Steel 18NCD6-CH (Carburized and hardened)
Heat-treated state
EN 18NCD6
Specify the intended service state — carburized, hardened and low-temperature tempered — for gears, splined shafts and bearing rings needing a 58–62 HRC wear case over a tough core; machine beforehand.
Values for the CH condition
Other 18NCD6 tempers and conditions
18NCD6 is listed in 7 conditions; see the grade overview at 18NCD6.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard as-supplied bar state: lowest hardness and best machinability for rough-cutting gear blanks before case hardening by carburizing and quenching. | 370 | 580 | 24 | 170 HB | — |
Normalized | Normalize at about 880–900 °C and air cool to refine and homogenize forgings and bar, either in preparation for carburizing or for medium-strength non-carburized parts. | 430 | 680 | 20 | 14 HRC | 7.8 % IACS |
Hot rolled | Most economical blank supply form; as-rolled tolerances and surface are coarse, so normalize or anneal before machining to reach usable structure and finish. | 440 | 700 | 19 | 15 HRC | 7.8 % IACS |
Cold drawn | Choose for small- and medium-diameter shaft blanks machined directly from bar: annealing plus cold drawing gives 580 MPa yield with close size tolerance and good surface, at reduced formability. | 580 | 700 | 12 | 16 HRC | 7.8 % IACS |
Q&T 28–34 HRC | Pick when the part runs through-hardened and tempered to 28–34 HRC without carburizing, for medium-strength shafts, or to verify the core properties of carburized components. | 800 | 1,000 | 15 | 31 HRC | — |
CHThis page Carburized and hardened | Specify the intended service state — carburized, hardened and low-temperature tempered — for gears, splined shafts and bearing rings needing a 58–62 HRC wear case over a tough core; machine beforehand. | 900 | 1,150 | 11 | 60 HRC | — |
Q&T 36–42 HRC | Use the lower tempering temperature route to 36–42 HRC for heavily loaded non-carburized shafts and connecting rods; tensile reaches 1250 MPa but elongation drops to 12% and machining is harder. | 1,050 | 1,250 | 12 | 39 HRC | — |
What is 18NCD6-CH?
18NCD6-CH is 18NCD6 heat treated to CH — specify the intended service state — carburized, hardened and low-temperature tempered — for gears, splined shafts and bearing rings needing a 58–62 HRC wear case over a tough core; machine beforehand. 18NCD6-CH has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 90% of steel grades. Elongation at break is 11% and the elastic modulus is 207 GPa (30 Msi). 18NCD6-CH 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; CH is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- High strength — 900 MPa (131 ksi), better than 90% 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 — 11%, worse than 89% of steel grades
18NCD6-CH properties
Typical room-temperature values for 18NCD6-CH; 15 are specific to this condition. Other listed values are 18NCD6 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
18NCD6-CH 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
18NCD6-CH has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 90% of steel grades. Elongation at break is 11% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
18NCD6-CH is rated for continuous service to 180°C (356 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 11.6 µm/m·K (6.44 µin/in·°F).
Electrical3
18NCD6-CH conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 18NCD6-CH takes about 29 MJ of energy and emits 2.1 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 25%.
Manufacturability7
18NCD6-CH'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 18NCD6-CH
Is 18NCD6 easy to machine?
In the annealed or normalized condition it turns and mills efficiently with carbide tooling at roughly 60–65 % of 1212 machinability. After carburizing and quenching, use grinding or hard turning with CBN only.
Can 18NCD6 be welded?
Carbon equivalent is about 0.6–0.7, so it is weldable with 150–250 °C preheat, low-hydrogen consumables and a post-weld temper. Do not weld in or near carburized surface layers.
Can 18NCD6 be formed, bent or molded?
The annealed condition suits hot forging at 1150–1200 °C with finishing above 850 °C, and moderate cold heading. Normalize after forging to refine the structure before carburizing.
What surface finishes work on 18NCD6?
No corrosion resistance: black oxide, phosphate, zinc or nickel plating, or rust-preventive oil on non-carburized surfaces. Carburized and ground tooth flanks are usually shot peened to raise bending fatigue life.
18NCD6 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 |
|---|---|---|
| CLow-carbon core of carburizing steel | 0.15 – 0.21 | 0.18 |
| Si | 0.1 – 0.4 | 0.25 |
| Mn | 0.5 – 0.9 | 0.7 |
| P | ≤ 0.04 | — |
| Smax; free-machining variants up to 0.020-0.035 | ≤ 0.04 | — |
| Cr | 0.8 – 1.15 | 0.95 |
| NiAFNOR grade digit 6 corresponds to Ni approx. 1.5% | 1.3 – 1.75 | 1.5 |
| Mo | 0.15 – 0.3 | 0.22 |
| Fe | balance | — |
18NCD6-CH — frequently asked
What is 18NCD6-CH used for?
18NCD6-CH is typically used for gears, shafts and pinions. In short: 8620-equivalent gear steel; mo-boosted hardenability; machines well before carburizing.
What is the yield strength of 18NCD6-CH?
18NCD6-CH has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 18NCD6-CH easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). In the annealed or normalized condition it turns and mills efficiently with carbide tooling at roughly 60–65 % of 1212 machinability. After carburizing and quenching, use grinding or hard turning with CBN only.
Can 18NCD6-CH be welded?
Not readily — weldability is rated not recommended (10/100). Carbon equivalent is about 0.6–0.7, so it is weldable with 150–250 °C preheat, low-hydrogen consumables and a post-weld temper. Do not weld in or near carburized surface layers.
What surface finishes work on 18NCD6-CH?
No corrosion resistance: black oxide, phosphate, zinc or nickel plating, or rust-preventive oil on non-carburized surfaces. Carburized and ground tooth flanks are usually shot peened to raise bending fatigue life.
Can 18NCD6-CH be formed, bent or molded?
The annealed condition suits hot forging at 1150–1200 °C with finishing above 850 °C, and moderate cold heading. Normalize after forging to refine the structure before carburizing.
What is the maximum service temperature of 18NCD6-CH?
18NCD6-CH 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 18NCD6-A and 18NCD6 QT-38?
A is the default condition — standard as-supplied bar state: lowest hardness and best machinability for rough-cutting gear blanks before case hardening by carburizing and quenching. QT-38: use the lower tempering temperature route to 36–42 HRC for heavily loaded non-carburized shafts and connecting rods; tensile reaches 1250 MPa but elongation drops to 12% and machining is harder. Yield strength is 370 MPa in A versus 1,050 MPa in QT-38.
Sources
- NF A35-551 — Aciers de cementation (18NCD6) — AFNOR (1987)
- EN 10084 — Case hardening steels (18NiCrMo5 / 18CrNiMo7-6 family) — CEN (2008)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (carburizing) — ASM International (1991)
- Machinery's Handbook, 31st ed. — machinability ratings — Industrial Press (2020)
- GB/T 3077 — (20CrNi2Mo/20CrNiMo ) — 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.