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AISI 316 L stainless steel is widely used as material to produce components by means of additive manufacturing. To increase the circular economy, the powders are collected and re-used after the printing process, thus the effect of powder recycling on microstructure and properties of printed components is of the utmost importance. This work focused the attention on non-metallic inclusions by examining virgin and recycled powders, and products printed by using both types of powders in a laser powder bed fusion (L-PBF) process.Recycled powders exhibit an irregular shape due to fragmentation, spatters and satellites and, compared to the virgin ones, have a higher gas (O, H and C) content. Both powders contain non-metallic inclusions with a larger quantity in the recycled ones.The printed samples have a similar microstructure, however those produced by using recycled powders exhibit voids of larger size and a little greater amount of inclusions. XRD and EDS examinations of inclusions extracted from the metallic matrix showed that they consist of a mix of amorphous and crystalline silica. Large part of these particles are already present in virgin powders and only a minor part forms during repeated printing operations. Accordingly, the quality of virgin powders is the factor that mainly affects the inclusion content of printed products indicating that the powder production process is the most critical stage of the whole manufacturing process.

In this study, the effects of cutting insert rake face forms and cutting parameters on the surface integrity in machining of AISI 316 L steel were investigated experimentally. The cutting forces occur during chip removal, surface roughness values on the machined surfaces with residual stresses on machined workpiece were measured, and metallurgical structure (microhardness and microstructural variations) of the surface layers formed as a result of machining were evaluated. The surface integrity was evaluated in terms of surface roughness, residual stress, microhardness, and microstructure analysis. In experiments, the best surface integrity results were obtained by cutting tools having QM form, and the worst surface integrity results were obtained by cutting tools having MR form. Under all these cutting conditions, it was observed that the surface integrity worsened when depth of cut and cutting feed were increased; however, the surface integrity improved when cutting speed was increased. In terms of cutting parameters, the best surface integrity was obtained with cutting speed 200 m/min, cutting feed 0.1 mm/rev, and depth of cut 1.25 mm; on the other hand, the worst surface integrity was obtained with cutting speed 125 m/min, cutting feed 0.3 mm/rev, and depth of cut 2.5 mm. [ABSTRACT FROM AUTHOR]

In this study, AISI 316 L austenitic stainless steel and AH36 low-alloy ship building steel pair were joined with flux-cored arc welding method by using E309LT1-1/4 filler metal under four different shielding gas compositions containing CO at different ratios. Microstructure, impact toughness of welded materials, and their microhardness distribution throughout joining were determined. In macro- and microstructure examinations, stereo optical microscope, scanning electron microscope (SEM), SEM/energy dispersive spectroscopy, and SEM/mapping analysis techniques were used. After notched impact toughness, fracture surfaces were examined using the scanning electron microscope. This study investigated effects of shielding gas composition on microstructure, impact toughness, and microhardness distribution of transition zone between AH36 steel and weld metal of joined material. It is observed that based on an increase in amount of CO in shielding gas, impact toughness values of the weldment decreased. Microhardness values change throughout weld metal depended on shielding gas composition. Moreover, an increase in amount of CO within shielding gas decreased δ-ferrite amount in weld metal. The increase in amount of CO within shielding gas leads to expanded transition zone in interface between AH36 and weld metal and also affects notched impact toughness values negatively due to the inclusion amounts occurring in weld metal and hence caused it to decrease. [ABSTRACT FROM AUTHOR]