CLADDING TECHNOLOGY SHANXI CO., LTDHot Forging Die Cladding Materials and Process Research and Application
Literature Overview
This 1992 publication from the Harbin Welding Research Institute, authored by Liu Renpei, Feng Zhimin, Pan Yongming, He Shi, and Dong Zuyue, represents a foundational contribution to the field of hot forging die surface engineering. The work addresses the critical challenge of extending die service life through weld overlay technology, which was a major industrial concern in China's heavy machinery and automotive sectors during the early 1990s. The study systematically investigates the selection of cladding materials, process parameters, and practical applications for hot forging dies subjected to extreme thermal and mechanical loading conditions.
Core Technical Content
Hot forging dies experience a combination of cyclic thermal stress, mechanical impact, abrasive wear, and chemical interaction with the workpiece material. The die surface temperature can reach 800-1000°C during forging operations, while the die body remains relatively cool, creating severe thermal gradients. This publication examines the use of high-speed steel, martensitic stainless steel, and nickel-based superalloy materials as overlay coatings on carbon and low-alloy steel die blanks.
The key process routes investigated include:
- Submerged arc welding (SAW) with multiple passes for thick overlay layers (typically 5-15 mm)
- Electroslag welding (ESW) for building up large areas of overlay on flat die surfaces
- Gas metal arc welding (GMAW) for localized repair and selective cladding
- Flame-cutting followed by plasma arc welding for precise surface preparation
Material Selection Criteria
| Overlay Material | Hardness (HRC) | Hot Hardness at 600°C | Thermal Fatigue Resistance | Typical Application |
|---|---|---|---|---|
| H13 (4Cr5MoSiV1) | 48-52 | Good | Excellent | General hot forging dies |
| 4Cr5W2VSiRE | 50-55 | Very Good | Excellent | High-temperature die faces |
| Cr12MoV | 55-60 | Moderate | Good | Impact-resistant die areas |
| Inconel 625 | 35-40 (solution treated) | Good | Outstanding | Severe thermal cycling zones |
| Stellite 6 | 40-45 | Very Good | Good | Abrasion-critical regions |
Process Parameters and Weldability Considerations
The research emphasizes the critical importance of preheating and interpass temperature control when cladding hardenable materials onto carbon steel substrates. For H13-based overlays on C45 or 45 steel die blanks, a preheat temperature of 250-350°C is recommended, with interpass temperatures maintained between 150-250°C to prevent cold cracking in the heat-affected zone. The dilution rate between the base metal and the overlay layer is a primary concern, as excessive dilution degrades the overlay's hot hardness and thermal fatigue resistance.
A multi-layer approach is typically employed, with the first layer serving as a transition buffer to reduce residual stresses and minimize dilution effects. The first layer often uses a material with better ductility, such as a nickel-based alloy or austenitic stainless steel, followed by the functional overlay layers. This approach reduces the risk of cracking at the bond line, which is the most common failure mode in die cladding applications.
Engineering Practice and Quality Control
In practical application, the following quality control measures are essential:
- Surface preparation: The die surface must be ground to remove scale, decarburized layers, and any pre-existing cracks. A smooth, oxide-free surface is critical for metallurgical bonding.
- Post-weld heat treatment: After cladding, the entire die assembly must be subjected to a tempering or solution treatment cycle to relieve residual stresses and optimize the microstructure of both the overlay and the heat-affected zone.
- Non-destructive testing: Magnetic particle inspection (MT) is applied to detect surface cracks, while ultrasonic testing (UT) is used to verify bond integrity and detect subsurface defects.
- Hardness verification: Cross-sectional hardness profiles must be measured to confirm that the overlay hardness meets specifications and that the transition zone is gradual rather than abrupt.
The study documents successful applications on automotive engine block forging dies, where the service life was extended from approximately 5,000-8,000 strokes (uncladded) to 30,000-50,000 strokes with proper overlay protection. This represents a five- to eight-fold improvement in productivity, justifying the additional cost of the cladding process.
Key Reflections
This early work from 1992 established important principles that remain relevant today. The emphasis on dilution control, transition layer design, and post-weld heat treatment continues to be the foundation of successful die cladding practice. The multi-layer strategy with a buffer layer is now considered standard practice in modern die repair operations. The study also highlights the importance of matching the overlay material's properties to the specific service conditions of each die region, rather than applying a uniform coating across the entire surface. This selective cladding approach, which recognizes that different areas of a die experience different types of wear and damage, is a principle that has been further refined in subsequent decades of research and practice.