A mid-ranged corrosion resistant 6Mo alloy with good strength
- Good corrosion resistance to moderate acids & sea-water
- 50% stronger than stainless steel
- Usable temperature limit of 1000°F
- AL6XN chemistry & specifications
- Hex head cap screw features and benefits
- AL6XN Datasheet
Originally developed to combat sea water corrosion, AL6XN has expanded its role as being good mid-range corrosion resistant alloy. AL6XN hex head cap screws are a low carbon, high purity, nitrogen-bearing "super-austenitic" stainless alloy. Also considered a 6Moly alloy, AL6XN screws are similar in chemistry and capabilities to Alloy 926 and SMO 254. With a higher nickel and molybdenum content than Duplex 2205 and Super Duplex 2507, it delivers better corrosion resistance while giving a more cost effective alternative to nickel super alloys like Inconel or Hastelloy in moderately corrosive conditions.
• Moderate general corrosion resistance
• Excellent chloride / salt water protection
• Good performance in phosphoric acid
• Moderate resistance to nitric acid
In chemical processes which utilize chlorides, such as paper mills and waste water, stress corrosion cracking (SCC) is a common culprit for 316L stainless failures. Duplex alloys will outlast environments that will cause SCC in 316 stainless, but for more severe low PH environments, hex head cap screws made from higher nickel content alloys like AL6XN will generally work better. For the most extreme situations, alloys with >45% nickel content like Hastelloy are often considered.
Outstanding Resistance to Salt Water
Seawater is where AL6XN hex head cap screws outperform so many alloys providing protection to stress corrosion cracking, pitting and crevice corrosion in a broad range of marine applications. AL6XN hex head cap screws contain a minimum of 6% molybdenum content and it is this addition of molybdenum that provides the greatest protection against pitting and crevice corrosion.
Electrical Resistivity: 535 Ohm-circ mil/ft
Ultimate Tensile Strength: 108 ksi
0.2% Yield Strength: 53 ksi
Density: 0.291 lb/in 3
• High molybdenum content provides enhanced corrosion protection in chloride environments.
• Carbon helps to prevent sensitization during welding
• Chromium enhances pitting and crevice corrosion resistance
• The interstitial strengthening effect of nitrogen gives AL6XN hex head cap screws good high strength properties
• Desalination plants depend on AL6XN hex head cap screws for the salt water corrosion protection
• Pulp bleaching equipment and piping
• The power industry uses AL6XN hex head cap screws where salt water and chlorides are present such as steam surface condensers, supercritical, high pressure, feed water heaters, steam surface condensers, flue-gas desulfurization equipment and in nuclear power water piping
• Chemical Processing - processing tanks, vessels and pipes as well as plate and frame heat exchangers.
Resources: AL6XN Torque Specs
It is important to differentiate between a AL6XN hex head cap screw and hex head bolt. Often people assume they are the same, but they are actually very different fasteners in terms of how they are manufactured, as well as from an application perspective. Regardless of your choice, AL6XN hex heads offer strong, stable joints because of their large head service.
The Hex Comparison
|Hex Head Cap Screw||Hex Head Bolts|
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AL6XN Hex Head Cap Screw Advantages
The most important feature of a AL6XN hex head cap screws is that it has a larger bearing surface area which provide better clamping pressure than other type of fastener such as a socket head cap screw. Additionally, since debris build up is less of an issue with this style of fastener verses a socket head cap screw, they are ideal of dirty applications where particles could clog up a socket. Though AL6XN socket heads are typically used for tight access applications, hex heads can be a better choice when there is only side clearance available for tightening.
AL6XN Specifications: ASTM A 240, ASTM B 688, ASME SA-240, ASME SB-688, ASTM B690, ASTM B691, ASTM A240, ASTM B688, ASME SA-240, ASME SB-688