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1.
Comparison of the mechanical properties of hardfacings made by standard coated stick electrodes and a newly developed rectangular stick electrode
Edvard Bjelajac, Andrej Skumavc, Gorazd Lojen, Mirza Manjgo, Tomaž Vuherer, 2024, izvirni znanstveni članek

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: 124; Prenosov: 8
.pdf Celotno besedilo (10,82 MB)
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2.
Experimental study of crack propagation through cladded 316L/S355 steel produced by the hot-roll bonding process
Edvard Bjelajac, Andrej Skumavc, Fidan Smaili, Gorazd Lojen, Jožef Predan, Tomaž Vuherer, 2023, izvirni znanstveni članek

Opis: A hot-rolled clad plate made of 316L stainless steel and S355 carbon steel was produced in a real industrial environment via GMAW welding, vacuuming, preheating to 1240 °C, and hot-roll bonding on four stand plate mills in nine passes with reduction rates between 20-6% per pass. The clad plates were solution annealed to achieve the usual delivery condition. Ultrasound testing showed a bonding rate of 100%. Metallographic examination revealed predominantly low concentrations of oxides at the interface. The tensile strength of the bond reached 155 MPa. The shear strength always satisfied the requirements of ASTM A264. It was observed that the concentration of oxide particles influenced the shear strength strongly. The lowest measured value was 172 MPa. Specimens notched in the base material and specimens notched in the clad layer were used in the Charpy impact test. In every case, only the notched layer broke, while the other layer was only bent. The absorbed energies were always higher than those of each material alone. Fracture mechanic tests gave similar results. The crack could not propagate from the notched layer into the other one, regardless of the material of the notched layer. Instead, delamination occurred. Due to delamination, K1c could not be determined, so KQ was given instead.
Ključne besede: clad plate, hot-roll bonding, shear strength, tensile strength, impact toughness, crack propagation
Objavljeno v DKUM: 28.03.2024; Ogledov: 87; Prenosov: 7
.pdf Celotno besedilo (18,79 MB)
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3.
Evaluation of the impact and fracture toughness of a nanostructured bainitic steel with low retained austenite content
Mihael Brunčko, Peter Kirbiš, Ivan Anžel, Leo Gusel, Darja Feizpour, Tomaž Irgolič, Tomaž Vuherer, 2023, izvirni znanstveni članek

Opis: The impact and fracture toughness of a nanostructured, kinetically activated bainitic steel was determined using Standard methods. Prior to testing, the steel was quenched in oil and aged naturally for a period of 10 days in order to obtain a fully bainitic microstructure with a retained austenite content below 1%, resulting in a high hardness of 62HRC. The high hardness originated from the very fine microstructure of bainitic ferrite plates formed at low temperatures. It was determined that the impact toughness of the steel in the fully aged condition improved remarkably, whereas the fracture toughness was in line with expectations based on the extrapolated data available in the literature. This suggests that a very fine microstructure is most beneficial to rapid loading conditions, whereas material flaws such as coarse nitrides and non-metallic inclusions are the major limitation for obtaining a high fracture toughness.
Ključne besede: evaluation of fracture toughness, impact toughness, nanostructured bainite, natural aging, low retained austenite content, kinetically activated bainite KAB
Objavljeno v DKUM: 16.02.2024; Ogledov: 262; Prenosov: 17
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4.
Deformation and energy parameters of fracture of steel of the main gas pipeline
P. O. Maruščak, Sergey Panin, Ulyana Polyvana, Tomaž Vuherer, Anna Guzanová, Janette Brezinová, 2015, izvirni znanstveni članek

Opis: By example of steel 17G1S, the regularities in the impact fracture of Charpy specimens at normal and low temperatures are described. The relationship between the energy parameters of fracture (impact toughness) and the deformation response of the material (the height of shear lips) of the specimens from the pipe steel is established. The micromechanisms of impact fracture of the material are described. At 20 °C and –30 °C, focal splitting of the material was observed on the fracture surface of specimens; at –60 °C, the material failed in a brittle manner by the mechanism of cleavage.
Ključne besede: impact toughness, main gas pipeline, failure analysis
Objavljeno v DKUM: 08.08.2017; Ogledov: 1057; Prenosov: 373
.pdf Celotno besedilo (2,03 MB)
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5.
The influence of simulated thermal cycle on the formation of microstructures of multi-pass weld metal
Danilo Rojko, Vladimir Gliha, 2005, izvirni znanstveni članek

Opis: The influence of weld thermal cycle on the micrstructural changes in weld metal by use of the simulated microstructures. We examined the kinetics of the formation of austenite from the starting microstructure. The simulated microstructures were prepared by the application of simulated thermal cycles with different peak temperatures on a sample of real single-pass weld metal. The reproduction of thermal cycles were carried out by the SMITWELD simulator. Special attention was dedicated to the influence of thermal cycle on the formation of microstructures, which can be potential triggers of brittle fracture (local brittle zones).
Ključne besede: welding, welded joints, multi-pass weld metal, simulated microstructure, impact toughness
Objavljeno v DKUM: 03.07.2017; Ogledov: 2262; Prenosov: 126
.pdf Celotno besedilo (223,13 KB)
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6.
Charpy toughness of vibrated microstructures
Bogdan Pučko, Vladimir Gliha, 2005, izvirni znanstveni članek

Opis: The aim of this study was to investigate the influence of vibration on impact toughness of weld metal. Studies were carried out on two welds, of which one had been welded with applying vibration during welding. From test plates samples were made to simulate heat affect in combination with or without vibration after solidification. In this way conditions at multi-pass welding were simulated. According to different conditions Charpy toughness on non standard specimens and fracture appearance were observed. Vibration during welding benefits impact energy of weld metal, especially if weld metal undergoes further heatb treatment.
Ključne besede: welded joints, impact toughness, vibration, Charpy toughness, SAW
Objavljeno v DKUM: 03.07.2017; Ogledov: 1024; Prenosov: 106
.pdf Celotno besedilo (118,79 KB)
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7.
Low temperature impact toughness of the main gas pipeline steel after long-term degradation
P. O. Maruščak, Irina Danyliuk, R.T. Biščak, Tomaž Vuherer, 2014, izvirni znanstveni članek

Opis: The correlation of microstructure, temperature and Charpy V-notch impact properties of a steel 17G1S pipeline steel was investigated in this study. Within the concept of physical mesomechanics, the dynamic failure of specimens is represented as a successive process of the loss of shear stability, which takes place at different structural/scale levels of the material. Characteristic stages are analyzed for various modes of failure, moreover, typical levels of loading and oscillation periods, etc. are determined. Relations between low temperature derived through this test, microstructures and Charpy (V-notch) toughness test results are also discussed in this paper.
Ključne besede: impact toughness, fracture, damage, gas pipeline, steel, degradation
Objavljeno v DKUM: 03.04.2017; Ogledov: 1376; Prenosov: 429
.pdf Celotno besedilo (699,32 KB)
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8.
9.
The fracture behaviour of global/local mis-matched weld joints provided on HSLA steels
Inoslav Rak, Nenad Gubeljak, Zdravko Praunseis, 2001, izvirni znanstveni članek

Opis: The fracture behaviour of thick section high strength steel weldments, that contain soft root passes, has been studied. Two different weld consumables with different strength mismatch (1>M>1) and fracture toughness properties in the WM have significantly increased the complexity of the mis-match effect and failure behaviour of weld joints, depending on the crack location and the thickness of the soft root layer. The aim was to explain the effect of strength heterogeneity between BM and WM and between different regions in WM (global/local mismatching). R-curves of WM and HAZ regions were also discussed. The conclusion is that the application of a welding procedure with a two-pass soft root layer, introduced for the purpose of reducing or even omitting preheating, can be recommended in mis-matched weld joints on steel grade HT80. Nevertheless, the alloying from BM, and the tempering effect of subsequent weld passes, have to be taken into account. They can cause reduction of the root region ductility and affect the local mismatch in WM and HAZ. The deterioration by providing a soft root layer can probably be reduced by a selected consumable and proper welding procedure. The final conclusion is that the application of a mismatched weld joint with a soft root layer can be recommended only if high root toughness can be provided.
Ključne besede: welding, welded joints, strength mismatching, fracture toughness, CTOD, hardness, impact toughness, HSLA steels
Objavljeno v DKUM: 01.06.2012; Ogledov: 1968; Prenosov: 139
.pdf Celotno besedilo (441,77 KB)
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10.
In-service damage of railway steel axles
O. Jasnìî, Tomaž Vuherer, Ju. I. Pindus, Andriy Sorochak, Ivan Samardžić, 2011, drugi znanstveni članki

Opis: The influence of temperature and specimens undercut place on impact toughness of railway axle material in service is investigated. The obtained results show inversely proportional dependence of impact toughness on undercut radius of specimens. The decrease of test temperature from +20 to –40 ºC decreases significantly the impact toughness and portion of ductile fracture.
Ključne besede: impact toughness, in-serice damage, railway axle, undercut
Objavljeno v DKUM: 01.06.2012; Ogledov: 1306; Prenosov: 93
.pdf Celotno besedilo (554,44 KB)
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