Abstract
Interstitial nitrogen can significantly change the electronic structure and bonding characteristics of austenite, and has an important influence on the properties of austenite. The bonding ...properties and properties of high nitrogen steel with different nitrogen element ratios were calculated. The alloy model with different nitrogen content is established, and the properties of energy, density of states and elastic constant are calculated. Increasing the nitrogen content will reduce the density of states and energy, significantly improving the stability of the cell. The crystal cells with different nitrogen content meet the mechanical stability. With the increase of nitrogen content, the elastic modulus, Poisson’s ratio gradually decreases, strength, shear strain and deformation resistance increase, and plasticity and ductility decrease.
Abstract
The effect of extrusion force on the microstructure and plasticity of the X2CrTiNb18 ferritic corrosion resisting steels joints which were welded by beam oscillation laser welding was ...studied. The cross section profile of welded joint beam oscillating fiber laser welding & extrusion (OLW&E) was similar to that of the beam oscillation laser welding (OLW), but the weld width of OLW&E was slightly narrow. The differences of microstructure between them were very obvious. In the OLW&E weld zone (WZ), on the one hand, the quantity of small grains increased obviously, and on the other hand they grew in a staggered state. In the plastic forming process, the deformation compatibility of welded joints was significantly improved, and its plasticity was increased by 21%.
This study is concerned with the effects of laser and arc arrangement on weld integrity for the hybrid laser arc welding processes. Experiments were conducted for a high-strength steel using a 4kW ...Nd: YAG laser and a metal active gas (MAG) welding facility under two configurations of arc–laser hybrid welding (ALHW) and laser–arc hybrid welding (LAHW). Metallographic analysis and mechanical testing were performed to evaluate the weld integrity in terms of weld bead geometry, microstructure and mechanical properties. The morphology of the weld bead cross-section was studied and the typical macrostructure of the weld beads appeared to be cone-shaped and cocktail cup-shaped under ALHW and LAHW configurations, respectively. The weld integrity attributes of microstructure, phase constituents and microhardness were analyzed for different weld regions. The tensile and impact tests were performed and fracture surface morphology was analyzed by scanning electron microscope. The study showed that ALHW produced joints with a better weld shape and a more uniform microstructure of lath martensite, while LAHW weld had a heterogeneous structure of lath martensite and austenite.
•ALHW joints a better weld shape uniformity microstructure.•The grain sizes in HAZ of LAHW were markedly greater compared to of ALHW.•The impact energy of weld joints of ALHW is lower than that of the LAHW.
•Aluminum/steel laser welded joints with copper and vanadium interlayers were fabricated and the intermetallic compounds were modified.•The Cu interlayer improves the joint strength and the V ...interlayer potentially removes Fe-Al intermetallic compounds completely.•First-principles calculations on intermetallic compounds reveal the brittleness mechanism of the compounds.•The relationship between the strength of welded joints and brittle compounds is explained.
Intermetallic compounds (IMCs) generated by direct laser welding of aluminum and steel decrease the strength of the joint. To evaluate the effect of alloying elements on the weldability of aluminum/steel dissimilar materials, the copper (Cu) and vanadium (V) were introduced into the interlayer to inhibit the generation of Fe-Al IMCs. Comparing with direct welding, Cu promotes the generation of Al2Cu and V transforms the disordered Fe/Al interface into a continuous Al/V interface to promote the generation of Al3V and Al21V2. In addition, the first-principles calculations were carried out to study the elastic properties and electronic properties of intermetallic compounds. The results show that high brittleness of FeAl, Fe2Al5 and FeAl3 results from strong covalent bonding and antibonding. The Fe(d) orbit hybridizes with Al(s) and Al(p) orbits while resonant peaks and wide pseudogap appear in the density of states. The low brittleness of Al2Cu results from the less count of covalent bonds with 76.2% of weaker antibonding; the low brittleness of Al21V2 results from the lower covalent bond strength with a maximum overlap bond population of 0.265. With the addition of Cu, the strength of the joint was increased to 63 MPa from 31 MPa. Furthermore, the addition of V completely prevents the formation of Fe-Al IMCs, which results in the highest joint strength (93 MPa). The results of the first-principles calculations and experiments are in good agreement.
•This study uses beam oscillation with fiber laser welding to join thin plates X2CrTiNb18 ferritic stainless steel. The resulting microstructure and mechanical properties of the welded area are ...studied and validated. We find that:•Beam oscillation changes the morphology and microstructure of the weld, forms an equiaxed grain zone in the weld, changes the growth direction of grains, and improves the deformation coordination of the grains.•The unidirectional mechanical properties of fiber laser welding (FLW) and oscillating fiber laser welding (OFLW) joints are indistinguishable. However, the OFLW joint has a significantly higher plastic formability than the FLW joint.•Beam oscillation markedly improves the plasticity and fracture toughness of the X2CrTiNb18 FSS joint.
This study adopted fiber laser welding (FLW) and oscillating fiber laser welding (OFLW) to weld 1.2 mm-thick X2CrTiNb18 ferritic stainless steel (FSS) in the form of square butt joint. The microstructure and mechanical properties of two types of joints were characterized and compared. The results showed that beam oscillation had a marginal effect on the unidirectional tension properties of the joints. However, the plasticity and fracture toughness of the joint were markedly increased. The beam oscillation changed the morphology and microstructure of the weld. It transformed the outer profile of the weld cross-section into an inverted trapezoid, and formed an equiaxed grain zone in the weld. Beam oscillation decreased the angle between the growth direction of columnar crystals around the equiaxed grains and the weld centerline, which improved the deformation coordination of the grains. The plasticity and fracture toughness of X2CrTiNb18-FSS joints were also improved accordingly.
Welding porosity and nitrogen content are considered significant factors affecting the mechanical properties of fusion-welding joints of high-nitrogen steel. In this study, a method of applying ...mechanical vibration in the welding process to reduce weld porosity and increase weld nitrogen content was investigated. The effects of mechanical vibration on porosity, tensile, and impact properties were analysed. The results indicated that the bubble floating speed in the vibrating weld pool is faster than that in the general welding mode. With the increase of mechanical vibration frequency, the porosity of the weld decreased at first and then rose. The tensile strength and impact energy increased first and then decreased, and the fracture surface indicated a ductile fracture.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The numerical simulation of high-strength low-alloy steel in the welding temperature field is carried out. The SYSWELD special welding analysis software is used to establish the geometry model of the ...butt joint of the flat Y-shaped groove. The temperature field of single-layer and multi-layers welding of 12 mm high-strength low-alloy steel provides a theoretical basis for the welding process and has engineering practical value.
In this paper, CO2 laser-metal active gas (MAG) hybrid welding technique is used to weld high strength steel and the optimized process parameters are obtained. Using LD Pumped laser with an emission ...wavelength of 532nm to overcome the strong interference from the welding arc, a computer-based system is developed to collect and visualize the waveforms of the electrical welding parameters and metal transfer processes in laser-MAG. The welding electric signals of hybrid welding processes are quantitatively described and analyzed using the ANALYSATOR HANNOVER. The effect of distance between laser and arc (D|> LA) on weld bead geometry, forming process of weld shape, electric signals, arc characteristic and droplet transfer behavior is investigated. It is found that arc characteristic, droplet transfer mode and final weld bead geometry are strongly affected by the distance between laser and arc. The weld bead geometry is changed from "cocktail cup" to "cone-shaped" with the increasing D|>LA. The droplet transfer mode is changed from globular transfer to projected transfer with the increasing D|> LA. Projected transfer mode is an advantage for the stability of hybrid welding processes.
This paper investigates the effects on corrosion mechanism and pitting resistance in high-nitrogen austenite steel laser-arc hybrid weld. Electrochemical corrosion technology was used to study the ...corrosion behavior in 3.5% NaCl solution. The conclusions as follow: Both from microcosmic and macroscopical analysis, the δ-ferrite precipitated from dendrites is preferentially be corroded and exfoliated. The growth pattern and dense degree of dendrites is found to be the most significant factors that affect the corrosion tendency. Compared to the arc acting area, the laser acting area at the weld bottom prefer better corrosion mechanism because of the enhancement of Laser keyhole action. Pitting corrosion mainly concentrated in the center of the small fir-tree crystals and leave regular special secondary pitting hole. This phenomenon only exists in the austenite welds with dendritic distribution. The coarse dendrites with large structure is the starting layer of exfoliation corrosion which promote the further erosion of Cl−. Through the study of the weld hardness, it is further proved that the laser acting area does have more uniform structure distribution and thus has excellent corrosion resistance. Research reveals that the hybrid weld has unique corrosion behavior which is different from the conventional Austenite stainless steel.
The present work reports results obtained using computer-based system techniques to investigate the metal transfer in laser-MAG hybrid welding. This arc characteristic information can be recorded by ...combining the sensing of the welding current and arc voltage with high speed imaging of the droplet transfer. An LD pumped green laser was used to overcome the strong interference from the welding arc. The arc energy determined mode of droplet transfer. When the arc energy is less than 4 kW, the transfer mode is short circuit transfer, or globular transfer or transfer mode between short circuit and globular. When the arc energy exceeds the 4.68 kW, the transfer mode is spray type. The laser energy has an important influence on the arc length, droplet size and the droplet velocity. When the arc energy is less than 4 kW, the attraction and compression of laser on arc play an important role, which caused the average arc length increases with increasing laser power. When the arc power is beyond 4.68 kW, the average arc length is decreasing with increasing laser power, which is attributed to expansion of the arc plasma, and enhancement of jet force of metal vapor on droplet. The droplet velocity decreases with increasing laser power, which is attributed to the attraction force of laser plasma to arc and the jet force of metal vapor produced by laser keyhole on droplet.
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