The effect of various heat treatment on hydrogen embrittlement resis tance of 30CrMnSiA steel has been studied experimentally.The results show that the application of sub-critical quenching at(Ac_3-10℃)or twice quenching at(Ac_3+20℃),between quenching at 900℃ and temp ering at 500℃,can raise the critical stress óc of the steel in tempered sorbite condition to hydrogen embrittlement by 9.6% and 7.9% respec- tively.Twice quenching at(Ac_3+20℃)after isothermal quenchnig can raise óc by 10.4%.Isothermal quenching at 370℃ can raise óc of plaet- notched specimens by 60%.The increase of the hydrogen embrittlement resistance is attributed to the fact that the existence of tough ferrite or retained austenite raises the plasticity and toughness of the matrix. The refining of grains,the change of α and β phases from lump to needle shape,the refining of dispersal carbide and the reduction of absorbed hydrogen content are also responsible for the reduction of he suscep- tibility to hydrogen embrittlement.

Electron microscopic techniques were adopted to investigate oxide films formed on Zircaloy-2 in superheated steam at 673 and 773K. The nodular corrosion appearing on black oxide films during oxidation transition was also investigated.Monoclinic,cubic,and tetragonal lattice structures in black oxide films formed both at 673 and 773K were identified.The proportion of cubic and tetragonal phases decr- eased with increase of temperature and single monoclinic lattice struc- ture was fouhd in white oxide films after oxidation transition.It may be seen from the high resolution lattice image that the oxide crystals consist of mosaics～20 nm in size,and a larger space on(100) and(010)planes in some places might be associated with the clusters of tin atoms.The feature of oxide/metal interface at nodules was characterized by protrusions,which looked like cauliflower with ripple marks on its surface.This might occur since nodules grew much faster than surrounding oxide.Pores(<10nm)existing on triple grain boun- daries in white oxide films were observed.The model for the forma- tion of nodular corrosion proposed by the author previosly is further discussed in the light of results obtained in the present work.

The polarization behavior of corroding metals aod alloys in molten salts is more complex than that in aqueous solution at room-temperature. The polarization curve equations containing more than five kinetic parameters have been derived.In these cases,initial values of parame- ters for Newton-Gause method should be optimized so that repeated calculation can be convergent.The procedure,using different range of polarization curve fitting and random trying method,to seek suitable initial values has been proposed in this paper.A computing program in BASIC for IBM-PC computer is worked out and the problems encountered in compiling the program are discussed.

When a large scale object is to be cathodically protected by impressed current,more than one anodes are usually installed at appropriate places and fed by a single potential controlled rectifier. In many such cases,some anodes may provide excessive current, causing overprotection,while others may bring about underprotection. In fact,different dc voltage is required for every individual anode to offer satisfactory protection.A reasonable solution to this problem is to develop multichannel controller in place of mono-channel controller such as the above-mentioned rectifier.In our previous study,a microcomputer based system for impressed current cathodic protection was established.Potential control was achieved by periodic adjustments of dc power output.In the present study,the new system is extended to multi-anode control.Each anode is driven by its own dc power module,the output of which is controlled independently.During the interval between the successive controls of the same anode channel, the computer can control over other anode channels.Thus in this new system every channel is indepent and can offer appropriate individual output.In this way,more uniform potential distribution can be achieved.Laboratory tests have verified these considerations through computerized 103-channel control system.

Niu Yan Zhang Jianqing and Wu Weitao (Corrosion Science Laboratory,Academia Sinica)(Institute of Corrosion and Protection of Metals,Academia Sinica)

Atmospheric corrosion test in laboratory is usually performed in a humidity cabinet to shorten the test duration.The main purpose of the new approach is to further increase severity of corrosion environment by means of promotion of water condensation on specimen surface.It is based on the exposure of lens-paper-covered specimens in humidity cabinet.Lens paper consists of long fibre with loosely netted texture. The capillarity of lens paper facilitates more water condensation from humid environment.Moreover,in the presence of lens paper, condensed water will spread out immediately instead of forming into drops.Vertical suspension of the specimen makes it easy to drain excessive water.As a result,a rather thick,uniform and reproducible water layer could be maintained on specimen surface.In water vapor saturated environment at 50℃,the thickness of such a water layer is typically about 40um.Experiments indicate that by means of such a simple arrangement,corrosion of specimen is significantly enhanced. Weight loss of bare mild steel specimen covered with lens paper is of an order of magnitude greater than that without it.The additional advantage of this new approach is that the rust stained lens paper after exposure could be reserved as permanent record of corrosion characteristics.

In order to understand the phenomenon and mechanism of environ- ment-enhanced crack growth in high strength steels,it is necessary to study the kinetics of electrochemical reactions occurring at the crack tip.In this paper,an experimental technique for simulating the electrochemical reaction at the crack tip of a propagating crackhas been developed.The small fresh surface of a broken notched specimen immersed in an aqueous solution,was used as the anode,and a fully oxidized large specimen of the same material was used as the cathode. The galvanic current transient between the anode and the cathode was measured immediately when the notched specimen was broken.To de- monstrate this new technique,an electrochemical reaction test for 40CrNi steel in 3.5%NaCl aqueous solution was conducted,and the kinetics equation of the reaction was obtained with the analysis of the test results.

Electrochemical behavior and surface composition of ferritic stain- less steels containing Cu and Nb in 1.0 mol.din~(-3) sulfuric acid solution have been investigated to evaluate the effects of alloying elements Cu and Nb on the corrosion resistance of ferritic stainless steel.The ac- tive dissolution current density of copper added steel is suppressed significantly because of the surface enrichment of metallic copper. From the measurements of the reactivation potential by a cathodic potential sweep of the passivated steel,it is found that the copper addition has a detrimental effect on the passivity.On the other hand, the addition of niobium improved the passivity of ferritic stainless steel. Auger Spectroscopy revealed that the niobium existed in the inner layer of passive film.Therefore with both niobium and copper added,the ferritic stainless steel shows excellent corrosion resistance,because active disolution is decelerated by copper addition and because passive film is improved by niobium addition.

The effect of various types of additives on corrosive wear and fric- tion coefficient of mild steel in dilute H_2SO_4 and NaCl solutions has been investigated.The results show that the additives exhibit certain inhibition ability for controlling wear in corrosive environment.The role of additives could be divided into three types in reducing material removal,(1)the inhibitor type,as(CH_2)_8N_4 or K_2Cr_2O_7 in low load, (2)the lubricant type,as sodium dodecyl benzene sulfonate(SDBS) in heavy duty and(3)the corrosive wear inhibitor type,as IMC-5 in serious situation,IMC-5 which consists of amide and functional groups could be used as an ideal composite additive for corrosive wear.

An investigation was carried out in situ on the crevice corrosion of titanium in hot acid NaCl solution by means of microelectrode technique, etc.The crevice corrosion rate of titanium increased with increasing temperature,concentration of Cl~-,H~+ and decreasing crevice gap. However,with increasing concentration of dissolved oxygen,the incubation period of crevice corrosion of Ti was prolonged.When the crevice corrosion of Ti occurred,the pH of solution within the crevice lowered down to about 0.9 and the potential of the metal in the crevice was below -650 mV(vs.0.1N KCl Ag/AgCl),meanwhile the current density of the crevice corrosion and activity of chloride ion within crevice increased enormously.The“self-catalysis mechanism”of crevice corrosion of titanium in hot acid NaCl solution is proposed according to the experimental results.

Laser surface alloying is an effective surface modification technique to improve corrosion resistance of metallic materials.In this paper laser sutface Cr-Ni-Si alloying on low alloy steel has been investigated and the effect of technological conditions of laser treatment and alloying composition on the corrosion resistance of surface alloy possessing uniform distribution of Cr,Ni and Si is diseussed.The experimental results indicated that the addition of silicon can remarkably improve the pitting resistance of the surface alloy.The mechanism of improved pitting resistance by silicon is that a protective film enriched with silicon has been formed on the surface.

The stress corrosion cracking,behavior in 3.5%NaCl aqueous solu- tion of SiC-/Al composite made by a squeeze casting method was investigated.The results showed,that the SiCw/Al composite was susceptible to stress corrosion cracking.The Kiscc was about 4.8-8.1 MPa which was only 1/2.5 of the Kic value.The mechanism of stress corrosion cracking of SiCw/Al composite was discussed on the basis of observation of fractograph with scanning electron microscopy.

Stress Corrosion Cracking(SCC)susceptibility of sensitized 1 Cr18Ni9Ti austenitic steel was investigated by measuring potgntiody- namie polarization curves(sean rates:10 mV/min and 20 mV/s)and using the slow strain rate test(SSRT)in the polythionic acid solution formed in the petroleum refinery. The results showed that there was a critical potential range between +60 and +1200 mV(SCE)in H_2S_xO_6 solution in refinery for stress corrosion cracking of sensitized 1 Cr18Ni9Ti stainless steel to occur. The metallographic studies of the fractured surface by SEM revealed intergranular and quasi-cleavage fracture in the critical potential zone.