Steel 8645-QT315
Heat-treated state
AISI/SAE 8645 · UNS G86450
QT315 = q&T 315 °C
Very high strength; avoid this temper range if impact toughness matters (tempered-martensite embrittlement).
Values for the QT315 condition
Other 8645 tempers and conditions
8645 is listed in 11 conditions; see the grade overview at 8645.
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 | — |
QT315This page 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-QT315?
8645-QT315 is 8645 heat treated to QT315 — very high strength; avoid this temper range if impact toughness matters (tempered-martensite embrittlement). 8645-QT315 has a yield strength of 1,515 MPa (220 ksi) and a tensile strength of 1,795 MPa (260 ksi) — stronger than 97% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi). 8645-QT315 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). Annealed is the default condition FabDigit quotes; QT315 is available on request or by drawing note.
Advantages
- High strength — 1,515 MPa (220 ksi), better than 97% of steel grades
Limitations
- Difficult to machine — 25/100, worse than 93% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
- Low fracture toughness — 50 MPa·√m (45.5 ksi·√in), worse than 86% of steel grades
8645-QT315 properties
Typical room-temperature values for 8645-QT315; 11 are specific to this condition. Other listed values are 8645 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
8645-QT315 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-QT315 has a yield strength of 1,515 MPa (220 ksi) and a tensile strength of 1,795 MPa (260 ksi) — stronger than 97% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8645-QT315 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-QT315 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-QT315 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-QT315's machinability is poor (25/100, worse than 93% of steel grades); weldability poor (30/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 8645-QT315
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.
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.
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 | — |
8645-QT315 — frequently asked
What is 8645-QT315 used for?
8645-QT315 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-QT315?
8645-QT315 has a typical yield strength of 1,515 MPa (220 ksi) and a tensile strength of 1,795 MPa (260 ksi) — stronger than 97% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 8645-QT315 easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% 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-QT315 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-QT315?
Not anodizable; protect with zinc/manganese phosphate, black oxide, electroless nickel or Cr plating — bake plated parts >40 HRC to relieve hydrogen.
Can 8645-QT315 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-QT315?
8645-QT315 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.