20) One component of C50 steel is heated to 830 Degree Centigrade, soaked it for some time and then quenched in oil. Again it is heated to 600 Degree Centigrade and quenched in oil. Name this process of heat treatment.

21) Which one of the following groups of quenching media is in order of their severity of the cooling rate, i.e. from slow to rapid cooling ?

22) Which one of the following processes is adopted to improve the internal structure of steel, which has been subjected to severe hammering ?

23) Which one of the following structures of steel is obtained due to the drastic cooling from the austenite structure ?

24) Which one of the following processes by which steel is heated to the required temperature and then cooled slowly in the furnace itself ?