Stainless steel plate

Stainless steel plate is often referred to as “corrosion-resistant steel” – it does not stain, corrode or rust as easily as normal carbon steel. It would however be misleading to say it is corrosion-proof. It differs significantly from standard carbon steel due to the amount of chromium present, which limits surface corrosion unlike carbon steel which will rust when exposed to air and any moisture in the atmosphere. Due to its anti-oxidation qualities, stainless steel is often a popular solution.

Where low maintenance and corrosion resistance is required, stainless steel plates are a natural choice and are used in a diverse range of applications from modern architecture for cladding or fascias, to the food hygiene industry due to its anti-bacterial qualities. Sunny Steel supplies stainless steel in a wide variety of grades and aesthetic finishes. There are many options available – for example adding carbon during the forming process will make the stainless steel more durable and stronger too. We can supply stainless steel in coils, sheets, plates and bars and ship the material worldwide.

Stainless specifications & grades

Since steel can be alloyed with an infinite number of combinations of alloying elements, a classification system has been developed to facilitate easy identification of the compounds used. Stainless steel has its own list of classifications, each of which will be explained in outline below.

Type 304 Stainless Steel	Type 321 Stainless Steel	UNS32750 SuperDuplex
Type 304L Stainless Steel	Type 347 Stainless Steel	UNS32760 SuperDuplex
Type 304H Stainless Steel	Type 410 Stainless Steel	1.4057 Stainless Steel
Type 316 Stainless Steel	UNS32205 Duplex
Type 316L Stainless Steel	Nitronic 30
Type 316H Stainless Steel

Stainless is a term that was adopted to cover a wide range of steel types and grades developed for corrosion or oxidation resistant applications. Stainless steels are essentially iron alloys containing a minimum of 10.5% chromium although other alloying elements (Nickel, Molybdenum, Titanium, Copper) may also be used in specific proportions to enhance their structure and properties such as formability, strength and cryogenic toughness.

The main condition for stainless steels is that they should be corrosion resistant for a stated application or environment. Selection of a suitable ‘grade’ of stainless steel must meet the corrosion resistance requirements along with the mechanical or physical properties needed to realize the overall service performance requirements. The stainless function of the steel comes from the chromium content to undergo passivation, forming an inert film of chromium oxide on the surface. This inert layer prevents further corrosion by hindering oxygen diffusion to the steel surface to stop corrosion from spreading into the bulk of the metal.

The 304 (A2) is the most widely used austenitic stainless-steel and this is also known as 18/8 to describe its composition of 18% chromium and 8% nickel. 304 stainless steel has good oxidation resistance in intermittent service up to 870 °C and in continuous service up to 925 °C.

The second most common austenitic stainless-steel is the 316 grade (A4), which is also called marine grade stainless, used primarily for its increased resistance to corrosion. Type 316 is essentially an austenitic chromium- nickel stainless steel that contains an additional 2-3% molybdenum. The molybdenum increases general corrosion resistance, improves resistance to pitting from chloride ion solutions (for example seawater and de-icing salts), and provides increased strength at elevated temperatures.

The uncomplicated answer is that 304 contains 18% chromium and 8% nickel while 316 contains 16% chromium, 10% nickel and 2% molybdenum. Both of these 300 grade steels are known for their exceptional welding and forming properties, which give them applications across a number of industries.

Grade 304 is a particular favourite in the food processing industries particularly in beer brewing, milk processing & wine making, pharmaceutical manufacture and petrochemicals. In this area benches, sinks, troughs, pressure vessels, heat exchangers, chemical containers and storage tanks are all produced from 304 stainless. The steel is very resistant to common acids and is very easy to fabricate into the items required, although some patina or staining may occur over a period of time.

This grade of stainless is also used in architectural applications for panelling, railings and trim as it will give a long service life and retain a good appearance. 304 stainless steel does have a weakness, it is liable to corrosion from chloride solutions, or from saline environments in coastal areas. Chloride ions may cause areas of corrosion, called ‘pitting’ which can pass beneath the protective chromium barriers to attack internal structures. Solutions with only 25 ppm of sodium chloride can have a corrosive effect.

For more robust applications within the marine environment of with contact from more powerful acids and chemicals grade 316 is recommended. This has virtually the same physical and mechanical properties as 304 stainless steel. 316 stainless steel is common in many industrial applications involving processing chemicals, as well as high-saline environments such as coastal regions and outdoor areas where de-icing salts are common. Because of its non-reactive qualities, 316 is also used in the manufacture of medical surgical instruments and in the pharmaceutical industry, where reaction vessels have to be clean beyond reproach, 316 is the material of choice.

In addition to this chromium content, stainless steels are often alloyed with other elements to enhance its properties.

Depending on the exact chemical composition of the stainless steel, they can fall into a number of different categories. This blog post will outline the different families and their properties.

Austenitic grade stainless steels contain at least 6% nickel and 16% chromium. Other elements such as molybdenum, copper, and titanium can be added to modify the steel to make them suitable for high-temperature applications or further improve corrosion resistance.

The nickel in austenitic stainless steels makes the metal suitable for low temperature or cryogenic applications, where other steels may become brittle.

Generally, austenitic stainless steels are non-magnetic and cannot be hardened by heat treatments.

This family of stainless steels has a large range of applications, including doors and windows, ovens, chemical tanks, and food processing equipment.

The major alloying element of ferritic stainless steels is only chromium in ranges from 10.5% to 18%, which provides them with a moderate level of corrosion resistance. These steels cannot be hardened by heat treatment processes and are always employed in the annealed condition.

Unlike austenitic stainless steels, the ferritic family is magnetic. Additionally, they do not suffer from stress corrosion cracking and thin sections of this type of stainless steel are weldable.

Common applications of ferritic stainless steels include cooking utensils, vehicle exhausts, and domestic appliances.

Martensitic stainless steels have chromium as their major alloying element but with a lower chromium content and higher carbon content than ferritic types.

This family has moderate corrosion resistance and poor weldability. They are often used for surgical instruments, fasteners, and springs.

Duplex (and SuperDuplex) stainless steels are a two-phase microstructure of 50% austenitic and 50% ferritic stainless steel. This provides the metal with increased strength and makes it resistant to stress corrosion cracking – but not at the same level of ferritic stainless steel. These grades of steel are also readily welded, and they have a high level of corrosion resistance.

These steels are commonly used for heat exchangers, off-shore installations, marine applications, and chemical plants.

This family of stainless steel contains both nickel and chromium and they develop extremely high tensile strengths with heat treatment. These steels are often supplied in a “solution treated” condition to allow it to be machined easily.

Precipitation hardening grade steels are often used for turbine blades, nuclear waste cakes, and mechanical components.

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Stainless steel is recognized for its strength, beauty, and resistance to corrosion. Not all stainless steel is alike, however. The metal comes in five distinct families and about 150 different grades.

What is stainless steel exactly?

Put simply, stainless steel is any one of the steel alloys that contains at least 10.5% chromium in the admixture of elements. Other elements can include nickel, molybdenum, or titanium to enhance a special characteristic of the alloy. For example, the addition of molybdenum increases the corrosion resistance of stainless steel and changes the alloy from grade 304 stainless steel to 316 stainless steel.

Stainless steel can be classified into one of five different types: austenitic, ferritic, martensitic, duplex (austenitic-ferritic), or precipitation. Each of these types can be subdivided into grades of stainless steel. Each grade features a different level of quality, durability, and temperature resistance.

Austenitic
The most common grades of steel, grades 304 and 316, are austenitic. This type of steel contains 16-26% chromium and up to 35% nickel. Typically, austenitic stainless steel has the highest corrosion resistance and is not hardenable by heat treatment. This family of stainless steel is also nonmagnetic, tough, and ductile. (Ductile refers to a metal’s ability to change shape without losing its strength.)

The most common type of austenitic steel is grade 304, sometimes called 18/8 because it contains 18% chromium and 8% nickel. Austenitic steels are commonly used in the aerospace and food-processing industries.

Generally, the physical properties of austenitic steel are similar to those of ferritic and martensitic steels. It’s the chemical composition that is different.

Ferritic
Ferritic steels have a low carbon content, less than 0.2%, making them non hardenable by heat treatment. They are only moderately hardenable by cold working. As a result, they have less anti-corrosion ability than austenitic steels. Standard ferritic steels contain 10.5-27% chromium and no nickel. The most popular grades of ferritic stainless steel include 409, 430, 439, and 441. Ferritic steel is commonly used for architectural applications and auto trim.

Martensitic
Typically containing 11.5-18% chromium and as much as 1.2% carbon (and sometimes nickel as well), martensitic steels are hardenable by heat treatment. Strong and ductile, these steels are also magnetic and feature moderate corrosion resistance. They often appear in the 400-level grades. Martensitic steel shows up in cutlery, wrenches, turbines, and surgical instruments.

Austenitic-ferritic (duplex)
Combining austenitic and ferritic stainless steels equally, duplex steels contain 21-27% chromium, 1.35-8% nickel, 0.05-3% copper, and 0.05-5% molybdenum. The combination of elements makes duplex steels stronger than either austenitic or ferritic steel by itself. Consequently, duplex steel often gets used in chemical processing and in crafting storage-tanks and containers that ship chemicals.

Precipitation Hardening
Precipitation-hardening stainless steel is noteworthy for its strength. This type of steel contains 15-17.5% chromium and 3-5% nickel along with aluminum, copper, and niobium, each less than 0.5% of the total mass of the steel. Precipitation-hardening steel’s corrosion resistance compares to that of austenitic steel. This kind of steel can be hardened with an aging treatment at fairly low temperatures. Metal workers use it to create long shafts for pumps or for valve spindles.

Stainless steel gets categorized into the types or the families outlined above, and then it is broken down further into grades.

What is the difference between a family and a grade of stainless steel?

The families of stainless steel are determined by the ratio of the metals that compose the alloy. The grades, by contrast, describe the properties of the type of steel, such as its toughness, magnetism, and corrosion resistance.

Many different organizations have developed their own systems for grading stainless steel. One of the most commonly used grading systems comes from the American Iron and Steel Institute (AISI). This organization employs a three-digit system to categorize stainless steel. When metallurgists and metal workers talk about grades 304 and 316, for instance, they are using the AISI grading model.

• Your Environment — The operating environment will affect the stainless steel you use. Choose a grade with the necessary strength, toughness, and resilience to withstand the temperatures, pH, stressors, and corrosion you will expose it to. A marine environment, for example, may require an alloy that includes molybdenum, which resists chloride ions.
• Formability or Weldability — If your application requires good formability, you’ll want to choose an austenitic or ferritic steel such as grades 304 or 430. Martensitic steel such as grade 410 is weaker and can crack. Also take into account the steel’s weldability if you plan to weld it to another metal.  
• Corrosion Resistance — The high levels of chromium in austenitic steels make them a good choice for harsh environments. Austenitic steels, particularly grade 316, offer the highest level of corrosion resistance. Less expensive martensitic stainless steel and ferritic stainless steel can also be good choices in corrosive settings.
• Strength, Ductility, and Toughness — How much weight will your application need to bear? How will it need to change shape without losing strength? What will it take to fracture the steel you choose? Stainless steel alloys containing chromium and nickel often provide the best combination of strength, ductility, and toughness.
• Cost and Availability — Austenitic stainless steels are usually the most expensive choices. That said, they’re also usually the best quality steels, so buyers may find they save money on maintenance and repairs in the long run.
• Magnetic Response — Some types of stainless steel are more magnetic than others. Adding chromium to an alloy tends to make it more magnetic, but adding nickel offsets or even eliminates the magnetism. Grades 316 and 310 are non-magnetic while grades in the 400 series are more magnetic.