The Difference Between S31803 and S32205
Developed in the 1930s for use in paper and pulp manufacturing, duplex stainless steels have a composition based on 22% chromium and a mixed austenite-ferrite microstructure that provides ideal mechanical properties. Today, these grades account for less than 80% of duplex, super duplex, and ultra-high-strength duplex stainless steel consumption.
Duplex stainless steels typically offer twice the strength and significantly improved corrosion resistance compared to the more common 304/316 austenitic stainless steel blends. This makes them ideal for engineers seeking materials for corrosive environments.
What is the difference between UNS S31803 and UNS S32205?
Increasing the chromium content of stainless steel increases its pitting resistance. However, the pitting resistance equivalent value (PREN), which measures the pitting resistance of an alloy, also includes many other elements in its formulation. This subtlety can explain how the difference between UNS S31803 and UNS S32205 came to be, and whether this difference is significant.
As duplex stainless steels evolved, their initial specification was designated UNS S31803. However, many leading manufacturers have been producing the grade to the upper end of the allowable specification. This reflects their desire to maximize the corrosion performance of the alloy, and the development of the AOD steelmaking process has allowed for tighter composition control. In addition, the process allows for adjustment of nitrogen addition levels, rather than just a background element.
As a result, the highest performing duplex grades seek to maximize the levels of chromium (Cr), molybdenum (Mo), and nitrogen (N). Based on the formula PREN = %Cr + 3.3 %Mo + 16 % N, the difference between a duplex grade at the lower end of the specification and one at the upper end can be as much as several points.
To differentiate duplex grades at the upper end of the composition range, another specification was introduced, UNS S32205. Duplex grades meeting the S32205 (F60) standard fully comply with the S31803 (F51) standard, but not vice versa. Therefore, S32205 can be dual certified to S31803.
UNS S31803 from Gnee Steel
Gnee Steel has a comprehensive range of duplex stainless steels. We stock S32205 round bars ranging in diameter from 5/8" to 18"
In addition, we stock a range of S32205 hollow bars in our UK warehouse and plates up to 3" thick in our Portland, USA warehouse.
