Steel 12Cr2Ni4A
GB 12Cr2Ni4A
12Cr2Ni4A, equivalent to AISI 9310, is a high-alloy nickel-chromium carburizing steel with deep hardenability and a tough core after case hardening.
Reference datasheet — 12Cr2Ni4A 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 QT condition
12Cr2Ni4A tempers and conditions
12Cr2Ni4A is supplied in 8 conditions, soft to hard. QT is the default FabDigit quotes; the values on this page are for it.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest and most machinable state — the condition gears are rough-cut and hobbed in before carburizing. | 450 | 700 | 20 | 240 HB | — |
Hot rolled | Mill supply condition for forging stock and for shops that will do their own annealing and carburizing. | 560 | 800 | 16 | 22 HRC | — |
Normalized | Grain-refining pre-treatment for forgings; gives a uniform structure and stable machining stock removal. | 620 | 850 | 17 | 26 HRC | — |
Cold drawn | Choose for close-tolerance small-diameter shafting and pins where machining allowance must be minimal. | 700 | 830 | 12 | 25 HRC | 5.7 % IACS |
Quenched and high-tempered, ~30–35 HRC | Higher tempering (550–650 °C) for shafts and fasteners machined to final size without carburizing, trading strength for toughness and cutability. | 830 | 1,000 | 15 | 32 HRC | — |
QTDefault Quenched and tempered | Standard GB/T 3077 property condition and the core state under a carburized case — pick when full through-strength with high toughness is needed. | 950 | 1,180 | 12 | 39 HRC | — |
Carburized, hardened and low-temperature tempered | The service condition for gears and races: hard wear-resistant case with compressive residual stress over a tough 35–42 HRC core. | 1,000 | 1,250 | 10 | 60 HRC | — |
Aerospace quality, vacuum-remelted / clean-steel bar | Specify for flight-critical gears and bearings where inclusion cleanliness governs bending and contact fatigue life. | 1,000 | 1,230 | 15 | 40 HRC | 5.7 % IACS |
What is 12Cr2Ni4A?
12Cr2Ni4A, equivalent to AISI 9310, is a high-alloy nickel-chromium carburizing steel with deep hardenability and a tough core after case hardening. It is used for heavy-duty and precision gear components and high-load shafts, and is available as hot-rolled, annealed, normalized, cold-drawn and vacuum-arc-remelted (VAR) bar and forgings. Carburized and tempered it gives about 950 MPa yield, 1180 MPa tensile, 12 % elongation and 370 HB (39 HRC), with service to roughly 200 °C. Machinability is low (score 32) and the heat-affected zone is crack-sensitive, so joints are avoided; 18Cr2Ni4WA is the higher-strength alternative. 12Cr2Ni4A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F). 12Cr2Ni4A has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Elongation at break is 12% and the elastic modulus is 210 GPa (30.5 Msi).
What is 12Cr2Ni4A used for?
- Aircraft gears
- High-load transmission shafts
- Planetary pinions and ring gears
- Spline couplings
- Precision gearbox pinions
- Bevel gear sets
- Rotorcraft drive gears
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- High strength — 950 MPa (138 ksi), better than 91% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Difficult to machine — 32/100, worse than 87% of steel grades
- High embodied carbon — 2.6 kg CO₂/kg, worse than 87% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
12Cr2Ni4A properties
Typical room-temperature values for 12Cr2Ni4A-QT; bars are the position among steel grades.
Physical3
12Cr2Ni4A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F).
Mechanical16
12Cr2Ni4A has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Elongation at break is 12% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
12Cr2Ni4A is rated for continuous service to 200°C (392 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
12Cr2Ni4A conducts electricity at 5.7 % IACS, worse than 80% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 12Cr2Ni4A takes about 36 MJ of energy and emits 2.6 kg of CO₂ — more than 89% of steel grades. Typical recycled content is 25%.
Manufacturability7
12Cr2Ni4A's machinability is poor (32/100, worse than 87% of steel grades); weldability poor (30/100); formability poor (30/100).
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. 12Cr2Ni4A is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 12Cr2Ni4A
Is 12Cr2Ni4A easy to machine?
Rough all gear teeth in the annealed (≤269 HB) state with coated carbide and generous coolant; after carburizing only grinding, honing or CBN hard-turning is practical.
Can 12Cr2Ni4A be welded?
Weld only before carburizing — preheat 250–350 °C, low-hydrogen or matching Ni-Cr filler, immediate post-weld temper; high hardenability makes the HAZ crack-sensitive.
Can 12Cr2Ni4A be formed, bent or molded?
Hot forge 1150–850 °C then normalize plus isothermal anneal to break up the bainitic/martensitic as-forged structure; cold forming limited to annealed bar.
12Cr2Ni4A 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 |
|---|---|---|
| CGB/T 3077 12Cr2Ni4A | 0.1 – 0.17 | 0.13 |
| Si | 0.17 – 0.37 | 0.27 |
| Mn | 0.3 – 0.6 | 0.45 |
| Cr | 1.25 – 1.65 | 1.45 |
| Ni | 3.25 – 3.65 | 3.45 |
| Curesidual | ≤ 0.25 | |
| PA-grade high quality; ≤0.020 for aerospace | ≤ 0.03 | |
| SA-grade high quality; ≤0.015 for aerospace | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on 12Cr2Ni4A?
No anodizing — protect with black oxide, manganese phosphate or oil; copper-plate areas to be masked from carburizing, and shot-peen tooth roots to boost bending fatigue.
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 12Cr2Ni4A in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 9310
How much does 12Cr2Ni4A cost?
12Cr2Ni4A is a standard-cost steel ($$), cheaper than about 71% 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.
12Cr2Ni4A — frequently asked
What is 12Cr2Ni4A used for?
12Cr2Ni4A is typically used for aircraft gears, high-load transmission shafts, planetary pinions and ring gears, spline couplings, precision gearbox pinions and bevel gear sets. In short: aerospace 9310-class gear steel; deep-hardening Ni-Cr case steel; VAR melt available.
What is the yield strength of 12Cr2Ni4A?
12Cr2Ni4A has a typical yield strength of 950 MPa (138 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 12Cr2Ni4A easy to machine?
Not especially — machinability is rated poor (32/100, worse than 87% of steel grades). Rough all gear teeth in the annealed (≤269 HB) state with coated carbide and generous coolant; after carburizing only grinding, honing or CBN hard-turning is practical.
Can 12Cr2Ni4A be welded?
Not readily — weldability is rated poor (30/100). Weld only before carburizing — preheat 250–350 °C, low-hydrogen or matching Ni-Cr filler, immediate post-weld temper; high hardenability makes the HAZ crack-sensitive.
What surface finishes work on 12Cr2Ni4A?
No anodizing — protect with black oxide, manganese phosphate or oil; copper-plate areas to be masked from carburizing, and shot-peen tooth roots to boost bending fatigue.
Can 12Cr2Ni4A be formed, bent or molded?
Hot forge 1150–850 °C then normalize plus isothermal anneal to break up the bainitic/martensitic as-forged structure; cold forming limited to annealed bar.
What is the maximum service temperature of 12Cr2Ni4A?
12Cr2Ni4A is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 12Cr2Ni4A-QT and 12Cr2Ni4A-A?
QT is the default condition — standard GB/T 3077 property condition and the core state under a carburized case — pick when full through-strength with high toughness is needed. A: softest and most machinable state — the condition gears are rough-cut and hobbed in before carburizing. Yield strength is 950 MPa in QT versus 450 MPa in A.
How much does 12Cr2Ni4A cost?
12Cr2Ni4A is a standard-cost steel ($$), cheaper than about 71% 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
- GB/T 3077 Alloy structural steels (2015)
- AMS 6265 — Steel Bars, Forgings and Tubing 3.2Ni-1.2Cr-0.12Mo (9310), VAR — 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 of Ni-Cr gear steels) — ASM International (1991)
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.