1. High Strength and Hardness
Carbon-Dominated Performance: Carbon content (0.1%~1.2%) directly determines hardness and strength. Quenching and tempering treatments form a high-hardness martensitic microstructure.
Low-Carbon Types (e.g., 410, 420): Hardness reaches HRC 40~50, suitable for wear-resistant components (e.g., pump shafts, valves).
High-Carbon Types (e.g., 440C, ZDP-189): Hardness exceeds HRC 60, ideal for high-end cutting tools and precision molds.
Strengthening Mechanisms: Achieves ultrahigh strength (tensile strength: 1800~2000 MPa) via carbide precipitation (e.g., Cr<sub>23</sub>C<sub>6</sub>) and dislocation strengthening.
2. Controllable Corrosion Resistance
Chromium-Based Passive Layer: Chromium content (12%~18%) forms a Cr-oxide passive layer, but high carbon reduces passivation efficiency, resulting in lower corrosion resistance compared to austenitic stainless steels.
Mild Corrosive Environments: Suitable for dry air or freshwater applications (e.g., 420 stainless steel for cutlery).
Harsh Environment Limitations: Avoid prolonged exposure to chlorides (seawater) or strong acids. Protective coatings (e.g., chromium plating) or surface nitriding can enhance resistance.
3. Heat Treatment Sensitivity
High Hardenability: Full martensitic transformation is achievable through rapid cooling (oil/air quenching), even in thick-section components (e.g., turbine blades).
Tempering Adjustability:
Low-Temperature Tempering (150~370°C): Retains high hardness for tools and bearings.
High-Temperature Tempering (540~700°C): Enhances toughness for structural parts (e.g., automotive drive shafts).
4. Magnetism
Ferromagnetic Material: The martensitic structure is magnetic, making it suitable for electromagnetic devices (e.g., motor housings, sensor casings). Note: Magnetism may weaken at elevated temperatures.
5. Machining Characteristics
Cold Working Challenges: High hardness increases cracking risk during cold forming. Preheating or hot working (forging at 800~1150°C) is often required.
Welding Difficulties: Post-weld cold cracking necessitates:
Preheating (200~300°C)
Compatible filler materials (e.g., AWS E410 electrodes)
Post-weld slow cooling or stress-relief tempering
6. Temperature Sensitivity
High-Temperature Limitations: Long-term service temperature should not exceed 650°C to avoid temper embrittlement or oxidation (surface coatings recommended).
Low-Temperature Brittleness: Impact toughness drops significantly below -50°C, making it unsuitable for extreme cold environments.
Typical Applications & Property Matching
| Property | Applications | Representative Grades |
|---|---|---|
| Ultrahigh Hardness | Surgical blades, precision tools | 440C, ZDP-189 |
| Wear Resistance | Bearings, pump/valve components | 420C, 440B |
| Moderate Corrosion + Strength | Turbine blades, fasteners | 410, 416 |
| Biocompatibility | Orthopedic implants (after surface modification) | 630 (17-4PH) |
Key Considerations
Material Selection: Balance hardness and corrosion resistance. High-carbon grades (e.g., 440C) are unsuitable for prolonged humid environments.
Process Control: Precise heat treatment parameters (quenching rate, tempering duration) are critical to avoid intergranular corrosion or brittle phase formation.
Martensitic stainless steel offers a "performance-tailored" solution for mechanical engineering, medical devices, and other industries by balancing strength, corrosion resistance, and cost through compositional and process optimization.