Steel SCM418-HR (Hot rolled)
Supply condition
JIS SCM418
Cheapest mill condition for parts that will be fully heat treated anyway; hardness scatter and decarb layer must be machined off.
Values for the HR 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 | — |
HRThis page 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-HR?
SCM418-HR is SCM418 supplied in the HR condition — cheapest mill condition for parts that will be fully heat treated anyway; hardness scatter and decarb layer must be machined off. SCM418-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi). SCM418-HR 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; HR is available on request or by drawing note.
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
SCM418-HR properties
Typical room-temperature values for SCM418-HR; 11 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-HR 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-HR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SCM418-HR 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-HR 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-HR 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-HR's machinability is good (57/100, better than 71% of steel grades); weldability good (55/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SCM418-HR
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-HR — frequently asked
What is SCM418-HR used for?
SCM418-HR 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-HR?
SCM418-HR has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is SCM418-HR easy to machine?
Reasonably — machinability is rated good (57/100, better than 71% 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-HR 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-HR?
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-HR 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-HR?
SCM418-HR 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.
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.