Assessing Mottled Indications when Digitally Radiographing Austenitic Stainless Steel Welds

When radiographing an austenitic stainless steel weld with an appreciable weld deposit size, selecting a low radiographic kilovoltage (keV) can contribute to producing a radiographic indication that is not an imperfection. The contributors to this mottled condition are both radiographical and metallurgical. Electrons from low keV can diffract or absorb when penetrating through the dendritic grain structure of a weld. The increase in keV, or using gamma ray–equivalent isotopes, produces a marked change in electron output and penetration in material.

A Novel Approach to Inhibit Intergranular Corrosion in Ferritic Stainless Steel Welds Using High-Speed Laser Cladding

Ferritic stainless steels are prone to localized corrosion phenomena such as pitting corrosion or intergranular corrosion, in particular when jointed by fusion welding processes. State-of-the-art techniques to avoid intergranular corrosion mainly consist of alternating alloy concepts or post-weld heat-treatments—all of which are associated with increased production costs. Hence, the present investigation seeks to introduce a novel approach for the inhibition of intergranular corrosion in ferritic stainless steel welds through the use of high-speed laser cladding. Here, vulnerable sites prone to intergranular corrosion along the weld seam area are coated with a chemically resistant alloy, whereby an overlap is achieved. Optical and electron microscopy as well as computer tomography and tensile tests reveal that the detrimental effects of intergranular corrosion in both stabilized and unstabilized ferritic stainless steel are substantially reduced. In addition to that, the effects of varying overlap widths on the identified corrosion phenomena are studied. Moreover, the resulting dilution and precipiation phenomena at the clad–sheet interface are thoroughly characterized by electron backscatter diffraction and energy dispersive X-ray spectroscopy, whereby interrelationships to corrosion resistance can be drawn. As a result of this investigation, the number of techniques for the inhibition of intergranular corrosion is enlarged, and substantial cost-saving potentials in the manufacturing industry are unlocked.

Comparative Research of Microstructure and Mechanical Properties of Stainless and Structural Steel Dissimilar Welds

The present study utilized a metal inert gas welding (MIG) to make a dissimilar weld of stainless steel AISI 304, 314, 316L, 420 grades and a standard structural steel S355MC. It refers to a weld joining two materials from different alloy systems commonly used in heat exchangers, pressure vessels, and power plant systems. Obviously, maintaining the integrity of such welds is of paramount importance to the safety issues. Therefore, detailed microscopic and experimental studies were performed to evaluate the reliability of these welds. The microscopic analysis did not reveal any presence of weld defects such as porosity or cracks, which ensured that MIG process parameters were properly selected. The performance of dissimilar welds was assessed by hardness and tensile tests. The hardness profiles revealed differences between austenitic and martensitic steel welds that later showed extremely high values in the heat-affected zone (HAZ), which caused fractures in this zone during tensile test. The welds of all austenitic steel grades withstood the tensile test, showing an average tensile strength of 472 MPa with fractures observed in the base metal zone. It made clear that the use of a filler rod 308LSI is suitable only for the austenitic stainless and structural steel dissimilar welds and not appropriate for martensitic-structural steel welds. The achieved results revealed that the higher hardness of the martensitic phase in the HAZ of AISI 420 is closely related with the formation of untempered coarse martensitic structure and higher carbon content.