Low-Dilution Overlay Welding Technology for Composite Wear-Resistant Thin Plates

Literature Overview

This 1997 paper by Zhao Kun, Cheng Zhiguo, Bai Fuping, and Zi Zhuanghui from the Harbin Welding Research Institute and Heilongjiang Provincial Boiler and Pressure Vessel Technical Inspection Institute presents an innovative approach to manufacturing composite wear-resistant plates: low-dilution single-pass overlay welding using flux-cored wire deposited on pre-formed powder blocks. The technique enables the production of thin substrate plates with thick overlay layers—a configuration that is extremely difficult to achieve using conventional multi-pass overlay welding due to excessive dilution and substrate thermal distortion.

Technical Innovation and Principle

The fundamental challenge in producing composite wear-resistant plates with thin substrates is dilution control. In conventional overlay welding, each pass deposits a layer of hardfacing alloy, but the heat input melts a portion of the previously deposited layer (and ultimately the substrate), diluting the alloy composition and reducing hardness. As the number of passes increases, the cumulative dilution effect can reduce the final surface hardness by 5–15 HRC, which may be unacceptable for wear-critical applications.

The pre-formed powder block approach solves this problem by providing a thick layer of hardfacing material that is only partially melted during the welding process. The welding arc melts the top surface of the powder block and a minimal amount of the substrate, while the bulk of the powder block remains solid and consolidates through plastic deformation and solid-state bonding. This results in:

Minimal dilution: Less than 5% substrate dilution in the final overlay layer
Thick deposit in single pass: 3–8 mm of wear-resistant material deposited in one welding pass
Low thermal input to substrate: Reduced distortion and residual stress in the thin base plate
Preserved alloy composition: Hardness and wear properties closely match the powder block composition

Process Parameters and Configuration

The manufacturing process involves several sequential steps:

Process Step	Parameter	Purpose
Substrate preparation	Grind to Ra ≤ 6.3 μm	Ensure clean, flat bonding surface
Powder block fabrication	Press or cast to 5–10 mm thickness	Provide thick hardfacing material source
Block attachment	Mechanical fastening or tack welding	Secure block to substrate before welding
Overlay welding	FCAW, 200–300 A, 25–32 V	Melt block surface and consolidate with substrate
Travel speed	80–150 mm/min	Control penetration depth and bead geometry
Post-weld treatment	Optional stress relief at 500–600°C	Reduce residual stress in thin substrate

Metallurgical Analysis

The resulting composite plate exhibits a characteristic microstructure:

Base metal: Low-carbon or low-alloy steel substrate, typically 6–12 mm thick
Bonding zone: A thin transition region (0.5–2 mm) with mixed composition, providing metallurgical and mechanical bonding
Overlay layer: The consolidated powder block material with minimal dilution, exhibiting the full hardness and wear resistance of the intended hardfacing alloy (typically 55–65 HRC for high-carbon, high-chromium compositions)

The bonding quality is critical for structural integrity. Insufficient bonding can lead to delamination under impact or cyclic loading. The bonding zone must be examined metallographically to verify complete fusion and absence of voids or inclusions.

Comparison with Conventional Methods

Method	Substrate Thickness	Overlay Thickness	Dilution Rate	Surface Hardness	Cost
Conventional multi-pass FCAW	12–20 mm	3–5 mm	15–30%	50–58 HRC	Moderate
Pre-formed powder block FCAW	6–12 mm	5–8 mm	<5%	55–65 HRC	Low–Moderate
Explosive cladding	6–10 mm	3–6 mm	0%	55–65 HRC	High
Thermal spray	6–12 mm	1–3 mm	0%	55–65 HRC	Moderate

The pre-formed powder block method offers a favorable balance of performance and cost, particularly for medium production volumes where the capital investment in explosive cladding equipment is not justified.

Engineering Applications and Quality Control

This technology is particularly suited for:

Wear plates for mining equipment (bucket liners, conveyor chutes)
Abrasion-resistant linings for material handling systems
Thin-shell components where weight reduction is important
Repair of worn thin-walled components where conventional overlay would distort the part

Quality control requirements include:

Visual inspection: Verify uniform coverage, absence of unmelted areas, and proper bead geometry
Hardness mapping: Measure hardness at multiple points across the overlay surface to verify uniformity (variation should be within ±3 HRC)
Bond strength testing: Peel or shear testing to verify adequate bonding between overlay and substrate
Dimensional verification: Confirm that substrate distortion is within acceptable limits (flatness ≤ 1 mm/m for typical applications)
Impact testing: For applications involving impact loading, verify that the composite plate can withstand specified impact energy without delamination

Study Insights and Implications

This paper represents a creative engineering solution to a persistent manufacturing challenge. The concept of using a pre-formed material block as a "soft" deposit source—where only the surface is melted while the bulk consolidates through plastic deformation—is elegant in its simplicity and effective in its execution. The technique leverages the well-established FCAW process while introducing a novel material delivery method that fundamentally changes the dilution equation.

For engineers in the steel pipe and pipe fitting industry, this technology has direct relevance to the manufacture of wear-resistant pipe linings. Pipelines transporting abrasive slurries (mining tailings, coal-water mixtures, cement slurry) require internal or external wear protection, and the ability to apply thick, low-dilution overlay layers to thin-walled pipe sections is a significant advantage over conventional multi-pass hardfacing.

The technique also aligns with modern manufacturing trends toward hybrid processes that combine the benefits of multiple manufacturing methods. By pre-forming the hardfacing material (through powder metallurgy or casting) and then consolidating it through welding, the process achieves properties that neither method alone could provide.

One area for further development is the automation of this process for production-scale manufacturing. The manual or semi-automated application described in the paper is suitable for prototype and small-batch production, but large-scale deployment would benefit from robotic implementation with consistent powder block placement and welding parameter control.

This collection of five studies spans the breadth of hardfacing and overlay welding technology, from large-scale industrial repair of heavy equipment to advanced alloy development and innovative manufacturing techniques. Together, they illustrate the fundamental engineering principle that successful hardfacing application requires integration of metallurgical knowledge, process expertise, and practical field experience. The common thread across all five papers is that the optimal hardfacing solution is one that balances performance requirements with economic constraints, and that this balance is achieved through careful alloy selection, disciplined process execution, and rigorous performance verification. Engineers working in steel pipe, pipe fitting, and welding technology should draw upon these studies as practical references for addressing similar challenges in their own applications, while always remembering that field conditions rarely match laboratory assumptions and that continuous learning from service experience remains the most valuable qualification tool available.