with proper interpass cooling to manage the thermal cycle.
Substrate preparation: Thorough surface cleaning and possibly local mechanical conditioning to ensure adequate fusion without preheating.

Engineering Insights

The elimination of post-weld heat treatment is particularly significant from a production standpoint. In the context of blast furnace charging bell manufacturing, where multiple units may be produced in series, removing the PWHT step dramatically reduces cycle time and furnace capacity requirements. The reduction in surface cracking indicates that the cold welding process may have inadvertently achieved a more favorable thermal cycle for the specific geometry and material combination involved.

Defect Analysis and Countermeasures

Common Defects in Surfacing Welds

Defect Type	Root Cause	Countermeasure
Surface cracks	High residual stress, hydrogen embrittlement	Low-hydrogen consumables, controlled heat input
Undercut	Excessive arc travel speed	Parameter optimization, proper torch angle
Porosity	Surface contamination, gas shielding issues	Thorough cleaning, proper shielding gas flow
Excessive dilution	High heat input, thick single pass	Multiple thin layers, reduced current
Poor fusion	Low arc energy, poor joint preparation	Increased penetration, proper edge preparation

Key Engineering Observations

The paper notes that while cold welding reduces surface cracking compared to hot welding, it does not completely eliminate it. This suggests that the fundamental metallurgical driving force for cracking—likely related to the carbon equivalent of the substrate and the cooling rate of the weld metal—remains present but is better managed through consumable selection and process control rather than thermal conditioning.

Integration with Engineering Practice

For engineers working on similar heavy equipment surfacing applications, this study demonstrates several important principles:

Process innovation from field experience: The cold welding approach emerged from repeated practical experimentation rather than purely theoretical analysis, highlighting the value of iterative field development.
Cost-benefit analysis of thermal treatment: When the metallurgical driving force for cracking can be managed through consumable chemistry rather than thermal conditioning, the economic case for eliminating PWHT becomes compelling.
Geometry-specific solutions: The success of cold welding on the charging bell geometry does not necessarily extend to all heavy section surfacing applications; the specific section thickness, restraint conditions, and material composition must be evaluated case by case.

Study Insights and Implications

This literature is notable for its practical orientation and clear demonstration of how process constraints can be overcome through consumable selection and parameter optimization rather than relying on thermal conditioning. For modern surfacing applications on thick-section components, the principles remain relevant: the goal should always be to minimize the thermal cycle severity through process design rather than compensating for an aggressive thermal cycle with post-weld treatment. The study also underscores the importance of field validation—over one year of practical service testing is essential to confirm that a new welding process delivers reliable results under actual operating conditions. Engineers should approach similar surfacing challenges with the mindset of questioning whether preheating and PWHT are truly necessary or merely traditional practices that have become entrenched without metallurgical justification.