8740 is a chromium nickel molybdenum steel with a lean, balanced alloy content. It heat treats reliably, machines well and is widely called out for aerospace bolts, fittings, clevises and machined hardware in the 125 to 180 ksi range.
Where 4340 is specified for the heaviest loads, 8740 covers the large middle ground of fasteners and fittings where cost and consistency matter as much as ultimate strength.
Stocked as bar and billet, annealed or heat treated to the ordered class, with aerospace fastener specifications available.
Sizes and stock
- Wire: through .950" DIA
- Round bar: through 11" DIA
- Custom shapes and forgings: per request
Processing capabilities
- Vacuum melted (VAR / VIM-VAR) stock with full melt traceability
- Normalize, anneal, quench and temper to the ordered condition
- Saw cutting, trepanning, gun drilling and rough machining
- Magnetic particle and ultrasonic inspection to AMS 2301 / AMS 2154 on request
Specifications
Material is released to the applicable specification with mill test reports and, on request, independent lab verification.
Why engineers specify 8740
- Reliable heat treat response across common strength classes
- Good machinability and cold formability for fastener production
- Widely specified for aerospace bolts and fittings
- Economical compared with higher alloy grades
Nominal chemistry
Percent by weight, nominal composition per the governing specification. The mill test report for your heat is the controlling document.
Typical mechanical properties
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Q&T, 125 ksi class | 125 ksi min | 100 ksi min | 16% min | - |
| Q&T, 160 ksi class | 160 ksi min | 142 ksi min | 12% min | - |
Typical published values for reference only, not for design. Properties vary with section size, product form and processing. Order to the specification and condition your drawing requires.
Typical applications
- Aerospace bolts and fasteners
- Fittings and clevises
- Machined hardware
- Shafts and couplings
Fabrication notes
Machining
Best machined in the annealed or normalized-and-tempered condition, then heat treated to final strength. Rough machining before hardening, with a finish pass after temper, controls distortion on long or thin sections. We can supply rough turned, trepanned or gun drilled stock so your first operation starts closer to net shape.
Welding
Weldable with low hydrogen practice, preheat appropriate to carbon equivalent and section size, and a post weld stress relief or full re-heat treat. For high strength conditions the weld and heat affected zone should be re-treated to restore properties.
Forming
Hot work in the annealed condition. Cold forming is limited at high hardness, so bend and form before hardening and follow with stress relief where the geometry is tight.
8740 compared with similar grades
4340
Higher hardenability and strength ceiling for heavier, more highly loaded parts.
4130
Lower carbon, very weldable tubing and structure grade at lower strength.
Designations and cross reference
- Material family
- Alloy Steels
Working from an obsolete, foreign or superseded designation? Send it over and we will cross reference it to a current grade and specification.
Quality, testing and traceability
Supplied aircraft quality with mill test reports, melt and heat traceability, and, on request, magnetic particle inspection to AMS 2301 or AMS 2300, ultrasonic inspection to AMS 2154, chemical assay, hardness and full mechanical testing.
We are AS9100D and ISO 9001:2015 registered. If our stock does not already carry the inspection your specification requires, we can quote the material with that work performed. More on our quality system
Available forms
Custom sizes converted from billet, plus saw cut, waterjet and near-net blanks. See custom conversions
8740 frequently asked questions
What is 8740?
8740 is a chromium nickel molybdenum steel with a lean, balanced alloy content. It heat treats reliably, machines well and is widely called out for aerospace bolts, fittings, clevises and machined hardware in the 125 to 180 ksi range.
What forms is 8740 available in?
We supply 8740 in wire, bar, forging. Custom sizes are converted from billet, and we can provide saw cut, waterjet or near net blanks so material arrives closer to your finished part.
What specifications can 8740 be supplied to?
Commonly ordered specifications include AMS 6322, AMS 6323, AMS 6324, AMS 6325, AMS 6327. Material is released to the specification and condition on your purchase order, with mill test reports supplied as standard.
What conditions can 8740 be ordered in?
We can supply Q&T, 125 ksi class, Q&T, 160 ksi class. If our stock is not already in the condition you need, we can quote it with the heat treatment performed before shipment.
Can you cut 8740 to size?
Yes. Saw cutting, waterjet, laser and shearing are available, along with trepanning, gun drilling, lathe turning and CNC machining, so you can order blanks or rough machined pieces rather than full lengths.
Do you provide test reports and additional testing on 8740?
Every order ships with mill test reports and heat traceability. If your print calls for ultrasonic inspection, penetrant dye, magnetic particle, chemical assay, micrography, hardness or mechanical testing and our stock does not already carry it, we can quote the material with that work performed.
Can 8740 be supplied to DFARS domestic melt requirements?
Tell us at quote stage if the order is DFARS or domestic melt restricted and we will confirm availability against that requirement before you commit.
What do you need to quote 8740?
Grade, form, dimensions, quantity, specification and condition, plus any testing or certification requirements and the date you need it. Send a drawing if you have one. Quotes are typically ready within 24 hours.
How does 8740 compare with 4340?
Higher hardenability and strength ceiling for heavier, more highly loaded parts.