Only three groups of metallic materials were available at that time 

 that, because of their corrosion resistance, could be considered for the selec- 

 tion of the hatch and bottom insert plate material. The three materials were 

 titanium, stainless steel, and monel. Titanium was the most desirable one as 

 its corrosion resistance was superior to the two other groups of materials. Its 

 compressive strength and tensile strength were higher than for the other two 

 groups of materials, and its specific gravity was the least, easing the opening 

 of the lightweight hatch by the crew from the capsule's interior in an emer- 

 gency. Unfortunately, the price of titanium forgings was about 500% higher 

 than for the other materials, and this made its use inapplicable. Thus the 

 choice was between monel and stainless steel, among which only type 316 

 satisfied the minimum requirement for corrosion resistance. Since the 

 strength of type 316 stainless steel was about equal to that of the monel 

 available, and since the desired shapes of type 31 6 stainless steel were more 

 readily available from the suppliers, it was selected as the material for fabri- 

 cation of the hatch and bottom insert plates. The mechanical and physical 

 properties of the type 316 stainless steel are shown in Table 2. 



Table 2. Properties of Type 316 Stainless Steel 



Property Typical 



Mechanical 



Yield strength 30,000 psi 



Tensile strength 75,000 psi 



Elongation at failure 50% 



Hardness B 75 



Chemical 



Carbon 0.08% 



Chromium 17% 



Nickel 12% 



Molybdenum 3% 



29 



