Effect of Different Treatment Processes on Microstructure and Wear Resistance of High-Alloy Cladding Layers: A Study Note

Literature Overview and Research Significance

The research by Wu Taiyong and Li Guoxue (2015) from Chongqing Huayu Electrical Group examines the influence of different post-weld treatment processes on the microstructure and wear resistance of high-alloy cladding layers. Published in Hot Working Technology, this study addresses a fundamental question in overlay engineering: how can the mechanical properties and service performance of a cladding layer be optimized through post-weld processing?

High-alloy cladding layers are widely used in applications requiring extreme wear resistance, such as mining equipment, cement mill liners, and industrial pumps. The as-welded microstructure of these overlays often contains a non-equilibrium mixture of phases that may not provide optimal wear performance. Post-weld heat treatment can significantly alter the phase composition, carbide distribution, and hardness profile, thereby enhancing the service life of the cladded component.

Post-Weld Treatment Methods Evaluated

The study evaluates several post-weld treatment methods, each with distinct effects on the overlay microstructure:

Each treatment method produces a distinct microstructural response, which in turn affects the wear resistance of the overlay. The selection of the optimal treatment method depends on the specific composition of the overlay material, the substrate material, and the service conditions.

Microstructural Analysis and Phase Evolution

The microstructure of high-alloy cladding layers is characterized by the presence of multiple phases, including martensite, austenite, ferrite, and various carbide types. The post-weld treatment significantly influences the distribution, morphology, and volume fraction of these phases.

As-Welded Microstructure

The as-welded overlay typically exhibits a dendritic solidification structure with:

• Primary carbides: Large (50-200 μm) Cr₇C₃, Mo₂C, or VC particles formed during solidification.
• Matrix: A mixture of martensite and retained austenite, depending on the cooling rate and alloy composition.
• Secondary carbides: Fine particles precipitated during cooling, often along grain boundaries.
• Segregation zones: Localized enrichment of alloying elements at dendrite boundaries.

Effect of Solution Treatment

Solution treatment at 1100-1200°C dissolves most of the secondary carbides and partially dissolves the primary carbides, resulting in a more homogeneous composition. The retained austenite fraction increases due to the high temperature exposure. However, excessive solution treatment can lead to grain coarsening and a reduction in hardness.

Effect of Aging Treatment

Aging treatment at 800-950°C promotes the precipitation of fine carbide particles from the supersaturated matrix. These fine precipitates provide significant strengthening through Orowan strengthening and precipitation hardening mechanisms. The aging treatment can increase the hardness of the overlay by 100-200 HV compared to the as-welded condition.

Effect of Quenching and Tempering

Quenching from 850-950°C produces a fully martensitic matrix, while tempering at 200-600°C controls the carbide precipitation and residual stress relief. The tempering temperature is critical: low tempering temperatures (200-300°C) produce fine carbides and high hardness, while high tempering temperatures (500-600°C) produce coarser carbides and improved toughness.

Effect of Cryogenic Treatment

Cryogenic treatment at -196°C transforms retained austenite to martensite, increasing the overall hardness and reducing the retained austenite fraction. This treatment is particularly effective for overlays with high carbon and alloy content, where significant retained austenite is present in the as-welded condition.

Wear Performance Evaluation

The wear resistance of the cladding layer is evaluated through standardized wear testing, typically using dry sliding wear against alumina balls or abrasion testing with alumina slurry. The following table summarizes the typical wear performance results:

The results demonstrate that aging treatment provides the most significant improvement in wear resistance, followed by combined aging and cryogenic treatment. Solution treatment alone may reduce wear resistance due to the dissolution of strengthening carbides without subsequent precipitation hardening.

Engineering Practice and Process Selection

The selection of the optimal post-weld treatment method depends on several factors:

1. Overlay composition: High-carbon, high-alloy overlays respond well to aging treatment, while lower-alloy overlays may benefit more from quenching and tempering.
2. Substrate compatibility: The thermal expansion mismatch between the overlay and substrate must be considered when selecting treatment temperatures to avoid cracking or delamination.
3. Component geometry: Thick sections may require slower cooling rates to prevent thermal cracking, while thin sections can tolerate more aggressive treatment cycles.
4. Service conditions: Applications requiring high impact resistance may benefit from tempering at higher temperatures, while pure abrasion applications can tolerate higher hardness.

A typical optimized treatment sequence for high-alloy cladding layers is:

1. Solution treatment: 1150°C for 1 hour to homogenize the composition.
2. Aging treatment: 900°C for 3 hours to precipitate fine strengthening carbides.
3. Cryogenic treatment: -196°C for 4 hours to transform retained austenite.
4. Tempering: 200°C for 2 hours to relieve residual stresses from cryogenic treatment.

This combined treatment produces a microstructure with high hardness, fine carbide distribution, and minimal retained austenite, resulting in superior wear resistance.

Quality Control and Defect Prevention

Post-weld treatment introduces additional quality risks that must be managed:

Summary and Implications

The research by Wu and Li demonstrates that post-weld treatment is a critical factor in determining the wear performance of high-alloy cladding layers. The aging treatment, particularly when combined with cryogenic treatment, provides the most significant improvement in hardness and wear resistance. The microstructural mechanisms behind these improvements—precipitation of fine carbides and transformation of retained austenite—are well understood and can be controlled through careful selection of treatment parameters. This study provides valuable guidance for engineers designing cladding processes for wear-critical applications, emphasizing the importance of post-weld processing in achieving optimal overlay performance. The findings are directly applicable to industrial applications in mining, cement, and power generation, where extended service life of cladded components translates to significant economic benefits.