For 10 points, name this principle alloy of iron that is known for its hardness and strength.
The rapid cooling of thin specimens of this substance in salt baths at various temperatures is used to generate isothermal transformation diagrams. An early form of this substance that originated in India is called its wootz variety. The interstitial-free type of this material has extremely low levels of carbon, unlike traditional types that have around one percent. Limestone is used to produce this material in the basic oxygen process, and a blast of air is used in the Bessemer process. This alloy contains around ten percent chromium in its "stainless" form. For 10 points, name this principle alloy of iron that is known for its hardness and strength. 
The rapid cooling of thin specimens of this substance in salt baths at various temperatures is used to generate isothermal transformation diagrams.
steel