Special Stainless Steels
UNS Number | UNS S66286 |
Industry Name | Alloy A286, Alloy 660, A-286, W.Nr.1.4980, X6NiCrTiMoVB25-15-2, SUH660 |
Product Forms | Billets, Bars, Forgings, Wires |
General Characteristics
Alloy 660 is an iron-base precipitation-hardening superalloy. It was originally developed to provide a cost-effective high-temperature fastener material, addressing the weakness of conventional austenitic stainless steels which lose strength rapidly above 500°C and expensive nickel-base superalloys for mass fastener production. Early stainless grades had limited creep resistance at 650~700°C while premium nickel alloys brought excessive material cost.
It retains stable creep and stress rupture strength under long-term thermal cycling, making it ideal for gas turbine bolts, studs, exhaust components and cryogenic structural fasteners. Compared to Inconel 718, Alloy 660 has much lower raw material cost but reduced maximum service temperature. It performs well up to 700°C while Alloy 718 can sustain higher loads above this temperature threshold. Compared to 321 and 316 stainless steel, Alloy 660 delivers vastly superior high-temperature creep strength, whereas stainless steels are not suitable for sustained load at elevated temperature.
Inconel is a trademark of high-performance nickel-based alloys developed by Special Metals Corporation.
Chemical compositions of Alloy A286 | Alloy 660
Ni | Mn | C | Si | S | Cr | Al | Ti | Mo | P | B | V | |
Min | 24 | 13.5 | 1.9 | 1 | 0.001 | 0.1 | ||||||
Max | 27 | 2 | 0.08 | 1 | 0.03 | 16 | 0.35 | 2.35 | 1.5 | 0.04 | 0.01 | 0.5 |
Automotive & Motorsport||Turbocharger clamping fasteners|Exhaust manifold studs and bolts|Valve spring retainers and spring seats|Hot-section fasteners|Wastegate spring components
Oil & Gas / Petrochemical||High-temperature bolting|Elevated-temperature wellhead fasteners|Steam turbine studs, bolts and nuts|Valve stem fasteners|Refinery furnace support hardware
Nuclear Power||Reactor auxiliary high-temperature fasteners|Core support assembly bolts and studs
Power Generation||Gas turbine auxiliary fasteners|Boiler tube support fasteners
Technical Standards | Product Form |
ASTM A453 Grade 660 | Bar, Stud, Bolt, Nut, Fastener |
AMS 5732 | Bar, Forging, Forged Billet, Ring |
AMS 5737 | Sheet, Plate, Strip |
AMS 5804 | Wire, Welding Wire |
AMS 5805 | Spring Wire |
EN 10269 | Bar, Plate, Sheet, Strip, Seamless Tube & Pipe, Wire, Welding Wire |
BS HR 201 | Plate, Sheet, Strip |
BS HR 601 | Wire, Welding Wire |
Product form | Size range (mm) |
Forged bar | Dia.70-500 |
Rolled bar | Dia.2.0-70 |
Flat bar | T4-50*W60-300 |
Wire | Dia.0.25-18.0 |
Plate | 1-25 * ≤1200 * ≤1200 |
Q1: Are Alloy A286 and Alloy 660 the same raw material for fastener production?
A: Yes. Both names refer to UNS S66286 iron-base precipitation hardening superalloy. A286 is the traditional trade name; Alloy 660 (Grade 660) originates from ASTM A453 for fastener applications. The raw material chemical composition is identical. The difference lies in purchasing specifications, melting route and inspection scope.
Q2: What melting practice do you use for Alloy 660 fastener-grade bar?
A: VIM+ESR. Premium aerospace quality uses Vacuum Induction Melting plus Vacuum Arc Remelting (VIM+VAR) to reduce inclusions, gas content and segregation for critical fastener raw material.
Q3: What delivery heat treatment condition and mechanical property classes are available for Alloy 660 raw bar for fasteners?
A: Alloy A286 / Alloy 660 fastener raw material is governed by ASTM A453, which establishes four classes: Class A, B, C and D. Each class defines a unique heat treatment cycle and corresponding mechanical properties.
· Class A: Solution treated + age hardened at lower temperature; moderate tensile strength, higher ductility.
· Class B: Solution treated + age hardened; higher tensile strength than Class A, reduced ductility.
· Class C: Solution treated + age hardened; higher strength than Class B, further reduced ductility.
· Class D: Solution treated + age hardened to the maximum specified tensile strength; lowest ductility among the four grades.
Raw bar is commonly supplied in solution-treated condition or as hot worked for customers to complete heat treatment during fastener forming. The required ASTM A453 class shall be clearly specified at order placement, to ensure the final fastener mechanical properties meet your design requirement.
Q4: What mechanical property limits can we expect from your Alloy A286 raw bar?
A: In solution treated condition, raw material has moderate hardness for forming. Final strength, creep and stress rupture properties are achieved after customer’s age hardening treatment. We provide raw material tensile and hardness test certificates.
Q5: What size range of round bar stock is available for fastener blanking / hot forging?
A: We offer billets and round bars from small cold-heading wire rod up to large diameter forged bars for heavy stud blanks. Tolerances can be supplied as hot rolled, peeled or centerless ground upon request.
Q6: Does Alloy 660 raw material have consistent grain size across the whole bar cross-section?
A: Grain size is controlled during solution treatment. Large diameter bars may show slight grain size variation from surface to center. We can specify grain size requirements and perform grain size testing for critical fastener raw material lots.
Q7: What non-destructive testing (NDT) can be applied on Alloy A286 raw bar?
A: Ultrasonic testing (UT) is standard for internal defects. Liquid penetration inspection (LP) can be performed for surface cracks.
Q8: Is Alloy A286 raw material prone to cracking during fastener hot heading or cold forming?
A: When material is properly solution annealed and grain size controlled, it is suitable for hot forging and limited cold heading. Poor surface condition, improper heating or non-compliant heat treatment of raw stock will increase cracking risk.
Q9: What certification documents come with Alloy 660 fastener-grade raw material?
A: Standard 3.1 material test certificate includes heat number, chemical analysis, tensile data, hardness and heat treatment records. For critical projects, 3.2 certification and additional test reports can be arranged.
Q10: Can Alloy 660 raw bar be used for nuclear auxiliary fastener blanks?
A: Yes, special heat melts with controlled residuals, low gas content and extended NDT can be supplied for nuclear auxiliary fastener raw material. Additional traceability and documentation requirements must be agreed before order placement.