Stainless Steel (Martensitic) (Fe+Cr+C)
Martensitic stainless steels are chromium-based (11.5–18% Cr) alloys with sufficient carbon (0.1–1.2%) to allow hardening by heat treatment. They achieve the highest hardness and strength of any stainless steel family — up to 60 HRC and 1,900 MPa — making them essential for cutlery, surgical instruments, turbine blades, and bearing applications. Their corrosion resistance is moderate compared to austenitic grades.
Properties
- Density
- 7,650–7,800 kg/m³
- Melting Point
- 1,400–1,480 °C
- Boiling Point
- ~2,750 °C
- Thermal Conductivity
- 24–29 W/(m·K)
- Electrical Resistivity
- 5.5–7.2 × 10⁻⁷ Ω·m
- Tensile Strength
- 500–1,900 MPa
- Yield Strength
- 275–1,600 MPa
- Hardness
- 20–60 HRC (heat-treatment dependent)
- Elongation
- 2–20%
- Crystal Structure
- BCT (Martensite)
Common Grades
- 410 (1.4006): General-purpose martensitic — 12% Cr, 0.15% C max. Pump shafts, valves, fasteners. Hardened to 35–40 HRC.
- 420 (1.4021): Higher carbon (0.3% C) for better hardness — 50–55 HRC. Surgical instruments, cutlery, plastic mold tooling.
- 440C (1.4125): High-carbon (1.0% C), highest hardness — 58–60 HRC. Bearings, knife blades, nozzles, valve seats.
- 17-4PH (1.4542): Precipitation-hardening grade — 17% Cr, 4% Ni, 4% Cu. Aerospace fasteners, turbine blades, nuclear components. Hardened by aging, not quenching.
Applications
- Cutlery & Blades: Kitchen knives, pocket knives, scissors, razor blades, industrial cutting tools
- Medical: Surgical scalpels, dental instruments, orthopedic implants (limited), forceps
- Turbomachinery: Steam turbine blades, compressor blades, hydroelectric runner wheels, pump impellers
- Oil & Gas: Valve stems, gate and ball valves, pump shafts, downhole tools (13Cr grades)
- Bearings: Ball and roller bearings (440C), races, precision shafts, wear-resistant components
FAQ
What makes martensitic stainless steel different from austenitic?
Martensitic grades can be hardened by heat treatment to very high hardness (up to 60 HRC) due to their higher carbon content and martensitic crystal structure. Austenitic grades cannot be hardened by heat treatment — they are always soft and ductile. However, martensitic grades sacrifice corrosion resistance and ductility for their superior hardness and wear resistance.
What is 17-4PH stainless steel?
17-4PH (Precipitation Hardening) is a unique martensitic grade that hardens through aging rather than quenching. It combines high strength (1,100–1,300 MPa), moderate corrosion resistance, and excellent toughness. It is hardened at low temperatures (480–620°C), minimizing distortion — making it ideal for precision aerospace and nuclear components.
Can martensitic stainless steel be welded?
Yes, but with significant precautions. Preheating (200–350°C), controlled interpass temperatures, and mandatory PWHT are required to prevent hydrogen-induced cracking in the martensitic HAZ. For less critical applications, austenitic filler metals (309L) can be used to create a ductile weld deposit, avoiding HAZ cracking issues.