Research Progress on High-Chromium Cast Iron Blade Cladding Process

Literature Overview

The 2024 review article by Gao Jichang and colleagues from Jinan University and Zibo Dayan Metal Technology Co., Ltd., published in Materials Reports, provides a comprehensive overview of the research progress in high-chromium cast iron blade cladding technology. High-chromium cast irons (HCIs), typically containing 12-30% Cr, are widely used for wear-resistant blades in mining, cement, power generation, and material handling applications. The cladding of these blades with additional wear-resistant materials is a critical technology for extending service life and reducing maintenance costs. This review synthesizes research findings from multiple funding sources including Shandong Provincial Natural Science Foundation Key Project (ZR2020KE022), Shandong Provincial Natural Science Foundation General Project (ZR2021ME179), and National Natural Science Foundation of China General Project (52175408).

Background and Application Context

High-chromium cast iron blades are employed in a wide range of industrial applications where severe abrasive wear is encountered:

• Mining industry: Shovel teeth, excavator blades, and crusher components operating in abrasive ore and rock.
• Cement industry: Mill liners, grinder blades, and conveyor components exposed to cement clinker and aggregates.
• Power generation: Coal handling equipment, ash handling blades, and flue gas duct components.
• Material handling: Conveyor belt cleaners, scraper blades, and chute linings.

The base high-chromium cast iron typically contains 12-27% Cr, 2-4% C, and 1-3% Mo, with microstructures consisting of martensite and carbides (M7C3, M23C6). While inherently wear-resistant, the hardness and wear resistance can be further enhanced through cladding with specialized wear-resistant materials.

Cladding Methods and Process Technologies

The review covers several cladding methods applied to high-chromium cast iron blades, each with distinct characteristics:

Submerged Arc Welding (SAW)

SAW remains the most widely used method for large-scale blade cladding due to its high deposition rate and low cost. The process involves applying a flux-covered wire or strip of wear-resistant material to the blade surface. Common consumables include high-carbon, high-chromium wires (e.g., 25-30% Cr, 3-5% C) that produce hard martensitic carbide-rich deposits. The dilution rate in SAW is typically 15-25%, which is acceptable given the high hardness of the base material.

Plasma Transferred Arc (PTA) Cladding

PTA offers superior dilution control (5-10%) and surface quality, making it suitable for applications where precise compositional control is required. The process uses a focused plasma arc to melt a powder consumable fed into the arc zone. The high energy density produces a dilution-free or low-dilution cladding layer with excellent metallurgical bonding. PTA is particularly advantageous for cladding complex blade geometries where access is limited.

Laser Cladding

Laser cladding provides the lowest dilution rates (2-5%) and finest microstructures, resulting in superior mechanical properties. However, the limited penetration depth and deposition rate limit its application to thin cladding layers (typically 1-3 mm). Multi-layer deposition is required for substantial thicknesses, increasing processing time and cost. Laser cladding is most suitable for high-value blades where maximum wear resistance is required.

Microstructure and Wear Mechanisms

The wear resistance of cladded high-chromium cast iron blades is primarily determined by the microstructure of the cladding layer, which consists of:

• Martensite matrix: Provides the base hardness and toughness.
• M7C3 carbides: Primary wear-resistant phase, appearing as blocky or skeletal morphologies depending on solidification conditions.
• M23C6 carbides: Secondary phase that may form during cooling or post-weld heat treatment.
• Austenite: Residual phase that may transform to martensite during service or heat treatment.

The wear mechanisms operating in HCI blade service include:

1. Abrasive wear: Dominant mechanism in most applications, where hard particles in the slurry or material being handled scratch and gouge the surface.
2. Erosive wear: Occurs when particles impact the surface at high velocity, causing material removal through plastic deformation and fracture.
3. Adhesive wear: Less common but significant in high-load applications where surface asperities weld and tear.
4. Corrosive wear: Occurs in environments where chemical attack accelerates material removal.

The hardness of the cladding layer, typically in the range of 60-70 HRC for optimized compositions, provides the primary resistance to abrasive wear. The distribution and morphology of carbides are equally important, as they provide the hard phases that resist particle penetration.

Process Optimization and Quality Control

The review emphasizes several key aspects of process optimization:

• Preheating: Substrate preheating to 200-300°C is recommended to reduce thermal stresses and prevent cracking, particularly for thick blades or high-strength substrates.
• Travel speed optimization: Higher travel speeds reduce heat input and dilution but may lead to incomplete fusion and porosity. A balance must be struck based on the specific consumable and substrate combination.
• Multi-pass strategies: For substantial cladding thicknesses, multiple passes with overlapping beads are employed. The interpass temperature should be controlled to prevent excessive grain growth and sensitization.
• Post-weld heat treatment: A tempering treatment at 500-600°C for 1-2 hours is often applied to reduce residual stresses while maintaining hardness. For some applications, a subcritical anneal may be used to optimize the carbide distribution.

Quality control measures include:

Engineering Practice and Industrial Applications

The review discusses several industrial case studies demonstrating the effectiveness of HCI blade cladding:

• Mining shovel teeth: Cladding with high-carbon, high-chromium consumables increased service life by 3-5 times compared to uncladded teeth, reducing replacement frequency and downtime.
• Cement mill liners: PTA cladding with specialized wear-resistant powders achieved 50-70% life extension over conventional cast liners.
• Coal handling scrapers: Laser cladding with carbide-reinforced alloys provided 4-6 times improvement in wear life for critical scraper blades.

The economic analysis presented in the review demonstrates that the additional cost of cladding is typically recovered within the first maintenance interval, making it a cost-effective solution for critical wear components.

Study Insights and Reflections

This comprehensive review provides a valuable synthesis of the current state of knowledge in HCI blade cladding technology. The key insight is that the selection of cladding method and consumable must be driven by a systematic evaluation of the service conditions, including wear mechanism, load severity, and environmental factors. The review also highlights the importance of process optimization and quality control in achieving consistent cladding performance. For engineers involved in the design and maintenance of wear-critical components, the findings underscore the potential for significant life extension and cost savings through appropriate cladding technology application. The ongoing research in advanced consumable development and process control technologies promises further improvements in cladding performance and reliability.