Steel 12KhN3A CARB
Heat-treated state
GOST 12KhN3A (12ХН3А)
CARB = carburized 900–930 °C + oil quench + 160–200 °C temper
The service condition for gears, worms and splines — very hard wear-resistant case over the tough Ni-Cr core.
Values for the CARB condition
Other 12KhN3A tempers and conditions
12KhN3A is listed in 8 conditions; see the grade overview at 12KhN3A.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition for heavy machining, deep drilling or cold forming before case hardening. | 380 | 620 | 22 | 200 HB | — |
Hot rolled | Mill condition of round bar and forging stock, machined then heat treated by the part maker. | 440 | 700 | 18 | 19 HRC | 7.5 % IACS |
Normalized | Grain refinement and uniform machinable structure prior to carburizing of forged parts. | 520 | 760 | 18 | 20 HRC | 7.5 % IACS |
Cold drawn | Bright bar with tight tolerance for small pins and shafts made with minimal machining. | 660 | 800 | 10 | 22 HRC | 7 % IACS |
Q&T high temper | Choose when a non-carburized, dimensionally stable tough shaft or fastener body is needed rather than a hard case. | 700 | 850 | 17 | 26 HRC | — |
QTDefault Quenched and tempered | Standard GOST acceptance condition; use for the tough core strength of carburized parts or for through-hardened medium-duty parts. | 760 | 980 | 13 | 30 HRC | — |
Carburized, hardened and finish ground | Final precision condition for ground gear teeth and bearing journals where distortion must be removed after case hardening. | 830 | 1,080 | 11 | 60 HRC | 6.5 % IACS |
CARBThis page Carburized 900–930 °C + oil quench + 160–200 °C temper | The service condition for gears, worms and splines — very hard wear-resistant case over the tough Ni-Cr core. | 850 | 1,150 | 10 | 60 HRC | — |
What is 12KhN3A CARB?
12KhN3A CARB is 12KhN3A heat treated to CARB — the service condition for gears, worms and splines — very hard wear-resistant case over the tough Ni-Cr core. 12KhN3A CARB has a yield strength of 850 MPa (123 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 88% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi). 12KhN3A CARB 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). QT is the default condition FabDigit quotes; CARB is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- High strength — 850 MPa (123 ksi), better than 88% of steel grades
Limitations
- Difficult to weld — 5/100, worse than 100% of steel grades
- Difficult to machine — 10/100, 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
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
12KhN3A CARB properties
Typical room-temperature values for 12KhN3A CARB; 12 are specific to this condition. Other listed values are 12KhN3A reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
12KhN3A CARB 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
12KhN3A CARB has a yield strength of 850 MPa (123 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 88% of steel grades. Elongation at break is 10% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
12KhN3A CARB is rated for continuous service to 180°C (356 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 11.4 µm/m·K (6.33 µin/in·°F).
Electrical3
12KhN3A CARB conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 12KhN3A CARB takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
12KhN3A CARB's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (5/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 12KhN3A CARB
Is 12KhN3A easy to machine?
Machine in the annealed or normalized state (HB ≤ 217) with carbide tooling and generous coolant; the tough Ni-Cr matrix is gummy and work-hardens, so finish grinding is normal after case hardening.
Can 12KhN3A be welded?
Weldable in the low-carbon soft state with 150–250 °C preheat, low-hydrogen consumables and post-weld stress relief; do not weld carburized or hardened zones.
Can 12KhN3A be formed, bent or molded?
Hot forge 1180–850 °C followed by normalizing; cold heading and bending only in the annealed condition with generous bend radii.
What surface finishes work on 12KhN3A?
Not anodizable — protect with phosphating, black oxide, oil, zinc or hard chrome; shot peening after carburizing markedly raises bending fatigue of gear roots.
12KhN3A 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 | 0.09 – 0.16 | 0.12 |
| Si | 0.17 – 0.37 | 0.27 |
| Mn | 0.3 – 0.6 | 0.45 |
| Cr | 0.6 – 0.9 | 0.75 |
| Ni | 2.75 – 3.15 | 2.95 |
| Curesidual | ≤ 0.3 | — |
| Moresidual, not intentionally added | ≤ 0.15 | — |
| S'A' = high-quality, low S/P | ≤ 0.03 | — |
| P'A' = high-quality, low S/P | ≤ 0.03 | — |
| Fe | balance | — |
12KhN3A CARB — frequently asked
What is 12KhN3A CARB used for?
12KhN3A CARB is typically used for gears, shafts and aerospace parts. In short: high core toughness; ni-Cr carburizing grade; tougher than Cr-Mn steels.
What is the yield strength of 12KhN3A CARB?
12KhN3A CARB has a typical yield strength of 850 MPa (123 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 88% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 12KhN3A CARB easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Machine in the annealed or normalized state (HB ≤ 217) with carbide tooling and generous coolant; the tough Ni-Cr matrix is gummy and work-hardens, so finish grinding is normal after case hardening.
Can 12KhN3A CARB be welded?
Not readily — weldability is rated not recommended (5/100). Weldable in the low-carbon soft state with 150–250 °C preheat, low-hydrogen consumables and post-weld stress relief; do not weld carburized or hardened zones.
What surface finishes work on 12KhN3A CARB?
Not anodizable — protect with phosphating, black oxide, oil, zinc or hard chrome; shot peening after carburizing markedly raises bending fatigue of gear roots.
Can 12KhN3A CARB be formed, bent or molded?
Hot forge 1180–850 °C followed by normalizing; cold heading and bending only in the annealed condition with generous bend radii.
What is the maximum service temperature of 12KhN3A CARB?
12KhN3A 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 12KhN3A-QT and 12KhN3A-A?
QT is the default condition — standard GOST acceptance condition; use for the tough core strength of carburized parts or for through-hardened medium-duty parts. A: softest condition for heavy machining, deep drilling or cold forming before case hardening. Yield strength is 760 MPa in QT versus 380 MPa in A.
Sources
- GOST 4543-2016 — Alloy structural steel bars — Rosstandart (2016)
- GB/T 3077 — Alloy structural steels (12CrNi3A/12CrNi3) — SAC (2015)
- Marochnik stali i splavov — grade 12ХН3А — Marochnik (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals (carburizing) — ASM International (2013)
- Alloy structural steel bar price levels — Mysteel / 1688 (2025)
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.