Performance of High-Chromium Cast Iron/Low-Carbon Steel Wear-Resistant Composite Plate Prepared by Surfacing and Hot Rolling

Literature Overview

This study, published in the Journal of Plasticity Engineering (2019, Vol. 26, No. 5, pp. 141–146), investigates a hybrid manufacturing approach combining surfacing with subsequent hot rolling to produce wear-resistant composite plates. The research team from the Shanxi Provincial Key Laboratory of Metallurgical Equipment Design Theory and Technology used high-chromium cast iron welding electrodes to deposit a surfacing layer on carbon steel plates, followed by symmetric stacking and multi-pass hot rolling on a four-high mill at reduction rates of 15%, 25%, and 30%. Characterization included SEM observation with EDS point and line scanning of the bonding interface and high-chromium iron layer, along with mechanical property testing.

Manufacturing Process Description

The manufacturing sequence follows a rational progression from surfacing through consolidation:

1. Surfacing: High-chromium cast iron (typically 20–30% Cr, 2–3% C) deposited onto low-carbon steel (Q235 or similar) base plates using SMAW or FCAW processes with appropriate electrode selection (e.g., D307-type or equivalent).
2. Symmetric stacking: Surfaced plates arranged with hardfacing layers facing inward to create a sandwich configuration.
3. Hot rolling: Multi-pass reduction on a four-high mill at elevated temperature (typically 1100–1200°C for the steel substrate, which may require reheating after surfacing).
4. Cooling: Controlled cooling rate to manage the final microstructure of both the steel substrate and the high-chromium iron layer.

Key Microstructural Findings

The study reports several important microstructural transformations induced by hot rolling:

Interface healing and improvement: Pre-existing cracks and voids at the original surfacing bonding interface are eliminated through plastic deformation during rolling. This is a critical finding because surfacing deposits inherently contain solidification defects (porosity, microcracks, lack of fusion) that compromise interfacial bond strength. The hot rolling process effectively consolidates these defects through hot working, analogous to the consolidation mechanism in diffusion bonding or hot isostatic pressing but achieved through conventional rolling equipment.

Carbide network breakdown: The eutectic carbide network (M7C3 chains) characteristic of as-cast high-chromium cast iron is fractured and dispersed during hot deformation. In the as-cast condition, the continuous M7C3 network provides hardness but severely limits ductility and fracture resistance. Hot rolling breaks this network into discrete, isolated carbide particles that maintain wear resistance while improving toughness.

Carbide-free zone formation: A carbide-free zone (CFZ) develops at the interface region, along with evidence of microstructural coexistence (organization symbiosis). The CFZ likely forms due to carbon diffusion from the high-chromium iron into the austenitic low-carbon steel during the hot rolling temperature exposure, creating a carbon-depleted zone adjacent to the steel substrate.

Shear strength improvement: The combination of defect healing, interface refinement, and plastic bonding results in significantly enhanced shear strength between the layers.

Engineering Practice Considerations

For pipeline and piping applications, this surfacing-rolling composite approach offers several advantages:

1. Cost-effective hardfacing: The base steel provides structural strength at low cost, while the high-chromium iron overlay provides wear resistance. This avoids the high cost of using high-chromium cast iron for the entire component.
2. Customizable thickness: The surfacing layer thickness (typically 3–15 mm) can be independently controlled from the substrate thickness, allowing optimization for specific service conditions.
3. Formability retention: Unlike cast high-chromium iron components, the composite plate retains some formability due to the ductile steel substrate, enabling bending and forming operations after manufacture.
4. Application suitability: Suitable for conveyor chutes, crusher liners, slurry pipes, and other components subjected to severe abrasive wear but requiring structural integrity.

However, several practical challenges must be addressed:

Key Questions and Critical Analysis

The study raises several questions regarding process scalability and long-term performance:

1. Thermal mismatch during service: The coefficient of thermal expansion difference between high-chromium cast iron (approximately 6.5–7.5 × 10⁻⁶/K) and low-carbon steel (approximately 12 × 10⁻⁶/K) creates thermal stresses during temperature cycling in service. The hot rolling process may partially relieve these stresses, but cyclic thermal loading will generate new stresses that could eventually cause interfacial delamination.
2. Reduction rate optimization: The study tests three reduction rates but does not identify a definitive optimum. Higher reduction rates (30%) likely provide better bonding but may thin the hardfacing layer excessively or introduce excessive work hardening. The optimal reduction rate depends on the specific application requirements for hardness, toughness, and remaining overlay thickness.
3. Rolling temperature window: The rolling temperature must be high enough to achieve plastic deformation of both materials but not so high as to cause excessive carbide coarsening in the high-chromium iron or austenite grain growth in the steel substrate. This window is typically narrow and requires careful process control.
4. Batch consistency: The surfacing quality (porosity, composition uniformity, layer thickness) directly affects the quality of the final composite plate. Statistical process control of the surfacing operation is essential for consistent composite plate quality.

Study Insights and Reference Value

This research demonstrates a practical and economically viable route to producing wear-resistant composite materials using conventional manufacturing equipment. The key insight—that hot rolling can simultaneously heal surfacing interface defects, refine the carbide network, and improve interfacial bonding—represents a significant process innovation. For the pipeline industry, this approach could be adapted to produce wear-resistant pipe sections for slurry service, mining applications, and material handling systems. The methodology also provides a template for other composite plate systems (e.g., Ni-based overlay/steel, Stellite/steel) where similar surfacing-rolling consolidation strategies may be applied. Engineers should note that this approach requires careful process development and qualification for each specific application, as the interplay between surfacing parameters, rolling conditions, and final microstructure is complex and system-specific.