Facts About Knives: What You Need to Know Part 1

10

THE BLADE

Today’s knives are descendants of tools used hundreds of thousands of years ago. While a primitive flint stone knife of the Stone Age may not seem to have much in common with a stainless steel knife of today, what is the same is a sharp edge on a hard substance. By today’s standards, even methods and materials were still very basic at the beginning of the 20th Century. However, this was to change very quickly with the widespread application of electricity to the industry, the invention and refinement of stainless steel, and more recently, computerization. The requirements of the First World War, coupled with strong competition, brought about phenomenal advances. The discovery of stainless steel was one of these advances.

THE DISCOVERY OF STAINLESS STEEL

Henry Brearley, the inventor of stainless steel, was born in Sheffield, England in 1871. Using the crucible process first, and then more successfully an electric furnace, Brearley made a number of different melts of 6% to 15% chromium with varying carbon contents. The first true stainless steel was melted on August 13, 1913. It contained 0.24% carbon and 12.8% chromium. To solve the problem he had been presented, Brearley was trying to find a more wear-resistant steel. To examine the grain structure of the steel he needed to etch (attack with acid) samples before examining them under the microscope. The etching re-agents he used were based on nitric acid, and he found that this new steel strongly resisted chemical attack. He then exposed samples to vinegar and other food acids such as lemon juice and found the same result. Brearley immediately realized the practical uses of the new material he had discovered.

At the time, cutting knives were made of carbon steel which had to be thoroughly washed and dried after use, and even then rust stains would have to be rubbed off using Carborundum stones. Initially, Brearley referred to his invention as ”rustless steel.” Later, Ernest Stuart, coined the phrase ”stainless steel” after experiments with vinegar failed to stain the steel. Today stainless steel is a generic term for a family of corrosion resistant alloy steels containing 10.5% or more of chromium. Krupp in Germany (ThyssenKrupp today) was also experimenting with stainless, acid-resistant steels at just about the same time as Brearley was conducting his experiments. Stainless steel development all but stopped as World War 1 raged.

After WW 1, in the early 1920’s, a whole variety of chromium and nickel combinations were tried. Dr. W. H. Hatfield is credited with the invention of 18/8 stainless steel (18% chromium, 8% nickel, austenitic grade stainless steel) in 1924. In just over ten years, the Brearley and Krupp discoveries had lead to the “400” series of martensitic stainless steel (commonly used for knife blades, surgical instruments, shafts, spindles and pins) and the “300” series of austenitic stainless steel. Today there are five basic categories of stainless steel. For the most part, these were invented between 1913 and 1935 in Britain, Germany, America and France.

THE UNIQUE ADVANTAGE OF STAINLESS STEEL

Stainless steel’s unique advantage over carbon steel, is its high resistance to corrosion. This resistance to corrosion is due to the naturally occurring chromium-rich oxide film formed on the surface of the steel. This film forms at the molecular level and is extremely thin; it is invisible to the human eye. This film or layer is described as passive, tenacious and self repairing. Passive means that it does not react to or influence other materials. Tenacious means that it clings to the layer of steel so that it is not transferred elsewhere. Self repairing means that if damaged or forcibly removed more chromium from the steel will be exposed to the air and this will form more chromium oxide, repairing or replacing the lost oxide film. Over a period of years a stainless steel knife can literally be worn away by daily use and by being re-sharpened, but will still remain stainless.

Silver plated cutlery will eventually wear through to the base alloy, but stainless steel cutlery cannot wear through. Initially, the cutlery industry was not able to simply take stainless steel as it was invented and use it with total success. The first stainless steel did not produce blades that held an edge nor could edges be put onto blades easily. It took almost 30 years of expensive research by large cutlery manufacturers to develop the right combination of alloys to produce the grade of stainless steel that is still used today. Today, with more than 75 years of cutlery steel technology behind it, the cutlery steel industry is highly sophisticated and constantly experimenting with new and improved methods.

Today’s cutlery steel manufacturers have fully integrated operations, computerized processes and control procedures that enable them to produce the highest quality medical and cutlery grade steels, at a lower cost than ever before. For example, recent developments have reduced the volume of steel ground away in the grinding operation, resulting in a more economically finished blade. Today, quality knives can be made almost 100% by machine or by using the skills of a master cutler. The two knife manufacturing processes will be discussed next week! Stay tuned for more information!

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