Steel SNCM815-QT (Quenched and tempered)
Heat-treated state
JIS SNCM815 · UNS G93106
Use where the part is loaded through-section without carburizing (shafts, bolts, high-toughness structural links).
Values for the QT condition
Other SNCM815 tempers and conditions
SNCM815 is listed in 7 conditions; see the grade overview at SNCM815.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition — pick it for heavy rough machining, deep drilling or cold sizing before carburizing. | 560 | 800 | 22 | 200 HB | — |
Normalized | Grain-refining treatment after forging; usually followed by tempering or annealing before machining. | 720 | 1,000 | 16 | 31 HRC | 7 % IACS |
NTDefault normalized and tempered (machining condition, ≤302 HB) | The standard aircraft-quality bar/forging supply condition: uniform, machinable, ready for gear cutting and subsequent carburizing. | 750 | 950 | 18 | 26 HRC | — |
Hot rolled | Cheapest mill condition for re-forging or re-heat-treating; too hard and variable for direct machining. | 800 | 1,100 | 13 | 36 HRC | 7 % IACS |
Cold drawn | Small-diameter precision bar for pins and small gear blanks where tight tolerance and good surface matter. | 820 | 950 | 12 | 29 HRC | 7 % IACS |
QTThis page Quenched and tempered | Use where the part is loaded through-section without carburizing (shafts, bolts, high-toughness structural links). | 980 | 1,180 | 15 | 36 HRC | — |
Carburized and hardened | The service condition for gears: deep 0.8–2.0 mm case for contact/bending fatigue with a very tough 4% Ni core. | 1,050 | 1,250 | 13 | 61 HRC | — |
What is SNCM815-QT?
SNCM815-QT is SNCM815 heat treated to QT — use where the part is loaded through-section without carburizing (shafts, bolts, high-toughness structural links). SNCM815-QT has a yield strength of 980 MPa (142 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi). SNCM815-QT 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). NT is the default condition FabDigit quotes; QT is available on request or by drawing note.
Advantages
- High strength — 980 MPa (142 ksi), better than 91% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to machine — 30/100, worse than 89% of steel grades
- High embodied carbon — 2.6 kg CO₂/kg, worse than 87% of steel grades
- Poor heat conductor — 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
SNCM815-QT properties
Typical room-temperature values for SNCM815-QT; 13 are specific to this condition. Other listed values are SNCM815 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SNCM815-QT 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).
Mechanical14
SNCM815-QT has a yield strength of 980 MPa (142 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNCM815-QT is rated for continuous service to 400°C (752 °F). It conducts heat at 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades. Thermal expansion is 11.6 µm/m·K (6.44 µin/in·°F).
Electrical3
SNCM815-QT conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of SNCM815-QT takes about 36 MJ of energy and emits 2.6 kg of CO₂ — more than 89% of steel grades. Typical recycled content is 25%.
Manufacturability6
SNCM815-QT's machinability is poor (30/100, worse than 89% of steel grades); weldability poor (25/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SNCM815-QT
Is SNCM815 easy to machine?
Machine in the annealed or N+T condition (~45% of 1212); gummy and work-hardening — use rigid setups, positive-rake carbide, generous coolant, and finish-grind after carburizing to remove heat-treat distortion.
Can SNCM815 be welded?
Poor weldability: high hardenability and 4% Ni give hard, crack-prone HAZ — if unavoidable, use low-hydrogen filler, 200–300 °C preheat and immediate post-weld temper; never weld carburized surfaces.
Can SNCM815 be formed, bent or molded?
Hot forge 1150–1200 °C, stop above 950 °C, then normalize and temper; cold forming limited to light straightening and thread rolling in the annealed condition.
What surface finishes work on SNCM815?
Shot peen tooth roots for fatigue; protect with oil, black oxide, phosphate or thin dense chrome — no anodizing, and avoid unbaked electroplating on high-strength sections due to hydrogen embrittlement.
SNCM815 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 |
|---|---|---|
| CJIS G 4103 SNCM815 | 0.12 – 0.18 | 0.15 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Ni | 4 – 4.5 | 4.25 |
| Cr | 0.7 – 1 | 0.85 |
| Mo | 0.15 – 0.3 | 0.22 |
| Curesidual, max | ≤ 0.3 | — |
| Fe | balance | — |
SNCM815-QT — frequently asked
What is SNCM815-QT used for?
SNCM815-QT is typically used for heavy-duty aerospace and helicopter gears, gearbox pinions, transmission shafts, bevel and spiral bevel gears, splined drive shafts and high-load bearing races. In short: deep case, tough core; 4% Ni carburizing grade; aerospace gear standard.
What is the yield strength of SNCM815-QT?
SNCM815-QT has a typical yield strength of 980 MPa (142 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is SNCM815-QT easy to machine?
Not especially — machinability is rated poor (30/100, worse than 89% of steel grades). Machine in the annealed or N+T condition (~45% of 1212); gummy and work-hardening — use rigid setups, positive-rake carbide, generous coolant, and finish-grind after carburizing to remove heat-treat distortion.
Can SNCM815-QT be welded?
Not readily — weldability is rated poor (25/100). Poor weldability: high hardenability and 4% Ni give hard, crack-prone HAZ — if unavoidable, use low-hydrogen filler, 200–300 °C preheat and immediate post-weld temper; never weld carburized surfaces.
What surface finishes work on SNCM815-QT?
Shot peen tooth roots for fatigue; protect with oil, black oxide, phosphate or thin dense chrome — no anodizing, and avoid unbaked electroplating on high-strength sections due to hydrogen embrittlement.
Can SNCM815-QT be formed, bent or molded?
Hot forge 1150–1200 °C, stop above 950 °C, then normalize and temper; cold forming limited to light straightening and thread rolling in the annealed condition.
What is the maximum service temperature of SNCM815-QT?
SNCM815-QT 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 SNCM815-NT and SNCM815-CH?
NT is the default condition — the standard aircraft-quality bar/forging supply condition: uniform, machinable, ready for gear cutting and subsequent carburizing. CH: the service condition for gears: deep 0.8–2.0 mm case for contact/bending fatigue with a very tough 4% Ni core. Yield strength is 750 MPa in NT versus 1,050 MPa in CH.
Sources
- JIS G 4103 — Nickel-chromium-molybdenum steels — JSA (2018)
- AMS 6265 — Steel bars/forgings 3.2Ni-1.2Cr-0.12Mo (9310), premium aircraft quality — SAE International (2019)
- SAE J404 — Chemical compositions of SAE alloy steels (9310) — SAE International (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals (carburizing) — ASM International (2013)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- MMPDS-typical low-alloy steel elastic and physical constants — Battelle/FAA (2023)
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.