CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Q235 Electrolytic De-Scaling Hammer Head by Plasma Cladding
Literature Overview
This study examines the application of plasma transferred arc (PTA) cladding to Q235 carbon steel electrolytic de-scaling hammer heads, a specialized tool used in aluminum electrolysis cells for removing oxide scale from cathode blocks. The research investigates the microstructural evolution, mechanical properties, and service performance of PTA-cladded hammer heads compared to conventional manufacturing methods.
Background and Application Requirements
Electrolytic de-scaling hammer heads operate in extreme conditions within aluminum reduction cells, experiencing:
- High temperature environment (850-960°C)
- Abrasive contact with aluminum oxide (Al2O3) scale
- Impact loading from hammering action
- Corrosive molten salt environment
- Thermal cycling stress
The conventional Q235 carbon steel hammer head has limited service life due to rapid wear and deformation. Plasma cladding offers a solution by applying a wear-resistant overlay while maintaining the structural integrity of the base material.
Plasma Cladding Process Parameters
| Parameter | Value | Notes |
|---|---|---|
| Plasma arc power | 8-12 kW | Depends on traverse speed |
| Traverse speed | 100-200 mm/min | Slower for thicker deposits |
| Powder feed rate | 200-400 g/min | Adjusted for desired dilution |
| Shielding gas | Argon (20-30 L/min) | Inert atmosphere protection |
| Powder material | Ni-based or Co-based alloy | With WC or Cr3C2 additions |
| Overlay thickness | 2-4 mm | Multi-pass for thicker layers |
| Dilution rate | 5-15% | Target for optimal properties |
Microstructure Analysis
Overlay Layer Microstructure
The PTA cladding powder typically consists of a Ni-based or Co-based binder alloy with hard carbide particles (WC or Cr3C2) as the reinforcement phase.
- Matrix: Austenitic or martensitic nickel/chromium alloy structure with fine grain size
- Hard phase: WC particles partially dissolved, with formation of M6C and M23C6 carbides
- Interface: Dilution zone showing gradient composition from base steel to overlay alloy
- Columnar grains: Growing from the interface into the overlay layer, typical of rapid solidification
Dilution Zone Characteristics
The dilution zone is critical for determining the overall performance of the cladded component:
| Zone | Composition | Hardness (HV) | Microstructure |
|---|---|---|---|
| Base material (Q235) | Fe + 0.2%C | 120-150 | Ferrite + pearlite |
| Dilution zone (0-0.5 mm) | Fe + Ni + Cr + C | 300-450 | Martensite + carbides |
| Overlay layer (0.5-4 mm) | Ni-Cr-Co + WC | 600-800 | Austenite + WC + carbides |
Mechanical Properties and Performance
Hardness Distribution
The hardness profile across the cladded hammer head shows a clear gradient from the soft base material to the hard overlay surface, which is beneficial for impact resistance while providing wear protection.
Wear Resistance
Abrasive wear testing demonstrates significant improvement in service life:
- Uncladded Q235: Wear rate of 25-35 × 10⁻⁶ mm³/N·m
- PTA cladded: Wear rate of 3-8 × 10⁻⁶ mm³/N·m
- Service life improvement: 3-5 times compared to conventional hammer head
Impact and Fatigue Performance
The PTA cladding maintains acceptable impact properties due to the gradient hardness structure:
- Impact energy: 15-25 J (base material) vs. 8-12 J (overlay surface)
- Fatigue life: Improved by 2-3 times due to reduced surface deformation
Quality Control and Defect Prevention
Common Defects in PTA Cladding
| Defect | Cause | Prevention |
|---|---|---|
| Cracking | High residual stress, poor powder quality | Optimize parameters, use ductile transition layer |
| Porosity | Inadequate shielding, powder moisture | Ensure proper gas flow, dry powder |
| Excessive dilution | High power, low traverse speed | Reduce power, increase speed |
| Poor adhesion | Surface contamination, wrong parameters | Thorough cleaning, parameter optimization |
| Uneven thickness | Operator skill, machine calibration | Automation, regular calibration |
Inspection Procedures
- Visual inspection: Check for surface defects, uneven thickness, and proper coverage.
- Hardness testing: Verify hardness profile meets specifications.
- Ultrasonic testing: Detect lack of fusion and internal defects.
- Metallographic examination: Confirm microstructure and dilution zone characteristics.
- Wear testing: Coupon samples for abrasive wear verification.
Engineering Practice Considerations
The successful application of PTA cladding to hammer heads requires careful consideration of several factors:
- Substrate preparation: Grinding to expose clean metal surface, removal of rust and scale
- Thermal management: Control of heat input to prevent distortion of the hammer head geometry
- Multi-pass strategy: Building up thickness gradually to minimize residual stress
- Post-processing: Stress relief heat treatment if required for dimensional stability
- Storage and handling: Protection of cladded surface before installation
Study Insights and Implications
This research demonstrates that PTA cladding is an effective technology for extending the service life of specialized tools operating in harsh environments. The plasma arc process offers excellent control over dilution rates and microstructure, enabling the creation of gradient structures that combine wear resistance with impact toughness. For engineers working with aluminum industry equipment, this approach provides a cost-effective alternative to complete component replacement, with significant savings in material and labor costs. The study also highlights the importance of process parameter optimization for achieving the desired balance between wear resistance and mechanical integrity in cladded components.