Steel SNC631 QT+IH
Heat-treated state
JIS SNC631
QT+IH = q&T core + induction hardened surface
Tough Q&T core with a hard wear- and fatigue-resistant surface for journals and gear teeth.
Values for the QT+IH condition
Other SNC631 tempers and conditions
SNC631 is listed in 9 conditions; see the grade overview at SNC631.
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 | — |
QT+IHThis page 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 QT+IH?
SNC631 QT+IH is SNC631 heat treated to QT+IH — tough Q&T core with a hard wear- and fatigue-resistant surface for journals and gear teeth. SNC631 QT+IH 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 18% and the elastic modulus is 205 GPa (29.7 Msi). SNC631 QT+IH 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; QT+IH is available on request or by drawing note.
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
Limitations
- Limited formability — 5/100, worse than 99% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
SNC631 QT+IH properties
Typical room-temperature values for SNC631 QT+IH; 22 are specific to this condition. Other listed values are SNC631 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SNC631 QT+IH 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 QT+IH 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 18% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNC631 QT+IH is rated for continuous service to 200°C (392 °F). It conducts heat at 37 W/m·K (21.4 BTU/hr·ft·°F), worse than 71% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SNC631 QT+IH conducts electricity at 6.9 % IACS, worse than 76% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of SNC631 QT+IH 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 QT+IH's machinability is poor (15/100, worse than 98% of steel grades); weldability poor (15/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SNC631 QT+IH
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.
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.
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 | — |
SNC631 QT+IH — frequently asked
What is SNC631 QT+IH used for?
SNC631 QT+IH 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 QT+IH?
SNC631 QT+IH 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 QT+IH easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% 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 QT+IH be welded?
Not readily — weldability is rated poor (15/100). 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 QT+IH?
Not anodizable; protect with phosphate + oil, black oxide, zinc or hard chrome plating, and grind/polish journals after heat treatment.
Can SNC631 QT+IH 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 QT+IH?
SNC631 QT+IH 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 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.