If you asked ten people which element they considered most important, you would likely receive ten unique responses. For example, many jewelers would choose diamond or gold as the most important element. Techies, on the other hand, would go with silicon. However, if you narrow the scope of the survey to metals, almost everyone would agree that steel is singularly important since its uses are so far-reaching. And for welding projects, stainless steel is the metal of choice for many applications.
Although stainless steel welding is ubiquitous, it still presents challenges. For example, if heating is not controlled, working with thin stainless steel tube can be difficult for manual welding and lead to warping, burn through, or other failures. Manufacturers must also address safety concerns when welding any stainless steel grade. Let’s narrow the focus to duplex stainless steel grades and establish guidelines for the best welding of this family of materials.
Types of Duplex Stainless Steel Grades
There are several distinct types of stainless steel, with ferritic and austenitic among these. Duplex stainless steel, however, can be considered as both—as shown in the figure below.
This balance between austenite and ferrite that duplex stainless steel grades share is achieved during the fabrication process. Initially, the alloys cool to 100 percent ferrite. However, as the temperature cools, some of the material changes to austenitic. This transition takes place between 1200°C and 1400°C (2200°F to 2550°F) and ceases at around 1000°C. It is a delicate process to ensure the desired austenite-ferrite balance for the specific grade. And there are many duplex stainless steel grades, including the ones listed below.
| PROPERTIES OF DUPLEX STAINLESS STEEL GRADES |
| Grade (UNS) | PRE | Hardness max (Rockwell C) | Tensile Strength (MPa) | Elongation min (%) |
| S31200 | 32 | 31 | 690 | 25 |
| S31260 | 37 | NA | 690 | 20 |
| S31803 | 31 | 31 | 620 | 25 |
| S32001 | 22 | 25 | 620 | 25 |
| S32003 | 30 | 31 | 690 | 25 |
| S32101 | 26 | 31 | 700 | 30 |
| S32202 | 27 | 31 | 650 | 30 |
| S32205 | 35 | 31 | 620 | 25 |
| S32304 | 26 | 32 | 600 | 25 |
| S32506 | 40 | 32 | 620 | 18 |
| S32520 | 41 | 32 | 770 | 25 |
| S32550 | 40 | 32 | 760 | 15 |
| S32750 | 42 | 32 | 795 | 15 |
| S32760 | 41 | 32 | 750 | 25 |
| S32808 | 39 | 32 | 700 | 15 |
| S32900 | 31 | 28 | 620 | 15 |
| S32906 | 40 | 32 | 800 | 25 |
| S32950 | 34 | 32 | 690 | 15 |
| S39274 | 42 | 32 | 800 | 15 |
| S81921 | 27 | 31 | 620 | 25 |
| S82011 | 26 | 31 | 655 | 30 |
| S82012 | 25 | 31 | 700 | 35 |
| S82013 | 25 | 31 | 620 | 30 |
| S82031 | 27 | 31 | 700 | 35 |
| S82121 | 27 | 30 | 650 | 25 |
Although the table above is not exhaustive, it does reflect that duplex stainless steel grade characteristics vary significantly. As a result, manufacturers can choose the grade most applicable for their project. These alloys are classified further according to characteristics and composition. For example, most alloys with a PRE between 31 and 39 are classified as standard; those with a PRE in the 20s are considered lean; alloys with a PRE higher than 40 are superalloys. The wide range of properties is the primary reason these alloys are useful across diverse applications and can accommodate multiple welding processes.
How to Best Weld for Duplex Stainless Steel
Duplex stainless steel grades lend themselves to common arc welding processes. And for the most consistent and accurate welds, GTAW, or TIG, welding is the best process choice. The most reliable way to ensure that your welds attain the highest quality possible is by employing an orbital welding process. Doing so will alleviate the physical strain that manual assembly requires and allows the welder to focus on equipment parameters such as current, wire feed, and speed to achieve optimal welds.
Arc Machines, Inc. is an industry leader in supplying advanced and high-quality welding equipment and service. This includes orbital welding machines, materials, and expertise to aid you when working with specialized pipes and tubes and a variety of duplex stainless steel grades. For inquiries regarding products, contact sales@arcmachines.com. For service inquiries, contact service@arcmachines.com. Arc Machines welcomes the opportunity to discuss your specific needs. Contact us to arrange a meeting.
