Strictly speaking, steel is just another type of iron alloy, and it's mainly including carbon steels, alloy steels, tool steels, and stainless steel four types.
First, steel is still essentially (and overwhelmingly) made from iron.
Second, there are literally thousands of different types of steel, many of them precisely designed by materials scientists to perform a particular job under very exacting conditions.
When we talk about "steel", we usually mean "steels"; generally speaking, steels fall into four groups: carbon steels, alloy steels, tool steels, and stainless steels. These names can be confusing because all alloy steels contain carbon (as do all other steels), all carbon steels are also alloys, and both tool sheets of steel and stainless steels are alloys too. Now, we will explain the four different sheets of steel as following.
The vast majority of steel produced each day (around 80–90 percent) is what we call carbon steel, though it contains only a tiny amount of carbon—sometimes much less than 1 percent. In other words, carbon steel is just basic, ordinary steel. Steels with about 1–2 percent carbon are called (not surprisingly) high-carbon steels and, like cast-iron, they tend to be hard and brittle; steels with less than 1 percent carbon are known as low-carbon steels and like wrought iron, are softer and easier to shape. A huge range of different everyday items is made carbon steels, from car bodies and warship hulls to steel cans and engine parts.
As well as iron and carbon, alloy steels contain one or more other elements, such as chromium, copper, manganese, nickel, silicon, or vanadium. In alloy steels, it's these extra elements that make the difference and provide some important additional feature or improved property compared to ordinary carbon steels. Alloy steels are generally stronger, harder, tougher, and more durable than carbon steels.
Tool steels are especially hard alloy steels used to make tools, dies, and machine parts. They're made from iron and carbon with added elements such as nickel, molybdenum, or tungsten to give extra hardness and resistance to wear. Tool steels are also toughened up by a process called tempering, in which steel is first heated to a high temperature, then cooled very quickly, then heated again to a lower temperature.
The steel you probably see most often in stainless steel—used in household cutlery, scissors, and medical instruments. Stainless steels contain a high proportion of chromium and nickel, are very resistant to corrosion
and other chemical reactions, and are easy to clean, polish, and sterilize.