How many types of steel are there

 How many types of steel are there

　　Steel is not a single product. There are currently more than 3,500 different types of steel with varying physical, chemical and environmental properties.

　　About 75% of the steel in use today was developed in the past 20 years. To rebuild the Eiffel Tower today, engineers would only need a third of the steel.

　　A new type of steel used in modern cars is stronger than before, yet weighs 35 percent less than before.