SMAW Cladding of Duplex Stainless Steel 2205 Process Research

Literature Overview

The paper by Wang Li, Gao Junsong, Wu Daowen, and Hei Penghui from the Luoyang Ship Material Research Institute, published in 2010 in the journal "Welding Machine," investigates the SMAW (shielded metal arc welding) cladding process for duplex stainless steel 2205. This research is particularly significant given the increasing demand for duplex stainless steels in marine, offshore, chemical, and oil and gas industries, where their combination of high strength and excellent corrosion resistance is highly valued.

Technical Background on Duplex 2205

Duplex stainless steel 2205 (UNS S31803 / EN 1.4462) contains approximately 22% Cr, 5–6% Ni, and 3% Mo, with a balanced ferrite-austenite microstructure (typically 40–60% ferrite). This microstructure provides:

The high strength of duplex 2205 is directly related to its ferrite content, but the ferrite phase is susceptible to intermetallic precipitation (σ, χ, and R phases) during prolonged exposure to temperatures between 600–900 °C. This makes heat input control during welding critically important.

Process Parameter Optimization

The authors systematically investigated the effects of welding current, arc voltage, travel speed, electrode diameter, and number of passes on the microstructure, mechanical properties, and corrosion resistance of the 2205 overlay layer.

Key process findings include:

• Welding current: Lower currents (60–90 A for 2.5 mm electrodes) produced narrower beads with higher dilution from the base metal, which can shift the microstructure toward more austenite. Higher currents (100–130 A) produced wider beads with lower dilution but risked excessive heat input.
• Travel speed: Slower travel speeds increased heat input per unit length, promoting grain growth and potential intermetallic formation. Optimal travel speeds of 15–25 cm/min were identified.
• Number of passes: Multi-pass cladding was preferred to control heat input per pass and improve the overall dilution profile. The first pass typically had the highest dilution, while subsequent passes had progressively lower dilution.
• Electrode selection: Duplex stainless steel electrodes (such as those conforming to AWS A5.4 E309L or E310L for transition layers, and E2209 for overlay layers) were evaluated. The choice of electrode composition directly affects the final microstructure of the overlay.

Microstructure and Performance Analysis

The microstructure of the SMAW-cladded 2205 overlay layer was analyzed through metallography and XRD. Key observations included:

• Ferrite-austenite ratio: The overlay layer typically exhibited 45–60% ferrite, which is within the acceptable range for duplex stainless steels. Excessive ferrite (>65%) can lead to reduced corrosion resistance, while insufficient ferrite (<35%) compromises strength.
• Dilution effects: The dilution rate from the carbon steel base metal was found to be 25–40% for the first pass and decreased to 10–20% for subsequent passes. This dilution introduces carbon and manganese into the overlay, which can promote the formation of secondary phases.
• Intermetallic phases: At heat inputs exceeding 1.5 kJ/mm, traces of σ-phase were detected at ferrite-austenite boundaries, indicating the need for strict heat input control.

Mechanical property results showed:

Corrosion resistance was evaluated through potentiodynamic polarization testing in 3.5% NaCl solution and intergranular corrosion testing per ASTM A923 Practice A. The overlay layers demonstrated significantly improved corrosion resistance compared to the base metal, with corrosion potential shifts of 150–300 mV in the positive direction.

Engineering Considerations

For practical SMAW cladding of duplex 2205, the following recommendations emerge from this study:

1. Preheating: 50–100 °C preheat is sufficient to prevent cold cracking, as duplex 2205 has lower susceptibility to hydrogen cracking than martensitic stainless steels.
2. Heat input control: Maintain heat input below 1.2 kJ/mm to prevent intermetallic precipitation.
3. Transition layer: When cladding over carbon steel or low-alloy steel, a transition layer of austenitic stainless steel (309L or 310L) is recommended to reduce dilution effects on the duplex overlay.
4. Post-weld treatment: Solution annealing at 1050–1100 °C followed by rapid cooling can restore the equilibrium ferrite-austenite ratio and dissolve any precipitated intermetallics.
5. Inspection: Visual inspection, magnetic particle inspection (MT) for surface defects, and ultrasonic testing (UT) for subsurface defects should be performed per NB/T 47002 or ASME V.

Study Insights and Reflections

The most significant contribution of this study is the demonstration that SMAW, despite being a relatively "crude" process compared to GTAW or GMAW, can produce acceptable duplex 2205 overlay layers when process parameters are carefully controlled. This finding is particularly valuable for field repair and maintenance applications where portable equipment is required.

The study also highlights an important practical consideration: the dilution problem in duplex stainless steel cladding is more severe than in austenitic stainless steel cladding because the ferrite-austenite balance is more sensitive to compositional changes. A 5% increase in dilution can shift the microstructure by 10–15% ferrite, which has measurable effects on both mechanical properties and corrosion resistance.

For engineers involved in the fabrication of duplex stainless steel clad pressure vessels or heat exchangers, this research reinforces the importance of welding procedure qualification and the need for qualified welders who can maintain consistent bead profiles and heat input levels. The transition from laboratory conditions to production welding requires careful attention to consumable consistency, joint preparation, and in-process monitoring.