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Martensitic Stainless Steel: Definition, Composition, Properties, Grades, Applications, and More
- John
What Is Martensitic Stainless Steel?
Martensitic stainless steel is a type of stainless steel with a body-centered tetragonal (BCT) crystal structure covered by the 400 series alongside ferritic stainless steel. It is primarily composed of 12-18% chromium and 0.1-1.2% carbon. Martensitic stainless steel can be hardened and strengthened by heat treatment for enhanced performance, but its corrosion resistance is generally lower than austenitic stainless steel.
It is widely used in cutlery, surgical instruments, valves, bearings, turbine blades, etc., where high strength and wear resistance are required. Martensitic stainless steel is part of the stainless steel family, which includes austenitic, ferritic, duplex, and precipitation hardening.
Chemical Composition of Martensitic Stainless Steel
Martensitic stainless steel is mainly made of iron, chromium, and carbon. It typically contains 12% to 17% chromium (Cr), which helps resist rust and corrosion. The amount of carbon (C) can vary from 0.1% to 1.2%.
The steel with up to 0.4% carbon is usually used in parts like pumps, valves, and shafts because of its strength. If more than 0.4% carbon, it’s more suitable for things that need to resist wear, such as knives, surgical blades, and molds.
Unlike the austenitic type, which is essentially chromium-nickel alloy, martensitic stainless steel usually doesn’t contain nickel (Ni), except for several specific grades. For example, nickel is added in 431 (1.4057) to increase toughness and ductility and in 1.4418 for better corrosion resistance (also the highest of all martensitic grades).
Other elements like boron (B), cobalt (Co), niobium (Nb), and titanium (Ti) can be added to improve performance at high temperatures.
Properties of Martensitic Stainless Steel
Martensitic stainless steel is a very special type of stainless steel. Here are three major reasons that make it unique:
- Very high strength and hardness after heat treatment.
- Magnetic, unlike austenitic stainless steel.
- Good wear resistance and moderate corrosion resistance.
Check the table below for the key properties of martensitic stainless steel:
| Property | Description | Performance | Remarks |
| Strength | Ability to withstand an applied force without failure. | High strength, especially in hardened and tempered conditions. | Martensitic steels have high tensile and creep strength, suitable for high-stress applications. |
| Hardness | Resistance to deformation or indentation. | Very high, especially after heat treatment, can reach up to 60 HRC. | Hardness increases with carbon content; secondary hardening occurs at 450-500°C. |
| Corrosion Resistance | Ability to resist deterioration due to chemical reactions. | Moderate, lower than austenitic grades. | Optimum corrosion resistance is attained in the hardened and tempered condition. |
| Heat Resistance | Ability to maintain performance at elevated temperatures. | Fair heat resistance, moderate for high-temperature applications. | Suitable for temperatures around 600°C in power generation and other industries. |
| Magnetic Properties | Attraction to a magnetic field. | Magnetic due to the martensitic structure. | Martensitic stainless steels exhibit magnetic properties similar to plain carbon steels. |
| Formability | Ease of being formed or shaped without cracking. | Limited, prone to cracking due to hardness and brittleness. | Forming processes usually require annealing to avoid cracking and stress. |
| Weldability | Ease of being welded without defects. | Poor weldability due to hardening during welding. | Preheating (400-600°F) and interpass temperature control are necessary to prevent cracking. |
| Machinability | Ease of being cut or shaped using machines. | Good machinability, particularly in the annealed or tempered condition. | Machining is easier in the softened (annealed) state; sulfur additions in 416 improve machinability. |
| Brittleness | Tendency to fracture or break with little deformation. | Can be brittle, especially after hardening without tempering. | Increased brittleness due to high hardness; tempering reduces brittleness and improves toughness. |
Advantages and Disadvantages of Martensitic Stainless Steel
Here are the advantages and benefits of martensitic stainless steel:
- High strength and hardness.
- Good wear resistance.
- Resistant to corrosion in mild environments.
- Can be heat treated for improved properties.
- Suitable for cutting tools and blades.
Disadvantages and limitations are listed below:
- Poor weldability.
- Susceptible to brittleness at low temperatures.
- Limited corrosion resistance in harsh environments.
- Requires precise heat treatment to avoid cracking.
- Less ductile than other stainless steel.
Heat Treatment and How Does Martensitic Structure Form in Stainless Steel?
The martensitic structure in stainless steel is formed by heating the steel to form austenite and then rapidly cooling (quenching) it, causing a diffusionless transformation of austenite into hard, brittle martensite.
Here’s how it happens:
1. Heating to Form Austenite (Austenitising)
Heat the steel to a high temperature, typically between 925°C – 1070°C (1700°F – 1950°F). At this temperature:
- The steel’s structure becomes austenitic, meaning the iron atoms arrange themselves in a face-centered cubic (FCC) lattice.
- Carbon atoms dissolve uniformly within this lattice.
2. Rapid Cooling (Quenching)
After reaching the desired temperature, the steel is rapidly cooled, or quenched, usually in:
- Oil
- Air
- Water
The choice of quenching medium depends on the specific alloy and desired properties.
3. Formation of Martensite
During quenching:
- The rapid cooling prevents carbon atoms from diffusing out of the iron lattice.
- As the temperature drops below the martensite start temperature (Ms), typically around 300°C to 400°C (570°F to 750°F), the austenitic FCC structure begins to transform into a body-centered tetragonal (BCT) structure, known as martensite.
- The transformation continues as the temperature decreases toward the martensite finish temperature (Mf), which can be below room temperature, sometimes as low as 150°C to 200°C (300°F to 390°F) below the Ms temperature.
- This transformation is a diffusionless process, meaning atoms shift positions without long-range diffusion.
4. Tempering to Improve Toughness
To mitigate brittleness:
- The steel undergoes tempering, which involves reheating to a lower temperature (typically between 200°C – 600°C).
- Tempering allows some lattice stresses to relax and precipitate carbides, enhancing toughness without significantly reducing hardness.
Martensitic Stainless Steel Grades
Take a look at the common grades in the martensitic stainless steel family:
| Grade | Equivalent Grade | Description | Application |
| 403 | EN 1.4003 / UNS S40300 | Martensitic stainless steel with controlled composition and 12% Chromium (Cr), designed for high-stress, high-temperature environments such as turbine components and compressors. | Steam turbine parts, compressor components, aerospace parts, high-temp blades |
| 410 | EN 1.4006 / UNS S41000 | Basic martensitic stainless steel with 12% Chromium (Cr), known for moderate corrosion resistance and good hardness after heat treatment. | Fasteners, turbine blades, cutlery, valve components |
| 416 | EN 1.4005 / UNS S41600 | Free-machining martensitic stainless steel with added Sulfur (S) for improved machinability, but with slightly reduced corrosion resistance and strength. | Gears, shafts, axles, screws |
| 416Se | AISI 416Se | Free-machining martensitic stainless steel with Selenium (Se) for enhanced machinability, providing a smoother surface finish compared to sulfur-based counterparts. | Screws, bolts, nuts, valve seats |
| 420 | EN 1.4021 / UNS S42000 | High Carbon (C) martensitic stainless steel that offers improved strength, hardness, and wear resistance after heat treatment. | Surgical instruments, cutlery, gears, valve parts |
| 420F | EN 1.4028 + S / UNS S42020 | Martensitic stainless steel with added Phosphorus (P) and Sulfur (S) for enhanced machinability, commonly used in high-speed machining applications. | Machined parts, pumps, valve components, screws |
| 431 | EN 1.4057 / UNS S43100 | Martensitic stainless steel with Nickel (Ni) for enhanced corrosion resistance, known for its high strength and toughness, especially in marine environments. | Aircraft parts, marine bolts, propeller shafts, pump shafts |
| 431F | AISI 431F | Free-machining version of 431 with added sulfur or selenium for enhanced machinability. | Valve components, pump shafts, parts requiring corrosion resistance and machinability. |
| 440A | EN 1.4109 / UNS S44002 | Martensitic stainless steel with even lower Carbon (C) than 440B, offering improved toughness and better corrosion resistance, though with reduced hardness. | Hunting knives, surgical scalpels, ball bearings, cutting tools |
| 440B | EN 1.4112 / UNS S44003 | Martensitic stainless steel with slightly lower Carbon (C) than 440C, providing a balance between hardness and improved toughness. | Knife blades, chisels, industrial valves, cutting tools |
| 440C | EN 1.4125 / UNS S44004 | High Carbon (C) martensitic stainless steel providing maximum hardness and wear resistance, with Chromium (Cr) for moderate corrosion resistance. | Bearings, knives, molds, surgical tools |
| 440F | EN 1.4104 / AISI 440F | Free-machining version of 440A with added sulfur for improved machinability. | Cutlery, surgical tools, knives, applications needing wear resistance and machinability. |
| 422 | EN 1.4935 / UNS S42200 | Martensitic stainless steel with added Molybdenum (Mo), Vanadium (V), and Tungsten (W), providing high strength and excellent heat resistance at elevated temperatures. | Turbine blades, aerospace parts, high-temperature bolts, fasteners |
| 17-4 PH | EN 1.4542 / UNS S17400 | *Precipitation-hardening stainless steel with a martensitic matrix offering high strength and moderate corrosion resistance. | Aerospace components, turbine blades, high-performance equipment requiring strength and corrosion resistance. |
*1.4418 has the highest corrosion resistance of all martensitic stainless steel, which isn’t listed in the table above.
What Is the Most Common Martensitic Stainless Steel Grade?
Grade 410 is the most common martensitic stainless steel due to its balance of good corrosion resistance, high strength, and hardness. It is also widely available and cost-effective, making it suitable for a wide range of applications.
Applications of Martensitic Stainless Steel
Here are some common industries and applications of martensitic stainless steel:
| Industry | Application |
| Automotive | Engine components, exhaust systems, fuel injectors, valves, etc. |
| Aerospace | Landing gear, fasteners, structural components, turbine blades, etc. |
| Medical | Surgical instruments, dental tools, orthopedic implants, scalpels, etc. |
| Oil & Gas | Pump shafts, valve parts, pipelines, wellhead components, etc. |
| Power Generation | Turbine blades, pump components, steam generators, valve seats, etc. |
| Defense | Gun barrels, knives, armor plating, missile components, etc. |
| Chemical Processing | Pumps, valves, heat exchangers, reactor components, etc. |
| Food Processing | Blades, cutting tools, meat grinders, conveyor belts, etc. |
Is Martensitic Stainless Steel Good for Knives?
Yes, martensitic stainless steel is good for knives due to its hardness, wear resistance, and ability to hold a sharp edge.
Martensitic vs. Austenitic vs. Ferritic vs. Duplex vs. Precipitation Hardened Stainless Steel
Compare the five classes of stainless steel in the table below:
| Property | Martensitic Stainless Steel | Austenitic Stainless Steel | Ferritic Stainless Steel | Duplex Stainless Steel | PH Stainless Steel |
| Crystal Structure | Martensitic (BCT) | Austenitic (FCC) | Ferritic (BCC) | Austenitic + Ferritic, usually 50% + 50% | Martensitic or Austenitic + Precipitation Hardening |
| Mechanical Strength | High strength, high hardness | High toughness, good ductility | Moderate strength, good toughness | High strength, superior fracture resistance | Very high strength after heat treatment |
| Corrosion Resistance | Moderate, prone to corrosion in harsh environments | Excellent, especially in acidic and chloride environments | Good, especially in oxidizing environments | Excellent, especially in chloride and marine environments | Good, but less than austenitic or duplex types |
| Weldability | Poor, requires pre- and post-heat treatment | Excellent, minimal impact from welding | Moderate, post-weld heat treatment required | Good, but cooling rate must be controlled | Good, but heat treatment required after welding |
| Heat Treatment | Quenching and tempering to adjust hardness | Cannot be hardened by heat treatment, cold work can strengthen | Not heat-treatable, can be strengthened by cold work | Maintains good properties after heat treatment | Strengthened by precipitation hardening heat treatment |
| Typical Applications | Blades, shafts, mechanical components | Food processing, chemical equipment, medical devices | Automotive exhaust systems, heat exchangers | Marine engineering, oil and gas pipelines | Aerospace, nuclear, high-strength applications |
What You Might Also Concern
Now that you have a deeper understanding of martensitic stainless steel, there are still some common issues that deserve your attention：
Can Martensitic Stainless Steel Rust?
Yes, martensitic stainless steel can rust because it contains less chromium, especially if not properly maintained.
Why is Martensitic Stainless Steel Always Tempered?
Martensitic stainless steel is always tempered to reduce brittleness and increase toughness. Tempering relieves internal stresses and improves mechanical properties, making the steel more suitable for practical use.
Can You Weld Martensitic Stainless Steel?
Yes, you can weld martensitic stainless steel, but it’s challenging as it is easy to crack and lose strength. Proper preheating and post-weld heat treatment are necessary to manage these issues.
Is Martensitic Stainless Steel Magnetic or Not?
Martensitic stainless steel is magnetic because it contains high levels of iron and has a martensitic crystal structure, which retains magnetic properties. The absence of sufficient nickel or other elements that would reduce magnetism allows it to remain magnetic.
Related Reading
Is Stainless Steel Magnetic?
What Is the Difference Between Martensitic and Austenitic Stainless Steel?
Martensitic stainless steel is hard, strong, and can be heat-treated, making it ideal for tools and cutlery, while austenitic stainless steel is non-magnetic, highly corrosion-resistant, and widely used in food processing and medical equipment due to its excellent weldability and formability.
Is Martensite or Austenite Stronger?
Martensite is stronger than austenite due to its harder, more brittle body-centered tetragonal (BCT) structure formed by rapid cooling (quenching), while austenite is softer and more ductile.
Summary & Furthermore
This article briefly explains the definition, composition, properties, structure formation, grades, applications, and other important aspects of martensitic stainless steel. To learn more about stainless steel or other steel types, check out our blog or contact our metal experts.
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