Welding Characteristics of Austenitic Stainless Steel

Austenitic stainless steel has good weldability and is currently the most widely used in industry. Generally, special technological measures are not required during welding. This paper analyzes in detail the occurrence of hot cracks, intergranular corrosion and stress during welding of austenitic stainless steel. Corrosion cracking, embrittlement of welded joints (low temperature embrittlement, σ phase embrittlement, fusion line embrittlement) causes and preventive measures.

Stainless steel is increasingly widely used in aviation, petroleum, chemical and atomic energy industries. Stainless steel is divided into chromium stainless steel, chromium-nickel stainless steel according to chemical composition, and ferritic stainless steel, martensitic stainless steel, austenitic stainless steel and Austenitic-ferritic duplex stainless steel.

Among stainless steels, austenitic stainless steel (18-8 type stainless steel) has better corrosion resistance than other stainless steels. Its strength is lower, but its plasticity and toughness are excellent; its welding performance is good, and it is mainly used for chemical containers, equipment and It is the most widely used stainless steel in industry at present.

Although austenitic stainless steel has many advantages, if the welding process is incorrect or the welding material is improperly selected, many defects will occur, which will ultimately affect the performance.



Welding Characteristics of Austenitic Stainless Steel

(1) Prone to Thermal Cracks

Hot cracks of austenitic stainless steel are relatively easy to produce defects during welding, including longitudinal and transverse cracks of welds, burr cracks, root cracks of backing welding and interlayer cracks of multi-layer welding, etc., especially when the nickel content is relatively high. High austenitic stainless steels are easier to produce.


(2) Intergranular Corrosion

Corrosion occurs between grains, which results in a loss of inter-grain bonding, almost complete loss of strength, and fracture along grain boundaries when stressed.


(3) Stress Corrosion Cracking

Corrosion damage of metal under the combined action of stress and corrosive medium. According to the stress corrosion cracking cases and experimental studies of stainless steel equipment and parts, it can be considered that under the combined action of a certain static tensile stress and a specific electrochemical medium at a certain temperature, the existing stainless steel has the possibility of producing stress corrosion .

One of the biggest features of stress corrosion is the selectivity in the combination of corrosive media and materials. It is easy to cause stress corrosion of austenitic stainless steel, mainly hydrochloric acid and chloride containing chloride ions, as well as sulfuric acid, nitric acid, hydroxide (alkali), seawater, water vapor, H₂S aqueous solution, concentrated NaHCO₃+NH₃+NaCl aqueous solution and other media Wait.


(4) Embrittlement of Welded Joints

After the weld of austenitic stainless steel is heated at high temperature for a period of time, the phenomenon of impact toughness will decrease, which is called embrittlement.
 

• 1. Low temperature embrittlement of weld metal (475 ℃ embrittlement)

• 2. Sigma-phase embrittlement of welded joints

• 3. The fusion line is brittle

Key Points for Selection of Electrodes for Austenitic Stainless Steel

Stainless steel is mainly used for corrosion resistance, but is also used as heat resistant steel and low temperature steel. Therefore, when welding stainless steel, the performance of the electrode must match the purpose of the stainless steel. Stainless steel electrodes must be selected according to the base metal and working conditions (including working temperature and contact medium, etc.).


Stainless steel grades and electrode type and grade comparison table