AISI Type 439 is resistant to attack by potable water and many mildly or moderately corrosive chemical environments which are oxidizing in nature. In various chloride solutions, studies have shown pitting resistance of Type 439 to be superior to that of Type 304. In addition, Type 439 is not subject to stress corrosion cracking which may cause premature failure of austenitic steels in chloride bearing environments such as hot waters used in heat exchangers.
Lower cost and stable price
Basically, Stainless Steels are “stainless” because the Chromium (Cr) content gives the greatest contribution towards corrosion resistance, NOT Nickel. In recent years, prices of Nickel have exploded and Nickel is a constituent of widely used “Austenitic” (300 series) stainless steel grades. Good news is that “Ferritic” (400 series) stainless steel have no or low Nickel content which result in lower and stability in pricing. Thus, why pay more for Nickel if you don't have to?
Ferritic special trump cards
The common “Ferritic” grades (400 series) include 409, 410, 430, 439 and 444 .Ferritic (400 series) actually outshine Austenitic (300 series) in several characteristics:-
• Ferritic usually Cheaper (because they have no or low nickel content)
• Lower thermal expansion (they expand less than austenitics when heated)
• Higher thermal conductivity (they conduct heat more evenly than austenitics)
• Excellent resistance to stress corrosion cracking
• Easier to cut and work
• Useful magnetism for wider applications