Effect of some organic inhibitors on corrosion and hydrogen absorption by high carbon steel

The actions of thiourea, allylthiourea, NN' diethylyhiourea, dicyclohexylamine, diamylamine, N-ethylaniline and N-diethylaniline on the cracking susceptibility of cold rolled high carbon steel wire (0.86%C) in IN H2SO4 at 40°C have been studied extensively. The results show that with increase in concentration of inhibitors, the inhibition efficiency increases in all cases. Amines show no marked effect on inhibition efficiency. The wire is not susceptible to cracking in the presence of amines. In presence of thiourea derivatives of low molecular weight, the wire is more susceptible to cracking, which is attributed to the presence of hydrogen sulphide released from the thiou-compounds. All thiourea derivatives are found to inhibit predominantly the cathodic reactions. Amines inhibit mainly the anodic reactions. The results have been discussed in the light of rate controlling steps of hydrogen discharge at cathode. (Dr. Inder Singh, Shri A.K. Dey and Prof. V.A. Altekar, National Metallurgical Laboratory)