CLADDING TECHNOLOGY SHANXI CO., LTDWear-Resistant Cladding Repair Technology for Cold Rolling Mill Rolls
Overview of the Literature
This 2006 study by Yu Chengkui of Wuhan University of Technology and Yang Zhenlin of the Tianjin Quality and Technical Supervision Bureau addresses a critical industrial problem: the restoration of worn cold rolling mill rolls through weld overlay cladding. Cold rolling mill rolls operate under extreme contact stress, abrasion, and thermal cycling, which progressively erodes the working surface and degrades strip surface quality. The authors propose a systematic repair cladding approach that combines substrate preparation, consumable selection, process parameter optimization, and post-weld treatment to restore functional performance.
Core Technical Approach
The fundamental challenge in cold roll repair cladding lies in achieving a hard, wear-resistant surface layer while maintaining adequate metallurgical bonding with the high-alloy cast steel substrate. Cold roll materials typically fall into categories such as chromium cast iron (e.g., 42CrMo or equivalent), high-speed steel, and cemented carbide-bonded substrates, each presenting different welding compatibility issues.
The repair strategy follows a multi-step sequence:
- Surface preparation: Grinding away the worn zone to expose sound base metal, followed by thorough cleaning to remove oxide scale and lubricant residue.
- Substrate preheating: Typically 250–400 °C depending on roll material and thickness, to reduce residual stress and minimize cracking risk.
- Transition layer deposition: A compatibility layer of austenitic stainless steel or nickel-based alloy is applied to bridge the metallurgical gap between the high-carbon substrate and the hard-facing overlay.
- Wear-resistant overlay: Hard-facing layers using cobalt-based (e.g., Stellite), chromium-carbide-based, or tungsten-carbide-reinforced consumables are deposited to achieve target hardness of 55–70 HRC.
- Post-weld treatment: Controlled cooling or tempering to relieve residual stresses without softening the overlay excessively.
Key Process Parameters and Consumable Selection
The following table summarizes typical process windows and consumable options identified in the study:
| Parameter | Recommended Range | Rationale |
|---|---|---|
| Substrate preheat temperature | 250–400 °C | Reduces cracking susceptibility in high-carbon substrates |
| Interpass temperature | ≤ 300 °C | Prevents excessive grain growth and cracking |
| Shielding gas (GTAW/SMAW) | Argon or Ar-2%O₂ | Ensures clean weld and appropriate arc stability |
| Heat input per pass | 0.5–1.5 kJ/mm | Minimizes dilution and maintains hard phase integrity |
| Overlay thickness per pass | 1.0–2.5 mm | Balances deposition rate with bonding quality |
| Post-weld tempering | 400–500 °C for 2 h | Relieves residual stress without significant hardening loss |
Consumable selection depends on the specific wear mechanism:
- Abrasive wear (rolling of low-carbon strip): Tungsten carbide–reinforced nickel or cobalt consumables provide superior hardness and wear resistance.
- Galling and adhesion (rolling of stainless or aluminum strip): Nickel-based hard-facing alloys with controlled carbide distribution reduce adhesion tendency.
- Combined wear and corrosion: Cobalt-based Stellite alloys offer balanced performance.
Common Defects and Countermeasures
The study identifies several recurring defects in cold roll repair cladding:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking in transition layer | High carbon content of substrate, excessive cooling rate | Increase preheat, use nickel-based transition consumable, reduce heat input |
| Porosity in overlay | Inadequate shielding, contaminated surface | Improve gas flow, mechanical cleaning, dry flux |
| Excessive dilution | High heat input, thin base metal preparation | Reduce current, increase travel speed, add more transition passes |
| Hardness variation across surface | Inconsistent consumable feed rate or arc length | Use automated or semi-automated deposition, monitor parameters |
| Bonding failure | Poor surface preparation, oxide inclusion | Thorough grinding to bare metal, acid pickling if needed |
Engineering Practice Implications
From a practical standpoint, this literature reinforces several principles that are equally applicable to modern cladding operations. First, the transition layer concept is not optional but essential when welding dissimilar materials with large differences in carbon equivalent and thermal expansion. Second, the interpass temperature control is a critical but frequently overlooked parameter; exceeding 300 °C in hard-facing applications leads to significant softening of the carbide network. Third, the study highlights the importance of post-weld mechanical finishing (grinding and polishing) to achieve the surface roughness required for strip quality, typically Ra ≤ 0.4 μm for precision cold rolling.
A notable insight from this work is the emphasis on process documentation and traceability, which the authors connect to quality supervision practices from the Tianjin Quality and Technical Supervision Bureau. In modern practice, this translates to the requirement for weld procedure qualification (WPQ) under standards such as NB/T 47014 or ASME IX, with documented parameter control throughout the repair operation.
Study Insights
The value of this 2006 study lies in its systematic approach to a well-known but persistently challenging problem. Cold roll repair cladding remains a high-stakes operation where failure can lead to production downtime costing thousands of dollars per hour. The authors' framework of substrate preparation, transition layer design, overlay selection, and post-weld treatment provides a transferable methodology that can be adapted to other heavy-duty cladding applications such as hot roll repair, forging die restoration, and mining equipment overlay. The integration of metallurgical understanding with practical process control parameters makes this reference particularly useful for engineers who need to develop or revise repair procedures.