Weldability of ferritic stainless steels

Weldability of Austenitic Stainless Steel

Introduction

Austenitic stainless steel is one of the more commonly used steels in the world. It is highly corrosion resistant and has excellent mechanical properties. It is an iron alloy containing chromium, nickel, and molybdenum, which is the essential components that give the steel its properties. Because austenitic stainless steel has excellent weldability, it is often used in applications involving welding, such as aircraft components, car parts, and medical device manufacturing.

Characteristics of Austenitic Stainless Steel

Austenitic stainless steel is a ferritic and austenitic alloy which provides superior corrosion resistance, strength and workability. The characteristic of this steel is its ability to be welded without suffering from welding defects or deformation. When welded, austenitic stainless steels advantage is that it is highly resistant to cracking, chip cracking and warping. This makes it an invaluable material for many industries and applications.

Because of its superior properties, austenitic stainless steel is an ideal material for applications that require corrosion resistance and high strength. The most common uses include piping systems, pressure vessels, storage tanks, and chemical processing equipment.

Benefits of Welding Austenitic Stainless Steel

Austenitic stainless steel is a great material for welding because it is strong, durable and it offers superior corrosion resistance. Unlike other types of stainless steel, austenitic stainless steel offers excellent weldability, even in the face of high temperature and pressure. It is also resistant to stress corrosion cracking, which is a common problem in welding metals.

When austenitic stainless steel is welded, it produces a weld bead with a low amount of carbon contamination, which reduces the likelihood of weld defects. This is a great benefit, as it allows the welding process to be completed quickly and efficiently. In addition, austenitic stainless steel has a higher melting point than other alloys and can easily maintain weld joints without the need for additional heat treatment processes.

Conclusion

Austenitic stainless steel has superior weldability and provides superior corrosion resistance, strength, and workability. It is an ideal material for many applications, particularly piping systems and storage tanks, as it offers excellent weldability and superior corrosion resistance. This superior corrosion and weldability also helps ensure that welds are completed quickly and efficiently, as it requires lower amounts of carbon contamination and can easily maintain weld joints without additional heat treatments. This makes austenitic stainless steel an invaluable and versatile material for many industries.

Weldability of Ferritic Stainless Steel

Ferritic stainless steels are a group of stainless steels which contain over 12% of chromium and have low carbon content. The primary benefit of ferritic stainless steel is its outstanding resistance to corrosion, even in acidic environments. Ferritic stainless steels are magnetic and are easily welded using Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW), and Submerged Arc Welding (SAW).

When welding ferritic stainless steel, the use of highly stressed arc weldments should be avoided due to the ferritic steels low power resistance when in a highly heated condition. Preheat and inter-pass temperatures play an important role in reducing the heat input and controlling shape distortions as well as welding residual stresses. Preheat temperatures should be 200-300°C and interpass temperatures should be between 150-200°C.

The used of the backing strip is advised when welding ferritic stainless steel. This strip absorbs the excess heat, prevents the need of expensive backing materials to be used and assist in controlling the weld pool. The back strip should be specified same material as the parent metal.

The welds should be inspected while they are still hot with visual and mechanical inspections to check for any cracks and flaws in the weld. Incomplete fusion, lack of penetration and cold lap should also be inspected and remedied correctly. If a visual inspection reveals no flaws, the welds should then be tested for hardness and checked for penetration, fusing and other imperfections.

When welding ferritic stainless steel it is important to take care of thermal stress. The welding residual stresses should be relieved after the welding process is complete by allowing the welds to cool slowly to room temperature. This thermal stress relief treatment helps to improve the corrosion resistance of the welds by reducing their susceptibility to intergranular corrosion.

Due to the physical characteristics of ferritic stainless steels, they are not suitable for high temperature applications and the use of avoid highly stressed arc weldments should be avoided. Preheat and interpass temperatures should be strictly adhered to and the use of a backing strip is highly recommended. Visual and mechanical inspections should be carried out as well as hardness tests and finally, stress relief treatments should also be performed to ensure that the welds have been properly welded and are able to withstand the harsh environment they may be exposed to.