ER2594 Super Duplex Stainless Wire

 

ER2594 is an austenitic-ferritic super duplex stainless steel TIG/MIG welding wire conforming to AWS A5.9. Engineered for joining super duplex grades such as UNS S32750 (SAF 2507) and UNS S32760, this wire delivers a weld deposit with a balanced austenite-ferrite microstructure, providing the combined advantages of austenitic stainless steel toughness and ferritic stainless steel stress corrosion cracking resistance.

 

With a nominal composition of 25% Cr, 9.5% Ni, and 3.6% Mo plus controlled nitrogen addition, ER2594 achieves a Pitting Resistance Equivalent Number (PREN) exceeding 40 - the threshold that defines "super duplex" performance - making it the standard filler metal for the most demanding seawater, chemical, and oil & gas environments.

 

 

• PREN > 40: Exhibits exceptional resistance to pitting and crevice corrosion in chloride-containing environments.
• Balanced Duplex Structure: Contains 40–60% ferrite, combining high strength with excellent resistance to stress corrosion cracking (SCC).
• High Mechanical Strength: Features a tensile strength of approximately 870 MPa-roughly double that of standard austenitic stainless steels.
• Low Impurity Content: Strict control over Sulfur (S ≤ 0.010%) and Phosphorus (P ≤ 0.020%) levels ensures a clean, crack-free weld metal.
• Nitrogen Strengthening: Controlled addition of nitrogen (N)-at approximately 0.25%-stabilizes the austenitic phase and enhances pitting corrosion resistance within the weld zone.
• Copper-Bearing Composition: Contains approximately 0.7% copper (Cu), which enhances corrosion resistance in sulfuric acid environments.

 

 

Element	Typical Deposit (%)
C	0.02
Cr	24.55
Ni	9.35
Mo	3.65
N	0.25
Cu	0.70
Mn	0.64
Si	0.42
P	0.014
S	0.006

 

 

Property	Typical Value
Tensile Strength (σb)	870 MPa
Yield Strength (σ0.2)	≥550 MPa
Elongation (δ5)	≥25%
Impact Toughness (−40°C)	≥125 J
Hardness	~28–32 HRC

 

 

 

Property	Value
AWS Classification	A5.9 ER2594
EN/ISO Designation	ISO 14343-A: W 25 9 4 N L
UNS Number	S32750-type deposit
Welding Processes	GTAW (TIG), GMAW (MIG)
Shielding Gas	Pure Argon (Ar ≥ 99.99%) or Ar + 2% N₂
Base Metal Match	UNS S32750, S32760, S32550 (SAF 2507, Zeron 100)

 

 

Polarity: DCEP (DC Electrode Positive).

 

 

Wire Diameter	Current (A)	Shielding Gas	Gas Flow
1.6 mm	80–140 A	Ar or Ar + 2% N₂	10–14 L/min
2.0 mm	100–170 A	Ar or Ar + 2% N₂	10–14 L/min
2.4 mm	120–200 A	Ar or Ar + 2% N₂	12–16 L/min

 

 

Wire Diameter	Current (A)	Voltage (V)	Shielding Gas
0.8 mm	100–180 A	18–24 V	Ar + 2% N₂
1.0 mm	120–220 A	20–26 V	Ar + 2% N₂
1.2 mm	150–280 A	22–28 V	Ar + 2% N₂

 

 

Welding of super duplex stainless steel requires strict process control to ensure that the weld zone achieves an appropriate balance between austenite and ferrite phases. Improper welding techniques can result in excessive ferrite content (thereby reducing toughness) or excessive austenite content (thereby reducing resistance to stress corrosion cracking).

 

Pre-weld Cleaning: All rust, oil, moisture, and surface contaminants must be removed from the weld bevels and adjacent areas. Contaminants can lead to porosity in the weld seam and compromise the material's corrosion resistance.

 

Interpass Temperature:Must be strictly controlled below 150°C (302°F). Excessive heat input promotes the precipitation of the sigma (σ) phase and disrupts the austenite-ferrite balance.

 

Arc Length: A short-arc welding technique should be employed. For TIG (Tungsten Inert Gas) welding, the arc length should be maintained within the range of 1–3 mm. A short arc helps minimize nitrogen depletion in the weld pool and minimizes the degree of oxidation.

 

Heat Input Control:The target heat input should be controlled between 0.5 and 2.5 kJ/mm. Heat input that is either too low or too high will adversely affect weld quality:

 

• Too Low → Leads to excessive ferrite content, thereby reducing toughness and corrosion resistance.
• Too High → Leads to the precipitation of sigma (σ) or chi (χ) phases, resulting in sensitization.

 

Shielding Gas: Pure argon, or a mixture of argon with 2% nitrogen, should be selected. Adding nitrogen to the shielding gas helps compensate for nitrogen depletion during the welding process and assists in maintaining the proper austenite phase content. The use of shielding gas mixtures containing CO₂ is strictly prohibited.

 

Back Purging (Back-blowing):For all root passes in pipes and enclosed structural components, back purging with inert gas is a mandatory process requirement. Pure argon or an argon/nitrogen mixture should be used for back purging. Back purging must be maintained continuously until the root pass is completely covered by at least two subsequent weld layers.

 

Post-weld Heat Treatment: For super duplex stainless steel, post-weld heat treatment is typically not required and is generally not recommended. If relevant specifications or standards mandate heat treatment, the sole acceptable treatment procedure is solution annealing at a temperature of 1050–1125°C, immediately followed by water quenching.

 

 

ER2594 is specified wherever the combination of high strength, pitting resistance, and SCC immunity is required in aggressive chloride environments:

 

 

 

 

 

•Store ER2594 in original sealed packaging in a dry environment (RH < 50%)

•Protect from carbon steel contamination - use dedicated stainless steel tools, clamps, and grinding discs

•Opened TIG rod tubes should be resealed after each use

•MIG spools should be stored in a rod oven or climate-controlled cabinet if ambient humidity exceeds 60%

•Never use carbon steel wire brushes on super duplex weld surfaces - use stainless steel or nylon brushes only

 

 

 

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