CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Weld Overlay Metals on Cold Shearing Blades
Overview of the Study Topic
Cold shearing blades are critical components in sheet metal processing industries, subject to severe abrasive and adhesive wear during repeated shearing operations. The study of weld overlay metals applied to cold shearing blades addresses a practical engineering challenge: extending blade service life through surface engineering while maintaining cutting edge integrity. This literature examines the microstructural evolution and mechanical performance of overlay weld metals deposited on blade substrates, providing insights into the relationship between overlay composition, solidification behavior, and in-service wear resistance.
Core Technical Content
The investigation centers on the microstructure of overlay weld metals used to restore or enhance the surface properties of cold shearing blades. The overlay process typically involves multi-pass submerged arc welding or shielded metal arc welding with specialized consumables designed to produce hard, wear-resistant surfaces. The study examines how cooling rates, dilution effects from the base metal, and multi-pass thermal cycles influence the final microstructure.
Microstructural Analysis
The overlay weld metals exhibit a complex microstructure characterized by martensitic transformation products, retained austenite, and dispersed carbide phases. The high carbon and alloying element content (typically 1.5–2.5% C with Cr, Mo, and V additions) promotes the formation of fine carbide networks within a martensitic matrix. During multi-pass welding, the earlier deposited layers undergo tempering due to subsequent passes, leading to a gradient in hardness and microstructure across the overlay thickness.
| Microstructural Feature | Characteristic | Engineering Significance |
|---|---|---|
| Martensite | High hardness (HRC 55–65) | Primary wear-resistant phase |
| Retained Austenite | 5–15 vol% | Contributes to toughness, prevents cracking |
| M₇C₃ and M₂C Carbides | 1–3 μm size, network distribution | Abrasive wear resistance |
| Tempered Martensite (in lower layers) | HRC 45–55 | Improved toughness in deeper sections |
Mechanical Properties
The overlay metals achieve surface hardness values in the range of HRC 58–65, significantly exceeding the base blade steel (typically HRC 50–55 for high-carbon chrome steels). The hardness gradient across the overlay thickness is a critical finding: the top layer achieves maximum hardness due to rapid cooling, while lower layers show reduced hardness from tempering effects. This gradient is actually beneficial for cold shearing applications, as it provides a hard cutting surface with a tougher subsurface to resist chipping.
Engineering Practice Integration
In practical application, the overlay welding of cold shearing blades requires careful process control to manage several competing requirements. The cutting edge geometry must be preserved during welding, the overlay must not introduce excessive residual stresses that could cause cracking, and the hardness must be uniform across the working face. The study highlights that interpass temperature control (maintained between 150–250°C) is critical to prevent excessive grain growth while ensuring adequate heat input for proper fusion.
Process Parameters and Their Effects
| Parameter | Typical Range | Effect on Overlay Quality |
|---|---|---|
| Heat Input | 2.5–4.0 kJ/mm | Higher values increase dilution and reduce hardness |
| Interpass Temperature | 150–250°C | Exceeding 300°C causes excessive softening |
| Number of Passes | 3–5 | More passes increase total thickness but risk over-tempering |
| Welding Speed | 300–500 mm/min | Faster speed reduces dilution, improves hardness |
| Preheating | 100–200°C | Prevents cold cracking in high-carbon substrate |
Common Defects and Countermeasures
The primary defects observed in overlay welding of cold shearing blades include surface cracking, porosity, and insufficient bond strength at the overlay-substrate interface. Surface cracking is attributed to the high carbon content of the overlay metal combined with rapid cooling; this is mitigated through controlled preheating and post-weld stress relief at 550–600°C. Porosity formation is associated with inadequate flux coverage or contaminated base metal surfaces, and is addressed through rigorous surface preparation and proper flux selection.
Key Reflections and Study Insights
The most significant insight from this literature is the recognition that the multi-pass thermal cycle, while sometimes viewed as a source of variability, actually contributes beneficially to the overlay microstructure by creating a hardness gradient that balances wear resistance with chipping resistance. This challenges the conventional assumption that uniform properties are always desirable. Furthermore, the study underscores the importance of considering the entire service environment—not just hardness but also the resistance to plastic deformation under repeated shearing loads. The retained austenite fraction, often considered undesirable in hardfacing applications, plays a crucial role in accommodating the cyclic plastic strains experienced during shearing operations.
For engineers involved in blade maintenance and restoration, the practical implication is clear: the overlay welding process must be tailored not merely to achieve maximum hardness, but to create a microstructure with appropriate toughness reserves. This requires a holistic approach to consumable selection, process parameter optimization, and post-weld treatment that considers the specific loading conditions of cold shearing service.