CLADDING TECHNOLOGY SHANXI CO., LTDStudy on Microstructure and Properties of Cladding Layer on Hot Shear Blades
Literature Overview and Context
Hot shear blades are critical components in steel mills used for cutting hot steel billets and slabs. These blades operate under extreme conditions including high temperatures, severe abrasive wear, and impact loading. To extend blade life, wear-resistant cladding layers are applied to the cutting edges using various welding processes.
This study investigates the microstructure and properties of the cladding layer on hot shear blades, providing insights into the relationship between cladding composition, microstructure, and service performance. The study also evaluates the effectiveness of different cladding alloys and processes for this demanding application.
Core Technical Findings
Cladding Layer Microstructure
The study examines cladding layers produced using different welding processes and filler metals:
| Process | Filler Metal | Microstructure | Hardness (HV) |
|---|---|---|---|
| SAW | Fe-Cr-C (4C-18Cr) | Martensite + M₇C₃ carbides | 850–900 |
| FCAW | Fe-Cr-C (3C-15Cr) | Bainite + M₇C₃ carbides | 800–850 |
| Oxy-acetylene | Fe-Cr-C (5C-20Cr) | Martensite + M₇C₃ + Fe₃C | 900–950 |
| Laser cladding | Fe-Cr-C (4C-18Cr) | Fine martensite + fine carbides | 900–950 |
The microstructure is primarily composed of a hard matrix phase (martensite or bainite) with dispersed carbide particles. The type and distribution of carbides significantly influence the wear resistance of the cladding layer.
Service Performance Evaluation
The study evaluates the cladding layer performance based on field trials:
| Cladding Type | Service Life (hours) | Failure Mode | Relative Performance |
|---|---|---|---|
| SAW (4C-18Cr) | 120–150 | Abrasive wear | 1.0 |
| FCAW (3C-15Cr) | 100–130 | Abrasive wear | 0.85 |
| Oxy-acetylene (5C-20Cr) | 150–180 | Chipping | 1.2 |
| Laser cladding (4C-18Cr) | 180–220 | Abrasive wear | 1.5 |
Laser cladding provides the longest service life due to the fine microstructure and low dilution, while oxy-acetylene cladding offers good life but is susceptible to chipping due to the presence of brittle cementite.
Wear Mechanisms
The study identifies the primary wear mechanisms in hot shear blade cladding:
- Abrasive wear: The dominant mechanism, caused by contact with hot steel and scale.
- Oxidative wear: Oxidation at high temperatures leads to scale formation and material loss.
- Thermal fatigue: Repeated heating and cooling cycles cause thermal stresses and cracking.
- Impact wear: Occasional impact loading can cause chipping or spalling.
Engineering Practice Implications
Process Selection for Hot Shear Blades
Based on the study findings, the following process recommendations can be made:
- Laser cladding: Preferred for high-performance applications where service life is critical. Offers fine microstructure, low dilution, and excellent wear resistance.
- SAW overlay: Suitable for general applications where cost is a concern. Provides adequate performance with good productivity.
- FCAW overlay: Useful for field repair applications where portability is required.
- Oxy-acetylene overlay: Should be avoided for new cladding due to brittleness, but may be used for emergency repairs.
Quality Control Requirements
For ensuring cladding layer quality, the following requirements should be implemented:
- Visual inspection: Check for porosity, cracks, and incomplete fusion.
- Hardness testing: Verify hardness within specified range (800–950 HV).
- Metallographic examination: Assess microstructure and carbide distribution.
- Wear testing: Conduct abrasion tests to verify wear resistance.
- Service monitoring: Track blade life and failure modes to optimize cladding specifications.
Maintenance and Repair Procedures
The study provides guidance on blade maintenance:
- Regular inspection: Inspect blades every 50 hours of operation.
- Recladding criteria: Reclad when cladding thickness is reduced to 50% of original.
- Grinding procedure: Grind to remove damaged cladding before recladding.
- Preheat requirements: Preheat to 150–200°C before recladding to reduce cracking.
- Post-weld treatment: Stress relieve at 550°C for 1 hour to reduce residual stress.
Key Questions and Reflections
A significant question raised by this study is the long-term performance of cladding layers under cyclic thermal loading. The study evaluates wear resistance under laboratory conditions, but in service, blades experience repeated heating and cooling cycles that can cause thermal fatigue cracking. Future work should investigate the effect of thermal cycling on cladding layer integrity.
Another reflection concerns the economic balance between cladding cost and service life. Laser cladding provides the longest service life but at significantly higher cost. Engineers must evaluate the total cost of ownership, including blade replacement frequency, downtime, and labor costs, to determine the optimal cladding process for each application.
Summary
The microstructure and properties of cladding layers on hot shear blades are critical for determining service performance. The study demonstrates that laser cladding provides the best wear resistance and longest service life, followed by SAW and FCAW overlay. Engineers should select cladding processes based on the balance of performance, cost, and productivity requirements. Future work should address the effect of thermal cycling on cladding integrity and develop predictive models for blade life estimation.
This concludes the five technical study notes on cladding and weld overlay topics. Each document provides a comprehensive analysis of the respective topic, covering core technical findings, engineering practice implications, and key reflections. The notes are designed to assist fellow engineers in understanding the core content and extracting key technical points for practical application.