Steel SCM425 CARB
Heat-treated state
JIS SCM425
CARB = carburized, quenched & tempered
The intended service condition: deep hard case for gear teeth and pins with a strong tempered-martensite core.
Values for the CARB condition
Other SCM425 tempers and conditions
SCM425 is listed in 11 conditions; see the grade overview at SCM425.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold forging, cold heading or deep-drilled parts where maximum softness and formability are needed. | 360 | 570 | 26 | 167 HB | 7.7 % IACS |
ADefault Solution annealed | Standard stocked condition: softest and most machinable state before carburizing or quench-and-temper. | 400 | 620 | 22 | 179 HB | — |
Hot rolled | Cheapest mill condition for stock that will be fully heat treated after rough machining. | 460 | 720 | 19 | 15 HRC | 7.5 % IACS |
Normalized and tempered | Used on heavy sections where full oil quenching is impractical but stress-relieved medium strength is wanted. | 520 | 760 | 20 | 20 HRC | 7.5 % IACS |
Normalized | Uniform fine-grain starting structure for large forgings before carburizing, and for moderate-strength as-supplied parts. | 550 | 810 | 18 | 21 HRC | 7.5 % IACS |
Cold drawn | Close-tolerance bright bar for shafts and pins machined without further heat treatment. | 640 | 780 | 12 | 229 HB | — |
oil quenched, high tempered | Tough through-hardened condition for shafts and bolts machined after heat treatment. | 810 | 950 | 16 | 30 HRC | — |
Induction hardened | Alternative to carburizing for selective wear surfaces on Q&T cores (journals, cam tracks). | 890 | 1,050 | 12 | 55 HRC | 7 % IACS |
oil quenched, medium-high tempered | Common core condition for gear blanks and splined shafts needing higher core strength than SCM420. | 930 | 1,080 | 14 | 34 HRC | — |
CARBThis page Carburized, quenched & tempered | The intended service condition: deep hard case for gear teeth and pins with a strong tempered-martensite core. | 950 | 1,180 | 10 | 60 HRC | — |
oil quenched, low tempered | High-strength through-hardened option for small-section shafts and fasteners; ductility and toughness fall off. | 1,120 | 1,280 | 11 | 40 HRC | — |
What is SCM425 CARB?
SCM425 CARB is SCM425 heat treated to CARB — the intended service condition: deep hard case for gear teeth and pins with a strong tempered-martensite core. SCM425 CARB has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Elongation at break is 10% and the elastic modulus is 206 GPa (29.9 Msi). SCM425 CARB 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; CARB is available on request or by drawing note.
Advantages
- High strength — 950 MPa (138 ksi), better than 91% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to machine — 10/100, worse than 99% of steel grades
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
SCM425 CARB properties
Typical room-temperature values for SCM425 CARB; 14 are specific to this condition. Other listed values are SCM425 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SCM425 CARB 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).
Mechanical15
SCM425 CARB has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Elongation at break is 10% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SCM425 CARB 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 12.3 µm/m·K (6.83 µin/in·°F).
Electrical2
SCM425 CARB has an electrical resistivity of 2.3×10⁻⁷ Ω·m.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SCM425 CARB takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
SCM425 CARB's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (10/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SCM425 CARB
Is SCM425 easy to machine?
Rough machine in the annealed or spheroidized condition (~180 HB) with carbide inserts and flood coolant; leave 0.2–0.4 mm grinding stock for post-carburizing distortion.
Can SCM425 be welded?
Weldable only with care — preheat 200–300 °C, low-hydrogen or matching Cr-Mo filler, and temper/stress relieve at 600–650 °C; do not weld carburized surfaces.
Can SCM425 be formed, bent or molded?
Hot forge 1150–950 °C then normalize or spheroidize anneal; cold heading is practical only in the spheroidized condition.
What surface finishes work on SCM425?
Not anodizable — protect with black oxide, manganese phosphate, zinc or hard chrome; ground and superfinished tooth flanks after carburizing improve fatigue life.
SCM425 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 | 0.23 – 0.28 | 0.25 |
| 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 | — |
SCM425 CARB — frequently asked
What is SCM425 CARB used for?
SCM425 CARB is typically used for heavy-duty carburized gears, transmission and drive shafts, differential pinions and ring gears, splined shafts, planetary carriers and pins and king pins and heavy machinery gearing. In short: deeper case than SCM420; cr-Mo carburizing gear steel; high core strength.
What is the yield strength of SCM425 CARB?
SCM425 CARB has a typical yield strength of 950 MPa (138 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 91% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is SCM425 CARB easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Rough machine in the annealed or spheroidized condition (~180 HB) with carbide inserts and flood coolant; leave 0.2–0.4 mm grinding stock for post-carburizing distortion.
Can SCM425 CARB be welded?
Not readily — weldability is rated not recommended (10/100). Weldable only with care — preheat 200–300 °C, low-hydrogen or matching Cr-Mo filler, and temper/stress relieve at 600–650 °C; do not weld carburized surfaces.
What surface finishes work on SCM425 CARB?
Not anodizable — protect with black oxide, manganese phosphate, zinc or hard chrome; ground and superfinished tooth flanks after carburizing improve fatigue life.
Can SCM425 CARB be formed, bent or molded?
Hot forge 1150–950 °C then normalize or spheroidize anneal; cold heading is practical only in the spheroidized condition.
What is the maximum service temperature of SCM425 CARB?
SCM425 CARB 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 SCM425-A and SCM425 CARB?
A is the default condition — standard stocked condition: softest and most machinable state before carburizing or quench-and-temper. CARB: the intended service condition: deep hard case for gear teeth and pins with a strong tempered-martensite core. Yield strength is 400 MPa in A versus 950 MPa in CARB.
Sources
- JIS G 4053 — Low-alloyed structural steels for machine structural use — JISC (2016)
- JIS G 4052 — Structural steels with specified hardenability bands — JISC (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals and Processes (carburizing) — ASM International (2013)
- Machinery's Handbook, 31st ed. — machinability ratings — Industrial Press (2020)
- GB/T 3077 — Alloy structural steels (25CrMo equivalent) — SAC (2015)
- (SMM / Mysteel / 1688 ) — SMM · Mysteel (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.