What kind of impact will the welding performance of 316L stainless steel have after undergoing cold

After cold processing strengthening, the welding performance of 316L stainless steel will be affected by the combined influence of microstructure changes, stress states and composition segregation, which may lead to the following problems: 

1. Increased risk of welding cracks

The influence of cold work hardening structure

Cold work leads to an increase in dislocation density and grain distortion. During welding, the heat input causes the grains in local areas (such as the heat affected zone HAZ) to grow rapidly, forming coarse martensite (residual α’ martensite resulting from strain-induced phase transformation), which increases brittleness and makes it prone to cold cracks (hydrogen-induced cracks) or hot cracks (pulling apart of low melting point eutectics). 

Case: When welding pipes with cold drawing deformation exceeding 20%, the martensite content in the heat-affected zone can reach 15% to 20%, and the crack sensitivity significantly increases. 

Residual stress superposition

The internal tensile stress remaining from cold processing and the welding stress (such as the cooling contraction stress of the weld seam) superimpose on each other, resulting in higher local stress concentration, which may cause **stress corrosion cracking (SCC)** or delayed cracks after welding. 

II. Intensified intergranular corrosion tendency

Risk of carbide precipitation

Although 316L is a super-low carbon stainless steel (with C ≤ 0.03%), cold processing can cause lattice distortion, accelerating carbon diffusion during welding. If the welding heat input is too high (such as in multi-layer welding without controlling the interlayer temperature), Cr₂₃C₆ may precipitate in the HAZ within the sensitization temperature range (450 - 850℃), resulting in chromium deficiency at the grain boundaries (Cr <12%), and a decrease in the resistance to intergranular corrosion. 

The indirect influence of martensitic phase transformation

The α’ martensite produced by cold working is ferromagnetic in nature and has a higher carbon content than austenite. During welding, the local carbon concentration gradient may promote the precipitation of carbides, further deteriorating the corrosion resistance. 

III. Mechanical Performance Inhomogeneity

Performance Difference between Weld Seam and Base Material

The strength of the base material after cold processing (such as σb can reach 700 MPa) is higher than that of the conventional annealed state (σb is approximately 500 MPa). However, the welding filler material (such as ER316L) is usually matched in the annealed state, resulting in the weld metal having a lower strength than the base material, forming an inhomogeneous joint. Under stress, it is prone to plastic deformation at the weld or HAZ. 

Decreased toughness

Cold working reduces the toughness of the base material (such as impact energy AKV) from the conventional state of 200J to 100-150J. The welding thermal cycle further reduces the toughness of the HAZ (especially in the coarse-grained zone), which may result in insufficient overall toughness of the joint. 

IV. Suggestions for Welding Process Adjustment

To improve the weldability of cold-worked 316L stainless steel, the process needs to be optimized specifically: 

Pre-welding treatment

If the cold deformation exceeds 15%, it is recommended to perform stress-relieving annealing (400-500℃ for 1 hour) before welding to reduce internal stress and the content of martensite.

Thoroughly clean the surface of oil stains and oxide scale to reduce the hydrogen source (to avoid cold cracks). 

Welding parameter control

Employ low heat input techniques (such as TIG welding, pulsed current), maintaining the interlayer temperature below 100℃ to minimize grain coarsening and carbide precipitation.

The preferred filler materials are ultra-low carbon welding wires (such as ER316L) or high-nickel welding wires (such as ER317L), enhancing crack resistance and corrosion resistance. 

Post-welding treatment

For important components, perform solution treatment (water quenching at 1050℃) to eliminate stress and cause the martensite to transform back into austenite; or use shot blasting treatment to introduce compressive stress on the surface to counteract the welding tensile stress. 

Summary

Cold working strengthening will cause problems such as increased crack sensitivity, decreased corrosion resistance, and uneven mechanical properties when 316L stainless steel is welded. These issues can be comprehensively improved through measures such as pre-weld annealing, strict temperature control, optimization of filler metals, and post-weld treatment. In practical applications, when the cold deformation exceeds 25%, it is recommended to prioritize using the annealed base metal for welding to avoid performance deterioration.