An electrochemical hydrogen permeation transient method was used to study the effect of environmental factors, such as pH.concentration of H_2S, temperature, concentration of NaCl and electrode potential, on the hydrogen entry in sulfide stress cracking (SSC) of steel. Experimental data showed that the conclusions obtained agree with those published in literature by various authors as obtained by traditional constant load, constant deflection or other methods.Accordingly, the authors hold that the electrochemical hydrogen permeation transient method would be a very useful means in studying the effect of environmental factors on SSC.

The effect of different tempering temperatures on diffusion coefficient of hydrogen, hydrogen solubility and time to failure in sulfide stress cracking (SSC) test of 2Cr13 stainless steel was studied by means of electrochemical hydrogen permeation technique and constant load SSC test etc. Experimental results show that as the tempering temperature changes, the variation of t_f corresponds well to the variation of the diffusion coefficient and solubility of hydrogen in the steel.Accordingly, the authors hold that the electrochemical hydrogen permeation technique may be used as a useful means in studying the susceptibility of steel to hydrogen embrittlement.

The impedance of aluminum polarized in a chloride solution by a series of anodic current densities from approximate 300μA/cm~2 to 30 mA/cm~2 was determined using a phase sensitive detector.The results show that the relation between log R_f (Faradaic resistance) and logi (applied current density) appears as a straight line with a slope equal to tg (-45°) and the relation between capacitance C and i also appears as a straight line.These results support such a proposition that the active area during anodic dissolution is a linear function of the applied anodic current while the real anodic current density remains practically unchanged so that the potential is also unchanged.

In order to clarify the effect of Cr and Mo on the propagation of localized corrosion of steels, the electrochemical behavior of pure Cr and Mo and of some stainless steels was studied under conditions similar to those existing inside occluded corrosion cells (OCC) of steels.Oxygen-free FeCl_2 and/or CrCl_3 solutions were used for experiments.Cr is passive if pH is higher than ca.1.8.Therefore Cr may retard the propagation of localized corrosion of steels in its early stage.But the hydrolysis of Cr~(3+) may change the pH to even lower values.At such low pH and high Cl~- co centration, Cr is active in the potential range of interest for localized corrosion of steels.Mo is passive in these more acidic conditions and the passivity of Mo in this potential range is attributed to the formation of a film of MoO_2, which is very stable and protective.Mo is thus effective to retard the propagation of localized corrosion of steels in its more advanced stage.

The author studied the SCC mechanism of 34CrNi3Mo steel in 30% NaOH solution, through potentiostatic SCC test based on fracture mechanics, electrochemical hydrogen permeation, acoustic emission and electrofractography.The results showed that above 50℃ SCC can occur when the potential is at free corrosion potential.When at 80℃, the potential is more positive than-1150mV (SCE) , the cracking belongs to active path corrosion (APC) type of SCC; When the potential is more negative than-1150mV (SCE) , the cracking belongs to hydrogen embrittlement (HE) type of SCC.Even in the same steel—environment system the mechanism of SCC may be changeable.Therefore it is not proper to say that SCC is only governed by a single mechanism.

It has been proved that most of the titanium alloys are susceptible to the so-called hot salt stress corrosion cracking under the combined action of high temperature, halide salt and stresses.In this paper the susceptibility of hot salt stress corrosion cracking of titanium alloy Ti-679 was investigated in the temperature range of 350～500°C.Experimental studies show that the microstructure of the alloy has pronounced effect on the susceptibility of H.S.S.C.C.It was shown that the threshold stress for H.S.S.C.C.of the specimens with α+β annealed structure was higher than that of the specimens with β annealed structure under the same hot exposure conditions.Experimental results also proved that the threshold stress of the specimens with compressive stress on the surface was higher than that of the specimens without it.Ion microprobe scanning analyses on the fractured surface showed that hydrogen was greatly concentrated at the crack surface and that hydrogen produced during the stress corrosion of titanium alloy by halide salt and subsequently absorbed by the alloy was responsible for cracking.

The hot-corrosion resistance of some commercial nickel-base cast superalloys containing different amounts of niobium were evaluated by crucible test and burner-rig test.Results indicated that the addition of niobium to those alloys containing smaller amount of chromium and forming Al_2O_3 scale was detrimental to their hot-corrosion resistance; the addition of a certain amount of niobium to those alloys having medium amount of chromium contents and forming Cr_2O_3 scale was beneficial; but when a relatively large amount of niobium was added, the hot-corrosion resistance of the superalloys decreased, because of the presence of massive η phase. On the basis of a large amount of analysis of corrosion products in the scale, it was shown that niobium could alter the composition of the oxide scales on the surface of the alloys studied, affecting their hot-eorrosion, esistance.

The ring-disk electrode has been used to study the potentiodynamic behaviour and electrochemical dissolution of A_3 steel in concentrated alkaline solution.The soluble Fe (Ⅱ) and Fe (Ⅲ) species were collected on the ring electrode when sweep measurement or galvanostatic polarization were made on A_3 steel disk electrode.The proportion of the collected current to the total current of oxidation or reduction has been measured.It was found that the collected current of soluble species was increased significantly with increasing temperature and KOH concentration. The electrochemical corrosion process of iron in concentrated alkaline solution was discussed.