Steel 8645
AISI/SAE 8645 · UNS G86450
8645 is a higher-carbon nickel-chromium-molybdenum alloy steel (UNS G86450) that quenches and tempers to greater tensile and yield strength than 8640 or 8642, for parts with higher load capacity.
Reference datasheet — 8645 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Annealed condition
8645 tempers and conditions
8645 is supplied in 11 conditions, soft to hard. Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault full anneal ~815 °C, slow cool | Softest condition for machining, deep drilling or cold forming before final quench and temper. | 425 | 715 | 20 | 197 HB | — |
Hot rolled | Lowest-cost mill condition for parts that will be fully heat treated after rough machining. | 500 | 830 | 17 | 22 HRC | 7.8 % IACS |
Cold drawn | Cold-drawn bar with tight size tolerance, bright finish and raised yield strength; best chip control for screw-machine work. | 680 | 800 | 12 | 229 HB | — |
Normalized | Uniform fine-grain structure and higher strength than annealed; used as a pre-machining or as-supplied condition for moderately loaded parts. | 690 | 1,090 | 18 | 33 HRC | — |
Q&T to 28–32 HRC | Common stock hardness band for shafting and gear blanks that must still be machinable. | 830 | 965 | 20 | 30 HRC | — |
Q&T 650 °C | Toughest quenched-and-tempered condition; choose for impact-loaded or notch-sensitive parts. | 860 | 1,000 | 21 | 31 HRC | — |
Q&T to 34–38 HRC | Higher hardness band where wear and load capacity outrank machining ease. | 1,040 | 1,170 | 17 | 36 HRC | — |
Q&T 540 °C | Balanced strength/toughness workhorse temper for machinery shafting and connecting rods. | 1,160 | 1,275 | 17 | 39 HRC | — |
Q&T 425 °C | High strength with usable ductility for heavily loaded shafts, gears and fasteners. | 1,380 | 1,550 | 13 | 45 HRC | — |
Q&T 315 °C | Very high strength; avoid this temper range if impact toughness matters (tempered-martensite embrittlement). | 1,515 | 1,795 | 11 | 51 HRC | — |
Q&T 205 °C | Maximum hardness and strength for wear parts; very low ductility and notch toughness. | 1,720 | 2,000 | 10 | 55 HRC | — |
What is 8645?
8645 is a higher-carbon nickel-chromium-molybdenum alloy steel (UNS G86450) that quenches and tempers to greater tensile and yield strength than 8640 or 8642, for parts with higher load capacity. It is supplied annealed, normalized, hot-rolled and cold-drawn as well as Q&T over a 205–650 °C tempering range and at 28-32 or 34-38 HRC; the annealed default condition is about 425 MPa yield, 715 MPa tensile, 20 % elongation and 197 HB (92 HRB), with service to 400 °C. At roughly 0.45 % C weldability is poor (score 30) and formability limited (score 35), so 8640 is the usual choice when welding or cold forming is required. 8645 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). 8645 has a yield strength of 425 MPa (61.6 ksi) and a tensile strength of 715 MPa (104 ksi) — weaker than 52% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
What is 8645 used for?
- heavy-duty shafts
- high-strength fasteners
- gears
- structural machine components
8645 properties
Typical room-temperature values for 8645-Annealed; bars are the position among steel grades.
Physical3
8645 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
8645 has a yield strength of 425 MPa (61.6 ksi) and a tensile strength of 715 MPa (104 ksi) — weaker than 52% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8645 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 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
8645 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 8645 takes about 34 MJ of energy and emits 2.4 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability6
8645's machinability is good (55/100, better than 62% of steel grades); weldability poor (30/100); formability fair (35/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 8645 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 8645
Is 8645 easy to machine?
Machine in the annealed or ≤32 HRC condition with rigid setups and coated carbide; above 40 HRC switch to CBN/ceramic or grinding.
Can 8645 be welded?
Poor weldability at 0.45 %C — preheat 250–350 °C, low-hydrogen consumables, and temper/stress relieve immediately after welding.
Can 8645 be formed, bent or molded?
Cold forming limited to mild bending in the annealed state; hot forge 1100–1200 °C and cool slowly to avoid quench cracks.
8645 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 |
|---|---|---|
| CSAE J404 heat analysis | 0.43 – 0.48 | 0.46 |
| 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 |
| P | ≤ 0.04 | |
| S | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 8645?
Not anodizable; protect with zinc/manganese phosphate, black oxide, electroless nickel or Cr plating — bake plated parts >40 HRC to relieve hydrogen.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 8645 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G86450
How much does 8645 cost?
8645 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
8645 — frequently asked
What is 8645 used for?
8645 is typically used for heavy-duty shafts, high-strength fasteners, gears and structural machine components. In short: highest-strength 86xx bar; poor weldability at 0.45 % C; quench-and-temper only.
What is the yield strength of 8645?
8645 has a typical yield strength of 425 MPa (61.6 ksi) and a tensile strength of 715 MPa (104 ksi) — weaker than 52% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 8645 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine in the annealed or ≤32 HRC condition with rigid setups and coated carbide; above 40 HRC switch to CBN/ceramic or grinding.
Can 8645 be welded?
Not readily — weldability is rated poor (30/100). Poor weldability at 0.45 %C — preheat 250–350 °C, low-hydrogen consumables, and temper/stress relieve immediately after welding.
What surface finishes work on 8645?
Not anodizable; protect with zinc/manganese phosphate, black oxide, electroless nickel or Cr plating — bake plated parts >40 HRC to relieve hydrogen.
Can 8645 be formed, bent or molded?
Cold forming limited to mild bending in the annealed state; hot forge 1100–1200 °C and cool slowly to avoid quench cracks.
What is the maximum service temperature of 8645?
8645 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 8645 Annealed and 8645-QT205?
Annealed is the default condition — softest condition for machining, deep drilling or cold forming before final quench and temper. QT205: maximum hardness and strength for wear parts; very low ductility and notch toughness. Yield strength is 425 MPa in Annealed versus 1,720 MPa in QT205.
How much does 8645 cost?
8645 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- 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.4 — Heat Treating — ASM International (1991)
- Low-alloy steel property tables (8600-series Q&T data) — ASM/MMPDS-derived compilations (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.