Steel SCM420 · heat-treated state
Steel SCM420 Carburized
Properties of the Carburized condition, compared with the other SCM420 tempers.
The intended service condition for gears and pinions — hard wear-resistant case over a tough Cr-Mo core.
What is SCM420 Carburized?
SCM420 Carburized is SCM420 heat treated to Carburized — the intended service condition for gears and pinions — hard wear-resistant case over a tough Cr-Mo core. SCM420 Carburized 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 12% and the elastic modulus is 207 GPa (30 Msi). SCM420 Carburized has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; Carburized is available on request or by drawing note.
Advantages
- High strength — 900 MPa (131 ksi), better than 90% of steel grades
Limitations
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Low fracture toughness — 65 MPa·√m (59.2 ksi·√in), worse than 76% of steel grades
SCM420 Carburized properties
Typical room-temperature values for SCM420 Carburized — 12 properties are specific to this condition; the rest are grade-level values shared by every SCM420 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
SCM420 Carburized has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical14
SCM420 Carburized 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 12% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
SCM420 Carburized 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 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
SCM420 Carburized conducts electricity at 7.8 % IACS, worse than 58% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SCM420 Carburized takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 55% of steel grades. Typical recycled content is 30%.
Manufacturability7
SCM420 Carburized's machinability is poor (15/100, worse than 98% of steel grades); weldability poor (15/100); formability good (60/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other SCM420 tempers and conditions
SCM420 is also supplied in 6 other conditions. The full side-by-side table is on the SCM420 overview.
- HRDefaultStandard stock condition for bar and billet destined for machining, forging or carburizing.440 MPa yield · 190 HB
- CarburizedThe intended service condition for gears and pinions — hard wear-resistant case over a tough Cr-Mo core.900 MPa yield · 60 HRC
- Q&TThrough-hardened condition for shafts and fasteners where core strength, not surface wear, governs.760 MPa yield · 31 HRC
- CDCold-drawn bar giving close size tolerance, bright finish and higher as-supplied strength for screw-machine work.620 MPa yield · 225 HB
- NormalizedUniform fine-grain structure for consistent machining and predictable response to carburizing.470 MPa yield · 207 HB
- AnnealedSoftest condition — pick it for cold forging, deep machining or heavy upsetting before carburizing.360 MPa yield · 163 HB
Working with SCM420 Carburized
Is SCM420 easy to machine?
Machine in the annealed or normalized state (≈62 % of AISI 1212); carbide inserts, 120–180 m/min turning, finish-grind after carburizing to hold size.
Can SCM420 be welded?
Weldable with low-hydrogen consumables at CE ≈ 0.55: preheat 150–250 °C, control interpass, and PWHT at 600–650 °C; never weld a carburized surface.
Can SCM420 be formed, bent or molded?
Spheroidize-anneal for cold heading and cold forging; hot forge 1100–1200 °C and finish above 900 °C, then normalize before machining.
What surface finishes work on SCM420?
No anodizing — protect with black oxide, manganese phosphate, zinc or Ni plating; after carburizing use shot peening plus grinding for maximum bending fatigue life.
SCM420 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 G 4053 | 0.18 – 0.23 | 0.2 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.6 – 0.85 | 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 | — |
SCM420 Carburized — frequently asked
What is SCM420 Carburized used for?
SCM420 Carburized is typically used for gears, industrial drive shafts and pins. In short: carburizing Cr-Mo bar.
What is the yield strength of SCM420 Carburized?
SCM420 Carburized 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 SCM420 Carburized easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% of steel grades). Machine in the annealed or normalized state (≈62 % of AISI 1212); carbide inserts, 120–180 m/min turning, finish-grind after carburizing to hold size.
Can SCM420 Carburized be welded?
Not readily — weldability is rated poor (15/100). Weldable with low-hydrogen consumables at CE ≈ 0.55: preheat 150–250 °C, control interpass, and PWHT at 600–650 °C; never weld a carburized surface.
What surface finishes work on SCM420 Carburized?
No anodizing — protect with black oxide, manganese phosphate, zinc or Ni plating; after carburizing use shot peening plus grinding for maximum bending fatigue life.
Can SCM420 Carburized be formed, bent or molded?
Spheroidize-anneal for cold heading and cold forging; hot forge 1100–1200 °C and finish above 900 °C, then normalize before machining.
What is the maximum service temperature of SCM420 Carburized?
SCM420 Carburized 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 SCM420-HR and SCM420-CD?
HR is the default condition — standard stock condition for bar and billet destined for machining, forging or carburizing. CD: cold-drawn bar giving close size tolerance, bright finish and higher as-supplied strength for screw-machine work. Yield strength is 440 MPa in HR versus 620 MPa in CD.
Can FabDigit make parts in SCM420 Carburized?
Yes — SCM420 Carburized is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- JIS G 4053 — Low-alloyed steels for machine structural use — JSA (2016)
- ASTM A29/A29M and SAE J404 (4118/4120 equivalence) — 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)
- GB/T 3077 — (20CrMo / 20CrMnMo comparison grades) — 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.