Steel 8640 · heat-treated state
Steel 8640 Normalized
Properties of the Normalized condition, compared with the other 8640 tempers.
Normalized ~900 °C and air cooled: uniform fine grain and moderate strength; typical pre-treatment before machining and final Q&T of forgings.
What is 8640 Normalized?
8640 Normalized is 8640 heat treated to Normalized — normalized ~900 °C and air cooled: uniform fine grain and moderate strength; typical pre-treatment before machining and final Q&T of forgings. 8640 Normalized has a yield strength of 690 MPa (100 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 80% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi). 8640 Normalized 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; Normalized is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- High strength — 690 MPa (100 ksi), better than 80% of steel grades
8640 Normalized properties
Typical room-temperature values for 8640 Normalized — 12 properties are specific to this condition; the rest are grade-level values shared by every 8640 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
8640 Normalized 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).
Mechanical16
8640 Normalized has a yield strength of 690 MPa (100 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 80% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8640 Normalized is rated for continuous service to 400°C (752 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
8640 Normalized conducts electricity at 7.8 % IACS, worse than 58% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of 8640 Normalized takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
8640 Normalized's machinability is fair (52/100, better than 52% of steel grades); weldability fair (40/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 8640 tempers and conditions
8640 is also supplied in 9 other conditions. The full side-by-side table is on the 8640 overview.
- HRDefaultStandard as-rolled bar for parts that will be heat treated after machining; cheapest stock form.570 MPa yield · 20 HRC
- Q&T 48-52 HRCLow-temper (≈205–260 °C) condition for maximum hardness/wear in small sections; notch-sensitive and difficult to machine — grind to size.1,620 MPa yield · 50 HRC
- Q&T 38-42 HRCHigh-strength condition (temper ≈425 °C) for heavily loaded pins, sprockets and fasteners where wear resistance outweighs toughness.1,275 MPa yield · 40 HRC
- Q&TGeneral commercial condition: oil quench from ~830 °C and temper ~540 °C for a balanced strength/toughness shaft or gear blank.1,000 MPa yield · 35 HRC
- Q&T 32-36 HRCCommon shaft/gear-blank hardness giving high fatigue strength while still machinable with carbide tooling.1,000 MPa yield · 34 HRC
- Q&T 28-32 HRCTough mid-hardness condition (temper ≈600 °C) for drill-pipe tool joints, sour-service and welded-then-tempered assemblies.860 MPa yield · 30 HRC
- CDCold-drawn bar with better size tolerance, straightness and surface than HR; higher yield strength but residual stress can cause distortion on machining.760 MPa yield · 25 HRC
- NormalizedNormalized ~900 °C and air cooled: uniform fine grain and moderate strength; typical pre-treatment before machining and final Q&T of forgings.690 MPa yield · 27 HRC
- AnnealedSoftest condition (full/spheroidize anneal ~840 °C, furnace cool) — best for deep machining, cold forming or thread rolling before hardening.380 MPa yield · 184 HB
Working with 8640 Normalized
Is 8640 easy to machine?
Machine in the annealed or ≤32 HRC Q&T condition with carbide tooling and rigid setups; rough before hardening and leave grind stock for finish sizes.
Can 8640 be welded?
Weldable with low-hydrogen consumables but requires ~200–300 °C preheat, interpass control and post-weld temper below the original tempering temperature to avoid martensitic cracking.
Can 8640 be formed, bent or molded?
Cold forming only in the annealed state and with generous bend radii; hot forge at 1050–1200 °C then normalize before final heat treatment.
What surface finishes work on 8640?
No natural corrosion protection — apply black oxide, phosphate + oil, zinc or hard-chrome plating; bake plated parts above ~38 HRC to relieve hydrogen embrittlement.
8640 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 |
| Mo | 0.15 – 0.25 | 0.2 |
| Pmax, SAE J404 wrought bar | ≤ 0.04 | — |
| Smax; 8640H/resulfurized variants differ | ≤ 0.04 | — |
| Fe | balance | — |
8640 Normalized — frequently asked
What is 8640 Normalized used for?
8640 Normalized is typically used for gears, shafts and bolts. In short: workhorse Ni-Cr-Mo bar.
What is the yield strength of 8640 Normalized?
8640 Normalized has a typical yield strength of 690 MPa (100 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 80% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 8640 Normalized easy to machine?
Reasonably — machinability is rated fair (52/100, better than 52% of steel grades). Machine in the annealed or ≤32 HRC Q&T condition with carbide tooling and rigid setups; rough before hardening and leave grind stock for finish sizes.
Can 8640 Normalized be welded?
With care — weldability is rated fair (40/100). Weldable with low-hydrogen consumables but requires ~200–300 °C preheat, interpass control and post-weld temper below the original tempering temperature to avoid martensitic cracking.
What surface finishes work on 8640 Normalized?
No natural corrosion protection — apply black oxide, phosphate + oil, zinc or hard-chrome plating; bake plated parts above ~38 HRC to relieve hydrogen embrittlement.
Can 8640 Normalized be formed, bent or molded?
Cold forming only in the annealed state and with generous bend radii; hot forge at 1050–1200 °C then normalize before final heat treatment.
What is the maximum service temperature of 8640 Normalized?
8640 Normalized is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 8640-HR and 8640-CD?
HR is the default condition — standard as-rolled bar for parts that will be heat treated after machining; cheapest stock form. CD: cold-drawn bar with better size tolerance, straightness and surface than HR; higher yield strength but residual stress can cause distortion on machining. Yield strength is 570 MPa in HR versus 760 MPa in CD.
Can FabDigit make parts in 8640 Normalized?
Yes — 8640 Normalized is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — General Requirements for 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.4 — Heat Treating (tempering curves for 86xx steels) — ASM International (1991)
- SAE J1268 hardenability / typical mechanical property tables for 8640 — SAE International (2019)
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.