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Knife Steel



Knife Steel

A knife in its simplest description is a cutting edge with a handle. To be good at its job it must take and hold a sharp edge. For steel to have good edge holding ability it needs to be able to be hardened and tempered. It is this ability to be hardened that makes knife steel different from many of the other grades or types of steel. It is also the characteristics of the steel after hardening which often dictate the quality of the knife. For instance if it is too brittle it is likely to break very easily even though it may be very hard.

The most important component in knife steel is carbon. Carbon allows steel to be hardened so that it will hold an edge. So called Carbon Steel is a generic name for many of the non-stainless knife steels. There are also many tool steels which can also be described as carbon steel. Tool steels, as the name suggests, are used for the manufacture of tooling for things such as moulds, punches and dies, etc. Most tool steels include alloys such as chromium, molybdenum, vanadium, tungsten and cobalt. These alloys give the steel better work characteristics.
Many carbon and tool steels are excellent for making knives, but usually require greater care than stainless steel knives to stop them from rusting.

Surgical steel is not a technical term and is used to describe a vast range of qualities and types of steels. Many of the steels which can be described as surgical steel are not suitable for knife making.

Stainless steel has at least 13% chromium added to it to make it less susceptible to rusting. It should be noted that stainless steel suitable for making knives will rust if exposed to salt water or acids. The addition of nickel to stainless steel gives it much greater resistance to rust but will not allow it to be hardened. As a result, 18/8* (18% chromium / 8% nickel) and 18/10** (18% chromium / 10% nickel) stainless steel saucepans are less susceptible to rust than knives. The only steels which can really be called non-rusting are the duplex stainless steels such as Sandvik's SAF2507. This however is quite unsuitable for the making of knives.

The main alloys added to stainless knife steel are:

    Silicon
      It assists in the forging and hot rolling components of steel manufacture
    Manganese
      It also assists in keeping the steel sound during hot processing
    Molybdenum
      This strengthens the carbides which are the hard edge-holding components of the steel
    Vanadium
      This is also a carbide former

GUSTAV EMIL ERN knives are made using steel of German specification 1.4116 for blades of 2mm thickness and under (filleting, paring, turning, etc) and specification 1.4110 for blades greater than 2mm (boning, cooks, butchers, etc)

DEWEY knives are produced using the following steels; D2, ATS34, K1073 and German steel 1.4110 and 1.4116.

German Spec US Spec Carbon Chromium Silicon Manganese Molybdenum Vanadium
1.4116 - 0.42-0.50 13.8-15.0 - - 0.45-0.60 0.10-0.15
1.4110 - 0.48-0.60 13.0-15.0 1.0 1.0 0.50-0.80 -
- 440B 0.85-0.95 17 <1 <1 0.9-1.3 0.07-0.12
- D2 1.5 12 0 0.4 0.8 0.9
- ATS34 1.03 13.75 .41 .25 3.56 0
1-4034 420 0.42-0.50 12.5-14.5 <1 <1 0 0
1-4125 440C 0.95-1.2 17 <1 <1 0.4-0.8 0

Stainless knife steel has advanced from its early stages and quality stainless knife steel is now on a par with the best carbon steels and is easier to care for. Many of the advances have been in the area of heat treatment. The quality of the heat treatment will decide the final quality of the blade. A well heat treated poor quality piece of steel will out perform a poorly heat treated good quality piece of steel.

The use of vacuum heat treating allows very fine control of temperature during the heat treating process. It is temperature control that decides the quality of the finished knife blade.

Hardening is the process of heating then quickly cooling metal. Nominally the metal is heated to around 1050 degrees celsius then cooled to around 60-70 degrees celsius. Blades can be ice hardened or deep frozen where they are cooled to around minus 70 degrees celsius. Ice hardening gives a harder finished product.

Tempering is performed after hardening to increase the toughness of steel. In tempering, steel is heated to around 400 degrees celsius and held at that temperature for around an hour. Increasing tempering temperatures reduces toughness and corrosion resistance whilst increasing hardness whereas lower tempering temperatures lead to an increase in toughness whilst decreasing hardness. It is very important that both hardening and tempering are matched to the steel type and carefully controlled.

Hardness is normally measured using the Rockwell C scale. It is a measure of the depth a point will penetrate into steel given a certain amount of force for a specific amount of time. Quality professional knives are typically around the 54 to 56 HRC. Machetes and axes are much lower, usually around 50 HRC or less and fine surgical tools can be up around 58 HRC. A small amount on the scale makes a big difference to the edge hardness.

If a knife is likely to be used in harsher conditions, such as chopping through bones, it should be a lower hardness, whereas a knife used for delicate slicing can be harder without the risk of breaking. It is important that the hardness of a knife is matched to its use. A higher hardness does not necessarily mean that it is a better knife.

GUSTAV EMIL ERN knives are treated using a vacuum process and ice hardening to ensure a consistent top quality finished product. DEWEY knives have always been treated by the same company. Each batch is processed individually taking into account the type of steel and end use of the knife.

*18/8 is AISI specification 301 stainless steel
**18/10 is AISI specification 304 stainless steel