Plain carbon steels

Plain carbon steel is an alloy of iron and carbon where the amount of carbon ranges from, 0.015% to 2%. This material has great strength and hardiness which are essential for motor bodies, appliances, apparatus, ships, containers, and the structures of buildings.

Carbon steel is by far the most widely used kind of steel. The properties of carbon steel depend primarily on the amount of carbon it contains. Most carbon steel has a carbon content of less than 1%. Carbon steel is made into a wide range of products, including structural beams, car bodies, kitchen appliances, and cans. In fact, there are 3 types of plain carbon steel and they are low carbon steel, medium carbon steel, high carbon steel, and as their names suggests all these types of plain carbon steel differs in the amount of carbon they contain. Indeed, it is good to precise that plain carbon steel is a type of steel having a maximum carbon content of 1.5% along with small percentages of silica, sulphur, phosphorus and manganese.

Classification of Plain carbon steels:-

Plain carbon steels are further subdivided into four groups:

1. low carbon steels (carbon < 0.30%): Often called mild steels, low-carbon steels are the most commonly used grades. They machine and weld nicely and are more ductile than higher-carbon steels.

2. medium carbon steels (0.30% < carbon < 0.60%): Increased carbon means increased hardness and tensile strength, decreased ductility, and more difficult machining.

3. high carbon steels (carbon > 0.60%): these steels can be challenging to weld. Preheating, postheating (to control cooling rate), and sometimes even heating during welding become necessary to produce acceptable welds and to control the mechanical properties of the steel after welding.

4. Very high carbon steels: very high-carbon steels are used for hard steel products such as metal cutting tools and truck springs. Like high-carbon steels, they require heat treating before, during, and after welding to maintain their mechanical properties.

   1. hypocutectoid steels (carbon < 0.80%).

   2. eutectoid steels (carbon = 0.80%). and

   3. hypereutectoid steels (carbon a 0.80%).

The classification of carbon steels into first three classes is of greater practical importance and is widely accepted one.

Limitations of plain carbon steel:

Like everything, the plain carbon steels do have some appreciable properties but also consists of some limitations. These are:

1. There cannot be strengthening beyond about 100000 psi without significant loss in toughness (impact resistance) and ductility.
2. Large sections cannot be made with a martensite structure throughout, and thus are not deep hardenable.
3. Rapid quench rates are necessary for full hardening in medium-carbon leads to shape distortion and cracking of heat-treated steels.
4. Plain-carbon steels have poor impact resistance at low temperatures.
5. Plain-carbon steels have poor corrosion resistance for engineering problems.
6. Plain-carbon steel oxidises readily at elevated temperatures.