What's the Deal with Steel?

Today, we are going to talk a little about metallurgy.

While material science and metallurgy could (and do) fill countless textbooks, PhD. theses, and patents, we’re going to start by defining steel and its closest relatives: cast iron, and wrought iron. In their simplest forms these three materials are composed of a combination of iron, carbon, and mix of other elements known as slag. With no impurities Elemental iron is quite soft and ductile. It is one of the oldest known elements and has been harvested in the form of iron ore, refined, and utilized around the world for millennia.

Wrought iron is mostly made up of elemental iron, contains less than 2% carbon by weight, and a large amount of included slag. It has fallen out of production due to the availability of cheap mild steel, but it was often used to make tools as well as architectural metalwork. The Eiffel tower is constructed mostly from wrought iron. This relatively low carbon form of iron approaches the material properties of its elemental cousin: it is soft enough to be worked (or wrought) by a blacksmith, and can be pounded into shape without fracturing. The included slag also forms a fibrous structure which increases the tensile strength of the workpiece.

Cast iron pan

Cast iron is similarly slag-heavy, but contains more carbon than its wrought counterpart. The additional carbon serves to lower the melting point which makes it more suitable for casting, but makes it hard, brittle, and unworkable when solid. Cast iron has historically been used for mass produced items that do not require much tensile strength, such as cookware and engine blocks.

The key difference between steel and other iron products is the removal of impurities (known as slag), precise tuning of the quantity of carbon, and a homogeneous distribution of that carbon throughout the iron matrix. These tight tolerances allow metallurgists to target specific properties such as hardness, ductility, toughness, and corrosion resistance and build an alloy that meets their specifications. Today, steel is produced by melting unrefined iron and introducing oxygen which binds with and removes excess carbon.  Much like wrought and cast iron, steel has been produced in some form for thousands of years.

So why are knives today generally made of steel? A knife made of wrought iron would be soft and malleable, it’s edge would deform and roll over quickly. Cast iron would make a brittle blade that would crack and chip. Steel can be pounded flat, have the hardness to keep an edge and the toughness to prevent chips. Knife makers select the type of steel they use based on the desired properties of the finished knife. Traditionally Western knives are made from softer steel which results in a tougher blade that is less prone to chipping, but the harder steels used in Japan can hold a finer edge for longer. A good maker will consider what the knife will be used for and select a blade material based on that.

At Togu, our Knives are made from VG-10 steel which strikes a great balance between the properties listed above. It is hard and durable, corrosion resistant, and takes a beautiful edge. Give our knives a try to feel the difference for yourself.