Knife Materials & HardnessMaterialCarbon Steel is an alloy of iron and carbon, often including other alloys such as vanadium and manganese. Carbon steel commonly used in knives has around 1.0% carbon. A typical carbon steel blade is inexpensive, can be very sharp, and holds its edge well. Carbon steel is normally easier to resharpen than most stainless steels, but is vulnerable to rust and stains. Some professional cooks, particularly those in Asia, are partial to carbon steel blades because of their reasonable cost, cutting power, and edge-holding ability; others find these advantages outweighed in the kitchen by the extra maintenance required, as these blades must be cleaned, dried, and lubricated after each use. New carbon-steel knives may also impart a metallic or "iron" flavor to acidic foods, although over time, the steel acquires a dark patina of oxidation which acts to block this process.
Stainless Steel is an alloy of iron, approximately 10-15% chromium, possibly nickel, and molybdenum, with only a small amount of carbon. Most consumer knives made from low-carbon stainless steel are considerably softer than carbon steel knives and must be regularly sharpened. They are however highly resistant to corrosion. The thin, flexible, shiny blades common in cheap kitchen knives are typically made of low-carbon, inexpensive stainless alloys. As they are difficult to sharpen, they are often made with serrations, which slow dulling and enable them to cut adequately when they do become dull.
High Carbon Stainless Steel normally refers to higher-grade, stainless steel alloys with a certain amount of carbon, which combines the best attributes of carbon steel and ordinary stainless steel. High carbon stainless steel blades do not discolor or stain, and maintain a sharp edge. Most of these 'high-carbon' stainless blades also feature higher quality alloys often including amounts of molybdenum, vanadium, cobalt, and other components to increase strength, edge-holding, and cutting ability. Examples of such steels include 440-C, AUS-8, AUS-10, ATS-34, ATS-55
Laminated blades incorporate the best features of multiple materials by creating a layered sandwich of different steel alloys (there are no laminated blades made of plastic or ceramic.) Such knives are a modern descendant of the ancient Japanese San Mai sword-making process. Typically harder, more brittle steel is sandwiched between two softer, tougher steel alloys, so that the blade combines the attributes of both metals. Many higher-quality Japanese (San Mai) and Scandinavian blades are made in this way. A laminated blade's edge can often be made harder than an ordinary stainless steel knife, in turn facilitating a more acute grind on the cutting blade (improving the knife's cutting abilities). In more expensive Japanese San Mai kitchen knives, a carbon steel core (usually of a chrome vanadium cobalt alloy) is laminated with outer layers of alternating hard and soft stainless alloys (up to 65 or more).This reduces corrosion while maintaining strength and flexibility.
Titanium.The better titanium knives are made with a sintering process on a matrix of titanium (Ti) and carbides (carbon combination), using powder metal technology (instead of metal casting). The sintering process melts the elements and recombines them under great heat and pressure. The carbides in the alloy allow for the blades to be heat-treated to a hardness required for knives.Very lightweight and durable, they stay sharper longer than steel and are relatively easy to sharpen.
Ceramic blades are both strong and brittle. They are stronger than steel and have an edge that is much thinner than steel making cutting considerably easier.The edge can last significantly longer than a steel blade with proper care. Because of their brittleness ceramic knives are best used for slicing (not chopping). Zirconium oxide, aluminum oxide and other ceramics, in pelletized form, are melted to form this very hard, very dense material. Like titanium, they do not impart any taste to food and are immune to corrosion. Because of the lightness of ceramics, they do not have the heft you might expect of a metal chefs knife. Although not as fragile as one might expect care should be taken not to drop ceramic knives to avoid breaking off the tip. Sharpening and repairs are done on diamond hones and professional sharpening is advised.
Hardness Knife manufacturers often advertise that their blades are of a certain Rockwell Hardness. The range of hardness for functional knife blades is usually between about RC50 and RC63. Surface hardness is a quick test used for quality assurance to determine if the proper heat treatment properties have been attained.
Higher hardness does not necessarily mean a knife is better. What it indicates is that with proper sharpening you should be able to attain a finer edge but that it will be harder to sharpen than a less hard knife. Depending on the chemistry of the knife, stainless steel should hold an edge longer as it is tougher than carbon steel, i.e. less susceptible to wearing away.
Most sharpening steels have a higher hardness than knives. The choice of steel, at least from a hardness perspective, is therefore less important.
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