Carbon Steel Grade 40 AISI 1040 JIS S40C
Carbon Steel Grade 40 is a widely used medium-carbon steel with good strength, toughness, machinability, and reliable heat treatment performance. It is commonly used for gears, shafts, connecting rods, bolts, and other mechanical parts that require balanced mechanical properties, moderate load capacity, and cost-effective performance in general engineering and industrial applications.
Product Description
Xiri Tool Steel is a leading supplier of 40 carbon steel in China. 40 steel is a widely used medium-carbon high-quality carbon structural steel, featuring excellent comprehensive mechanical properties and machinability. However, its hardenability is relatively low. It is commonly used to manufacture mechanical parts such as gears, shafts, connecting rods, and bolts that bear moderate loads. These parts can be used after quenching and tempering treatment or undergo surface hardening to enhance their wear resistance.
Whether you need 40# flat bars, steel plates, or round bars, we provide custom dimensions with machining or grinding services. Our materials are strictly tested to ensure premium metallurgical structure.
Carbon Steel Grade 40 is a high-quality medium-carbon steel. Its designation originates from the Chinese national standard GB/T 699, where ‘40’ denotes an average carbon content of 0.40%. This carbon content range (0.37%–0.44%) underpins all its outstanding properties, striking a perfect balance between the malleability of low-carbon steel and the rigidity of high-carbon steel. This makes it a true all-rounder.
Chemical Composition of Carbon Steel Grade 40
| C | Si | Mn | P | S |
| 0.37-0.45 | 0.17-0.37 | 0.70-1.00 | ≤0.035 | ≤0.035 |
Supply Form & Size Range of Carbon Steel Grade 40
We supply Carbon Steel Grade 40 in various forms to meet your manufacturing needs:
Round bar: Diameter 16mm – 1000mm
Steel Plate / Flat: Thickness 16mm – 800mm x Width 200mm – 2000mm
Surface: Black, Peeled, Rough machined or Grinded.
Core Performance of Grade 40 Carbon Steel
A material’s market appeal ultimately hinges on its properties. Grade 40 carbon steel’s enduring popularity stems from its ‘golden combination’ of performance characteristics:
- Superior Strength and Hardness: Following normalising or quenching and tempering heat treatment, Grade 40 carbon steel exhibits significantly enhanced strength and hardness. This enables it to withstand substantial loads and stresses without deformation or fracture, making it particularly suitable for manufacturing critical components subjected to alternating stresses, such as shafts, gears, and connecting rods.
- Good plasticity and toughness: Compared to higher-carbon steels, 40 carbon steel maintains considerable plasticity and toughness alongside its high strength. Its elongation after fracture (δ5) can reach 19%, ensuring the material undergoes deformation rather than sudden brittle fracture upon impact. This provides a degree of deformation buffer, enhancing safety and reliability in use.
- Outstanding machinability: The cutting performance of medium-carbon steels is a key advantage. Grade 40 carbon steel possesses moderate hardness, exhibits excellent chip breaking during machining, causes relatively low tool wear, and achieves high surface finish. This directly translates to increased machining efficiency on your production line, reduced tooling costs, and superior surface quality of your products.
- Reliable heat treatment capability: 40 carbon steel responds sensitively to heat treatment processes such as quenching, tempering (normalising), and normalising. Through different heat treatment pathways, you can flexibly ‘customise’ its final properties—whether requiring higher surface hardness (via surface hardening) or core properties combining strength and toughness (via tempering), 40 carbon steel can meet your requirements.
- Economy and accessibility: As one of the most widely used carbon structural steels, Grade 40 benefits from mature production processes, high output volumes, and cost advantages over alloy steels. This makes it an ideal choice for achieving optimal economic efficiency while maintaining performance.
Extensive Application Fields of Grade 40 Carbon Steel | The Pervasive Backbone of Industry
The balanced properties of 40 carbon steel render it ubiquitous across virtually all heavy industries and high-end manufacturing sectors:
Automotive Manufacturing: Engine crankshafts, camshafts, connecting rods; transmission gears, drive shafts; and various high-strength bolts are classic applications of 40 carbon steel subjected to quenching and tempering.
Machinery and Machine Tools: As the ‘mother machine of industry,’ critical transmission components in machine tools—such as guide rods, lead screws, spindles, gears, and worms—are extensively manufactured from 40 carbon steel to ensure precision and stability.
Moulds and Fixtures: For plastic moulds, die-casting mould bases, and various fixtures requiring moderate strength and wear resistance without stringent demands, 40 carbon steel offers exceptional value for money.
Heavy Mining Machinery: Heavy components like rollers, shafts, and gears in mining machinery endure immense impact and abrasion, where Grade 40 carbon steel’s strength and toughness provide essential resilience.
General Hardware and Structural Components: From high-strength pins and connecting rods to various bases and brackets, Grade 40 carbon steel is ubiquitous in applications demanding ‘robust durability’.
Our advantages in Processing Grade 40 Carbon Steel
We fully recognise that consistent material quality forms the bedrock of smooth production lines and reliable end products for our customers. Consequently, every batch of Grade 40 carbon steel leaving our premises undergoes a rigorous, end-to-end quality assurance system:
- Rigorous Source Selection and Refined Ingots: Employing advanced techniques such as Ladle Furnace Refining (LF) and vacuum degassing, we effectively reduce harmful impurities like phosphorus and sulphur, along with gas content in molten steel, establishing a high-quality foundation through precise chemical composition control.
- Precision rolling, microstructure control: We strictly regulate rolling temperature, deformation, and cooling rates. Through controlled rolling and cooling techniques, we ensure the steel achieves a uniform, fine-grained microstructure. Grain size is pivotal in determining a steel’s strength and toughness; fine grains signify higher strength and superior toughness.
- End-to-End Non-Destructive Testing: From continuous cast billets to finished steel products, we employ non-destructive testing techniques such as ultrasonic flaw detection to examine potential internal defects including shrinkage cavities, white spots, and cracks. This ensures material internal density and eliminates any potential safety hazards.
- Comprehensive Physical and Chemical Testing: Our laboratory is equipped with a full suite of testing apparatus. Each batch of steel undergoes:
Chemical composition spectral analysis: Ensuring precise compliance with elements including C, Si, Mn, P, and S.
Mechanical property testing: Measuring tensile strength, yield strength, elongation, impact energy, and Brinell/Rockwell hardness on universal testing machines, impact testers, and hardness testers to guarantee performance data fully meets or exceeds national standards.
Metallographic Analysis: High-magnification microscopy examines microstructures (e.g., pearlite, ferrite distribution, grain size) to evaluate heat treatability and ultimate service performance at the microscopic level.
- Traceable Identification and Management: We maintain a comprehensive product traceability system. Each bundle and individual piece of steel bears clear identification, ensuring full information transparency throughout the entire process—from order placement to production, inspection to shipment—delivering 100% quality assurance.
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Why Manufacturers Choose Huangshi Xiri
Huangshi Xiri combines international-standard steel grades, a complete tool steel portfolio, strict quality control and reliable global supply. We match DIN / JIS / AISI equivalents precisely, offer cutting and heat-treatment services, and control every step from smelting to inspection. With stable capacity, on-time delivery and responsive technical support, we help manufacturers reduce risk, save costs and run production with confidence.
Contact Us
Contact Huangshi Xiri today for quotations, grade selection and technical support on tool steel, mold steel and alloy steel. Whether you need samples, cutting-to-size service or long-term supply for your projects, our engineers and sales team are ready to respond quickly with professional advice and reliable solutions for your manufacturing needs.
