Automatic Submerged Arc Surfacing of Blast Furnace Charging Bell and Hopper Mating Surfaces

Literature Overview

This paper, published in Shandong Metallurgy in 2000 by Pan Yubin and colleagues from Jinan Iron and Steel Group, addresses a persistent operational challenge in ironmaking: the rapid wear of mating surfaces between the charging bell and the hopper in blast furnaces. The authors propose an automatic submerged arc surfacing (SAW) welding process that employs a two-layer strategy—a transition layer of 1Cr18Ni9Ti (austenitic stainless steel) followed by a hardfacing layer of 3Cr2W8 (high-chromium cast iron equivalent). This study is particularly relevant to engineers working on refractory equipment repair and heavy-duty surfacing applications.

Core Technical Approach

The fundamental problem lies in the extreme wear conditions experienced by the bell-hopper interface during continuous blast furnace operation. The mating surfaces undergo constant sliding contact with iron ore, sinter, and coke burden, resulting in severe abrasive wear. Conventional repair methods—such as manual arc welding with carbon steel electrodes—provide insufficient hardness and wear resistance, leading to frequent shutdowns for maintenance.

The two-layer surfacing strategy is well-conceived from a metallurgical standpoint:

Layer	Material	Function	Key Properties
Transition layer	1Cr18Ni9Ti	Stress relief, crack prevention	High ductility, low CTE mismatch
Hardfacing layer	3Cr2W8	Wear resistance	Hard carbides (MC type), high hardness

The 1Cr18Ni9Ti transition layer serves a critical metallurgical purpose. The coefficient of thermal expansion difference between the carbon steel base material and the high-carbon, high-chromium hardfacing alloy is significant. Without a ductile buffer layer, thermal stresses during welding and subsequent service would generate transverse cracks at the interface. The austenitic structure of 1Cr18Ni9Ti, stabilized by titanium to prevent sensitization, provides the necessary plasticity to accommodate these stresses.

Process Parameters and Technical Details

The paper describes the use of automatic submerged arc surfacing, which offers several advantages over manual methods for this application:

Consistent weld quality: Automatic feed control ensures uniform wire deposition rate
Flux protection: The submerged arc process provides excellent slag coverage, minimizing spatter and oxidation
Productivity: Higher deposition rates compared to SMAW
Reproducibility: Parameters can be precisely controlled and repeated

The paper mentions both uphill and downhill welding orientations. This is significant because the bell and hopper mating surfaces are curved geometries that cannot be easily positioned for flat welding. Uphill welding (welding against gravity) produces a narrower, deeper weld bead with good penetration, while downhill welding produces a wider, flatter bead. For surfacing applications, the choice depends on whether deeper fusion or a wider coverage is desired.

Engineering Practice Insights

From my experience in heavy equipment repair, I note several practical considerations that extend beyond what the paper explicitly addresses:

Preheating: The base material (typically Q235 or Q345 carbon steel for blast furnace structures) should be preheated to 150–200°C to reduce hydrogen-induced cracking risk, especially when welding thick sections.
Interpass temperature control: Maintaining interpass temperatures below 250°C is essential to prevent excessive grain growth in the transition layer and to minimize thermal distortion of the thin-walled hopper structure.
Post-weld treatment: A low-temperature stress relief at 550–600°C for 2 hours per 25 mm of thickness can significantly reduce residual stresses without compromising the hardness of the 3Cr2W8 layer.
Surface preparation: The mating surfaces must be machined to a minimum roughness of Ra 6.3 μm before surfacing to ensure proper adhesion of the first layer.

Common Defects and Countermeasures

Defect	Cause	Countermeasure
Transverse cracking at interface	High CTE mismatch, hydrogen	Use transition layer, preheat, low-hydrogen flux
Porosity	Flux moisture, surface contamination	Dry flux, clean base surface
Excessive dilution	High welding current, large wire diameter	Reduce current, use smaller wire (φ3.2 mm)
Surface cracks in 3Cr2W8 layer	High carbon content, rapid cooling	Post-weld stress relief, controlled cooling

Study Insights and Implications

This paper, though published over two decades ago, remains highly relevant. The metallurgical principles of using a ductile transition layer between dissimilar materials are universally applicable in surfacing engineering. The specific material combination of 1Cr18Ni9Ti and 3Cr2W8 is a classic pairing that balances adhesion strength with surface hardness.

The reported extension of service life and maintenance intervals demonstrates the economic value of proper surfacing design. In modern blast furnace practice, where downtime costs exceed $100,000 per hour, even a modest extension of repair intervals represents substantial savings. I would recommend that engineers consider this approach for similar heavy-wear applications in mining, cement, and power generation industries where sliding contact between large rotating or reciprocating components causes progressive wear.