Steel SCM420
JIS SCM420
SCM420 (20CrMo) is a low-carbon chromium-molybdenum case-hardening steel, the workhorse carburizing grade of the JIS SCM series, giving a hard case over a tough core.
Values for the HR condition
SCM420 tempers and conditions
SCM420 is supplied in 7 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed (full / spheroidize annealed) | Softest condition — pick it for cold forging, deep machining or heavy upsetting before carburizing. | 360 | 560 | 27 | 163 HB | 7.9 % IACS |
HRDefault Hot rolled | Standard stock condition for bar and billet destined for machining, forging or carburizing. | 440 | 660 | 22 | 190 HB | — |
Normalized (≈870–920 °C, air cool) | Uniform fine-grain structure for consistent machining and predictable response to carburizing. | 470 | 720 | 21 | 15 HRC | 7.8 % IACS |
Cold rolled | Cold-rolled strip for stamped/formed parts that will later be carburized. | 580 | 720 | 14 | 17 HRC | 7.8 % IACS |
Cold drawn | Cold-drawn bar giving close size tolerance, bright finish and higher as-supplied strength for screw-machine work. | 620 | 760 | 13 | 20 HRC | 7.8 % IACS |
Quenched and tempered | Through-hardened condition for shafts and fasteners where core strength, not surface wear, governs. | 760 | 980 | 17 | 31 HRC | — |
Carburized, hardened & low-temperature tempered (case 58–62 HRC) | The intended service condition for gears and pinions — hard wear-resistant case over a tough Cr-Mo core. | 900 | 1,150 | 12 | 60 HRC | — |
What is SCM420?
SCM420 (20CrMo) is a low-carbon chromium-molybdenum case-hardening steel, the workhorse carburizing grade of the JIS SCM series, giving a hard case over a tough core. It is supplied as hot-rolled, cold-drawn, annealed or normalized bar and forgings for gears, shafts and pins, then carburized, quenched and finish ground to size. Weldability is acceptable with low-hydrogen consumables at CE ≈ 0.55, but carburized surfaces must never be welded and the steel has no corrosion resistance. SCM415 is the alternative where a shallower case and lower core strength are acceptable. SCM420 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). SCM420 has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 50% of steel grades. Elongation at break is 22% and the elastic modulus is 207 GPa (30 Msi).
What is SCM420 used for?
- Gears
- Industrial drive shafts
- Pins
Limitations
- Low fracture toughness — 65 MPa·√m (59.2 ksi·√in), worse than 75% of steel grades
SCM420 properties
Typical room-temperature values for SCM420-HR; bars are the position among steel grades.
Physical3
SCM420 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 has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 50% of steel grades. Elongation at break is 22% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
SCM420 is rated for continuous service to 400°C (752 °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 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 SCM420 takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
SCM420's machinability is good (60/100, better than 83% of steel grades); weldability good (55/100); formability good (60/100).
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. SCM420 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SCM420
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.
Manufacturability
The process limits FabDigit applies to SCM420. Every SCM420 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better60 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Better60 / 100 |
|---|---|
| Weldability | Better55 / 100 |
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 |
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.
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).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SCM420 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- JIS
- G 4053 SCM420
- Similar grades
- 20CrMo
How much does SCM420 cost?
SCM420 is a standard-cost steel ($$), cheaper than about 71% 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.
SCM420 — frequently asked
What is SCM420 used for?
SCM420 is typically used for gears, industrial drive shafts and pins. In short: carburizing Cr-Mo bar.
What is the yield strength of SCM420?
SCM420 has a typical yield strength of 440 MPa (63.8 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 50% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is SCM420 easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% 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 be welded?
Yes — weldability is rated good (55/100). 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?
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 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?
SCM420 is rated for continuous use to about 400°C (752 °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.
How much does SCM420 cost?
SCM420 is a standard-cost steel ($$), cheaper than about 71% 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.
Can FabDigit make parts in SCM420?
Yes — SCM420 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. 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; 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.