Super Austenitic Stainless Steel

CIVMATS
GRADES
Super Austenitic Stainless Steel

904L

254SMo

654SMo

926

Introduction

Overview

The concept of super austenitic stainless steel comes with super ferritic stainless steel and super duplex stainless steel. A typical example is a super austenitic stainless steel containing 6% molybdenum and 7% molybdenum. These steel grades have been developed for industries with harsh conditions such as petrochemical, chemical, paper and offshore systems.

Development of Super Austenitic Stainless Steel

To cope with Austenitic intergranular corrosion susceptibility after welding, titanium and tantalum were added as carbide stabilizing elements in early times. With the advent of AOD and VOD refining techniques in 1960s, carbon content in stainless steel was reduced to less than 0.03%. The new technique improved steel purity meanwhile solved the issue of intergranular corrosion susceptibility post welding. As a result, since 1980s, new Austenitic stainless steel developed thereafter are basically ultra-low carbon type.

However, industrial development posts greater challenges on stainless steel performance, such as resistance to comprehensive corrosion of harsh media. With increased chromium, nickel and molybdenum, along with addition of other elements such as copper and silicon on the basis of 304 and 316, come new high alloy grades such as 317LM (containing 4.5%Mo), 904L, 316L mod (urea grade), 347 (nitric acid grade), 348 (nuclear grade) and the like.

Another phenomenon contributing to the development of super austenitic stainless steel was the wide application of nitrogen to stainless steel tubes since 1970s. For example, AL-6XN is a nitrogen version of AL-6X. Adding nitrogen and increasing molybdenum content to 6% on the basis of high molybdenum 904L comes Alloy 926.

Features of Super Austenitic Stainless Steel

Among all stainless steels, super austenitic stainless steel has the most demanding technical requirements and is the most difficult steel variety. Since super austenitic stainless steel is high in nickel and molybdenum meanwhile it contains copper and nitrogen elements, it is hard to melt, easy to segregate and crack. Therefore, super austenitic stainless steel can be a kind of caliber that tells the steel mill technology. Like other commonly used Cr-Ni austenite, super austenitic stainless steels features good cold and hot workability.

Applications

1) Oil and petrochemical equipment, such as bellows in petrochemical equipment;
2) Pulp, paper bleaching equipment, such as pulp digester, bleaching equipment;
3) Power plant flue gas desulfurization device, the main use parts: body of flue tower, flue, door panel, internal parts, sprinkler system, etc.;
4) Offshore systems or seawater treatment, such as thin-walled condensing pipes and seawater desalination equipment cooled by seawater in power plants;
5) Salt industry, such as salt or desalination equipment;
6) Heat exchangers, especially those working under a chloride ion environment;
7) Others