Steel SNCM630 QT-H
Heat-treated state · default condition
JIS SNCM630
QT-H = q&T per JIS G4103
Standard commercial supply condition: ≥1080 MPa tensile with good toughness for shafts and high-load fasteners.
Values for the QT-H condition
Other SNCM630 tempers and conditions
SNCM630 is listed in 11 conditions; see the grade overview at SNCM630.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Pick for deep machining, cold sawing or before final quench-and-temper. | 640 | 850 | 20 | 24 HRC | — |
Hot rolled | Cheapest stock form for parts that will be fully heat treated after rough machining. | 700 | 980 | 16 | 29 HRC | 5.8 % IACS |
Normalized | Pick for uniform grain and moderate strength on large forgings before final heat treatment. | 780 | 1,030 | 17 | 31 HRC | — |
Cold drawn | Pick for close-tolerance small-diameter bar where a bright finish is needed before final heat treatment. | 800 | 950 | 12 | 28 HRC | 5.7 % IACS |
high-temperature temper | Pick when maximum toughness and machinability are wanted in a heat-treated part. | 910 | 1,030 | 18 | 32 HRC | — |
QT-HDefaultThis page Q&T per JIS G4103 | Standard commercial supply condition: ≥1080 MPa tensile with good toughness for shafts and high-load fasteners. | 1,000 | 1,150 | 17 | 34 HRC | — |
Q&T then gas/plasma nitrided | Pick when a Q&T core must carry load while the surface needs wear and fatigue resistance without distortion. | 1,000 | 1,150 | 14 | 34 HRC | 5.5 % IACS |
Q&T 34–38 HRC | Balanced strength/toughness condition for gear shafts and heavily loaded machine parts. | 1,050 | 1,170 | 16 | 36 HRC | — |
Q&T 38–42 HRC | Pick for high-strength airframe/landing-gear-type parts where some toughness is still required. | 1,180 | 1,300 | 13 | 40 HRC | — |
low-temperature temper | Pick for maximum strength shafts, tool holders and dies; grind after treatment. | 1,330 | 1,450 | 11 | 44 HRC | — |
near as-quenched strength | Only for wear-critical, low-toughness-demand parts; notch and hydrogen sensitivity are high. | 1,450 | 1,600 | 9 | 48 HRC | — |
What is SNCM630 QT-H?
SNCM630 QT-H is SNCM630 heat treated to QT-H — standard commercial supply condition: ≥1080 MPa tensile with good toughness for shafts and high-load fasteners. SNCM630 QT-H has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 92% of steel grades. Elongation at break is 17% and the elastic modulus is 205 GPa (29.7 Msi). SNCM630 QT-H 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).
Advantages
- High strength — 1,000 MPa (145 ksi), better than 92% of steel grades
- Polishes to a fine finish — 72/100, better than 92% of steel grades
Limitations
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Low electrical conductivity — 5.5 % IACS, worse than 81% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
- Poor heat conductor — 34 W/m·K (19.6 BTU/hr·ft·°F), worse than 77% of steel grades
- Limited formability — 22/100, worse than 76% of steel grades
SNCM630 QT-H properties
Typical room-temperature values for SNCM630 QT-H; 13 are specific to this condition. Other listed values are SNCM630 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SNCM630 QT-H 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).
Mechanical16
SNCM630 QT-H has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 92% of steel grades. Elongation at break is 17% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNCM630 QT-H is rated for continuous service to 400°C (752 °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
SNCM630 QT-H conducts electricity at 5.5 % IACS, worse than 81% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of SNCM630 QT-H takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability8
SNCM630 QT-H's machinability is fair (38/100, worse than 80% of steel grades); weldability poor (30/100); formability poor (22/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SNCM630 QT-H
Is SNCM630 easy to machine?
Machine in the annealed or ≤34 HRC condition with rigid setups, carbide tooling and 60–120 m/min; above 40 HRC use ceramic/CBN or grinding.
Can SNCM630 be welded?
Poor weldability due to high hardenability — preheat 250–350 °C, low-hydrogen or matching filler, and immediately post-weld temper below the original tempering temperature.
Can SNCM630 be formed, bent or molded?
Hot forge 1150–900 °C then slow cool/anneal; cold forming is impractical above ~250 HB.
What surface finishes work on SNCM630?
Not anodizable; use phosphate + oil, black oxide, zinc or Zn-Ni plating (bake 190 °C ≥4 h to de-embrittle), nitriding or hard chrome for wear.
SNCM630 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 | 0.25 – 0.35 | 0.3 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.35 – 0.6 | 0.48 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Ni | 2.5 – 3.5 | 3 |
| Cr | 2.5 – 3.5 | 3 |
| Mo | 0.5 – 0.7 | 0.6 |
| Curesidual max | ≤ 0.3 | — |
| Fe | balance | — |
SNCM630 QT-H — frequently asked
What is SNCM630 QT-H used for?
SNCM630 QT-H is typically used for aircraft landing gear, high-strength bolts and shafts. In short: highest strength in family; 4340-class Ni-Cr-Mo steel; deep-hardening heavy sections.
What is the yield strength of SNCM630 QT-H?
SNCM630 QT-H has a typical yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is SNCM630 QT-H easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% of steel grades). Machine in the annealed or ≤34 HRC condition with rigid setups, carbide tooling and 60–120 m/min; above 40 HRC use ceramic/CBN or grinding.
Can SNCM630 QT-H be welded?
Not readily — weldability is rated poor (30/100). Poor weldability due to high hardenability — preheat 250–350 °C, low-hydrogen or matching filler, and immediately post-weld temper below the original tempering temperature.
What surface finishes work on SNCM630 QT-H?
Not anodizable; use phosphate + oil, black oxide, zinc or Zn-Ni plating (bake 190 °C ≥4 h to de-embrittle), nitriding or hard chrome for wear.
Can SNCM630 QT-H be formed, bent or molded?
Hot forge 1150–900 °C then slow cool/anneal; cold forming is impractical above ~250 HB.
What is the maximum service temperature of SNCM630 QT-H?
SNCM630 QT-H 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 SNCM630 QT-H and SNCM630-A?
QT-H is the default condition — standard commercial supply condition: ≥1080 MPa tensile with good toughness for shafts and high-load fasteners. A: pick for deep machining, cold sawing or before final quench-and-temper. Yield strength is 1,000 MPa in QT-H versus 640 MPa in A.
Sources
- JIS G4103 Nickel-chromium-molybdenum steels — JSA (2018)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19: Fatigue and Fracture — ASM International (1996)
- ASM Handbook Vol.16: Machining — ASM International (1989)
- MMPDS-style typical property data for 4340-class low-alloy steels — Battelle/FAA (2022)
- GB/T 3077 (30Cr2Ni2Mo comparison) — SAC (2015)
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.