What are the Properties of Stainless Steel and its Applications?

Stainless steel has become ubiquitous in our modern world, used in every walk of life from kitchen utensils and medical devices to turbine engine components and buildings.

To suit these numerous applications, many different grades of stainless steel exist, but what do each of them bring to the table, and how were they discovered?

The History of Stainless Steel

Before Stainless Steel

Before stainless steel, materials such as cast iron and even steel, similar to what we term today as carbon steel, were being made and used all over the world.

There are specific accounts of large-scale steel-making using refinery forges in Prague and Nuremberg as early as 1574.

Key Discoveries in Stainless Steel Composition

Stainless steel is mostly iron, with carbon interspersed the same as carbon steel, but what makes stainless steel special, is the presence of three more elements, in not-insignificant proportions; Nickel, Molybdenum and Chromium.

Nickel

In 1751, Swedish mineralogist Axel Fredrik Cronstedt discovered Nickel whilst working in Los, Sweden. The element was extracted from copper ore dug from Cobalt mines

The name Nickel comes from the Swedish “Kupfer nickel”, meaning copper-sprite, a name the miners gave to the ore as it appeared to have a supernatural presence (sprite), making it hard to extract copper from.

Molybdenum

Carl Wilhelm Scheele discovered, among many other elements, Molybdenum in 1778. The German-Swedish chemist also discovered oxygen, Manganese and Tungsten.

Molybdenum increases both the corrosion resistance and high-temperature strength in most alloys, including stainless steel.

Chromium

In 1797, Nicolas-Louis Vauquelin discovered Chromium, an element that presents with a shiny lustre, it is used extensively in alloying as well as plating to add corrosion resistance and aesthetic effect.

When was the First Stainless Steel Invented?

Using the newly discovered elements in their testing, previously unknown John T Woods and John Clark registered a patent for a “water resistant steel” at the British patent office in 1872.

Building on the work of Pierre Berthier in 1821, by incorporating higher concentrations of chromium, the material was resistant to corrosion in a way that had never been seen before.

Coincidentally, Pierre Berthier is also credited for his role in the development of another non-rusting metal; Aluminum, after he discovered the ore used to extract it; Bauxite, in the 1820’s

What Type of Stainless Steel was Invented First?

Whilst there is some discussion about what type of stainless steel was first made, Albert Marcel Portevin published a paper on the different types of the newly discovered material he has witnessed in his testing.

Through his descriptions of the method of manufacture and material properties, the three material types are closely related to the modern Austenitic, Ferritic and Martensitic alloys we know today.

The first patent for a ferritic grade of stainless steel was filed by Frederick M Becket and Christian Dantsizen, in 1912. Eduard Maurer and Benno Strauss too were awarded two patents in 1912, one for Austenitic and one for Martensitic stainless steel.

Why are there so many grades of Stainless Steel?

With a precise combination of alloying elements and manufacturing processing, materials can be made that serve many different purposes, all from the same basic elements of iron, carbon and chromium.

Most Common Stainless Steel Grades

303 Grade

High sulfur content makes this Austenitic stainless steel very easy to machine, at the cost of slightly less corrosion resistance and toughness.

This material is often used for:

  • Gears
  • Springs
  • Fasteners
  • Fittings

304 Grade

304 grade stainless steel is probably the most commonly used grade, with excellent all round properties including high corrosion resistance, strength and ductility. The latter meaning it is very easy to work with bending, cutting and punching operations, making it cheap to manufacture with.

It is commonly used for:

  • Corrosion resistant frameworks and enclosure
  • Bracketry
  • Pipework

316 Grade

Commonly referred to as the “food grade” stainless steel, it is also an austenitic stainless steel with similar properties to 304 grade. The difference comes in its larger proportion of molybdenum. This gives even better corrosion resistance.

Common uses include:

  • Medical and food processing equipment
  • Marine applications such as ladders, lashing points, etc.

416 grade

416 stainless steel is a martensitic grade that again uses sulfur to improve machinability. The high sulfur content however causes manganese sulfide inclusions, further reducing its strength and drastically reducing its weldability.

416 grade can be heat treated, and as such is often used in:

  • Valve components
  • Fasteners
  • Motor shafts

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