Zhuojin Pipe Fitting Co., LtdLow-Dilution Surfacing Technology for Composite Wear-Resistant Thin Plates
Literature Overview
Published in Welding in 1997 by Zhao Kun, Cheng Zhiguo, and Bai Fuping from the Harbin Welding Research Institute, and Zī Zhuanghui from the Heilongjiang Provincial Labor Department Boiler and Pressure Vessel Technical Inspection Institute, this paper introduces an innovative low-dilution surfacing technique for manufacturing composite wear-resistant thin plates. The research addresses a significant challenge in the production of wear-resistant composite plates: achieving thick, high-alloy surfacing layers on thin base plates without excessive dilution that would compromise the wear resistance of the deposited alloy.
Core Technical Innovation
The Dilution Problem
In conventional surfacing welding of thin plates, the base metal contributes a significant fraction of the deposited weld metal, a phenomenon known as dilution. For thin base plates (e.g., 6–10 mm), the dilution rate can exceed 30–40%, which substantially reduces the alloy content of the final deposit and degrades its wear resistance. This is particularly problematic for high-alloy wear-resistant surfacing alloys, where even moderate dilution can reduce hardness by 10–20 HRC.
The authors' solution was to employ a pre-formed powder block (or powder cake) as an intermediate layer between the base plate and the surfacing deposit. The powder block, composed of the desired high-alloy composition, acts as a dilution barrier, ensuring that the surfacing weld metal is alloyed primarily from the powder block rather than from the base plate.
Process Description
The low-dilution surfacing process involves the following steps:
| Step | Description | Purpose |
|---|---|---|
| 1 | Prepare base plate (thin carbon steel, 6–12 mm) | Provide structural support |
| 2 | Form powder block on base plate surface | Create dilution barrier with desired alloy composition |
| 3 | Fuse powder block to base plate by welding | Create metallurgical bond between base and powder block |
| 4 | Apply surfacing layer over fused powder block | Deposit wear-resistant alloy with minimal dilution |
| 5 | Inspect and finish | Verify bond quality, hardness, and dimensions |
The key innovation is the use of the powder block as a sacrificial alloying source. When the surfacing arc melts the powder block surface, the molten pool is composed primarily of the high-alloy powder composition, with only minor contribution from the base metal through the fused powder block layer. This effectively decouples the surfacing deposit composition from the base metal composition.
Technical Parameters
| Parameter | Specification | Rationale |
|---|---|---|
| Base plate thickness | 6–12 mm | Thin plate construction for weight savings |
| Powder block thickness | 8–15 mm | Sufficient material for surfacing without excessive dilution |
| Powder block composition | High-alloy wear-resistant (Cr, Mo, V, C) | Provides desired wear resistance |
| Surfacing wire | Flux-cored wire matching powder block composition | Ensures consistent alloy content |
| Welding method | GMAW with flux-cored wire | High deposition rate, good process control |
| Dilution rate achieved | < 10% (vs. 30–40% in conventional process) | Maintains high-alloy deposit properties |
| Final composite plate thickness | 14–27 mm (base + powder block + surfacing) | Adequate structural and wear performance |
Microstructural and Mechanical Properties
The low-dilution process produces surfacing deposits with properties closely matching the nominal composition of the high-alloy powder:
| Property | Conventional Process | Low-Dilution Process | Improvement |
|---|---|---|---|
| Hardness (HRC) | 35–42 | 45–55 | 30–40% increase |
| Dilution rate | 30–40% | < 10% | Significant reduction |
| Hard phase volume fraction | Low (due to dilution) | High (matching nominal composition) | Improved wear resistance |
| Bond strength (base to deposit) | Good | Good (through powder block interface) | Comparable |
Engineering Practice Applications
Application Areas
The composite wear-resistant thin plates produced by this technique are suitable for a wide range of industrial applications:
| Application | Wear Mechanism | Required Properties |
|---|---|---|
| Conveyor belt liners | Abrasive wear from bulk material | High hardness, good impact resistance |
| Chute linings | Abrasive + impact wear | High hardness, good toughness |
| Mill liners | Abrasive + impact wear | High hardness, good fatigue resistance |
| Excavator bucket teeth | Abrasive + impact wear | High hardness, good toughness |
| Pump impellers | Erosion-corrosion wear | High hardness, corrosion resistance |
Quality Control Considerations
The quality of the composite plate depends on the integrity of the bond between the base plate, powder block, and surfacing layer. The following quality control measures are recommended:
| Inspection Method | Location | Purpose |
|---|---|---|
| Visual inspection (VT) | All surfaces | Surface defects, porosity, undercut |
| Magnetic particle testing (MT) | Base-powder block interface | Bond cracks |
| Ultrasonic testing (UT) | Powder block-surfacing interface | Internal voids, lack of fusion |
| Hardness profiling | Through-thickness | Verify hardness gradient and dilution control |
| Peel/shear test | Bond interface | Verify bond strength |
Study Insights and Reflections
This paper presents a clever and practical solution to the dilution problem in thin-plate surfacing welding. The concept of using a pre-formed powder block as a dilution barrier is elegant in its simplicity—it transforms a two-layer problem (base metal + surfacing) into a three-layer system (base metal + powder block + surfacing), where the powder block provides both the desired alloy composition and the structural interface between the base and the surfacing layer.
From a metallurgical perspective, the powder block serves multiple functions: it acts as an alloying reservoir for the surfacing weld pool, it provides a metallurgical bridge between the dissimilar base and surfacing metals, and it can be designed to have a composition that promotes good wetting and bonding with both the base metal and the surfacing alloy. This multi-functional role makes the powder block a critical component of the overall process design.
I note that the paper is from 1997, which predates modern additive manufacturing techniques that could potentially produce powder blocks with more precise composition control and reduced porosity. The application of modern powder metallurgy techniques—such as cold isostatic pressing (CIP) or hot isostatic pressing (HIP) of the powder blocks—could further improve the quality and consistency of the composite plates.
The economic advantage of this technique lies in the ability to use thin, inexpensive carbon steel base plates as the structural substrate, while achieving the wear resistance of expensive high-alloy materials through the powder block and surfacing layers. This approach can reduce material costs by 30–50% compared to solid high-alloy plates of equivalent wear performance, while maintaining the structural integrity required for industrial applications.
In conclusion, this paper introduces a significant process innovation—the low-dilution surfacing technique using pre-formed powder blocks—that enables the production of composite wear-resistant thin plates with high-alloy properties on economical base materials. The technique addresses a fundamental limitation of conventional surfacing welding on thin plates and opens up new possibilities for cost-effective wear-resistant component design in heavy industry. The principles underlying this approach remain relevant today and could be further enhanced through modern powder processing and welding technologies.