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This Bulletin reports an extensive study on the effect of microfissures on the corrosion performance and mechanical properties of austenitic stainless steel weld metals. This program was sponsored by Welding Research Council Stainless and Nickel Alloys Committee.

Eight different modified and commercial electrodes provided by Lincoln Electric Company, ESAB and Hobart together with the weld pads from previous programs were used in this investigation. Microfissure evaluation was performed by the Fissure Bend Test to determine the microfissure distribution and microfissure density. Typical features of microfissuring were characterized by the optical light microscope (OLM) and scanning electric microscope (SEM).

Pitting corrosion testing was performed in terms of CPT to evaluate the corrosion resistance of fissure-containing and fissure-free samples in ferric chloride solutions. It was found that CPT is a function of the microfissure level; with the increase in microfissure level a decrease in CPT is noted for both 308L and 316L materials. The corrosion performance of E308L, E316L, E308H and E316H weld deposits with and without microfissures were also evaluated by cyclic polarization testing.

Tensile testing of E308L and E316L weld deposits with and without microfissures was carried out. The result shows that microfissures affect the ductility of 316L and especially of 308L. There is little effect on yield or tensile strength of 316L, less effect on yield strength of 308L, but a significant effect on tensile strength of 308L. The fracture of modified E308L exhibited a flat transverse break bounded by a narrow shear lip, meanwhile modified E316L exhibited a classic cup-and cone rupture.

Fatigue testing of E308L and E316L weld metal samples with and without microfissures showed that microfissures act as stress raisers in the weld metals and greatly decrease the fatigue properties of E308L and E316L weld metal samples. The fracture evaluation in SEM shows that the failure initiation site in microfissure-containing sample was from the microfissures with characteristic of hot cracking, and from secondary cracking for fissure-free samples.

The creep test results revealed that modified E316H with 0 FN (fissure-containing deposits) had superior creep resistance, followed by commercial E316H and E308H; the modified 308H with 0 FN (fissure-containing) samples showed the poorest performance. Creep strength of austenitic stainless weld metals is apparently a function of ferrite. Secondary cracking caused by sigma phase (high ferrite content) is the main factor in affecting creep properties for E316H deposits, as were the microfissures for modified E308H deposits (low ferrite content). The test results for commercial E308H and E316H are consistent with the creep database for 308 and 316 welds. Ferrite Number shows a linear relationship with Larson Miller Parameter as a function of creep testing.

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Published: 2005 Number of Pages: 122 File Size: 1 file , 4.3 MB