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Opis: Heat-affected zones (HAZs) in real welds are usually quite narrow, and consequently most standard mechanical tests are difficult or even impossible. Therefore, simulated microstructures are often used for mechanical tests. However, the most often used weld thermal cycle simulator produces only a few millimeters wide area of simulated microstructure in the middle of specimens. Consequently, these kind of simulated specimen are not suitable for standard tensile tests, and even for Charpy impact tests, the simulated area can be too narrow. Therefore, to investigate the mechanical properties of a fine-grain heat-affected zone in 18CrNiMo7-6 steel, two methods were used for simulation of as-welded microstructures: (a) a weld thermal cycle simulator, and (b) as an alternative, though not yet verified option, austenitizing in a laboratory furnace + water quenching. The microstructures were compared and mechanical properties investigated. The grain sizes of the simulated specimens were 10.9 μm (water-quenched) and 12.6 μm (simulator), whereby the deviations from the real weld were less than 10%. Both types of simulated specimen were used for hardness measurement, Charpy impact tests, and fatigue tests. Water-quenched specimens were large enough to enable standard tensile testing. A hardness of 425 HV, yield strength Rp02 = 1121 MPa, tensile strength Rm = 1475 MPa, impact energy KV = 73.11 J, and crack propagation threshold ΔKthR = 4.33 MPa m0.5 were obtained with the water quenched specimens, and 419 HV, KV = 101.49 J, and ΔKthR = 3.4 MPa m0.5 with the specimens prepared with the simulator. Comparison of the results confirmed that the annealed and quenched specimens were suitable for mechanical tests of FG HAZs, even for standard tensile tests. Due to the use of simulated test specimens, the mechanical properties determined can be linked to the FG HAZ microstructure in 18CrNiMo7-6 steel.
Ključne besede: weld joint, fine-grained HAZ, simulation of microstructure, hardness, impact toughness, tensile properties, fatigue crack growth, 18CrNiMo7-6 steel
Objavljeno v DKUM: 05.12.2024; Ogledov: 0; Prenosov: 4
Celotno besedilo (5,22 MB)
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Opis: Cladding with a stick electrode is one of the oldest arc processes for adding a deposit on a base material. The process is suitable for outdoor working, but the disadvantages are low productivity and large dilution rates. In this work, a simple solution is proposed, which would enable cladding of a larger area with one pass and decrease the dilution rate at the same time—a new type of electrode was developed, exhibiting a rectangular cross-section instead of a round one. Hardfacings, welded with E Fe8 electrodes according to EN 14 700 Standard were welded on mild steel S355 J2 base material with three different coated stick electrodes. The first one was a commercially available, standard, round hardfacing electrode, the second was the same, but with a thinner coating, and the third one was a newly developed rectangular electrode. All three types had equal cross-sections of the metallic core and the same type of coating. Manufacturing of the rectangular electrodes in the laboratory is explained briefly. One- and multi-layer deposits were welded with all three types. Differences were observed in the arc behavior between the round and rectangular electrodes. With the rectangular electrode, the microstructure of the deposit was finer, penetration was shallower, and dilution rates were lower, while the hardness was higher, residual stresses predominantly compressive, and the results of instrumented Charpy impact tests and fracture mechanics tests were better.
Ključne besede: hardfacing, dilution rate, hardness, Charpy impact toughness, residual stress, fracture toughness
Objavljeno v DKUM: 14.05.2024; Ogledov: 298; Prenosov: 20
Celotno besedilo (10,82 MB)
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Ključne besede: martensite, Ti-6Al-4V, microstructure, tensile strenght, selective laser melting
Objavljeno v DKUM: 26.01.2024; Ogledov: 285; Prenosov: 19
Celotno besedilo (17,10 MB)

Opis: Magistrsko delo je bilo osredotočeno na preučevanje obločnega varjenja čepov s konstrukcijskim jeklom. V preiskavi so bili uporabljeni visokotrdnostni varilni čepi oz. vijaki razreda 8.8, katerih varivost smo preverili skozi uporabo vizualnega ocenjevanja, mehanskih preizkusov, kamor spadata upogibni in natezni preizkus, makro preiskav in meritev trdot. V nalogi smo želeli ugotoviti, ali je trenutni postopek varjenja, ki ga uporabljamo v podjetju Preis Sevnica, d. o. o., primeren za varjenje čepov iz tovrstnega materiala. Če je odgovor ne, potem smo želeli izboljšati postopek v tej smeri, da bi se lahko na zvarjenih čepih izognili dodatnemu (preventivnemu) pretaljevanju zvara s postopkom TIG. V magistrskem delu bom predstavil celotno raziskavo, ki se je začela s preučevanjem varilnih standardov, člankov in materialnih lastnosti, končala pa z analiziranjem podatkov, pridobljenih iz eksperimentalnega dela, ter zbranih zaključkov.
Ključne besede: obločno varjenje čepov, mehanski preizkusi, meritve trdot, upogibni preizkusi, natezni preizkusi, makro preiskave, visokotrdnostni varilni čepi, konstrukcijsko jeklo
Objavljeno v DKUM: 16.09.2021; Ogledov: 1286; Prenosov: 88
Celotno besedilo (5,18 MB)

Opis: V podjetju GKN Driveline Slovenija prihaja do težav pri izdelavi kletk ležajev za homokinetični zglob, in sicer pri prebijanju okenc na kletki, v katero so vstavljene ležajne kroglice. V podjetju želijo zagotoviti daljšo življenjsko dobo nosilca orodja za prebijanje in so se odločili v prvi fazi preiskati ali je uporabljen predpisani material in/ali je toplotno obdelan kot predvideva tehniška dokumentacija. Naloga zajema pregled prelomnih površin, kemijsko analizo, preiskavo mikrostrukture in merjenje trdote. Vse preiskave so privedle do ugotovitve, da sta material in toplotna obdelava materiala v skladu s tehniško dokumentacijo. Rešitev je potrebno zato poiskati bodisi v drugem materialu, drugačni obdelavi ali v spremembi konstrukcije nosilca.
Ključne besede: GKN, Nosilec žiga, Metalografska preiskava, Meritve trdote
Objavljeno v DKUM: 10.11.2017; Ogledov: 1146; Prenosov: 150
Celotno besedilo (3,87 MB)