What is AISI 4140 steel?
AISI 4140 is a medium-carbon, low-alloy steel of the 41xx chromium-molybdenum family. It is used in the quenched and tempered condition for shafts, gears, rings, flanges and pressure-containing parts.
Chromium raises hardenability and wear resistance. Molybdenum suppresses temper embrittlement and holds strength at elevated temperature. Between them, a section of 100 mm or more will harden through to a uniform tempered martensite. That is the reason 4140 dominates open-die forging shops. One grade covers a wide range of strength levels, and the level is set by the tempering temperature alone.
Three delivery conditions are normally specified. Annealed material is soft, 241 HB maximum, and is meant for machining and heat treatment by the customer. Normalised material has a refined, uniform grain structure. Quenched and tempered material, written +QT, is supplied at a defined strength band and is the usual condition for finished forgings.
Our steel is melted by the EAF + LF + VD route: electric arc furnace, ladle furnace refining, then vacuum degassing. This lowers hydrogen, oxygen and sulphur. It is the practice normally required for forged pressure parts and for heavy sections.
Specifications AISI 4140 forgings are supplied to
- ASTM A29/A29M-23, general requirements for hot-wrought carbon and alloy steel bars
- ASTM A322, alloy steel bars, standard grades
- ASTM A668/A668M, carbon and alloy steel forgings for general industrial use
- EN 10250-3, open-die steel forgings for general engineering, alloy special steels
- EN 10083-3, steels for quenching and tempering, now superseded by EN ISO 683-2
- JIS G4105 (SCM440) and GB/T 3077 (42CrMo)
- NACE MR0175 / ISO 15156 for sour-service parts, 22 HRC maximum
Note on editions. ASTM A29/A29M-91 is withdrawn. Orders should reference the current edition, or state the exact edition the drawing requires.
Chemical composition of AISI 4140
AISI 4140 contains 0.38-0.43 % C, 0.75-1.00 % Mn, 0.15-0.35 % Si, 0.80-1.10 % Cr and 0.15-0.25 % Mo. Phosphorus is held to 0.035 % max and sulphur to 0.040 % max. The balance is iron.
| Grade | C | Mn | P max | S max | Si | Cr | Mo | Ni | Fe |
|---|---|---|---|---|---|---|---|---|---|
| AISI 4140 | 0.38-0.43 | 0.75-1.00 | 0.035 | 0.040 | 0.15-0.35 | 0.80-1.10 | 0.15-0.25 | n/a | Bal. |
| 42CrMo4 (1.7225) | 0.38-0.45 | 0.60-0.90 | 0.025 | 0.035 | 0.40 max | 0.90-1.20 | 0.15-0.30 | n/a | Bal. |
Why the two rows differ. 42CrMo4 allows slightly wider carbon and chromium than AISI 4140, and tighter phosphorus and sulphur. The grades cross-reference, but they are not identical. Where a drawing calls for one and the mill certificate shows the other, the purchase order has to say which standard governs.
Data compiled by Jiangyin Jiangnan Metal Co., Ltd. from ASTM A29/A29M and EN 10083-3. Heat analysis for every forging is reported on the EN 10204 certificate.
Mechanical properties of AISI 4140 by ruling section
Strength falls as section size rises. A quench cannot cool the core of a heavy forging as fast as a thin bar, so a 4140 forging of 200 mm ruling section will not meet the values quoted for a 25 mm bar.
| Ruling section d (mm) | Yield Rp0.2 min (MPa) | Tensile Rm (MPa) | Elongation A min (%) | Reduction Z min (%) | Impact KV min (J) |
|---|---|---|---|---|---|
| d ≤ 16 | 900 | 1100-1300 | 10 | 40 | n/a |
| 16 < d ≤ 40 | 750 | 1000-1200 | 11 | 45 | 35 |
| 40 < d ≤ 100 | 650 | 900-1100 | 12 | 50 | 35 |
| 100 < d ≤ 160 | 550 | 800-950 | 13 | 50 | 35 |
| 160 < d ≤ 250 | 500 | 750-900 | 14 | 55 | 35 |
| Condition | Tensile Rm | Yield Rp0.2 | Elongation | Hardness |
|---|---|---|---|---|
| Annealed (+A) | approx. 655 MPa | approx. 415 MPa | approx. 25 % | 241 HB max |
| Normalised (+N) | approx. 1020 MPa | approx. 655 MPa | approx. 18 % | approx. 302 HB |
| Q&T, high-strength bar | 896 MPa (130 ksi) min | 758 MPa (110 ksi) min | 13 % min | 28-34 HRC |
| Q&T, sour service | per order | per order | per order | 22 HRC max |
How to specify. State the ruling section, the required property band, where the test coupon is taken from, and how many tests per heat or lot. "4140 Q&T" on its own is not a complete requirement.
Physical properties
| Property | Value | Unit |
|---|---|---|
| Density | 7.85 | g/cm³ |
| Modulus of elasticity | 205-210 | GPa |
| Poisson’s ratio | 0.27-0.30 | n/a |
| Thermal conductivity at 100 °C | approx. 42.6 | W/m·K |
| Specific heat, 0-100 °C | approx. 473 | J/kg·K |
| Mean thermal expansion, 20-100 °C | approx. 12.3 | ×10⁻⁶/K |
| Electrical resistivity | approx. 0.22 | µΩ·m |
| Critical point Ac1 | approx. 730-745 | °C |
| Critical point Ac3 | approx. 790-800 | °C |
| Martensite start Ms | approx. 310-330 | °C |
AISI 4140 equivalent grades worldwide
The European equivalent of AISI 4140 is 42CrMo4 / 1.7225. Japan uses SCM440, China 42CrMo, the UK EN19 (709M40) and France 42CD4.
| Region | Standard | Designation | Note |
|---|---|---|---|
| USA | ASTM A29 / SAE J404 | 4140, UNS G41400 | Reference grade |
| Europe | EN 10083-3 / EN ISO 683-2 | 42CrMo4 | Most common substitute |
| Germany | DIN / Werkstoff | 1.7225 (42CrMo4), 1.7227 (42CrMoS4) | 1.7227 is the re-sulphurised free-machining variant |
| Japan | JIS G4105 | SCM440 | Different P and S limits |
| China | GB/T 3077 | 42CrMo | Domestic production grade |
| United Kingdom | BS 970 | EN19, now 709M40 (708M40 also cited) | 709M40 has Mo 0.25-0.35 |
| France | AFNOR NF A35-552 | 42CD4 | n/a |
| International | ISO 683-17 | B43 | Bearing-quality route |
Substitution warning. These grades cross-reference. They are not automatic substitutes. Whether one can replace another depends on the product standard, the delivery condition, the ruling section, the test sampling and the wording of the mill certificate, not on the grade name.
How AISI 4140 is forged
AISI 4140 is heated to 1150-1200 °C, forged down to a minimum finishing temperature of 850 °C, then cooled slowly in ashes, sand or a furnace.
| Stage | Temperature | Practice |
|---|---|---|
| Heating | 1150-1200 °C | Controlled ramp, soak until the section is uniform |
| Forging finish | 850 °C min | Stop before the steel drops into the two-phase range |
| Cooling after forging | Slow | Ashes, sand or furnace. Never still air on heavy sections |
| Post-forge anneal | 830-850 °C | De-hydrogenation or isothermal anneal for heavy forgings |
Slow cooling matters more for 4140 than for plain carbon steel. At roughly 1 % chromium the steel will air-harden in heavy sections, and an uncontrolled cool from forging heat can leave untempered martensite, quench cracks or hydrogen flaking. Heavy 4140 forgings are cooled under control here. Where the section warrants it, they are given a de-hydrogenation anneal before rough machining.
Heat treatment routes
| Treatment | Temperature | Cooling | Result |
|---|---|---|---|
| Annealing | 830-850 °C | Furnace cool | Soft and machinable, 241 HB max |
| Normalising | 870-900 °C | Still air | Refined, uniform grain |
| Hardening | 830-880 °C | Oil or polymer quench | Martensite, temper immediately |
| Tempering | 480-680 °C | Air | Sets the final strength band |
| Stress relief, annealed | 600-650 °C | Still air | Removes machining stress |
| Stress relief, hardened | 500-550 °C | Still air | Must stay below the tempering temperature |
| Nitriding, optional | 500-530 °C | Furnace | Surface 600-700 HV for wear resistance |
Tempering rule of thumb. Higher tempering temperature gives lower strength and higher toughness. Avoid the 250-400 °C range, where 4140 is prone to temper embrittlement.
AISI 4140 forgings we produce
We open-die forge AISI 4140 to customer drawings in ten standard forms, supplied as-forged, rough-machined or finish-machined.
Forged rings and seamless rolled rings
Ring-rolled to near-net section for bearing housings, slew rings, gear blanks and pump casings. See our seamless rolled rings.
Forged shafts and spindles
Stepped shafts, eccentric shafts, crankshafts and pinion blanks for pumps, gearboxes, compressors and mill drives.
Forged flanges
Weld-neck, blind, slip-on and special-profile flanges for pressure vessels, columns, towers and heat exchangers.
Forged discs and disks
Solid and bored discs for turbine wheels, couplings, valve discs and tube sheets.
Forged round bars
Upset and drawn bars, ultrasonically tested, for machining into valve stems, rods and fasteners.
Forged sleeves, bushings and hollow bars
Bored and trepanned hollows for subsea, downhole and compressor service.
Forged blocks and blanks
Rectangular blocks for valve bodies, die holders and manifolds.
Forged gear blanks
Toothed blanks and gear rings for power transmission and mill drives. See our forging rings.
Open-die forging capability
| Form | Size range | Single-piece weight |
|---|---|---|
| Seamless rolled rings | OD 200-4000 mm, wall 20-450 mm, height up to 1200 mm | 20 kg to 20 t |
| Shafts | Ø 80-1200 mm, length up to 12 000 mm | 50 kg to 30 t |
| Discs and blanks | Ø 200-2500 mm, thickness 50-800 mm | 30 kg to 25 t |
| Flanges | Ø 100-3500 mm | 10 kg to 15 t |
| Blocks | 2000 × 1500 × 800 mm max | 50 kg to 25 t |
| Hollow bars and sleeves | OD 150-1500 mm, ID from 60 mm | 20 kg to 18 t |
Tolerances are as-forged to EN 10250-1, or machined to your drawing. Machining allowance is agreed at quotation stage. Minimum order is one piece for sizes above 500 kg.
Where AISI 4140 forgings are used
AISI 4140 is specified where a part needs high strength and fatigue resistance in a section too heavy for plain carbon steel, but not heavy enough to justify nickel-alloyed 4340.
| Industry | Typical AISI 4140 forged parts |
|---|---|
| Oil and gas, subsea | Wellhead components, Christmas-tree bodies, hangers, mandrels, drill collars, sucker rod couplings, hollow bars |
| Pressure vessels | Tube sheets, forged flanges, nozzles, shell rings and closures for air receivers and shell-and-tube heat exchangers |
| Valves | Valve bodies, bonnets, stems, seat rings and blocks for ball, gate, globe, check and plug valves |
| Power transmission | Gear blanks, gear rings, pinion shafts, spindles, coupling hubs, gearbox shafts |
| Pumps and compressors | Pump shafts, plunger rods, impeller hubs, compressor rotors, crankshafts |
| Mining and cement | Mill pinions, trunnions, crusher shafts, mixer shafts, rolls for cement, sugar and concrete plants |
| Heavy machinery and marine | Forged wheels, rolls, manifolds, rudder stocks and shafting for shipbuilding |
| Process and chemical plant | Column and tower flanges, silo and preheater rings, crystalliser parts, process module forgings |
Testing, NDT and certification
Every AISI 4140 forging is supplied with a material certificate to EN 10204 3.1, or 3.2 with third-party witness, and ultrasonic testing to the acceptance class stated on the order.
| Check | Standard | Notes |
|---|---|---|
| Chemical analysis | ASTM A751 / EN 10204 | Heat analysis, product analysis optional |
| Tensile test | ASTM A370 / ISO 6892-1 | Coupon location agreed at order stage |
| Impact test | ASTM E23 / ISO 148-1 | Charpy V-notch, temperature per order |
| Hardness survey | ASTM E10 / E18 | Mandatory for NACE MR0175 parts, 22 HRC max |
| Ultrasonic testing | EN 10228-3, SEP 1921, ASTM A388 | Class agreed at order stage |
| Magnetic particle | EN 10228-1 / ASTM E1444 | Surface indications |
| Grain size | ASTM E112 | Typically 5 or finer |
| Hardenability | ASTM A255 | Jominy end-quench for 4140H |
| Certificate | EN 10204 3.1 or 3.2 | 3.2 witnessed by TUV, BV, SGS, Lloyd’s or your own inspector |
Additional tests and third-party witness can be arranged. State the requirement with the enquiry so the inspection plan is priced into the quotation.
How to order AISI 4140 forgings
Send a drawing or the finished dimensions to sales@steelforgepieces.com and we quote within one working day.
- Send the drawing or dimensions. A PDF, DWG or STEP file, or simply OD, ID and height for a ring.
- State the grade and standard. AISI 4140, 42CrMo4 or SCM440, with the controlling specification and its edition.
- State the delivery condition. Annealed, normalised, or quenched and tempered to a named strength band.
- State the ruling section and test requirements. Coupon location, number of tests, impact temperature, hardness limits.
- State NDT and certification. UT class and standard, MT scope, EN 10204 3.1 or 3.2.
- State quantity and machining. As-forged, rough-machined with allowance, or finish-machined.
If you are not sure which of these to specify, send the drawing together with the service conditions: pressure, temperature, medium, and whether the service is sour. We will propose a specification for your approval.
Frequently asked questions about AISI 4140
What is AISI 4140 steel?
AISI 4140 is a chromium-molybdenum low-alloy steel with about 0.40 % carbon, 0.95 % chromium and 0.20 % molybdenum. It is normally supplied quenched and tempered. The combination of high tensile strength, good toughness, fatigue strength and deep hardenability makes it the most commonly forged general engineering steel.
What is the European equivalent of AISI 4140?
The European equivalent is 42CrMo4, material number 1.7225, specified in EN 10083-3 and now in EN ISO 683-2. Japan uses JIS SCM440, China GB/T 3077 42CrMo, the UK BS EN19 or 709M40, France AFNOR 42CD4 and the USA UNS G41400. The grades are close but not identical, so the purchase order should state the controlling standard.
What is the chemical composition of AISI 4140?
AISI 4140 contains 0.38 to 0.43 % carbon, 0.75 to 1.00 % manganese, 0.15 to 0.35 % silicon, 0.80 to 1.10 % chromium and 0.15 to 0.25 % molybdenum. Phosphorus is limited to 0.035 % maximum and sulphur to 0.040 % maximum. The balance is iron.
What tensile strength can AISI 4140 forgings reach?
It depends on the ruling section. Quenched and tempered to the 42CrMo4 +QT bands of EN 10083-3, sections up to 16 mm reach 1100 to 1300 MPa, sections of 40 to 100 mm reach 900 to 1100 MPa, and sections of 160 to 250 mm reach 750 to 900 MPa. Annealed material is about 655 MPa at 241 HB maximum.
At what temperature is AISI 4140 forged?
AISI 4140 is heated to 1150 to 1200 °C and soaked until the section is uniform. Forging stops at a minimum of 850 °C. The forging is then cooled slowly in ashes, sand or a furnace to avoid hydrogen flaking and quench cracking. Heavy sections normally get a de-hydrogenation or isothermal anneal straight after forging.
How is AISI 4140 heat treated?
Annealing is 830 to 850 °C then furnace cool. Normalising is 870 to 900 °C then still air. Hardening is 830 to 880 °C then an oil or polymer quench, followed by tempering at 480 to 680 °C to the required strength. Stress relieving is 600 to 650 °C for annealed material and 500 to 550 °C for hardened material.
Can AISI 4140 be welded?
AISI 4140 has a carbon equivalent of roughly 0.80 and is classed as difficult to weld. It needs preheat of about 300 to 350 °C, low-hydrogen consumables, controlled interpass temperature and post-weld heat treatment below the previous tempering temperature. Where the design allows it, design the joint out and forge the part in one piece.
Is AISI 4140 suitable for sour service?
Yes, when it is quenched and tempered to a fully tempered martensitic structure with hardness held at 22 HRC maximum, in line with NACE MR0175 and ISO 15156. State the requirement on the purchase order so the tempering temperature, hardness survey and test frequency are set accordingly.
What is the difference between AISI 4140 and AISI 4340?
AISI 4340 adds about 1.8 % nickel to the same chromium-molybdenum base. The nickel gives deeper hardenability and better low-temperature toughness, so 4340 is preferred for very heavy sections and high-integrity shafts. AISI 4140 costs less, machines more easily and is adequate for most sections up to roughly 250 mm ruling section.
Who supplies AISI 4140 open-die forgings?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It forges AISI 4140 rings, seamless rolled rings, shafts, flanges, discs, bars, sleeves and blocks to customer drawings, with heat treatment, ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, and EN 10204 3.1 or 3.2 certification. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659.
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu, China. We supply forged rings, shafts, flanges, discs and bars in carbon steel, alloy steel, tool steel, stainless steel and nickel alloys.
Jiangyin sits in the Yangtze River delta between Shanghai and Nanjing, in one of China’s densest clusters of forging and heavy-machinery plants, with direct access to the ports of Shanghai and Zhangjiagang. We forge to customer drawings rather than to a catalogue. The normal order is one drawing, a grade, a delivery condition and a test requirement, quoted and produced as a single lot.
| Legal name | Jiangyin Jiangnan Metal Co., Ltd. |
|---|---|
| Type | Open-die forging factory, manufacturer rather than trading company |
| Address | No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China |
| Telephone | +86-189-2135-9659 |
| sales@steelforgepieces.com | |
| Website | www.steelforgepieces.com |
| Materials | Carbon steel, alloy steel, tool steel, stainless steel, nickel alloys |
| Processes | Open-die forging, seamless ring rolling, heat treatment, rough and finish machining, NDT |
| Export markets | Europe, North America, the Middle East, South-East Asia, South America, Australia |
Need a price for an AISI 4140 forging?
Send the drawing or the dimensions, the grade, the delivery condition and the quantity. We reply with a price, a weight and a lead time within one working day.