Steel SNCM420-QT (Quenched and tempered)
Heat-treated state
JIS SNCM420
Through-hardened condition used for the JIS acceptance test and for uncarburized shafts requiring ≥980 MPa.
Values for the QT condition
Other SNCM420 tempers and conditions
SNCM420 is listed in 8 conditions; see the grade overview at SNCM420.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard as-supplied bar condition: softest state for gear cutting, hobbing and deep machining before carburizing. | 455 | 700 | 22 | 197 HB | — |
Normalized | Use to homogenize forgings and refine grain before carburizing; better chip control than annealed. | 560 | 830 | 18 | 235 HB | — |
Hot rolled | Cheapest mill condition for rough-turned blanks that will be normalized or annealed by the gear shop. | 570 | 870 | 16 | 24 HRC | 7.5 % IACS |
Cold drawn | Pick for small-diameter shafts and pins needing tight tolerance and good surface straight off the bar. | 660 | 820 | 12 | 22 HRC | 7.5 % IACS |
QTThis page Quenched and tempered | Through-hardened condition used for the JIS acceptance test and for uncarburized shafts requiring ≥980 MPa. | 900 | 1,080 | 17 | 34 HRC | — |
Deep carburized (>1.5 mm case) + double quench & temper | For large module wind-turbine and marine gears needing deep case depth and refined grain from a second quench. | 980 | 1,230 | 13 | 60 HRC | 7 % IACS |
Carburized, hardened & tempered | Standard gear condition: 0.6–1.5 mm effective case at 58–62 HRC over a 30–40 HRC tough core; grind after treatment. | 1,000 | 1,250 | 12 | 60 HRC | — |
Aircraft quality | Choose for aerospace transmission gears and bearings where AMS-class inclusion cleanliness and maximum bending fatigue life are required. | 1,030 | 1,280 | 15 | 60 HRC | 7 % IACS |
What is SNCM420-QT?
SNCM420-QT is SNCM420 heat treated to QT — through-hardened condition used for the JIS acceptance test and for uncarburized shafts requiring ≥980 MPa. SNCM420-QT has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Elongation at break is 17% and the elastic modulus is 205 GPa (29.7 Msi). SNCM420-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). A is the default condition FabDigit quotes; QT is available on request or by drawing note.
Advantages
- High strength — 900 MPa (131 ksi), better than 90% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to machine — 38/100, worse than 80% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
SNCM420-QT properties
Typical room-temperature values for SNCM420-QT; 16 are specific to this condition. Other listed values are SNCM420 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SNCM420-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).
Mechanical16
SNCM420-QT has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Elongation at break is 17% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNCM420-QT is rated for continuous service to 300°C (572 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
SNCM420-QT conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of SNCM420-QT takes about 32 MJ of energy and emits 2.3 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability7
SNCM420-QT's machinability is fair (38/100, worse than 80% of steel grades); weldability poor (25/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SNCM420-QT
Is SNCM420 easy to machine?
Cut gear teeth and finish all features in the annealed/normalized state (~60 % of 1212); after carburizing only grinding, honing or hard-turning with CBN is practical.
Can SNCM420 be welded?
Weldable only before carburizing with low-hydrogen consumables, 200–300 °C preheat and immediate stress relief/temper; welding carburized surfaces is not permitted.
Can SNCM420 be formed, bent or molded?
Hot forge at 1150–1200 °C down to ~900 °C then normalize; cold heading and light cold forming are possible in the spheroidize-annealed condition.
What surface finishes work on SNCM420?
Grind after case hardening to remove distortion and any high-carbon surface layer; protect with black oxide, manganese phosphate, zinc or hard chrome — avoid processes that risk hydrogen embrittlement, or bake within 4 h at 190 °C.
SNCM420 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 | 0.17 – 0.23 | 0.2 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.4 – 0.7 | 0.55 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Ni | 1.6 – 2 | 1.8 |
| Cr | 0.4 – 0.65 | 0.5 |
| Mo | 0.15 – 0.3 | 0.22 |
| Curesidual, max | ≤ 0.3 | — |
| Fe | balance | — |
SNCM420-QT — frequently asked
What is SNCM420-QT used for?
SNCM420-QT is typically used for aircraft gears, high-load gearbox gears and pinions, helicopter transmission components, racing and motorsport gearsets, heavy-duty drive shafts and bearing races. In short: SAE 9310 gear equivalent; deep case, high core toughness; aerospace VAR quality available.
What is the yield strength of SNCM420-QT?
SNCM420-QT has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SNCM420-QT easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% of steel grades). Cut gear teeth and finish all features in the annealed/normalized state (~60 % of 1212); after carburizing only grinding, honing or hard-turning with CBN is practical.
Can SNCM420-QT be welded?
Not readily — weldability is rated poor (25/100). Weldable only before carburizing with low-hydrogen consumables, 200–300 °C preheat and immediate stress relief/temper; welding carburized surfaces is not permitted.
What surface finishes work on SNCM420-QT?
Grind after case hardening to remove distortion and any high-carbon surface layer; protect with black oxide, manganese phosphate, zinc or hard chrome — avoid processes that risk hydrogen embrittlement, or bake within 4 h at 190 °C.
Can SNCM420-QT be formed, bent or molded?
Hot forge at 1150–1200 °C down to ~900 °C then normalize; cold heading and light cold forming are possible in the spheroidize-annealed condition.
What is the maximum service temperature of SNCM420-QT?
SNCM420-QT is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SNCM420-A and SNCM420 AQ-VAR?
A is the default condition — standard as-supplied bar condition: softest state for gear cutting, hobbing and deep machining before carburizing. AQ-VAR: choose for aerospace transmission gears and bearings where AMS-class inclusion cleanliness and maximum bending fatigue life are required. Yield strength is 455 MPa in A versus 1,030 MPa in AQ-VAR.
Sources
- JIS G 4053 — Low-alloyed structural steels for machine structural use — JSA (2016)
- SAE J404 — Chemical Compositions of SAE Alloy Steels (4320/8620/9310) — SAE International (2020)
- AMS 6265 — Steel Bars, Forgings, Tubing 3.2Ni-1.2Cr-0.12Mo, premium aircraft quality — SAE International (2019)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 4A/4D — Steel Heat Treating and Carburizing — ASM International (2013)
- GB/T 3077 — Alloy structural steels (20CrNi2Mo comparison) — SAC (2015)
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.