Abstract
The mechanical properties and microstructure evolution caused by dynamic loads of 316L stainless steel, fabricated using the Laser Engineered Net Shaping (LENS) technique and hot forging method were studied. Full-density samples, without cracks made of 316L stainless steel alloy powder by using the LENS technique, are characterized by an untypical bi-modal microstructure consisting of macro-grains, which form sub-grains with a similar crystallographic orientation. Wrought stainless steel 316L has an initial equiaxed and one-phase structure, which is formed by austenite grains. The electron backscattered diffraction (EBSD) technique was used to illustrate changes in the microstructure of SS316L after it was subjected to dynamic loads, and it was revealed that for both samples, the grain refinement increases as the deformation rate increases. However, in the case of SS316L samples made by LENS, the share of low-angle boundaries (sub-grains) decreases, and the share of high-angle boundaries (grains of austenite) increases. Dynamically deformed wrought SS316L is characterized by the reverse trend: a decrease in the share of high-angle boundaries and an increase in the share of low-angle boundaries. Moreover, additively manufactured SS316L is characterized by lower plastic flow stresses compared with hot-forged steel, which is caused by the finer microstructure of wrought samples relative to that of additive samples. In the case of additively manufactured 316L steel samples subjected to a dynamic load, plastic deformation occurs predominantly through dislocation slip, in contrast to the wrought samples, in which the dominant mechanism of deformation is twinning, which is favored by a high deformation speed and low stacking fault energy (SFE) for austenite.
Highlights
Nowadays, there is rapid development of additive techniques for manufacturing structural elements
The second factor that conditions the plastic flow of additively manufactured SS316L is that the steel undergoes a cyclical heating and cooling process during manufacturing, which leads to both recovery and an increase in the ferrite content at grain boundaries, i.e., a phase that is characterized by nearly 2 times less tensile strength than that of austenite
The2020, second factor that conditions the plastic flow of additively manufactured SS316L is that the 14 of steel undergoes a cyclical heating and cooling process during manufacturing, which leads to both recovery and an increase in the ferrite content at grain boundaries, i.e., that is characterized
Summary
There is rapid development of additive techniques for manufacturing structural elements. It is possible to use metal alloys for additive manufacturing (AM); because of the mechanical properties of this material group ( a high melting point), it was necessary to develop technologies other than those used for plastics. Easier control of the structure is possible, compared to other methods [5,6].The results obtained by OPTOMEC company (manufacturer of LENS, Albuquerque, NM, USA), indicate that additive manufactured 316 stainless steel manufactured with use of their device is characterized by a fine-grain cellular microstructure (grains size of several microns), with yield strength twice that of conventionally shaped SS316L [7]
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