Study Note on Manual Arc Cladding for Tool Manufacturing and Repair

Research Context and Industrial Significance

The 2000 study by Wan Weiguo from the Steel Research Institute of Maanshan Steel Company, published in "Tool Technology," addresses the application of manual arc cladding welding (SMAW) for tool manufacturing and repair. In the steel industry, tools such as dies, punches, hammers, and cutting tools are subjected to severe impact, abrasion, and wear. The replacement of entire tools is often uneconomical, and cladding with a hardfacing alloy provides a cost-effective and efficient alternative.

Core Technical Content

Application Categories

Manual arc cladding for tool applications can be categorized as follows:

Electrode Selection Criteria

The selection of hardfacing electrode for tool cladding depends on the service conditions:

Chromium-based electrodes (D256, D257, D266):

• Hardness: 50–60 HRC
• Microstructure: Martensite + carbides (Cr₇C₃, Cr₂₃C₆)
• Applications: High abrasion, moderate impact
• Limitation: Poor crack resistance; requires post-weld tempering

Nickel-based electrodes (D507, D537, D538):

• Hardness: 40–50 HRC (as-welded); 35–45 HRC (tempered)
• Microstructure: Austenite + carbides (Ni₃B, Ni₃Si)
• Applications: Moderate abrasion, good impact resistance
• Advantage: Self-bonding; no preheating required for many applications

Cobalt-based electrodes (D507, D508):

• Hardness: 45–55 HRC
• Microstructure: Austenite + carbides (WC, Co₃W)
• Applications: High temperature abrasion, corrosion
• Advantage: Retains hardness at elevated temperatures

High-carbon electrodes (D207, D212):

• Hardness: 55–65 HRC
• Microstructure: Martensite + cementite
• Applications: Severe abrasion, low impact
• Limitation: Very brittle; high cracking tendency

Process Parameters for Manual Arc Cladding

Microstructural Control

The microstructure of the cladding layer is determined by the cooling rate, which is influenced by:

1. Base material thermal conductivity: High conductivity (e.g., copper tools) leads to rapid cooling and hard, brittle microstructures.
2. Preheating temperature: Higher preheat slows cooling, promoting bainitic or tempered martensitic microstructures.
3. Interpass temperature: Maintaining interpass temperature prevents excessive cooling between passes.
4. Overlay thickness: Thicker overlays have lower cooling rates in the center, resulting in softer microstructures.

For Cr-based hardfacing electrodes, the as-welded microstructure is typically martensitic with dispersed carbides. This provides high hardness but poor toughness. Post-weld tempering at 500–600 °C transforms the martensite to tempered martensite, reducing hardness by 5–10 HRC but significantly improving toughness and reducing cracking susceptibility.

Common Defects and Countermeasures

Engineering Practice: Tool Cladding Procedure

A typical procedure for cladding a cold work die using manual arc welding:

1. Surface preparation: Machine the wear area to a shallow V-groove (60° included angle, 2–3 mm depth). Remove all oil, rust, and oxide.
2. Preheating: Heat the die to 300–400 °C using induction heating or furnace. Maintain temperature during welding.
3. First pass: Deposit a thin root pass with a compatible electrode (e.g., E7018 for steel base) to establish a sound bond.
4. Overlay passes: Deposit 2–4 passes of Cr-based hardfacing electrode (e.g., D256). Maintain interpass temperature at 300–400 °C.
5. Post-weld treatment: Stress relief at 550–600 °C for 1–2 h. This tempers the martensitic microstructure and reduces residual stress.
6. Finishing: Grind and polish the clad surface to the required geometry and finish.
7. Quality control: Hardness testing (minimum 50 HRC), visual inspection, and functional testing.

Case Study: Punch Repair

A cold extrusion punch made of 40Cr steel was worn after 50,000 strokes. The punch was repaired by cladding the tip with 3 mm of Cr-based hardfacing (D256 electrode). The procedure included:

• Preheating to 350 °C
• 3 passes of hardfacing with interpass temperature 350 °C
• Post-weld tempering at 580 °C × 2 h
• Grinding to final geometry

The repaired punch achieved 55 HRC hardness at the tip and lasted for an additional 120,000 strokes before the next repair was required. This represents a significant improvement in service life and cost savings compared to full punch replacement.

Key Technical Insights

1. Dilution management is critical: The hardness and wear resistance of the overlay are directly affected by dilution. For high-carbon hardfacing electrodes, dilution of 20–30% is acceptable, but beyond 40%, hardness drops significantly.
2. Post-weld heat treatment is essential for Cr-based overlays: As-welded Cr-based overlays are very hard but brittle. Tempering at 550–650 °C improves toughness while retaining adequate hardness.
3. Electrode baking is non-negotiable: Manual arc electrodes must be baked at 300–350 °C for 1–2 h before use to remove moisture and prevent hydrogen cracking.
4. Multi-pass cladding improves quality: Multiple thin passes produce a finer microstructure and reduce cracking susceptibility compared to a single thick pass.
5. Operator skill is paramount: Manual arc cladding is highly dependent on operator skill. Proper technique (consistent travel speed, proper electrode angle, adequate overlap) is essential for quality.

Summary

Manual arc cladding for tool manufacturing and repair is a mature, cost-effective technology that extends tool life by providing wear-resistant overlay layers. The success of the process depends on proper electrode selection, process parameter control, dilution management, and post-weld heat treatment. For steel industry applications, Cr-based hardfacing electrodes are the most commonly used, providing hardness in the 50–60 HRC range with adequate impact resistance after tempering. The technology is particularly valuable for repair operations where full tool replacement is uneconomical. Engineers should note that manual arc cladding requires significant operator skill and strict adherence to welding procedure specifications to ensure consistent quality.