What is the difference between pig iron and steel?

Pig Iron(cast Iron):- Pig Iron contains about 4 percent carbon as impurity along with other impurities like sulphur, phospurous,silicon and manganese. Pig iron is very hard and brittlewhich is unfit for many uses.Where as
Steel: Steel is an alloy Iron and 0.1 to 1.5% of carbon. Which can be used for making nails, screws, girders, bridges, railway lines etc.