An examination of chromium substitution in stainless steels
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INTRODUCTION
CHROMIUM is a critical element that plays an essential role in a number of applications. The United States is completely dependent upon foreign sources of chromium. If these sources were disrupted for a lengthy time period the consequences could be very serious. A recent study ~ summarizes chromium usage and considers what could be done to minimize the impact of a prolonged shortage. Of immediate interest is the partial substitution of chromium in stainless steel. Wrought stainless steels consume approximately half the chromium used in this country. A large part of this tonnage is represented by the 300 series of stainless steels in general, and by Type 304 in particular. Because of the large amount of chromium used in stainless steels, the potential for chromium conservation in these materials is quite large. The aim of the present study was to determine if other alloying elements could replace part of the chromium in stainless steels. Surprisingly little has been done in this area, probably because chromium has been relatively inexpensive and abundant in the past. Several studies have been made of stainless steels with lower chromium contents. Haddick e t a l 2 found that several Fe-13Mn-16Cr alloys exhibited good corrosion resistance in boiling NH4F + NHaNO3, in boiling HNO3 + CrO3, and in oxidation tests in air. Chen and Stephens 3 investigated the corrosion behavior of a number of 12 pct chromium alloys in 1.0 N H2SO4 and 1.0 N NaC1 solutions. An optimized alloy composition containing 12Cr-10Ni-I.5Si-IAI-2Mo was found to behave comparably to Type 304 stainless steel in these environments. Other studies have been made of the oxidation resistance of Fe-A1 alloys. 4'5 While such alloys often display excellent high temperature oxidation resistance there is little evidence to suggest that the ambient temperature aqueous corrosion resistance of these materials approaches that of stainless steels. Many alloying elements can modify the corrosion behavior of Fe-Cr or Fe-Ni-Cr stainless steels. 6 Most of the studies dealing with alloying effects have been done with materials containing 15 pct or more chromium. Frequently, specific alloying effects depend upon the presence of chromium. For example, molybdenum additions to stainless steels improve the corrosion resistance in reducing acids and improve the pitting resistance in chloride solutions. However, Mo additions to iron alone do not produce similar S. FLOREEN is Research Fellow with Inco Alloy Products Company Research Center, Sterling Forest, Suffern, NY 10901. Manuscript submitted July 31, 1981.
METALLURGICAL TRANSACTIONS A
effects. Thus, it is possible that at some sufficiently low level of chromium the beneficial effects of Mo would disappear. Therefore, while one may select promising alloying additions to substitute for chromium, it is not certain how effective these elements will be in low chromium alloys. With this caution in mind it is possible to select a number of different alloying elements that appear as promising candidates for parti
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