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DISCOVER THE AESTHETIC OF METAL
Guide to Martensitic Stainless Steel
Table of Contents
Martensitic steel is achieved by heating until the atoms rearrange, then quenching rapidly to make it stay in that condition. It is hardenable stainless steel. Steel factories can adjust their mechanical properties by heat treatment, like quenching and tempering, to meet special requirements. Martensitic stainless steel is mainly used for steam turbine blades, tableware, surgical instruments, razor blades, and frames for most weight-bearing or load-bearing objects that carry heavy loads.
Martensitic Stainless Steel Composition
Martensitic stainless steel is characterized by its body-centered tetragonal (BCT) crystal structure, formed through rapid quenching, which enables exceptional hardness and strength.
Chromium (Cr): 12% –17%
Martensitic stainless steel primarily consists of iron, carbon, and chromium. It contains 12% to 17% chromium, which gives it corrosion resistance. Cr bonds with carbon to form carbides, reducing free Cr availability. Its corrosion resistance is lower than that of Austenite.
Carbon (C): 0.1–1.2%
The critical element for martensite formation is carbon. Martensitic stainless steel can be high- or low-carbon steel. Higher carbon (e.g., 0.6–1.2% in the 440 series) maximizes hardness (up to 60 HRC) but increases brittleness and reduces weldability. Low-carbon variants (0.1%–0.25%) offer better formability and moderate corrosion resistance, like Type 410.
Iron (Fe): Balance
Forms the primary matrix of the alloy.
Molybdenum (Mo): 0–2.5%
Enhances strength, creep resistance, and pitting corrosion resistance, especially in high-temperature grades like 422.
Nickel (Ni): ≤2.5% (except in PH grades)
Improves toughness and corrosion resistance (e.g., Grade 431 with 1.25–2.5% Ni).
Manganese (Mn): ≤1% & Silicon (Si): ≤1%
Aid deoxidation during melting and stabilize austenite during heat treatment.
Sulfur (S) or Selenium (Se)
S and Se can improve machinability. They will be found in free-machining grades (e.g., 416, 420F).
Specialized Elements (B, Co, Nb, Ti)
Additions of boron, cobalt, niobium, and titanium improve the high-temperature properties, particularly creep resistance. This makes martensitic stainless steel ideal for turbine blades.
Properties
Due to its body-centred tetragonal (BCT) crystal structure, martensitic stainless steel enables exceptional hardness and strength through heat treatment. Here, Topson Steel will provide a detailed analysis of its key properties:
Corrosion Resistance
Martensitic stainless steel has decent corrosion resistance in relatively mild environments. While not as resistant as austenitic grades, it performs well under certain conditions with proper care and maintenance. Prone to pitting and stress corrosion cracking (SCC) in chloride/sulfuric acid environments.
Strength
Martensitic stainless alloys can be hardened through heat treatment processes such as quenching and stress relieving or quenching and tempering (commonly referred to as QT). The specific composition of the alloy and the rapid cooling rate during quenching facilitate the formation of martensite. Untempered martensite is characterized by low toughness, making it brittle. In contrast, tempered martensite provides the steel with good hardness and high toughness, as demonstrated below.
Tensile strength: Ranges from 70,000–286,000 psi (480–1,970 MPa), scalable via heat treatment.
Hardness: Annealed condition: ~97 HRB; hardened condition: Up to 60 HRC (e.g., 440C).
Ductility: Low ductility in the as-quenched state; tempering (150–700°C) restores toughness.
Physical Properties
Martensitic stainless steels are ferromagnetic due to their BCT crystal structure. Ferromagnetic in all conditions (annealed/hardened) enables sorting via magnets but complicates welding. Their density is about 7,800 kg/m³, and their thermal conductivity is low, contributing to welding challenges like cold cracking.
Common Grades
Martensitic stainless steel is available in various grades, each specifically tailored for different applications. The most common grades include 410, 420, 431, and 440.
Grade 410
Type 410 is a general-purpose grade with a maximum carbon content of 0.15%. It contains approximately 11.5% chromium, which provides it with good corrosion resistance and moderate strength. Therefore, it’s often found in cutlery and kitchen utensils.
Grade 420
Type 420 increases the carbon content to 0.15% minimum for improved strength, wear resistance, and hardness. This makes it suitable for applications requiring sharp cutting edges or high abrasion resistance. Grade 420 is divided into two types: 420J1 and 420J2, based on their carbon content.
420J1 steel is a lower carbon steel (0.16–0.25%), which enhances corrosion resistance but limits hardness, and is commonly applied in food preparation tools, surgical instruments, and decorative parts.
420J2 steel is a higher carbon steel (0.26–0.40%), which enables greater hardness and wear resistance. It is used in kitchen knives, scissors, bearings, and low-cost blades.
Grade 431
Type 431 has added nickel content for improved corrosion resistance. As a martensitic grade, it can achieve high mechanical properties through quenching and tempering, making it ideal for high-stress applications in aerospace, marine, and industrial sectors.
Grade 440C
Grade 440 boasts the highest hardness among martensitic steels, including 440A, 440B, and 440C. Type 440C contains 0.95-1.20% carbon for the highest hardness. 440A and 440B are tougher than 440C. The chromium level of grade 440C is around 16-18%. You can find it in knife blades and bearings.
Applications
Martensitic stainless steels are valued for their corrosion resistance and high strength, which vary depending on their carbon content. They also exhibit excellent wear resistance.
Up to about 0.4% C
In compositions with up to about 0.4% carbon, these steels are primarily valued for their mechanical properties. They are commonly used in applications such as pumps, valves, and shafts.
Above 0.4% C
When the carbon content exceeds 0.4%, the focus shifts to their wear resistance. In this case, they are often found in products such as cutlery, surgical blades, plastic injection molds, and nozzles.
One notable example is grade EN 1.4313 (CA6NM), which is utilized in nearly all hydroelectric turbines worldwide, including those at the massive “Three Gorges” dam in China.
Limitations of Martensitic Stainless Steel
Martensitic stainless steel, while versatile, has its limitations.
Martensitic stainless steel is prone to developing pitting and crevice corrosion in environments with high chloride content.
Martensitic stainless steel is prone to cracking during welding and forming, particularly in grades with high carbon content.
Martensitic stainless steel tends to lose toughness at lower temperatures.
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