What AISI 4337 is
AISI 4337, also written SAE 4337 and numbered UNS G43370, is a medium-carbon nickel-chromium-molybdenum low-alloy steel. It runs about 0.35 to 0.40% carbon, 1.65 to 2.00% nickel, 0.70 to 0.90% chromium and 0.20 to 0.30% molybdenum. Specifiers reach for it when a part has to carry high stress and take a knock, and when the section is too thick to through-harden in a plain chromium-molybdenum steel. Jiangyin Jiangnan Metal forges 4337 into rings, shafts, flanges and discs for pump, valve, gearbox and offshore work.
Nickel is what separates 4337 from the 41xx chromium-molybdenum steels such as AISI 4140. It raises toughness at any given strength level and it deepens the hardened zone. A 200 mm 4337 shaft will through-harden on an oil quench where a 4140 shaft of the same size comes out with a soft core.
Molybdenum does a second job here. It suppresses temper embrittlement, which matters because 4337 is normally tempered high, 540 to 650 °C, to reach its service properties.
Carbon sits a little lower than in AISI 4340, so 4337 tempers back to slightly lower hardness and keeps more impact energy. That trade suits components under reversing or shock loading rather than pure static tension: crankshafts, connecting rods, heavy gear blanks, pump plungers, drill-string tooling.
AISI 4337 chemical composition
Per SAE J404 and ASTM A29, AISI 4337 runs C 0.35 to 0.40%, Mn 0.60 to 0.80%, Si 0.15 to 0.35%, Ni 1.65 to 2.00%, Cr 0.70 to 0.90% and Mo 0.20 to 0.30%, with phosphorus held to 0.035% and sulphur to 0.040% maximum. Balance iron.
| Element | C | Si | Mn | P max | S max | Cr | Ni | Mo |
|---|---|---|---|---|---|---|---|---|
| Minimum | 0.35 | 0.15 | 0.60 | — | — | 0.70 | 1.65 | 0.20 |
| Maximum | 0.40 | 0.35 | 0.80 | 0.035 | 0.040 | 0.90 | 2.00 | 0.30 |
34CrNiMo6, the grade usually supplied against 4337 enquiries
Most enquiries written against AISI 4337 are filled with EN 34CrNiMo6 (material number 1.6582). It is the closest grade European and Asian mills carry, but the chemistry is not the same: 34CrNiMo6 runs roughly double the chromium and a little less nickel. Tell us on the enquiry which specification governs and we will quote against that one.
| C | Si | Mn | Cr | Ni | Mo | S |
|---|---|---|---|---|---|---|
| 0.30–0.38 | ≤ 0.40 | 0.50–0.80 | 1.30–1.70 | 1.30–1.70 | 0.15–0.30 | 0.015–0.035 |
Melting practice: forging stock for both grades is electric-arc melted, ladle refined and vacuum degassed. Vacuum degassing holds hydrogen under 2 ppm, which is what keeps heavy sections free of flaking. ESR stock is available on request.
AISI 4337 mechanical properties
Quenched and tempered, AISI 4337 and 34CrNiMo6 reach 1 200 to 1 400 MPa tensile with 0.2% proof stress over 1 000 MPa in sections to 16 mm. Hardenability falls off with section size, so the guaranteed tensile band drops to 800 to 950 MPa between 160 and 250 mm. The table below gives the +QT minima to EN 10083-3.
| Section Ø (mm) | Tensile strength Rm (MPa) | Yield strength Rp0.2 (MPa) | Elongation A (%) | Impact KV at 20 °C (J) |
|---|---|---|---|---|
| d ≤ 16 | 1 200 – 1 400 | ≥ 1 000 | ≥ 9 | ≥ 35 |
| 16 < d ≤ 40 | 1 100 – 1 300 | ≥ 900 | ≥ 10 | ≥ 45 |
| 40 < d ≤ 100 | 1 000 – 1 200 | ≥ 800 | ≥ 11 | ≥ 45 |
| 100 < d ≤ 160 | 900 – 1 100 | ≥ 700 | ≥ 12 | ≥ 45 |
| 160 < d ≤ 250 | 800 – 950 | ≥ 600 | ≥ 13 | ≥ 45 |
Above 250 mm we agree properties case by case and prove them on a prolongation test piece cut from the forging itself. Sub-zero impact testing at −20, −40 or −46 °C is available for offshore and arctic work.
AISI 4337 equivalent grades
The closest equivalents to AISI 4337 are UNS G43370 in the USA, 34CrNiMo6 / 1.6582 in the EN system, SNCM447 in Japan, 817M40 (EN24) in the UK, 35NCD6 in France, 34CrNi3Mo in China and 38KhN3MFA in Russia. Treat none of them as a drop-in substitute without checking the governing specification first.
| Country / system | Standard | Designation |
|---|---|---|
| USA | SAE J404 / ASTM A29 | AISI 4337, UNS G43370 |
| Europe | EN 10083-3 | 34CrNiMo6, 1.6582 |
| Germany | DIN 17200 | 34CrNiMo6 |
| United Kingdom | BS 970 | 817M40, EN24 |
| France | AFNOR NF A35-552 | 35NCD6 |
| Japan | JIS G4103 | SNCM447 |
| Italy | UNI 7845 | 34CrNiMo6 |
| China | GB/T 3077 | 34CrNi3Mo |
| Russia | GOST 4543 | 38KhN3MFA |
We forge the neighbouring grades too: AISI 4140, 42CrMo4, AISI 4145, 18CrNiMo7-6 and AISI 8630.
AISI 4337 compared with 4340 and 4140
Carbon is the only thing separating AISI 4337 from AISI 4340: 0.35 to 0.40% against 0.38 to 0.43%. Nickel, chromium and molybdenum ranges are identical. Both carry about 1.8% nickel, which gives them roughly three times the hardenable section of AISI 4140, a chromium-molybdenum steel with no deliberate nickel addition.
| Property | AISI 4337 | AISI 4340 | AISI 4140 |
|---|---|---|---|
| Carbon, % | 0.35 – 0.40 | 0.38 – 0.43 | 0.38 – 0.43 |
| Nickel, % | 1.65 – 2.00 | 1.65 – 2.00 | — |
| Chromium, % | 0.70 – 0.90 | 0.70 – 0.90 | 0.80 – 1.10 |
| Molybdenum, % | 0.20 – 0.30 | 0.20 – 0.30 | 0.15 – 0.25 |
| Typical +QT tensile, MPa | 1 000 – 1 400 | 1 080 – 1 500 | 850 – 1 100 |
| Through-hardening limit, oil | ≈ 150 mm | ≈ 150 mm | ≈ 60 mm |
| Relative impact toughness | Highest of the three | High | Moderate |
| Relative cost | High | High | Low |
Heat treatment of AISI 4337 forgings
AISI 4337 forgings anneal at 820 to 850 °C with a furnace cool, normalise at 860 to 900 °C in still air, harden from 830 to 860 °C into oil, and temper between 540 and 650 °C. Stay out of the 250 to 450 °C tempering range. It produces temper embrittlement and a sharp drop in impact energy.
| Operation | Temperature | Cooling | Result |
|---|---|---|---|
| Forging | 1 150 – 900 °C | Slow cool in pit | Min. 3:1 reduction ratio |
| Annealing | 820 – 850 °C | Furnace cool to 600 °C | ≤ 248 HB, machinable |
| Normalising | 860 – 900 °C | Still air | Grain refinement |
| Hardening | 830 – 860 °C | Oil quench | Martensitic structure |
| Tempering | 540 – 650 °C | Air | Target strength band |
| Stress relief | 550 – 600 °C | Furnace cool | After rough machining |
These cycles are for guidance. The cycle we actually run is set against the ruling section of your part and the properties written on your drawing, and it is recorded on the heat treatment chart issued with the EN 10204 3.1 certificate.
AISI 4337 forgings we manufacture
We forge AISI 4337 into seamless rolled rings, shafts, flanges, discs, sleeves, bushings, gear blanks, cylinders, blocks and round bars. Rings roll from 200 to 4 000 mm outside diameter. Shafts go to 8 000 mm long. Single-piece weight reaches about 30 tonnes. Everything is made to drawing; there is no standard catalogue.
- AISI 4337 forged ringsRolled and open-die, 200–4 000 mm OD
- AISI 4337 forged shaftsStepped, hollow and eccentric, to 8 m
- AISI 4337 forged flangesWeld-neck, blind, slip-on, custom
- AISI 4337 forged discsUpset-forged blanks and tube sheets
- AISI 4337 forged barsRound, square and flat sections
- AISI 4337 sleeves and bushingsBored and trepanned hollows
- AISI 4337 gear blanksPinion and wheel forgings
- AISI 4337 valve partsBodies, stems, seat rings
- AISI 4337 eccentric shaftsCrank and cam forgings
How we make and verify AISI 4337 forgings
Every part goes through the same five stages: EAF + LF + VD melting of the stock, open-die forging or ring rolling between 1 150 and 900 °C at a minimum 3:1 reduction ratio, quench and temper, 100% ultrasonic inspection to ASTM A388 or EN 10228-3, then release under an EN 10204 3.1 or third-party 3.2 certificate.
Melting and forging stock
Stock is electric-arc melted, ladle refined and vacuum degassed. Low hydrogen is the point. Flaking in heavy Ni-Cr-Mo sections is the failure that most often shows up later as ultrasonic indications, and vacuum degassing is what prevents it. Where a specification calls for it we source ESR remelted stock instead.
Forging
Open-die presses and ring mills work the ingot between 1 150 °C and 900 °C. We hold a minimum 3:1 reduction ratio so the as-cast structure breaks down fully and grain flow follows the part contour. Final-pass deformation stays above 20% to keep grain size down.
Testing and documentation
Chemistry is checked by optical emission spectrometry on every heat. Mechanical testing follows ASTM A370 or ISO 6892-1 on prolongation pieces. Ultrasonic testing runs to ASTM A388, EN 10228-3 or SEP 1921 at whichever quality class you specify. Magnetic particle inspection to ASTM E709 and hardness mapping are available on request. Dimensional reports, heat treatment charts and EN 10204 3.1 certificates ship with every consignment. Where 3.2 certification is written into the order, it is countersigned by SGS, Bureau Veritas, TÜV or Lloyd's Register.
Where AISI 4337 forgings are used
AISI 4337 forgings go into parts that carry reversing or impact loads at high stress: pump shafts and plungers, valve bodies and stems, gearbox pinions and gear blanks, compressor and turbine rotor shafts, crankshafts and connecting rods, drill-string tooling, and subsea and wellhead hardware for offshore oil and gas.
Pumps and compressors
Chemical pump shafts, plunger pump rods and industrial air-compressor shafts, where fatigue strength under rotating-bending load is the design driver.
Valves and pressure equipment
Forged bodies, bonnets, stems and valve seat rings for ball, gate, globe, check and plug valves. Tube sheets and flanges for shell-and-tube heat exchangers and air receivers.
Power transmission
Gear blanks, pinion shafts, spindles and couplings for industrial gearboxes, gas compressors and turbine drive trains.
Oil, gas and offshore
Subsea and deepwater production hardware, wellhead and Christmas tree components, drill collars and other drill-string tooling. Parts for sour service are ordered against NACE MR0175 / ISO 15156 hardness limits, which normally means tempering high enough to hold 22 HRC maximum.
Heavy machinery and marine
Crankshafts, connecting rods, forged rolls, eccentric shafts, mill pinions and rudder stocks for shipbuilding, mining equipment and pulp-and-paper machinery.
AISI 4337 questions and answers
Is AISI 4337 the same as 34CrNiMo6?
No. They are close, but not the same. AISI 4337 carries 0.70 to 0.90% chromium and 1.65 to 2.00% nickel, while 34CrNiMo6 carries 1.30 to 1.70% of each. In practice 34CrNiMo6 is what most European and Asian mills supply against a 4337 enquiry, and the two behave similarly once quenched and tempered. If your drawing calls up SAE J404 or ASTM A29 specifically, say so on the enquiry and we will source true 4337 chemistry.
What is the difference between AISI 4337 and AISI 4340?
Carbon content. AISI 4337 has 0.35 to 0.40% carbon against 0.38 to 0.43% for AISI 4340. Nickel, chromium and molybdenum ranges are identical. The lower carbon gives 4337 slightly less peak strength and slightly better impact toughness and weldability. For most quench-and-temper applications the two are interchangeable within the same strength band.
Can AISI 4337 be welded?
Yes, but it needs care. With a carbon equivalent around 0.85 the grade hardens in the heat-affected zone, so weld in the annealed or normalised condition, preheat to 200 to 300 °C, use low-hydrogen consumables, and stress relieve at 550 to 600 °C afterwards. Welding a fully quenched-and-tempered 4337 forging will locally destroy its properties unless the whole part is re-heat-treated.
What is the maximum size of AISI 4337 forging you can produce?
Single-piece weights to about 30 tonnes. Seamless rolled rings from 200 to 4 000 mm outside diameter, shafts to 8 000 mm long, discs to 2 500 mm diameter, bars from 80 to 1 200 mm. Send the drawing and we will confirm whether the part fits our press and ring mill.
What certificates come with the forgings?
Every consignment ships with an EN 10204 3.1 material test certificate covering heat number, chemical analysis, mechanical test results, heat treatment record and ultrasonic report. EN 10204 3.2 certification countersigned by SGS, Bureau Veritas, TÜV or Lloyd's Register is available when specified at order stage.
What is the lead time and minimum order quantity?
Typical lead time is 25 to 45 days from drawing approval, depending on section size and heat treatment route. There is no fixed minimum order quantity. We quote single prototype forgings as well as production batches, though unit price falls sharply above about five pieces of the same part.
Do you supply AISI 4337 for sour service?
Yes. For NACE MR0175 / ISO 15156 sour service we temper to hold 22 HRC maximum and include hardness survey results in the certificate. Give us the service environment on the enquiry, partial pressure of H₂S, temperature and chloride content, so we can confirm the grade is suitable before quoting.
What information do you need to quote?
A drawing or the rough dimensions, the quantity, the specification and delivery condition (+A, +N or +QT), any NDT class, and the certificate level. If you do not have a drawing, outside diameter, inside diameter, length or thickness and the material grade are enough for a budget price. Send it to sales@steelforgepieces.com and you will normally have a quotation within 24 hours.