Steel 12Cr2Ni4A QT-HT
Hardness band
GB 12Cr2Ni4A
QT-HT = 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.
Values for the QT-HT 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 |
QT-HTThis page 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 QT-HT?
12Cr2Ni4A QT-HT is 12Cr2Ni4A heat treated to QT-HT — higher tempering (550–650 °C) for shafts and fasteners machined to final size without carburizing, trading strength for toughness and cutability. 12Cr2Ni4A QT-HT has a yield strength of 830 MPa (120 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 87% of steel grades. Elongation at break is 15% and the elastic modulus is 210 GPa (30.5 Msi). 12Cr2Ni4A QT-HT 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; QT-HT is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- High strength — 830 MPa (120 ksi), better than 87% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
Limitations
- High embodied carbon — 2.6 kg CO₂/kg, worse than 87% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
- Low electrical conductivity — 5.7 % IACS, worse than 80% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
12Cr2Ni4A QT-HT properties
Typical room-temperature values for 12Cr2Ni4A QT-HT; 11 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 QT-HT 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 QT-HT has a yield strength of 830 MPa (120 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 87% of steel grades. Elongation at break is 15% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
12Cr2Ni4A QT-HT is rated for continuous service to 450°C (842 °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 QT-HT 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 QT-HT 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 QT-HT's machinability is fair (38/100, worse than 80% of steel grades); weldability poor (30/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 12Cr2Ni4A QT-HT
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 QT-HT — frequently asked
What is 12Cr2Ni4A QT-HT used for?
12Cr2Ni4A QT-HT 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 QT-HT?
12Cr2Ni4A QT-HT has a typical yield strength of 830 MPa (120 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 87% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 12Cr2Ni4A QT-HT easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% 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 QT-HT 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 QT-HT?
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 QT-HT 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 QT-HT?
12Cr2Ni4A QT-HT is rated for continuous use to about 450°C (842 °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.