Patent Number: 048636827
Section: description

DETAILED DESCRIPTION OF THE INVENTION This invention is particularly directed to a potential deficiency of susceptibility to irradiation degradation which may be encountered with chromium-nickel austenitic stainless steels comprising Type 304 and related high chromium-nickel alloys such as listed in Tables 5-4 on pages 5-12 and 5-13 of the 1958 edition of the Engineering Materials Handbook, edited by C. L. Mantell. These alloys comprise austenitic stainless steels of about 18 to 20 percent weight of chromium and about 9 to 11 percent weight of nickel, with up to a maximum of about 2 percent weight of manganese, and the balance iron with incidental impurities. This invention comprises a modified Type 304 austenitic stainless steel and a specific alloy composition including precise ratios of added alloying ingredients, as well as given limits on certain components of the standard austenitic stainless steel alloy. The alloy composition of this invention accordingly comprises the basic iron, chromium, nickel and manganese with the chromium in a percent weight of about 18 to 20, nickel in a percent weight of about 9 to 11 and manganese in a percent weight of about 1.5 to 2, with the balance iron and incidental impurities, except for the following fundamental alloying ingredients and requirements. The carbon component of the alloy is limited to a percent weight of 0.02 to about 0.04 percent weight. Also, a combination of niobium and tantalum is included together in a total of a minimum of 14 times the carbon percent weight, up to maximum of about 0.65 percent weight of the overall alloy, and with the niobium of the combination limited to a maximum of about 0.25 percent weight of the overall alloy. Thus, the tantalum of the combination can range up to about 0.4 percent weight of the overall alloy. Aside from the carbon content and the combination of niobium and tantalum in their given fundamental proportions, the other components of the alloy of this invention, including some incidental ingredients, comprises the following in approximate percent weight: ______________________________________ Iron Balance Chromium 18.0-20.0 Nickel 9.0-11.0 Manganese 1.5-2.0 Phosphorus 0.005 maximum Sulfur 0.004 maximum Silicon 0.03 maximum Nitrogen 0.03 maximum Aluminum 0.03 maximum Calcium 0.01 maximum Boron 0.003 maximum Cobalt 0.05 maximum ______________________________________ The foregoing specific austenitic stainless steel alloy composition, among other attributes, provides a high degree of resistance to stress corrosion cracking regardless of exposure to irradiation of high levels and/or over prolonged period, without incurring long term induced radioactivity. As such, the alloy composition of this invention is well suited for use in the manufacture of various components for service within and about nuclear fission reactors whereby it will retain its integrity and effectively perform over long periods of service regardless of the irradiation conditions. Moreover, the alloy composition of this invention additionally minimizes irradiation induced long term radioactivity whereby the safety and cost requirements for its disposal following termination of service are reduced, and of greatly shortened period. The following comprises an example of a preferred austenitic stainless steel alloy composition of this invention. ______________________________________ Alloy Ingredient Percent Weight ______________________________________ Carbon 0.033 Chromium 19.49 Nickel 9.34 Tantalum 0.40 Niobium 0.02 Sulfur 0.003 Phosphorus 0.001 Nitrogen 0.003 Silicon 0.03 Iron Balance ______________________________________ Physical Properties ______________________________________ Yield, KSI 40.0-47.0 Elongation, % 48-52 Grain Size (ASTM) 9.5 Hardness. R.sub.B ______________________________________