CLADDING TECHNOLOGY SHANXI CO., LTDPractice of High-Strength Wear-Resistant Alloy Overlay on Sintering Machine Tail Scrapers
Literature Overview and Background
This study documents the practical application of high-strength wear-resistant alloy weld overlay on sintering machine tail scrapers, a critical component in the iron ore sintering process of steel manufacturing. Sintering machines are large-scale continuous equipment used to agglomerate fine iron ore particles into a porous material suitable for blast furnace charging. The tail scraper (also called the discharge scraper or end scraper) operates at the discharge end of the sintering machine, scraping the cooled sinter cake from the bed plate. This component is subjected to severe abrasive wear from the hard sinter material, as well as thermal cycling and mechanical impact, leading to frequent failures and costly downtime.
Failure Analysis and Requirements
The study begins with a thorough failure analysis of conventional tail scrapers made from plain carbon steel (Q235 or Q345). The primary failure mode is progressive abrasive wear on the scraping edge, which reduces the effective scraping angle and eventually results in incomplete discharge of sinter material. This causes material accumulation, increased power consumption, and potential damage to the sintering bed. The typical service life of an unclad scraper in a modern sintering plant is only 2–4 weeks, necessitating frequent replacement and causing significant production disruption.
The engineering requirements for the overlay solution include:
- Hardness of at least 50 HRC at the scraping edge to resist abrasive wear
- Sufficient impact toughness to withstand mechanical loading without spalling
- Good bonding strength with the carbon steel substrate
- Resistance to thermal degradation at operating temperatures of 200–400 °C
- Overlay thickness of 5–8 mm to provide adequate wear life
- Compatibility with field welding conditions (limited access, ambient atmosphere)
Overlay Material Selection and Application
The study evaluates several overlay alloy systems and ultimately selects a high-strength martensitic stainless steel composition containing approximately 12–14% Cr, 0.8–1.2% C, and trace amounts of Mo and V. This composition produces a microstructure of tempered martensite with fine chromium carbide (Cr7C3) precipitates, offering an excellent balance of hardness (52–58 HRC) and toughness. The martensitic structure provides inherent wear resistance, while the chromium content offers adequate corrosion resistance against the slightly acidic environment of the sintering process.
The overlay is applied using flux-cored arc welding (FCAW) with a wire diameter of 1.6 mm. The process parameters are optimized as follows:
| Parameter | Value | Rationale |
|---|---|---|
| Current | 320–380 A | Adequate penetration without excessive dilution |
| Voltage | 28–32 V | Stable arc, good wetting |
| Travel speed | 250–350 mm/min | Controlled heat input |
| Wire stick-out | 18–22 mm | Consistent arc characteristics |
| Preheat | 100–150 °C | Prevent cold cracking in HAZ |
| Interpass temperature | <200 °C | Limit grain growth |
| Number of passes | 3–4 | Achieve target thickness with low dilution |
Performance Results and Practical Outcomes
The study reports that the overlaid tail scrapers achieved a service life of 6–10 months, representing a 10–20 times improvement over the unclad baseline. Metallographic examination of the worn surface after service confirms that the wear mechanism is primarily micro-ploughing and micro-cutting by hard sinter particles, with minimal adhesive wear or fatigue spalling. The overlay layer exhibits a uniform hardness distribution of 52–56 HRC across the cross-section, indicating good metallurgical homogeneity.
The bonding strength between the overlay and the Q345 substrate was verified by macrographic examination of cross-sections, revealing complete fusion without lack-of-bond defects. Hardness traverse measurements show a gradual transition from 180 HV in the base metal to 700 HV in the overlay, with no abrupt hardness discontinuity that could promote cracking under impact loading.
Study Insights and Reflections
This case study is particularly instructive because it demonstrates the practical value of weld overlay technology in solving real-world engineering problems with significant economic impact. The sintering machine tail scraper application is a textbook example of where localized wear protection through weld overlay is far more cost-effective than replacing the entire component with a wear-resistant material. The study's systematic approach—beginning with failure analysis, proceeding through material selection and process optimization, and concluding with performance validation—serves as an excellent model for engineers tackling similar wear-related challenges.
One key insight is the importance of matching the overlay composition to the specific wear mechanism. In this case, the abrasive wear from hard sinter particles is effectively countered by a martensitic stainless steel with fine carbide dispersion. A harder, more brittle overlay (such as a high-carbon white iron) might have achieved higher hardness but would have been prone to spalling under the impact loading experienced by the scraper. The study reinforces the principle that wear resistance is not solely a function of hardness but requires a careful balance of hardness, toughness, and thermal stability.