AISI 4140 Alloy Steel Round Bar
AISI 4140 is a chromium-molybdenum alloy steel round bar with excellent hardenability, high strength, superior toughness, and good fatigue resistance. Diameter from 16mm to 800mm, available in hot rolled, normalized, annealed, and Q&T conditions for demanding applications in oil & gas, automotive, aerospace, and heavy machinery.
| Material | Alloy Steel (Cr-Mo) |
|---|---|
| Grade / Standard | AISI 4140 / SAE 4140 |
| Diameter | 16mm - 800mm |
| Length | 3m / 6m / 12m (or cut to length) |
| Delivery Condition | hot_rolled / normalized / quenched_tempered / annealed |
| Surface Treatment | bare / polished / coated |
| MOQ | 1 Ton |
| Delivery Time | 15-30 Days / Limited Stock |
| Loading Port | Tianjin / Shanghai / Qingdao |
Overview of AISI 4140 Alloy Steel Round Bar
AISI 4140 is one of the most versatile and widely specified alloy steel round bars in global engineering and manufacturing. Classified as a chromium-molybdenum (Cr-Mo) alloy steel with carbon content of 0.38-0.43%, chromium 0.80-1.10%, and molybdenum 0.15-0.25%, this grade delivers an exceptional combination of high strength, excellent toughness, superior hardenability, and good fatigue resistance. AISI 4140 round bar is the industry benchmark for components operating under high stress, impact loading, and demanding service conditions.
Shandong Tanglu Metal Material Co., Ltd. supplies premium AISI 4140 alloy steel round bar conforming to ASTM A829, AISI/SAE 4140, EN 42CrMo4 (1.7225), and GB/T 3077 42CrMo standards. Produced through advanced electric arc furnace (EAF) or ladle refining furnace (LF) steelmaking with vacuum degassing, our 4140 bars offer consistent chemistry, fine grain structure, and reliable mechanical properties from surface to core. Whether for oil & gas drilling equipment, heavy-duty gears, aerospace components, or high-performance automotive parts, AISI 4140 delivers the strength and reliability demanded by the most critical applications.
Key Features and Technical Advantages
The defining advantage of AISI 4140 alloy steel is its outstanding hardenability — the chromium and molybdenum alloying elements enable through-hardening in sections up to 75mm (3 inches) diameter with oil quenching, and even larger sections with water quenching. This ensures uniform mechanical properties from surface to core, eliminating the soft core problem common in carbon steels.
AISI 4140 round bar is manufactured through hot rolling, cold drawing, forging, and turning/peeling processes. Hot rolled and normalized bars provide a cost-effective starting material for subsequent machining and heat treatment. Quenched & tempered (Q&T) bars are supplied ready-to-machine or ready-to-use with tensile strength ranging from 850 MPa to 1080 MPa depending on section size and tempering temperature. The grade also responds exceptionally well to nitriding, achieving surface hardness up to HRC 60-65 for maximum wear resistance while maintaining a tough ductile core.
Our 4140 bars are available in diameter range from 16mm to 800mm, with standard lengths of 3m, 6m, and 12m. All bars undergo ultrasonic testing for internal soundness, and each heat is verified for chemical composition, mechanical properties, microstructure, and grain size. Custom heat treatment and surface grinding services are available to meet specific application requirements.
Main Applications of AISI 4140 Round Bar
AISI 4140 alloy steel round bar is the material of choice for the oil & gas industry, used extensively for drill collars, downhole tool components, mud motor shafts, stabilizer blades, and wellhead equipment. Its combination of high strength, toughness, and fatigue resistance makes it ideal for the extreme cyclic loading and impact conditions encountered in drilling operations.
In the automotive and motorsport sectors, 4140 is used for crankshafts, connecting rods, axle shafts, suspension components, steering linkage, and high-performance transmission gears. The aerospace industry relies on 4140 (and its vacuum-arc remelted variant 4140 VAR) for landing gear components, actuator shafts, and structural fasteners. Heavy machinery applications include hydraulic press cylinders, forging die inserts, injection mold bases, extrusion screws, press brake tooling, and heavy-duty coupling shafts.
Other key applications include high-strength bolts and studs (ASTM A193 B7, ASTM A320 L7), forging blanks for flanges and fittings (per ASTM A182 F11/F22), wind turbine main shafts and gearbox components, railway axle shafts and wheel sets, mining equipment drill rods and crusher shafts, and defense/military vehicle suspension and drivetrain components.
Why Choose Us for AISI 4140 Alloy Steel Round Bar
Shandong Tanglu Metal Material Co., Ltd. sources AISI 4140 alloy steel round bar from Tier-1 Chinese special steel mills with EAF/LF/VD steelmaking and continuous casting facilities. We maintain strict chemistry control within AISI 4140 specification limits, with particular attention to residual element control (Cu, Sn, As) and gas content (O₂ ≤ 20ppm, H₂ ≤ 2ppm, N₂ ≤ 80ppm) to ensure optimal toughness and fatigue performance.
We offer comprehensive heat treatment services including normalizing, annealing, quenching & tempering, stress relieving, and nitriding. Bars can be supplied in rough-turned, peeled, or precision-ground condition per customer requirement. With monthly supply capacity of 5,000 tons of alloy steel bars and export experience to over 50 countries, we support both standard stock sizes and custom project specifications. Each shipment includes original mill test certificate (MTC) per EN 10204 3.1 standard, with EN 10204 3.2 and third-party inspection (SGS, BV, TÜV, ABS, DNV, LR) available upon request.
📐 Dimension & Size Table
| Diameter (mm) | Length (m) | Weight (kg/m) | Tolerance (Hot Rolled) |
|---|---|---|---|
| 16 | 6 / 12 | 1.578 | ± 0.40mm |
| 20 | 6 / 12 | 2.466 | ± 0.40mm |
| 25 | 6 / 12 | 3.853 | ± 0.50mm |
| 30 | 6 / 12 | 5.549 | ± 0.50mm |
| 35 | 6 / 12 | 7.553 | ± 0.50mm |
| 40 | 6 / 12 | 9.864 | ± 0.60mm |
| 45 | 6 / 12 | 12.485 | ± 0.60mm |
| 50 | 6 / 12 | 15.413 | ± 0.80mm |
| 60 | 6 / 12 | 22.195 | ± 0.80mm |
| 70 | 6 / 12 | 30.210 | ± 1.00mm |
| 80 | 6 / 12 | 39.458 | ± 1.10mm |
| 90 | 6 / 12 | 49.940 | ± 1.20mm |
| 100 | 6 / 12 | 61.654 | ± 1.30mm |
| 120 | 6 / 12 | 88.780 | ± 1.50mm |
| 150 | 3 / 6 | 138.722 | ± 1.80mm |
| 180 | 3 / 6 | 199.759 | ± 2.20mm |
| 200 | 3 / 6 | 246.617 | ± 2.50mm |
| 250 | 3 / 6 | 385.339 | ± 3.50mm |
| 300 | 3 / 6 | 554.888 | ± 4.50mm |
| 400 | 3 / 6 | 986.467 | ± 6.00mm |
| 500 | 3 | 1541.354 | ± 8.00mm |
| 600 | 3 | 2219.549 | ± 10.0mm |
| 700 | 3 | 3021.040 | ± 12.0mm |
| 800 | 3 | 3945.827 | ± 14.0mm |
* Custom sizes available upon request. Tolerances per relevant international standards.
🔬 Chemical Composition
| Element | Min | Max | Display Value | Note |
|---|---|---|---|---|
| C | 0.38 | 0.43 | 0.38-0.43 | Per AISI 4140 specification |
| Mn | 0.75 | 1.00 | 0.75-1.00 | |
| Si | 0.15 | 0.35 | 0.15-0.35 | |
| Cr | 0.80 | 1.10 | 0.80-1.10 | Hardenability element |
| Mo | 0.15 | 0.25 | 0.15-0.25 | Hardenability element |
| P | - | 0.035 | ≤0.035 | |
| S | - | 0.040 | ≤0.040 | 0.025% max for improved toughness |
| Cu | - | 0.30 | ≤0.30 | Residual element |
| Ni | - | 0.30 | ≤0.30 | Residual element |
* Chemical composition may vary by heat, thickness and specification. Please refer to the actual mill test certificate.
⚙️ Mechanical Properties
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Tensile Strength (Normalized) | ≥850 | MPa | Normalized condition |
| Yield Strength (Normalized) | ≥655 | MPa | Normalized condition |
| Tensile Strength (Q&T) | 900-1080 | MPa | Quenched & tempered 540-650°C |
| Yield Strength (Q&T) | ≥750 | MPa | Q&T condition, ≤75mm section |
| Elongation | ≥14 | % | Gauge length 50mm, Q&T |
| Reduction of Area | ≥45 | % | Q&T condition |
| Brinell Hardness (Annealed) | 197-255 | HBW | Maximum annealed hardness |
| Brinell Hardness (Q&T) | 260-320 | HBW | Typical Q&T range |
| Impact Energy (Charpy V) | ≥35 | J | At 20°C, Q&T condition |
| Surface Hardness (Nitriding) | 60-65 | HRC | After gas/plasma nitriding |
| Fatigue Limit | ≥480 | MPa | 10⁷ cycles, Q&T condition |
| Modulus of Elasticity | 205-215 | GPa | Room temperature |
* Values shown are minimum requirements unless otherwise stated.
📦 Commercial Information
| Packaging | Standard seaworthy export packing. Alloy steel round bars bundled in hexagonal bundles with 4-6 high-strength steel strapping bands per bundle, weight typically 2-5 tons per bundle. Plastic or wooden end caps for bars over 60mm diameter. Each bundle clearly tagged with heat number, grade, diameter, length, and heat treatment condition. VCI (Volatile Corrosion Inhibitor) wrapping available for precision ground bars. Custom packaging including wooden crates for premium bars or air shipment. |
|---|---|
| Payment Terms | T/T (Telegraphic Transfer),L/C (Letter of Credit),D/P (Documents against Payment),Western Union |
| Price Term | FOB,CFR,CIF,EXW |
| Supply Capacity | 5,000 Tons/Month (Alloy Steel Bars) |
| Loading Port | Tianjin / Shanghai / Qingdao |
Why Choose Our AISI 4140 Alloy Steel Round Bar?
Superior Hardenability & Through-Thickness Strength
Chromium-molybdenum alloy system enables through-hardening in sections up to 75mm (oil quench) with uniform mechanical properties from surface to core, eliminating the soft core limitation of carbon steels.
Comprehensive Size Range & Conditions
Diameter from 16mm to 800mm with lengths 3m-12m. Available in hot rolled, normalized, annealed, Q&T, rough turned, peeled, and precision ground conditions to suit every stage of manufacturing.
Excellent Fatigue & Impact Resistance
High endurance limit (≥480 MPa at 10⁷ cycles) and superior Charpy impact toughness make AISI 4140 ideal for cyclically loaded components, shock-loaded parts, and safety-critical applications.
Nitriding Capability for Extreme Wear
Responds exceptionally to gas nitriding, plasma nitriding, and salt bath nitriding, achieving surface hardness HRC 60-65 with a tough ductile core. Ideal for wear-resistant surfaces on shafts and gears.
Mill Certified Quality & Full Traceability
EN 10204 3.1/3.2 certification with UT testing for internal soundness, complete chemistry, mechanical properties, microstructure, and grain size verification. Third-party inspection available.
🏭 Applications of AISI 4140 Alloy Steel Round Bar
AISI 4140 alloy steel round bar is the definitive material for high-stress, safety-critical applications across multiple industries. In oil & gas, it is used for drill collars, mud motor shafts, stabilizers, downhole tools, and wellhead components. The automotive and motorsport sectors rely on 4140 for crankshafts, connecting rods, axle shafts, suspension components, and high-performance transmission gears. Heavy machinery applications include hydraulic cylinders, forging dies, injection mold bases, extrusion screws, and heavy-duty coupling shafts. After nitriding, 4140 provides exceptional surface wear resistance for valve stems, piston rods, and pump components. The grade is also the primary raw material for high-strength fasteners (ASTM A193 B7, ASTM A320 L7) and forged flanges (ASTM A182 F11/F12/F22) used in pressure vessel and piping systems.
📋 Quality & Certification
Our Certifications
- ✅ ISO 9001:2015
- ✅ CE Marking
- ✅ ABS
- ✅ DNV GL
- ✅ Lloyd's Register (LR)
- ✅ Bureau Veritas (BV)
- ✅ SGS Certified
- ✅ NK
- ✅ RINA
Mill Certificate Type
- 📋 EN 10204 3.1
- 📋 EN 10204 3.2
- 📋 Original Mill Certificate
- 📋 Third Party Inspection Available
- 📋 Certificate of Origin
❓ Frequently Asked Questions
What is AISI 4140 alloy steel round bar?
AISI 4140 is a chromium-molybdenum (Cr-Mo) alloy steel round bar specified under AISI/SAE 4140 standard with carbon content 0.38-0.43%, chromium 0.80-1.10%, and molybdenum 0.15-0.25%. It is one of the most widely used alloy steel grades globally, offering an exceptional combination of high strength, excellent hardenability, superior toughness, and good fatigue resistance. The bar is suitable for high-stress shafts, gears, bolts, dies, and safety-critical components in oil & gas, automotive, aerospace, and heavy machinery industries.
What is the equivalent grade of AISI 4140?
AISI 4140 has equivalent grades in multiple international standards: SAE 4140 (US), ASTM A829 4140 (US), EN 42CrMo4 / 1.7225 (European EN 10083), DIN 42CrMo4 (German), JIS SCM440 (Japanese JIS G4105), GB 42CrMo (Chinese GB/T 3077), and BS 708M40 (British). These grades are generally considered equivalent and interchangeable for most applications, though exact verification against specific project requirements and standards is recommended, particularly for pressure equipment and aerospace applications.
What is the difference between AISI 4140 and AISI 4340?
The primary difference is the addition of nickel in AISI 4340 (1.65-2.00% Ni). This gives AISI 4340 significantly greater hardenability (through-hardens in sections up to 150mm), higher ultimate tensile strength (up to 1800 MPa in Q&T), and superior impact toughness at low temperatures. However, AISI 4340 is more expensive and may require more complex heat treatment. AISI 4140 is preferred for most general high-strength applications where through-hardening in sections ≤75mm is sufficient, offering the best balance of performance and cost among alloy steel grades.
What heat treatments are available for AISI 4140?
AISI 4140 responds well to: 1) Normalizing (850-900°C, air cool) — uniformizes grain structure. 2) Annealing (800-850°C, furnace cool) — softens for maximum machinability (HBW ≤217). 3) Quenching (oil quench 830-860°C) & Tempering (400-700°C) — achieves tensile 900-1080 MPa with controlled toughness. 4) Stress relieving (600-650°C) — reduces residual stresses after machining. 5) Nitriding (500-530°C, 20-100 hours) — achieves surface hardness HRC 60-65 without distortion. 6) Induction hardening — selective surface hardening for shaft journals. 7) Austempering — produces bainitic structure for superior toughness.
Can AISI 4140 be welded?
AISI 4140 can be welded, but requires careful procedures due to its alloy content and hardenability. Preheating to 200-300°C is essential, and interpass temperature should be maintained. Low-hydrogen welding consumables (such as E10018-D2 or ER80S-D2) are recommended. Post-weld heat treatment (PWHT) at 580-620°C is strongly advised to relieve stresses and restore toughness. Without proper preheat and PWHT, the heat-affected zone (HAZ) will form hard martensite, leading to cracking risk. For critical welded assemblies, consult with a welding engineer for specific WPS/PQR qualification.
What surface hardening methods are suitable for AISI 4140?
AISI 4140 responds exceptionally to: 1) Gas nitriding (500-530°C) — achieves HRC 60-65 surface with 0.2-0.5mm case depth, minimal distortion, excellent for precision shafts and gears. 2) Plasma/ion nitriding (380-550°C) — faster cycle, precise control, environmentally friendly. 3) Induction hardening — selective surface hardening (HRC 50-58) for shaft journals, bearing seats, and gear teeth. 4) Carburizing (850-950°C) — achieves HRC 58-62 with 0.5-2.0mm case depth, but risk of grain coarsening. 5) Carbonitriding — similar to carburizing but lower temperature, thinner case. Nitriding is generally preferred for 4140 as it provides the hardest surface with the least distortion.
What sizes and lengths are available for AISI 4140 round bar?
AISI 4140 alloy steel round bar is available in diameter range from 16mm to 800mm. Standard lengths include 3 meters, 6 meters, and 12 meters, with custom cut-to-length service supported. For diameters up to 250mm, standard hot rolled or cold drawn bars are available. For diameters 250-800mm, bars are typically forged and rough-turned. Precision ground bars are available in diameters 16-300mm with tolerance h6/h7/h9. Tolerance per ISO 286 or DIN 1013 depending on condition. Special lengths up to 18 meters available for selected sizes upon project request.
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