Cladding Welding Insert Technology for Blast Furnace Receiving Hopper and Distributor Liner Plates

Literature Overview

This 2003 publication from the Shandong Metallurgical Research Institute and Jinan Iron and Steel Group, authored by Wang Lichuan and colleagues, documents the development and application of cladding welding insert technology for blast furnace receiving hopper and distributor liner plates. Published in "Shandong Metallurgy," this work represents practical industrial metallurgical engineering addressing severe wear problems in ironmaking operations.

Blast furnaces operate under extremely harsh conditions with temperatures reaching 1500–2000 °C at the tuyere level, combined with abrasive wear from molten iron, slag, and raw materials. The receiving hopper and distributor (also known as the charging device or skip loader) are critical components that must withstand both thermal and mechanical degradation while maintaining precise geometric tolerances for proper furnace operation.

Core Technical Approach

The cladding welding insert technology described in this publication involves the fabrication of wear-resistant insert plates that are welded onto the base structure of the hopper and distributor components. This approach combines the economic advantages of steel fabrication with the wear resistance of specialized overlay materials.

Material Selection

Component	Base Material	Overlay Material	Target Hardness
Hopper wall	Q235 / Q345	Cr-Mo high carbon steel	45–55 HRC
Hopper bottom	Q235 / Q345	High Cr cast iron equivalent	55–65 HRC
Distributor raceway	Q345	Medium Cr alloy steel	40–50 HRC
Distributor center plate	Q345	High Cr-Mo alloy	50–60 HRC

Process Parameters

The overlay welding process parameters for insert fabrication:

Parameter	Hopper Inserts	Distributor Inserts
Welding process	SAW (sintered flux)	GTAW / SAW
Wire diameter	3.2 mm	2.4–3.2 mm
Current	350–500 A	150–300 A
Voltage	28–34 V	18–24 V
Travel speed	150–250 mm/min	80–150 mm/min
Preheat	100–150 °C	150–200 °C
Layers	2–3	3–5
Layer thickness	6–10 mm	4–8 mm

Technical Points and Interpretation

Wear Mechanism Analysis

Understanding the wear mechanisms is essential for selecting appropriate overlay materials:

Abrasive wear: Dominant mechanism in the receiving hopper where raw materials (iron ore, coal, flux) impact and slide across surfaces. Hardness is the primary resistance factor.
Erosive wear: Occurs at the distributor where charged materials are distributed onto the furnace burden surface. The angle of impact and velocity determine wear severity.
Thermal fatigue: Cyclic temperature changes cause cracking in the overlay layer, reducing effective service life.
Corrosive wear: In the lower hopper region, hot dust and gases can cause chemical attack on the overlay surface.

Insert Design Considerations

The insert plate design incorporates several important features:

Geometric tolerance: Inserts must maintain precise dimensions to ensure proper material flow through the hopper and even distribution from the distributor
Thermal expansion accommodation: Slots or expansion joints prevent cracking due to differential thermal expansion between inserts and base structure
Welding accessibility: Insert geometry must allow proper welding access from all sides
Replacement convenience: Modular design enables individual insert replacement without dismantling the entire component

Overlay Layer Metallurgy

The microstructure of the overlay layer determines its wear resistance characteristics:

Microstructural Feature	Contribution to Wear Resistance
Hard carbides (Cr7C3, Fe3C)	Primary abrasive resistance
Martensitic matrix	High hardness, toughness
Fine grain structure	Improved toughness and fatigue resistance
Low retained austenite	Dimensional stability during service

The sintered flux composition plays a critical role in achieving the desired microstructure. Typical flux compositions include:

Base flux: 60–70% (SiO2, Al2O3, CaF2, MgO)
Alloy additions: 20–30% (Cr, Mo, Mn, C powders)
Deoxidizers: 3–5% (FeSi, Al)
Binders: 5–7% (water glass, organic binders)

Integration with Engineering Practice

Service Life Improvement

The application of cladding welding insert technology has demonstrated significant service life improvements:

Component	Before (unclad)	After (clad inserts)	Improvement Factor
Hopper wall	6–12 months	24–36 months	3–4×
Hopper bottom	3–6 months	18–24 months	4–6×
Distributor raceway	12–18 months	36–48 months	3–4×
Distributor center	6–12 months	24–36 months	3–4×

Economic Analysis

The economic justification for cladding welding insert technology is compelling:

Initial cost: Insert fabrication and installation costs 3–5× the cost of plain steel fabrication
Replacement frequency: Reduced by 3–6× compared to unclad components
Downtime reduction: Fewer replacements mean less furnace downtime
Total cost of ownership: 40–60% reduction over 5-year period

Quality Control Measures

The following quality control procedures are implemented:

Material verification: Chemical composition and hardness testing of overlay wire and flux
Welding procedure qualification: WPS/PQR qualification per NB/T 47014 or equivalent
In-process inspection: Visual examination after each layer, MT for critical areas
Final inspection: Hardness testing, dimensional verification, PT/MT examination
Service monitoring: Regular inspection during operation to detect early failure signs

Key Questions and Reflections

The primary technical challenge in blast furnace component cladding is achieving a balance between wear resistance and toughness. Extremely hard overlay materials (above 65 HRC) tend to be brittle and susceptible to cracking under impact loading. The optimal hardness range of 50–60 HRC provides adequate wear resistance while maintaining sufficient toughness for the impact and thermal cycling conditions in blast furnace service.

Another important consideration is the thermal management of the insert plates. During blast furnace operation, the hopper and distributor surfaces can experience rapid temperature changes from ambient to several hundred degrees Celsius. The coefficient of thermal expansion mismatch between the overlay layer and base plate creates thermal stresses that can lead to delamination or cracking. The insert design must accommodate this through proper geometry and welding sequence.

The 2003 publication reflects the practical engineering approach of Chinese metallurgical industry at that time, where cost-effectiveness and reliability were paramount. The technology described is straightforward and well-suited for industrial application, requiring minimal specialized equipment beyond standard welding capability.

Study Insights and Implications

This literature demonstrates the successful application of cladding welding insert technology in a demanding industrial environment. The blast furnace receiving hopper and distributor are critical components whose integrity directly affects furnace campaign length and production efficiency. The insert technology provides a practical solution that significantly extends component life while maintaining acceptable costs.

The key insight from this work is that the most effective wear protection strategy combines proper material selection with thoughtful design. The insert concept allows for localized application of expensive overlay materials only where needed, while the modular design facilitates maintenance and replacement. This approach is consistent with the principles of value engineering and life-cycle cost optimization.

The publication also highlights the importance of understanding the specific wear mechanisms in each component location. Different areas of the hopper and distributor experience different combinations of abrasive, erosive, and thermal wear, requiring tailored overlay material selection for each location. This location-specific approach maximizes the effectiveness of the cladding investment.