5140 Alloy Steel: Composition, Properties, and Applications

5140 alloy steel is a chromium-based low-alloy steel known for its reliable strength, toughness, and hardenability combination. These characteristics make it a versatile choice for many engineering applications requiring dependable performance under stress. At Aobo Steel, we supply high-quality 5140 steel suitable for your manufacturing needs.

1. 5140 Alloy Steel Chemical Composition

The precise chemical composition of 5140 steel can vary slightly depending on the specific standard (e.g., SAE, ASTM). However, a typical composition includes:

Element	Carbon (C)	Silicon (Si)	Manganese (Mn)	Phosphorus (P)	Sulfur (S)	Chromium (Cr)
Minimum (%)	0.38	0.15	0.6			0.8
Maximum (%)	0.45	0.35	1	0.035	0.035	1.2

The key alloying element is Chromium (Cr), which significantly enhances the steel’s hardenability compared to standard carbon steels. This means 5140 can achieve greater hardness and strength through heat treatment.

2. 5140 Alloy Steel Heat Treatment and Mechanical Properties

The final mechanical properties of 5140 steel are highly dependent on the heat treatment applied. Understanding this process is crucial for achieving the desired performance in your components. Aobo Steel has extensive experience with tool and alloy steels, and we understand the importance of proper heat treatment.

2.1 Annealing

In its annealed condition, 5140 steel is softer and more ductile, making it easier to machine. Typical hardness in the annealed state ranges from 150-200 HB.

2.2 Quenching and Tempering

This is the most common heat treatment for 5140 to balance high strength, hardness, and toughness.

• Quenching: Involves heating the steel to an appropriate austenitizing temperature (around 850-870°C) and then cooling it rapidly.
• Tempering: Following quenching, the steel is reheated to a lower temperature and held for a set time. This process reduces brittleness and adjusts the final strength and hardness.

• Lower tempering temperatures result in higher strength and hardness.
• Higher tempering temperatures result in lower strength but improved ductility and toughness.
  • Hardness after quenching and tempering can typically range from 250 HB up to around 400 HB or more depending on the chosen tempering parameters. Tensile and yield strength will vary based on the heat treatment cycle used.

2.3 Hardenability

Thanks to its chromium content, 5140 steel exhibits good hardenability. This means it can achieve significant hardness at the surface and deeper into the material during quenching, which is beneficial for larger components or parts requiring consistent hardness throughout their cross-section.

3. 5140 Alloy Steel Equivalents to

• SAE/AISI: 5140
• ASTM: A29/A29M
• ISO: 683-1 (similar grade concept)
• DIN: 41Cr4 / 42Cr4 (Material No. 1.7035)
• JIS: SCR440

4. 5140 Alloy Steel Applications

The balanced properties of 5140 steel make it suitable for a wide range of components subjected to moderate-to-high stress and wear:

• Machinery Parts: Shafts, axles, gears, spindles, connecting rods.
• Automotive Components: Engine and transmission parts requiring good strength and wear resistance.
• Fasteners: High-strength bolts and studs.
• Tooling Components: Fixtures, jigs, and certain tool holders where good strength is needed (though not typically a primary cutting tool material).