General Guidelines for Welding Duplex Stainless Steels - Requirements for Welding Consumables

The Welding of Duplex Stainless Steel General Guidelines - Requirements for the Welding Material

Duplex stainless steel (DSS) is a type of austenitic-ferritic stainless steel that contains both chromium and nickel, typically in a ratio of 2:1. Its name indicates that it consists of two phases (Duplex) of different microstructure, providing the material with higher strength and greater corrosion resistance than conventional austenitic stainless steel (SS).

In order to achieve its excellent strength and corrosion resistance, DSS must be welded correctly. To ensure successful welding of DSS, welders must select the appropriate welding materials. There are several important factors to consider when selecting the welding materials for DSS welds, including chemical composition, microstructure, strength, corrosion resistance, the type of welding process, the welding position and weld quality.

Chemical Composition: In order to weld duplex stainless steel, it is important to select the appropriate welding material with the correct chemical composition and filler material. The chemical composition of the welding materials used to weld DSS must be well matched to the base material of the component being welded. This will ensure that the weld metal and the base material have comparable mechanical properties and a similar corrosion resistance.

Microstructure: The microstructure of the welding material must also be taken into account when selecting the appropriate weld material. It is essential to select welding materials with a microstructure that is well matched to the DSS. A weld metal characterised as a duplex microstructure is ideal, with at least 50% austenite and 50% ferrite present. However, superduplex materials, with higher proportions of both austenite and ferrite, may be used if desired.

Strength: Strength is an important factor when selecting the welding materials for duplex stainless steel. In order to ensure the weld metal has superior strength to the base material, welding materials with a minimum specified tensile strength of around 550-720 MPa should always be selected.

Corrosion Resistance: Corrosion resistance is also a key factor when selecting the welding materials for duplex stainless steel. The welding material should have a minimum specified corrosion resistance in order to preserve the superior corrosion resistance of DSS. The most suitable welding material for DSS is a superduplex alloy, which offers a superior corrosion resistance to that of both austenitic and ferritic stainless steels.

Welding Process: The welding process should also be considered when selecting the welding materials for DSS. Generally, DSS can be successfully welded using a variety of welding processes such as gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW), and gas metal arc welding (GMAW). In addition, higher alloyed weld materials can be used in specific welding processes such as those requiring automated welding processes or welding techniques involving high welding speeds.

Position: The welding position must also be considered when selecting the welding materials for duplex stainless steel. Different welding positions require different weld materials in order to ensure satisfactory welds. For example, welding in the vertical-down position requires a more alloyed weld material to ensure a high-strength weld with sufficient corrosion resistance.

Weld Quality: The weld quality is also an important factor when selecting the welding materials for duplex stainless steel. It is essential that the welding materials used in duplex stainless steel welds are of high quality and adhere to the stringent requirements of the relevant welding certification standards. The welding materials should be inspected and tested thoroughly in order to ensure meeting the weld quality requirements.

In conclusion, selecting the appropriate welding materials for duplex stainless steel welds is essential for successful welding of DSS. When selecting the welding materials for DSS welds, factors such as chemical composition, microstructure, strength, corrosion resistance, welding process, welding position, and weld quality must all be taken into consideration in order to ensure satisfactory welds.

The single-phase and dual-phase stainless steel welding has its own requirements for welding materials, especially for wire and electrodes.

First of all, the welding wire and electrode should support the joint of the two materials to be joined, and at the same time it should not have too much reaction, so as not to affect the corrosion resistance of the welded joint.

In addition, when selecting the welding wire and electrode, special attention should be paid to their chemical composition. The material of the two parts to be welded should be consistent with or close to the composition of the welding wire and electrode, and the composition should not affect the corrosion resistance of the welding joint.

Finally, it is necessary to pay attention to the selection of the surface cleaning of the welding material. The surface of the two materials should be free of oil, water, dust and other foreign matter, so that its oxide layer is not affected.

In short, when single-phase or dual-phase stainless steel welding, the selection of welding materials must be correct, so as to ensure that it can be welded firmly, with good effect and without influence on the corrosion resistance.