The characteristic curve of SCC as well as the nucleation and propagation of cracking of stable austenitic alloy(4J29)in aqueous solution of 3.5% NaCl were investigated.Furthermore,the behavior of hydrogen-induced delayed fracture of this alloy was studied in hydrogen charging condition.The similarity between the behavior of SCC and the hydrogen-induced delayed fracture indica- ted that the nature of SCC of the alloy in aqueous media with Cl~- was hydrogen- induced cracking. The effect of CH~+ and H~+ concentration on SCC of the 4329 alloy was also included in this study.

A simulated crevice corrosion cell was used to study the anolyte within crevice of Steel Cr18Ni9Ti in 3% NaCl sulotion.As the anodic current increased the pH value decreased rapidly and the alloying element Cr was the main factor for the lowering of pH value of anolyte within crevice.It was found that the Cr(Ⅲ)existed in the form of stable soluble hydroxy-chloro-complexes in the occluded solution within crevice.The insoluble hydroxide Cr(OH)_3 precipitate was not observed.It was deduced that the passive film on the surface of the stainless steel within crevice was destroyed by the formation of hydroxy-chloro- complexes through a process of characteristic adsorption of Cl~- ions onto the passive film and then combination with Cr,which was the main component in the passive film.Thus corrosion inside crevice was accelerated.

The effect of secondary phase on stress corrosion cracking propagation was studied and its mechanism was discussed according to electrochemical behavior of each phase in the duplex stainless steel with austenitic or ferritic matrix. The polarization curve of each phase was measuredin situ by a technique of shielding microstrueture selectively.It was confirmed that the secondary phase (δ-phase in austenite-basesteel or γ-phase in ferrite-basesteel)has the effect of hindering crack from propagation and it acts as a cathode under such a condition that stress corrosion cracking is hampered.Therefore the authors consider the improbable anodie dissolution of the secondary phase as one of main reasons of hindering crack propagation with aresult of increased stress corrosion resistance of the duplex stainless steel.

The morphology and mechanism of corrosion,of the internals of the stripper of the urea plant were studied by SEM,AES and TEM spectrometry etc.It was found that intergranular corrosion IGC ocurred for 316L stainless steel in the non- sensitized condition and that there was no Cr depletion,instead,P and Si were enriched at grain boundary regions.The P content at the grain boundary was two orders of magnitude greater than that of the average.However,there was no segregation of P or Si at grain boundary region in high purity 25Cr-22Ni- 2Mo-N samples cut from the internals which did not suffer from IGC in the same environment. Therefore,the authors consider that segregation of P and Si at grain boundaries is one of the important reasons for IGC of non-sensitized 316L SS in the urea medium.

By means of electrochemical method (EPR method),the effects of various materials and different sensitizing conditions on sensitization degree of Austenic stainless steels are investigated,using the Fe-11% Ni-Cr(6～18%)stainless steels as simulated chromium depleted region.For stainless steels containing no molybdenum it was found that active dissolution occurs at chromuim depleted regions with less than 16% Cr.Thus EPR method is more sensitive than Stra- uss method.After the test,the surfaces of samples were examined by optical microscope.The results are as follows:as the grain boundaries or the vicini- ties of inclusions,pits are first observed with certain directions,then they join with each other to form corrosion grooves.

The anodic polarization curve of ferritic stainless steel in 0.5M sulfuric acid solution at 298°K has two active disolution current peaks,but that of ferritic stainless steel With niobium has only one active disolution current peak,it is suggested that niobium prevents the sensitization of alloy. The composition of the passive film formed by means of potentiostatic oxidation in depth-profiles has been analysed by means of argon ion sputter- etching and Auger electron spectroscopy.Chromium was enriched in the passive film.The degree of Cr-enrichment in the passive film increased with an increasing anodic potential of film formation,and the degree of Cr-enrich- ment of the passive film of stainless steel with niobium is higher than that with- out it.

The crystallographic orientations of Cd and Cd-Ti electrodeposited layer on the high strength steel 30CrMnSiNi2A have been studied by x-ray diffraction technique.The axes of textures of deposited layer have been measured.The results are as follows:〈11■2〉,〈11■2〉+〈10■0〉for the electrodeposited Cd in the cyanide and non-cyanide bath,respectively.〈11■0〉+〈10(?)0〉for the electrodeposited Cd-Ti(0,3～0.6%)in the non-cyanide bath.Due to a little maltose(brightener)added in the non-cyanide bath of eleetrodeposite Cd-Ti, the tendency of preferred orientation has increased.A little titanium in the deposited layer plays an important role in the change of orientation and hydrogen absorption.Therefore,the trend of hydrogen embrittlement of the steel is reduced.

The weight changes due to hot corrosion of Ni-Cr(Cr 15～25),Ni-Cr-Al- Ti (Cr 15～25,Al 2～4,Ti 2～4),and Ni-Cr-Al-Ti-Ce(Ce0.07-0.39)systems have been determined at 900℃ in both pure Na_2SO_4 and 75% Na_2SO_4-25% NaCl salt bath.It has been established that the hot corrosion degradation of Ni-Cr alloys was more evident in the salt mixture than in pure Na_2SO_4.The hot corrosion behaviour of Ni-Cr-Al-Ti alloys was superior to that of the binary Ni-Cr alloys in the salt mixture.However similar results were not obtained in pure Na_2SO_4 salt.The beneficial effect of adding Ce to the Ni-Cr- Al-Ti alloys was significant in pure Na_2SO_4 but not in Na_2SO_4+NaCl salt mixture.

The mechanism of corrosion-inhibiting action of benzeneacetonitriles was investigated by measuring the corrsion rates with gravimetrie method.The effect of introducing different funetional groups into the para-position of the benzene ring and an isopropyl in the α-position on the inhibiting efficiency is discussed. The analysis of the kinetics of dissolution of steel in HCl solution and the characteristic relationship between the inhibiting efficiency and temperature suggests that chemisorption is the mechanism of the inhibiting action of benzeneacetonitriles.Introducing electron-donating groups into the para-position increases the inhibiting efficiency while introducing electron-withdrawing groups into the para-position decreases the inhibiting efficiency.An isopropyl group in the α-position will either raise or reduce the inhibiting efficiency.