Steel SCM421-CD (Cold drawn)
Supply condition
JIS SCM421
Pick for small shafts and pins needing close size and good finish straight from bar, with minimal machining.
Values for the CD condition
Other SCM421 tempers and conditions
SCM421 is listed in 8 conditions; see the grade overview at SCM421.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard stocked machining condition — softest, most uniform structure before carburizing or cold forming. | 350 | 560 | 25 | 170 HB | — |
Isothermally annealed | Preferred pre-carburizing condition for gears: uniform ferrite-pearlite, low distortion and consistent hobbing behaviour. | 380 | 600 | 23 | 180 HB | 7.8 % IACS |
Hot rolled | Cheapest mill condition for parts that will be rough-machined then carburized; hardness scatter is highest. | 430 | 680 | 20 | 14 HRC | 7.8 % IACS |
Normalized | Used to refine grain and homogenize forgings before carburizing, or as a moderate-strength as-supplied core condition. | 460 | 720 | 20 | 16 HRC | 7.8 % IACS |
CDThis page Cold drawn | Pick for small shafts and pins needing close size and good finish straight from bar, with minimal machining. | 590 | 700 | 12 | 16 HRC | 7.8 % IACS |
Q&T core condition | Direct-hardened (non-carburized) use for shafts and fasteners where a tough medium-strength body is enough. | 780 | 950 | 15 | 30 HRC | — |
Carburized, quenched & low tempered | The service condition for gears and splines: hard wear/pitting-resistant case (0.6–1.5 mm typical) over a tough alloyed core. | 930 | 1,180 | 12 | 60 HRC | — |
Carburized + hard finished | Carburized condition with tooth flanks ground/honed after heat treat for high-accuracy, low-noise, high-load gearing. | 950 | 1,250 | 11 | 60 HRC | 7.5 % IACS |
What is SCM421-CD?
SCM421-CD is SCM421 supplied in the CD condition — pick for small shafts and pins needing close size and good finish straight from bar, with minimal machining. SCM421-CD has a yield strength of 590 MPa (85.6 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 76% of steel grades. Elongation at break is 12% and the elastic modulus is 206 GPa (29.9 Msi). SCM421-CD 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). A is the default condition FabDigit quotes; CD is available on request or by drawing note.
Advantages
- Easy to machine — 67/100, better than 95% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
- High strength — 590 MPa (85.6 ksi), better than 76% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
SCM421-CD properties
Typical room-temperature values for SCM421-CD; 23 are specific to this condition. Other listed values are SCM421 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SCM421-CD 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).
Mechanical13
SCM421-CD has a yield strength of 590 MPa (85.6 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 76% of steel grades. Elongation at break is 12% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SCM421-CD 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
SCM421-CD 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 SCM421-CD takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
SCM421-CD's machinability is good (67/100, better than 95% of steel grades); weldability fair (42/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SCM421-CD
Is SCM421 easy to machine?
Machine in the annealed or isothermally annealed state (≈170–200 HB) with coated carbide; leave grinding stock for post-carburizing distortion, and expect only grinding/EDM once the case is hardened.
Can SCM421 be welded?
Weldable only before carburizing — preheat 200–300 °C, low-hydrogen consumables, and temper immediately after; never weld a carburized surface.
Can SCM421 be formed, bent or molded?
Hot forge 1150–1200 °C then normalize or isothermally anneal; cold heading and upsetting need a spheroidized structure.
What surface finishes work on SCM421?
No anodizing; protect uncoated parts with Mn/Zn phosphate, black oxide, oil or zinc plating (bake to avoid hydrogen embrittlement); shot peening after carburizing raises bending fatigue significantly.
SCM421 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 |
|---|---|---|
| C | 0.17 – 0.23 | 0.2 |
| Si | 0.15 – 0.35 | 0.25 |
| Mnhigher than SCM415/418/420 — source of the deeper hardenability | 0.7 – 1 | 0.85 |
| 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 | — |
SCM421-CD — frequently asked
What is SCM421-CD used for?
SCM421-CD is typically used for heavy-duty transmission gears, differential ring and pinion gears, planetary pinions, splined shafts, axle shafts and bearing races. In short: JIS 4320 equivalent; deeper case than SCM418; heavy-duty gear grade.
What is the yield strength of SCM421-CD?
SCM421-CD has a typical yield strength of 590 MPa (85.6 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 76% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is SCM421-CD easy to machine?
Reasonably — machinability is rated good (67/100, better than 95% of steel grades). Machine in the annealed or isothermally annealed state (≈170–200 HB) with coated carbide; leave grinding stock for post-carburizing distortion, and expect only grinding/EDM once the case is hardened.
Can SCM421-CD be welded?
With care — weldability is rated fair (42/100). Weldable only before carburizing — preheat 200–300 °C, low-hydrogen consumables, and temper immediately after; never weld a carburized surface.
What surface finishes work on SCM421-CD?
No anodizing; protect uncoated parts with Mn/Zn phosphate, black oxide, oil or zinc plating (bake to avoid hydrogen embrittlement); shot peening after carburizing raises bending fatigue significantly.
Can SCM421-CD be formed, bent or molded?
Hot forge 1150–1200 °C then normalize or isothermally anneal; cold heading and upsetting need a spheroidized structure.
What is the maximum service temperature of SCM421-CD?
SCM421-CD 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 SCM421-A and SCM421 CH-CG?
A is the default condition — standard stocked machining condition — softest, most uniform structure before carburizing or cold forming. CH-CG: carburized condition with tooth flanks ground/honed after heat treat for high-accuracy, low-noise, high-load gearing. Yield strength is 350 MPa in A versus 950 MPa in CH-CG.
Sources
- JIS G 4053 — Low-alloyed steels for machine structural use — JSA (2016)
- GB/T 3077 — Alloy structural steels (20CrMnMo / 20CrMo comparison) — SAC (2015)
- 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 gear steels) — ASM International (1991)
- Machinery's Handbook (machinability ratings) — Industrial Press (2020)
- Gear steel bar datasheets (SCM420/SCM421, 20CrMnMo) — Daido Steel / Sandvik / Baosteel (2023)
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.