Steel 12Cr2Ni4A CARB
Heat-treated state
GB 12Cr2Ni4A
CARB = 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.
Values for the CARB condition
Other 12Cr2Ni4A tempers and conditions
12Cr2Ni4A is listed in 8 conditions; see the grade overview at 12Cr2Ni4A.
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 | — |
CARBThis page 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 CARB?
12Cr2Ni4A CARB is 12Cr2Ni4A heat treated to CARB — the service condition for gears and races: hard wear-resistant case with compressive residual stress over a tough 35–42 HRC core. 12Cr2Ni4A CARB has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,250 MPa (181 ksi) — stronger than 92% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi). 12Cr2Ni4A CARB 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). QT is the default condition FabDigit quotes; CARB is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 85/100, better than 99% of steel grades
- High strength — 1,000 MPa (145 ksi), better than 92% of steel grades
Limitations
- Difficult to machine — 10/100, worse than 99% of steel grades
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited formability — 5/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
12Cr2Ni4A CARB properties
Typical room-temperature values for 12Cr2Ni4A CARB; 15 are specific to this condition. Other listed values are 12Cr2Ni4A reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
12Cr2Ni4A CARB 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 CARB has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,250 MPa (181 ksi) — stronger than 92% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
12Cr2Ni4A CARB is rated for continuous service to 180°C (356 °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 CARB 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 CARB 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 CARB's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (10/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 12Cr2Ni4A CARB
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.
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.
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 | — |
12Cr2Ni4A CARB — frequently asked
What is 12Cr2Ni4A CARB used for?
12Cr2Ni4A CARB 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 CARB?
12Cr2Ni4A CARB has a typical yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,250 MPa (181 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 12Cr2Ni4A CARB easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% 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 CARB be welded?
Not readily — weldability is rated not recommended (10/100). 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 CARB?
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 CARB 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 CARB?
12Cr2Ni4A CARB 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 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.