The slow strain rate technique(SSRT)was used to evaluate the influence of nitrogen on SCC behavior of 00Cr18Ni5Mo3Si2 duplex stainless steel in 30%MgCl_2(boiling)solu- tion.It was found that the 00CrMo3SiCl_2 steel containing 0.11% nitrogen showed the best resistance to SCC.The critical cracking potentials of three steels with different content of nirogen were measured.The results showed that nitrogen increased the SCC critical po- tential,but the effect of nitrogen was weakened by anodic polarization.When the external polarization potential was more than-350mV(SCE),the effect of nitrogen was not obvi- ous.Nitrogen influenced the SCC behavior of the duplex steel by varying the proportion of two phases in the steel.By using SEM,EDAX and metallographic techniques,it was found that the anodic polarization weakened the effect of nitrogen on SCC behavior of the du- plex stainless steel.Under the condition of natural corrosion,γ phase retarded propagation of cracks:under lower anodic potentials both α and γ phases have a certain retardant ef- fect on the propagation of cracks:under higher anodic potentials the retardant effect of phases disappeared.It was mought that the anodic polarization potentials made the electro- chemical protection effect of α phase to γ phase disappear.

After immersion in 30%MgCl_2 solution (boiling),the surface films of the 00CrlSNi5Mo3Si2 steels with different nitrogen contents were analyzed.Nitrogen was found to enrich in the surface film,and the higher the nitrogen content in the duplex stain- less steel was,the more amount of nitrogen was enriched in the surface film.Enrichment of Ni and Mo was influenced by nitrogen content with the content of nitrogen≥0.073% for Ni alone,and≥0.11% for both Ni and Mo.The combined effect of nitrogen and Mo increased the passivation ability of the surface film.The potentiostatic immersion test showed that anodic polarization thickened the surface film and weakened the effect of ni- trogen.A simulated occluded cell (OC) was used to study the chemical changes in the OC of the duplex stainless steel in 0.5N NaCl solution (50℃,pH=7).It was found that nitro- gen had little effect on either the pH fall or Cl~- enrichment in the OC,and that there was no NH_4~+ in the OC.TEM analysis showed that dislocation changed from layer structure in- to net structure and that stacking fault enrgy increased with the increase of nitrogen con- tent.

Low temperature hot corrosion (LTHC)behavior of Fe-Cr alloys with 5 to 50 (wt)% of chromium in the presence of a K_2SO_4-Na_2SO_4 salt film was studied in O_2- 0.1,0.5 and 1.0% (SO_2+SO_3) gas environments in the temperature range of 560 to 750℃.Corrosion kinetics were measured gravimetrically,and corrosion product scales were physically examined and chemically analyzed.The experimental results indicate that the alloys with chromium contents below a certain critical value are subject to LTHC.The LTHC is related to the formation of a low melting complex sulfate containing K,Na and Fe.Fe~(3+) is believed to take part in the reduction reaction,and the countertransport of Fe~(3+)/Fe~(3+)carries the reduction reaction of O_2 and SO_3 to the melt/gas interface,which is responsible for the rapid corrosion.It is also indicated that the addition of chromium re- sults in higher LTHC resistance of iron base alloys.

The effect of tempering temperature on the stress corrosion cracking behavior of 42CrMo high strength steel in 3.5% NaCl aqueous solution has been studied with Auger electron spectroscopy,electron microscopy and fracture mechanics method.Results show that,in the quenched and low temperature tempered conditions,42CrMo steel has very low K_(ISCC) and fractures intergranularly.With the rise of tempering temperature from 300℃ to 500℃.K_(ISCC) increases apparently and the fractography changes from intergranu- lar mode to a mixture of transgranular dimpled rupture and intergranular mode.Analyses show that the stress corrosion cracking behavior is mainly controlled by the distribution of carbide.In the quenched and low temperature tempered conditions,preddominant distribu- tion of carbide along prior austenitic grain boundaries is the main cause leading to inter- granular fracture and very low K_(ISCC).In high temperature tempered conditions,the com- bined effects of the coarsening of the carbide along the grain boundaries and the precipita- tion of much carbide within grains result in the apparent increase of K_(ISCC) and the change of fractography from intergranular to mixed mode.

The stress corrosion cracking (SCC) behavior of 45MnSiV pre-stressing high strength steel has been studied with slow strain rate tests (SSRT),electro-chemical and fractographic techniques.The SSRT were performed in saturated Ca(OH)_2 solutons,at various applied potentials from-1200 to-400mV(SCE).Some HCl was added to the solution in order to adjust the pH within the range 12.5～5.In addition,the cases that concrete has been polluted by Cl~- ion or SO_2 have also been investigated.The experiments are so designed as to truthfully imitating the service conditions of steel in concrete.The re- suits have shown that no SCC of 45MnSiV pre-stressing steel was observed in the concrete which has not been polluted.If some HCI.NaCl or SO_2 penetrate the concrete and decrease the pH value,SCC which appears to be related to anedic dissolution occurs.The best ca- thodic protection potential is in the vicinity of-800mV (SCE).Howevr,if the applied po- tential is lower than-900mV(SCE),cracking will occur which results from the ingress of hydrogen into steel,irrespective of any other conditions.

Effects of sulfate-reducing bacteria(SRB)on corrosion of mild steel were investigated with weight-loss method,polarization technique and SEM.Experimental results showed that dur- ing growth of SRBs an unknown volatile phosphorus compound would be formed,which might be corrosive to mild steel.Iron sulfide and hydrogen sulfide produced by the organ- ism made a major contribution to corrosion of mild steel.And in media with the presence of SRBs.additional ferrous ions stimulated the induced corrosion to a great extent.Atomic ration of iron to sulfur in corrosion products of mi]d steel in the culture LFYS of SRBs was about 2.1.A modified mechanism of anaerobic corrosion of mild steel induced by SRBs was proposed.

For the 18-8 stainless steel/Cl~- system,polarization scans and linear polarization tests were performed with specimens stressed above yield point and stress free in simulated occluded solutions of different pH and Cl~- concentration representing the chemical condi- tions of different stages in occluded corrosion cell.The results showed that the corrosion of stressed specimens started to accelerate below a critical pH value of about 1.8 at 90℃. while the stress free specimens had a critical pH value about 1.5.The passivating effect al- so decreased for stressed alloy.The open-circuit potentials of both stressed and sterss free specimens dropped suddenly from about-200mV(SCE) in passive region to-400mV (SCE) in active region when pH decreased below the critical value,indicating that the pas- sive film had been ruptured completely.The potential/pH diagrams were constructed by superimposing the above potentiodynamic polarization curves,potential/time curves,and the hydrogen equilibrium curves and immunity border lines which were determined experi- mentally in simulated OC solutions.The potential/pH diagrams interpreted the thermody- namic as well as kinetic behaviour inside stressed cracks.

An apparatus for measuring the potential distribution on a flat specimen immersed in an electrolyte was used to study stress corrosion cracking of α-brass/ammonia system un- der mode Ⅱ loading.in which the maximum normal stress site at the notch tip is different from that of maximum shear stress.The apparatus was connected with a computer to con- trol a micro-reference electrode(MRE).The MRE scanned a micro-region on a specimen. Potential distribution around the notch tip was measured during strew corrosion cracking, and was displayed in three-dimensions and in isopotential contour by a plotter.The poten- tial varied slightly around the notch region scanned by MRE and the notch could be recog- nized on the equipotential contour map for unstressed specimen.When stress was applied, strained atoms at edge of the notch were much more subject to corrosion than other atoms.As a result,potential peak was formed symmetrically to the notch.The peak be- came unsymmetrical during stress corrosion cracking.Corrosion speed at the site of the maximum normal stress was much higher than at any other point.Therefore,an active path was formed along the direction of the maximum normal stress after a period of time. This indicated that a crack would nucleate.If the specimen was tested continuously,a crack could then be observed. In this system,the site and duration of a crack nucleation could be measured.The role of normal stress and shear stress could be distinguished.

The inhibiting effect of arsenic on dezincffication of CuZn32 and CuZn38 alloys in 1% CuCl_2 solution has been investigated by means of immersion,electrochemical and sur- face analysis techniques.Experimental results show that the effects of various states of ar- senic on dezincification are different.The arsenious ion in medium has no influence on dezincification.The electrodeposited arsenic as a protective coating on brass can prevent dezincification.The surface-impregnated As formed through ion beam bombardment has similar effect on dezincification as electrodeposited As.The As as bulk-alloying additive has obvious effect on inhibiting dezincification.The relationship of dezincification depth to the content of As in brass follows an empirical equation:D=D_0/(1+B·C~n). It was found that a black film forms oh the surface of brass containing As in 1% CuCl_2 solution.This black film which has been shown to be composed of CuCl by XPS and AES has a protective effect on dezinceification.Based on the experimental results an action mechanism of As in inhibiting dezincification can been proposed:As in brass may decrease the over-voltage of the reaction Cu~(2+)→CuCl and raise the over-voltage of the reaction Cu~(2+)→Cu~0.So the insoluble CuCl film can form on the surface of brass contain- ing As and prevent dezincification.

By using slow strain rate tests (SSRT),inhibitive effects of arsenic additions in brass and of additions of As-containing anions into solution upon the susceptibility to stress cor- rosion cracking (SCC)of 70/30 brass in LV NaNO_2 were studied respectively.The results indicated that arsenic contents from ca.0.03 to 0.1 (wt%) in the brass gave rise to cer- tain inhibition of SCC and the inhibitive effect became more pronounced with the increase of applied potential ranging from-100 to+100mV (SCE)where the alloy is normally susceptible to SCC.But.such contents were unable to suppress cracking completely.On the contrary,excessive arsenic addition in the brass,e,g.reaching 0.45% As,caused dele- terious effect on SCC.In contrast,additions of arsenical anions into nitrite solution were considerably effective on inhibiting the SCC of brass.The comparison made between the effects of arsenite and arsenate additions at identical arsenic concentration,i.e.1g/l As, showed that the relative effects of arsenite and arcenate on the inhibition varied with the variation of applied potential,the former anion being more effective than the latter at the potential of-100mV(SCE) but reversed order of the effects of those two anions being observed at the potential above-50mV(SCE).Increasing arsenic concentration from 0. 1 to 10g/l in the solution enhanced the inhibitive effect.At applied potional of-100mV (SCE),1g/l of arsenic,as added with arcenite,made the brass totally immune in 1N NaNO_2.hnmune potential could be further promoted up to-50mV(SCE)when the ar- senic concentration reached 10g/l.Experimental evidence proved that arsenic addition in either brass (in effective amount)or nitrite solution not only had an effect on slowing down the crack propagation rate,but also on increasing stress level for crack initiation.

The effect of CeO_2 surface coating on the high temperature oxidation kinetics of Fe- 25Cr alloy and the Cr/Fe atom ratio in the surface layer of oxide film was investigated by Rutherford-Backscattering Spectrum (RBS) and resonant Nuclear Reaction Analgsis (RNA).The results indicated that the oxide growth rate of CeO_2 surface coated Fe-25Cr reduced about 26%,and that the Cr/Fe atom ratio in surface layer of oxide film was twice that for the alloy without CeO_2 surface coating.RBS spectra also showed that CeO_2 content in the surface layer of the oxide film reduced with oxidation time.This effect may result from the overlap of Cr_2O_3 on CeO_2.

Oxidation behavior of zircaloy-4 in 1000℃～1400℃ flowing steam was studied, and rate laws of the weight-gain as well as the growth of the oxide and alpha layers were obtained.Weight-gain and thickness growth of the oxide layer in general followed the parabolic rate laws.In the long term oxidation at temperatures above 1225℃,the isother- mal oxidation,curve of zircaloy-4 transformed in shape during oxidation.The dependence of the weight-gain and thickness growth rate laws on temperature observed the Arrhenius Equation.Also conducted was the measurement of stress change during oxidation at tem- perature of 650℃～800℃ for zirconium and zircaloy-4 by a bending method.The struc- ture and composition of the oxide films were examined under AES and SEM.