Match Column-I with Column- II
(P) Nitriding (I) Process of heating steel to redness and then cooling it very slowly
(Q) Annealing (II) Process of heating steel in presence of NH3 and producing hard coating of Iron Nitride on the surface of steel
(R) Tempering (III) process of heating steel to redness and then cooling it suddenly by plunging it into water or oil
(S) Quenching (IV) Process of heating quenched steel to a temperature well below redness and then cooling it slowly