Corrosion behavior of 19 low alloy steels with different compositions under different atmospheric conditions is reported in this paper. The time of exposure extends as long as 15 years at 10 experimental sites typical of diferent atmospheres. The results show that corrosion behavior of steels varies remarkably with atmospheric conditions. Alloying elements such as Cu, Ti, Re, Mn are beneficial to the improvement of atmospheric corrosion resistance, with Cu being the most effective. Rust layers are investigated by means of X-ray diffractometer, SEM, EPMA aswell as electrochemical techniques. Regression equation expressing the relation between weight loss and time has been derived from short-term experimental data through statstical treatment,and is used for finite extrapolation forecast. It is observed that the corrosion resistance of the low alloyed Mn steel placed at the site of a river bridge is inferior to that of carbon steel on extended exposure.

The authors have proved in this paper that the inhiditon of pitting corrosion of GCrl5 steel by sodium molybdate in near-neutral solution is not due to depolarization of Na_2MoO_4 but to competitive adsorption of M0O_4~(2-) with Cl~-. Thus, Mo accumulates at active sites on the metal surface and the corrosive activity of Cl~- decreases. A complex passive film containing Fe~(3+) and Mo~(6+) has also been formed on the metal surface. According to the model of competitve adsorption of MoO_4~(2-) with Cl~-, a linear relationship detween the logarithm of the critical concentration of MoO_4~(2-) and the logarithm of the concentration of Cl~- can be derived as logCMoO_4~(2-)= A logC_(Cl)~-+B vnd the experimental critical values of CmoO_4~(2-) are in good agreement with Values predicated dy the above equation.

AC impedance measurement in frequency domain usually takes a lony time, resulting in change of the electrode surface which in turn affects the accuracy of measurement. The time domain method is adopted in our laboratory by setting up a transient signal recording syatem consisting of a Z—80 microprocessor and an I/0 interface. The system has such functions as signal generation, data sampling data storing and data processing. A 8.2mV potentialstep generated by D/A is applied to the cell via potentiostat and the transient response current is recorded simultaneously. Data averaging and data smoothing technique efficiently improve the ratio of signal to noise. We select the Laplacian transform algorithm in which the exponential and linear function are used as an approximation of the sampled data Signal recording and data processing proceed automatically.

The method described in part I has been used to determine AC Impedance of the dummy cells and electro-chemical systems. The measured results pretty well agree with those obtained by theoritical calculations.The complex plane plot for Pt/Fe ( CN)_6~(3-)/Fe (CN)_6~(4-) system appears as a straight line with unit slope. Both Z′～ω~(-1/2) and Z" ~ω~(-1/2) relations are linear, verifing that the electrode process is mass-transfer-controlled. The obtained averaging diffusion coefficient of Fe ( CN)_6~(?) and Fe ( CN)_6~(4-) is 7.24 ×10~(-6)cm~2/s.The impedance plane plots for Fe/H_2SO_4 are semicirclar showing that the electrochemical reaction is charge-transfer-controlled. The charge transfer impedance R_r increases with decrease in concentration of H_2SO_4. When corrosion inhibitor IN7 is added to 1 N H_2SO_4/Fe system, the charge transfer impedance apparently increases from 85.3Ω·cm~2 to 286Ω·cm~2.

The effect of deformation on hydrogen permeation in iron is related to tension state as well as the initial and boundary conditions of experiments When initial condition is that specimens are hydrogen free, dislocation is hydrogen trap。When initial condition is that specimens are precharged to a steady state, and then, charging is discontinued so that hydrogen is released from the specimens, dislocation carries hydrogen and accelerates hydrogen evolution. Under the second case, if the boundary condition is that charging is maintained, dislocation accelerates trapping of hydrogen; and if charging is stopped, dislocation accelerates hydrogen evolution.

In this paper, the passive films of aluminum-copper alloy treated with K_2Cr_2O_7 and nitrogen-containing passivation agent(8108) were studied by XPS respectively. The results show that the former contains Cr_2O_3 species besides the main component A1_2O_3, the latter contains AlN and aitrogencontaining complexes in addition to Al_2O_3.It is interesting to note that no opper signal can be detected on the surfaces of both passive films. Both films, moreover, show a definite mangnesium peak although magnesium content in the alloy is very low.

Some characteristic parameters of hydrogen embrittlement (HE) of 20g steel in SMA-1, SAF and HCl detergent solutions were measured by methods of mechanics, fracture mechanics and electrochemistry. The results reveal that the electrochemical hydrogen permeation transient method canbe adopted to evaluate the susceptibility to HE of mild steels in detergents. The 20g steel has the lowest susceptibility to HE in SMA-1 detergent solution and the highest susceptibility in HC1 detergent. In this respect, SMA-1 is considered a highly effective and safe detergent in contact with 20g steel.

The structure and the hot-corrosion resiance of cast nickel-base superalloy M38 irradiated by CO_2 laser beam of 1.3kW output have been examinated by microscopy, SEM, EMPA, X—ray diffraction analysis and potential measurements in contrast with those unirradiated. The hot corrosion tests were carried out in the crucible with saltmixture of 75% Na_2SO_4 and 25% NaCl at 900℃ for 15hr, 35hr, 55hr, 80hrand 95.5h, respectively. The results show that the remelted-solidifying surface layer irradiated by laser besm may be regarded as an integrated effective coat due to its much better corrosion resistance(particularly, no obvious grain boundary penetraion corrosion) and the firm bonding between the irradiated urface layer and the base material.

The hydrogen distribution in metals can be measured by means of laser hydrogeh detector set up in the authors' laboratory. The results show: 1. Relative hydrogen index D_H may be used to indicate relative content of hydrogen, with consfant background hydrogen in steel 2. The hydrogen content is related to the time of hydrogen penetration and the distance between the surface and the point measured; 3. The measurement of the hydrogen distribution in various welded joints shows that such distribution varies with time. Our practice proves that the hgdrogen detector set up in our laboratory can be used to measure local hydrogen distribution in metals.