Steel SNCM625 CARB
Heat-treated state
JIS SNCM625
CARB = carburized, hardened and low-temper
For large gears and pins needing a hard wear case over a very tough, deeply hardened Ni-Cr-Mo core.
Values for the CARB condition
Other SNCM625 tempers and conditions
SNCM625 is listed in 10 conditions; see the grade overview at SNCM625.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition for deep machining, hobbing or cold work before final quench and temper. | 480 | 730 | 22 | 215 HB | — |
Hot rolled | Mill-supplied stock intended for re-heat-treatment; not for direct load-bearing use. | 570 | 880 | 16 | 25 HRC | 7.5 % IACS |
Normalized | Uniform fine-grain structure for large forgings before carburizing or final Q&T; note this grade air-hardens strongly. | 640 | 930 | 18 | 27 HRC | 7.4 % IACS |
Cold drawn | Small-diameter precision bar with better surface and straightness; strength from cold work, low ductility. | 700 | 850 | 11 | 24 HRC | 7.5 % IACS |
Q&T 28–32 HRC (high-temper, maximum toughness) | Pick when impact toughness and machinability after heat treatment matter more than peak strength. | 860 | 990 | 20 | 30 HRC | 7.2 % IACS |
QTDefault Quenched and tempered | Standard supplied condition: ≥940 MPa tensile with high toughness for shafts, large gear blanks and heavy-duty machine parts. | 880 | 1,000 | 20 | 30 HRC | — |
Q&T + gas/plasma nitrided | Choose for low-distortion wear and fatigue improvement on finish-machined Q&T parts. | 880 | 1,000 | 18 | 58 HRC | 7.2 % IACS |
CARBThis page Carburized, hardened and low-temper | For large gears and pins needing a hard wear case over a very tough, deeply hardened Ni-Cr-Mo core. | 950 | 1,150 | 12 | 60 HRC | 6.6 % IACS |
Q&T 32–36 HRC (medium temper) | Higher-strength gear and shaft condition, still readily machinable and a good nitriding base. | 990 | 1,120 | 17 | 34 HRC | 7.2 % IACS |
Q&T 36–40 HRC (low temper, high strength) | Near the practical hardness ceiling for this 0.25 % C grade; use where wear and strength dominate and toughness margin is accepted. | 1,100 | 1,250 | 14 | 38 HRC | 7.1 % IACS |
What is SNCM625 CARB?
SNCM625 CARB is SNCM625 heat treated to CARB — for large gears and pins needing a hard wear case over a very tough, deeply hardened Ni-Cr-Mo core. SNCM625 CARB has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 91% of steel grades. Elongation at break is 12% and the elastic modulus is 206 GPa (29.9 Msi). SNCM625 CARB 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). QT 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 weld — 5/100, worse than 100% of steel grades
- Difficult to machine — 10/100, worse than 99% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
SNCM625 CARB properties
Typical room-temperature values for SNCM625 CARB; 22 are specific to this condition. Other listed values are SNCM625 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SNCM625 CARB 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).
Mechanical16
SNCM625 CARB has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 91% of steel grades. Elongation at break is 12% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
SNCM625 CARB is rated for continuous service to 180°C (356 °F). It conducts heat at 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
SNCM625 CARB conducts electricity at 6.6 % IACS, worse than 76% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SNCM625 CARB takes about 34 MJ of energy and emits 2.4 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
SNCM625 CARB's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (5/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SNCM625 CARB
Is SNCM625 easy to machine?
Machine in the annealed or 28–32 HRC condition with rigid setups, coated carbide, ~80–140 m/min and generous feed; leave grinding stock for post-hardening finishing.
Can SNCM625 be welded?
Poor weldability due to high hardenability — preheat 250–350 °C, use low-hydrogen/matching filler, keep interpass temperature and temper immediately after welding.
Can SNCM625 be formed, bent or molded?
Hot forge 1050–1200 °C with slow controlled cooling (air hardens readily); cold forming limited to mild straightening in the annealed state.
What surface finishes work on SNCM625?
Not anodizable — protect with oil, phosphate, black oxide, zinc or hard-chrome plating; nitriding or induction hardening gives wear resistance, and tempered martensite takes a fine polish.
SNCM625 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 | 0.2 – 0.3 | 0.25 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.35 – 0.6 | 0.48 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Ni | 3 – 3.5 | 3.25 |
| Cr | 1 – 1.5 | 1.25 |
| Mo | 0.15 – 0.3 | 0.22 |
| Curesidual, max | ≤ 0.3 | — |
| Fe | balance | — |
SNCM625 CARB — frequently asked
What is SNCM625 CARB used for?
SNCM625 CARB is typically used for large industrial gears, heavy-duty drive shafts, gear pinions and gear blanks, spline shafts, mill and crane drive components and nitrided wear sleeves. In short: high-hardenability Ni-Cr-Mo steel; heavy-section gear steel; supplied in HRC bands.
What is the yield strength of SNCM625 CARB?
SNCM625 CARB has a typical yield strength of 950 MPa (138 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 91% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is SNCM625 CARB easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Machine in the annealed or 28–32 HRC condition with rigid setups, coated carbide, ~80–140 m/min and generous feed; leave grinding stock for post-hardening finishing.
Can SNCM625 CARB be welded?
Not readily — weldability is rated not recommended (5/100). Poor weldability due to high hardenability — preheat 250–350 °C, use low-hydrogen/matching filler, keep interpass temperature and temper immediately after welding.
What surface finishes work on SNCM625 CARB?
Not anodizable — protect with oil, phosphate, black oxide, zinc or hard-chrome plating; nitriding or induction hardening gives wear resistance, and tempered martensite takes a fine polish.
Can SNCM625 CARB be formed, bent or molded?
Hot forge 1050–1200 °C with slow controlled cooling (air hardens readily); cold forming limited to mild straightening in the annealed state.
What is the maximum service temperature of SNCM625 CARB?
SNCM625 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 SNCM625-QT and SNCM625-A?
QT is the default condition — standard supplied condition: ≥940 MPa tensile with high toughness for shafts, large gear blanks and heavy-duty machine parts. A: softest condition for deep machining, hobbing or cold work before final quench and temper. Yield strength is 880 MPa in QT versus 480 MPa in A.
Sources
- JIS G4103 — Nickel-chromium-molybdenum steels — Japanese Standards Association (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machinery's Handbook, 31st ed. (machinability and heat-treat data) — Industrial Press (2020)
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.