Steel SNC631
JIS SNC631
SNC631 is a through-hardening nickel-chromium structural steel in the JIS SNC family, equivalent to AISI 3130, where nickel provides toughness and impact resistance at medium strength.
Reference datasheet — SNC631 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the QT condition
SNC631 tempers and conditions
SNC631 is supplied in 9 conditions, soft to hard. QT is the default FabDigit quotes; the values on this page are for it.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest supply condition for deep machining, cold sawing or subsequent heat treatment. | 400 | 630 | 26 | 190 HB | — |
Hot rolled | Mill-condition black bar bought as feedstock for forging and later heat treatment. | 470 | 760 | 20 | 17 HRC | 7.5 % IACS |
Normalized | Uniform fine grain for forgings before final Q&T, or moderate-strength as-supplied parts. | 550 | 810 | 21 | 21 HRC | — |
Cold drawn | Close-tolerance bright bar for small shafts machined without further heat treatment. | 660 | 800 | 12 | 235 HB | — |
QTDefault Quenched and tempered | Standard commercial condition meeting JIS G4053 mechanical requirements — best strength/toughness balance for shafts and forgings. | 750 | 900 | 20 | 27 HRC | — |
Q&T core + induction hardened surface | Tough Q&T core with a hard wear- and fatigue-resistant surface for journals and gear teeth. | 750 | 900 | 18 | 55 HRC | 6.9 % IACS |
Q&T 28–32 HRC (temper ≈ 570–600 °C) | Higher-strength shafting and bolting where toughness is still important. | 840 | 980 | 17 | 30 HRC | — |
Q&T 32–36 HRC (temper ≈ 520–560 °C) | For highly loaded gears, splines and pins where wear resistance outweighs ductility. | 940 | 1,080 | 15 | 34 HRC | — |
Q&T 36–40 HRC (temper ≈ 450–500 °C) | Maximum practical strength level for this grade; toughness drops and machining is difficult. | 1,060 | 1,200 | 13 | 38 HRC | — |
What is SNC631?
SNC631 is a through-hardening nickel-chromium structural steel in the JIS SNC family, equivalent to AISI 3130, where nickel provides toughness and impact resistance at medium strength. It is used for shafts, forgings and connecting rods and is available as bar and forging stock in annealed, normalized, hot-rolled, cold-drawn, Q&T (28-32, 32-36 and 36-40 HRC) and Q&T plus induction-hardened conditions. The default Q&T condition gives 750 MPa yield, 900 MPa tensile, 20 % elongation at 269 HB / 27 HRC, with service to about 400 °C and machinability 55. Weldability is only fair and the steel corrodes bare; SCM435 is the usual lower-cost alternative at similar strength, with SNCM439 where higher strength and toughness are needed. SNC631 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). SNC631 has a yield strength of 750 MPa (109 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 84% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
What is SNC631 used for?
- shafts
- structural forgings
- connecting rods
Advantages
- High strength — 750 MPa (109 ksi), better than 84% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
SNC631 properties
Typical room-temperature values for SNC631-QT; bars are the position among steel grades.
Physical3
SNC631 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
SNC631 has a yield strength of 750 MPa (109 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 84% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNC631 is rated for continuous service to 400°C (752 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SNC631 conducts electricity at 7.2 % IACS, worse than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of SNC631 takes about 32 MJ of energy and emits 2.4 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability8
SNC631's machinability is good (55/100, better than 62% of steel grades); weldability fair (35/100); formability poor (30/100).
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. SNC631 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SNC631
Is SNC631 easy to machine?
Machine in the annealed or ≤300 HB Q&T state with rigid setups and coated carbide; above 32 HRC use ceramic/CBN or finish-grind.
Can SNC631 be welded?
Fair weldability only — preheat 200–300 °C, low-hydrogen consumables, and temper/stress-relieve immediately after welding to avoid cracking.
Can SNC631 be formed, bent or molded?
Hot forge 1050–1200 °C, finish above 850 °C, then normalize; cold forming is limited to mild straightening in the annealed condition.
SNC631 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 | 0.27 – 0.35 | 0.31 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.35 – 0.65 | 0.5 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Ni | 2.5 – 3 | 2.75 |
| Cr | 0.6 – 1 | 0.8 |
| Curesidual, max | ≤ 0.3 | |
| Fe | balance |
What surface finishes work on SNC631?
Not anodizable; protect with phosphate + oil, black oxide, zinc or hard chrome plating, and grind/polish journals after heat treatment.
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).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SNC631 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- 3130
How much does SNC631 cost?
SNC631 is a budget-cost steel ($), cheaper than about 90% 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.
SNC631 — frequently asked
What is SNC631 used for?
SNC631 is typically used for shafts, structural forgings and connecting rods. In short: tough Ni-Cr shaft steel; impact strength at medium hardness; lower strength than SNCM439.
What is the yield strength of SNC631?
SNC631 has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 84% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is SNC631 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine in the annealed or ≤300 HB Q&T state with rigid setups and coated carbide; above 32 HRC use ceramic/CBN or finish-grind.
Can SNC631 be welded?
With care — weldability is rated fair (35/100). Fair weldability only — preheat 200–300 °C, low-hydrogen consumables, and temper/stress-relieve immediately after welding to avoid cracking.
What surface finishes work on SNC631?
Not anodizable; protect with phosphate + oil, black oxide, zinc or hard chrome plating, and grind/polish journals after heat treatment.
Can SNC631 be formed, bent or molded?
Hot forge 1050–1200 °C, finish above 850 °C, then normalize; cold forming is limited to mild straightening in the annealed condition.
What is the maximum service temperature of SNC631?
SNC631 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 SNC631-QT and SNC631-A?
QT is the default condition — standard commercial condition meeting JIS G4053 mechanical requirements — best strength/toughness balance for shafts and forgings. A: softest supply condition for deep machining, cold sawing or subsequent heat treatment. Yield strength is 750 MPa in QT versus 400 MPa in A.
How much does SNC631 cost?
SNC631 is a budget-cost steel ($), cheaper than about 90% 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.
Sources
- JIS G 4053 — Low-alloyed steels for machine structural use — JSA (2016)
- GB/T 3077 — Alloy structural steels (30CrNi3 equivalent) — SAC (2015)
- 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)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
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.