CLADDING TECHNOLOGY SHANXI CO., LTD309L Plus 316L Strip Cladding Submerged Arc Welding Process Test
Literature Overview
This 2012 study by Zou Hua, Zhang Shiguo, Huang Wen, and Li Fengmei (Nanjing Debang Metal Equipment Engineering Co. and Nanjing Sanbang Metal Composite Materials Co.) presents a systematic process investigation of strip cladding using 309L and 316L filler materials via submerged arc welding (SAW). The study is particularly relevant to the fabrication of clad-plate pressure vessels and heat exchangers used in the chemical and petrochemical industries, where the combination of corrosion resistance and mechanical strength is essential.
Core Technical Content
The study investigates the strip cladding process using a two-layer approach: a transition layer of 309L (high nickel austenitic stainless steel) followed by a corrosion-resistant layer of 316L (molybdenum-bearing austenitic stainless steel). The base material is typically a carbon steel or low-alloy steel plate. The 309L layer serves as a dilution buffer, absorbing the carbon and alloying elements from the base material and preventing the formation of brittle intermetallic compounds at the interface. The 316L layer provides the final corrosion-resistant surface.
Process Parameters
| Parameter | 309L Transition Layer | 316L Corrosion Layer |
|---|---|---|
| Strip thickness | 3.0–4.0 mm | 3.0–4.0 mm |
| Strip width | 40–50 mm | 40–50 mm |
| Welding current | 400–550 A | 350–500 A |
| Welding voltage | 25–32 V | 24–30 V |
| Travel speed | 250–400 mm/min | 250–400 mm/min |
| Flux type | Low-alkali, low-hydrogen | Low-alkali, low-hydrogen |
| Flux moisture | ≤0.5% | ≤0.5% |
| Preheating temperature | 100–150°C | 100–150°C |
| Interpass temperature | ≤200°C | ≤200°C |
Microstructure and Performance
The microstructure at the 309L/base material interface consists of a narrow heat-affected zone (HAZ) with ferrite-austenite microstructure. The 309L layer itself exhibits a fully austenitic microstructure with some delta ferrite (typically 5–15%), which helps to prevent hot cracking. The 316L layer shows a similar austenitic microstructure with lower carbon content, ensuring good corrosion resistance.
| Test Item | 309L Layer | 316L Layer | Standard Requirement |
|---|---|---|---|
| Hardness (HV) | 180–220 | 160–200 | ≤250 |
| Tensile strength (MPa) | ≥520 | ≥480 | ≥480 (316L) |
| Elongation (%) | ≥35 | ≥40 | ≥35 |
| Bend test (180°) | Pass | Pass | No cracking |
| Intergranular corrosion (ASTM A923) | Pass | Pass | No attack |
| Bond strength (peel test) | ≥30 MPa | — | ≥20 MPa |
Quality Control and NDT
The quality of the strip cladding is verified through several non-destructive testing (NDT) methods:
- Magnetic particle testing (MT): Detects surface and near-surface cracks in the 309L and 316L layers.
- Ultrasonic testing (UT): Evaluates the bonding quality at the 309L/base material interface and detects internal defects.
- Radiographic testing (RT): Inspects the weld seam for porosity, lack of fusion, and inclusions.
- Peel test: Measures the bond strength between the cladding layer and the base material.
Engineering Practice Integration
The 309L+316L strip cladding process is widely used in the fabrication of heat exchanger tubesheets, pressure vessel heads, and pipe spools in the chemical and petrochemical industries. The process offers several advantages over single-layer cladding:
- The 309L transition layer effectively controls dilution, ensuring that the 316L layer maintains its specified chemical composition and corrosion resistance.
- The two-layer approach allows for independent optimization of the transition and corrosion layers, enabling better control of mechanical properties and corrosion resistance.
- The SAW process provides high deposition rates and consistent weld quality, making it suitable for large-scale production.
However, the process also presents challenges. The welding speed must be carefully controlled to avoid excessive dilution at the 309L/base material interface. The flux must be kept dry and free from contamination to prevent porosity. The interpass temperature must be maintained below 200°C to avoid sensitization and intergranular corrosion susceptibility in the 316L layer.
Key Reflections and Study Insights
This study provides a comprehensive process investigation of the 309L+316L strip cladding process, offering valuable guidance for engineers involved in the fabrication of clad-plate pressure vessels and heat exchangers. The use of a two-layer approach is a well-established practice in the industry, and the study confirms its effectiveness in achieving high-quality cladding with controlled dilution. The systematic evaluation of welding parameters, microstructure, and mechanical properties provides a solid foundation for process optimization and quality assurance. One important insight from this study is the critical role of the 309L transition layer in preventing the formation of brittle chromium carbides at the interface. The high nickel content of 309L stabilizes austenite and reduces the risk of cracking during welding and service. This study also highlights the importance of rigorous NDT in ensuring the quality of the cladding, particularly at the critical 309L/base material interface where lack of fusion and cracking are most likely to occur.