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Showing papers on "Weldability published in 2012"


Book ChapterDOI
TL;DR: In this paper, microstructural and physical properties of the Ni-based superalloy CM247LC were investigated by using a stereological study of scanning electron microscope (SEM) micrographs.
Abstract: The use of a selective laser melting (SLM) powder-bed method to manufacture Ni-based superalloys components provides an economic approach for low production run components that operate under a high-temperature and stress environment. A major concern with the SLM of precipitation hardenable Ni-based superalloys is their high susceptibility to cracking, which has been heavily documented in the field of welding. Weld cracking may occur either during processing (hot cracking, liquation cracking and ductility-dip cracking) or during the post weld heat-treatment stage (strain-age cracking). Due to the complex thermal history of SLM fabricated material there is the potential for all of these mechanisms to be active. In this investigation, cuboidal coupons of the Ni-based superalloy CM247LC were fabricated by the SLM of argon gas atomised powder. Parametric studies were performed to investigate the influence of the process parameters (laser scan speed, power and scan spacing) on the cracking density and morphology through conducting a stereological study of scanning electron microscope (SEM) micrographs. Further microstructural evidence is presented, illustrating the different crack morphologies observed as well as suggesting the responsible mechanisms. Finally a postfabrication Hot Isostatic Pressing (HIP) treatment was performed to investigate its utility in ‘healing’ the internal cracks, and providing a route to retro-fix the cracking problem in the heat treatment stage of production. The findings highlight the need for process models of the SLM method in order to understand the thermal history and the laser fabricated structures observed. Introduction The discipline of additive layer manufacture (ALM) has been steadily growing since the 1980’s and now encompasses a wide variety of technologies. They all share the common feature of producing a three dimensional shape by combining two dimensional ‘slices’ of a predetermined thickness. In recent years, ALM technologies have been developed to push the field forward from ‘rapid-prototyping’ towards ‘rapid-manufacturing’ and the production of fully dense and functional metallic components. In terms of laser fabrication there are now two key technologies for the rapid manufacture of fully-dense metallic components; Direct Laser Fabrication (DLF or any ‘Blown Powder’ system) and ‘Selective Laser Melting (SLM) Powder-Bed’ manufacturing. Comprehensive reviews of the different ALM methods can be found elsewhere [1-4]. SLM powder-bed technology has attracted the interest of aerospace manufacturers for several key reasons including: The elimination of the need the expensive tooling associated with forging and investment casting; the immediate recyclability of the unused metal powder, and the significant reduction in the ‘design-to-component’ time thus allowing for actual physical testing and many design iterations. The present study aims to assess the microstructural and physical characteristics of the SLM fabricated Ni-based superalloy for high-temperature application. Weld Cracking Laser fabrication process can be considered analogous to a continuous laser welding process. Due to this, an alloy weldability can be used as an indication as to its processability by SLM. Figure 1 [5] shows a number of typical Ni-based superalloys plotted according to their Al and Ti contents (γ′ forming elements). The alloys lying above the dotted line show a high volume fraction of the γ′ phase and are typically considered unweldable due to their cracking susceptibility. This relationship between the cracking susceptibility and γ′ fraction is attributed to the precipitation hardening that occurs within the aging temperature of the alloy; reheating the material to within this region (either in the welding process or as part of a post-weld heat treatment (PWHT)) results in hardening accompanied by a reduction in ductility leaving the material prone to cracking [5]. A review of the relevant literature highlighted four potential cracking mechanisms associated with welding and reheating of Ni-based superalloys, which are: Figure 1. Plot showing increasing cracking susceptibility with γ′ forming elements (Al and Ti) [5]. Alloys lying above the dotted line are particularly susceptible to cracking during welding or PWHT. Solidification Cracking Also referred to as ‘Hot-Tearing’, is reported to occur within the solidifying melt pool (or the mushy zone) where the material is in

164 citations


Journal ArticleDOI
TL;DR: In this article, the microstructure evolution of aluminized coatings during the hot stamping process is discussed, and an analysis of the cracking of the coating caused by the formation of brittle Fe-Al intermetallic phases and their high temperature deformation is presented.
Abstract: In the present contribution, recent developments of coatings for hot stamped steels are reviewed. The use of bare steel in the initial hot stamping technology is discussed, including the application of lubricant oils which are used as oxidation inhibitors on bare steel surfaces. The aluminized coatings are introduced, focusing on the microstructure evolution of aluminized coatings during the hot stamping process. An analysis of the cracking of the coating, caused by the formation of brittle Fe–Al intermetallic phases and their high temperature deformation, is presented. The development of a ductile aluminide coating formed during the diffusion treatment of an aluminized coating is discussed. This aluminide coating can endure both high temperature oxidation and severe plastic deformation. The recently developed galvanized and galvannealed coatings are also reviewed and the influence of the gas atmosphere during the heating cycle on the coating stability is emphasized. The solutions which have been proposed to avoid liquid Zn-induced embrittlement are analyzed. The use of Zn–Ni alloy coating, which is characterized by a higher melting temperature, is reviewed. The behavior of sol–gel hybrid coatings on hot stamped steels is discussed. The possible use of the recently developed Al–Zn alloy coatings, dual layer Zn–Al and Zn–Al–Mg coatings is also introduced. The application of Zn–Al–Mg post-process galvanizing is also discussed. In each case, all available information related to the weldability, paintability, and corrosion resistance of the coating systems is also reported. Finally, the advantages and technical challenges associated with each type of coating are reviewed.

159 citations


Journal ArticleDOI
TL;DR: In this article, the effect of different beam scanning patterns on the microstructure and mechanical properties of Ti-6Al-4V alloy joints by electron beam welding was investigated, and the results showed that the weld metal is full of cross-cross acicular α′ martensitic structure, while the base metal is of equiaxed structure.

138 citations


Journal ArticleDOI
TL;DR: This review describes metallurgical aspects of the microalloying of steel, such as niobium addition, and discusses advantages of TMCP in terms of weldability, which is reduced upon alloying.

128 citations


Journal ArticleDOI
TL;DR: In this paper, the state-of-the-art and trends in welding of duplex stainless steels are discussed based on input from the worldwide welding community, including users and producers of steel and welding consumables as well as literature.
Abstract: A steel will not become widely accepted and used unless it can be successfully welded without too many limitations. Contemporary duplex stainless steel grades fulfil these requirements with some grade dependent differences. The duplex stainless steel family has, during the last decade, been extended with new lean grades and recently also highly-alloyed hyperduplex grades. Most welding recommendations are very similar to those of the 1990’s. However, the introduction of new grades and the increased use of newer welding methods has somewhat changed the perception of what is possible. This paper discusses the state-of-the-art and trends in welding of duplex stainless steels. It is based on input from the worldwide welding community, including users and producers of steel and welding consumables as well as literature. In most cases, there is consensus on recommendations but variations reflecting differences in practices exist in particular for newer steel grades where limits in e.g. allowable energy inputs are less well documented.

97 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the lower boundary of an explosive welding lower boundary in the physical coordinates "pressure-time-temperature" and "collision angle-collision velocity".

83 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of tool rotational speed and traverse speed on welding of AISI 430 (X6Cr17, material number 1.4016) ferritic stainless steels by friction stir welding method are examined.

79 citations


Journal ArticleDOI
TL;DR: In this article, the work carried out on welding of AISI 304 and Monel 400 using Gas Tungsten Arc Welding (GTAW) technique to examine the weldability, mechanical and metallurgical properties is reported.

78 citations


DOI
01 Jan 2012
TL;DR: In this paper, 3.17mm-thick, AA7075 Al-alloy plates both in the Oand T6-temper conditions were joined by friction-stir welding using four different weld parameters.
Abstract: Al-alloys are widely used in the transportation industries due to their low density and excellent formability properties. These alloys, which are problematic in fusion-welding processes, can be successfully joined by friction-stir welding. Particularly high-strength AA7075 alloy is considered to be non-weldable by fusion welding. Friction-stir welding, being a solid-state joining technique, can also be successfully used in joining other difficult-to-weld alloys. In this study, 3.17-mm-thick, AA7075 Al-alloy plates both in the Oand T6-temper conditions were joined by friction-stir welding using four different weld parameters. Microstructural and mechanical characterizations of the joints produced were obtained with detailed optical microscopy investigations, extensive hardness measurements and tensile tests. The effect of temper condition on the joint performance was determined in addition to the effect of the weld parameters on the joint quality.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of friction stir welding (FSW) parameters on the weldability and the characteristics of dissimilar weld of aluminum alloys, called AA2024-T4 and AA7075-O are investigated.
Abstract: In the present article, the effect of friction stir welding (FSW) parameters on the weldability and the characteristics of dissimilar weld of aluminum alloys, called AA2024-T4 and AA7075-O are investigated. A number of FSW experiments are carried out to obtain high-quality welds by adjusting the rotational and welding speeds. The weldability and blending of two materials are evaluated by using the macrostructural analysis to observe whether making a notch in a threaded cylindrical tool will lead to a better blend rather than the threaded taper tool or it will have no effects. The mechanical properties of the welds are studied through microhardness distribution and tensile tests. Furthermore, the microstructure analysis is performed to study the influence of the pin profile and the rotational speed on the grain size. Moreover, in the present study, one of the most major goals is to obtain high-quality welds by spending as little expenditure as possible. Therefore, it prevents using complicated and insupportable high welding speed equipments.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the weldability window of the stainless steel pipe and the carbon steel pipe was determined by the use of available semi-empirical relations, and the impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation.
Abstract: Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.

Journal ArticleDOI
TL;DR: In this paper, the influence of the plastic behavior of two aluminium alloys, very popular in welding construction, on friction stir weldability was analyzed. And the relationship between weldability, material flow during FSW and the plastic behaviour of the base materials, at different temperatures, was analyzed and compared.

Journal ArticleDOI
TL;DR: In this article, the microstructure features of a series of microalloyed steels (X70, X80, and X100) as well as a Grade 100 steel are characterized using optical microscopy (OM) and scanning electron microscopy.
Abstract: Microalloyed steels are used widely in oil and gas pipelines They are a class of high-strength, low-carbon steels that contain small additions (in amounts less than 01 wt pct) of Nb, Ti, and/or V The steels may contain other alloying elements, such as Mo, in amounts exceeding 01 wt pct Precipitation in these steels can be controlled through thermomechanical-controlled processing, leading to precipitates with sizes that range from several microns to a few nanometers Microalloyed steels have good strength, good toughness, and excellent weldability, which are attributed in part to the presence of the nanosized carbide and carbonitride precipitates Because of their fine sizes, wide particle size distribution, and low volume fractions, conventional microscopic methods are not satisfactory for quantifying these precipitates Matrix dissolution is a promising alternative to extract the precipitates for quantification Relatively large volumes of material can be analyzed so that statistically significant quantities of precipitates of different sizes are collected In this article, the microstructure features of a series of microalloyed steels (X70, X80, and X100) as well as a Grade 100 steel are characterized using optical microscopy (OM) and scanning electron microscopy (SEM) A chemical dissolution technique is used to extract the precipitates from the steels Transmission electron microscopy (TEM) and X-ray diffraction (XRD) are combined to analyze the chemical composition of these precipitates Rietveld refinement of the XRD patterns is used to quantify fully the relative amounts of these precipitates The size distribution of the nanosized precipitates is quantified using dark-field imaging (DF) in the TEM The effects of microalloying content, finish rolling temperature (FRT), and coiling temperature (CT)/interrupted cooling temperature (ICT) on the grain size and the amount of nanoprecipitation are discussed Individual strengthening contributions from grain size effects, solid-solution strengthening, and precipitation strengthening are quantified to understand fully the strengthening mechanisms for these steels

Journal ArticleDOI
TL;DR: In this article, the authors investigated the weldability of high-density polyethylene sheets via heat assisted friction stir welding and effect of process parameters on microstructure and mechanical properties of welded plates.
Abstract: The aim of this study was to investigate the weldability of high-density polyethylene sheets via heat assisted friction stir welding and effect of process parameters on microstructure and mechanical properties of welded plates. The parameters under study were included pin rotational speed, transverse speed of tool and shoulder temperature. Tensile and bend tests were done in order to evaluate mechanical behavior of material. The results showed that polyethylene plates could be welded with joint characteristics similar to base material. This could be accomplished by operating with a high shoulder temperature and rotational speed as well as low transverse speed. Moreover, when process parameters were properly selected to provide sufficient heat, the weld nugget would extend to base material. Consequently, a remarkable improvement was observed in joint efficiency. Also, based on microstructure observations and mechanical test results, it could be concluded that, tool coating improved mechanical properties and surface quality of weld. Key words: Friction stir welding, polyethylene, mechanical properties, microstructure.

Journal ArticleDOI
TL;DR: In this paper, one lean, one standard 22 %Cr and one superduplex stainless steel were autogenously laser welded bead-on-plate and MIG-laser hybrid welded with recommended fillers.
Abstract: There is a growing interest in the use of low energy input welding methods, often with little or no addition of filler material, for welding of duplex stainless steels. In the present study, therefore one lean, one standard 22 %Cr and one superduplex stainless steel were autogenously laser welded bead-on-plate and MIG-laser hybrid welded with recommended fillers. The energy inputs ranged from 0.1–0.6 kJ/mm. Ferrite contents were generally high (65–99 %) with autogenous laser welding resulting in the highest levels. The addition of fillers had a larger effect on ferrite content than increasing energy inputs. Evaluation of weld metal ferrite content and the tendency to form nitrides suggest that the superduplex steel, closely followed by the lean grade, are most suited for low energy input welding. The standard 22 % Cr steel requires the most careful optimization of procedures to produce an acceptable weld metal microstructure. The overall conclusion is that low energy input welding methods could be applied to duplex stainless steels. However, high nitrogen grades are more suitable and care must be taken to ensure sufficient austenite formation.

Journal ArticleDOI
11 Feb 2012-JOM
TL;DR: In this article, Alloy design criteria, melt processing experiences, and heat treatment are discussed with respect to the as-processed and heat-treated microstructures and selected mechanical properties.
Abstract: The high-temperature components within conventional supercritical coal-fired power plants are manufactured from ferritic/martensitic steels. To reduce greenhouse-gas emissions, the efficiency of pulverized coal steam power plants must be increased to as high a temperature and pressure as feasible. The proposed steam temperature in the DOE/NETL Advanced Ultra Supercritical power plant is high enough (760°C) that ferritic/martensitic steels will not work for the majority of high-temperature components in the turbine or for pipes and tubes in the boiler due to temperature limitations of this class of materials. Thus, Ni-based superalloys are being considered for many of these components. Off-the-shelf forged nickel alloys have shown good promise at these temperatures, but further improvements can be made through experimentation within the nominal chemistry range as well as through thermomechanical processing and subsequent heat treatment. However, cast nickel-based superalloys, which possess high strength, creep resistance, and weldability, are typically not available, particularly those with good ductility and toughness that are weldable in thick sections. To address those issues related to thick casting for turbine casings, for example, cast analogs of selected wrought nickel-based superalloys such as alloy 263, Haynes 282, and Nimonic 105 have been produced. Alloy design criteria, melt processing experiences, and heat treatment are discussed with respect to the as-processed and heat-treated microstructures and selected mechanical properties. The discussion concludes with the prospects for full-scale development of a thick section casting for a steam turbine valve chest or rotor casing.

DOI
07 Dec 2012
TL;DR: In this article, the authors developed a Computational Fluid Dynamics model to study steel weld pool hydrodynamics during conduction mode laser spot welding, and concluded that free surface deformations and instabilities have a strong impact on the fluid flow and heat transfer in weld pools, and should therefore be accounted for in weld pool simulations.
Abstract: Extending the weldability of novel materials, and improving the weld quality by tailoring weld microstructures are key factors to obtain the welding techniques demanded in the modern manufacturing industries. This can be done, for example, by feeding chemical elements from a consumable wire into the weld pool during welding. The mixing of chemical components in the weld pool and the resulting post-solidification weld microstructures are influenced by weld pool hydrodynamics. Weld pool hydrodynamics is known to be primarily driven by Marangoni forces acting at the free liquid surface, i.e by tangential gradients in surface tension along the liquid surface due to pronounced lateral gradients in temperature and surface active element concentration. In this research, we develop a Computational Fluid Dynamics model to study steel weld pool hydrodynamics during conduction mode laser spot welding. It is concluded that free surface deformations and instabilities have a strong impact on the fluid flow and heat transfer in weld pools, and should therefore be accounted for in weld pool simulations. With increasing the surface active element concentration and laser power, the weld pool flow becomes highly unstable and can no longer be accurately modeled with a flat surface assumption. More accurate predictions of weld pool physics can be made if the free surface, solidification stage, and three-dimensionality are taken into account. This reduces the need for the use of unphysical parameter fittings widely reported in literature.

Journal ArticleDOI
TL;DR: In this paper, precise observations of the segregation of B, P, and C to the grain boundaries are made using site-specific atom probe tomography and nanoSIMS. And they reveal that these atoms were less likely to cluster together in the presence of C, providing insight into the likely mechanisms behind the segregation behavior in this complex, multicomponent alloy.
Abstract: Small additions of B, P, and C can result in dramatic changes in the mechanical performance and welding behavior of Inconel 718. Although additions of B and P improve the mechanical properties, they have a detrimental effect on weldability. Adding C mitigates the negative effect on welding while retaining the improvements in mechanical performance. In this study, precise observations of the segregation of B, P, and C to the grain boundaries are made using site-specific atom probe tomography and NanoSIMS. Changes in the segregation behavior provide a quantitative explanation for the welding response, where hot cracking is attributed to the formation of a eutectic film. Calculations of the relative positions of the B, P, and C revealed that these atoms were less likely to cluster together in the presence of C, providing insight into the likely mechanisms behind the segregation behavior in this complex, multicomponent alloy.

Journal ArticleDOI
TL;DR: In this paper, the effects of weld current on the microstructural characteristics, mechanical properties, and fracture modes were investigated using optical microscopy (OM) and scanning electron microscopy(SEM).
Abstract: In this paper, resistance spot weldability of high-Mn steels were investigated in order to get high reliability in welded joints of automotive components. Microstructural characterizations, cross-tensile test (CTT), microhardness tests of spot welded parts were conducted. The effects of weld current on the microstructural characteristics, mechanical properties, and fracture modes were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The hardness in the weld nugget was observed to be lower than that in the base metal (BM). In CTT, the failure initiation was observed to occur at the boundary of the weld nugget. Also welding imperfections of welded parts were investigated. Liquation cracking in heat affected zone (HAZ), porosity, and shrinkage cavity were found most common welding defects in welded parts. Furthermore, the effects of welding imperfections on weld quality and failure criteria were identified and discussed.

Journal ArticleDOI
TL;DR: In this paper, the tensile properties, strain distribution, fracture mechanisms, and microstructure of electron beam welded Ti-5Al-5V-5Mo-3Cr (Ti-5553) in the as-welded condition were investigated in order to evaluate the weldability of the titanium alloy.

Journal ArticleDOI
02 Mar 2012-JOM
TL;DR: In this paper, the weldability of different zinc-coated steels with aluminum is discussed, using a 2.5kW ultrasonic spot welding welder, and the results show that soft hot-dipped zinc (DX56-Z)-coated steel results in better weld performance than hard (galv-annealed) zinc coatings (DX53-ZF).
Abstract: Dissimilar joining of aluminum to steel sheet in multimaterial automotive structures is an important potential application of ultrasonic spot welding (USW). Here, the weldability of different zinc-coated steels with aluminum is discussed, using a 2.5-kW USW welder. Results show that soft hot-dipped zinc (DX56-Z)-coated steel results in better weld performance than hard (galv-annealed) zinc coatings (DX53-ZF). For Al to hard galv-annealed-coated steel welds, lap shear strengths reached a maximum of ~80% of the strength of an Al-Al joint after a 1.0 s welding time. In comparison, welds between Al6111-T4 and hot dipped soft zinc-coated steel took longer to achieve the same maximum strength, but nearly matched the Al-Al joint properties. The reasons for these different behaviors are discussed in terms of the interfacial reactions between the weld members.

Journal ArticleDOI
TL;DR: In this paper, the basic concepts for applying the friction stir welding (FSW) process to components made from titanium alloy are described. But, there is no consolidated experience, even at the international level, on the behaviour of the FSW process for titanium alloys; however, the main results obtained from recent studies in the field and data provided by the Institute further to tests conducted in relation to research projects aimed at the aeronautics sector.
Abstract: The article describes the basic concepts for applying the friction stir welding (FSW) process to components made from titanium alloy. As is well known, titanium and its alloys are demanding applications for FSW due to the high mechanical strength, high melting temperature, low thermal conductivity, susceptibility to atmospheric contamination, and the high tendency for embrittlement of the material due to the absorption of interstitial elements (O, N, and H). Hence, the process parameters have great influence on the microstructure and properties of the welded joint. To date, there is no consolidated experience, even at the international level, on the behaviour of the FSW process for titanium alloys; however, this article reports the main results obtained from recent studies in the field and data provided by the Institute further to tests conducted in relation to research projects aimed at the aeronautics sector. In particular, it is pointed out that the use of conventional tools (consisting of ‘Shoulder To...

Journal ArticleDOI
Fatih Hayat1
TL;DR: The similar and dissimilar resistance spot weldability of 6061-T6 and 7075-T651 aluminium alloys was investigated in this article, where microstructure, microhardness, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electron probe micro-analyses (EPMA) were conducted to study the effects aging heat treatment had on similar-and dissimilar RSW joints.
Abstract: The similar and dissimilar resistance spot weldability of 6061-T6 and 7075-T651 aluminium alloys was investigated in this study. Resistance spot weldability of commercial and aged samples in different variations was examined. The microstructure, microhardness, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electron probe micro-analyses (EPMA) were conducted to study the effects aging heat treatment had on similar and dissimilar resistance spot welded (RSW) joints. In addition, tensile shear tests were performed to determine the mechanical properties and fracture behaviour of welded joints. The tests concluded that pre-weld aging heat treatment improves mechanical properties.

Journal ArticleDOI
TL;DR: Wang et al. as discussed by the authors reviewed the welding technologies of low activation martensitic steel (CLAMs), a kind of RAFM steel with Chinese intellectual property rights, and focused on the weldability of CLAMs by different welding methods.

Journal ArticleDOI
TL;DR: In this article, the weld seam can block the adhesive crack propagation, and the adhesive improves the stress distribution, so they can offer a synergistic effect, while the weld edge can also influence the strength as a cracking source.
Abstract: This paper presents the research on weldability of magnesium alloy AZ61 sheets by overlap laser welding, adhesive bonding, and laser seam weld bonding processes. Microstructures and mechanical properties of the joints are investigated. In overlap laser welding, the joint fractures at the interface between the sheets and maximum shear strength can reach 85% of that of the base metal. Off-center moment during tensile shear test can lead to the strength loss, while the weld edge can also influence the strength as a cracking source. Adhesive bonded joint can offer high tensile shear failure force but low peel strength. Laser weld bonded joint offers higher tensile shear failure force than either laser welded joint or adhesive bonded joint does, and the improved failure load is due to combined contribution of the weld seam and the adhesive. The weld seam can block the adhesive crack propagation, and the adhesive improves the stress distribution, so they can offer a synergistic effect.

Journal ArticleDOI
TL;DR: In this article, commercially pure titanium sheets were welded by resistance spot welding at various welding parameters and the welded joints were subjected to tensile-shearing tests in order to determine the strength values.
Abstract: In this study, commercially pure titanium sheets (American Society for Testing and Materials grade 2) were welded by resistance spot welding at various welding parameters The welded joints were subjected to tensile-shearing tests in order to determine the strength values In addition, the hardness and microstructural examinations were carried out in order to examine the influence of welding parameters on the welded joints The experimental results showed that increasing electrode force, welding current and welding time increased the tensile-shearing strength of the welded specimens Hardness measurement results indicated that welding nugget had the highest hardness and this was followed by the heat-affected zone and the base metal Microstructural examinations showed the growth of the weld nugget grains with increasing heat input Besides, due to plastic deformation during the welding process, twins were formed and at the same time twins increased with increasing electrode force, welding current and welding time

Journal ArticleDOI
TL;DR: In this paper, submicron size intergranular M5B3 particles are identified for the first time in the present work by transmission electron microscopy, and were found to be the primary cause of heat-affected zone (HAZ) grain boundary liquation cracking in the alloy.
Abstract: Gleeble thermomechanical simulation and microstrucutural analyses of laser beam weldability of a newly developed precipitation-hardened nickel-base HAYNES alloy 282 were performed to better understand the fundamental cause of heat-affected zone (HAZ) cracking and how to prevent the cracking problem in the material. Submicron size intergranular M5B3 particles are identified for the first time in the present work by transmission electron microscopy, and were found to be the primary cause of HAZ grain boundary liquation cracking in the alloy. Complete dissolution of the liquating M5B3 particles by preweld heat treatment exacerbated rather than reduced susceptibility to cracking, which could be attributed to nonequilibrium intergranular segregation of boron atoms, liberated by the complete dissolution of the boride particles, during cooling from heat treatment temperature. Consequently, to reduce the HAZ cracking, a preweld heat treatment that reduces the volume fraction of the M5B3 particles while minimizing nonequilibrium grain boundary boron segregation is necessary, and this is possible by heat treating the alloy at 1353 K to 1373 K (1080 °C to 1100 °C). Further improvement in cracking resistance to produce crack-free welds is achieved by subjecting the alloy to thermomechanically induced grain refinement coupled with the preweld heat treatment at 1353 K (1080 °C). A Gleeble hot ductility test showed that formation of the crack-free welds is unexplainable by mere reduction in grain size without considering the effect of grain refinement on intergranular liquid produced by subsolidus liquation of the M5B3 borides.

Journal ArticleDOI
TL;DR: In this article, the authors examined the spot welding characteristics of transformation induced plasticity assisted steels, which contain δ-ferrite as a consequence of their aluminium concentrations of 3·5 or 5·6 wt-% and which also have high carbon contents of 0·3 or 0·4 wt% when compared with conventional automotive steels.
Abstract: We examine here the spot welding characteristics of transformation induced plasticity assisted steels, which contain δ-ferrite as a consequence of their aluminium concentrations of 3·5 or 5·6 wt-% and which also have high carbon contents of 0·3 or 0·4 wt-% when compared with conventional automotive steels. The resistance spot welds are tested in both shear and cross-tensile tests in order to determine the so called ductility ratio, which is a parameter associated with the fitness of such welds for automotive applications. With an increase in the δ-ferrite fraction from 0·19 to 0·5, the hardness variation across the weld and heat affected zone is decreased approximately from 400 to 150 HV. It seems that the presence of stable δ-ferrite is helpful in reducing hardness variations and in achieving a significant ductility ratio of 0·39.

Journal ArticleDOI
TL;DR: In this article, the laser weldability of hot-press-forming steels with and without Al-Si coating was examined, and the influence of the process parameters on the weld strength was investigated.
Abstract: There is an increasing demand for ultrahigh-strength steel in automotive industries to facilitate the manufacture of lightweight vehicles without compromising their security features. Although transformation-induced plasticity and dual phase steels have strengths of under 1 GPa, boron-alloyed steel obtained after the hot-press process has a strength of over 1500 MPa. Al–Si-coated steel has been developed to prevent excessive oxidation during high-temperature processes, but the Al–Si coating is known to lower weld properties. In this research, the laser weldability of hot-press-forming steels with and without Al–Si coating was examined. The specimens were laser-welded in butt and overlap joints by using disk and fiber lasers. The influence of the process parameters on the weld strength was investigated.

Patent
27 Mar 2012
TL;DR: In this article, a gas shielded arc welding method was proposed by using a welding steel wire composed of a steel wire stock containing by mass 001-010% C, 02-12% Si, 10-25% Mn, 005-020% Ti, 0003-0020% S, ≤ 0020% P, 0005-05% Mo, 0.5-03% Cr, ≤05% Cu, 000 5-002% Al, and 00005-00050% B; and gaseous mixture containing 10-50 volume % Co
Abstract: PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method by which weld metal having a superior strength and toughness is obtained, even in multi-layer welding with high heat input and high interpass temperature, and by which improved weldability is demonstrated by reducing the mount of the occurrence of spatter and of formation of slag at welding SOLUTION: Welding is performed by using: a welding steel wire composed of a steel wire stock containing by mass 001-010% C, 02-12% Si, 10-25% Mn, 005-020% Ti, 0003-0020% S, ≤0020% P, 005-05% Mo, 005-03% Cr, ≤05% Cu, 0005-002% Al, and 00005-00050% B; and gaseous mixture containing 10-50 volume % Co 2 and 50-90 volume% Ar as a shielding gas, thereafter time required until the bead of the final pass is cooled from 800°C to 500°C is adjusted to 15-450 seconds COPYRIGHT: (C)2005,JPO&NCIPI