Steel 8115 CARB-QT
Heat-treated state
AISI/SAE 8115 · UNS G81150
CARB-QT = carburized, quenched & tempered
Final service condition for gears and shafts: hard wear-resistant case over a tough low-carbon core.
Values for the CARB-QT condition
Other 8115 tempers and conditions
8115 is listed in 6 conditions; see the grade overview at 8115.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Softest stock condition for machining of gear blanks before carburizing. | 310 | 480 | 32 | 137 HB | — |
Hot rolled | Lowest-cost mill bar form; scale and decarb layer must be machined off. | 330 | 525 | 27 | 149 HB | 7.8 % IACS |
Normalized | Uniform fine-grained structure and better machined finish before case hardening. | 370 | 560 | 28 | 163 HB | — |
Cold drawn | Tight tolerance, bright surface and higher yield for shafts and pins machined near size. | 495 | 585 | 15 | 170 HB | — |
Q&T | Direct quench and temper of small sections when moderate core strength but no case is required. | 620 | 830 | 18 | 25 HRC | — |
CARB-QTThis page Carburized, quenched & tempered | Final service condition for gears and shafts: hard wear-resistant case over a tough low-carbon core. | 750 | 1,000 | 12 | 60 HRC | — |
What is 8115 CARB-QT?
8115 CARB-QT is 8115 heat treated to CARB-QT — final service condition for gears and shafts: hard wear-resistant case over a tough low-carbon core. 8115 CARB-QT has a yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). 8115 CARB-QT 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). ANN is the default condition FabDigit quotes; CARB-QT 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 — 750 MPa (109 ksi), better than 84% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
Limitations
- Difficult to machine — 12/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
8115 CARB-QT properties
Typical room-temperature values for 8115 CARB-QT; 14 are specific to this condition. Other listed values are 8115 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
8115 CARB-QT 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).
Mechanical15
8115 CARB-QT has a yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8115 CARB-QT is rated for continuous service to 180°C (356 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
8115 CARB-QT 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 8115 CARB-QT takes about 26 MJ of energy and emits 1.9 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 30%.
Manufacturability7
8115 CARB-QT's machinability is not recommended (12/100, worse than 99% of steel grades); weldability poor (15/100); formability good (65/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 8115 CARB-QT
Is 8115 easy to machine?
Machine to near-final size in the annealed or normalized state (≈70 % of 1212); allow grinding stock for post-carburizing distortion.
Can 8115 be welded?
Readily weldable before heat treatment with low-hydrogen consumables and modest preheat; avoid welding on carburized cases.
Can 8115 be formed, bent or molded?
Good cold heading and bending in the annealed condition; hot forge 1100–1200 °C and normalize afterwards to refine grain.
What surface finishes work on 8115?
Not anodizable — protect with black oxide, phosphate, zinc or zinc-nickel plating (bake to avoid hydrogen embrittlement) or oil; grind and shot-peen for peak gear fatigue life.
8115 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 |
|---|---|---|
| Ccarburizing carbon level | 0.13 – 0.18 | 0.16 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 0.2 – 0.4 | 0.3 |
| Cr | 0.3 – 0.5 | 0.4 |
| Mo | 0.08 – 0.15 | 0.12 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
8115 CARB-QT — frequently asked
What is 8115 CARB-QT used for?
8115 CARB-QT is typically used for carburized gears, pins, small shafts and case-hardened fasteners. In short: lean-alloy carburizing grade; hard case, tough core; small-section case hardening.
What is the yield strength of 8115 CARB-QT?
8115 CARB-QT has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 8115 CARB-QT easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Machine to near-final size in the annealed or normalized state (≈70 % of 1212); allow grinding stock for post-carburizing distortion.
Can 8115 CARB-QT be welded?
Not readily — weldability is rated poor (15/100). Readily weldable before heat treatment with low-hydrogen consumables and modest preheat; avoid welding on carburized cases.
What surface finishes work on 8115 CARB-QT?
Not anodizable — protect with black oxide, phosphate, zinc or zinc-nickel plating (bake to avoid hydrogen embrittlement) or oil; grind and shot-peen for peak gear fatigue life.
Can 8115 CARB-QT be formed, bent or molded?
Good cold heading and bending in the annealed condition; hot forge 1100–1200 °C and normalize afterwards to refine grain.
What is the maximum service temperature of 8115 CARB-QT?
8115 CARB-QT is rated for continuous use to about 180°C (356 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 8115-ANN and 8115 CARB-QT?
ANN is the default condition — softest stock condition for machining of gear blanks before carburizing. CARB-QT: final service condition for gears and shafts: hard wear-resistant case over a tough low-carbon core. Yield strength is 310 MPa in ANN versus 750 MPa in CARB-QT.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 — Hardenability Bands for Alloy H Steels — SAE International (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (Carburizing) — ASM International (1991)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
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.