Carbon steel knives need special care and cleaning to prevent rust, to allow them to develop the patina without damaging the blade, and they need more frequent sharpening than their stainless steel counterparts. So, why are there people who prefer them?
First, it’s important to understand the mineral and chemical properties. Steel is not a metal, it is an alloy of several compounds that also has allotropic properties. These two qualities are what allow us to play with the recipe of steel and adapt it to our needs.
Because it is an alloy of several compounds, we can add or remove ingredients to the mixture (or adjust the quantities of each one) to change the chemical and mechanical properties of the steel.
Because it is an allotropic metal, we can apply different thermal treatments to change its internal structure and adjust the parameters of hardness, tenacity, edge retention, etc. This process is especially important, because a bad steel with a good heat treatment will give better results than a good steel with a mediocre treatment.
What differentiates stainless steel from carbon steel?
In the first place, it’s important to point out that there are no perfectly stainless steels. The correct term would be “low oxidizable” or “less oxidizable”steel. The term in English to refer to this type of steels is “stainless” or “without stain”.
The basic ingredients of carbon steel are iron and carbon. They are never alone in the ingot (which is the technical way to call a “piece” of metal), but they are the ingredients that cannot be absent.
The ingredients of stainless steel are iron, carbon … and chromium. The chromium carbides are those that give the blade greater flexibility, greater resistance to abrasion, greater retention of the edge (and therefore also more difficulty for resharpening), and also provide resistance to corrosion. That’s why crossbow steel or naval steel are so popular in the artisan manufacture of cutlery.
We speak of stainless steels when the concentration of chromium exceeds 13%. This material can be found in carbon knives in concentrations lower than this percentage for its mechanical properties, since chromium levels above 0.3% will increase the toughness and abrasion resistance, although the effect on the oxidation of the sheet would be minimal.
The percentage of carbon in the ingot influences another classification that causes some buyers to doubt their purchase. If the carbon concentration is less than 0.25%, it is said to be low carbon, whereas if the alloy exceeds 0.60%, it is then classified as high carbon steel, a term that sometimes confuses the client. A buyer may not be sure he is buying a stainless sheet, when really, it has nothing to do with that.
A knife’s carbon concentrations are not usually greater than 2.5% – 2.8% carbon (some manufacturers of steels of very high quality, such as the ZDP-189 ensure that their mixture carries a 3 % of this element, which is probably the highest concentration used in cutlery). Increasing the content above these amounts doesn’t increase the favorable properties of the knife but instead makes them fragile and brittle. As in all mixtures, each ingredient has its optimum operating range.
Other elements used in different proportions in cutlery, depending on the properties that we want to present the sheet, are: Nickel, Molybdenum, Tungsten (or Wolfram), Cobalt, Manganese, Phosphorus, Vanadium, Silicon and Boron as the most used elements.
What advantages does carbon steel have over stainless steel?
Carbon Steels are very popular in the artisanal cutlery because they can be easily forged, have a reliable strength and hardness and have finer edges than what stainless steel provides. The retention of a sharp edge is a controversial issue in these pieces: on the one hand they dull more easily than stainless steel, but on the other hand, they can be re-sharpened much more easily.
What advantages does stainless steel have over carbon steel?
Mainly its low maintenance. Stainless steel is manufactured from sheets that oxidize at a very low level, retain the edge very well and reach great hardness. The presence of chromium carbides makes the sheet resistant to corrosion and abrasion and allows it to maintain a sharp edge (better than a similar sheet made of carbon steel that has received the same heat treatment which greatly influences the ability to get and maintain a good edge). On the other hand, this resistance to abrasion means that once the edge has been lost, it is more difficult to “tear off” particles.
Why are the Japanese famous for their carbon steel knives?
In Japan they have devoted themselves to the manufacture of carbon steel knife blades of the highest quality, not only because of the excellent performance of the material when used properly, but also because of the Japanese devotion to tradition.
Japanese forged knives draw their expertise directly from the craftsmen who forged katanas from centuries past. The traditions and secrets of gunsmiths were passed down from generation to generation until the steel technique was perfected (they had no other choice of metal, since Japan is a country with low quality iron deposits and in the past, had limitations on foreign imports. While in Toledo, the blades forged were equal to or better than the Japanese, Japan’s forging techniques are much more laborious but therefore, much more precise, because they have had to compensate for the limited accessibility to quality materials).
Due to a series of political changes on the island and a series of prohibitions that fell on the samurai and on the possession of katanas, the artisans found themselves faced with a problem. While there was now no need to make swords with their fine blades, It was natural to then take this knowledge and apply it to something much more mundane: kitchen knives.
All the expertise and tradition that for centuries was put into the manufacture of these legendary weapons was now being used to produce authentic works of art whose purpose was very different from the previous one: prepare food in the kitchen. That is why finely worked steel now serves the chef, allowing him to give the perfect cut with each pass.
Following the Japanese mentality of “shokunin”, which refers to the artisan who has dedicated his life to a trade, perfecting his technique to elevate his work to the category of art, the Japanese knife makers were away from any attempt at innovation and they aspired only to improve and to perfect the technique that their teachers once taught them.
And thanks to that, today we can enjoy the fruits of these great craftsmen, knives in the kitchen that not only have their own soul, but drink directly from the knowledge and tradition of the forge of katanas. If we consider that the island of Japan now has access to steel imports from all corners of the globe and access to the new advances in metallurgy that have brought impressive improvements in steel, we can now say that we are in a period of history in which science and tradition have come together to bring edges as our kitchens have never known before.
As a final note and curious fact, we have previously spoken of the fact that the poor Japanese iron deposits led to the development of their great mastery in the forging techniques. Did you know that this same predicament prompted the creation of some of the most famous swords in the world, the katanas, that have that peculiar curved blade? I invite you to investigate the “why.”