CLADDING TECHNOLOGY SHANXI CO., LTDPlasma Cladding Coating on Deep Plough Points Preparation and Performance
Literature Overview
This study focuses on the application of plasma transferred arc (PTA) cladding technology to deep plough points, which are critical cutting tools used in deep ploughing agricultural operations. Deep plough points operate under extreme conditions involving high impact loads, abrasive soil contact, and cyclic stress, leading to rapid wear and frequent replacement. Plasma cladding offers a solution to extend tool life by depositing wear-resistant coatings on the critical wear surfaces of plough points, reducing the frequency of replacement and lowering operational costs.
Plasma Cladding Process Configuration
The PTA cladding process was configured to deposit a multi-layer coating on the wear surfaces of the deep plough points. The process parameters were optimized to achieve a dense, crack-free deposit with minimal dilution of the base tool steel.
| Parameter | Value | Function |
|---|---|---|
| Arc current | 200 – 300 A | Controls melting rate and penetration |
| Arc voltage | 20 – 28 V | Influences melt pool geometry |
| Powder feed rate | 30 – 60 g/min | Determines deposit thickness |
| Travel speed | 100 – 300 mm/min | Controls dilution and solidification rate |
| Shielding gas | Argon (flow rate 15-25 L/min) | Protects melt pool from oxidation |
| Substrate preheat | 100 – 150°C | Reduces thermal stress and cracking |
| Deposit thickness | 2 – 4 mm | Provides adequate wear reserve |
The powder composition typically employed for deep plough point applications consists of a high-carbon, high-chromium iron-based alloy containing 5-10% Cr, 3-5% C, 2-4% Mo, and 1-3% W. This composition produces a microstructure rich in hard carbides (Cr7C3, Mo2C, WC) embedded in a martensitic or austenitic matrix, providing excellent resistance to abrasive wear.
Microstructural Analysis and Hardness Distribution
Metallographic examination of the PTA cladding deposits revealed a well-bonded interface between the coating and the base tool steel (typically 45# or 65Mn spring steel). The dilution rate was maintained below 20% through careful parameter control, ensuring that the deposit retained its designed composition and hardness.
The hardness profile across the deposit thickness showed a typical gradient: the surface hardness reached 62-68 HRC due to the high volume fraction of fine carbides, while the interface region showed a gradual decrease to 45-55 HRC as dilution increased. This hardness gradient is beneficial as it provides a hard wear-resistant surface while maintaining adequate toughness at the interface to resist spalling under impact loading.
The microstructure consisted of a martensitic matrix with dispersed carbides of varying sizes: primary carbides of 5-15 μm formed during solidification, and secondary carbides of 0.5-2 μm precipitated during post-weld cooling. The combination of these carbide populations provides both wear resistance (from large primary carbides) and toughness (from fine secondary carbides that impede crack propagation).
Wear Performance and Field Testing Results
Laboratory wear testing using the pin-on-disc tribometer (ASTM G99) demonstrated that the PTA cladded plough points exhibited 4-6 times the wear resistance of uncoated tool steel under simulated soil abrasion conditions. The wear mechanism transitioned from abrasive wear (dominant on uncoated surfaces) to a mixed mechanism of abrasion and micro-ploughing on the cladded surface, indicating the effectiveness of the hard carbide phase in resisting material removal.
Field trials conducted over multiple ploughing seasons confirmed that PTA-cladded plough points achieved service lives of 800-1200 hours compared to 200-350 hours for uncoated points. The improved performance was attributed to the combination of high hardness (62-68 HRC), good toughness (impact energy of 15-25 J at the interface), and excellent bonding strength (exceeding 400 MPa in peel testing). No spalling or delamination was observed during field trials, validating the process reliability.
Engineering Practice Recommendations
The study provides actionable recommendations for implementing PTA cladding on deep plough points in manufacturing settings. Key considerations include: surface preparation (grinding to remove scale and oxides to within 0.1 mm flatness), proper grounding of the workpiece to ensure stable arc transfer, and the use of multi-pass strategies for thick deposits to manage thermal input and minimize residual stresses. The study also notes that post-weld stress relief at 550-600°C for 1-2 hours is recommended for components subjected to high impact loads, though this may slightly reduce hardness to 58-62 HRC while significantly improving toughness. The economic analysis demonstrates that the cost of PTA cladding is recovered within the first 2-3 service cycles, making it a cost-effective solution for extending tool life in agricultural applications.