Stainless steel is known for its durability, corrosion resistance, and overall clean look. Generally, there are five different types of stainless steel, each having a different chemical composition and properties. One such type is martensitic stainless steel, which has incredible strength and offers moderate protection against corrosion and rust. Let’s discuss this material type in detail, along with its history, grades, benefits, and more!
What is Martensitic Stainless Steel?
Martensitic stainless steel has a body-centered tetragonal crystal structure and a magnetic character. It has a high strength-to-weight ratio and can be easily hardened by different treatments, such as heat and aging. This high mechanical strength, compared to other types of stainless steel, renders it suitable for fabricating and producing medical instruments, valves, and turbine parts.
History of Martensitic Stainless Steel
German microscopist Adolf Martens first observed the body-centered tetragonal structure, which is known today as “martensite.” However, the primary discovery of martensitic stainless steel is often connected with Harry Brearley of the Brown-Firth research laboratory in Sheffield, England.
In 1915, The New York Times then published an article officially announcing the discovery of the material.
Brearley applied for a patent for this material in the same year, and this stainless steel or alloy was then marketed under the brand “Staybrite” by Fifth Vickers in England. Adolf Martens also applied to get a patent, but he wasn’t granted one until 1919.
Grades of Martensitic Stainless Steel
There are different grades of martensitic stainless steel primarily due to the difference in metal concentration. Let’s discuss a few of them:
Grade 410
Grade 410 is a general-purpose heat-treatable martensitic steel with 11.5% to 13% chromium. It has high strength, but its corrosion resistance properties aren’t that high compared to other types of stainless steel. To increase the resistance, you can treat the 410 steel with a series of processes, such as hardening and polishing. Common applications of this grade include cutlery and kitchen utensils.
Grade 420
Grade 420 is a high-carbon steel known for its high hardness. After heat treatment, it can reach a Rockwell hardness of 50 HRC. It contains around 12% to 14% chromium and offers good corrosion and wear resistance. This grade can be used for manufacturing different medical instruments, such as scissors, needles, and other machine parts.
Grade 431
Featuring 15% to 17% chromium, grade 431 is another type of martensitic stainless steel. It’s heat-treatable and has high tensile strength, which enables it to withstand stress during different processes without any deformation. The best part about this is that it’s also resistant to oxidation and scaling and finds applications in medical implants, pump shafts, and industrial facilities.
Grade 440
Grade 440 has 0.20% to 1.60% carbon and 16% to 18% chromium and comes in four different variants, including 440 A, 440 B, 440 C, and 440 F. The high carbon content in this series contributes to incredible strength and wear resistance. It’s also machinable in its annealed condition, which is helpful in applications such as high-end knives, watches, and marine environments.
Chemical Composition of Martensitic Stainless Steel
Now that you are aware of the various grades of martensitic stainless steel, let’s now look at the chemical composition of each:
| Grades | C | Mn | Si | Cr | Ni | Mo | P | S |
| 410 | 0.15 | 1 | 0.5 | 11.5 – 13 | – | – | 0.04 | 0.03 |
| 420 | 0.15 – 0.40 | 1 | 1 | 12.0 – 14.0 | – | – | 0.04 | 0.03 |
| 431 | 0.2 | 1 | 1 | 15.0 – 17.0 | 1.25 – 2.00 | – | 0.04 | 0.03 |
| 440 (A) | 1.25 – 2.00 | 1 | 1 | 16.0 – 18.0 | 0.75 | – | 0.04 | 0.03 |
Manufacturing Process of Martensitic Stainless Steel
The manufacturing of martensitic stainless steel involves a series of steps, such as:
- The first step is the collection of raw materials like chromium and carbon as well as other alloying elements (Nickel (Ni), Molybdenum (Mo), and Manganese (Mn)).
- These raw materials are then placed inside a furnace, which is subjected to high heat and turns into a molten form.
- This molten material is then cast into different shapes ranging from sheets to plates and bars.
- If the application requires high strength, the material undergoes hot working (quenching) and cold working.
Nowadays, emerging technologies like additive manufacturing (laser powder bed fusion) are also becoming part of the production process of martensitic stainless steel to achieve complex shapes.
Properties of Martensitic Stainless Steel
Martensitic stainless steel has some unique properties that allow it to be used in mildly corrosive and high-stress environments. Let’s discuss these in detail:
Strength and Hardness
Martensitic stainless steel shows excellent tensile strength of up to 275 MPa in annealed conditions. This strength and hardness is due to the presence of carbon and a unique microstructure that typically develops in the material during cooling. To further increase this property, you can increase the carbon content or give heat treatment.
Corrosion Resistance
Martensitic steel offers moderate corrosion resistance, but compared to austenitic and ferritic steels, it’s quite low. This limits their ability to be used in oxidizing or reducing environments. However, they find applications in situations where high strength and hardness are needed.
If you want to improve this material’s corrosion resistance, you can subject it to different heating treatments. The addition of 0.2% nitrogen can also reduce the chances of intergranular corrosion, which often occurs in this steel.
Magnetism
When it comes to magnetic properties, martensitic steel is classified as a hard ferromagnetic group, which means it’s quite tough to magnetize and demagnetize. The stress induced by hardening makes the material show permanent magnetic properties. All this impacts the steel’s corrosion resistance and poses some other challenges during fabrication.
Martensitic stainless steel also has some disadvantages, such as it can become brittle at high temperatures. So you have to carefully handle it during manufacturing to avoid fractures. On top of this, they are also not weldable, which makes them quite unsuitable to be used as construction materials for pressure vessel parts.
Mechanical Properties
Here’s a table that gives you insights into the mechanical properties of martensitic steel:
| Type or Grade | Minimum Yield Stress | Tensile Strength | Minimum Elongation |
| 410 | 50 MPa (65 ksi) | 650–850 MPa (94–123 ksi) | 15 |
| 420 | 600 MPa (87 ksi) | 650–850 MPa (94–123 ksi) | 12 |
| 431 | 700 MPa (100 ksi) | 900–1,050 MPa (131–152 ksi) | 12 |
Applications of Martensitic Stainless Steel
Now let’s look at the diverse applications of martensitic stainless steel to understand how they are a part of diverse industries:
Automotive
- Exhaust systems
- Turbochargers
- Engine component
Aerospace
- Aircraft Engines
- Structural parts
- Turbine blades
Medical
- Implants and surgical equipment due to their biocompatibility
Architecture
- Cladding
- Sculptures
- Facades
- Furniture
Food Processing
- Blades for food slicing and dicing
- Mixers
- Dough rollers
- Slicers
- Grinders
If we compare martensitic steel with other stainless steel types like austenitic and ferritic, it has low corrosion resistance. Not only this, but the chemical composition is also different since martensitic steels contain a high carbon content that contributes to their strength. It’s also more wear-resistant than the other two types.
Conclusion
Martensitic stainless steel is everywhere, from basic medical equipment like scissors to architectural elements such as cladding. If you are looking for some top-quality martensitic steel for your needs, Jianglin has your back. We can offer you diverse grades of this material at a competitive price so you can create the desired products without any issues. Get in touch with us today to end the hassle of finding the best stainless steel!
