A286 / Alloy 660 for excellent high temperature oxidation resistance

A286 screws, also known as Alloy 660 screws are stainless steel alloy which contains iron, nickel and chromium. A286 12 point screws are known for their high strength, creep resistance and oxidation resistance at elevated temperatures once age hardened.  As a result, A286 screws provide high levels of strength from room temperature up to about 1300°F (700°C).

A286 12 point screws are also mildly corrosion resistant. While they should not be used for strong acid environments, they provide excellent oxidation resistance up to 1500°F (815°C) in conditions that would typically be found in high temperature exhaust streams.

 A286 Stainless Steel High Temperature Usage

Applications

Because of the properties of Alloy 660 / A286, these screws are often found in high temperature engine, manifold, exhaust and turbine applications as well as off-shore oil & gas applications. In addition, A286 / Alloy 660 is also non-magnetic and finds a niche in non-magnetic cryogenic equipment.

Resources: A286 Torque Specs

Screw Types12 Point ScrewsButton Head Cap ScrewsFlat Head ScrewsHex Cap ScrewsPan Head ScrewsSet ScrewsSocket Head Cap ScrewsTamper Resistant Security Screws, Torx ScrewsVented Screws


A286 / Alloy 660 12-Point Screw Features & Benefits

The driver of a A286 12-point screw uses two overlapped hexagon shapes, creating 12-points and a flanged underside. These are also referred to as ferry cap screws or 12 point flange screws. The advantages of this head style include:

  • Higher torque capability compared to a socket head cap screw
  • Lack of recess to trap fluid or debris.
  • As the heads are generally smaller than a hex, A286 / Alloy 660 12-point screws are often used situations where installation space is tight and saving weight is critical.

The overall disadvantage is the extra cost involved in forming the heads.

The Controversy of 6 vs. 12 point Bolts

There is much debate over which bolt is better. Some say that the more points a nut or bolt has – such as a 12-point bolt - the less chance you have to round it off. And that the additional contact points of a 12 point screw give you more surface to apply load. While the jury is out as to the accuracy of this, it’s the application that should dictate whether the benefits of a 12 point screw out weight the additional costs of making them. 

 


A286 / Alloy 660 Chemistry, Specifications, Cold Working & Heat Treatments

A-286 / Alloy 660 Heat Treatments:  There are several heat treatment combinations for A-286 (Alloy 660) all with slight variations in performance. They can be specified via an AMS number or Class: A, B, C or D,  with most common specified as class A or D.   The grades A, B and C all have the same minimum tensile strength and minimum yield strength of 130ksi and 85ksi respectively. However grade D has a significantly better yield with a min tensile of 130ksi and a min yield of 105ksi. By AMS numbers, the most common for A286 / Alloy 660 is AMS 5737 (same as Grade A) and then AMS 5732 (same as Grade B).

A286 / Alloy 660 Cold Worked: For additional strength, A286 could be aged and cold worked to achieve a min ultimate tensile strength of 160ksi upon request

A-286 Specifications: ASTM A453, AMS 5525, AMS 5732, AMS 5737, AMS 5804, EN 1.4980, GE B50T1181, GE B50T12, GE B50T81, UNS S66286, Werkstoff 1.4980

A 286 Chemistry


Mechanical Properties

A286 Stainless Steel Tensile Properties

A-286 Tensile Curves

 

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