SAE 4140 – UNS G41400
Chromium-molybdenum low-alloy steel for quenching and tempering
Medium-carbon Cr-Mo steel, oil hardenable, supplied annealed or quenched and tempered. It combines good mechanical strength, toughness and fatigue resistance in medium sections. It is the base for shafts, oil and gas forgings (API 6A) and ASTM A193 B7 bolting.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | G41400 |
| W.Nr./EN | 42CrMo4 – 1.7225 (EN ISO 683-2) |
| DIN | 42CrMo4 |
| JIS | SCM440 |
| Trade names | 4140, 42CrMo4, Gerdau/Villares 4140 |
| Others | ABNT 4140; GB 42CrMo; ASTM A193 B7 bolting (4140/4142-type chemistry) |
Standards by product form
| Form | Standard |
|---|---|
| Bar (composition) | SAE J404 / ASTM A29 / ABNT NBR NM 87 |
| Quenched and tempered bar | ASTM A434 (classes BB, BC, BD) |
| Forging | ASTM A668 / API 6A (75K) to customer specification |
| Mechanical tubing | ASTM A519 |
| Plate | ASTM A829 |
| Bolting | ASTM A193 B7 / B7M; A320 L7 / L7M; nuts A194 2H / 2HM / 4 / 7 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7228.40.00 | 7228.40 | 7228.40.0000 | 7228 40 90 |
| Hot-rolled bar | 7228.30.00 | 7228.30 | 7228.30.8041 | 7228 30 61 |
| Plate (> 10 mm, width ≥ 600 mm) | 7225.40.90 | 7225.40 | 7225.40.3050 | 7225 40 40 |
| Seamless pipe | 7304.19.00 | 7304.19 | 7304.19.5050 | 7304 19 10 |
| Welded pipe | 7306.19.00 | 7306.19 | 7306.19.5150 | 7306 19 00 |
| Flange and fitting | 7307.91.00 | 7307.91 | 7307.91.5030 | 7307 91 00 |
Tariff class: alloy steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
Pipe: 7304.19 and 7306.19 are line pipe for oil and gas pipelines; boiler, heat exchanger or process tubes go under 7304.39/7304.59 (seamless) and 7306.30/7306.50 (welded).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
SAE J404 / ASTM A29
| Element | Range (%) |
|---|---|
| C | 0.38 – 0.43 |
| Mn | 0.75 – 1.00 |
| P | ≤ 0.035 |
| S | ≤ 0.040 |
| Si | 0.15 – 0.35 |
| Cr | 0.80 – 1.10 |
| Mo | 0.15 – 0.25 |
| Fe | balance |
Mechanical properties
Quenched and tempered, section Ø 40–100 mm (EN 10083-3 / ISO 683-2, 42CrMo4 +QT); properties fall as the section increases
| Property | Value |
|---|---|
| Yield strength | ≥ 650 MPa |
| Tensile strength | 900 – 1,100 MPa |
| Elongation | ≥ 12% |
| Charpy V (20 °C) | ≥ 35 J |
| Hardness, Q&T (commercial) | ≈ 28 – 34 HRC (typical) |
| Hardness, annealed | ≤ 241 HB |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Melting range | ≈ 1,415 – 1,500 °C |
| Modulus of elasticity | ≈ 205 GPa |
| Thermal conductivity (20 °C) | ≈ 42 W/m·K |
| Thermal expansion (20–100 °C) | ≈ 12.2 µm/m·K |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Up to ≈ 400–450 °C without relevant loss of properties (always below the tempering temperature); B7 up to ≈ 450 °C. For H2S, limit to ≤ 22 HRC (NACE MR0175/ISO 15156). |
| Heat treatment | Annealing 820–850 °C, slow furnace cooling. Normalizing 870–900 °C in air. Hardening: austenitize 840–870 °C, oil or polymer. Tempering 540–680 °C according to the desired hardness (avoid 250–400 °C, embrittlement range). Accepts nitriding, induction and flame hardening. |
| Welding | Limited weldability (high CE): preheat 200–320 °C, low-hydrogen electrodes AWS E8018-B2 / E9018-D1 or E11018-M according to the required strength, controlled interpass and stress relief/tempering right after welding. Avoid welding in the quenched and tempered condition without a qualified procedure. |
| Machining | Good in the annealed condition (≈ 65% of 1212); quenched and tempered (28–32 HRC) machinable with carbide. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Shafts, spindles and axle shafts
- Oil and gas forgings (bodies, bonnets, hangers – API 6A 75K)
- ASTM A193 B7 / B7M and A320 L7 studs and bolts (including for Petrobras)
- Quenched and tempered or nitrided gears and pinions
- Connecting rods, crankshafts and spiders
- Drilling tools and subs (drill collars, connections)
- Molds and mold bases
- Track pins and joints of heavy machinery
Alternatives: SAE 4340 for large sections or higher toughness; 4130 for better weldability; 4145H/modified 4145 for drill collars; 8550 (34CrAlNi7) when a nitrided surface > 900 HV is required.
SAE 4140: complete guide
Medium-carbon alloy steel, not carbon steel
4140 is a chromium-molybdenum low-alloy steel with medium carbon (C 0.38 – 0.43%). That is why it is also called Cr-Mo steel. Chromium and molybdenum increase hardenability, that is, the depth that quenching reaches in the part. Manganese helps hardenability and acts as a deoxidizer. Chromium, close to 1%, does not make the steel stainless: in a humid environment the part needs oil, paint, nitriding or another coating.
Why it is so widely used in forgings
4140 forges well and responds predictably to quenching and tempering. Quenched and tempered, it resists impact, fatigue and deformation, which is why it is the base for shafts, connecting rods, pins and forged bodies. The final strength depends on the temper and the section: the larger the section, the lower the strength in the core. For large sections, SAE 4340 has more hardenability.
Annealing and machining
Forging, rolling and welding leave stresses and uneven hardness. Annealing at 820 – 850 °C, with slow furnace cooling, homogenizes the structure and lowers the hardness to at most 241 HB. In that condition 4140 machines well. Quenched and tempered (28 – 32 HRC), it machines with carbide. Dustre performs annealing, quenching and tempering in its own furnaces under its heat treatment service.
4140 for Petrobras studs and bolts ("4140 PET")
In orders for studs and threaded rod for Petrobras, 4140 sometimes appears as "4140 PET"*. This name is not a standard designation: what defines the material is the ASTM bolting specification. Supply requirements for flanged-joint bolting call for ASTM A193, A194, A320, A370 and A962, and 4140 is the chemical base of grades B7, B7M, L7 and L7M.
- A193 B7 (−48 to 540 °C): quenched and tempered Cr-Mo. Up to Ø 2½": tensile ≥ 860 MPa (125 ksi) and yield ≥ 724 MPa (105 ksi); Ø 2⅝ – 4": ≥ 795 / 655 MPa; Ø 4⅛ – 7": ≥ 690 / 515 MPa. Max. hardness 321 HBW / 35 HRC. A194 2H nut.
- A193 B7M (−48 to 350 °C): same steel, tempered at ≥ 620 °C, max. hardness 235 HBW / 99 HRB checked on 100% of parts, tensile ≥ 690 MPa (100 ksi). It is the option for H2S service (NACE MR0175 / MR0103). A194 2HM nut.
- A320 L7 (−100 to 250 °C): quenched and tempered 4140 for low temperature, same tensile properties as B7 up to Ø 2½" and Charpy ≥ 27 J (20 ft·lbf) at −101 °C. A194 grade 4 or 7 nut.
Usual purchasing requirements: rolled threads (not cut); stress relief 55 °C below the tempering temperature when threads are rolled after heat treatment; no coating unless zinc-nickel (ASTM B841) with hydrogen embrittlement relief (ASTM B850) is ordered; no zinc coating above 200 °C. The Petrobras standard for flange studs and nuts (N-2796*) and the current purchase requisition prevail. For diameters above 2½" at low temperature, see 4340 (A320 L43).
Frequently asked questions
What is the chemical composition of SAE 4140?
Per SAE J404 / ASTM A29: C 0.38 – 0.43; Mn 0.75 – 1.00; P ≤ 0.035; S ≤ 0.040; Si 0.15 – 0.35; Cr 0.80 – 1.10.
Which standards cover SAE 4140?
Bar (composition): SAE J404 / ASTM A29 / ABNT NBR NM 87. Quenched and tempered bar: ASTM A434 (classes BB, BC, BD). Forging: ASTM A668 / API 6A (75K) to customer specification. Mechanical tubing: ASTM A519. Plate: ASTM A829. Bolting: ASTM A193 B7 / B7M; A320 L7 / L7M; nuts A194 2H / 2HM / 4 / 7.
Up to what temperature can SAE 4140 be used?
Up to ≈ 400–450 °C without relevant loss of properties (always below the tempering temperature); B7 up to ≈ 450 °C. For H2S, limit to ≤ 22 HRC (NACE MR0175/ISO 15156).
Which materials can replace SAE 4140?
SAE 4340 for large sections or higher toughness; 4130 for better weldability; 4145H/modified 4145 for drill collars; 8550 (34CrAlNi7) when a nitrided surface > 900 HV is required.
Is 4140 a carbon steel?
No. It is a medium-carbon low-alloy steel, with 0.38 – 0.43% C, 0.80 – 1.10% Cr and 0.15 – 0.25% Mo (SAE J404 / ASTM A29). Chromium and molybdenum give the hardenability that plain carbon steel lacks.
Is 4140 steel weldable?
With restrictions. The high carbon equivalent (≈ 0.78) requires preheating of 200 – 320 °C, a low-hydrogen electrode, controlled interpass and stress relief or tempering right after welding.
Does 4140 resist corrosion?
Not like a stainless steel. The chromium in 4140 is close to 1% and does not form a passive layer. In a humid environment the part needs protection: oil, paint, nitriding or coating.
What is the difference between 4140 and 4340?
4340 has 1.65 – 2.00% nickel and greater hardenability. For the same reference (Ø 40 – 100 mm, quenched and tempered), 34CrNiMo6 has a yield strength ≥ 800 MPa, versus ≥ 650 MPa for 42CrMo4. Use 4140 in medium sections and 4340 in large sections or when the core needs more toughness.
What is 4140 PET steel?
It is the name used in orders for 4140 intended for Petrobras flange studs and bolts*. It is not a standard designation: the material should be ordered by the bolting specification, usually ASTM A193 B7 (B7M for H2S, A320 L7 for low temperature), with A194 2H, 2HM or 7 nuts and the supply procedure requirements (rolled threads, hardness, 3.1 certificate).
