CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Hard Overlay Wear-Resistant Lining Plates in Electric Shovel Buckets
Literature Overview
This 2011 publication by Wang Hui, Tang Linlin, Wang Meng, and Yu Bing from Shandong Borun Industrial Technology Co., Ltd. addresses a critical engineering challenge in open-pit mining operations: the accelerated wear of electric shovel bucket components under severe abrasive conditions. The paper, published in the journal Open-Pit Mining Technology, presents a systematic approach to extending the service life of mining equipment through the strategic application of hard overlay welding technology. The authors demonstrate that conventional carbon steel bucket plates, typically made from Q345 or Q460 grades, suffer from rapid material loss when handling abrasive ores, particularly in iron ore and copper mine operations where silica content exceeds 30%.
Core Technical Content
The study focuses on the selection and application of hard-facing alloys suitable for electric shovel bucket geometry. The primary challenge lies in balancing wear resistance with impact toughness, as bucket teeth and cutting edges experience both abrasive sliding contact and repeated impact loading from rock fragments. The authors evaluated several hard overlay systems, including chromium carbide-based alloys (CrC type), cobalt-based alloys (CoCr type), and iron-based alloys (Fe-based with high carbon content).
Material Selection and Process Parameters
The recommended hard overlay system employs a multi-layer approach: a transition layer to ensure metallurgical compatibility with the base steel, followed by one or more layers of the final hard-facing alloy. Typical process parameters for submerged arc welding (SAW) overlay, which is the predominant method for large bucket components, are summarized below.
| Parameter | Transition Layer | Hard Overlay Layer |
|---|---|---|
| Welding current (A) | 400-500 | 350-450 |
| Arc voltage (V) | 28-32 | 26-30 |
| Travel speed (mm/min) | 200-300 | 150-250 |
| Flux type | Rutile basic | Basic |
| Electrode type | H08Mn2SiA | Hard-facing wire (e.g., CH-12) |
| Layer thickness per pass (mm) | 2-3 | 2-4 |
| Preheat temperature (°C) | 150-200 | 100-150 |
| Interpass temperature (°C) | < 250 | < 200 |
Metallurgical Considerations
The transition layer composition is critical. For Q345 base steel overlaid with chromium carbide hard-facing alloy, the transition layer typically contains 0.4-0.6% C, 1.5-2.5% Mn, and 0.3-0.5% Si to reduce the carbon dilution effect from the base metal and minimize the formation of brittle intermetallic compounds at the interface. The hardness profile across the overlay typically shows a gradient from approximately 250 HV at the base metal to 600-700 HV at the surface, with the transition zone exhibiting 350-450 HV.
Engineering Practice and Defect Analysis
In practical implementation, several challenges arise. The first is undercut at the overlay-to-base interface, which creates stress concentration points under impact loading. The second is cracking in the overlay layer during cooling, particularly when the carbon equivalent of the deposited metal exceeds 0.6%. The third is insufficient bond strength between the transition layer and base metal due to inadequate preheat or excessive travel speed.
The authors report that field trials at an iron ore mine in Shandong Province demonstrated a 3-5 times improvement in service life compared to uncladded bucket plates. The overlay layer thickness was maintained at 8-12 mm, with periodic re-cladding performed when approximately 60% of the overlay had been consumed, ensuring the transition layer remained intact.
Common Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Undercut | Excessive arc voltage or travel speed | Reduce voltage by 2-3 V; slow travel speed |
| Surface cracks | High carbon equivalent; rapid cooling | Increase preheat to 200°C; add post-weld stress relief at 600°C for 2 h |
| Incomplete bonding | Surface contamination; insufficient penetration | Thorough surface preparation (grind to bare metal); increase current by 10% |
| Porosity | Moist flux; base metal contamination | Dry flux at 250°C for 2 h; remove rust and oil from base |
Study Insights and Implications
The practical value of this work lies in its field-oriented approach. Unlike laboratory studies that focus solely on microstructural optimization, this publication addresses the real-world constraints of mining operations: limited welding windows, harsh environmental conditions, and the need for rapid turnaround. The emphasis on multi-layer overlay with a proper transition layer reflects the engineering reality that metallurgical compatibility cannot be sacrificed for the sake of maximum hardness. Engineers working on similar applications should note that the overlay geometry must conform to the stress distribution of the bucket component; overlaying flat surfaces where the component experiences bending is less effective than overlaying the actual wear surfaces identified through field observation.