Overlay Strengthening of Blast Furnace Equalizing Valve Sealing Surfaces Using Tungsten Carbide Infiltration Technology

Literature Overview

This paper by Ge Qixin and Li Chunyan from Angang Mechanical Manufacturing Company, published in Angang Technology (1992, No. 1, pp. 20-22), reports on the practical application of tungsten carbide (WC) infiltration technology for overlay welding reinforcement of blast furnace equalizing valve sealing surfaces. The study documents a dramatic improvement in service life—from approximately two months to more than three times that duration—while simultaneously allowing an increase in blast furnace top pressure by 0.02 MPa. This is a classic example of applied metallurgical engineering solving a critical industrial problem.

Engineering Problem Analysis

The blast furnace equalizing valve is a critical component in the blast furnace top pressure regulation system. It operates under cyclic pressure loading with gas containing abrasive particles (dust, coke fines, and other particulates) at pressures of 0.07-0.08 MPa. The sealing surface is subjected to:

• Abrasive wear: Continuous contact with particulate-laden gas stream
• Pressure cycling: Repeated opening and closing under gas pressure
• Thermal loading: Moderate temperature exposure from hot blast furnace gases
• Impact loading: Valve closure against the seat surface under gas pressure

The original overlay materials—Sormat (a tungsten carbide-based hardfacing alloy) and Alloy 337 (a cobalt-based hardfacing alloy)—provided only two months of service life. This short interval necessitated frequent maintenance shutdowns, resulting in significant production losses.

WC Infiltration Technology

The WC infiltration overlay technology involves depositing a tungsten carbide layer through a specialized overlay welding process that achieves high WC content in the weld deposit. The key metallurgical features of WC-infiltrated overlay deposits include:

The infiltration process involves creating a molten pool that selectively wets and infiltrates WC particles, creating a composite structure with WC particles dispersed in a metallic matrix. The high hardness of WC (approximately 2400 HV) provides exceptional abrasive wear resistance, while the metallic matrix provides toughness and bonding strength.

Process Description

The detailed process described in the paper involves the following key steps:

1. Surface preparation: The valve sealing surface is ground to remove existing overlay material and ensure a clean, flat substrate. Surface roughness is controlled to promote proper wetting of the WC particles.
2. WC layer application: A layer of WC particles (typically 0.1-0.3 mm in size) is applied to the prepared surface.
3. Overlay welding: A specialized welding process (likely gas torch or electric arc) melts the surface to create a molten pool that infiltrates the WC particles.
4. Multi-pass deposition: Multiple passes are applied to build up the required overlay thickness while maintaining uniform WC distribution.
5. Post-weld treatment: The overlay surface is ground and finished to achieve the required dimensional accuracy and surface finish for sealing.

Performance Results and Analysis

The results demonstrate a more than threefold improvement in service life under conditions that are actually more severe than the original design:

• Original conditions: 0.07-0.08 MPa operating pressure, ~2 months service life
• Improved conditions: 0.09-0.10 MPa operating pressure, >6 months service life

This improvement has cascading benefits for blast furnace operation:

• Increased top pressure: Higher top pressure improves blast furnace efficiency and reduces coke consumption (coke ratio)
• Reduced maintenance frequency: Fewer valve replacements mean less production interruption
• Higher furnace productivity: Extended maintenance intervals allow for more continuous operation
• Lower operating costs: Reduced consumable costs, labor costs, and production losses

Study Insights and Reflections

This case study exemplifies the power of targeted materials engineering to solve specific industrial problems. The WC infiltration technology provides a hard, wear-resistant surface that dramatically extends component life in abrasive service. The ability to operate at higher pressures with the reinforced valve represents a system-level benefit that extends beyond the valve itself to the entire blast furnace operation.

From a metallurgical perspective, the success of WC infiltration depends on achieving good bonding between the WC particles and the metallic matrix. Poor infiltration leads to particle pull-out during service, which accelerates wear. The infiltration quality is influenced by particle size, particle shape, infiltration temperature, and cooling rate. These factors must be carefully controlled in production to ensure consistent results.

For engineers considering similar applications, the key lesson is that overlay welding technology selection should be driven by the specific wear mechanism and operating environment. WC-based overlays excel in abrasive wear but may be less suitable for adhesive or erosive-corrosive wear. Material selection must always be matched to the dominant wear mechanism.