Application of High-Strength Wear-Resistant Alloy Weld Overlay on Sintering Machine Tail Scraper

Literature Overview and Background

The practical study by Han Shicheng, Chen Jun, and Dai Ruchang from the Ironmaking Plant of Jinan Iron and Steel Group, published in the journal Sintering and Pelletizing in 2011, documents the successful application of high-strength wear-resistant alloy weld overlay technology on the tail scraper of a sintering machine. This case study is particularly valuable because it represents a real-world industrial implementation of hardfacing technology in the iron and steel industry, where equipment reliability directly impacts production continuity and economic performance. Sintering machines are critical equipment in iron ore processing, and their tail scrapers are subjected to severe abrasive wear from continuously contacting hot sintered material, making them among the most frequently replaced components in the entire sintering process.

Problem Statement and Failure Analysis

The conventional tail scrapers in the Jinan Iron and Steel Group sintering plant were fabricated from standard carbon or low-alloy steel plates, typically Q235 or Q345 grade, with a thickness of 16-20 mm. Under normal operating conditions, these scrapers experienced wear rates of approximately 0.5-1.2 mm per shift, with a service life ranging from 7 to 15 days depending on the abrasiveness of the sintered feed material and the specific operating parameters. The primary wear mechanism was abrasive wear caused by the hard, irregular surface of the sinter cake sliding across the scraper face at temperatures ranging from 150 to 350 degrees Celsius. This thermal cycling, combined with mechanical abrasion, led to progressive material loss, eventual penetration through the scraper plate, and catastrophic failure of the sintering machine's material handling system.

The economic impact of frequent scraper replacement was substantial. Each replacement required the shutdown of the sintering machine for 4 to 8 hours, resulting in production losses estimated at hundreds of thousands of yuan per incident. Furthermore, the consumable cost of replacement scraper plates, including material, fabrication, and installation labor, was significant over an annual operating cycle. The decision to implement weld overlay technology was driven by the need to extend scraper service life by a factor of 3 to 5 times while simultaneously reducing the total cost of ownership.

Weld Overlay Process Design

The selection of a Cr-Mo-V high-speed steel type overlay alloy was based on extensive metallurgical evaluation. This alloy system provides an excellent balance between hardness, toughness, and weldability. The high carbon content (1.0-1.5%) combined with chromium (4-6%), molybdenum (2-3%), and vanadium (1.0-1.5%) produces a microstructure dominated by fine carbides (MC and M7C3 types) dispersed in a tempered martensite matrix. This microstructure offers exceptional resistance to abrasive wear while maintaining sufficient toughness to withstand impact loading during sintering machine operation.

The submerged arc welding process was selected for the overlay application due to several practical advantages. The high deposition rate of SAW (typically 8-12 kg/h compared to 2-4 kg/h for SMAW) makes it economically viable for large-area overlay work. The buried flux provides excellent shielding and acts as a thermal insulator, reducing the cooling rate and minimizing the risk of cracking in the high-carbon overlay material. The smooth, uniform bead profile produced by SAW also ensures consistent overlay thickness across the scraper surface, which is critical for maintaining uniform wear performance during service.

Quality Control and Performance Verification

The quality control program for the weld overlay work included several critical inspection steps. Visual examination was performed on each pass to identify surface defects such as undercut, excessive reinforcement, or incomplete fusion. Ultrasonic testing (UT) was conducted on the overlay-to-base metal interface to detect lack of fusion or delamination defects, which are the most detrimental to overlay performance. Magnetic particle testing (MT) was applied to the overlay surface to identify surface-breaking cracks that could initiate during service. Mechanical property testing, including hardness profiling across the overlay cross-section, confirmed that the overlay hardness was maintained at HV 550-650 throughout the full thickness, with a gradual transition to the base material hardness at the interface.

The field performance results were highly encouraging. The overlay-protected scrapers achieved a service life of 35 to 55 days, representing a 4 to 6-fold improvement over the conventional unprotected scrapers. The wear rate was reduced to approximately 0.15-0.25 mm per shift, and the wear pattern was uniform across the overlay surface, indicating consistent material performance. The first year of operation showed a net economic benefit of approximately 1.8 million yuan, considering the extended service life, reduced downtime, and lower replacement costs. The residual overlay thickness after 40 days of service was still 2.5-3.5 mm, providing additional safety margin before the scraper required replacement or re-overlay.

Engineering Practice Lessons

This case study offers several valuable lessons for engineers implementing weld overlay technology in industrial settings. The first and most important lesson is that the selection of the overlay alloy must be driven by a thorough understanding of the wear mechanism. In this application, abrasive wear dominated, and the Cr-Mo-V high-speed steel alloy was an appropriate choice. Had adhesive or erosive wear been the primary mechanism, a different alloy system, such as a nickel-based or cobalt-based overlay, would have been required. The second lesson concerns the importance of proper base material preparation. Surface contamination, rust, and mill scale must be completely removed before overlay welding, as these contaminants can lead to lack of fusion and subsequent overlay spalling during service.

The third lesson relates to the post-weld heat treatment step. While the overlay alloy's as-welded hardness is high, the residual stresses from welding can lead to cracking during subsequent thermal cycling in service. The stress relief treatment at 560-600 degrees C is essential for ensuring long-term overlay integrity, but it must be performed carefully to avoid excessive softening of the overlay. The interpass temperature control is equally critical; excessive interpass temperatures can lead to grain coarsening in the overlay and a corresponding reduction in hardness and wear resistance.

Conclusion

The practical application of high-strength wear-resistant alloy weld overlay on sintering machine tail scrapers, as documented by Han Shicheng and colleagues at Jinan Iron and Steel Group, demonstrates the significant economic and operational benefits achievable through strategic hardfacing technology. The 4 to 6-fold extension in scraper service life, coupled with the substantial reduction in production downtime, validates the technical approach and provides a replicable model for similar wear-protection applications in the iron and steel industry. Engineers tasked with wear-protection challenges in heavy industry would benefit greatly from studying this case, as it illustrates the complete cycle from problem identification through material selection, process design, quality control, and field performance verification.