4Cr13 stainless steel is a martensitic stainless steel widely used in industrial and daily applications due to its good combination of hardness, corrosion resistance, and wear resistance. Below is a detailed overview:
1. Chemical Composition
The main chemical components (weight percentage) of 4Cr13 are:
Chromium (Cr): 12.00% – 14.00% (the core element for corrosion resistance, forming a passive oxide film on the surface)
Carbon (C): 0.36% – 0.45% (high carbon content promotes martensitic transformation, enhancing hardness after heat treatment)
Silicon (Si): ≤0.60%
Manganese (Mn): ≤0.80%
Phosphorus (P): ≤0.035%
Sulfur (S): ≤0.030%
Iron (Fe): Balanced
2. Mechanical Properties
The mechanical properties of 4Cr13 are significantly influenced by heat treatment. Typical values are as follows:
Property Annealed State Quenched and Tempered State
Tensile strength ≥590 MPa ≥1000 MPa
Yield strength ≥345 MPa ≥800 MPa
Elongation (in 50mm) ≥18% ≥10%
Hardness ≤201 HB (Rockwell B ≤93) 40 – 48 HRC (varies with tempering)
3. Physical Properties
Density: ~7.75 g/cm³
Melting point: 1470 – 1510°C
Thermal conductivity: ~25 W/(m·K) (at room temperature)
Coefficient of thermal expansion: ~10.5 × 10⁻⁶/°C (20 – 100°C)
Magnetic: Yes (due to its martensitic structure)
4. Key Characteristics
High Hardness and Wear Resistance: After quenching and tempering, it achieves high hardness (40 – 48 HRC), making it suitable for wear-resistant parts.
Moderate Corrosion Resistance: The chromium content (12% – 14%) forms a protective oxide film, enabling it to resist corrosion in atmospheric, fresh water, and weak acid/alkali environments. However, it is less resistant than austenitic stainless steels (e.g., 304) and is prone to rust in high-chloride or strong acid environments.
Heat Treatability: It can be hardened through quenching and tempering, allowing adjustment of hardness and toughness to meet different application requirements.
Machinability: In the annealed state, it has good machinability; however, the hardened state is difficult to machine and usually requires grinding.
5. Heat Treatment Processes
Annealing: Heat to 800 – 900°C, hold for 2 – 4 hours, then cool slowly in the furnace. This process softens the material, reduces internal stress, and improves machinability.
Quenching: Heat to 1050 – 1100°C, hold until fully austenitized, then quench in oil or water. This step transforms the structure into martensite, significantly increasing hardness.
Tempering: Reheat the quenched material to 200 – 700°C (depending on desired performance), hold, and cool. Low-temperature tempering (200 – 300°C) retains high hardness; medium-temperature tempering (400 – 500°C) balances hardness and toughness; high-temperature tempering (600 – 700°C) reduces hardness but improves ductility.
6. Typical Applications
Cutting Tools: Scissors, knives, blades, and surgical instruments (benefiting from high hardness and moderate corrosion resistance).
Mechanical Components: Valves, pump shafts, bearings, and bushings (for wear resistance and corrosion resistance in general environments).
Daily Hardware: Kitchen utensils, hardware tools, and watch cases (balancing durability and appearance).
Mold Industry: Small molds requiring certain corrosion resistance and wear resistance.
7. Limitations
Corrosion Resistance: Not suitable for harsh environments such as seawater, strong acids, or high-chloride solutions (e.g., swimming pool water), as it may suffer pitting or rusting.
Weldability: Welding is difficult due to its high carbon content, which can lead to cracking in the heat-affected zone. Pre-heating and post-weld annealing are usually required if welding is necessary.
High-Temperature Performance: Long-term use at temperatures above 300°C may reduce its mechanical properties and corrosion resistance.
In summary, 4Cr13 stainless steel is a cost-effective martensitic stainless steel, ideal for applications requiring high hardness, moderate corrosion resistance, and wear resistance, such as cutting tools, mechanical parts, and daily hardware. Its performance can be flexibly adjusted through heat treatment to adapt to different working conditions.