CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Open-Arc Weld Overlay Process Parameters on Microstructure and Hardness of High-Chromium Alloy
Overview and Background
High-chromium alloys, particularly those containing 12–28% Cr, are extensively used in applications requiring resistance to oxidation, corrosion, and wear at elevated temperatures. Open-arc weld overlay (typically SMAW or GMAW) is a widely used method for depositing these alloys due to its equipment simplicity and field applicability. The literature under study systematically investigates how open-arc weld overlay process parameters influence the microstructure and hardness of high-chromium alloy deposit layers, providing practical guidance for optimizing wear and corrosion performance in industrial applications.
Experimental Design and Parameter Matrix
The study employs a systematic experimental approach with the following parameter ranges:
| Parameter | Level 1 | Level 2 | Level 3 | Unit |
|---|---|---|---|---|
| Welding current | 120 | 160 | 200 | A |
| Arc voltage | 20 | 24 | 28 | V |
| Travel speed | 3 | 5 | 7 | mm/s |
| Electrode/wire diameter | 2.5 | 3.2 | 4.0 | mm |
| Number of passes | 3 | 5 | 7 | passes |
The heat input (Q) was calculated using the standard formula Q = ηUI / v, where η is the arc efficiency (0.75–0.85 for open-arc processes). The resulting heat input range was approximately 0.5 to 3.5 kJ/mm, covering both low and high heat input conditions.
Microstructural Analysis
The microstructural evolution with varying process parameters revealed several important trends:
- Low heat input conditions (Q < 1.0 kJ/mm): The deposit exhibits fine dendritic structures with abundant primary Cr₂₃C₆ and M₇C₃ carbides. The microstructure is characterized by fine grain size (10–20 μm) and high carbide volume fraction (25–35%). Hardness values reach 650–750 HV.
- Medium heat input conditions (Q = 1.0–2.0 kJ/mm): Dendritic structures become coarser, and carbide morphology transitions from primary to more equiaxed shapes. Grain size increases to 30–50 μm, and carbide volume fraction decreases to 15–25%. Hardness values are in the range of 500–620 HV.
- High heat input conditions (Q > 2.0 kJ/mm): Coarse dendritic or even columnar structures dominate. Significant carbide dissolution occurs, and the matrix becomes more austenitic. Grain size exceeds 80 μm, and hardness drops to 350–480 HV.
The following table summarizes the relationship between heat input and key microstructural properties:
| Heat Input (kJ/mm) | Grain Size (μm) | Carbide Volume Fraction (%) | Matrix Phase | Hardness (HV) |
|---|---|---|---|---|
| 0.5–1.0 | 10–20 | 25–35 | Ferritic | 650–750 |
| 1.0–2.0 | 30–50 | 15–25 | Ferritic + austenitic | 500–620 |
| 2.0–3.5 | 80–150 | 5–15 | Predominantly austenitic | 350–480 |
Hardness and Wear Performance Correlation
The study establishes a clear correlation between process parameters, microstructure, and mechanical performance:
- Peak hardness is achieved at moderate heat inputs (1.2–1.8 kJ/mm) where the balance between carbide formation and matrix strength is optimal.
- Wear resistance follows a similar trend but with a broader optimal range, as the toughness of the matrix also contributes to wear performance under impact loading conditions.
- Corrosion resistance is enhanced at lower heat inputs due to the higher ferritic content, which provides better resistance to pitting and intergranular corrosion in chloride-containing environments.
Process Recommendations and Engineering Application
Based on the study findings, the following process recommendations are proposed:
- For wear-dominated applications (e.g., mining equipment, cement mills): Use lower heat input (0.8–1.5 kJ/mm) with multiple thin passes (≤ 3 mm per pass) to maximize carbide content and hardness.
- For corrosion-dominated applications (e.g., chemical processing, marine environments): Use moderate heat input (1.5–2.5 kJ/mm) to achieve a balanced ferritic-austenitic microstructure with good corrosion resistance.
- For combined wear and corrosion applications: Use a two-layer approach—a transition layer at moderate heat input followed by a surface layer at lower heat input to achieve both toughness and hardness.
- Interpass temperature should be maintained below 200 °C to prevent excessive grain growth and carbide coarsening in multi-pass deposits.
Key Reflections and Study Insights
The most significant finding is that the open-arc weld overlay process parameters have a profound and predictable influence on the microstructure-hardness-performance relationship in high-chromium alloys. The study demonstrates that process optimization is not merely about achieving maximum hardness but rather about tailoring the microstructure to the specific service requirements. The heat input serves as the master variable that governs the entire microstructural evolution, from grain size to carbide morphology to phase composition. Engineers should recognize that the same alloy deposited under different process conditions can yield dramatically different performance characteristics, and that process parameter selection must be driven by application requirements rather than convenience or habit. The study also highlights the importance of understanding the underlying metallurgical mechanisms—carbide precipitation, phase transformation, and grain growth kinetics—rather than relying solely on empirical parameter optimization. This mechanistic understanding enables engineers to extrapolate process recommendations to new applications and alloy compositions with confidence.