Pig-iron is brittle because it contains a high percentage of carbon as impurity. Pig-iron is the product obtained from the smelting of iron ores in a blast furnace. It is a crude form of iron and contains about 4% carbon, along with other impurities such as silicon, sulfur, and phosphorus. The high percentage of carbon in pig-iron makes it brittle and weak, as it tends to form carbon inclusions in the iron matrix, leading to cracks and fractures under stress. Therefore, pig-iron needs to be refined further to remove impurities, including carbon, to make it stronger and more ductile.