Steel 6120 CARB
Heat-treated state
AISI/SAE 6120 · UNS G61200
CARB = carburized, Quenched and Tempered
The intended service condition for gears, pinions and cams — hard wear-resistant case over a tough Cr-V core.
Values for the CARB condition
Other 6120 tempers and conditions
6120 is listed in 9 conditions; see the grade overview at 6120.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize Annealed | Choose for severe cold heading/upsetting of fastener and gear blanks. | 340 | 530 | 32 | 150 HB | 7.8 % IACS |
ADefault Solution annealed | Standard soft stocking condition for machining, cold forming and carburizing blanks. | 370 | 570 | 29 | 163 HB | — |
Hot rolled | Cheapest mill condition for bar and forging stock that will be re-heat-treated anyway. | 400 | 620 | 24 | 179 HB | 7.5 % IACS |
Normalized and tempered | Stress-relieved normalized bar for structural parts needing dimensional stability and impact toughness. | 420 | 620 | 27 | 180 HB | 7.5 % IACS |
Normalized | Uniform fine-grain structure and better toughness than as-rolled; usual pre-treatment before carburizing or machining of forgings. | 440 | 655 | 25 | 190 HB | 7.5 % IACS |
Cold drawn | Pick for tight-tolerance bright bar with higher yield strength and better surface without heat treatment. | 600 | 700 | 13 | 207 HB | — |
Q&T 22–28 HRC | Through-hardened condition for tough shafts and structural fasteners where a moderate strength level is enough. | 650 | 830 | 20 | 25 HRC | — |
CARBThis page Carburized, Quenched and Tempered | The intended service condition for gears, pinions and cams — hard wear-resistant case over a tough Cr-V core. | 750 | 1,000 | 12 | 60 HRC | — |
Q&T 30–35 HRC | Highest practical through-hardened strength for this 0.20 % C grade; use in small sections only. | 820 | 1,000 | 16 | 32 HRC | — |
What is 6120 CARB?
6120 CARB is 6120 heat treated to CARB — the intended service condition for gears, pinions and cams — hard wear-resistant case over a tough Cr-V core. 6120 CARB has a yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). 6120 CARB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). A is the default condition FabDigit quotes; CARB is available on request or by drawing note.
Advantages
- High strength — 750 MPa (109 ksi), better than 84% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
6120 CARB properties
Typical room-temperature values for 6120 CARB; 10 are specific to this condition. Other listed values are 6120 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
6120 CARB has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical13
6120 CARB has a yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
6120 CARB is rated for continuous service to 200°C (392 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
6120 CARB conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 6120 CARB takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
6120 CARB's machinability is fair (52/100, better than 52% of steel grades); weldability good (55/100); formability good (58/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 6120 CARB
Is 6120 easy to machine?
Machines well annealed or normalized (~60 % of 1212) with carbide tooling and flood coolant; finish-grind after carburizing since the case is essentially unmachinable.
Can 6120 be welded?
Weldable with low-hydrogen consumables; preheat 150–250 °C and post-weld temper, and never weld carburized surfaces.
Can 6120 be formed, bent or molded?
Cold head and bend in the annealed or spheroidized condition; hot forge 1150–1200 °C and finish above ~900 °C, then normalize to restore grain size.
What surface finishes work on 6120?
No corrosion resistance bare — use black oxide, phosphate-and-oil, zinc or hard chrome; shot-peen carburized gear roots for fatigue life and bake after plating to avoid hydrogen embrittlement.
6120 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 – 0.22 | 0.2 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.7 – 0.9 | 0.8 |
| V0.10 % min per SAE J404 | ≥ 0.1 | 0.15 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
6120 CARB — frequently asked
What is 6120 CARB used for?
6120 CARB is typically used for gears, structural fasteners and shafts. In short: fine-grain carburizing grade; tough Cr-V gear core; moderate hardenability only.
What is the yield strength of 6120 CARB?
6120 CARB has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 6120 CARB easy to machine?
Reasonably — machinability is rated fair (52/100, better than 52% of steel grades). Machines well annealed or normalized (~60 % of 1212) with carbide tooling and flood coolant; finish-grind after carburizing since the case is essentially unmachinable.
Can 6120 CARB be welded?
Yes — weldability is rated good (55/100). Weldable with low-hydrogen consumables; preheat 150–250 °C and post-weld temper, and never weld carburized surfaces.
What surface finishes work on 6120 CARB?
No corrosion resistance bare — use black oxide, phosphate-and-oil, zinc or hard chrome; shot-peen carburized gear roots for fatigue life and bake after plating to avoid hydrogen embrittlement.
Can 6120 CARB be formed, bent or molded?
Cold head and bend in the annealed or spheroidized condition; hot forge 1150–1200 °C and finish above ~900 °C, then normalize to restore grain size.
What is the maximum service temperature of 6120 CARB?
6120 CARB 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 6120-A and 6120 QT-32?
A is the default condition — standard soft stocking condition for machining, cold forming and carburizing blanks. QT-32: highest practical through-hardened strength for this 0.20 % C grade; use in small sections only. Yield strength is 370 MPa in A versus 820 MPa in QT-32.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 / ASTM A304 — Hardenability requirements for alloy steel bars — SAE / ASTM (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (carburizing of Cr-V steels) — ASM International (1991)
- Machinery's Handbook, 31st ed. (machinability ratings, alloy steel heat treatment) — Industrial Press (2020)
- GB/T 3077 (20CrV comparison grade) — 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.