Incoloy - Model 800 -High Performance Alloys

INCOLOY nickel-iron-chromium alloy 800 was introduced to the market in the 1950s to fill the need for a heat- and corrosion-resistant alloy with a relatively low nickel content since nickel was, at the time, designated a “strategic” metal. Over the past forty years it has been widely used for its strength at high temperatures and its ability to resist oxidation, carburization, and other types of high-temperature corrosion. Applications include furnace components and equipment, petrochemical furnace cracker tubes,
pigtails and headers, and sheathing for electrical heating elements.

In 1963, the alloy was approved by the ASME Boiler and Pressure Vessel Committee, and the design stresses were published in Code Case 1325. For the first time, aluminum and titanium were listed as purposeful additions (at 0.15 to 0.60% each), and annealed material was differentiated from solution-annealed material. The new terms “Grade 1, annealed at approximately 1800°F
(980°C)” and “Grade 2, annealed at approximately 2100°F (1150°C)” came into use. The Code Case covered Sections I and VIII, and listed design stresses for Grade 1 to 1100°F (593°C) and for Grade 2 to 1500°F (816°C).

Over the next few years, the Committee made several revisions. In 1965, extruded tube was accepted as Grade 2 material without heat treatment. By the following year, ASTM specifications had been approved for INCOLOY alloy 800, and these were listed to replace those covering INCONEL alloy 600. In 1967, an external pressure vessel chart for Grade 1 was added, and the following year the same addition was made for Grade 2.

In 1969, design stresses were increased as a result of changes in the criteria to determine those stresses. The minimum tensile strength curve was increased 10% and the rupture criterion was increased from 62.5 to 67% of the extrapolated 100,000 hour rupture strength. Six months later, the Case was changed from covering Sections I and VIII to Section I only since the design
stresses for Section VIII had been included in Table UNF-23. There were also two sets of design stresses listed for each grade, one giving the values when the two-thirds yield strength criterion was used, the other when 90% of yield strength was used.

INCOLOY alloy 800H (UNS N08810)

It had been known for some time that higher carbon alloy 800 had higher creep and rupture properties than low-carbon material. For that reason, Special Metals had melted to a carbon range of 0.05 to 0.10% except for special orders where customers specified a lower carbon content. The carbon range of 0.05 to 0.10% is within the ASTM and ASME specification limits for alloy 800 and is in the upper portion of that range.

Special Metals generated data for this material and presented them to the ASME Code. The Code approved higher design stresses for Section I and Divisions 1 and 2 of Section VIII, which appeared in Code Case 1325- 7. Note that alloy 800H required not only a carbon range of 0.05 to 0.10% but also an average grain size of ASTM 5, or coarser.

With the issuance of Code Case 1325-7 and the common use of the term “800H”, there was no longer a need to refer to “Grade 2” because it was replaced by 800H, and the material that had been called Grade 1 became, simply, INCOLOY alloy 800.