the Pacific Ocean are shown graphically in Figure 11 for sea water 

 and in Figure 12 for the bottom sediments,, 



There was no measurable corrosion of the silicon and silicon- 

 molybdenum cast irons at either depth. 



In sea water at both depths the other cast irons behaved 

 similarly to the steels as is clearly shown by comparing the curves 

 in Figure 5 with those in Figure 11, This similarity also obtains 

 for the specimens partially embedded in the bottom sediment at the 

 5,500 foot depth; compare Figure 6 with Figure 12 „ At the 2,350 

 foot depth there is an anomaly in that the corrosion rates of the 

 cast irons increase with time (Figure 12) whereas those of the steels 

 tend to be constant with time. The reason for this increase is not 

 apparent at this time. 



The corrosion rates of the austenitic cast irons in sea water 

 are shown graphically in Figure 13 and in the bottom sediment in 

 Figure 14. The corrosion rates of these alloys in sea water also 

 decrease with time of exposure at both depths with the rates at 

 2,350 feet being lower than those at 5,500 feet„ However, such 

 was not the case in the bottom sediments. For some presently in- 

 explainable reason the corrosion rates after 400 days of exposure 

 at a depth of 6,780 feet were much lower than after 750 days of 

 exposure at a depth of 5,640 feet as well as slightly lower than 

 after 1,064 days of exposure at a depth of 5,300 feet. This is the 

 only group of alloys which behaved in this manner. At a depth of 

 2,350 feet the average corrosion rates were about the same for both 

 periods of exposure and, again, were lower than for the other groups 

 of alloys except the cast irons after 200 days of exposure (Figure 12). 



The statistical curves and the 95 percent confidence limits for 

 the two groups of cast irons both in the water and the bottom sediments 

 are shown in Figures 15, 16 and 17. Very few values were outside 

 the 95 percent confidence limits; one value after 1,064 days of 

 exposure in the bottom sediment at 5,500 feet, one value after 197 days 

 of exposure in the sea water at 2,350 feet, one after 400 days of 

 exposure in the bottom sediment at 5,500 feet and one after 400 days 

 of exposure in the bottom sediment at 2,350 feet. 



Mechanical Properties 



The percent changes in the mechanical properties of the exposed 

 cast irons are given in Table 7. The mechanical properties of Ni- 

 Resist No. 4 were not affected but those of Ni-Resist D-2c were 

 significantly lowered. 



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