Two different methods of rapid manufacturing-electron beam additive manufacturing (EBAM) and laserengineered net shaping (LENS)-were used in order to fabricate NiTi elements. Microstructure and martensitic transformation temperatures of initial materials in the form of wire or spherical powder were established. The samples fabricated using LENS technique showed martensitic transformation temperature (MTT) at 2 26°C (represented by maximum martensite peak maximum in DSC) which was lower in comparison with raw powder. In the case of samples fabricated using EBAM, the MMT reached 2 19°C. The peaks of martensite and reverse transformations were diffuse due to differences in grain size and composition across the sample. Aging at 500°C for 2 h caused not only separation of R-phase during cooling of both samples, but also formation of sharper and higher transformation peaks as well as shift of MTT to higher temperatures. Microstructural investigation showed columnar grains, near the interface of deposited element and base plate, growing perpendicular to the plate surface. The grains showed axial fiber texture <001> along the growth direction. STEM micrographs revealed the presence of elongated particles enriched in Ti. Formation of Ti-rich particles during the process led to the depletion of Ti in the matrix and contributed to increase in MTT in comparison with initial NiTi powder. LENS-deposited sample additionally contained higher dislocation density in the austenite. Compression stress/strain curves of EBAM-deposited sample revealed deformation of martensite only, while the LENS-deposited one showed almost complete superelastic effect in compression mode up to 3%.
In the paper the results of metallographic examination and mechanical properties of electron beam welded joint of quenched and tempered steel grade S690QL are presented. Metallographic examination revealed that the concentrated electron beam significantly affect the changes of microstructure in the steel. Parent material as a delivered condition (quenched and tempered) had a bainitic-martensitic microstructure at hardness about 290 HV0.5. After welding, the microstructure of heat affected zone is composed mainly of martensite (in the vicinity of the fusion line) of hardness 420 HV0.5. It should be noted, however, that the microstructure of steel in the heat affected zone varies with the distance from the fusion line. The observed microstructural changes were in accordance with the CCT-S transformation diagram for the examined steel.Keywords: electron beam welding, high strength quenched and tempered steel, microstructure
The paper shows the results of metallographic examination and mechanical properties of electron beam welded joints of quenched and tempered S960QL and Weldox 1300 steel grades. The aim of this study was to examine the feasibility of producing good quality electron beam welded joints without filler material.Metallographic examination revealed that the concentrated electron beam significantly affects the changes of microstructure in the weld and the adjacent heat affected zone (HAZ) in both steel grades. The microstructure of the welded joints is not homogeneous. The four zones, depending on the distance from the weld face, can be distinguished. Basically, the microstructure of the weld consists of a mixture of martensite and bainite. However, the microstructure of HAZ depends on the distance from the fusion line. It is composed of martensite near the fusion line and a mixture of bainite and ferrite in the vicinity of the base material.Significant differences in mechanical properties of the welded joints were observed. For a butt welded joint of the S960QL steel grade the strength is at the level of the strength of the base material (R m = 1074 MPa). During the bending test the required angle of 180° was achieved. The impact strength at -40°C was 71,7 J/cm 2 . In the case of the Weldox 1300 steel grade butt welded joints exhibit high mechanical properties (R m = 1470 MPa), however, the plastic properties are on the lower level than for the base material.Keywords: electron beam welding, high strength quenched and tempered steel, weld microstructure
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