CLADDING TECHNOLOGY SHANXI CO., LTDCladding Repair of Hot Shearing Blades Using Weld Overlay Techniques
Literature Overview
This study, authored by Wan Weiguo from the Steel Research Institute of Maanshan Steel Company in 1992, addresses the critical industrial challenge of restoring worn hot shearing blades through weld overlay cladding techniques. Hot shearing blades operate under extreme thermal cycling, mechanical impact, and abrasive contact with hot steel, leading to accelerated wear at the cutting edge. The economic cost of replacing entire blades is substantial, making repair through cladding a highly attractive alternative. This early work represents one of the pioneering applications of weld overlay in Chinese heavy industry, reflecting the practical engineering philosophy of the era.
Core Technical Content
The fundamental approach involves depositing a wear-resistant and heat-resistant alloy layer onto the worn cutting edges of hot shearing blades using arc welding overlay processes. The selection of cladding materials is governed by several critical factors, including thermal conductivity matching with the base steel, resistance to thermal shock at operating temperatures exceeding 900°C, and the ability to maintain a sharp cutting edge under repeated impact loading.
Cladding Material Selection Criteria
| Parameter | Requirement | Rationale |
|---|---|---|
| Operating temperature | >900°C | Blades contact hot rolled steel |
| Thermal conductivity match | Within 20% of base steel | Minimize thermal stress at interface |
| Hardness retention at temperature | >40 HRC at 600°C | Maintain cutting ability |
| Thermal fatigue resistance | >500 cycles without cracking | Resist thermal cycling |
| Toughness | Sufficient to resist impact | Prevent catastrophic fracture |
Process Parameters and Considerations
The welding process parameters must be carefully controlled to ensure proper bond strength and minimize dilution of the cladding alloy. Key parameters include welding current, arc voltage, travel speed, and interpass temperature. For hot shearing blade repair, the following general guidelines apply:
- Preheating temperature: 200–300°C to reduce residual stress and prevent cracking
- Interpass temperature: Maintain below 350°C to avoid grain coarsening
- Post-weld cooling rate: Controlled slow cooling to minimize thermal gradients
- Number of overlay passes: Typically 2–3 layers for adequate thickness and composition control
- Post-weld heat treatment: Stress relief at 550–650°C for 1–2 hours
Metallographic Analysis and Defect Assessment
The interface between the base steel and the cladding layer is the most critical region for structural integrity. Dilution from the base metal can significantly alter the composition of the first overlay layer, potentially reducing hardness and wear resistance. Metallographic examination reveals the microstructure evolution from the base steel through the dilution zone into the fully alloyed cladding layer. Common defects observed include:
- Lack of fusion at the root layer due to insufficient preheating
- Cracking in the cladding layer due to high carbon and alloy content
- Pores caused by hydrogen pickup during welding
- Excessive dilution leading to reduced hardness in the first pass
Engineering Practice Integration
From a practical standpoint, the repair of hot shearing blades through cladding offers significant economic benefits compared to full blade replacement. The typical service life extension achieved through proper cladding repair is 2–3 times that of the worn blade before repair. However, the success of the repair depends heavily on the operator's skill in controlling process parameters and the quality of the cladding consumables used.
A systematic approach following the PDCA cycle can be applied: Plan the repair procedure based on wear pattern analysis, Do the cladding with controlled parameters, Check the repair quality through hardness testing and visual inspection, and Act by refining procedures based on service performance feedback.
Key Reflections and Study Insights
This 1992 study represents an important milestone in the application of cladding technology in China's steel industry. The practical orientation of the research reflects the engineering challenges of that era, where economic efficiency was paramount. Modern cladding technologies, including laser cladding and plasma transferred arc welding, have significantly improved the quality and consistency of blade repair, but the fundamental principles established in this work remain valid. The emphasis on material selection, process control, and quality verification continues to guide contemporary cladding engineering practice. The study also highlights the importance of field experience in developing effective repair procedures, as laboratory testing alone cannot capture the full complexity of industrial service conditions. Understanding the historical evolution of cladding technology provides valuable context for appreciating the sophistication of modern approaches and the enduring relevance of fundamental metallurgical principles in engineering practice.