1. Overview

SAE 1521 is a typical medium-carbon and medium-manganese structural steel. According to the SAE (Society of Automotive Engineers) steel numbering system, "15" represents medium-carbon high-manganese steel, while "21" indicates a target carbon content of approximately 0.21%. This material offers excellent strength and toughness in its untreated state and achieves significantly enhanced hardness and wear resistance through heat treatment processes such as normalizing, quenching, and tempering.

（1）Chemical Composition (Typical Range, wt.%)

• Carbon (C): 0.18–0.23

• Manganese (Mn): 1.00–1.30

• Silicon (Si): ≤0.35

• Phosphorus (P): ≤0.040

• Sulfur (S): ≤0.050

The increase in manganese content helps improve hardenability and promotes the formation of stable austenitic structures at high temperatures.

（2）Microstructure

• Untreated: Predominantly pearlite and ferrite, a ferrite-pearlite structure.

• After Normalizing: Grain refinement and a more uniform microstructure.

• After Quenching: Predominantly martensitic structure, yielding higher hardness.

2. Mechanical Properties

（1）Hot Rolled State:

• Tensile Strength (σUTS, MPa): 450–600

• Yield Strength (σY, MPa): 280–350

• Elongation (ε, %): ≥25

• Brinell Hardness (HBW): 120–170

（2）After Normalizing:

• Tensile Strength (σUTS, MPa): 500–650

• Yield Strength (σY, MPa): 300–380

• Elongation (ε, %): ≥20

• Brinell Hardness (HBW): 140–190

（3）After Quenching and Tempering:

• Tensile Strength (σUTS, MPa): 800–950

• Yield Strength (σY, MPa): 550–700

• Elongation (ε, %): ≥12

• Brinell Hardness (HBW): 200–300

3. Heat Treatment Process Guidelines

（1）Normalizing:

• Heating Temperature: 850–900°C, air cooling.

• Purpose: Homogenize the structure, refine grain size, and improve machinability.

（2）Quenching:

• Heating Temperature: 850–880°C, oil or water quenching.

• Purpose: Form martensite to increase hardness and wear resistance, but toughness decreases.

（3）Tempering:

• Temperature Range: 150–600°C, depending on the desired hardness and toughness.

• Purpose: Stabilize martensite, relieve internal stresses, and enhance toughness and dimensional stability.

（4）Carburizing:

• Temperature: 900–950°C, surface carburization depth controlled by time.

• Purpose: Form a high-carbon surface layer, which after quenching, forms a hardened shell, while the core retains good toughness.

4. Machining and Welding Properties

• Machining: Best machinability in the normalized state. Stable cutting parameters can extend tool life.

• Cold Working: Suitable for general cold bending and stamping, but significant strain hardening occurs, requiring retained tempering.

• Welding: Moderate, preheating at 150–300°C is recommended, and post-weld heat treatment should be performed to prevent cracking.

5. Corrosion Resistance and Surface Treatment

• Corrosion Resistance: As a carbon steel, it has limited resistance to atmospheric and freshwater corrosion, easily oxidizing.

• Surface Protection: Common methods include painting, hot-dip galvanizing, phosphating, and chroming to extend service life.

6. Typical Applications

• Gears, Connecting Rods, Pins: Carburized or quenched and tempered parts used in high-wear, load-bearing components.

• Shafts: Such as drive shafts and half shafts, requiring good strength and toughness.

• Agricultural and Engineering Machinery: Plow tips, chain components, etc., requiring both wear resistance and impact toughness.

7. International Standards Comparison

• SAE: SAE 1521, Society of Automotive Engineers standard

• ASTM: A29 1521, part of ASTM A29 medium-carbon steel group

• UNS: G15210, general designation for ferritic carbon steel

• JIS: S22C, Japanese standard for medium-carbon steel, slightly lower manganese content

• EN: C22E (1.1151), European standard for low-alloy steel, composition differences to be confirmed

8. Conclusion

SAE 1521 carbon steel, designed with medium carbon and adequate manganese content, offers good strength and toughness in its untreated state. By undergoing various heat treatments, its hardness and wear resistance can be significantly improved. Widely used in automotive, mechanical manufacturing, and agricultural equipment sectors, it is an excellent choice for components that require a balance of performance and cost.

9. Preferred Material Choice, Trust in Bolaisheng

As a professional supplier of carbon steel and alloy materials, Shanghai Bolaisheng Metal Products Co., Ltd. is committed to providing high-performance, stable-quality carbon steel products, including SAE 1521 among our extensive inventory. We offer customized processing, material certification, and fast delivery services to meet diverse customer needs.

We are not only a material supplier but your reliable partner in metal solutions.
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