Steel SCM418
JIS SCM418
SCM418 is a JIS chromium-molybdenum carburizing steel close to AISI 4118, with slightly higher carbon than SCM415 for a stronger core in medium-duty automotive gears.
Reference datasheet — SCM418 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the A condition
SCM418 tempers and conditions
SCM418 is supplied in 9 conditions, soft to hard. A is the default FabDigit quotes; the values on this page are for it.
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 |
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?
SCM418 is a JIS chromium-molybdenum carburizing steel close to AISI 4118, with slightly higher carbon than SCM415 for a stronger core in medium-duty automotive gears. It is supplied hot-rolled, annealed, spheroidize-annealed, normalized, cold-drawn and quenched and tempered, and is finished by carburizing, carbonitriding or induction hardening. Default properties are 355 MPa yield, 560 MPa tensile, 26% elongation and 163 HB (84 HRB), with machinability about 65% of AISI 1212. It has no corrosion resistance and must be welded before case hardening; SCM421/4320 gives deeper hardenability in heavier sections. SCM418 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). SCM418 has a yield strength of 355 MPa (51.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 73% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
What is SCM418 used for?
- Automotive transmission gears
- Differential pinion gears
- Splined drive shafts
- Steering worm and pinion parts
- Piston pins
- Sprockets
- Hardened bushings
Advantages
- Easy to machine — 62/100, better than 89% of steel grades
- Ductile — tolerates forming and impact — 26%, better than 82% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
SCM418 properties
Typical room-temperature values for SCM418-A; bars are the position among steel grades.
Physical3
SCM418 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 has a yield strength of 355 MPa (51.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 73% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SCM418 is rated for continuous service to 200°C (392 °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 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 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's machinability is good (62/100, better than 89% of steel grades); weldability good (55/100); formability good (58/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SCM418 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SCM418
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SCM418 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 4118
How much does SCM418 cost?
SCM418 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SCM418 — frequently asked
What is SCM418 used for?
SCM418 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?
SCM418 has a typical yield strength of 355 MPa (51.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 73% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is SCM418 easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% 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 be welded?
Yes — weldability is rated good (55/100). 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?
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 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?
SCM418 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 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.
How much does SCM418 cost?
SCM418 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.