S32760

S32760 maintains high strength at moderate temperatures:

Long-term thermal stability and microstructural stability:

S32760 exhibits good microstructural stability when in service at temperatures ≤ 300°C for extended periods.

Note:

Prolonged exposure to temperatures between 300-500°C may lead to 475°C embrittlement (spinodal decomposition of the ferrite phase), resulting in reduced toughness. Therefore, long-term use within this temperature range is not recommended.

Prolonged exposure in the 600-900°C range may lead to the precipitation of the sigma phase (an intermetallic compound), which significantly reduces corrosion resistance and toughness. Solution treatment must quickly pass through this temperature range.

S32760 is more sensitive to harmful phase precipitation than 2205, requiring strict control of cooling rates during heat treatment and welding to quickly pass through the sensitive temperature range.

Antioxidant Performance:

S32760 can form a protective oxide layer below ≤ 800°C, offering better antioxidant properties than austenitic stainless steels. For long-term service at higher temperatures, it is recommended to evaluate oxidation weight gain.

Heat treatment system

The heat treatment of S32760 has a decisive impact on the final microstructure and properties, with common specifications as follows:

1. Solution treatment (for obtaining the optimal duplex microstructure and comprehensive properties):

Heat to 1050-1125°C, hold for sufficient time (approximately 2-4 minutes per inch of thickness), then water quench or rapid air cool.

To achieve the ideal duplex microstructure of approximately 50% ferrite and 50% austenite for optimal corrosion resistance.

2. Stress relief treatment (after welding/cold working):

Heat to 650-750°C, hold for 1-2 hours, then air cool. Used to eliminate residual stress.

However, note that sigma phase precipitation may occur in this temperature range; it is recommended to carefully evaluate its impact on corrosion resistance.

Note:

• Heat treatment should quickly pass through the sensitive temperature range of 600-900°C to avoid precipitation of σ phase and χ phase.
• The solution treatment temperature should not be too high (> 1125°C), otherwise the ferrite content will be excessive, affecting toughness and corrosion resistance.
• It is recommended to perform pickling or passivation after heat treatment to remove surface scale

Welding Performance and Process Key Points

32760 has good welding properties, but strict control of process parameters is required:

1. Recommended welding methods:

TIG (GTAW), MIG (GMAW), SMAW, SAW, FCAW.

2. Heat input control:

It is recommended that the heat input be 0.5-2.5 kJ/mm, and the interpass temperature be ≤ 100-150°C to avoid grain coarsening in the heat-affected zone and precipitation of harmful phases.

3. Protective gas:

It is recommended to use a mixed gas of Ar + 1-2% N₂, which can increase the austenite content in the weld metal, thereby improving the toughness and corrosion resistance of the weld.

4. Filler metal:

It is suggested to use super duplex stainless steel welding materials such as ER32760 (Zeron 100X) or ERNiCrMo-10 that are matched or over-matched to the base metal to ensure that the corrosion resistance of the weld is not lower than that of the base metal.

5. Post-weld treatment:

It is recommended to perform pickling or passivation to restore the corrosion resistance of the heat-affected zone and remove welding oxidation color. Pickling is more effective than mechanical cleaning in removing chromium-depleted layers.

Comparison of Magnetic Properties and Application Selection

Applicable Media

Seawater and chloride solutions:

Excellent resistance to pitting corrosion, crevice corrosion, and stress corrosion cracking.

2. Oxidizing acids:

Such as nitric acid (≤40%), with superior corrosion resistance.

3. Reducing acids:

Such as sulfuric acid (≤40%), hydrochloric acid (low concentration) - the Cu/W formulation makes it superior to S32750.

4. Organic acids:

Acetic acid, citric acid, formic acid, etc.

5. Alkaline solutions:

Sodium hydroxide, potassium hydroxide, etc.

6. Chloride-containing gas media:

Petroleum and natural gas exploration and processing environments, compliant with NACE MR0175 standard.

7. High-temperature water vapor (temperature limitations should be noted).

Note:

S32760 is not resistant to extreme strongly reducing media such as hydrofluoric acid and high-temperature concentrated hydrochloric acid. In hydrogen-containing environments, duplex stainless steels are susceptible to hydrogen embrittlement and require careful evaluation. 475°C embrittlement and σ-phase precipitation are long-term usage conditions that should be avoided.