A steel drill bit may refer to either a drill bit made of steel or a drill bit designed to drill through steel. The precise meaning of the term depends on the context in which it is used. Steel is the most commonly-used material in drill bits, and bits are available in different grades of steel with cheaper bits typically being made of less-durable material. The term "steel drill bit" may mean a drill bit that is specifically made for drilling through steel. Tempered steel is a very durable material and specialized drill bits are needed to drill through this type of steel successfully.
Most ordinary drill bits are made of steel. Better bits are typically made of higher-carbon steel, and can withstand more use and abuse before either becoming dull or breaking. Bits designed to drill through masonry are typically made of high-quality steel, and are very hard, but still wear out more rapidly than ordinary drill bits, as masonry causes much more wear and tear on a drill bit even when a hammer drill is used. Heat buildup can shorten the working life of any drill bit as excess heat can ruin the temper of the steel and make it much more prone to breaking.
Some types of steel drill bits are designed to drill through very hard tempered steel. Ordinary drill bits are often able to drill through mild steel, although this causes wear and can lead to excessive heat buildup. Normal drill bits typically fail badly when used to attack high-carbon steel, as they are typically not as hard as the material that they are being used to drill and are thus unable to drill through it effectively.
Specialized steel drill bit sets make use of more expensive steel that is exceptionally hard. This steel is able to drill through other steel with relative ease, although heat buildup can still be a problem. Bits used to drill through a great deal of hard steel should be cooled and lubricated with oil in accordance with the recommendations of their manufacturers. Many larger varieties of steel drill bit are designed to be used in tools that automatically apply a stream of oil to cool the bits.
The most modern and durable steel drill bits are made from high speed steel (HSS). This alloy is designed to survive use in tools that operate at high speeds and is more durable even than the high-carbon steel used in normal steel drilling bits. Even HSS bits require cooling when used for a protracted period of time, however.