Complex compounds of iron, chromium, and molybdenum are highly detrimental to toughness and corrosion resistance, particularly the resistance to localized chloride attack. The graph shows the time-temperature exposures required for a 50% reduction in impact strength due to isothermal precipitation of undesirable secondary phases for various duplex stainless steels.
The kinetics of σ/χ precipitation is greatest in the range of about 1500 to 1700°F. The time required to degrade properties depends on the temperature and the alloy content. The increased N content of modern duplex stainless steels significantly decreases the rate of the σ/χ precipitation reactions making it possible to weld these grades without loss of properties due to formation of intermetallic phases. Once intermetallic phases have formed, the only means of removing them and restoring properties is a full solution anneal followed by rapid cooling.
Volume 4D, Heat Treating of Irons and Steels ⇒ Heat Treated High-Alloy Steels ⇒ Heat Treating of Austenitic and Duplex Stainless Steels ⇒ Duplex Stainless Steels
