Showing papers on "Heat-affected zone published in 1996"

Effect of Boron on Intra-granular Ferrite Formation in Ti-Oxide Bearing Steels

Abstract: The effect of B on microstructure and toughness at the heat affected zone after welding thermal cycle simulations has been investigated in steels containing titanium oxide particles. The titanium oxide is identified as Ti2O3 with cation vacancies, which contribute to preferential nucleation of MnS and TiN precipitates on Ti2O3. The Mn-depleted zone is formed around Ti2O3 after the precipitation of MnS. The Ti2O3, particles with TiN and Mn-depleted zone act as preferential nulceation sites for intra-granular ferrite. The segregation of B at austenite grain boundaries suppresses effectively the nucleation of grain boundary ferrite. Ferrite nucleation at the interface between Ti2O3 and austenite matrix is not affected by B addition because of B-depleted zone arisen from the diffusion of segregated B into Ti2O3 via cation vacancies. Consequently the B addition to steels with Ti2O3 promotes the formation of fine intra-granular ferrite grains so that the toughness in heat affected zone is improved even after large heat input welding.

Programmable friction stir welding process

Abstract: A variable pin length stir friction welding method wherein the stir friction welding pin penetrates the workpiece as the workpiece translates. The stir friction welding pin starting at a zero penetration and extending to the depth needed to repair a weld or to make a weld. Then withdrawing the pin to zero penetration as the work is translated. The weld path is thus ramped into and out of the workpiece leaving no holes which need to be repaired. Circumferential welds can be made by keeping the pin extended to the welding depth for at least one complete revolution of the weld.

Prediction of Residual Stresses in Welded T- and I-Joints Using Inherent Strains

Abstract: In order to develop a predicting method of residual stresses in fillet welded T- and I-joints, a concept of inherent strain, being regarded as a source of the residual stresses, was introduced. With the proposed method, the residual stress of an interested weldment may be predicted by performing an elastic analysis, in which the inherent strain is replaced to equivalent distributed loads. The inherent strain distributions in various welded T- and I-joints were investigated by numerical simulations. The results showed that the inherent strains distributing in flange side and in web side of the several joints are almost the same. The inherent strains vary not only with the average temperature rise due to welding, but with the geometric ratio of the joints. Being simplified by a trapezoid curve, the inherent strain distribution in a fillet weld was expressed by formulas, in which heat input, material properties, and geometric dimensions were taken into account. Welding residual stresses in T- and I-joints, predicted by the proposed method employing the derived formulas, were compared with those obtained by thermal elasto-plastic analysis, and good agreement was recognized. The validity of the proposed method was also confirmed by experiments.

Dilution in single pass arc welds

Abstract: A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged are welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiency can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization.

Microstructures relevant to brittle fracture initiation at the heat-affected zone of weldment of a low carbon steel

Abstract: Charpy toughness of the heat-affected zone (HAZ) of weldment of a low carbon steel has been investigated by means of an instrumented Charpy test and fractographic analysis. Microstructures were varied with thermal cycles simulating double-pass welding. The ductile-brittle transition temperature is the most deteriorated at an intermediate second-cycle heating temperature. The origin of the difference in the transition temperatures has been analyzed to exist in the brittle fracture initiation stage. Fractographic examination correlating with microstructural features has revealed that the brittle fracture initiation site is associated with the intersection of bainitic ferrite areas with different orientations rather than the martensite-austenite constituents. The role of the constraint of plastic deformation on the brittle fracture initiation is discussed.

Analysis of heat-affected zone phase transformations using in situ spatially resolved x-ray diffraction with synchrotron radiation

Abstract: Spatially resolved X-ray diffraction (SRXRD) consists of producing a submillimeter size X-ray beam from an intense synchrotron radiation source to perform real-time diffraction measurements on solid materials. This technique was used in this study to investigate the crystal phases surrounding a liquid weld pool in commercial purity titanium and to determine the location of the phase boundary separating the high-temperature body-centered-cubic (bcc) β phase from the low-temperature hexagonalclose-packed (hcp) α phase. The experiments were carried out at the Stanford Synchrotron Radiation Laboratory (SSRL) using a 0.25 × 0.50 mm X-ray probe that could be positioned with 10-µm precision on the surface of a quasistationary gas tungsten arc weld (GTAW). The SRXRD patterns were collected using a position-sensitive photodiode array in a φ-2φ geometry. For this probe size, integration times of 10 s/scan at each location on the specimen were found adequate to produce high signal-to-noise (S/N) ratios and quality diffraction patterns for phase identification, thus allowing real-time diffraction measurements to be made during welding. The SRXRD results showed characteristic hcp, bcc, and liquid diffraction patterns at various points along the sample, starting from the base metal through the heat-affected zone (HAZ) and into the weld pool, respectively. Analyses of the SRXRD data show the coexistence of bcc and hcp phases in the partially transformed (outer) region of the HAZ and single-phase bcc in the fully transformed (inner) region of the HAZ. Postweld metallographic examinations of the HAZ, combined with a conduction-based thermal model of the weld, were correlated with the SRXRD results. Finally, analysis of the diffraction intensities of the hcp and bcc phases was performed on the SRXRD data to provide additional information about the microstructural conditions that may exist in the HAZ at temperature during welding. This work represents the first directin situ mapping of phase boundaries in fusion welds.

Influence of Shielding Gas Composition and Welding Parameters on the N-content and Corrosion Properties of Welds in N-alloyed Stainless Steel Grades

Abstract: TIG welding using different heat inputs, arc lengths and shielding gas nitrogen contents was performed. The aim was to evaluate the possibilities to avoid nitrogen losses on welding or even increase the weld metal nitrogen content and thereby improve the corrosion properties and, in the case of duplex grades, also to improve the phase balance. Three different nitrogen-alloyed duplex grades and one superaustenitic grade were investigated. The corrosion resistance in terms of CPT, Critical Pitting Temperatue, of the super duplex material was found to be strongly correlated to the nitrogen content of the weld metal. In the case of the superaustenitic weld metal, the increased nitrogen content was found to be associated with an increased pore formation, leading to a lower corrosion resistance and thereby masking the positive effect of the increased introgen content. In order to illuminate the nitrogen exchange reactions between the arc, weld pool, and shielding gas, stationary weld experiments were also performed. The results from these stationary trials indicated that the net weld pool nitrogen content could be qualitatively understood if the various fluxes involved in the nitrogen transport between the plasma arc, weld pool and weld pool-shielding gas were considered. At short times the weld pool was limited in area and the nitrogen content of the weld pool increased due to high nitrogen activity in the arc. At longer times the nitrogen escaped from the weld pool to the shielding gas. This flux became then the dominating factor due to the increased weld pool area exposed to the shielding gas. The situation then approached the equilibrium conditions that were expected from the gas nitrogen activity and weld pool alloy composition according to thermodynamic calculations using the Thermo-Calc database.

アルミクラッド鋼インサート抵抗溶接法の検討 鋼/アルミニウムの異材接合に関する研究(第1報)

Abstract: The dissimilar spot welding of aluminum and steel sheet with insert of aluminum clad steel sheet was investigated. The study was conducted considering the application to the fabrication of automobile body, which effective to decrease its weight. To clarify the properties of intermetallic compounds to be formed at the steel and aluminum bonding interface, the mechanical properties were measured using the balks of four kinds of intermetallic compound in Fe-Al binary system. The mechanical properties of spot welded joint of aluminum and steel sheet with or without insert of aluminum clad steel sheet were measured using cross tension test and the microstructure of welded joint by this process were observed.The intermetallic compounds of FeAl and Fe3Al had comparatively higher ductility and the Fe2Al5 and FeAl3 had high hardness and low ductility, so that the Fe2Al5 intermetallic compound were formed at spot welded zone of the aluminum and steel resulting in the deterioration of strength. The dissimilar metal spot welded joint by using insert of aluminum clad steel sheet had excellent tensile strength in cross tension test and fractured in the base metal of aluminum alloy. Two nuggets of aluminum to aluminum and steel to steel were obtained independently by this process. These two nuggets and clad interface by hot rolling contributed to keeping the joint strength. It was confirmed the dissimilar welded joint of aluminum and steel having the strength equal to that of similar welded of aluminum alloy were obtained using this process.

Mathematical models for control of weld bead penetration in the GMAW process

Abstract: This paper presents the effects of welding process parameters on weld bead penetration for the gas metal arc welding (GMAW) process. Welding process parameters included wire diameter, gas flow rate, welding speed, arc current and welding voltage. The experimental results have shown that weld bead penetration increased as wire diameter, arc current and welding voltage increased, whereas an increase in welding speed was found to decrease the weld bead penetration. However, the weld bead penetration is not affected significantly by gas flow rate changes. Mathematical equations for study of the relationship between welding process parameters and weld bead penetration have also been computed by employing a standard statistical package program, SAS.

Pulsed Nd:YAG Laser Cutting of Al/Li/SiC Metal Matrix Composites

Abstract: This paper presents the pulsed laser cutting behavior of an Al-Li/SiC metal matrix composite. SEM and EDX examinations were conducted to study the influences of laser cutting parameters on the quality of the machined surface. Through proper process control it was found possible to minimize the heat affected zone (HAZ) and to improve the quality of the machined surface. An empirical formula relating the width of the HAZ and the laser cutting parameters was proposed. Furthermore, a theoretical model has been successfully applied to predict the maximum depth-of-cut for the composite. Finally, the optimum condition for achieving high cutting efficiency with minimum material damage was recommended.

The Weld Cracking Susceptibility of High Hardness Armour Steel.

Abstract: : The work detailed in this paper was performed to determine the likelihood of cracking during and after welding of 10 mm thick, high hardness, armour steel plate in conditions of high restraint All welding was performed using the pulsed gas metal arc welding process in the flat position High restraint conditions were tested using the Y-groove test Welds were performed with ferritic, austenitic and duplex austenitic /ferritic electrodes Underbead cracking, a typical form of hydrogen induced cracking, was observed in the hardened region of the heat affected zone of ferritic welds where the heat input was 05 kJ/mm and the preheat was 750C or less No cracking was observed at this heat input when the preheat was raised to 1500C When the heat input was raised to 12 kJ/mm, no cracking was observed, even when preheat was not used Underbead cracking was not observed in either austenitic or duplex welds However, the duplex welds were found to be susceptible to weld metal solidification cracking when the heat input used was low, 05 kJ/mm These cracks did not occur when the heat input was raised to 12 kJ/mm

Stress corrosion crack repair by plasma arc welding underwater welding

Abstract: Stress corrosion cracking damage to stainless steels and nickel base superalloys is repaired by underwater plasma transferred arc welding which under conditions which reduce residual tensile stresses in the weld and adjacent portions of the repaired structure.

Effects of moisture contamination and welding parameters on diffusible hydrogen

Abstract: Two experiments were conducted on gas-shielded flux cored arc welding. The first one tested the effects of shielding gas moisture contamination and welding parameters on the diffusible hydrogen content. The second compared the hydrogen levels of various unused electrodes with the diffusible hydrogen they produced in the weld. An empirical equation has been developed that can predict the diffusible hydrogen in weld metal for gas-shielded flux cored arc welding. Estimating diffusible hydrogen is possible using measured welding parameters, shielding gas dew point, and total hydrogen of the consumable. The equation is suitable for small-diameter electrodes and welding parameter ranges commonly used for out-of-position welding.

TIG welding method and welding torch therefor

Abstract: A TIG welding method is usually carried out in a manner that a tungsten electrode is inserted into a weld groove portion of a member to be welded, an electric voltage is applied to a current conducting portion provided for the tungsten electrode while flowing a shield gas means to thereby generate an arc between the tungsten electrode and the member to be welded to form a molten pool of the member, a welding wire is inserted into the molten pool, and a welding torch is then operated to perform a welding process In the improvement of the TIG welding method, the shield gas means is composed of an inner shield gas (13) flowing from a periphery of the tungsten electrode (3) to a front end thereof inserted into the weld groove portion (2a) of the member (1a) to be welded and an outer shield gas (14) flowing towards the weld groove angle from an outside of the inner shield gas (13) to prevent the molten pool from being oxidized and to prevent oxygen in air from being involved The TIG welding torch for carrying out the method is specifically provided with the inner and outer shield gas flow means, and further provided with a central shield gas flow means

Inertia-friction welding of SiC-reinforced 8009 aluminium

Abstract: Inertia-drive friction welding (IFRW) of an 8009 Al alloy (Al-8.5 Fe-1.7 Si-1.3 V, wt%) reinforced with 11 volume per cent SiC particles (8009/SiC/11p) has been investigated. Inertia-drive friction welds were made with constant energy at two levels of axial force. The microstructures of the base material and the welds were characterized using optical and scanning electron microscopy, while the mechanical properties were evaluated using microhardness and tensile testing. Examination of weld sections revealed that the hot deformation experienced during welding produced a homogenized microstructure with a uniform distribution of SiC particles along the bond line. No evidence of a chemical reaction between the SiC and the matrix was found in any of the welds, but cracking of some of the larger SiC particles was observed in the base material as well as in the IFR welds. The average microhardness of the various heat-and-deformation affected zones (HDZs) of the welds did not vary greatly from that of the base material, and no weld induced weak regions were discerned. The room-temperature (RT) tensile strength of the IFR welds exceeded 90 per cent of the base material. The weld tensile specimens failed at the outer edge of the HDZ for all of the welds tested. The fracture surface of the 8009 matrix of tensile samples for both the base material and the welds exhibited a dimpled appearance indicating a ductile failure, while fracture through the SiC appeared to occur in a brittle fashion. IFRW has proven effective in joining 8009/SiC/11p with little loss in RT hardness and tensile properties.

A theoretical study on electrical and thermal response in resistance spot welding

Abstract: The effect of contact resistance including constriction and contamination resistance has been a major hurdle for the thermoelectrical analysis of the resistance spot welding process. In this paper, a simple model was suggested and used for calculating the electrical and thermal response of the resistance spot welding process to investigate the influence of contacting forces on the formation of weld nuggets. The electrode surface of the contact interface was assumed to be axisymmetric and its microasperities to have a trapezoidal cross-section. These microasperities were considered as the one-dimensional contact resistance elements in the finite element formulation. The contamination film was assumed to be a nonconducting oxide layer, which is very brittle, so that it is broken to some number of pieces when a contacting pressure is being applied. The crushed films were assumed to be distributed at regular intervals and to conserve their size and number during the welding process. The simulation results revealed that the proposed model can be successfully used to predict the effect of the contact resistance on the electrical and thermal response of the resistance spot welding process.

Method for joining two parts of different kinds by heterogeneous butt welding, and uses thereof

Abstract: An end portion of each of two parts (10, 11) is machined and the machined end portions of the parts (10, 11) are arranged in facing positions to form a welding bevel (13) extending in a longitudinal direction between the parts (10, 11), whereafter a filler metal is deposited into the welding bevel (13). The welding bevel is a narrow bevel with side walls at an aperture angle of no more than 5° relative to the longitudinal central plane of the bevel (13). A nickel alloy comprising 18-32 % of chromium is deposited into the welding bevel. The method is particularly suitable for joining a pressurised water nuclear reactor vessel tubing and an austenitic stainless steel primary circuit pipe.

Apparatus and method for laser welding the inner surface of a tube

Abstract: A laser welding apparatus and method are used to weld the inner surface of small diameter tubes such as nuclear heat exchanger tubes. A weld filler metal carried by a rotatable laser weld head is fed into the weld zone to produce deeply penetrating weldments of low profile. The apparatus and method can effectively be used to repair cracks in heat exchanger tubes to thereby provide extended service life.

Advanced consumable electrodes for gas metal arc (GMA) welding of high strength low alloy (HSLA) steels

Abstract: This invention relates to solid, bare, consumable wire electrodes for gas metal arc (GMA) welding of high strength low alloy (HSLA) steels. The electrodes require little or no preheat, interpass and post soak temperature controls. The invention also relates to the method of welding and weld deposits produced therefrom.

High speed rotating automatic arc welding device

Abstract: PROBLEM TO BE SOLVED: To provide a high speed rotating automatic arc welding device having suitability to the welding on-site at a high position and high welding efficiency in high welding quality. SOLUTION: This device is composed of rail 5 parallel fitted with a welding line 201 extended in the perpendicular direction in a work 200 with plural magnet devices 6, an automatic welder 10 vertically welding downward by the high speed rotating arc welding with a rotation welding torch 1 through an arc sensor while travelling on the rail 5, a welding condition setting panel of a welding control device having handles for setting the welding condition and an operational pendant for finely adjusting the welding condition at an operator side. Then, a semi-automatic welding torch 20 is inserted into a connecting metallic tool at the base end side of the rotation welding torch so as to be freely attached/detached and commonly supply a welding electric source, shield gas and welding wire.

Laser edge welding member and its welding method

Abstract: PROBLEM TO BE SOLVED: To enhance productivity by forming a weld zone in which plural superposed parts formed on the end face of a weld joint are connected and alternately crossed and thereby laser-welding the superposed part in one welding operation. SOLUTION: While a laser welding machine 9 is moved along a welding line, it is also moved in the width direction of a weld joint 4 in the manner of continuously and alternately crossing a first and a second superposed part 6, 7 formed on the end face of the weld joint 4. Then, a laser beam is emitted from the laser welding machine 9, heating the end face of the weld joint 4 to form a weld zone 8. Thus, the superposed part is surely welded, with the formation of welding defects effectively eliminated.

Friction welding of Al-Al, Al-steel, and steel-steel samples

Abstract: Friction welding of Al- Al, Al- steel, and steel- steel studs is compared. Transient heat generation and temperature rise during the welding process were modeled. Tensile tests and microhardness measurements across the weld zone were carried out. The metallurgical changes in the heat- affected zone were examined by SEM. Temperature rise at the interface plane was computed and related to weld properties. The affecting parameters on weld quality were identified by statistical analysis. Results show that interaction of weld parameters significantly affect yield, tensile, and breaking strength, and the heat- affected zone on the Al side is wider for Al-steel welds.

Preventing weld hot cracking by synchronous rolling during welding

Abstract: Based on the mechanical point of view of hot cracking in weldments, a new method, accomplished by synchronous rolling during welding (SRDW) along both sides of the weld at a suitable distance behind the welding arc, has been developed for preventing weld hot cracking. The theory behind this method was also examined. Three-dimensional simulative computations of displacement and strain fields produced by SRDW were carried out by means of the finite element method to reveal the mechanism of the new method and provide a theoretical basis for parameter choice. With a specially developed equipment for welding and synchronous rolling, experiments were performed to investigate the effectiveness and feasibility of this method in preventing weld hot cracking in high-strength aluminum alloy 2024-T4. Results show that weld hot cracking in 2024-Al alloy can be effectively prevented and the mechanical properties of welded joints can also be improved by the new method. It is an important new solution to weld hot cracking in welding of sheet metals.

Narrow gap laser beam welding method

Abstract: PROBLEM TO BE SOLVED: To accomplish a narrow gap of joining part by irradiating a filler wire through narrow gap width with supplying a filler wire and executing build up welding from an inner part toward an outer part. SOLUTION: For example, when a thick plate 1 is butt welded, a narrow gap width 7 of a part to be welded is set narrower. A filler wire 9 is inserted into a welding part in the gap 7a. The filler wire part 9 is irradiated with a laser beam from a torch 2 through a gap 7a and a weld metal 4 is formed. Further, while the filler wire 9 is supplied to an irradiating part, a layer is formed with moving the torch 2 in the vertical direction. By repeating this, a multi-layer welding is quickly executed while building up one by one layer. Thus, the gap width 7 is made smaller as a result, welding deformation is turned to smaller, good welding is made possible and cost is reduced as well.