Different types of Stainless Steel

DIFFERENT TYPES OF STAINLESS STEEL

Introduction

As we know about Stainless steel is gernic term used to represent the family of corrosion resistance alloys. Did you know Like steel, stainless steels are relatively poor conductors of electricity. We all know that Stainless steel can be rolled into sheet, plates, bars, wire, and tubing. These can be used in cookware, cutlery, surgical instrument, vehicles, construction material in large buildings, industrial equipment, and storage tanks and tankers for chemicals and food products. So today we are going to know about types of stainless steel and what the uses of these are.

Different Types of Stainless Steel

Ferritic stainless steel
Austenitic stainless steel
Martensitic stainless steel
Duplex stainless steel
Precipitation hardening stainless steel

Ferritic stainless steel (https://www.instagram.com/p/Cg1NlIjhwnl/?igshid=YmMyMTA2M2Y= )

ferritic stainless steels, carbon is kept to low levels and the chromium content can range from 10.50 to 30.00%. ferritic stainless steels contain primarily ferritic microstructures at all temperatures and cannot be hardened through heat treating and quenching. Stainless steel grade 430 is a non-hardenable steel containing straight chromium, and belongs to the ferritic group of steels. Stainless steel grade 430 is known for its good corrosion resistance and formability, coupled with practical mechanical properties.

Now that you have a basic understanding of how Ferritic steel alloys differ from other varieties of stainless steel, you are probably curious about how this affects the performance of ferritic steel. There are some properties to be aware of.

Properties of Ferritic Stainless Steels

STAINLESS GRADES WHICH HAVE GOOD DUCTILITY AND FORMABILITY

Carbon is what gives steel its hardness — yet carbon also contributes to making steel more brittle and less ductile. Because ferritic steel contains low carbon levels — as little as 0.03 percent — they tend to possess above average ductility. As a result, ferritic steels can be shaped extensively without risk of weakening.

The low carbon content of ferritic steels also gives them excellent formability properties, meaning they can be formed into various shapes without encountering problems such as necking or cracking.

The benefits of ferritic steel's low-carbon composition do come with certain trade-offs to be aware of. For instance, ferritic steels cannot be hardened through heat treatment. Furthermore, certain types of ferritic steel may exhibit problems when welded — for instance, unwanted cracking along the heat-affect zone.

TYPES OF STAINLESS EXHIBITING LOW THERMAL EXPANSION

Another key benefit of ferritic steels is their naturally low coefficient of thermal expansion. This simply indicates the fact that ferritic steels will undergo less expansion as they take on heat. Instead, the metal will retain its fixed dimension much more readily. As you can imagine, this property is especially important for metals that will be used for high-temperature applications.

STAINLESS KNOWN TO HAVE HIGH THERMAL CONDUCTIVITY

Ferritic steels demonstrate excellent thermal conductivity attributes, meaning they allow heat to move efficiently through them. As a result, ferritic steels are a popular choice for furnace and boiler heat exchangers, and other applications involving the transfer of heat.

STAINLESS STEEL WITH HIGH OXIDATION RESISTANCE

Finally, ferritic stainless steel exhibits a stellar degree of resistance to oxidation, especially at high temperatures. This resistance has to do with the formation of a protective chromium-oxide film on the surface of the steel. Manufacturers can improve oxidation resistance even more by including aluminum and/or silicon when producing ferritic steel.

The most common uses of ferritic stainless steel are the following:

As part of automotive exhaust system silencers, automotive tubing, and catalytic converter casings.
Interiors of appliances, particularly washing machine drums, kitchen sinks, dishwashers, and some cooking utensils
Water tanks, solar water heaters, and microwave oven elements

Austenitic stainless steel (https://www.instagram.com/p/Cg1NlIjhwnl/?igshid=YmMyMTA2M2Y=)

Austenitic stainless steels are the most widely used variant of stainless steel. They contain very low levels of carbon and high amounts of nickel and chromium, which are the main contributors to their formability, corrosion-resistance and wear-resistance. They are also non-magnetic in their annealed state but can become slightly magnetic when cold worked.

Austenitic stainless steels are categorised in the 200 and 300 series in the AISI/SAE grade system, which contain between 2% to 20% of nickel and between 16% to 30% of chromium. The 300 series of austenitic stainless steels are chromium-nickel alloys, with at least 8% nickel, which is the minimum amount required to convert all the ferrite into austenite in an 18% chromium stainless steel.

The 200 series was developed in the 1940s as an economical alternative to the 300 series. It was developed to use nitrogen in addition to a lower amount of nickel at a time when nickel was much more expensive and scarce.

304 stainless sheet is the most common and most widely used of the nickel-based austenitic stainless steels. The grade 304 usually consists of around 8% nickel and 18% chromium.

316 stainless sheet is another commonly used grade that has an additional 2% of molybdenum which results in higher corrosion resistance.

The properties of austenitic stainless steel

Austenitic stainless steels are characterised by their face-centred cubic (FCC) crystal structure, which is attained when a sufficient quantity of austenitizing elements such as nickel, manganese, carbon and nitrogen are added to the alloy of iron and chromium.

Austenitic stainless steels can be produced to be very soft with a yield strength of about 200 MPa and they can be strengthened by cold working, which can raise the yield strength by up to a factor of ten. Unlike ferritic alloys, they can retain their ductility at cryogenic temperatures and their strength at high temperatures.

Their corrosion resistance can range from regular everyday use to highly specified use such as in boiling seawater. Despite their superiority among stainless steels, austenitic steels have inferior resistance to cyclic oxidation compared to ferritic alloys and they are also susceptible to stress corrosion cracking.

The endurance limit of austenitic steels is lower (~30% of their tensile strength) than ferritic steels (~50 - 60% of their tensile strength) which means they are more prone to fatigue failure.

Further, austenitic stainless steels, with the addition of nickel, are suitable for low temperature or cryogenic applications. Other elements such as silicon, aluminium and niobium may be added to give the steel certain properties such as resistance to halide pitting or oxidation. Sulphur or selenium can be added to certain steel grades to improve their machinability

Due to the austenitic stainless steel being the most common type of stainless steel, it also has the most applications—some of which include:

Automobile parts
Food and beverage equipment,
Storage vessels and pipes for corrosive liquids
Industrial equipment
Different kinds of architecture

Martensitic stainless steel (https://www.instagram.com/p/Cg1NlIjhwnl/?igshid=YmMyMTA2M2Y=)

Developed as a stainless steel that is resistant to corrosion while also possible to strengthen through heat treatment, martensitic stainless steels are basically alloys that are similar to carbon or low alloy steels with a structure to ferritic steels. It has a body-centered tetragonal crystal structure and is classified as a hard ferromagnetic group. It has incredibly good ductility and toughness which decreases as its overall strength increases.

The strength that it gets from heat treatment depends on the carbon content of the steels. Higher carbon content means higher potential strength and hardness and lower ductility and toughness.

The properties of Martensitic stainless steel

The structures of martensitic stainless steels are body centered tetragonal (bct) and they are classified as a hard ferro magnetic group. In the annealed condition, these steels have tensile yield strengths of around 275 N/sq mm and hence they can be machined, cold formed, or cold worked in this condition. These stainless steels have good ductility and toughness properties, which decrease as strength increases. Martensitic stainless steels can be moderately hardened by cold working. These stainless steels are typically heat treated by both hardening and tempering to yield strength levels up to 1900 N/sq mm. The strength obtained by heat treatment depends on the carbon content of the steels. Increasing the carbon content increases the strength and hardness potential but decreases ductility and toughness. The higher carbon grades are capable of being heat treated to a hardness of 60 HRC.

Martensitic stainless steels may be heat treated, in a similar manner to conventional steels, to provide a range of mechanical properties, but offer higher hardenability and have different heat treatment temperatures. They are subject to an impact transition at low temperatures and possess poor formability. Their thermal expansion and other thermal properties are similar to conventional steels. They may be welded with caution when matching filler metals are used but cracking can be a feature.

All martensitic stainless steels are ferro magnetic. Due to the stresses induced by the hardening transformation, these stainless steels exhibit permanent magnetic properties if magnetized in the hardened condition. For a given grade, the coercive force tends to increase with increasing hardness, rendering these stainless steels more difficult to demagnetize. These stainless steels are not used as permanent magnets to any significant extent.

Cold working increases the coercive force of these steels changing their behaviour from that of a soft magnet to a weak permanent magnet. If parts of cold worked martensitic stainless steel are exposed to a strong magnetic field, the parts can be permanently magnetized and, therefore, able to attract other ferro magnetic objects. Apart from possibly causing handling problems, the parts would be able to attract bits of iron or steel which will, if not removed, impair corrosion resistance. It is therefore prudent to either electrically or thermally demagnetize such parts if they have been subjected to a strong magnetic field during fabrication.

Martensitic stainless steels can be tested by nondestructive testing using the magnetic particle inspection method, unlike austenitic stainless steels.

Martensitic stainless steel, when compared to other types of stainless steel has a relatively low profile—and its good tensile strength in combination with moderate corrosion resistance and heat resistance makes it perfect for these kinds of applications:

Surgical equipment
Dental equipment
Wires, screws, springs, blades, and cutting tools
Hydroelectric engines,
Sporting equipment industry

Duplex stainless steel (https://www.instagram.com/p/Cg1NlIjhwnl/?igshid=YmMyMTA2M2Y= )

Duplex stainless steel is a very useful metal that is used the world over. It gets its name from the fact that it consists of two different grades of metal.

Essentially, Duplex is a Fe-Ni-Cr alloy that has a two-phase ferritic-austenitic stainless-steel microstructure when it is at room temperature.

Duplex sheet are characterized by high chromium (19–28%) and molybdenum (up to 5%) and lower nickel contents than austenitic stainless steels. The most used duplex stainless steels are the 2205 (22% Chromium, 5% Nickel) and the 2507 (25% Chromium, 7% Nickel); 2507 is known as “super duplex” due to its higher resistance to corrosion.

The advantage of combining ferritic and austenitic grades is that the resultant metal has a metallurgical structure that consists of two phases and therefore benefits from the properties of both microstructures.

These properties make duplex steel highly sought after in heavy industries, like oil and gas nuclear and chemical processing.

Duplex stainless steel has an array of various benefits such as:

· Strength: Duplex stainless steels have approximately double the strength of regular austenitic or ferritic stainless steels.

· Toughness and ductility: Duplex stainless steels exceed the toughness and ductility of ferritic grades although they are not as touch as austenitic grades.

· Corrosion resistance: As with all stainless steels, corrosion resistance depends mostly on the composition of the stainless steel, with chromium, molybdenum and nitrogen content being the most important. Duplex stainless steels are extremely corrosion resistant and even in chloride and supplied environments, duplex stainless steels exhibit very high resistance to stress corrosion cracking (SCC). SCC is a type of corrosion that takes place when a particular set of factors are present: Tensile stress, corrosive environment and a sufficiently high temperature.

· Heat Resistance: Duplex stainless steel has higher heat conductivity and lower thermal expansion than austenitic steels. Duplex grades can easily be used down to temperatures of at least -50°C because at low temperatures they have better ductility that ferritic grades of steel.

· Cost: Duplex stainless steels have lower nickel and molybdenum contents than their austenitic counterparts. This lower alloying content means that duplex stainless steels can be lower in cost. Further to this, it is also possible that the thickness of duplex stainless steel can be reduced as it has an increased yield strength. Thinner products mean that significant weight savings can be made.

· Weldability: Duplex stainless steels tend to have good weldability and all standard welding processes can be used although they are not quite as easily welded as the austenitic grades.

Applications of Duplex

The extensive benefits of Duplex stainless steel mean that it can be used in many different are used in:

· Chemical processing, transport and storage

· Pipes for production and transportation of oil and gas

· Oil and gas exploration and offshore rigs

· Oil and gas refining

· Marine environments

· Pollution control equipment

· Pulp & paper manufacturing

· Chemical process plant

Precipitation hardening stainless steel (https://www.instagram.com/p/Cg1NlIjhwnl/?igshid=YmMyMTA2M2Y= )

Precipitation hardening stainless steels are metals that have martensitic or semi-austenitic properties and contain high percentages of chromium and nickel. These steels are used in various industrial applications because of their high strength, corrosion resistance and hardness. Precipitation hardening stainless steels get their high tensile strength from undergoing a series of heat treatments. This specialized heat treatment process includes the addition of Copper, Aluminum and Titanium to enhance the steel’s corrosion resistance. Here’s everything you need to know about precipitation hardening stainless steels:

STAINLESS STEEL CLASSIFICATIONS

Precipitation hardening stainless steels are put into three groups based on their properties after the heat treatments. These alloy groups are martensitic, semi-austenitic and austenitic.

Austenitic Alloys: Austenitic stainless steels largely retain their structure after the heat treatment process. The alloy should undergo annealing, reheating and hardening treatments. The steel should be heated to no more than 2050 degrees Fahrenheit during the annealing procedure. Precipitation occurs during the reheating process, which increases the hardness and strength of the steel.

Martensitic Alloys: Martensitic stainless steels should be heated to no more than 1950 degrees Fahrenheit during the annealing heating process. During the cooling part of the process, this material undergoes a classification transformation from austenite to martensite.

BENEFITS OF PRECIPITATION HARDENING STAINLESS STEEL

One of the significant benefits of using precipitation hardening steels is that they can be treated to take on many favorable properties. These characteristics include:

Corrosion Resistance: Precipitation hardening steels have greater corrosion resistance than standard stainless steels, which is particularly beneficial when the steel is used in an outdoor or extreme weather application. The corrosion resistance of the steel can generally be enhanced during the heat treatment process.

Formability: Many grades of semi-austenitic stainless steel can be molded without any heat treatments. On the other hand, martensitic stainless steels are tough both before and after the heat treatment process and are therefore not easily formed.

Weldability: Unlike other stainless steel alloys, precipitation hardening steels can be readily welded through standard fusion and resistance methods. Remember that special care should be taken during the heat treatment process to ensure that the optimum mechanical properties for weldability are achieved.

PRECIPITATION HARDENING STAINLESS STEEL

STAINLESS STEEL CLASSIFICATIONS

Precipitation hardening stainless steels are put into three groups based on their properties after the heat treatments. These alloy groups are martensitic, semi-austenitic and austenitic.

PRECIPITATION HARDENING STAINLESS STEEL APPLICATIONS

Because of the hardness and high tensile strength of this classification of stainless steels, many applications are in the high technology or aerospace engineering fields. These steels are used to manufacture the following components:

· Gears

· Valves

· Shafts

· Specialized engine components

· Turbine blades

· Molding dies

If you require stainless steel for whatever reason then contact Raisun Metal Zone Pvt. Ltd. https://www.raisunmetals.com/ or vizinox.com We are the manufacturer of stainless steel sheets and coils. we believe in quality service as well as a brilliant service to our customers.

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Different types of Stainless Steel