Showing papers on "Weldability published in 2004"

Review of resistance spot welding of steel sheets Part 1 Modelling and control of weld nugget formation

Abstract: Resistance spot welding is the principal method of welding sheet steel products. In practice, the manufacture of welds of acceptable quality depends on the definition of optimum welding parameters and the implementation of suitable controls to ensure constant weld quality over a long production run. The ability to make a weld is best defined by a weldability lobe outlining the available manufacturing tolerances between minimum and maximum limits. Both two- and three-dimensional weldability lobes exist defined in terms of weld time, welding current and electrode force. Production variables influencing weld growth are discussed, particularly the effect of electrode diameter. The importance of welding machine characteristics relative to weld growth is highlighted. In particular, the rigidity of the machine coupled with the weight and frictional effects developed in the electrode head assembly are shown to be important factors influencing weld growth. Also important are the electrical characteristics of the machine, including transformer configuration current waveform and current ‘off’ time in the nonconducting part of the waveform. A reliable control philosophy is an essential requirement of any inprocess feedback system if high quality spot welds are to be produced in high volume. Various model simulations indicate that changes, with time, in electrode/sheet and sheet/sheet interfacial resistances control weld nugget formation and growth. The relative contributions of these resistances are discussed. Heat generation and temperature distribution in the weldare determined by the current and force distribution across these interfaces. One-, two- and three-dimensional models have been developed to describe the temperature distribution in the weld zone and weld nugget growth. These models have limited application due to inadequate input data to describe the transient conditions appertaining in the weld zone. Current waveform, inductance effects, and friction/rigidity of the electrode head assembly, are not considered. Neural networks and fuzzy logic control have shown promise in classifying weld quality into predetermined groupings. The way forward is to adopt a multidisciplinary approach, taking into account the various interactions between the thermal, electrical, mechanical and metallurgical phenomena developed during the welding process. Models describing these phenomena should be interlinked to simulate heat generation and growth in the weld zone. The resulting model could be coupled with experimentally developed trends to optimise inputs to a neural network, the output of which is used, through a fuzzy logic controller, to take appropriate corrective action to ensure the required weld quality. It is stressed that any mathematical simulation or control system must take into account changes that occur at the welding electrodes as a consequence of electrode wear. The latter are discussed in Part 2 of this review.

Fracture behaviour of aluminium alloy 2219–T87 welded plates

Abstract: Aluminium alloy AA 2219 is used in aerospace applications because of its good weldability, stress corrosion resistance, and mechanical properties over a wide temperature range of + 250 to - 250 ° C. The elastic-plastic fracture toughness JIc has been measured on 7.4 mm thickness autogenous alternating current tungsten inert gas welded plates of 2219-T87 alloy in the as welded condition, using a single specimen technique. The present paper elucidates the variation of JIc across the weld joint. The toughness was evaluated at three different locations across the weld, namely, in the weld, fusion boundary, and heat affected zones, and compared with parent metal toughness. It was found that the fracture toughness across the weld was higher than the parent metal toughness. The fusion boundary had the lowest toughness among the three zones across the weld joint. The variation of toughness among the different zones is explained with reference to fractographic observations.

Process Adjustments to Improve Fracture Behaviour in Resistance Spot Welds of EHSS and UHSS

Abstract: In recent years new types of sheet steels, combining higher strength with better ductility have been developed. Some of these steels have shown limited weldability compared to mild steels. The hardness of the welds for these steels stretches from 380 HV for DP 600 to approximately 500 HV for TRIP (Transformation Induced Plasticity) and boron steels. Static peel tests of eight types of steels resulted in plug failures for the DP 600 steels, but some interfacial failures for higher strength steels. Generally, welds with a hardness exceeding 400–450 HV caused unstable fractures. To modify the hardness of the weld an in-process tempering of weld martensite was performed on a TRIP steel. Guidance to a proper tempering pulse was obtained through simulation of phase transformation and cooling of the weld. Welding experiments showed that the weld hardness could be reduced to approximately 350 HV, i.e. below the limit where interfacial failures start to occur.

Welding of High Nitrogen Steels

Abstract: In the present article, an attempt was made to review the weldability of high nitrogen steels. In the last few years, a lot of work has been put into a better understanding and processing of this class of steels. Through our metallurgical knowledge, it is obvious that the nitrogen content in the weld zone is the essential factor. It is a major task to identify all parameters influencing nitrogen content in the weld metal.

Explosive Welding of Aluminum to Aluminum: Analysis, Computations and Experiments

Abstract: 6061 T0 aluminum alloy was joined to 6061 T0 aluminum alloy by explosive welding. This is a process in which the controlled energy of a detonating explosive is used to create a metallic bond between two similar or dissimilar materials. The welding conditions were tailored to produce both wavy and straight interfaces. A three‐pronged study was used to establish the conditions for straight weld formation: (a) analytical calculation of the domain of weldability; (b) characterization of the explosive welding experiments carried out under different conditions, and (c) 2D finite differences simulation of these tests using the explicit Eulerian hydrocode Raven with a Johnson‐Cook constitutive equation for the Al alloy. The numerical simulation and the analytical calculations confirm the experimental results and explain the difficulties met for obtaining a continuous straight interface along the entire weld.

Effects of calcium carbonate, talc, mica, and glass‐fiber fillers on the ultrasonic weld strength of polypropylene

Abstract: The objective of this work was to study the differences in the ultrasonic weld strength of polypropylene compounds with different fillers. The fillers were calcium carbonate, talc, mica, and glass fibers. The welder parameters were varied to determine the optimum set. These welder parameters were the weld time, weld force, trigger force, and amplitude. The results indicated that the weld time had the greatest effect on the weld strength of each of the filled compounds. Unfilled polypropylene had the highest weld strength under the optimum welding conditions, which were used as the baseline welding conditions. For each given filler, the weld strength was reduced as the filler loading increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1986–1998, 2004

Analytical Study on Deformation and Strength in HAZ-Softened Welded Joints of Fine-Grained Steels

Abstract: A fine-grained steel has the same components and weldability as a mild steel, whereas a conventional high-strength steel has lower weldability due to its alloying elements. The occurrence of softening caused by coarsening in the heat-affected zone (HAZ) of welded parts of the fine-grained steels and mechanical design of welded parts including weld HAZ-softening becomes much important. Mechanical properties of the HAZ-softening joint are examined by considering the characteristics of the tensile strength under the theory of the strength of undermatched joints. The effects of the mechanical and geometrical heterogeneity on tensile strength of the HAZ-softened joint are studied by using the large-deformation finite-element analysis. The design of the HAZ-softened joint is possible considering welding conditions and tensile strength of the joint that mostly overreach the strength of the base metal. The deformation behaviour and the fracture characteristics in HAZ-softened joints under the consideration of the actual use are furthermore investigated.

Magnetic Pulse Welding Aluminium Tubes to Steel Bars

Abstract: Magnetic pulse welding (MPW) is a high-speed, solid-state welding process that is applicable to tube-to-tube or tube-to-bar configurations. Detailed information on how to adapt the process to applications for joining dissimilar materials is not available in published materials. The document discusses the MPW process development for welding Al tubes to steel bars. Welding trials were conducted to weld annealed 6061 Al tubes of 0.065-in. wall thickness to 1010 steel bars of a 1.875-in. nominal diameter. A 90-kJ machine was used in the work. This work indicates that Al tubes can be successfully welded to steel bars using MPW. It is found that the stand-off distance between the Al tube and the steel bar is a dominant factor for achieving a sound weld. Adding receding angles to the bars can promote MPW weldability.

High-power CO2 laser-MIG hybrid welding for increased gap tolerance. Hybrid weldability of thick steel plates with a square groove

Abstract: High power enhancement of laser processors has recently led to laser welding being used for the joining of thick steel plates. For example, the literature includes a study on the practical application of a 45 kW CO2 laser for the welding of thick steel plates,1 although few such applications have thus far been documented. The limited application of lasers to welding of thick steel plates is attributable to the narrow gap tolerance provided and the small laser beam diameter that leads to unacceptable welding defects, such as underfills, melt-through, and porosities.

Steel products for shipbuilding

Abstract: Product designs and properties of 6 steel products for shipbuilding are described. They are new TMCP (thermo-mechanical control process) steel plates, weldable with high heat input, for container ships and LP (longitudinal profile) plates, both contribute to the increase in productivity at shipyards through the large reduction of welding time, anti-corrosion steel plates for crude oil tankers NAC5 which contribute to high performance of ships from the viewpoint of corrosion, cladded steel plates for chemical tankers, anti-corrosion pipes, JFE-MARINE-COP, used in crude oil tankers for loading and unloading crude oil, and shapes for shipbuilding which are produced using TMCP to realize weldability as good as steel plates.

Effect of Grain Size on the Weldability of Cast Alloy 718

Abstract: Electron beam welding was conducted on cast alloy 718 with varying grain sizes obtained using Microcast (MX™) and conventional cast (CC) techniques. The average value per section of Total Crack Length (Av. TCL) was measured on each cross section and used to represent the material's weldability. It was found for the first time that the grain size had a reduced effect on the weldability of cast alloys, relative to that reported in the literature for wrought alloys; i.e., increased grain size in the range of 90–3000 microns resulted in improved weldability. This was determined to be related to the probability of welds intersecting grain boundaries and causing grain boundary microfissuring. The conclusion from the experimental analysis is corroborated by the use of a Weibull-type analysis to evaluate the probability of a weld microfissure occurring relative to the grain size. As grain size increases, the probability of the weld intersecting the grains is reduced, and thus, the likelihood of microfiss...

Hydrogen assisted stress-cracking behaviour of electron beam welded supermartensitic stainless steel weldments

Abstract: Supermartensitic stainless steel (SMSS) grades are gaining popularity as an alternate material to duplex and super duplex stainless steels for applications in oil and gas industries. The weldability of these steels, though reported to be better when compared to conventional martensitic stainless steels, so far has been addressed with duplex stainless steel electrodes/fillers. This work addresses the stress-cracking behaviour of weldments of a high-grade supermartensitic stainless steel (11% Cr, 6.5% Ni and 2% Mo) in the presence of hydrogen. Welds were produced with matching consumables, using electron beam welding (EBW) process. Weldments were subjected to slow strain rate tests in 0.1 M NaOH solution, with introduction of hydrogen into the specimens by means of potentiostatic cathodic polarisation at a potential of −1200 mV versus Ag/AgCl electrode. Reference tests were performed in air for comparison, and the results suggest that both the SMSS base material and the EB weld metal are susceptible to embrittlement under the conditions of hydrogen charging.

Comparison of preheat predictive methods

Abstract: Four methods of preheat temperature prediction were compared for structural steels, from a mild steel and a TS780 grade steel with carbon contents between 0.034% and 0.234% C. The BS method and the CEN method predict almost the same preheat temperatures except for the carbon-reduced steels. The prediction by the AWS hydrogen-control method and the CE T method are conservative for mild steels and C-Mn steels. All the methods predict the same preheat temperatures for the TS780MPa steel with 0.11% C. However, only the CEN method can properly predict necessary preheat temperatures for the Cu-precipitated steel grade TS780MPa. Necessary preheat temperatures for very low carbon line-pipe steel grade API X80 is preferably predicted by the AWS hydrogen-control method and CEN method. Significant discrepancy in the prediction by these methods solely stems from a difference of carbon equivalency employed. All the preheat predictive methods are intended for avoiding HAZ cold cracking. It is necessary to consider the likelihood of weld metal cold cracking in determining the necessary preheating temperature when welding high strength steels with improved weldability.

Ultrahigh strength welded joint and ultrahigh strength welded steel pipe excellent in cold cracking resistance of weld metal, and methods for producing the same

Abstract: The present invention, in a welded joint of steel sheets and a steel pipe body having a tensile strength of 800 MPa or more (over X100 in API Standards), provides: the welded joint of the steel sheets and the steel pipe produced by forming a steel sheet into a cylindrical shape and welding both the ends thereof, both excellent in cold cracking resistance; and methods for producing them. The present invention includes an ultrahigh strength welded joint and an ultrahigh strength welded steel pipe excellent in the cold cracking resistance of a weld metal, characterized in that the amount of non-diffusible hydrogen in the inner side weld metal is 0.01 ppm or more. It is preferable that the ratio of the non-diffusible hydrogen amount to the total hydrogen amount in said inner side weld metal is 0.5% or more. Further, it is preferable that Mo carbide is contained by not less than 1 piece/μm2 in said inner side weld metal. The present invention also includes a method for producing said welded joint and welded steel pipe, characterized by welding the butted portion from the inner side and thereafter welding it from the outer side so that the reheating temperature of the inner side weld metal may reach within the range from 500° C. to 700° C.

Preparation method of iron nickel alloy/copper composite wire material

Abstract: A composite FeNi alloy/Cu wire 4J50/Cu is made of the copper rod cored FeNI alloy ingot through vacuum high-temp treating, squeezing at 900-950 deg.C, cold drawing and heat treating. Its advantages are high electric and thermal conductivities, better weldability, and good sealing performance to glass and ceramics.

Influence of pre- and post-weld heating on weldability of modified 9Cr-1Mo(V-Nb) steel pipe under shielded metal arc and tungsten inert gas welding processes

Abstract: Welding of modified 9Cr–1Mo(V–Nb) steel pipes has been carried out via shielded metal arc (SMA) and tungsten inert gas (TIG) welding processes. The weld joints have been produced using different preheating temperatures, followed by post-weld heat treatment (PWHT) at various temperatures. The microstructures of the weld and of the heat affected zone (HAZ) of the weld joints have been studied under the optical microscope and correlated with the preheating and PWHT. The average hardness of the weld and different regions of the HAZ, and tensile properties of the weld joints have also been studied and correlated with the preheating and PWHT. The tensile properties of the SMA and TIG weld joints produced using preheating and PWHT at various temperatures are compared and correlated with their microstructures. It is noted that a comparatively high preheating temperature of the order of 573 K is beneficial, and PWHT is necessary to reduce the susceptibility to cold cracking of weld joints of the present s...

Welded joint and welding material

Abstract: PROBLEM TO BE SOLVED: To provide a welded joint and a welding material having excellent corrosion resistance in an environment where metal dusting is easy to be generated such as a heat exchange type hydrocarbon reforming device and a waste heat recovering device, and further having excellent high temperature strength and weldability. SOLUTION: In the welded joint having excellent metal dusting resistance, a base material and a weld zone both have a composition comprising, by mass, 0.01 to 0.45% C, 0.01 to 2% Si, 0.01 to 2% Mn, ≤0.03% P, ≤0.01% S, 15 to 35% Cr, 40 to 78% Ni, >2 to COPYRIGHT: (C)2006,JPO&NCIPI

Weldability Study of Resistance Spot Welds and Minimum Weld Button Size Methodology Development for DP Steel

Abstract: Weldability is one of the manufacturing concerns for the application of newly developed advanced high strength steels, which have tensile strengths above 440 MPa. The successful utilization of advanced high strength steels depends on not only the steel product development, but also car body and structure design consideration and optimization. The resistance spot weldabilities of five different material combinations, DP500EG/CRS to DP500EG/CRS, DP500EG to Mild EG, and Mild EG/CRS to Mild EG/CRS, were investigated in this study. An optimized welding schedule was established for each material combination. In addition, a methodology to determine the minimum button size was proposed to accommodate the existing commercial practice in the resistance spot welding specifications. A brief review with simple failure mode estimation formulas of standard tensile shear and cross tension tests was also introduced and discussed to aid AHSS applications.