CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Hot Shear Blade Overlay Welding Electrodes
Literature Overview
The paper by Yang Qingxiang, Wang Airong, Ren Xuejun, and Yao Mei from the School of Materials Engineering at Yanshan University, published in Welding in 1997, describes the development of specialized welding electrodes for the overlay repair and hardening of hot shear blades. Hot shear blades in steel mills and metal processing facilities are subjected to extreme operating conditions, including temperatures above 600 degrees Celsius, high impact forces, and abrasive contact with hot steel slabs. The service life of these blades is often limited by wear, chipping, and thermal fatigue cracking, making the development of effective overlay welding consumables a critical industrial need.
Operating Conditions and Failure Analysis
Hot shear blades operate under a combination of thermal, mechanical, and chemical degradation mechanisms. During the shearing process, the blade edge contacts steel slabs at temperatures of 800-1200 degrees Celsius, causing rapid heating of the blade edge. This thermal cycling induces thermal fatigue, leading to the initiation and propagation of cracks at the blade edge. Simultaneously, the high compressive and shear forces during cutting cause abrasive and adhesive wear, progressively reducing the blade thickness and compromising cutting performance.
The authors conducted a comprehensive failure analysis of used hot shear blades and identified the primary failure modes as edge chipping, thermal cracking, and excessive wear. The microstructural examination of worn blade edges revealed a decarburized layer, coarse carbide distribution, and microcracks in the heat-affected zone. These observations guided the design requirements for the overlay welding electrodes.
| Failure Mode | Root Cause | Design Requirement |
|---|---|---|
| Edge chipping | High hardness with low toughness | Balanced hardness and impact toughness |
| Thermal cracking | Thermal cycling and low thermal conductivity | High thermal fatigue resistance |
| Excessive wear | Soft matrix and coarse carbides | Fine, hard, thermally stable carbides |
| Decarburization | Carbon loss at high temperature | Sufficient carbon content in deposit |
Electrode Design and Performance
The authors designed a series of iron-based welding electrodes with a high-chromium, high-carbon composition, incorporating tungsten and vanadium to promote the formation of fine, thermally stable carbides. The optimal electrode composition included approximately 12-14 wt% Cr, 3.0-3.8 wt% C, 2.0-3.0 wt% W, and 1.0-2.0 wt% V, with the balance being iron and minor amounts of manganese and silicon.
The deposited overlay layer exhibited a microstructure of martensite and retained austenite with a high volume fraction of M7C3 and MC carbides. The hardness of the overlay layer was measured at 60-66 HRC at room temperature and retained above 52 HRC after exposure at 600 degrees Celsius for four hours. The impact toughness, measured using a Charpy V-notch test, was maintained at 8-12 J/cm2, indicating acceptable resistance to chipping under impact loading.
The wear resistance was evaluated using a dry sliding wear test against a steel counterface at both room temperature and 600 degrees Celsius. The overlay layer showed a wear rate of 0.05-0.08 mm3/N.m at room temperature and 0.12-0.18 mm3/N.m at 600 degrees Celsius, representing a 3-5 times improvement over the base blade material. The thermal fatigue resistance was assessed through thermal shock testing, where the overlay layer survived 200-300 thermal cycles between 25 and 800 degrees Celsius without cracking, compared to only 50-80 cycles for the uncladded blade material.
Field Application and Practical Considerations
The developed electrodes were field-tested on hot shear blades in a steel mill, where they demonstrated a significant extension of blade service life. The overlay thickness was applied in the range of 3-5 mm, with a typical two-pass welding procedure. The first pass served as a transition layer to ensure good bonding with the base steel, while the second pass provided the full wear-resistant and thermally stable overlay. Field trials showed that the service life of overlaid blades was extended by a factor of 3-4 compared to conventional blade materials without overlay.
A practical consideration identified during field trials was the need for proper preheating and interpass temperature control. Preheating the blade to 250-350 degrees Celsius before welding and maintaining the interpass temperature below 400 degrees Celsius were essential to prevent hot cracking and ensure adequate toughness in the deposited weld metal. Post-weld stress relief at 550-600 degrees Celsius for one hour further improved the crack resistance and stability of the overlay layer.
Study Reflections
This paper provides a clear example of how fundamental metallurgical research can be directly translated into practical industrial solutions. The systematic approach of failure analysis, material design, laboratory testing, and field validation represents a rigorous engineering methodology that remains applicable today. The emphasis on balanced properties, particularly the combination of high hardness with adequate toughness and thermal fatigue resistance, highlights the complexity of designing wear-resistant materials for severe service conditions. The work also demonstrates the importance of considering process parameters alongside material composition in achieving optimal overlay performance.