THE SYNERGISTIC EFFECT BETWEEN EROSION AND CORROSION IN ACIDIC SLURRYMEDIUM

The synergism between erosion and corrosion of various types of steels in 10 wt.% H2SO4 + 15 wt.% corundum sand (60 mesh) has been studied b y means of a newly designed electrochemically instrumented slurry pot apparatus. The electrochemical measurements under static and rotative condition and the relationship between element distribution and erosio n-corrosion (E-C) properties of rapidly and slowly solidified cast all oy D7 (Cr30Ni17Mo2Cu) have been further investigated to illustrate the synergistic mechanism. The results showed that the percentage of the synergism of either carbon steel or stainless steel was very large (32 -99%). At a given flow velocity, the total E-C weight loss rate and th e weight loss rate due to synergism decreased in the order of X60, AIS I321, AISI316L and F5 (Cr25Ni25Mo4Si2Cul). As flow velocity increased from 2.5 to 10 m s(-1), the passive current density of all of stainles s steels increased. The breakaway velocity of AISI321 in the test medi um is about 7.5 m s(-1). Although the hardness of rapidly solidified a s-cast D7 and slowly solidified aged D7 was almost the same, their E-C behaviors differed greatly from each other. The rapid solidification could decrease the differences in the amount of Cr, Mo, Ni, Cu, Si dis tributed between gamma phase and sigma phase, and the corrosion rate o f rapidly solidified as-cast D7 was near zero. As a result, its E-C ra te was also low. In contrast, the above mentioned elements are distrib uted markedly inhomogeneously between gamma phase and sigma phase for slowly solidified aged D7 and its corrosion rate and E-C rate were lar ge.