Steel 8740 SR-Norm
Heat-treated state
AISI/SAE 8740 · UNS G87400
SR-Norm = stress relieved / tempered after normalizing
Use for welded 4130/8740 tube and bracket assemblies where the weld HAZ must be softened and stresses removed.
Values for the SR-Norm condition
Other 8740 tempers and conditions
8740 is listed in 11 conditions; see the grade overview at 8740.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full anneal ~815 °C, slow cool | Softest condition — choose for deep machining, cold forming or before final quench and temper. | 415 | 696 | 22 | 201 HB | — |
HRDefault Hot rolled | Most stocked mill condition for bar and forging stock destined for later heat treatment. | 440 | 725 | 20 | 15 HRC | 7.8 % IACS |
~870 °C, air cool | Uniform fine-grain structure for forgings and weldments before final heat treatment; higher strength than annealed. | 605 | 930 | 16 | 27 HRC | — |
Cold rolled | Thin strip/sheet form for stamped parts that will be heat treated after forming. | 620 | 780 | 13 | 20 HRC | 7.8 % IACS |
SR-NormThis page Stress relieved / tempered after normalizing | Use for welded 4130/8740 tube and bracket assemblies where the weld HAZ must be softened and stresses removed. | 620 | 860 | 18 | 25 HRC | 43 W/m·K |
Cold drawn | Pick for close-tolerance straight bar with better surface and higher as-supplied yield strength than hot rolled. | 635 | 745 | 15 | 18 HRC | 44 W/m·K |
quenched and tempered to 862 MPa min UTS (AMS 6322 / NAS fastener class) | Aerospace bolt/stud condition where maximum ductility and hydrogen-embrittlement margin are wanted. | 795 | 900 | 18 | 28 HRC | — |
Quenched and tempered | General engineering condition for shafts, gears and fasteners needing ~1000 MPa with good toughness. | 900 | 1,000 | 16 | 30 HRC | — |
quenched and tempered to 1034 MPa min UTS | Standard aircraft bolt / high-strength stud condition — best strength-to-toughness compromise for 8740. | 965 | 1,080 | 15 | 34 HRC | — |
quenched and tempered to 1241 MPa min UTS | High-strength condition for landing-gear pins, race-car and driveline parts; watch notch sensitivity and hydrogen embrittlement. | 1,180 | 1,290 | 12 | 40 HRC | — |
quenched and tempered to ~1517 MPa UTS (low temper) | Maximum practical strength for 8740; only for smooth, well-designed parts with strict hydrogen and stress-raiser control. | 1,420 | 1,550 | 10 | 47 HRC | — |
What is 8740 SR-Norm?
8740 SR-Norm is 8740 heat treated to SR-Norm — use for welded 4130/8740 tube and bracket assemblies where the weld HAZ must be softened and stresses removed. 8740 SR-Norm has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 78% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi). 8740 SR-Norm has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; SR-Norm is available on request or by drawing note.
Advantages
- High strength — 620 MPa (89.9 ksi), better than 78% of steel grades
8740 SR-Norm properties
Typical room-temperature values for 8740 SR-Norm; 21 are specific to this condition. Other listed values are 8740 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
8740 SR-Norm has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical17
8740 SR-Norm has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 78% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8740 SR-Norm is rated for continuous service to 425°C (797 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 12.6 µm/m·K (7 µin/in·°F).
Electrical3
8740 SR-Norm conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 8740 SR-Norm takes about 29 MJ of energy and emits 2 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 30%.
Manufacturability7
8740 SR-Norm's machinability is fair (50/100, worse than 53% of steel grades); weldability fair (48/100); formability poor (28/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 8740 SR-Norm
Is 8740 easy to machine?
Machines well at 180–250 HB (≈65% of 1212) with carbide at 120–180 m/min; above 35 HRC drop to rigid setups, low speed and positive coolant, or machine before final temper.
Can 8740 be welded?
Weldable by TIG/MIG/SMAW with matched or ER80S-D2 filler but needs 200–300 °C preheat, low hydrogen practice and a post-weld temper; never leave a high-strength Q&T part as-welded.
Can 8740 be formed, bent or molded?
Cold form only in the annealed condition with generous radii; hot forge 1050–1200 °C then normalize — quench in oil from 830–845 °C and temper to the target strength.
What surface finishes work on 8740?
No natural corrosion resistance: use cadmium, zinc or zinc-nickel plating, phosphate + oil, or black oxide, and bake 190–220 °C after plating for parts above ~1000 MPa to avoid hydrogen embrittlement; nitriding gives a hard wear surface.
8740 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | 0.38 – 0.43 | 0.4 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 0.4 – 0.7 | 0.55 |
| Cr | 0.4 – 0.6 | 0.5 |
| Mohigher Mo than 8640 | 0.2 – 0.3 | 0.25 |
| Pmax; 0.025 max for aerospace AMS grades | ≤ 0.04 | — |
| Smax; 0.025 max for aerospace AMS grades | ≤ 0.04 | — |
| Fe | balance | — |
8740 SR-Norm — frequently asked
What is 8740 SR-Norm used for?
8740 SR-Norm is typically used for aircraft-quality bolts and studs, high-strength shafts and spindles, forged industrial components, threaded rod and tie bars, clevis pins and linkage parts and machined couplings and flanges. In short: standard Ni-Cr-Mo bar.
What is the yield strength of 8740 SR-Norm?
8740 SR-Norm has a typical yield strength of 620 MPa (89.9 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 78% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 8740 SR-Norm easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Machines well at 180–250 HB (≈65% of 1212) with carbide at 120–180 m/min; above 35 HRC drop to rigid setups, low speed and positive coolant, or machine before final temper.
Can 8740 SR-Norm be welded?
With care — weldability is rated fair (48/100). Weldable by TIG/MIG/SMAW with matched or ER80S-D2 filler but needs 200–300 °C preheat, low hydrogen practice and a post-weld temper; never leave a high-strength Q&T part as-welded.
What surface finishes work on 8740 SR-Norm?
No natural corrosion resistance: use cadmium, zinc or zinc-nickel plating, phosphate + oil, or black oxide, and bake 190–220 °C after plating for parts above ~1000 MPa to avoid hydrogen embrittlement; nitriding gives a hard wear surface.
Can 8740 SR-Norm be formed, bent or molded?
Cold form only in the annealed condition with generous radii; hot forge 1050–1200 °C then normalize — quench in oil from 830–845 °C and temper to the target strength.
What is the maximum service temperature of 8740 SR-Norm?
8740 SR-Norm is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 8740-HR and 8740-CD?
HR is the default condition — most stocked mill condition for bar and forging stock destined for later heat treatment. CD: pick for close-tolerance straight bar with better surface and higher as-supplied yield strength than hot rolled. Yield strength is 440 MPa in HR versus 635 MPa in CD.
Can FabDigit make parts in 8740 SR-Norm?
Yes — 8740 SR-Norm is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 — Hardenability Bands for Alloy H Steels — SAE International (2019)
- AMS 6322 / AMS 6327 — Steel Bars, Forgings and Tubing 0.40C Ni-Cr-Mo (8740) — SAE International (2020)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- MMPDS-17 Metallic Materials Properties Development and Standardization — Battelle/FAA (2022)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- Mysteel / SMM (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.