What is 904L steel?

What is 904L steel?

First of all, we must first know what material 904L alloy is, and what is the difference between it and duplex stainless steel?
What material is 904L alloy? Based on a 20% chromium and 25% nickel content, 904L is a higher alloying austenitic stainless steel that has been developed for applications containing dilute liu acids.
904L Component Analysis:
Carbon ≤ 0.02% Chromium 19.00-23.00%
Manganese ≤ 2.00% Nickel 23.00-28.00%
Silicon ≤ 1.00% Molybdenum 4.00-5.00%
Phosphorus ≤ 0.045% Copper 1.00-2.00%
Sulfur ≤ 0.035%

What is the difference between 904L and duplex stainless steel?
Austenitic stainless steel is widely used due to its availability, lower cost, reasonable corrosion resistance and good impact toughness. Increasing the content of chromium and molybdenum will significantly improve the pitting resistance of austenitic stainless steel. In the case of 904L alloys (UNS N08904, 1.4539), 1-2% copper is also added, which is known to be very resistant to strong reducing acids such as liu acid and phosphoric acid. Therefore, it has been widely used in many chemical process industrial applications of plates and rods.
The high nickel content of 904L alloy means that it is much more expensive than ordinary stainless steel. As a result, the 904L alloy has been replaced by the more cost-effective Super duplex stainless steel (SDSS). The yield strength of super duplex stainless steel is 2-3 times that of 904L alloy, which means that it can be used at a smaller thickness to get the same function. The PREN of super duplex steel is greater than 40, while the PREN of alloy 904L is greater than 43, so it is roughly comparable.
However, Ferralium 255 (UNS S32550, F61, 1.4507) also utilizes the same increased copper content as the 904L alloy and therefore has excellent corrosion resistance to various reducing acids. The increased strength also gives it better wear resistance compared to Ferralium 255, making it ideal for use in mixers and agitators.
The main reason to continue using 904L alloy instead of super duplex stainless steel is if the operating temperature is below or above the reasonable operating range of SDSS. Because it is austenite, it can still maintain its impact toughness at low temperatures (-196℃).