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ZERON 100 Super Duplex Compared to Generic S32760 Super Duplex.

ZERON® 100, developed as a wrought super duplex in the 1980s, was given the code UNS S32760 in 1989.  Since that time several other super duplex alloy compositions have been made, and other manufacturers have begun to produce product to the S32760 designation.  Not all versions produced meet the same expected properties of ZERON 100; wide limits in composition and specifications that require only minimum heat treat temperatures permit a wide range of final properties.

Strict control of composition is necessary to get proper balance properties in the duplex structure, as well as preventing or minimizing precipitation of deleterious third phases, such as nitrides, sigma, chi, etc.  Nitrides reduce toughness and resistance to corrosion. The intermetallic phases sigma & chi, lower toughness and corrosion resistance by depleting the surrounding matrix of chromium and molybdenum.    Alpha prime, which occurs in thick sections when product is cooled too slowly, often by improper quench, significantly reduces toughness, and is NOT visible by optical microscopy.

In random tests of generic S32760 versus ZERON 100, Rolled Alloys laboratories found that ZERON 100 had a higher critical pitting temperature

  • 75°C versus 45°C in ASTM G48 Method A
  • 90°C versus 62°C in seawater
  • No cracking in NACE sulfide tests, where the generic UNS S32760 cracked. 

Several oil companies have had failures where poor heat treatment of S32760 led to high concentrations of sigma phase, low impact properties and increased brittleness.  ZERON 100, with its more stringent production controls, has not had a similar history.  ZERON 100 is capable of meeting impact toughness demands up to 70 Joules at temperatures as low as -70°C with the standard ZERON 100, and 90 Joules, at -70°C with ZERON 100 AFP™ (Advanced Forging Process).  This has been done with products as large as 51.25”, 10,000# hubs. 

To ensure full compliance with the specification, and minimize undesirable phases and to ensure maximizing of properties requires strict control.  Heat treatment must be clearly defined and fully monitored; minimum and maximum temperatures specified, time at temperature, or in quench established.  Product must be ferritiscope tested at random on all components to ensure proper balance.  In-situ metallurgy should be used to further document any are of concern.  Sacrificial testing should be performed. 

Rolled Alloys produces ZERON 100 above the demands of industry norms, such that ZERON 100 offers superior corrosion resistance, impact toughness, and resistance to HISC compared with generic UNS S32760.