In simple words, steels are deformable alloys of iron with carbon and other elements, generally manganese, silicon, sulphur, and phosphorus.

CLASSIFICATION OF STEELS AND STEEL MAKING PROCESSES:
    There is no unique universally adopted classification of steels because they have got extreme variation in their properties, as produced by different methods.  They can be classified by following features:
    1. APPLICATION : Furnace and Boiler Steels, Steels for railway Transport, Structural Steels, Ball-Bearing, Tool Steels Spring Steels, Transformer steels, Stainless Steels Gun Steels , Tube Steels , Etc.
    2. QUALITY: Depending on the difference in allowed concentration  of harmful impurities, i.e. plain, quality and high quality grades.
    3. COMPOSITION: Here they are grouped into, carbon steels, low, medium and high alloyed steels.
    4. BY THE NATURE OF STEEL SOLIDIFICATION IN MOULDS: Killed, Semi-    Killed and Rimming Steels.
    5. BY THE MANUFACTURING PROCESS:     
        a. BY THE TYPE OF STEEL MAKING PLANT: Converter Steel, Open Hearth Steel, Electric Steel, Electro Slag Remelted Steel, Etc.
        b. BY THE TYPE OF PROCESS:  Basic and Acid Open hearth steel, basic and acid electric steel, vacuum degassed steel, steel treated with synthetic slags, inert gas blown steel, etc.
        c. By the state of metal: In solid state (ex: sponge iron), in electrolyte state, in powdered state, in pasty state, in molten or cast state.