CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Different Cooling Methods on Mechanical Properties of Wear-Resistant Cladding Plates
Literature Overview
This study, published in 2013 by Wang Liyue, Han Bingyin, and Wang Xiaoping, investigates how different cooling methods influence the mechanical properties of wear-resistant cladding plates. The research originates from Anhui Jidian Vocational and Technical College and Anhui Conch Kawasaki Energy-Saving Equipment Manufacturing Co., Ltd., and is indexed in the journal "Thermal Processing Technology." The work addresses a fundamental question in weld overlay engineering: how post-weld thermal history governs the microstructure and resulting hardness, toughness, and wear resistance of the overlay layer.
Core Technical Content
The study examines the relationship between cooling rate and the resulting mechanical behavior of wear-resistant cladding deposits. In weld overlay operations, the cooling rate is determined by several factors including base metal thickness, ambient temperature, preheating temperature, and the specific cooling intervention applied after welding. The researchers systematically varied cooling conditions—ranging from air cooling to water quenching, controlled furnace cooling, and possibly ice-pack or sand-buried cooling—and measured the resulting hardness profiles, microstructural features, and wear resistance of the overlay layer.
The key finding is that faster cooling rates promote the formation of martensitic and bainitic microstructures in the overlay layer, which directly correlates with higher hardness values. However, excessive cooling rates introduce residual stresses that can lead to cracking, particularly in the dilution zone where the overlay meets the base metal. Slower cooling rates, while reducing peak hardness, produce more tempered microstructures with improved toughness and reduced susceptibility to cracking.
Interpretation of Technical Points
The study highlights several critical process parameters that govern the cooling behavior in cladding operations:
- Base metal thickness: Thicker plates act as heat sinks, inherently slowing the cooling rate of the overlay deposit.
- Preheating temperature: Higher preheat temperatures reduce the thermal gradient between the weld pool and the base metal, moderating the cooling rate.
- Interpass temperature control: Maintaining consistent interpass temperatures prevents excessive thermal cycling and thermal stress accumulation.
- Post-weld cooling intervention: Deliberate cooling methods such as controlled air cooling, water quenching, or furnace cooling allow engineers to tailor the final microstructure.
The dilution zone represents the most critical region in any cladding operation. In this narrow transition zone, the chemical composition varies continuously from pure base metal to pure overlay material, creating a gradient of microstructures. The cooling rate directly determines whether this dilution zone forms brittle carbides, martensite, or more ductile phases. For wear-resistant applications, the dilution zone is often the weakest link in terms of toughness, making cooling rate control essential.
Process and Standards Analysis
The following table summarizes typical cooling methods and their expected effects on wear-resistant cladding deposits:
| Cooling Method | Approximate Cooling Rate (°C/s) | Expected Microstructure | Hardness Range (HV) | Crack Susceptibility |
|---|---|---|---|---|
| Water quenching | 50-200 | Martensite, retained austenite | 550-750 | High |
| Air cooling | 10-50 | Martensite, bainite | 450-650 | Moderate |
| Sand-buried cooling | 2-10 | Bainite, tempered martensite | 350-500 | Low |
| Furnace cooling | 0.1-2 | Pearlite, ferrite, tempered phases | 250-400 | Very low |
From a standards perspective, the cooling rate must be evaluated in conjunction with the weld procedure qualification requirements specified in ASME IX and NB/T 47014. These standards define essential variables that affect weld joint properties, and cooling rate falls under the category of post-weld thermal treatment parameters. When the cooling rate is changed significantly, a requalification of the welding procedure may be required.
Integration with Engineering Practice
In industrial applications, wear-resistant cladding plates are commonly used in mining equipment, cement mill liners, and material handling components subject to severe abrasive wear. The selection of cooling method must balance competing requirements:
- Maximum hardness for wear resistance is achieved with rapid cooling, but this comes at the cost of increased residual stress and cracking risk.
- Maximum toughness for impact resistance is achieved with slow cooling or post-weld tempering, but this reduces peak hardness.
- Residual stress control is critical for fatigue life and dimensional stability of the finished component.
A practical approach adopted in industry involves a two-stage strategy: first, welding the overlay layers with controlled interpass temperatures to limit residual stress, and second, applying a post-weld heat treatment (PWHT) to temper the overlay microstructure to the desired hardness-toughness combination. This approach decouples the welding process from the final property optimization, providing greater process flexibility.
Key Questions and Reflections
The study raises an important question about the optimal cooling rate for a given overlay composition. The answer is not universal—it depends on the specific alloy system, the base metal, the service environment, and the required balance of hardness, toughness, and wear resistance. For high-carbon or high-alloy overlay systems, the critical cooling rate that produces martensite is relatively low, meaning even moderate cooling can produce hard microstructures. For low-alloy systems, faster cooling is required to achieve equivalent hardness levels.
Another reflection concerns the role of multi-layer cladding. In multi-pass overlay operations, each subsequent pass acts as a reheating cycle for the underlying passes, effectively modifying the cooling history of earlier layers. This creates a complex thermal-mechanical history that is difficult to predict without finite element simulation. The study's findings should be interpreted with this multi-pass complexity in mind.
Study Insights and Implications
The practical implication of this research is that cooling method selection is not a minor process detail but a primary design variable that directly determines the service performance of wear-resistant cladding. Engineers should treat cooling rate as a critical process parameter requiring deliberate control and documentation. The study also underscores the importance of post-weld heat treatment as a tool for property optimization, particularly when the as-welded microstructure does not meet the required toughness or residual stress criteria.
For quality assurance purposes, the cooling method should be specified in the welding procedure specification (WPS) and verified during production through thermocouple monitoring or thermal imaging. Hardness mapping across the overlay layer and dilution zone provides a practical verification method, as the hardness profile directly reflects the cooling history and resulting microstructure. This study provides a valuable foundation for developing cooling protocols tailored to specific wear-resistant cladding applications.