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INCOLOY alloy 27-7MO Sheet and Plate UNS S31277
Overview
INCOLOY® alloy 27-7MO (UNS S31277) is an advanced 7% molybdenum super-austenitic stainless steel offering corrosion resistance in most environments superior to 6% molybdenum super-austenitic stainless steels. In many
environments alloy 27-7MO offers resistance approaching that of much more highly alloyed materials such as INCONEL alloys 625, 22, and C-276. Alloy 27-7MO products typically contain 27% nickel, 22% chromium, 7.2% molybdenum, and 0.34% nitrogen. Its limiting chemical composition is presented in Table 1. The alloy's content of nickel and nitrogen produce a stable austenitic structure. By virtue of its content of molybdenum, chromium, and nitrogen, alloy 27-7MO offers excellent resistance to pitting and crevice corrosion. The nickel, nitrogen, and molybdenum provide resistance to reducing media while a high content of chromium offers resistance to oxidizing media. Alloy 27-7MO performs well in mixed acid environments, especially those containing oxidizing and reducing acids. The alloy's contents of nickel and nitrogen result in resistance to stress corrosion cracking and attack by caustic media. Alloy 27- 7MO offers excellent resistance to corrosion in seawater and brine. It also resists stress corrosion cracking in all concentrations of sodium chloride up to saturation at the boiling point. It is resistant to the aggressive media encountered in air pollution control systems such as flue gas desulfurization equipment for high-sulfur coal-fired electric power utilities. Applications for INCOLOY alloy 27-7MO are found in the pollution control, power, marine, chemical processing, pulp and paper and oil and gas industries. The alloy offers a unique combination of corrosion resistance, high strength and ease of fabrication at an economical price. Alloy 27-7MO is available in standard product forms including plate, sheet, rod, bar, wire rod, pipe, tube, and forging stock.
| Chemistry | ||||||||
|---|---|---|---|---|---|---|---|---|
| Chemical Requirements | ||||||||
| Ni | Cr | Mo | Mn | C | Si | Cu | Fe | |
| Max | 26.0 | 20.5 | 6.5 | 3.00 | 0.02 | 0.5 | 1.5 | Bal. |
| Min | 28.0 | 23.0 | 8.00 | 0.5 | ||||
Applications
Applications for INCOLOY alloy 27-7MO are found in the pollution control, power, marine, chemical processing, pulp and paper and oil and gas industries. The alloy offers a unique combination of corrosion resistance, high strength and ease of fabrication at an economical price. Alloy 27-7MO is available in standard product forms including plate, sheet, rod, bar.
Corrosion Resistance
Pitting Resistance Equivalency Number - A means of comparing the corrosion resistance of alloys is by their Pitting Resistance Equivalency Number or 'PREN'. Alloys exhibiting higher PREN values are generally found to be more resistant to localized corrosion than those with lower PREN values. The PREN can be calculated by several different equations based upon the chemical composition of the alloys. Some equations are applicable to stainless steels while others are better applied to nickel-based alloys. The equation used here is generally accepted as being applicable to a wide range of alloy compositions. When comparing alloys by their PREN it is absolutely necessary that the same equation be used for all materials to be compared. Comparing alloys by PRENs generated from different equations will give erroneous results. For more information on the use of PRENs to compare the corrosion resistance of materials, refer to the Special Metals publication, “High Performance Alloys for Resistance to Aqueous Corrosion” or visit the Special Metals website, www.specialmetals.com. PRENs for alloy 27-7MO and similar materials are seen in Table 5. Based on these values of PREN, alloy 27-7MO would be predicted to offer significantly better corrosion resistance than alloy 25-6MO (and similar grades of super-austenitic Resistance to Corrosion by Seawater Nickel-chromium alloys and austenitic and super-austenitic stainless steels containing molybdenum are well known for their resistance to corrosion in seawater and marine environments. A test program conducted at the LaQue Center for Corrosion Technology in Wrightsville Beach, North Carolina (a laboratory well known for marine corrosion testing) produced data showing that INCOLOY alloy 27-7MO offers corrosion-resistance superior to many of the corrosion-resistant alloys commonly used in marine service. Samples of sheet to which Teflon crevice devices were attached were exposed to flowing natural seawater.
| Tensile Data | |||||
|---|---|---|---|---|---|
| Mechanical Property Requirements | |||||
| Ultimate Tensile | Yield Strength (0.2% OS) | Elong. | R/A | Hardness | |
| Cold Finished/Annealed | |||||
| Min | 120 KSi | 60 KSi | 50 | Rb 95 | |
| Max | |||||
| Hot Finished/Annealed | |||||
| Min | 827 MPa | 414 MPa | |||
| Max | |||||
Machinability RATING: 27% of B-1112
TYPICAL STOCK REMOVAL RATE: 45 surface feet/minute with high speed tools, 125 surface feet/minute with carbide.
| Machining Guide | |||||
|---|---|---|---|---|---|
| Operation | Tool Type | Speed SFPM | Feed Inch Per Rev. | Depth in Cut Inch | Cut Type |
| Turning | WC | 68 | .009-.016 | .050-.100 | Rough |
| 88 | .006-.009 | .011-.015 | Finish | ||
| HSS | 18 | .007-.011 | .025-.045 | Rough | |
| 21 | .003-.008 | .008-.011 | Finish | ||
| Facing | WC | 68 | .009-.016 | .040-.075 | Rough |
| 88 | .006-.009 | .011-.015 | Finish | ||
| HSS | 18 | .007-.011 | .025-.045 | Rough | |
| 21 | .003-.008 | .008-.011 | Finish | ||
| Boring | WC | 42 | .009-.016 | .043-.060 | Rough |
| 53 | .006-.009 | .012-.015 | Finish | ||
| Drilling | HSS | 18 | .003-.007 | - | Rough |
| 25 | .002-.004 | - | Finish | ||
| Reaming | HSS | 25 | .006-.010 | - | Rough |
| 35 | - | .012-.015 | Finish | ||
| Shaping | WC | 20 | - | .060-.090 | Rough |
| 30 | .005-.010 | .018-.025 | Finish | ||
| HSS | 13 | - | .050-.080 | Rough | |
| 15 | .005-.010 | .018-.025 | Finish | ||
| Milling | HSS | 15 | 1/2-1 IPM | .100-.200 in. cut | Rough |
| 25 | Finish | ||||
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