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65Mn chemical composition and mechanical properties
Introduction to the Chemical Composition, Mechanical Properties, and Main Applications of 65Mn Steel
65Mn is a high-quality carbon spring steel that contains manganese as an alloying element. The addition of manganese improves the hardenability of the steel, allowing it to be hardened effectively in oil even for components with a diameter of 12mm. Compared to silicon steel, 65Mn has less surface decarburization, making it ideal for applications where surface integrity is crucial. After heat treatment, 65Mn exhibits better overall mechanical properties than plain carbon steel, though it is prone to overheating sensitivity and temper embrittlement.
This type of steel is widely used in the production of various springs, such as flat springs, round springs, leaf springs, valve springs, clutch reeds, brake springs, and cold-drawn coil springs. It is also suitable for manufacturing parts like spring rings, grinding machine spindles, and spring chucks. Due to its excellent elastic limit, strength limit, yield ratio, fatigue resistance, and anti-relaxation properties, 65Mn is preferred in applications requiring high durability and performance under repeated stress.
In terms of chemical composition, 65Mn contains:
- Carbon (C): 0.62–0.70%
- Silicon (Si): 0.17–0.37%
- Manganese (Mn): 0.90–1.20%
- Sulfur (S): ≤0.035%
- Phosphorus (P): ≤0.035%
- Chromium (Cr): ≤0.25%
- Nickel (Ni): ≤0.30%
- Copper (Cu): ≤0.25%
Mechanically, 65Mn offers impressive properties:
- Tensile strength (σb): ≥980 MPa (100)
- Yield strength (σs): ≥784 MPa (80)
- Elongation (δ10): ≥8%
- Reduction of area (ψ): ≥30%
- Hardness: ≤302HB (hot rolled), ≤321HB (cold drawn + heat treated)
The recommended heat treatment process involves quenching at 830°C ± 20°C in oil, followed by tempering at 540°C ± 50°C (or ±30°C if specified). When delivered, hot-rolled 65Mn can be in either heat-treated or non-heat-treated condition, while cold-drawn material is typically supplied in a heat-treated state.
In addition to its mechanical advantages, 65Mn is known for its good metallurgical quality, uniform structure, and minimal surface defects. This makes it suitable for precision applications such as machine tool screws, cutting tools, and bearing collars. Its ability to maintain performance under high wear conditions also makes it a popular choice in railway tracks and other heavy-duty environments.
Overall, 65Mn is a versatile and reliable steel grade, especially for spring and high-stress components where strength, elasticity, and durability are essential.
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