Steel SCM418 CARB
Heat-treated state
JIS SCM418
CARB = carburized, quenched and low-temperature tempered
The service condition for gears and splines: hard wear/pitting-resistant case with compressive residual stress over a tough core.
Values for the CARB condition
Other SCM418 tempers and conditions
SCM418 is listed in 9 conditions; see the grade overview at SCM418.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Pick for cold heading, cold extrusion or heavy cold forming of gear blanks and shafts. | 330 | 520 | 30 | 145 HB | 7.9 % IACS |
ADefault Solution annealed | Default stocked bar condition: softest reliable state for turning, hobbing and shaping before carburizing. | 355 | 560 | 26 | 163 HB | — |
Hot rolled | Cheapest mill condition for parts that will be fully heat treated anyway; hardness scatter and decarb layer must be machined off. | 400 | 620 | 22 | 179 HB | — |
Normalized | Standard pre-treatment before carburizing: refines grain, homogenizes forgings and stabilizes distortion. | 450 | 700 | 20 | 207 HB | — |
Cold drawn | Bright, size-accurate bar for small shafts and pins made on automatics; higher yield but lower ductility. | 580 | 700 | 12 | 207 HB | — |
Quenched and tempered | Use when the part is not carburized but needs a tough medium-strength body (shafts, fasteners, links). | 740 | 930 | 18 | 29 HRC | — |
Induction hardened | Used where only a journal or tooth flank needs hardness; case is shallower and softer than carburizing because base carbon is low. | 760 | 950 | 13 | 45 HRC | 7.5 % IACS |
Carbonitrided, quenched and tempered | Choose for thin (0.2–0.5 mm) very hard cases on small gears/pins at lower process temperature and less distortion than gas carburizing. | 850 | 1,100 | 10 | 61 HRC | 7.5 % IACS |
CARBThis page Carburized, quenched and low-temperature tempered | The service condition for gears and splines: hard wear/pitting-resistant case with compressive residual stress over a tough core. | 880 | 1,150 | 11 | 60 HRC | — |
What is SCM418 CARB?
SCM418 CARB is SCM418 heat treated to CARB — the service condition for gears and splines: hard wear/pitting-resistant case with compressive residual stress over a tough core. SCM418 CARB has a yield strength of 880 MPa (128 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 89% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi). SCM418 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 — 880 MPa (128 ksi), better than 89% 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
- Low fracture toughness — 35 MPa·√m (31.9 ksi·√in), worse than 94% of steel grades
SCM418 CARB properties
Typical room-temperature values for SCM418 CARB; 16 are specific to this condition. Other listed values are SCM418 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SCM418 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).
Mechanical16
SCM418 CARB has a yield strength of 880 MPa (128 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 89% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SCM418 CARB is rated for continuous service to 180°C (356 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
SCM418 CARB 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 SCM418 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%.
Manufacturability6
SCM418 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 SCM418 CARB
Is SCM418 easy to machine?
Turn, hob and shape in the annealed/normalized state (≈65 % of AISI 1212) with carbide at 120–180 m/min; after carburizing only grinding or hard turning with CBN is practical.
Can SCM418 be welded?
Weldable with low-hydrogen consumables plus 200–300 °C preheat and 600–650 °C stress relief; never weld carburized surfaces.
Can SCM418 be formed, bent or molded?
Hot forge 1100–1200 °C then normalize; cold heading and extrusion require spheroidize-annealed CHQ stock.
What surface finishes work on SCM418?
No corrosion resistance — protect with phosphate + oil, black oxide, zinc plating (bake to avoid hydrogen embrittlement) or shot peen the tooth roots for extra bending fatigue life.
SCM418 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 |
|---|---|---|
| CJIS G4053 SCM418 | 0.16 – 0.21 | 0.18 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.3 | 0.22 |
| Niresidual max | ≤ 0.25 | — |
| Curesidual max | ≤ 0.3 | — |
| Fe | balance | — |
SCM418 CARB — frequently asked
What is SCM418 CARB used for?
SCM418 CARB is typically used for automotive transmission gears, differential pinion gears, splined drive shafts, steering worm and pinion parts, piston pins and sprockets. In short: JIS 4118 equivalent; medium-duty gear steel; good machinability annealed.
What is the yield strength of SCM418 CARB?
SCM418 CARB has a typical yield strength of 880 MPa (128 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 89% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is SCM418 CARB easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Turn, hob and shape in the annealed/normalized state (≈65 % of AISI 1212) with carbide at 120–180 m/min; after carburizing only grinding or hard turning with CBN is practical.
Can SCM418 CARB be welded?
Not readily — weldability is rated not recommended (10/100). Weldable with low-hydrogen consumables plus 200–300 °C preheat and 600–650 °C stress relief; never weld carburized surfaces.
What surface finishes work on SCM418 CARB?
No corrosion resistance — protect with phosphate + oil, black oxide, zinc plating (bake to avoid hydrogen embrittlement) or shot peen the tooth roots for extra bending fatigue life.
Can SCM418 CARB be formed, bent or molded?
Hot forge 1100–1200 °C then normalize; cold heading and extrusion require spheroidize-annealed CHQ stock.
What is the maximum service temperature of SCM418 CARB?
SCM418 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 SCM418-A and SCM418 CARB?
A is the default condition — default stocked bar condition: softest reliable state for turning, hobbing and shaping before carburizing. CARB: the service condition for gears and splines: hard wear/pitting-resistant case with compressive residual stress over a tough core. Yield strength is 355 MPa in A versus 880 MPa in CARB.
Sources
- JIS G 4053 — Low-alloyed steels for machine structural use — JSA (2016)
- GB/T 3077 — Alloy structure steels (20CrMo comparison) — SAC (2015)
- ASTM A29/A29M and SAE J404 (4118 chemistry) — ASTM / SAE (2020)
- 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-Mo steels) — ASM International (1991)
- SMM / Mysteel alloy structural bar price quotes (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.