It is believed that an overload may have significant influence on fatigue crack growth in air, but what influence it would have on corrosion fatigue crack growth in sea water was seldom reported. In this paper, the intermittent overload which simulated a sltuation that a number of small wave loads follow a big wave overload was investigated to see what would happen to the cracks in critical position, such as undercuts in weld toe or inherent defects in base metal for offshore structures. The results showed that in 3.5％ NaCl solution the overload effect on fatigue crack growth was still active, but the retardation effect of a single overload in tension was less than that in air. The reason for this may be very complex, which related to the dissolution reaction, solution pumping action as well as the effect of corrosion products. It was also found that there was little difference between the crack growth rates in 3.5％ NaCl solution when the overload ratio changed from 1.5 to 2. Fractographic observations of some specimens from SEM showed that high plastic strain appeared in the overload band and secondary cracks were found near those high strain areas.

The corrosion inhibition of carbon steel by benzyltripenyl phosphonium bromide (BPB) and 1,4-di(triphenyl phosphonium bromide) butylane (DPBB)in 0.5MH_3PO_4 solution Containing CNS-,I~- was investigated by gravimetric, potentiodynamic and impedance determination techniques. The experimental results show that the synergistic effect of corrosio inhibition appears between above-mentioned anions and phosphonium salts. The synergistic effect was closely relevant to the concentratio ratio of anion to phosphonium salt. The adsorption of BPB or DPBB on carbon steel follows Bockris-Swinkels isotherm in 0.5MH_3PO_4 solution without anion at 25℃. But adding anions into 0.5M H_3PO_4 solution containing BPB or DPBB, the interaction among adsorbed species became significant. Thus, a free energy parameter f was introduced into the Bockris-Swinkels isotherm as follows θ/(1-θ)~n·[θ+n(1-θ]~(n-1)/n~1·exp (-fθ)=C/55.5exp(-△G_a~0/RT)

The crack growth of 15Mn steel with various microstructures in 3.5％ NaCl solution was investigated, It is found that the microstructures of steels have Considerable influence on corrosion fatigue. With increasing Stress intensities,crack closure effect decreases and average hydrogen content at crack tip increases. The fracture modes vary from striations to intergranular fracture and then to quasi-cleavage fracture with crack growth. The relation between electrochemical conditions and mechanical variables is discussed. The componund mechanisms of corrosion fatigue are proposed. A fracture-mode-map of 15Mn steel is worked out.

The anodie behavior of Ti in H_3PO_4, H_2SO_4 and HCl solutions has been studied by steady state and transient electrochemical techniques and XPS technique. The experimental results are as follows. (1) The titanium hydride TiH is detected from the XPS of titanium electrode self-activated in these solutions, and it is proposed that the atomic hydrogen formed in self-activation process diffuses into the titanium metal lattice and partially forms titanium hydride. (2)Thesecond anodic peak, which is not found in steady-state polarization curve, appears in volatmmogram at about-0.12V and is assigned to the oxidation of atomic hydrogen. The oxidizing process is controlled by the diffusion of atomic hydroogen in titanium metal lattice as evidenced by the fact that the peak current is propotional to v~(1'2). Therefore, the Kelly's mechanism of the anodic tprocess of titanium in these solutions must be modified by considering vhe formation and oxidation of atomic hydrogen. The AC impedances erify this conclusion qualitatively.

A corrosion-resistant surface is obtained on steel by a two-step anodization Process in a borate solution to which 8-hydroxyquinoline(HQ) is added in the second step. Polarization and impedance measurements have been made in an aqueous chloride medium to characterize the samples and to assess the influence of the EDA additive and chromate post-treatment. It has been shown that the resulting layer acts mainly as an interphase inhibitor of oxygen cathodic reduction. Significant improvements in corrosion resistance of posttreated samples are found especially when EDA was added to HQ containing solution for anodic treatment. It is also verified from impedance data that Rp and R_f, which are relevant to the two eapaeitive loops in the diagram, are both significant for evaluating the protective effectiveness of the inhibitve layer.

The corrosion behavior of plain 12CrMoV, mild steel, hot-dip aluminized 12CrMoV and mild steel was studied in SO_3 from decomposition of ferric sulfate by using a specially designed apparatus. The experimental results indicated that accelerated corrosion of plain 12CrMoV and mild steel was caused by SO_3 from decomposition of ferric sulfate. Corrosion products on plain 12CrMoV and mild steel specimens were the same, mainly ferric sulfate and ferrous sulfate, with no sulfide of metals either on surface or at scale/substrate interrace. The corrosion resistance of hot-dip aluminized 12CrMoV and mild steel were better than that of either uncoated steel. The corrosion products on surface of hot-dip aluminized 12CrMoV specimen were alumina and aluminum sulfate only while aluminum sulfate and ferric sulfate were found at coating/substrate interface. From the experimental results, possible mechanism of corrosion was proposed.

Corrosion of steel in concrete is one of the important research:toplcs. Based on the corrosion process, a couple of electrochemical techniques have been tried to measure the corrosion of rebar. This paper reports some preliminary results on it using AC impedance technique. Because the experimental data could not fit the impedance plot of simple equivalent circuit, the authors determined the corrosion of specimens in terms of impedance modulus

The passive property of new type maraging stainless steel 0 Crl2Ni5MnMoCuAlTiREB is researched in the passive state formation, the stability, and localized damage of passive film by means of various electrochemical detection methods and TEM. The results show that the passive pioperty of the steel in solid solution state is not so good and it can be improved by short time aging. After a long time aging, the passive property will gradually lower again because of the precipitation of intermetallic compound. Optimum stability of passive film is obtained with proper heat treatment, but the critical passive current density i. is larger. Deformation in solid solution state decreases the stability of passive film formed on aged steel, but hardly affects the pitting breakdown potential φ_b.

Plate of spring steel 50CrV for making driving leafspring of locomotive was surface hardened by CO_2 laser beam. The hardened zonee was characterized by a microstructure with very fine martensite and trace of residual austenite. Measurements of the surface residual stress were performed. The results showed that the surface stress state was compressive in the hardened zone, while it was tensile in the heat effected zone, and that the change of hardness was in good agreement with the change of the stress from compressive to tensile. Obviously, the compressive state of the stress in the hardened zone may be due to the volume expansion associated with the martensitic transformation. Corrosion potential distribution and dynamic potential polarizatign behaviour of the laser hadened zone in dilute solutions of Na_2SO_4, NaOH and H_2SO_4 etc. was studied. It followed that the hardened zone exhibited higher corrosion resistance than both it's vicinity of heat effected zone and the untreated substrate. The passivation range of the laser hardened zone widened significantly and the corrosion current of passivation range decreased greatly, in some, cases, by nearly one order of magnitude as compared with that of untreated substrate. The corrosion behavior was discussed in relation to it's characteristic microstructure and stress state of the laser hardened zone.

Pd-Ti surface alloy was produced by bombarding a Pd-plated Ti alloy with Xe ions. The electron spectroscopic profile analyses show that the distribution of Pd is quite homogeneous through the surface layer, which consists of Ti, Pd and their oxides, nitrides etc. Near the surface TiO_2 is the principal component of the passive film formed. The Pd/Ti ratio is large and decreases with depth from the surface inwardly. In boiling 1NH_2SO_4 the average corrosion rate of the Pd·Ti surface alloy is about 1/60 of Ti alloy matrix after 6 hours of immersion, and corrosion rate in the near-surface region is less by three orders of magnitude. It is expected that the Pd-Ti surface alloy by IBM would be better than the Pd-Ti bulk alloy and Pd-implanted alloy for corrosion protection.

The concentration distribution of hydrogen at crack tip of austenitic stainless steel 321 after stress corrosion and polarization was determined by LT-1A type Ion Microprobe Mass Analyzer(KYKY). Although the concentration of hydrogen at crack tip after stress corrosion cracking at open circuit or under cathodic polarization is higher than that under anodie polarization, yet the cracking time of the latter is much shorter than that of the former. Although the hydrogen evolved during stress corrosion can enter and can be enriched in the crack tip region, yet the amount of enrichment is not sufficient to cause cracking. It is concluded that anodic dissolution plays a controlling role during stress corrosion cracklng of this system.

Conversion of the mild steel surface from active to passive state took place during heating of ammonium sulfite cooking. The results of surface analyses indicated that under passive conditions, a passive film was formed on the steel surface in ammonium sulfite liquors. The film consists of double layers, the outer layer being(NH_4)_2Fe(SO_3)_2·H_2O crystals; and the inner layer, iron oxide. Under active conditions,a loose mixture which was mostly FeS was formed on the steel surface. Several environmental effects on passivation were also investigated. Three simple corrosion prevention techniques were tried in the pulp mill, by which the corrosion rate of rotary spherical digester can be controlled under 0.2mm/y.