Carbon steel is an alloy of iron and carbon, often including other elements such as vanadium and manganese. Carbon steel commonly used in knives has around 1.0% carbon (ex. AISI 1095), is inexpensive, and holds its edge well. Carbon steel is normally easier to resharpen than most stainless steels, but is vulnerable to rust and stains. The blades should be cleaned, dried, and lubricated after each use and new carbon-steel knives may impart a metallic or “iron” flavour to acidic foods, though over time, the steel will acquire a patina of oxidation which will prevent corrosion. Good carbon steel will take a sharp edge, but is not so hard as to be difficult to sharpen, unlike some grades of stainless steel.
Stainless steel is an alloy of iron, approximately 10–15% chromium, possibly nickel, and molybdenum, with only a small amount of carbon. Typical stainless steel knives are made of 420 stainless, a high-chromium, low-end stainless steel alloy often used in flatware. Most consumer grades of low-carbon stainless are considerably softer than carbon steel and more expensive grades of stainless, and must be more frequently sharpened though most are highly resistant to corrosion.
High carbon stainless steel normally refers to higher-grade, stainless steel alloys with a certain amount of carbon, and is intended to combine the best attributes of carbon steel and ordinary stainless steel. High carbon stainless steel blades do not discolour or stain, and maintain a sharp edge for a reasonable time. Most ‘high-carbon’ stainless blades are made of higher-quality alloys than less-expensive stainless knives, often including amounts of molybdenum, vanadium, cobalt, and other components intended to increase strength, edge-holding, and cutting ability.
Laminated blades combine the advantages of a hard, but brittle steel which will hold a good edge but is easily chipped and damaged, with a tougher steel less susceptible to damage and chipping, but incapable of taking a good edge. The hard steel is sandwiched (laminated) and protected between layers of the tougher steel. The hard steel forms the edge of the knife; it will take a more acute grind than a less hard steel, and will stay sharp longer.
Titanium is lighter and more wear-resistant, but not the hardest metal in the world. However it is more flexible than steel. Titanium does not impart any flavour to food. It is typically expensive and not well suited to cutlery.
Ceramic knives are very hard, made from zirconium dioxide, and retain their sharp edge for a long time, are light in weight, do not impart any taste to food and do not corrode. Suitable for slicing fruit, vegetables and boneless meat. Ceramic knives are best used as a specialist kitchen utensil. Recent manufacturing improvements have made them less brittle.
Plastic blades are usually not very sharp and are mainly used to cut through vegetables without causing discolouration. They are not sharp enough to cut deeply into flesh, but can cut or scratch skin.