c.lled the kinetic boundary!6).The pure sulfidztion and pure oxidation has been found when the oxygen partial pressure is greatly lower or higher than the critical one. The purpose of this paper is to examine the influence of addition agents in Fe-Cr alloy,mainly silicon,on the transition from oxide formation to the for- mation of sulfide-rich corrosion products. 1 Experimental The alloys were melted in a vacuum furnace,and the compositions of alloys were as follow (wt%):Fe25Cr:Fe-base,Cr-24.49,Si-0,Al-0,C-0.018,RE-0; Fc25Cr1.5Si0.5Al:Fe-base,Cr-16.75,Si-1.47,A1-0.46,C-0.10,RE-0.05. The latter was cast into rod of 20mm in diameter.Fe25Cr alloy was further hct rolled at 1050C after casting into rod cf 100mm in diameter.All the rods were annealed for 2.5h at 950C,and then machined into 12mm in diameter, finally cut into slice specimen of 612mm x 1.5mm.All the specimens were drilled near the end to make hcles of 1.2mm in diameter fer suspension.Each of the specimen was mechanically polished to obtain the smooth surface. The kinetic me:surements were carried cut in an apparatus,in which weigt of specimen were weighed by a stainless steel spring.High purity gases (HaS- 99.5%,H2-99.998%,Ar-99.997%)were used.The rates of the gases were monitored by flow meters to obtain the desired partial pressure of oxygen and sulfur. The water composition was made by bubbling argon with the constant flow rate through two water containers.The temperatures of the first container immersed in a thermostat controlled within +0.2C is higher than that of the second container immersed in another thermostat controlled also within t0.2.C. Thus the supersaturated water composition was made in the first container and condensed in the second container.and finally the saturated water compcsition at the same temperature with the second thermestat can be obtained. The temperature of the furnace was controlled with a Pt-Pt-10%Ru thermo- ccup!e within +2C.The experiments were carried out at 1023K and 1223K, respectively. The scales were examined by X-ray diffraction and scanning electron micro- scpy· 2 Experimental Results 2.1 Kinetics Corrosion kinetics of Fe25Cr and Fe17Cr1.5Si0,5A lalloys in H2-H20-H2S 605协 、 五 几 丁 。 一 ， ， 一 砚 ， 扭 二 写 一 ， 一 。 ， 一 ， 一 ， 一 ， 一 。 。 一 ， 一 。 ， 一 。 ， 一 。 ， 一 。 ， 一 。 。 己 · “ · 住 。 五 ” ， 记 ， 功 。 · 二 五。 住 一 卜 ， 五 盯 ， · 了 ， ， 一 。 ‘ ， 一 。 · · 红 土 “ 五 上 土 。 “ 。 · 一 一 石 〔 土 “ · ， · 一 ， 手 不 。 、 呱 早 冬 一 一