CLADDING TECHNOLOGY SHANXI CO., LTDWear-Resistant Cladding Repair Process for Cold Rolling Rolls
Literature Overview
Cold rolling rolls experience extreme contact pressure, sliding friction, and thermal loading during steel strip production, leading to surface damage including galling, pitting, and wear that degrades strip surface quality and dimensional accuracy. This literature focuses on the cladding repair process for cold rolling rolls, examining welding procedure development, microstructural evolution, and wear performance evaluation of the overlay layers. The study addresses the unique challenges of roll repair cladding, including the need for high surface hardness, good bonding strength with the roll body, resistance to delamination under hydrodynamic lubrication conditions, and compatibility with subsequent grinding operations.
Welding Process Parameters and Procedure Development
The cladding repair of cold rolling rolls typically employs submerged arc welding (SAW) for build-up and gas metal arc welding (GMAW) or plasma transferred arc (PTA) for the final wear-resistant overlay layer. The process design must account for the cylindrical geometry of the roll, which creates variable heat input conditions as the arc traverses the curved surface. Preheating is generally not required for low-carbon steel roll bodies, but the thermal expansion mismatch between the roll body and the overlay material must be managed to prevent excessive residual stress.
| Process Parameter | SAW Build-up | GMAW Overlay | PTA Overlay |
|---|---|---|---|
| Current (A) | 400–600 | 180–260 | 180–300 |
| Voltage (V) | 28–35 | 22–28 | 18–24 |
| Travel speed (mm/min) | 200–400 | 300–600 | 400–800 |
| Wire/powder feed (g/min) | — | 200–400 | 150–300 |
| Shielding gas | Flux | Ar+CO2 | Ar |
| Typical layer thickness (mm) | 3–5 per pass | 1.5–3 per pass | 1.0–2.0 per pass |
The overlay material selection for cold rolling rolls typically involves chromium-based high-carbon alloys containing 12–20% Cr and 1.5–3.0% C, which form a high volume fraction of Cr7C3 and M7C3 carbides responsible for wear resistance. Alternatively, tungsten carbide composite powders applied via PTA provide exceptional abrasion resistance for severe service conditions. The critical requirement is that the overlay material must be grindable to achieve the precise surface finish (typically Ra 0.1–0.4 μm) required for cold rolling operations.
Microstructural Characteristics and Wear Mechanisms
The overlay layer microstructure consists of a eutectic matrix of martensite and primary carbides. The primary carbides, predominantly Cr7C3 with some M23C6, are distributed as angular or skeletal shapes in the martensitic matrix. The hardness of the composite structure typically reaches HV 1200–1600, providing excellent resistance to abrasive wear from steel strip surfaces. However, the brittle nature of the high-carbon martensitic structure means that the overlay must be designed to resist impact-induced cracking from strip edge contact and roll loading transients.
Wear mechanisms in cold rolling service include adhesive wear from steel strip contact, abrasive wear from surface contamination, and rolling contact fatigue from cyclic Hertzian contact pressure. The overlay design must address all three mechanisms simultaneously. The high volume fraction of hard carbides resists abrasive wear, while the ductile martensitic matrix accommodates plastic deformation and prevents carbide pullout that would initiate adhesive wear. The bonding strength between the overlay and roll body must exceed 200 MPa to prevent delamination under the tensile component of contact stress at the roll surface.
Grinding Compatibility and Surface Quality
A critical aspect of cold rolling roll cladding repair is the compatibility of the overlay material with subsequent grinding operations. The overlay must be ground to achieve the required cylindrical accuracy (typically within 0.01 mm diameter) and surface roughness without generating grinding-induced cracks or excessive subsurface damage. Materials with excessive carbide content or high hardness gradients are prone to grinding cracks that propagate into the overlay and compromise roll integrity. The study recommends a two-layer approach: a transition layer of lower carbon content (0.5–0.8% C) applied directly to the roll body, followed by the high-carbon wear-resistant overlay. This gradient design reduces thermal stress at the fusion boundary and improves grinding performance by providing a more ductile subsurface zone that arrests crack propagation.
Post-grinding inspection using magnetic particle testing (MT) or penetrant testing (PT) is essential to detect any grinding-induced surface cracks. The grinding parameters themselves must be carefully controlled: moderate wheel speed (30–40 m/s), low workpiece speed (20–30 m/min), and generous coolant flow to minimize grinding heat input that could alter the overlay microstructure and reduce hardness.
Study Insights and Reflections
This literature underscores the complexity of cold rolling roll repair cladding as a multidisciplinary challenge involving welding metallurgy, tribology, machining, and mechanical design. The key insight is that overlay material selection cannot be based solely on hardness values; the material must simultaneously satisfy wear resistance, bonding strength, thermal stability, and machinability requirements. Engineers must adopt a systems-level approach where each process step — from preheating through final grinding — is optimized in the context of the overall repair objective. The economic consideration of roll repair versus replacement also requires careful analysis of overlay life versus initial repair cost, as the wear life of a properly executed overlay can extend roll service life by multiple production campaigns, providing substantial cost savings over roll replacement.