CLADDING TECHNOLOGY SHANXI CO., LTDHigh-Strength Wear-Resistant Steel Overlay Process for Scraper Conveyors
Overview and Application Context
Scraper conveyors are workhorse equipment in mining, cement, power generation, and bulk material handling industries. They transport abrasive materials such as coal, ore, slag, and cement clinker through enclosed troughs. The scraper chains and scraper plates experience severe abrasive wear, leading to frequent replacement and high maintenance costs. Weld overlay cladding with high-strength wear-resistant steel alloys offers a proven solution to extend service life and reduce operational costs. This study examines the overlay process development and optimization for scraper conveyor components.
Core Technical Points
Material Selection for Scraper Conveyor Overlay
The overlay alloy must balance hardness (for wear resistance) with toughness (to resist impact from material loading) and weldability (to ensure reliable bonding to the base steel):
| Overlay Alloy Type | Hardness (HRC) | Impact Energy (J) | Typical Application |
|---|---|---|---|
| High-carbon martensitic | 50–58 | 15–25 | General abrasive wear |
| Medium-carbon martensitic | 45–52 | 25–40 | Mixed abrasive/impact wear |
| High-chromium cast iron | 55–62 | 5–15 | Severe abrasive wear |
| Composite (martensite + carbide) | 48–55 | 20–35 | Combined abrasive/impact |
For scraper conveyors handling coal and ore, medium-carbon martensitic alloys (e.g., Cr5Mo1V or Cr8Mo2V) are typically preferred because they provide adequate hardness while maintaining sufficient impact resistance.
Process Parameters and Welding Technique
The overlay is typically performed using submerged arc welding (SAW) or flux-cored arc welding (FCAW) for high deposition rates:
| Parameter | SAW Range | FCAW Range | Notes |
|---|---|---|---|
| Current | 350–500 A | 250–400 A | Higher current for larger cross-section |
| Voltage | 28–35 V | 30–40 V | Controls arc stability |
| Travel speed | 200–400 mm/min | 150–350 mm/min | Affects bead width and penetration |
| Wire diameter | 3.2–4.0 mm | 1.2–1.6 mm | Matches equipment capacity |
| Preheat temperature | 150–250 °C | 100–200 °C | Reduces cracking risk |
| Interpass temperature | 200–300 °C | 150–250 °C | Controls cooling rate |
Multi-pass overlay is standard practice, with a transition layer (lower carbon, higher toughness) applied first, followed by the wear-resistant surface layer. The transition layer minimizes cracking at the interface between the ductile base steel and the hard overlay.
Defect Prevention and Quality Control
Common defects and their prevention:
- Cracking: Prevented by controlling carbon equivalent (CE < 0.6% for the transition layer), maintaining adequate preheat and interpass temperatures, and avoiding excessive restraint.
- Porosity: Controlled by using low-hydrogen flux or shielded flux-cored wire, and ensuring proper drying of consumables.
- Incomplete fusion: Addressed by ensuring adequate current and proper stringer bead technique.
- Surface defects: Detected by visual inspection and magnetic particle testing (MT) per JB/T 4730.
Performance Verification
Post-overlay testing should include:
- Hardness testing: Verify surface hardness meets specification (typically 45–55 HRC for scraper applications).
- Impact testing: Charpy V-notch test at service temperature to confirm adequate toughness.
- Wear testing: Pin-on-disc or abrasion test to quantify wear rate improvement.
- Bond strength testing: Peel or shear test to verify interface integrity.
- NDT: MT or PT of all overlay surfaces to detect surface-breaking defects.
Engineering Practice Integration
In field applications, scraper conveyor overlay programs typically target the scraper plates and chain links that experience the most severe wear. The overlay thickness is usually 3–6 mm, which provides a service life extension of 3–5 times compared to unclad components. Engineers should design the overlay geometry to avoid sharp corners where stress concentration can initiate cracking, and should incorporate a gradual transition from clad to unclad areas to distribute stresses.
Study Insights and Implications
The practical value of this study lies in its systematic approach to process optimization for a specific industrial application. The key insight is that overlay alloy selection must be driven by the actual wear mechanism—abrasive, impact, or mixed—rather than by simply maximizing hardness. A 58 HRC overlay may fail prematurely under impact loading, while a 48 HRC overlay with better toughness may deliver superior overall service life. Engineers should conduct a thorough wear mechanism analysis before specifying overlay alloys, and should always include transition layers when the hardness difference between base and overlay exceeds 100 HV. This study reinforces the principle that successful overlay engineering requires integration of materials science, welding metallurgy, and tribology knowledge.