Steel SNCM439
JIS SNCM439 · EN 34CrNiMo6
SNCM439 is a JIS G 4053 nickel-chromium-molybdenum low-alloy structural steel supplied in the quenched-and-tempered condition, corresponding closely to AISI/SAE 4340 and GB/T 3077 40CrNiMoA.
Values for the HR condition
SNCM439 tempers and conditions
SNCM439 is supplied in 13 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
- Annealed
- HR
- CR
- CD
- Normalized
- Q&T 28-32 HRC
- Q&T
- Nitrided
- Q&T 32-36 HRC
- Q&T 36-40 HRC
- Q&T 40-44 HRC
- Q&T 45-49 HRC
- Q&T 50-54 HRC
Compare all 13 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full/spheroidize anneal ~810–840 °C, slow cool | Softest condition — use for heavy machining, deep boring or cold forming before final Q&T. | 470 | 745 | 22 | 217 HB | — |
HRDefault Hot rolled | Standard mill-stock condition for bars and forging feedstock that the user will heat treat later. | 620 | 900 | 15 | 26 HRC | — |
Cold rolled | Choose for thin strip/sheet with good surface and tighter thickness before heat treatment. | 760 | 950 | 10 | 29 HRC | 7 % IACS |
Cold drawn | Pick for close-tolerance bright bar used directly on lathes/screw machines without further heat treatment. | 850 | 1,000 | 10 | 30 HRC | — |
870 °C, air cooled | Uniform fine-grain structure for forgings before Q&T; already quite strong but low toughness for a Ni-Cr-Mo steel. | 860 | 1,280 | 12 | 39 HRC | — |
Tempered ~600–650 °C | Toughest practical Q&T level — best for impact-loaded shafts, connecting rods and parts to be welded or nitrided. | 870 | 1,000 | 17 | 30 HRC | — |
Quenched and tempered | Standard delivery condition for shafts and highly loaded parts; JIS spec minima 985 MPa UTS / 885 MPa YS. | 950 | 1,080 | 15 | 34 HRC | — |
Q&T core + gas/plasma nitrided case | Choose for wear-resistant, fatigue-strong shaft journals and spindles with a tough Q&T core and minimal distortion. | 950 | 1,080 | 14 | 34 HRC | 7 % IACS |
Tempered ~570–620 °C | Common general-purpose strength/toughness balance for gear shafts and heavy fasteners. | 1,000 | 1,100 | 15 | 34 HRC | — |
Tempered ~520–570 °C | Higher strength for medium-section shafts and tooling holders where machining is still required. | 1,150 | 1,250 | 13 | 38 HRC | — |
Tempered ~450–520 °C | Use when wear and high yield are needed and impact loading is moderate; machining becomes difficult. | 1,300 | 1,400 | 12 | 42 HRC | — |
Tempered ~370–430 °C | High-strength aerospace/landing-gear class level; needs careful grinding and hydrogen-relief baking after plating. | 1,500 | 1,650 | 10 | 47 HRC | — |
Low-temperature temper ~200–260 °C | Maximum-strength/wear condition (≈1900 MPa); brittle and notch-sensitive — grind only, avoid sharp corners. | 1,620 | 1,900 | 8 | 52 HRC | — |
What is SNCM439?
SNCM439 is a JIS G 4053 nickel-chromium-molybdenum low-alloy structural steel supplied in the quenched-and-tempered condition, corresponding closely to AISI/SAE 4340 and GB/T 3077 40CrNiMoA. Its high hardenability gives a uniform strength-toughness balance through large sections, so it is used for heavy shafts, gear shafts, connecting rods, bolts, die holders and aircraft or heavy-machinery load-bearing parts; typical Q&T bar runs 620 MPa yield, 900 MPa tensile, 15 % elongation and 260 HB (26 HRC), with tempers on file from 28-32 HRC up to 50-54 HRC plus nitrided. Limits are poor weldability (preheat plus post-weld temper required), corrosion resistance no better than plain carbon steel so coating or plating is needed, and sensitivity to hydrogen embrittlement and temper embrittlement at high hardness. Where section size is smaller, 42CrMo4/4140 is the cheaper alternative. SNCM439 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). SNCM439 has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 78% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
What is SNCM439 used for?
- Heavy-section drive shafts
- Gear shafts and pinions
- Connecting rods
- High-strength bolts and studs
- Mould bases and die holders
- Aerospace fittings
- Torsion bars
- Heavy machinery load-bearing parts
Advantages
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- High strength — 620 MPa (89.9 ksi), better than 78% of steel grades
SNCM439 properties
Typical room-temperature values for SNCM439-HR; bars are the position among steel grades.
Physical3
SNCM439 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
SNCM439 has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 78% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
SNCM439 is rated for continuous service to 400°C (752 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
SNCM439 conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SNCM439 takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability6
SNCM439's machinability is fair (45/100, worse than 65% of steel grades); weldability fair (35/100); formability fair (35/100).
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. SNCM439 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SNCM439
Is SNCM439 easy to machine?
Machine in the annealed or ≤32 HRC condition with rigid setups, carbide tooling and generous coolant; above 40 HRC switch to CBN turning or grinding.
Can SNCM439 be welded?
Weldable only with care — preheat 250–350 °C, low-hydrogen filler, interpass control and immediate post-weld temper below the last tempering temperature; avoid welding in high-strength tempers.
Can SNCM439 be formed, bent or molded?
Cold forming limited to the annealed condition; hot forge 1150–1200 °C, finish above 900 °C and slow-cool/normalize before machining and Q&T.
Manufacturability
The process limits FabDigit applies to SNCM439. Every SNCM439 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better45 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair35 / 100 |
|---|---|
| Weldability | Better35 / 100 |
SNCM439 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 |
|---|---|---|
| CJIS G 4053 | 0.36 – 0.43 | 0.4 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Ni | 1.6 – 2 | 1.8 |
| Cr | 0.6 – 1 | 0.8 |
| Mo | 0.15 – 0.3 | 0.22 |
| Curesidual max | ≤ 0.3 | |
| Fe | balance |
What surface finishes work on SNCM439?
Takes phosphate, black oxide, hard chrome, zinc or cadmium plating and paint well; bake at 190–220 °C after plating to relieve hydrogen, and nitride or QPQ for wear surfaces.
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).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SNCM439 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does SNCM439 cost?
SNCM439 is a standard-cost steel ($$), cheaper than about 61% 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.
SNCM439 — frequently asked
What is SNCM439 used for?
SNCM439 is typically used for heavy-section drive shafts, gear shafts and pinions, connecting rods, high-strength bolts and studs, mould bases and die holders and aerospace fittings. In short: workhorse Ni-Cr-Mo bar.
What is the yield strength of SNCM439?
SNCM439 has a typical yield strength of 620 MPa (89.9 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 78% of steel grades. Strength varies by condition: see the 13 listed tempers.
Is SNCM439 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the annealed or ≤32 HRC condition with rigid setups, carbide tooling and generous coolant; above 40 HRC switch to CBN turning or grinding.
Can SNCM439 be welded?
With care — weldability is rated fair (35/100). Weldable only with care — preheat 250–350 °C, low-hydrogen filler, interpass control and immediate post-weld temper below the last tempering temperature; avoid welding in high-strength tempers.
What surface finishes work on SNCM439?
Takes phosphate, black oxide, hard chrome, zinc or cadmium plating and paint well; bake at 190–220 °C after plating to relieve hydrogen, and nitride or QPQ for wear surfaces.
Can SNCM439 be formed, bent or molded?
Cold forming limited to the annealed condition; hot forge 1150–1200 °C, finish above 900 °C and slow-cool/normalize before machining and Q&T.
What is the maximum service temperature of SNCM439?
SNCM439 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 SNCM439-HR and SNCM439-CD?
HR is the default condition — standard mill-stock condition for bars and forging feedstock that the user will heat treat later. CD: pick for close-tolerance bright bar used directly on lathes/screw machines without further heat treatment. Yield strength is 620 MPa in HR versus 850 MPa in CD.
How much does SNCM439 cost?
SNCM439 is a standard-cost steel ($$), cheaper than about 61% 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.
Can FabDigit make parts in SNCM439?
Yes — SNCM439 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- JIS G 4053 Low-alloyed steels for machine structural use — JSA (2016)
- GB/T 3077 (40CrNiMoA) — SAC (2015)
- SAE J404 / ASTM A29 (4340) — SAE / ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- MMPDS-16 (4340 typical properties) — Battelle/FAA (2021)
- Machinery's Handbook, machinability ratings — Industrial Press (2020)
- Mysteel / SMM (2025)
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.