Zhuojin Pipe Fitting Co., LtdOverlay Welding Repair of Crusher Grate Plates Under High-Temperature Abrasive Service
Literature Overview
This paper by Huang Taiming of the Chongqing Iron and Steel Construction Department, published in Welding (1991, Issue 1), addresses a critical maintenance challenge in the sintering plant: the rapid wear of grate plates in an F1500×2520 fully water-cooled single-roll crusher. The grate plates are subjected to abrasive impact from hot ore particles at approximately 750°C. The original high-temperature wear-resistant alloy overlay had suffered severe degradation in less than one year of service, rendering the equipment inoperable.
Core Technical Problem Analysis
The service environment imposes a dual challenge: high-temperature oxidation combined with severe mechanical abrasion. At 750°C, conventional carbon steel or low-alloy steels experience accelerated oxidation and thermal softening, while the mechanical impact of ore particles imposes cyclic loading that promotes fatigue cracking of the overlay layer. The water-cooling arrangement provides some thermal protection, but the thermal cycling between hot ore contact and coolant exposure introduces additional thermal stress that degrades the bond between the substrate and the overlay.
From a metallurgical standpoint, the key requirements for the repair overlay are:
| Performance Requirement | Target Specification | Rationale |
|---|---|---|
| Hardness at operating temperature | ≥ 45 HRC at 750°C | Resist abrasive wear under thermal softening |
| Thermal shock resistance | Survive ΔT > 500°C cycles | Accommodate ore-to-coolant temperature swings |
| Bond strength to substrate | ≥ 200 MPa shear | Prevent overlay spalling under impact |
| Service life | > 2 years before re-overlay | Reduce downtime and maintenance cost |
Overlay Welding Process Selection and Parameters
The repair strategy involves multi-layer overlay welding with a graded composition approach. The first layer serves as a transition zone between the base steel and the wear-resistant top layer, while subsequent layers progressively increase in alloy content. Typical process parameters for such applications include:
| Layer | Electrode Type | Current (A) | Voltage (V) | Travel Speed (mm/min) | Layer Thickness (mm) |
|---|---|---|---|---|---|
| Transition layer | E5015 or E5016 | 180–220 | 24–28 | 300–400 | 2–3 |
| Intermediate layer | Nickel-based or austenitic | 200–250 | 26–30 | 250–350 | 3–4 |
| Wear-resistant layer | High-carbon high-chromium | 220–280 | 28–32 | 200–300 | 4–6 |
Key Process Considerations
- Preheating: The base plate should be preheated to 200–250°C to reduce thermal gradients and minimize residual stress. This is particularly critical given the water-cooling system that may already impose thermal distortion.
- Interpass temperature control: Maintaining interpass temperature below 300°C prevents excessive grain growth in the overlay and reduces the risk of cracking in the high-carbon layers.
- Welding sequence: A systematic multi-pass sequence with overlapping coverage of at least 50% ensures uniform dilution and prevents cold laps. The weave width should be controlled to 3–4 times the electrode diameter.
- Post-weld treatment: Stress-relief annealing at 550–600°C for 2 hours per 25 mm of thickness can significantly reduce residual stresses that would otherwise promote overlay spalling during service.
Defect Analysis and Countermeasures
Based on metallurgical analysis of similar failures, the following defect modes are commonly observed:
- Overlay spalling: Caused by high dilution (>30%) leading to a hard, brittle martensitic structure at the overlay-substrate interface. Countermeasure: Use a nickel-based or austenitic transition layer to reduce dilution effects.
- Cracking in overlay: High-carbon chromium layers are susceptible to hot cracking due to low melting point eutectics at grain boundaries. Countermeasure: Add niobium or vanadium to refine grain structure and reduce eutectic formation.
- Thermal fatigue cracking: Repeated thermal cycling causes intergranular cracking parallel to the surface. Countermeasure: Introduce elements that promote columnar grain growth perpendicular to the surface, facilitating crack deflection.
Engineering Practice Implications
This case study highlights a broader principle in refractory overlay engineering: the overlay system must be designed as a composite, not a monolithic layer. The graded composition approach—transition, intermediate, and functional layers—mirrors the design philosophy used in thermal barrier coatings for gas turbine blades. In modern practice, this concept has evolved into multi-layer plasma-sprayed systems and laser-clad composites that offer superior thermal shock resistance.
For engineers working on similar applications in mining, cement, or power generation industries, the key takeaway is that overlay life is governed not by peak hardness alone but by the combination of thermal stability, oxidation resistance, and bond integrity. A hardness of 55 HRC at room temperature is meaningless if the material oxidizes rapidly at 750°C or if the overlay delaminates after 500 thermal cycles. The Chongqing Iron and Steel experience demonstrates that systematic overlay design, informed by metallurgical analysis and field feedback, can extend service life by 2–3 times compared to ad-hoc repair approaches.