The Story of Steel

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October 8, 2022

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October 8, 2022

Whether for gauges, custom level switches or custom temperature probes, at Homershams we use steels almost every day.

But what is steel?
When is it used and are there different types available?

The Story of Steel

The discovery that the addition of carbon to iron, forms an entirely new material (Steel) was such an important one, that it spawned a new era and marked the end of the iron and bronze ages (in that order). Steel was such an extraordinary invention that it revolutionised warfare and engineering. Steel swords will cleave bronze, which in turn will cleave pure iron shields and weapons.

Folks in the Indian sub-continent were making excellent steel as early as the 15th century. This so called “Wootz” steel was made by encasing layers of iron with layers of vegetable material and placing it in a furnace. The process created an almost homogeneous compound of evenly distributed carbon through the iron, forming good steel. In Spain, Toledo steel was being made possibly even earlier. This steel became the metal of choice for the Roman legions.

Knives and tools used today are the product of thousands of years of knowledge, whose antecedents are the Damascus steel blades of Europe, and the brilliant craftsmanship of the Japanese Katana Sword.

Stainless Steel

Stainless Steels are formed by the addition of Chromium to ordinary steel. Stainless Steel celebrated its hundred-year anniversary in 2015. Anyone who has left mild steel outside will be well aware of the effects of corrosion and rust. Technically, this corrosion is called Oxidation. The chromium of Stainless steel forms a protective layer of Chromium Oxide to prevent any further oxidation taking place.

As with many discovery’s, Stainless Steel was discovered by mistake. An engineer testing steel sample squares for impact resistance, left a pile of scrapped material outdoors and went on his summer break. On his return he noticed that all the metal was discoloured except for a sample that had a high Chromium content.

Stainless steel was born.

The reader is probably used to seeing numbers such as Stainless 304 or 316 in industry, or numbers like 18-8 in domestic life. They both mean the same thing; they describe the alloyed materials that make the steel.

There are numerous designation standards of stainless steel types. Further, non-technical designations such as “18-8” are a very generic means of identification. For example 18-8 refers to a stainless steel with approximately 18% Chromium and 8% Nickel and may refer to any of the 300 series (e.g. 302, 304, 305, 384 & XM7) a very common alloy for cutlery.

Nickel Super-Alloys

In aerospace and elsewhere high performance is required, high Nickel (or Cobalt) so called “Super-Alloys” are manufactured. These are not steels at all and most often contain no iron at all. Typically Nickel contents are around 70%, with chromium and around 10% Titanium or Aluminium.

For example Inconel 600 contains almost 80% Nickel and 16% Chromium.

High nickel alloys are especially good at high temperatures, where some alloys can be used at 70% of their melting point.

At Homershams we have customers that ….

Perform heat treatment hardening
Forge Stainless steels
Forge Aluminium
Harden tool steel for special tools
Produce Ductile iron for pipes
Forge mild steels

We can supply several instruments useful for these industries such as,

Infrared cameras specific for metals
Infrared thermometers specific for metals
Custom thermocouple probes (K, S, R, T, J etc.)
Thermocouple simulators, calibrators, loop instruments
Protective sleeves for high temperature (molten metal, furnaces etc)

Hardening Metals

What the Japanese Katana-master knows through years of experience, and we now understand scientifically, is that the hardness of steel can be controlled by how we cool heated metal. Homershams have a number of customers involved in metal hardening; from automotive steering components, to drill bit manufacture to welded pipes in critical applications.

Intuitively it seems obvious to make steel as hard as possible, but this isn’t necessarily so. A very hard metal is also very brittle. The Samurai warrior’s sword would shatter in battle in this case, but would briefly have held an extremely sharp edge.

Cooling of the Katana is controlled by coating with clay of different thicknesses that cool at different rates such that the shaft is flexible (i.e. tough) but the blade is very sharp (i.e. hard). Thin clay is applied to the cutting edge, and thicker clay to the body. It is then heated to “the colour of the morning sun” before being quenched in water. Until this quenching, the blade is actually straight and the characteristic curve only occurs as it cools unevenly.

(Actually the Katana is even more complex than that. A centre piece of high quality flexible iron was placed within the steel and then repeatedly folded within the steel, 8-times. Folding is an example of exponential growth, and 8 folds = 32,000 layers of metal! )

Damascus steel

No-one is 100% sure how Damascus steel was made. It’s very beautiful and been prized since ancient times. However the art of making it was lost to antiquity although many have tried to re-create the process. Some believe that damasking was caused by carbon nano-tubes, inadvertently made by ancient forgers.