What is 35NCD6 steel?
35NCD6 is a nickel-chromium-molybdenum steel for quenching and tempering. It carries 0.30–0.38 % carbon, 1.30–1.70 % nickel, 1.30–1.70 % chromium and 0.15–0.30 % molybdenum, and after hardening and tempering it reaches 900–1100 MPa tensile strength in sections of 100 to 160 mm. Designers use it for heavily loaded shafts, gears and rings that are too thick for a chromium-molybdenum steel to harden through.
The name follows the French AFNOR system:
- 35
- Carbon in hundredths of a percent, so about 0.35 % carbon.
- NCD
- The alloying elements by content: N for nickel, C for chromium, D for molybdenum.
- 6
- The content of the first alloying element multiplied by four, so about 1.5 % nickel.
NF A35-552, the French standard behind the name, has been withdrawn. Today the steel is ordered as 34CrNiMo6 (1.6582): bars to EN ISO 683-2, which replaced EN 10083-3 in 2018, and open-die forgings to EN 10250-3. Plenty of drawings still say 35NCD6, and we treat the two names as the same steel.
Nickel gives the steel its toughness, most of all at low temperature, and together with chromium and molybdenum it lets thick sections harden right through. For a ruling section of 100 to 160 mm, EN 10083-3 asks for a minimum yield strength of 700 MPa from 34CrNiMo6 and only 550 MPa from 42CrMo4. On the Jominy end-quench test, its hardenability band still requires 44 HRC at 50 mm from the quenched end.
Chemical composition of 35NCD6
| Element | Min | Max | What it does in the steel |
|---|---|---|---|
| Carbon (C) | 0.30 | 0.38 | Sets the hardness and strength reached on quenching |
| Silicon (Si) | – | 0.40 | Deoxidiser; adds a little strength |
| Manganese (Mn) | 0.50 | 0.80 | Deoxidiser; adds hardenability |
| Phosphorus (P) | – | 0.025 | Residual; kept low for toughness |
| Sulfur (S) | – | 0.035 | Residual; kept low for toughness and transverse ductility |
| Chromium (Cr) | 1.30 | 1.70 | Main hardenability element; strength after tempering |
| Molybdenum (Mo) | 0.15 | 0.30 | Hardenability; reduces temper embrittlement |
| Nickel (Ni) | 1.30 | 1.70 | Toughness, especially at low temperature |
| Iron (Fe) | Balance | Base metal | |
Older French datasheets give silicon as 0.10–0.40 % and allow up to 0.035 % phosphorus. If your drawing calls up NF A35-552, tell us which limits the certificate should show.
35NCD6 equivalent grades: 34CrNiMo6, AISI 4340, EN24
Cross-reference charts put several grades next to 35NCD6, but only 34CrNiMo6 has the same limits. The rest are close relatives, and the gaps show up when an inspector checks the mill certificate against the drawing.
| Standard or system | Designation | How close |
|---|---|---|
| France, AFNOR NF A35-552 (withdrawn) | 35NCD6 | This grade |
| Europe, EN ISO 683-2 and EN 10250-3 | 34CrNiMo6 | Same composition limits |
| Europe, material number | 1.6582 | Number of 34CrNiMo6 |
| USA, AISI/SAE | 4340 | Comparable; less chromium, more nickel |
| USA, AISI | 4337 | Comparable; less chromium, more nickel |
| UK, BS 970 | 817M40 (EN24) | Comparable; more carbon, less chromium |
| Japan, JIS G 4053 | SNCM439, SNCM447 | Comparable; less chromium, more nickel |
| Russia, GOST 4543 | 38Kh2N2MA | Comparable Ni-Cr-Mo steel |
| Italy, UNI (former) | 35NiCrMo6 | Former Italian name |
| Sweden, SS | 2541 | Cross-reference listing |
| Grade | C | Mn | Cr | Ni | Mo |
|---|---|---|---|---|---|
| 35NCD6 / 34CrNiMo6 | 0.30–0.38 | 0.50–0.80 | 1.30–1.70 | 1.30–1.70 | 0.15–0.30 |
| AISI 4340 | 0.38–0.43 | 0.60–0.80 | 0.70–0.90 | 1.65–2.00 | 0.20–0.30 |
| 817M40 (EN24) | 0.36–0.44 | 0.45–0.70 | 1.00–1.40 | 1.30–1.70 | 0.20–0.35 |
Chromium is the quickest way to tell them apart. A certificate showing 1.1 % chromium fits EN24 but not 34CrNiMo6, and 0.8 % fits only AISI 4340 of the three. Swapping one grade for another needs the buyer's written approval.
Mechanical properties of 35NCD6
How strong a 35NCD6 part can be made depends on its ruling section, the thickness that decides how fast the core cools in the quench. Table 4 gives the minimums from the bar standard.
| Property | ≤ 16 mm | 16–40 mm | 40–100 mm | 100–160 mm | 160–250 mm |
|---|---|---|---|---|---|
| Yield strength Re or Rp0.2, min, MPa | 1000 | 900 | 800 | 700 | 600 |
| Yield strength, min, ksi | 145 | 131 | 116 | 102 | 87 |
| Tensile strength Rm, MPa | 1200–1400 | 1100–1300 | 1000–1200 | 900–1100 | 800–950 |
| Tensile strength, ksi | 174–203 | 160–189 | 145–174 | 131–160 | 116–138 |
| Elongation A, min, % | 9 | 10 | 11 | 12 | 13 |
| Reduction of area Z, min, % | 40 | 45 | 50 | 55 | 55 |
| Impact energy KV at +20 °C, min, J | not specified | 45 | 45 | 45 | 45 |
| Hardness, HBW, for information | 359–404 | 331–380 | 298–359 | 271–331 | 240–286 |
For open-die forgings the reference is EN 10250-3. Its first column covers all sections up to 250 mm diameter at the values the bar standard gives for 160–250 mm, and the table runs on to a ruling section of 660 mm. The bigger the section, the lower the minimum, because the core of a heavy forging cools more slowly.
| Property | t ≤ 160 mm (d ≤ 250 mm) | 160 < t ≤ 330 mm (250 < d ≤ 500 mm) | 330 < t ≤ 660 mm (500 < d ≤ 990 mm) |
|---|---|---|---|
| Yield strength Rp0.2, min, MPa | 600 | 540 | 490 |
| Tensile strength Rm, min, MPa | 800 | 750 | 700 |
| Elongation A, longitudinal, min, % | 13 | 14 | 15 |
| Elongation A, tangential, min, % | 9 | 10 | 11 |
| Impact energy KV, longitudinal, min, J | 45 | 45 | 40 |
| Impact energy KV, tangential, min, J | 22 | 22 | 20 |
| Hardness, HBW, for information | 240 | 225 | 213 |
Soft annealed (+A), the limit is 248 HBW. After quenching and tempering, hardness follows the tensile strength, so read the hardness rows as a guide. Orders that name EN 10250-3:2022 are tested to the values in that edition.
Physical properties
Density is 7.85 g/cm³ at 20 °C. Thermal conductivity is about 38 W/(m·K), specific heat 460 J/(kg·K) and electrical resistivity 0.19 Ω·mm²/m, with a mean expansion of 11.1 × 10⁻⁶ per K between 20 and 100 °C. Ac1 lies near 715 °C, Ac3 near 770 °C and Ms near 320 °C, so hardening starts above 830 °C and tempering stays below 700 °C.
Forging and heat treatment of 35NCD6
We forge 35NCD6 hot, let it cool slowly, and then harden and temper it. Hardening takes the part above Ac3 and quenches it in oil or polymer; tempering brings it back to the strength on the drawing. Figure 1 puts the temperature windows side by side.
| Operation | Temperature | Cooling | Purpose |
|---|---|---|---|
| Hot forging | 1100 to 850 °C (2010 to 1560 °F) | Slow, in a furnace or under cover | Shape the part and break down the cast structure; finish above 850 °C |
| Normalising (+N) | 850–880 °C (1560–1615 °F) | Air | Even out the forged grain before hardening or machining |
| Soft annealing (+A) | 650–700 °C (1200–1290 °F) | Slow, in the furnace | Bring hardness down to 248 HBW max for machining |
| Hardening | 830–860 °C (1525–1580 °F) | Oil or polymer | Form martensite through the section |
| Tempering | 540–660 °C (1005–1220 °F) | Air | Set strength and toughness; a higher temperature gives lower strength |
| Stress relieving | About 50 °C below the tempering temperature | Slow | Remove machining or straightening stresses without losing strength |
Temper as soon as the part has cooled from the quench. A hardened Ni-Cr-Mo forging left standing untempered can crack.
Keep tempering out of the 250 to 400 °C range. Ni-Cr-Mo steels lose impact toughness there, an effect called tempered martensite embrittlement.
Large 35NCD6 forgings are prone to hydrogen flakes, fine internal cracks that open as the part cools. Vacuum-treated steel and slow cooling after forging prevent them, and the ultrasonic test after heat treatment would show them up.
Machining and welding
Rough machining goes best in the soft annealed or normalised condition. We normally rough machine before quenching, since a thinner section hardens deeper, and finish machine after tempering.
35NCD6 is hard to weld and is not meant for welded structures. If a weld cannot be avoided, it needs a qualified procedure: preheat of around 300 °C and stress relieving after welding, usually near 600 °C and always below the tempering temperature of the part.
35NCD6 forgings we make
At Jiangyin Jiangnan Metal all 35NCD6 work is forged to the customer's drawing. Typical parts include:
- Seamless rolled rings, forged rings and profiled rolled rings
- Gear rings and bearing rings
- Plain and stepped shafts, pump and plunger shafts, spindles
- Eccentric shafts and crankshafts
- Flanges, discs, blanks and tube sheets
- Round bars, square bars and blocks
- Hollow forgings: pipes, sleeves, bushings and cylinders
- Valve stems, seat rings and valve blocks
- Gear blanks, wheels and rolls
| Outside diameter | 100 to 6000 mm |
|---|---|
| Length | 100 to 12000 mm |
| Weight per piece | 10 to 15000 kg |
| Hydraulic press | 4500 t |
| Forging hammers | 1 t, 3 t, 6 t and 9 t |
| Ring rolling mills | 3 m and 6 m |
| Heat treatment | Annealing, normalising, hardening and tempering |
| Supply condition | As forged, or machined to drawing |
With 35NCD6, the section thickness usually decides how large a part can be. Send the finished dimensions and the properties you need, and we will confirm the forging size and heat treatment before we quote. Other grades are covered on our forging capability page.
Where 35NCD6 forgings are used
Buyers pick 35NCD6 for thick parts that take heavy, repeated loads and must not fail in a brittle way.
| Industry | Equipment | 35NCD6 forgings |
|---|---|---|
| Pumps | Plunger pumps, chemical process pumps | Plunger and pump shafts, rolled rings |
| Power transmission | Gearboxes, turbines, gas compressors | Gear rings, pinion shafts, spindles, forged bars |
| Oil and gas | Onshore and offshore production equipment, air and nitrogen compressors | Sleeves, bushings, discs, eccentric shafts |
| Valves | Ball, gate, globe, check and plug valves | Valve stems, seat rings, valve blocks |
| Process mills | Cement mills, sugar mills, concrete mixers | Crankshafts, drive shafts, heavy open-die parts |
| Shipbuilding and heavy machinery | Propulsion systems, cranes, rolling mills | Propeller shafts, wheels, rolls |
How a 35NCD6 forging is made
Every 35NCD6 forging follows the route below, and each step is recorded against the heat number.
- MeltingSteel is melted in an electric arc furnace, refined by VOD and remelted by ESR. The heat number follows the part all the way to the certificate.
- Heating and forgingIngots or billets are heated to about 1100 °C and forged on the 4500 t press or a hammer. Ring blanks are upset, punched and rolled to size on the 3 m or 6 m ring mill. Forging stops above 850 °C.
- Slow coolingForgings cool slowly in a furnace or under cover so hydrogen cannot crack the core, and are then normalised or annealed.
- Rough machiningA rough cut gives a clean surface for ultrasonic testing and a thinner section for quenching.
- Quenching and temperingParts are hardened from 830–860 °C in oil or polymer and tempered at 540–660 °C to the strength class on the order.
- TestingUltrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, plus tensile, impact and hardness tests on material from the same heat and heat treatment batch.
- Certificate and dispatchFinal dimensional check, heat number marking, EN 10204 3.1 certificate or 3.2 with a third-party inspector, then export packing.
Testing and certificates for 35NCD6 forgings
| Check | Standard or method | Notes |
|---|---|---|
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Acceptance class agreed on the order |
| Chemical composition | Cast analysis of the heat | Reported on the certificate |
| Tensile test | Rm, Re or Rp0.2, A, Z | Test bar from the same heat and heat treatment batch |
| Impact test | Charpy V-notch, KV at the specified temperature | Set of three specimens, test temperature as ordered |
| Hardness | Brinell, HBW | Survey across the forging |
| Magnetic particle testing | On request | Surface defects after machining |
| Metallography | On request | Grain size and microstructure |
| Inspection certificate | EN 10204 3.1 or 3.2 | 3.2 countersigned by a third-party inspector |
What to send for a 35NCD6 quotation
A sketch is enough to get started, but the details below will get you a price sooner.
| Item | Why it matters |
|---|---|
| Drawing or finished dimensions | Sets the forging size, weight and machining allowance |
| Quantity and delivery date | Decides batching and lead time |
| Grade and standard | 35NCD6 to NF A35-552, 34CrNiMo6 to EN 10250-3, or your own specification |
| Required properties and ruling section | Decides the heat treatment and which table of minimums applies |
| Delivery condition | +QT, +N or +A; as forged, rough machined or finish machined |
| Testing | Ultrasonic standard and acceptance class, extra impact or hardness tests |
| Certificate | EN 10204 3.1, or 3.2 with the name of the inspection body |
Estimate the weight of your part
Finished weight in 35NCD6 at 7.85 g/cm³. The forging itself weighs more because of the machining allowance.
Estimated weight
Email these sizesFrequently asked questions about 35NCD6
What is 35NCD6 steel?
It is the French AFNOR name for a nickel-chromium-molybdenum steel for quenching and tempering, with 0.30–0.38 % carbon, 1.30–1.70 % nickel, 1.30–1.70 % chromium and 0.15–0.30 % molybdenum. The current European name is 34CrNiMo6 (1.6582).
What is the equivalent of 35NCD6?
34CrNiMo6, material number 1.6582, has the same limits under EN ISO 683-2 and EN 10250-3. AISI 4340, AISI 4337, 817M40 (EN24) and SNCM439 are close, but their carbon, chromium or nickel ranges differ.
Is 35NCD6 the same as AISI 4340?
No. AISI 4340 has 0.70–0.90 % chromium and 1.65–2.00 % nickel, while 35NCD6 has 1.30–1.70 % of each. Carbon is higher in 4340 too, at 0.38–0.43 %. One cannot replace the other without the buyer's approval.
Is 35NCD6 the same as EN24 (817M40)?
No. EN24 (817M40) has 0.36–0.44 % carbon and 1.00–1.40 % chromium, against 0.30–0.38 % and 1.30–1.70 % in 35NCD6. Nickel is the same at 1.30–1.70 %, yet a certificate for one grade does not prove the other.
What tensile strength can 35NCD6 reach?
Under EN 10083-3 it runs from 1200–1400 MPa for sections up to 16 mm down to 800–950 MPa for 160–250 mm. A 100 to 160 mm section is specified at 900–1100 MPa with at least 700 MPa yield.
How hard is 35NCD6?
248 HBW at most in the soft annealed condition. Quenched and tempered to 900–1100 MPa it sits at about 270–330 HBW; the exact range is agreed on the order and checked with a Brinell survey.
How is 35NCD6 heat treated?
Harden from 830–860 °C with an oil or polymer quench, then temper at 540–660 °C to the strength you need. Normalise at 850–880 °C and soft anneal at 650–700 °C with slow furnace cooling. Keep tempering out of the 250 to 400 °C range.
What is the forging temperature of 35NCD6?
Forge between 1100 °C and 850 °C and stop before the part drops below 850 °C. Heavy forgings then cool slowly in a furnace or under cover to avoid hydrogen flakes.
Can 35NCD6 be welded?
Only with care. It is hard to weld and not meant for welded structures. Where a weld cannot be avoided, use a qualified procedure with preheat around 300 °C and stress relieving below the tempering temperature of the part.
Can you supply 35NCD6 forgings with an EN 10204 3.2 certificate?
Yes. A 3.1 certificate comes with every forging as standard. For 3.2, name the inspection body in your enquiry so the inspector can be booked to witness the tests.
Standards and references
- NF A35-552, French standard for steels for quenching and tempering (withdrawn); source of the 35NCD6 designation
- EN ISO 683-2:2018, alloy steels for quenching and tempering; replaced EN 10083-3:2006
- EN 10250-3:1999 and EN 10250-3:2022, open die steel forgings for general engineering purposes, alloy special steels
- EN 10228-3, ultrasonic testing of ferritic or martensitic steel forgings
- SEP 1921, ultrasonic testing (Stahl-Eisen-Prüfblatt)
- ASTM A388/A388M, ultrasonic examination of steel forgings
- EN 10204, metallic products, types of inspection documents
- BS 970 (817M40) and SAE J404 / ASTM A29 (4340), for the comparable grades in Table 3
- Lucefin Group, 34CrNiMo6 technical card, for Table 5, the hardness rows and the physical properties
- Published 34CrNiMo6 datasheets of European steelmakers, for the temperatures in Table 6
Values on this page are standard minimums or typical ranges for guidance. The purchase order and the standard edition named on it take precedence.