Über den Einfluß von Thioharnstoff und Thioharnstoff-Derivaten als Beizinhibitoren auf die Wasserstoffaufnahme,die Inhibitorwirksamkeit und die Wechselbiegefestigkeit von Kohlenstoffstahl bei der Säurebeizung

Influence of thiourea and its derivatives as pickling inhibitors on hydrogen pickup, degree of inhibition and fatigue load of carbon steel during pickling in acids The influence of additions of thiourea (TU), N-methyl-TU, N, N′-tetramethyl-TU, N-phenyl-TU, N, N′-diethyl-TU and N, N′-diphenyl-TU upon the acid pickling of mild steel (1,0 M H₂SO₄ at 50° C) was investigated. Measured were inhibitor efficiency, uptake of hydrogen and alternating bending strength of the samples as functions of inhibitor type and inhibitor concentration. With all inhibitors a maximum of inhibitor efficiency and alternating bending strength and a minimum of hydrogen uptake was found in the same inhibitor concentration range of about 0,001 M. Compared to pickling in pure sulfuric acid at this optimum concentration the inhibitor efficiency is between 95,2 and 98,4%, the decrease of the hydrogen uptake between 8,6 and 63,3% and the increase of the alternating bending strength between 20,0 and 43,4%, depending upon the kind of inhibitor. The alternating bending strength increases roughly linearly with decreasing hydrogen content of the samples. In the optimum concentration range the inhibitor efficiency and the alternating bending strength increase, the hydrogen uptake decreases roughly linearly with increasing adsorption area or increasíng molecular weight of the inhibitors.