Characteristics of Stainless Steel Welding by Welding Materials Companies

Welding-induced embrittlement of the weld and heat-affected zone is a process characterized by non-uniform heating and cooling, which leads to microstructural inhomogeneity. In welded joints, the ductile-to-brittle transition temperature of the weld metal and heat-affected zone is typically higher than that of the base metal, making the base metal the weakest link in the joint. The heat input during welding significantly influences both the mechanical strength of low-alloy high-strength steels and the properties of their heat-affected zones. Compared with hot-rolled and normalized steels, low-carbon quenched-and-tempered steels exhibit a more pronounced tendency toward heat-affected-zone embrittlement due to excessive lattice distortion energy. Therefore, during welding, the heat input should be carefully controlled within a specified range.

In low-carbon tempered steels, the heat-affected zone (HAZ) located outside the weld heat-affected zone is heated to temperatures above the tempering range, particularly in the region near Ac1, resulting in a softening zone characterized by reduced strength. As the heat input from the welding consumables and the preheating temperature increase, the microstructural softening in the HAZ becomes more pronounced; however, the tensile strength of the softening zone still exceeds the lower limit specified in the base-material standard. Therefore, provided that the welding procedure is properly optimized, the issue of HAZ softening in this type of steel will not compromise the service performance of the welded joint.

Stainless steel welding

Austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and austenitic–ferritic duplex stainless steel—according to their microstructure, stainless steels can be classified into these four categories. The following discussion will focus on the welding characteristics of austenitic stainless steel and duplex stainless steel.

(1) Austenitic Stainless Steel Welding

Austenitic stainless steel joints, which are easier to weld than other types of stainless steel, exhibit low susceptibility to hydrogen embrittlement and maintain excellent ductility and toughness across all temperatures. The primary welding challenges for welding material companies include hot cracking, embrittlement, intergranular corrosion, and stress corrosion. Additionally, due to their relatively poor thermal conductivity and coefficient of linear expansion, welding stresses and distortions tend to be significant. During welding, it is advisable to use the lowest possible heat input, avoid preheating, and keep the interpass temperature below 60°C; weld beads should be staggered to minimize heat input. Furthermore, welding speed should not be excessively increased, and the welding current should be reduced.

(2) Austenite-Ferrite Dual-Phase Stainless Steel Welding

Austenitic–ferritic duplex stainless steel is a two-phase stainless steel composed of austenite and ferrite. It combines the advantageous properties of both austenitic and ferritic steels, resulting in high strength, excellent corrosion resistance, and good weldability. Currently, the main grades of duplex stainless steel available from welding-material manufacturers are CR18, CR21, and CR25. The primary characteristics of welding this type of steel are: lower thermal sensitivity compared with austenitic stainless steels; reduced susceptibility to embrittlement after welding and less coarsening of ferrite in the heat-affected zone compared with purely ferritic stainless steels; consequently, it exhibits superior weldability.

Due to its excellent weldability, this type of steel does not require preheating or post-weld heating. Thin plates should be welded using TIG welding, while thick plates can be welded using shielded metal arc welding; in the latter case, special electrodes with a composition similar to that of the base metal or low-carbon austenitic electrodes should be used. For more information on welding materials companies, follow Phoenix New Materials.