Setsuo Aso, Shoji Goto and Yoshinari Komatsu
Department of Materials Science and Engineering, Faculty of Engineering and Resource Science,Akita University, Akita 010-8502
Slurry erosion rate (WS) generally depends on the slurry flow rate in a power law as follows,
where k is a constant, V is a slurry flow rate and n is an exponent. The n-value usually falls between 2 to 3 for metals, although there are some observation which exist outside this range. Consequently, there is no clear definite value assigned to the n exponent. The reason for this may be the difference in the mechanism of attack caused by the simultaneous and synergistic interaction between erosion and corrosion. This being so, it seems useful to separate the action of slurry erosion into those factors, namely one dominated by erosion, another dominated by corrosion and the third being synergistic interaction between erosion and corrosion. This holds true even in multi-phase alloy like high-chromium white irons.
Fe-(15, 25)%Cr-C-B alloys are modified high-chromium white irons that contain boron ranging from 0.5 to 2.5 mass%. These alloys possess a good slurry erosion resistance compared to that of an ordinary type of high-chromium white iron. The reason for this is the presence of boron. The addition of boron tend to produce hard boride and/or borocarbide. It also prevent the formation of pearlite.
A slurry flow rate with the range of 4.5 to 10.3 m/s was used. The low slurry flow rate region was corrosion-dominated while the high slurry flow rate region was erosion-dominated. The experiments also indicate a n-value range of 3.3 to 4.9 when a tap water slurry is used. Whereas for a seawater slurry, a range of 0.4 to 3.2 was observed. Therefore, the change in n-value may mainly be attributed to the degree of corrosiveness of the slurry. Fe-(15, 25)%Cr-C-B alloys possessed a good slurry erosion resistance compared with both SUS430 and SUS304 stainless steels in tap water slurry. Moreover, Fe-25%Cr-C-B alloys possess an excellent slurry erosion resistance even in the slurries containing sea water and 40 vol% sand.
(Received March 17, 1998; In Final Form June 10, 1998)
erosion, corrosion, high-chromium white iron, sand erosion, boron, wear
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