LIANYUNGANG DAPU METAL CO.LTD
+86 15751198808

Austenitic vs Martensitic Stainless Steel: Key Differences You Need to Know

How do austenitic and martensitic stainless steels fit into the broader stainless steel classification
Facebook
Twitter
Reddit
LinkedIn

Stainless steel has become one of the most widely used materials across many industries due to its remarkable ability to resist rusting and its strength and durability. Different classifications exist, the most common being the austenitic and martensitic grades. However, it is necessary to know the differences between these two types of stainless steel to know which material should be utilized for certain engineering, manufacturing or design specifications. This paper seeks to compare austenitic and martensitic stainless steel and enumerate their structure, mechanical properties, and recommended usages to make better decisions more educated.

What are the main differences between austenitic and martensitic stainless steel?

What are the main differences between austenitic and martensitic stainless steel
What are the main differences between austenitic and martensitic stainless steel

The distinction between Austenitic and martensitic stainless steels rests in their microstructure, composition, and even their properties. Composed mainly of iron, chromium, and nickel, Austenitic stainless steels are labeled as bulk face centered cubic (BCC ) crystals. They have good corrosion resistance as well as non-magnetic characteristics. They provide great ductility and toughness which makes them usable for regions with high formability such as kitchenware and marine environments. On the other hand, martensitic stainless steel has a body-centered cubic or body-centered tetragonal structure only upon being hardened and has a greater volume fraction of carbon and lower chromium content. This microstructure offers superior Strength and hardness but corrosion resistance is majorly affected when compared to austenitic grades. Because of this strength and hardness, its applications are mainly cutlery, surgical instruments, and high-strength tools.

Given their ingredients, how do they vary from one another?

Austenitic stainless steels are high in chromium (16-26%), nickel (6-22%) and low in carbon (0.08 and below), which makes these steels outstanding in terms of corrosion resistance and non-magnetic. Their FCC structure has its high nickel content to thank for that. On the other hand, martensitic stainless steels contain about 12-18 grade of chromium but only a trace of nickel and a higher level of carbon content with values ranging between 0.1 to as high as 1.2 percent. Heat treating oneself to a higher level of carbon hardness and strength is achievable, but make note that this comes at the cost of higher levels of corrosion, making it less suitable than austenitic grades. Both compositions are designed with the idea of encasing certain mechanical properties while ensuring the elements suited its environment at the same time.

What changes in microstructure should one look out for?

A dominant FCC crystal microstructure is apparent in all grades of austenitic stainless steel due to consistent application of high levels of nickel in all temperatures. Not only does this imbue excellent toughness and ductility in the material, but it also has outstanding non-magnetic properties. On the other hand, martensitic stainless steel has a body stainless steel with body-centered tetragonal fusion structure formed through die-cast in a (water) quenched state during the heat treatment process. This microstructure is known to exhibit high levels of hardness and strength but is tough at the same time making it angsty at the thought of barring the high corrosion resistance it is known to have inherited from the austenitic grades.

How do you compare their mechanical properties?

Ductile/brittle transition temperature is reduced in austenitic stainless steels. Therefore, they possess good ductility and toughness even at cryogenic temperature, avoiding catastrophic failure. Also, they can be stated to have moderate strength levels, but their strength can be increased by working hard. Martensitic stainless steels possess relatively low ductility but high hardness and tensile strength due to BCT cell structure and high temperature and heat treatment. They exhibit poor toughness which makes them unfit for application where inertia or impact loads will be applied on the material. These varying mechanical characteristics render each type to suit defined operational demands.

Which type of stainless steel offers better corrosion resistance?

Which type of stainless steel offers better corrosion resistance
Which type of stainless steel offers better corrosion resistance

Martensitic grades suffer from intergranular corrosion weakness, and this is an area that a wide range of austenitic stainless steels are able to defeat due to their addition of more nickel and chromium, which makes the oxide level passive and removes oxidation and rust. Because of this, austenitic grades are more dominant than martensitic grades, which do not have those alloying additions, even though those martensitic grades are harder and stronger. Overall, because of these reasons, austenitic grades are better suited in conditions where moisture, acids, or chlorides are present.

What factors influence corrosion resistance in stainless steel?

  • Chromium Content: As vanadium, Niobium, or tantalum levels increase in steel by wt%(>= 5%) and Cr is present in the follow-up percentage, the volumetric fraction of the passive zone increases, leading to the passive zone being stable on this scale until the passive zone bursts (which is beyond the yield point). This creates a barrier protecting against oxidation, allowing the environment to account for it.
  • Nickel and Molybdenum Additions: Additional nickel supplements the mass in essence and enhances the layer, reinforcing the anti-corrosive properties that come along with it, particularly in highly acidic solutions; as for Molybdenum when present, it increases protection against localized corrosion resistance such as pitting or taking place under low circumferences.
  • Environmental Conditions: Climate parameters like moisture, temperature, and even corrosive elements such as salt, acid, or chemicals have a great impact on the rate and degree of corrosion. For harsh environments in which strong attack is expected, special alloy compositions are necessary.
  • Surface Finish: Improving the surface finish leads to lower chances of crevice corrosion due to the absence of potential sites that can become depassivated and allow corrosion. Polish and passivation did help improve total corrosion resistance regardless of variations in the stainless steel alloys.
  • Heat Treatment and Fabrication: Heat treatment or mechanical processing that alters microstructure or introduces surface defects can render corrosion resistance ineffective. Processes, including welding, should be controlled to avoid sensitization and promote localized corrosion.
  • Cleaning and Maintenance: Cleaning occasionally is essential to eliminate pollutants such as chloride ions or organic substances that can damage the protective oxide layer. Routine care avoids the accumulation of deposits that may be harmful during service and guarantees sufficient corrosion-resistant properties of the material after many years in use.

How does nickel content influence the resistance to corrosion?

Nickel content greatly enhances stainless steel’s corrosion resistance by fortifying the austenite phase, strengthening its structure under corrosive conditions. It also enhances the chromium oxide passive layer, reducing oxidation and pitting in aggressive environments. Higher nickel levels are particularly important in preventing stress corrosion cracking, particularly in areas with high levels of chlorides, thus making it an important alloying element in materials designed to withstand very corrosive environments.

Are there specific environments where one type performs better?

Certain types of stainless steel outperform others in certain environments due to composition variations. For instance, austenitic stainless steels, which contain more nickel and chromium, are preferred in marine environments or chemical processing plants due to their resistance to pitting and stress corrosion cracking. By contrast, ferritic stainless steels fulfill their purpose in less aggressive environments as they are cheaper and have good corrosion resistance. Particularly, duplex stainless steels offer the advantages of ferritic and austenitic stainless steels and possess excellent resistance to localized corrosion while still withstand high effects in a chloride environment.

How does heat treatment affect austenitic and martensitic stainless steels?

How does heat treatment affect austenitic and martensitic stainless steels
How does heat treatment affect austenitic and martensitic stainless steels

The differences in microstructure and properties provide an argument as to why heat treatment affects differently austenitic and martensitic stainless steels. It should be noted that austenitic stainless steels are non-hardenable by heat treatment and remain corrosion resistance and non-magnetic because of the high chromium and nickel content. These steels are combined with stress relieving and ductility enhancement processes while maintaining mechanical strength. On the contrary, heat treatment processes greatly affect martensitic stainless steels. They can be hardened and subsequently tempered to increase strength and wear resistance, but this reduces corrosion resistance compared to austenitic grades. So heat treatment parameters have to be selected to achieve a given performance for a specific application.

Explain the significance of quenching for martensitic stainless steel?

Quenching is a crucial heat treatment process for martensitic stainless steel to develop an elevated level of hardness and strength. Comprehensively, the steel, during quenching, is raised to the austenitizing temperature of between 950° and 1,050°, which precipitates a polycrystallization of gamma-phase with an austenite structure. The material is then quickly cooled using either water, oil, or air to transform the attained austenite into martensite, which has the body-centered tetragonal (BCT) configuration. This transformation effectively enhances the material mechanical properties of the steel with respect to tensile and yield strength and even improves the wear resistance of the product.

Some critical concerns include the rate of cooling, which should be high enough to avoid soft phases like ferrite or pearlite forming, and the choice of a cooling material, which has a bearing on residual stress and any distortion that will be witnessed. After the cooling process, tempering is commonly used to relieve internal stresses while at the same time improving toughness to achieve hardness and ductility. Strict adherence to these conditions guarantees that specific micro-structural and performance requirements are obtained for industrial applications.

Is it possible to harden austenitic stainless steel through heat treatment?

The hardenability of austenitic stainless steels is not achievable using conventional heat treatment such as quenching and tempering. The face-centered cubic (FCC) lattice structure shows no phase change during heating or quenching cycles. However, it is work hardened by industrial deformation processes that include rolling, drawing, and hammering, which increases its strength. Further, nitriding, carburizing, or other surface hardening processes can modify some properties of steel at the surface but not the overall material.

How does the amount of carbon affect the effects of heat treatment?

In steel, the amount of carbon concentration is a good predictor of how the material would react to the heat treatment process. Increased carbon concentration raises the hardness, strength, and hardenability of steel by producing harder solutions of martensite upon quenching. However, too much carbon increases brittleness and decreases ductility. In contrast, a lower amount of carbon makes it difficult to harden the steel resulting in retaining its softer ductile form after the heat treatment. Critical temperatures of phase transformation increases with iron carbon percentage and hence affect annealing, normalizing and tempering processes. Carbon content must be controlled to ensure the material has the balance of the properties necessary for the intended applications.

What are the typical applications for austenitic and martensitic stainless steels?

What are the typical applications for austenitic and martensitic stainless steels
What are the typical applications for austenitic and martensitic stainless steels

Stainless steels show immense potential in maritime, food processing, and other corrosion-exposed areas, making them extremely popular among industrial sections. Architectural structures, kitchen utensils, and medical instruments also harness these alloys’ unique formability and weldability. Martensitic stainless steels, on the contrary, are deemed more valuable with high-strength applications such as automated components and surgical instruments. On the other hand, these materials can be used in places facing the reality of corrosion, such as certain aerospace components, because they are strong yet lightly prone to corrosion.

Which sectors use austenitic stainless steel most?

  • Food and Beverage Industry: Due to its excellent hygienic properties and resistance to abnormal conditions, austenitic stainless steels are primarily focused on the food and beverage industry as it can withstand very high temperatures. This material is also used for mixing tanks and conveyor belts.
  • Chemical and Pharmaceutical Industries: These materials help in environments that induce sweat, as they don’t pit and crack and are resistant to corrosive elements. Therefore, they make perfect sense to be used in reactors, pipes, and valves in such settings.
  • Shipbuilding & Marine Platforms: Austenitic steel containing high levels of chromium and nickel is a major seawater corrosion-resistant alloy utilized in the shipbuilding and offshore platform industries and desalination plants.
  • Modern Construction: Due to their strength, durability, and appealing outlook, austenitic stainless steels are commonly used in structural parts, architectural cladding, and decorative panels in modern construction.
  • Medical Devices/Healthcare Instruments: Austentic stainless steel is useful in manufacturing medical instruments, surgical tools, and implants. The alloy remains quite reactive in all applications, enhancing patient safety and durability.

What are martensitic stainless steels used for?

  • Knives and Scissors: The principal application for knives, scissors, and surgical blades based on martensitic stainless steel is that they are exceptionally hard and edge holding guards from wear. Precision blades are manufactured with control heat treatment processes to enhance functionality.
  • Turbine Blades: Because of its good strength-to-weight ratio and wear and fatigue resistance, martensitic stainless steel is applicable in the aerospace industry for turbo blades shafts and landing gear parts which should be highly durable and should withstand high stress
  • Automotive Industry: Electrical martensitic stainless steel is used to develop transmission components, exhaust systems, and structural reinforcements. Owing to its impressive mechanical properties and impact resistance, the material can withstand harsh service conditions.
  • Engineering and Industrial Tools: Parts such as gears, fasteners, and valves use martensitic stainless steel, which is tough and able to withstand heavy loads and wear, even under adverse conditions.
  • Medical Instruments: The material is corrosion resistant and can be heat treated, which makes it suitable for the manufacture of specialized surgical instruments and medical precision devices.

What factors account for differences in their applications?

The degree of application of martensitic stainless steel is determined by its several characteristics, such as hardness, tensile strength, corrosion, and heat treatability. For example, martensitic materials are reported to possess temperatures ranging from -254°C to 760 °C due to the presence of the low-carbon martensitic structure phase. Such properties enable the material to perform reliably in extreme environments involving various mechanical stresses, such as aerospace equipment, gas turbines, and aircraft turbine engines, especially in shafts and blades.

In the automotive sector, martensitic stainless steel is used in dynamic systems such as transmission components and exhaust systems because it has moderate corrosion resistance, which is enhanced by chromium content, generally around 12 14, and impact toughness where mechanical strength and durability over the environmental factors is required. Also, since it can withstand periodic structural loads, it is employed in the reinforcement of structures.

For engineering tools and industrial usages, high wear resistance (achieved with a Rockwell Hardness value often exceeding HRC 50 for treated grades) is ideal for gears, fasteners, and valves. Such tools have to endure continuous heavy loading and still remain accurate in severe operating environments. The strategic heat treatment of the material is also appropriate for distinct tools which require toughness along with fatigue resistance for prolonged usage and exertion.

How do austenitic and martensitic stainless steels compare in terms of weldability?

How do austenitic and martensitic stainless steels compare in terms of weldability
How do austenitic and martensitic stainless steels compare in terms of weldability

When comparing the weldability of austenitic and martensitic stainless steels, it can be said that austenitic is much easier to work with. Due to the alloy’s high amount of chromium and nickel, they have good structural stability. As a result, the chance of cracking or warping during welding is very low. Heat treatment methods cannot harden austenitic grades because of their low carbon content. This leads to the welded areas being less likely to suffer from the precipitation of carbides and the threat of intergranular corrosion. In stark contrast, martensitic stainless steels are quite susceptible to hardening and forming stress cracks when welded. Because of their higher contents of carbon, preheating as well as post-weld heat treatments are sometimes a prerequisite, otherwise it creates a greater risk to crack and decreases the quality of the weld which makes things more complicated.

What challenges are associated with welding of martensitic stainless steel?

Most of the issues concerning the welding of martensitic stainless steel steel is associated with the same factor: its high carbon content, which increases the chances of hydrogen cracking and hardening in an area subjected to extreme heat. Preheat is one of the treatments that can help solve this, which helps to lessen the range of temperatures and stress within the region. Thereafter, post-weld heat treatment can help to reduce internal stresses and, in turn, soften the hard, brittle microstructure. However, if this treatment is not implemented, the whole welded structure can become weak and be prone to fractures when exposed to mechanical stress. Another point that should be considered is to avoid rapid cooling; otherwise, brittle cracking would be experienced.

Why do you think welding austenitic stainless steels is easier?

The composition of austenitic stainless steels, characterized by low carbon levels and high amounts of chromium and nickel, enhances their ductility and overall corrosion resistance, making them one of the easiest materials to weld. This also ensures low cracking tendencies in the weld zone and increased tolerance to thermal stresses induced during the welding process. Because austenitic grades do not undergo a substantial amount of phase change during heating and cooling cycles, the chances of forming martensitic, untreated brittle phases are decreased significantly. When melting consumables such as ER308L or ER316L, low interpass temperature within 150°C / 300°F decreases distortion while still providing joint integrity and reducing the chances of carbide precipitation. In most instances, there is no need for thermal treatment of the welded material after a joint has already been made.

What precautions should be taken when welding these types of stainless steel?

The following are significant factors to be considered while welding austenitic stainless steels. First of all, it is necessary to maintain cleanliness. Remove grease, oil, and rust to avoid inclusions or porosity in the weld. Besides, using suitable filler metals such as ER308L or ER316L maintains nominal chances of carbide precipitation and otherwise being compatible with base materials. It is equally important to have controlled input to the weld to limit the amount of area exposed to heat and thus warpage or stresses. At the same time, argon or argon-helium mixtures are needed for the purpose of shielding as this would help avoid the risk of the weld surface being tainted by exposure to atmospheric air. Preheating is generally not required, but using an interpass temperature that is suitable, usually below or at 300 degrees F, does help limit amounts of distortion. Finally, appropriate pickling or passivation before lifting the concentrated hydrogen peroxide film restores the lost original corrosion resistance after welding.

How do austenitic and martensitic stainless steels fit into the broader stainless steel classification?

How do austenitic and martensitic stainless steels fit into the broader stainless steel classification
How do austenitic and martensitic stainless steels fit into the broader stainless steel classification

One of the most important classifications of stainless steel is austenitic and martensitic. The two differ in their microstructure, mechanical properties, and alloying elements. According to the face-centered cubic (FCC) crystal structure, austenitic stainless steels contain a high amount of corrosive-resistant chromium and nickel and are, therefore, very ductile and formable. Austenitic steels are non-magnetic materials that retain their strength at elevated and sub-zero temperatures and can be used for the production of chemical processing equipment or food-grade equipment.

Unlike austenitic stainless steels, martensitic stainless steels have a very distinctive body-centered tetragonal (BCT) structure and are primarily known for their strength and hardness. Controlled heat treatments of these microstructures allow to alter many of the mechanical properties of martensitic stainless steels. Martensitic steels have enhanced carbon but low corrosion resistance in contrast to austenitic grades; therefore, martensitic steels are able to be used in areas where wearing resistance is essential, such as cutlery, turbines, and medical instruments. All the above mention families of steels show how stainless steels were developed depending on different industrial needs.

What are the differences between different grades of stainless steel?

Due to their differences in microstructure, chemical composition, mechanical properties, and end-use, austenitic, martensitic, and ferritic stainless steels can be easily distinguished. Austenitic stainless steels, which have a face-centered cubic (FCC) structure, have a high content of chromium (16 to 26%) and nickel (8 to 12%). These steels are classified as paramagnetic, are highly resistant to corrosion and retain good ductility and impact strength at the cryogenic temperature range. Most tensile strength is within 515 to 690 MPa, which makes them very popular in food processing, chemical and also architectural applications.

On the other hand martensitic stainless steels are characterized by a body-centered tetragonal (BCT) structure, higher carbon content of 0.1 to 1.2% and moderate chromium content of 12 to 18%. Due to the high carbon content, these steels are hardenable by heat treatment, making them high in strength (895 to 1035 MPa tensile strength) and hardness but low in corrosion resistance as per austenitic grades. These magnetic steels find applications in wear-resistant tools such as knives, turbine blades, and surgical blades.

On the other hand, stainless steels, classified as Ferritic, are said to have a BCC (body-centered cubic) structure. These ferritic steels are said to contain a high chromium percentage ( 10.5-18%) and low carbon content (less than 0.2%), allowing them to be magnetic and provide great stress corrosion cracking resistance. Compared to the austenitic steels, its degree of formability and corrosion resistance is low, but on the positive side, it has good thermal conductivity, good oxidation resistance, and a tensile strength of about 410-550MPa. Due to its cost efficiency alongside undoubted performance under high temperatures, ferritic steels are used to make automotive exhaust systems, industrial equipment, and decorative trims.

How are these types related to the 300 and 400 series stainless steels?

The 400 grade steel may be further divided into Martensitic and ferritic, while the 300-grade steel may be divided into austenitic. The 300 austenitic does contain chromium and nickel around 16 -20 % and between 6 to 22% respectively. Kind of steels that have their FCC structure (face-centered cubic) element have low magnetism and combine high resistivity against corrosion, good formability, and good weldability properties. Common alloys include 304 (18% chromium, 8% nickel) and 316 (16-18% chromium, 10-14% nickel, with 2-3% molybdenum for enhanced pitting resistance), which can provide tensile strength in the range of 515 to 750 MPa.

The 400 series includes martensitic and ferritic steels. For instance, ferritic grades are magnetic and include 430, which has 16 to 18% chromium and has some resistance to corrosion with a range spanning 410 to 550 MPa in terms of tensile strength. Martensitic types include 410, which has 11.5 to 13.5% of chromium and 0.15% of carbon, and 420 which has 12-14% of chromium with increased carbon. These grades are also magnetic but have high hardness levels with a higher yield strength of up to 1035 megapascals after heat exposure. It is worth noting, however, that these have lower corrosion resistance levels than their counterparts in the 300 series. This scenario demonstrates the technical link between the composition and microstructure in these stainless steel families in different industrial applications.

Can you name some other types of stainless steel apart from the ones you’ve mentioned above?

Duplex stainless steels represent a hybrid category combining the attributes of austenitic and ferritic structures. These alloys typically contain 22-25% chromium, with varying amounts of nickel and molybdenum, offering high strength, excellent corrosion resistance, and improved toughness compared to purely ferritic grades. Super duplex variants further enhance resistance to chloride stress corrosion cracking and pitting. Precipitation-hardening stainless steels are another group, characterized by their ability to achieve exceptional strength through heat treatment, leveraging elements such as aluminum, copper, or niobium in their composition. Additionally, specialized ferritic grades, like the stabilized 441 (18% chromium, titanium-stabilized), provide excellent formability and high-temperature oxidation resistance, making them suitable for demanding applications. These categories expand the versatility of stainless steels, meeting diverse industrial requirements.

Reference sources

Austenite

Martensite

Steel

Frequently Asked Questions (FAQs)

Q: What are the main differences between austenitic and martensitic stainless steel?

A: The main differences between austenitic and martensitic stainless steel lie in their crystalline structure, chemical composition, and physical properties. Austenitic stainless steel contains higher levels of nickel and chromium, is non-magnetic, and has excellent corrosion resistance. Martensitic stainless steel, on the other hand, has higher carbon content, is magnetic, and can be hardened through heat treatment.

Q: Which type of steel is more corrosion-resistant?

A: Austenitic stainless steel is generally more corrosion-resistant compared to its martensitic counterparts. This is due to its higher chromium content, which forms a protective oxide layer on the surface. However, the actual corrosion resistance of stainless steel depends on the specific grade and environmental conditions.

Q: How do the physical properties of austenitic and martensitic stainless steel differ?

A: Austenitic stainless steel is typically softer, more ductile, and has better formability than martensitic stainless steel. Martensitic stainless steel, on the other hand, is harder, stronger, and more brittle. The physical properties of each type of steel depend on the specific grade and heat treatment.

Q: What are common applications for austenitic stainless steel?

A: Austenitic stainless steel is often used in applications requiring high corrosion resistance and good formability. Common uses include kitchen equipment, food processing machinery, chemical tanks, and architectural applications. The 300 series stainless steels, which are austenitic, are widely used in various industries.

Q: What are typical applications for martensitic stainless steel?

A: Martensitic stainless steel is often used in applications requiring high strength and hardness. Common uses include knife blades, surgical instruments, turbine blades, and valve components. The 400 series stainless steels, which include martensitic grades, are frequently used in these applications.

Q: How does the heat treatment process differ between austenitic and martensitic stainless steel?

A: Austenitic stainless steel cannot be hardened through heat treatment, while martensitic stainless steel can. Martensitic stainless steel undergoes a phase transformation during heat treatment, allowing it to be hardened and tempered. This difference is due to their distinct crystalline structures and chemical compositions.

Q: What is the difference between 300 and 400 series stainless steels?

A: The 300 series stainless steels are primarily austenitic, while the 400 series includes ferritic and martensitic grades. The 300 series is known for its excellent corrosion resistance and non-magnetic properties, while the 400 series offers higher strength and magnetic properties. The choice between these steel grades depends on the specific application requirements.

Q: How do austenitic and martensitic stainless steels compare in terms of weldability?

A: Austenitic stainless steels tend to have better weldability compared to martensitic stainless steels. Austenitic grades are less prone to cracking and distortion during welding. Martensitic stainless steels often require preheating and post-weld heat treatment to prevent cracking and achieve desired properties.

Understand DAPU
Recently Posted
Contact Form Demo