Electrochemical investigation of the surface layers composition of highly alloyed steels after heat treatment

The heat treatment of steels is one of the effective technological process allowing to form its necessary properties. In this case the changing of qualitative and quantitative composition of surface layers during heat treatment results in significant effect on performance characteristics of relevant products. The electrochemical behavior of carbides of different composition (MC, M$_3$C, M$_6$C) formed in the surface layers of highly alloyed steels (as an example, the steel grade C105W1) in the process of heat treatment at different temperatures with following drawing back process has been investigated. It has been established that on anodic voltammograms, formed in 40% NaOH solution (at scan potentials area from -1.0 V to +0.2 V and v=1 mV/s) the clear peak current of M3C carbide at -0.60 $\div$ -0.50 V is recording. In these conditions the peak current of M$_6$C carbide (E=-0.30 $\div$ -0.20 V) appears little and MC carbide forms only small wave in the potential area from -0.15 V to -0.05 V, which can be used for quantitative determination of M3C carbide containing. It has been shown that clear expressed analytical signal of M$_6$C carbide is formed at v=80 mV/s, in this case peak current of M$_3$C carbide appears little and signal of MC carbide is eliminated. It has been found that in 10% H$_3$PO$_4$ solution at v=80 mV/s in the potential area from +1.3 V to +1.2 V only one peak current of MC carbide appears. On the basis of received results it is concluded that in steel samples without processing heat treatment the MC carbide phase does not occur, and in hot quenching samples the quantity of formed MC carbides become similar after drawing back process. The containing of M$_3$C carbide increases with heat treatment temperature rising, and analogous dependence for M$_6$C carbide has been observed. Therefore, the optimal conditions of electrochemical control of carbide phase containing in surface layers of highly alloyed steels have been established and the possibility of its realization for development of steel heat treatment and drawing back processes for corresponding metal properties forming has been shown.