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Weldability prediction of high strength steel S960QL after weld thermal cycle simulation
Marko Dunđer, Tomaž Vuherer, Ivan Samardžić, 2014, izvirni znanstveni članek

Opis: This paper presents weld thermal cycle simulation of high strength steel S960QL, and describes influence of cooling time t8/5 on hardness and impact toughness of weld thermal cycle simulated specimens. Furthermore, it presents analysis of characteristic fractions done by electron scanning microscope which can contribute to determination of welding parameters for S960QL steel.
Ključne besede: high strength steels, S960QL steel, weldability, weld thermal cycle simulation, hardness, toughness
Objavljeno: 03.07.2017; Ogledov: 2028; Prenosov: 94
.pdf Celotno besedilo (1,16 MB)
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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: 03.07.2017; Ogledov: 1471; Prenosov: 80
.pdf Celotno besedilo (223,13 KB)
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Suitability of heat treatment for crack resistance of material in the connection part of heavy transporter for liquid slag
Tomaž Vuherer, Ljubica Milović, Milorad Zrilić, Ivan Samardžić, Vladimir Gliha, 2013, kratki znanstveni prispevek

Opis: The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the materal in the cnnection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT.
Ključne besede: weld, heat treatment, residual stress, stress relaxation, crack resistance
Objavljeno: 03.07.2017; Ogledov: 1565; Prenosov: 60
.pdf Celotno besedilo (552,83 KB)
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Characterization of heterogeneous arc welds through miniature tensile testing and Vickers-hardness mapping
Stjin Hertelé, Jonas Bally, Nenad Gubeljak, Primož Štefane, Patricia Verleysen, Wim De Waele, 2016, izvirni znanstveni članek

Opis: The heterogeneity of arc-welded connections is often ignored in structural assessments, giving rise to inaccuracies. Improved assessments taking into account heterogeneity require the characterization of local constitutive properties. We have compared two methods to do this: Vickers-hardness mapping and miniature tensile testing. Whereas the former is more straightforward to apply, the latter provides full-range stress-strain data. This paper discusses an experimental comparison of both methods on a heterogeneous arc weld. Miniature tensile tests were performed, using digital image correlation to measure the strain. The specimens were indented to compare their stress-strain response with Vickers hardness. Notwithstanding that small natural flaws invalidated some tests, reliable stress-strain curves were obtained. Vickers hardness testing is a convenient alternative if the yield and ultimate tensile strength are the only points of interest and the corresponding conversion inaccuracy is acceptable.
Ključne besede: arc weld, heterogeneity, hardness, miniature tensile testing, digital image correlation
Objavljeno: 14.03.2017; Ogledov: 563; Prenosov: 298
.pdf Celotno besedilo (797,43 KB)
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Flaw acceptability assessment detected in HSLA steel weld joints
Inoslav Rak, 1999, izvirni znanstveni članek

Opis: The flow size in weld joint can be determined by non destructive examination (NDE). Because of different mateials, and loading as well as because of the possible effect of corrosive environment the question arises how to assess reliably the allowable falw size in different weld joint parts. The presence of flaws is obvious but the possibilities of their revealing are limited and not always posssible. The flaw size and distribution are the essential parameters for the structure capacity of bearing under high loading the weld joint. The larger is the allowable flaw size anticipated, the safer is the welded structure, and the easiest is the detection of the flaw size by NDE methods. Thus for assessing the safety of complex loaded welded structure, machine parts or equipment life time, it is obligatory to consider the requirements of different "Fitness for Purpose" systems. The article presents the possibility of assessing the detected flaw by means of NDE if the material fracture toughness of the area where the fatigue crack tip located is known. The fatigue crack represents the severest discontinuity that can occur in a welded joint. The principles of IIW Guidance on Assessment of The Fitness for Purpose of Welded Structures - IIW/IIS-SST-1157-90 and BS PD 6493 and separately ETM that treats mis-matched weld joints are shown and used.
Ključne besede: zvarni spoji, dopustna velikost napake, lomna žilavost, trdnostna heterogenost, primernost za uporabo, weld joint, allowable flaw size, fracture toughness, strength mis-match, fitness for purpose
Objavljeno: 10.07.2015; Ogledov: 810; Prenosov: 9
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Measurement of strain caused by residual stresses in a welded joint using neutron diffraction
Nenad Gubeljak, Jelena Vojvodič-Tuma, Hans-Georg Preismeyer, 1999, izvirni znanstveni članek

Opis: The distribution and amount of residual stresses can significantly contrubute to the fatigue fracture behaviour of welded joints in structures. Interior residual stresses, which interact with the plane strain state, are more dangerous than residual stresses at the surface of the welded joint. If the surface of the welded joint is mechanically treated (e.g. shapering), then significant differences between the stress stated at the surface and within the volume occur. Hence, different non-destructive methods (e.g. gamma radiation, neutron diffraction) have been developed to determine strains caused by residual stresses in the volume of polycrystalline materials. However, the measurement of strains caused by residual stresses becomes difficult for large samples. In this paper the measurement procedure on a sample taken from the weld joint is presented and the effecet of residual stresses on fatigue crack propagation is assessed for low and high cycle loading fatigue.
Ključne besede: zaostale napetosti, zvarni spoj, neutronski lom žarkov, utrujenostno širjenje razpoke, neutron diffraction method, residual stresses, fatigue crack propagation, weld joint
Objavljeno: 10.07.2015; Ogledov: 636; Prenosov: 15
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Role of residual stresses on fracture properties of under-matched butt weld
Inoslav Rak, Vladimir Gliha, 1999, izvirni znanstveni članek

Opis: Under-matched weld joints were adopted for producing a penstock of 47 mm wall thickness and 4200 mm diameter, to improve the weldability. The isothermal Robertson wide plate test on the under-matched weld joints, were the allowable stress level was 0.6 of the yield stress, proved that the longitudinal stresses caused the crack propagation alog the weld joint to deviate into tough base material where it was arrested. The arrest temperature was between -10 and -20°C. The behaviour of the crack propagation was the reason to omit the thermal stress relieving of the pipe section and on circumferential weld joints executed on this side. One can always take into consideration the role of axial residual stresses when assessing whether to use, or not, under-matched weld joints in severer loaded structures.
Ključne besede: strjeni zvar z nižjo mejo tečenja, zaostale napetosti, potek loma, lastnosti ujetja, lomna žilavost, under-matched weld joint, residual stresses, fracture path, arrest properties, fracture toughness
Objavljeno: 10.07.2015; Ogledov: 862; Prenosov: 23
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Wear resistance of coke-crushing hammers
Franc Zupanič, 2013, izvirni znanstveni članek

Opis: This work investigated several methods for improving the wear resistance of the 42CrMo4 tool steel used for coke-crushing hammers. The methods embraced heat treatment for obtaining different combinations of strength and ductility of the bulk steel, and surface-engineering processes comprising TiN thin-film deposition using magnetron-sputtering, nitriding and WC/Ni weld deposit surfaced by gas metal arc (GMA) method. The wear-resistance was tested under industrial conditions. Oil quenching and tempering significantly increased the wear resistance in comparison to the as-received condition. Conversely, nitriding and TiN-hard coating did not show any significant improvement. WC/Ni weld deposit provided the best protection against wear, which was caused predominantly by hard abrasive particles present in the coke.
Ključne besede: zvarni spoj, mikrostrukture, obrabna odpornost, toplotna obdelava, obraba, kladivo, weld deposition, microstructure, impact coke crusher, heat treatment, wear, hammer
Objavljeno: 10.07.2015; Ogledov: 1008; Prenosov: 49
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Vloga in nastanek mikrostrukturnih sestavin M-A v zvarnih spojih maloogljičnih visokotrdnostnih konstrukcijskih jekel
Zdravko Praunseis, Masao Toyoda, Alojz Križman, Mitsuru Ohata, 2001, pregledni znanstveni članek

Opis: The existence of martensite-austenite constituents in the weld metal and heat-affected zone seriously reduces the fracture toughness of the welded joint. Therefore, we have investigated the formation of the martensite-austenite constituents when high-strength low-alloy steel is welded with a high heat input or using multi-pass welding. This paper deals with the effects of martensite-austenite constituents on the fracture toughness, the metallurgical features of the martensite-austenite constituents, and the prevention and elimination of the martensite-austenite constituents in the welded joints.
Ključne besede: arc welding, high-strength low-alloy steels, microstructure, martensite-austenite constituents, weld metal, heat-affected zone, cooling rate
Objavljeno: 01.06.2012; Ogledov: 1355; Prenosov: 85
.pdf Celotno besedilo (985,12 KB)
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Determination of lower bound fracture toughness of a high strength low alloy steel welded joint
Nenad Gubeljak, 2005, izvirni znanstveni članek

Opis: The use of high-strength low-alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distortion. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along thevcrck front. In the case of through thickness specimens, at least one local brittle microstructure is incorporatedin the process zone at the vicinity of the crck tip. Hence, unstable fracture occurred with small or without stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and that of base metal are insignificant, the future toughness of a weld metal can be significantly lower.
Ključne besede: welded joints, fracture mechanics, Crack tip opening displacement, high strength seeel weld, mismatch effects, fracture toughness, resistance curves
Objavljeno: 01.06.2012; Ogledov: 1538; Prenosov: 84
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