Get to Know your Stainless Steel

Your kitchen is full of stainless steel, but not all stainless steel is the same, there are different grades and each comes with its own pro's and con's. As a business it makes business sense to understand these grades of stainless steel in order to purchase the best kitchen hardware for the job at hand and how best to maintain it.

Get to Know your Stainless Steel

An alloy of iron, stainless steel is used primarily in situations where oxidation and corrosion might cause problems. For its price, no other material can perform the function that stainless steel does. Over half a century ago, scientists discovered that imparting a minimum of 12% chromium to steel gives it resistance to corrosion.

When applied to steel, chromium reacts with oxygen and forms chromium oxide which creates a passive film to atmospheric elements such as moisture and oxygen. This film is what offers protection to the underlying metal. The term stainless steel comes from the fact that the metal stays shiny. This is due to the overlying chromium oxide layer.

The purpose of stainless steels chromium oxide coating is to protect hard steel from:

  • Degenerative atmospheric conditions such as moisture, carbon dioxide, sulphur, salt, electrical fields, and chloride compounds.
  • Artificially produced and natural chemicals such as ozone.
  • Weather extremes such as winter.

The roots of this alloy find its way back to 1821 when a French Scientist known as Berthier discovered that iron became resistant to some acids when alloyed with chromium. A point worth noting is that all types of steel will corrode when exposed to water and oxygen. However, as an international standard, it is accepted that if less than 0.1mm of the stainless steel surface is what is corroded; the material is durable and is fit for the chosen application.

Another fact to note is that the higher the amount of chromium there is in the hard steel (low carbon steel), the more enhanced the above properties shall be. Additionally, these features can be enhanced further by the addition of elements such as nitrogen, nickel, and molybdenum.

So despite all the aforementioned formidable properties of steel, what makes stainless steel the most used metal in the world?

  • Sheer Strength. This is why stainless steel is the number one option in building and construction industries. Not only is it stronger, but much lighter than iron that would be used for the same purpose.
  • Aesthetic appeal. The shiny aspect of stainless steel, you have to admit, is quite appealing. Additionally, it can also be polished to a wide variety of surface finishes. This factor takes the crudeness out of the product.
  • Long life cycle. Stainless steel will easily outlast any building product. Additionally, it is easy to maintain plus it costs lower than most of the other products.
  • Environmentally Friendly. Stainless steel is 100% recyclable, and in fact, most steel products that are currently in use contain around 50-80% recycled material.

Sub-Categories of Stainless Steel Include: Ferritic, Martensitic, Austenitic, Duplex, and Superalloys

Austenitic Grades

Widely referred to as the 300 series, the austenitic grades are the most commonly used alloys in stainless steel applications. The most popular alloy in this grade is the iron-chromium-nickel steel which is, in fact, the real 300 series. Due to their ultra-high chromium and nickel content, austenitic steels have unusually fine mechanical properties and are also the most corrosion resistant among all stainless steels. They cannot be hardened by heat treating but are significantly hardened by cold-working.

This group is comprised

  • Straight Grades

Straight grades contain a maximum carbon content of .08%. A common fallacy is that straight grades include a minimum carbon content of .03%. This is not true. The fact is, if the material meets the conditions of being a straight grade, the minimum carbon content cannot be an issue.

  • Low Carbon Grades

Known as the ‘L' grades, they are typically used in the provision of corrosion resistance after a welding operation. The L is used to describe the stainless steel type as being a low carbon. To avoid carbide precipitation, the carbon content should be kept under .03%. The reason for this is when steel is heated to critical temperatures; the carbon in it will precipitate out, combine with chromium and gather on the grain boundaries. This will efficiently deprive steel off the chrome which is vital for its anti-corrosion properties. Thus, reducing the carbon content ensures that this scenario does not readily happen.

  • High Carbon Grades

Referred to as the ‘H' grades, they typically contain a maximum carbon concentration of .10% and a minimum of .04%. The H grades come in handy when the material to be used requires being subjected to extremely high temperatures. The high carbon content, therefore, is essential to ensure that the material retains its strength at these temperatures.

Stainless Steel Austenitic Grades Include:

Type 304

The most popular among the austenitic grades, 304 contains 8% nickel and 18% chromium. It is primarily used in chemical processing equipment for beverage, food, and dairy industries. It is also employed in heat exchangers and for handling chemicals. The most common use of Stainless steel 304 within a commercial environment is sink bowls and sink tops, sink units and wash hand basins.

Type 316

It contains about 12% nickel and 17% chromium. Also, it contains molybdenum. The primary applications of 316 are in the pulp and paper industry, chemical processing, and food and beverage processing. The molybdenum content should be kept at a minimum of 2%.

Type 317

Because it is used in highly corrosive environments, 317 have a higher molybdenum content than 316 which should be kept at a minimum of 3%. It finds its application in stacks containing scrubbers.

Type 317 L

As previously stated, the L implies a low carbon content which is why 317 L has a maximum carbon content of .03%. Additionally, it contains silicon which is concentrated to a maximum of .75% to exert extra corrosion resistance.

Type 317 LM

It is a low carbon steel which has molybdenum. The molybdenum content is placed at a minimum of 4%.

Type 317 LMN

In addition to the 4% molybdenum content, it also contains nitrogen at a minimum of .15% concentration.

Type 321

Developed for extra corrosive resistance due to repeated exposure to critical temperatures, 321 are created by the addition of titanium. It is used in the aircraft industry.

Type 347

Developed to be used in similar conditions as 321, type 327 is designed by addition of tantalum or columbium. It also finds its applications in the airline industry.

Stainless Steel Martensitic Grades Include:

This grade of steels was developed to provide corrosion resistance to stainless steel alloys that can be hardened by heat treating. Because of this reason, they do not contain nickel and thus are straight chromium steels. Additionally, they are also magnetic. They are mainly used where; strength, hardness, and wear and tear resistance is required.

Type 410

It contains the lowest alloy content among the basic stainless steel types. It is a low cost, heat treatable, general purpose stainless steel. It is widely used in instances where the corrosive content is not severe.

Type 414

Improves corrosion resistance by having nickel added to it and is used cutlery and springs.

Type 420

Has increased carbon content to enhance mechanical properties. Widely used in screw machine parts.

Type 430

Stainless steel 430 is also a food grade stainless steel, though it contains only 16 to 18 percent chromium and is better used in applications where demand for corrosion resistance is only moderately high. It is suitable for splash backs, equipment housings, paneling, table tops, kitchen utensils, low-cost sinks, fasteners, flue liners, refrigeration components, baffle grease filters, and more. Due to its excellent finish, it is also often used in decorative trim.

Stainless Steel Ferritic Grades Include:

They are typically superior to martensitic grades but are not of the same quality as austenitic grades. Similar to martensitic grades, they contain no nickel. They are usually used in automotive parts such as exhaust system.

Types 405

It contains aluminium that prevents the steel from hardening as it cools from being exposed to high temperatures.

Type 430

Another basic ferritic grade, it is not as corrosive resistant as type 304. However, it still offers high resistance to corrosives such as sulphur gases and nitric acid.

Stainless Steel Duplex Grades

Being a combination of austenitic and ferritic material, duplex grades are the latest addition to the stainless steel family.

Super Alloy Grades

Superalloys contain significant amounts of molybdenum and nickel. They are more expensive and are difficult to find.

Knowing your stainless steel is not only necessary but vital. This knowledge might save you from incurring a lot of unnecessary costs because of purchasing the wrong kind of stainless steel for your kitchen.

At Die-Pat is happy to guide you through your stainless steel selection. Contact us, and we will gladly cater to your needs.

Further Information...

Find out more about us and our products by calling us on 01327 311144 or emailing us at sales@die-pat.co.uk

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