Showing papers on "Weldability published in 1998"

Iron aluminides: present status and future prospects

Abstract: This paper constitutes a broad survey of the physical, mechanical and corrosion properties of Fe3Al alloys, as well as a review of principal processing methods. This class of alloys, once thought to be inherently brittle, is shown to possess moderate ductility, provided that mechanical testing is carried out in an inert environment. Methods to improve mechanical properties by alloying and microstructural control are described. The influence of alloying elements on corrosion and stress corrosion resistance and weldability also is reviewed.

Improving the weldability and service performance of nickel-and iron-based superalloys by grain boundary engineering

Abstract: The principal limitation of today’s Ni- and Fe-based superalloys continues to be their susceptibility to intergranular degradation arising from creep, hot corrosion, and fatigue. Many precipitation-strengthened superalloys are also difficult to weld, owing to the formation of heat-affected zone (HAZ) cracks during postweld heat treatments (PWHTs). The present work highlights significant improvements in high-temperature intergranular degradation susceptibility and weldability arising from increasing the relative proportion of crystallographically “special” low-Σ CSL grain boundaries in the microstructure. Susceptibility to intergranular degradation phenomena is reduced by between 30 and 90 pct and is accompanied by decreases in the extent and length of PWHT cracking of up to 50-fold, with virtually no compromise in mechanical (tensile) properties upon which the functionality of these specialty materials depends. Collectively, the data presented suggest that “engineering” the crystallographic structure of grain boundaries offers the possibility to extend superalloy lifetimes and reliability, while minimizing the need for specialized welding techniques which can negatively impact manufacturing costs and throughput.

HSLA-100 steels: Influence of aging heat treatment on microstructure and properties

Abstract: The structural steels used in critical construction applications have traditionally been heat-treated low-alloy steels. These normalized and/or quenched and tempered steels derive strength from their carbon contents. Carbon is a very efficient and cost-effective element for increasing strength in ferrite-pearlite or tempered martensitic structures, but it is associated with poor notch toughness. Furthermore, it is well known that both the overall weldability and weldment toughness are inversely related to the carbon equivalent values, especially at high carbon contents. The stringent control needed for the welding of these traditional steels is one of the major causes of high fabrication costs. In order to reduce fabrication cost while simultaneously improving the quality of structural steels, a new family of high-strength low-alloy steels with copper additions (HSLA-100) has been developed. The alloy design philosophy of the new steels includes a reduction in the carbon content, which improves toughness and weldability.

CO{sub 2} laser beam welding of magnesium-based alloys

Abstract: Magnesium has gained increased attention in recent years as a structural metal--especially in the automotive industry--necessitating the development of welding techniques qualified for this new application. Lasers are known to be an excellent tool for joining metals. This paper presents results of recent investigations on the weldability of several cast and wrought magnesium-based alloys. Plates with a thickness of 2.5--8 mm were butt joint welded with and without filler metal using a 2.5-kW CO{sub 2} laser. The investigations showed that magnesium alloys can be easily laser welded in similar and dissimilar joints. The beam characteristics of the laser leads to small welds and a deep penetration depth. Crackfree welds exhibiting low porosity and good surface finish can be achieved with appropriate process parameters. Generally, the laser welding leads to either no change or a small increase in hardness in the fusion zone (FZ) and in the heat-affected zone (HAZ) relative to the base metal. Less promising results were obtained for the cast alloy QE22, in which cracking in the age-hardened condition and a significant decrease in hardness occurred. Laser welded die cast alloys showed an extremely high level of porosity in the weld.

Superalloys with improved oxidation resistance and weldability

Abstract: Improved Ni, Fe and Co based superalloys having excellent oxidation resistance and weldability. The superalloys are obtained by at least partially replacing the Ni in conventional superalloys with Pd. The alloys may also contain strengtheners and modifiers such as Co, W, Mo, V, Ti, Re, Ta, Nb, C, B, Zr, Y, and Hf. The superalloy has good strength, improved weldability and excellent oxidation resistance suitable for use in many aerospace and power generation turbine applications. A preferred embodiment comprises (in wt %) 1-9% (Al+Ti), 0-0.01% B, 0-0.15% C, 0-25% Co, 5-30% Cr, 0-10% Fe, 0-0.009% (Hf+Y+Sc), 1-15% (Mo+W), 0-8% (Nb+Ta), 40-68% Ni, 4-32% Pd, 0-10% (Re+Rh), 0-5% V, and 0-0.015% Zr.

Metallurgical method for processing nickel- and iron-based superalloys

Abstract: A method is provided for improving the microstructure of nickel- and iron-based precipitation strengthened superalloys used in high temperature applications by increasing the frequency of "special", low-.SIGMA.CSL grain boundaries to levels in excess of 50 9'0. Processing entails applying specific thermomechanical processing sequences to precipitation hardenable alloys comprising a series of cold deformation and recrystallization-annealing steps performed within specific limits of deformation, temperature, and annealing time. Materials produced by this process exhibit significantly improved resistance to high temperature degradation (e.g. creep, hot corrosion, etc.), enhanced weldability, and high cycle fatigue resistance.

Gas shielded arc welding flux cored wire

Abstract: Realized is a welding wire containing flux used for a gas shielded arc welding of a direct current/positive polarity mode, with use of which a quantity of sputter generated is small, a good weldability is realized and a weld metal with an excellent toughness is obtained in all the welding positions under application of a welding current in the range of a low current to a medium current, or in a definite manner in the range of 50 to 300 A. The flux contains 0.7 to 3 wt % Al, 0.1 to 1.0 wt % Mg and 1.2 to 5 wt % BaF 2 , each content being a value in wt % to a total weight of the wire and the sum of a content of Al plus a content of Mg multiplied by 3 being in the range of 1.3 to 5 wt %, a filling ratio of the flux to the total weight of the wire is in the range of 5 to 30 wt %, a total Mn content in a steel sheath and the flux combined is in the range of 0.2 to 1.9 wt % and a total Si content in the steel sheath and the flux combined is in the range of 0.001 to 0.9 wt %.

Laser beam welding of AZ31B-H24 magnesium alloy

Abstract: The laser beam weldability of AZ31B magnesium alloy was examined with high power CW CO{sub 2} and pulsed Nd:YAG lasers. The low viscosity and surface tension of the melt pool make magnesium more difficult to weld than steel. Welding parameters necessary to obtain good welds were determined for both CW CO{sub 2} and pulsed Nd:YAG lasers. The weldability of the magnesium alloy was significantly better with the Nd:YAG laser. The cause of this improvement was attributed to the higher absorption of the Nd:YAG beam. A lower threshold beam irradiance was required for welding, and a more stable weldpool was obtained.

Deterioration of weldability of long-term aged HP heat-resistant cast steel containing Nb, Mo, and W

Abstract: Summary The purpose of this study is to clarify the mechanism of weld cracking in the HAZ of long-term aged HP heat-resistant cast steel containing Nb, Mo, and W during repair. The results obtained may be summarised as follows: The results obtained in butt welding cracking tests using as-cast specimens and aged specimens (aged for 247 Msec) suggest that ductility-dip cracking occurs in the HAZ of the aged specimens and that this cracking mainly propagates through the microconstituents precipitated at the dendrite grain boundaries. The results obtained in the elevated temperature high-speed tensile tests of aged specimens and as-cast specimens in the temperature range 673–1473 K suggest that the aged specimens sustain an especially heavy loss of ductility in the temperature range below 773 K. The results obtained in the elevated temperature high-speed tensile tests and small-sized U-groove restraint cracking tests at 773 K using aged specimens and specimens aged at 1323 K suggest that the hot ductility of ...

High strength cold rolled steel sheet and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide a high strength cold rolled steel sheet having >=780 MPa tensile strength and >=70 MPa amount of baking hardening and combining excellent stretch-flange formability, spot weldability, delayed fracture resistance, and impact resistance. SOLUTION: A steel stock, having a composition in which 1.5-3.5%, by weight, Mn and 0. 005-0.10% Nb are contained and further the amounts of C, Si, P, S, Al, and N are regulated to proper values, respectively, is heated to a temperature at which the amount of Nb unentered into solid solution becomes >=0.003%, finish rolled at 950 to 800 deg.C finish rolling delivery-side temperature, coiled at 700 to 400 deg.C coiling temperature, and cold rolled. The resultant steel sheet is annealed at >=800 deg.C annealing temperature, rapidly cooled continuously down to =15 deg.C/min cooling rate, and then cooled rapidly down to room temperature. By this procedure, a structure composed essentially of fine bainitic structure of <=2.5 μm average grain size is provided.

A study on transverse weld cracks in thick steel plate with the FCAW process

Abstract: The transverse crack in thick plate welding is discussed with respect to deposited metal. In recent years, many of the new steel developments such as thermo-mechanical controlled process (TMCP) have been intended to improve weldability. When TMCP steel is used to achieve high strength with lean composition, the weld metal is more likely to suffer hydrogen cracking than the heat-affected zone (HAZ) of the base steel. Weld metal hydrogen cracking is even more likely if alloying is necessary to match the strength and toughness of the base metal. This is primarily due to the more highly alloyed weld metal's increased susceptibility to hydrogen cracking (Ref. 1). One type of cold crack, referred to as a transverse crack, is caused by the complex interaction of the diffusible hydrogen supply, tensile residual stress and susceptible microstructure. This form of cracking generally is not encountered when welding plate sections less than 10 mm thick. However, when thicker sections (50 mm or more) are welded, welds are subjected to more rapid cooling accompanied by more severe cooling stresses (Ref. 2).

Effect of filler metal composition on weldability of Al-Li alloy 1441

Abstract: Hardness, tensile properties, and hot cracking susceptibility of Al–Li alloy 1441 were evaluated with respect to different filler alloys AA 2319, AA 4043, and AA 5356, as well as the parent alloys. The hardness in the as welded condition was 70–90 HV and improved by 20, 30, 40, and 40 HV after heat treatment with AA 4043, AA 5356, and AA 2319, and 1441 fillers respectively. Tensile strength showed similar trends as hardness in the as welded and heat treated conditions. The hot cracking tendency was the maximum for welds deposited with 1441 filler and the minimum for welds deposited with AA 5356 filler, both values being less than the cracking tendency for autogenous welds. Hot cracking tendency was correlated with grain size, segregation distance, and distribution of the low melting phases.

High pwder Nd-YAG laser welding of SiC particle reinforced aluminium alloy 2124

Abstract: The effects of different Nd-YAG laser output waveforms on the weldability of a SiC particle reinforced aluminium alloy 2124 have been studied. The results show that although the square waveform can produce the greatest depth-of-penetration among the three different waveforms studied, i.e. continuous wave, sine wave and square wave, a high level of porosity was observed in the weld. Alternatively, porosity free welds with a reasonable depth-of-penetration can be obtained by using a sine waveform operated at high peak powers. However, the results also show that it would be difficult to stop theformation of aluminium carbides entirely in the fusion zone simply by varying the laser output parameters and the waveform. In order to stop the, formation of carbides, a new laser joining technique has been developed. This involved brush plating of nickel on the joining surfaces before laser welding. The results of the corrosion tests of the weld zone show that welding with a nickel coating would result in a ...

CO2 laser weldability of aluminium alloys (Report 1): Effect of welding conditions on melting characteristics

Abstract: Summary A series of systematic studies was undertaken to clarify the effect of CO2 laser welding conditions on melting characteristics, porosity formation, cracking susceptibility, hardness profiles, macro- and micro-distribution of Mg, and tensile properties of aluminium alloys. Bead-on-plate welding was performed on different commercially available alloys such as A5052, 5083, 5182, 6061 and 7N01 with a CO2 laser under various conditions of laser power, welding speed and defocused distance. In this paper, the influence of various welding conditions on melting characteristics was investigated from a fundamental viewpoint. In particular, laser beam modes and pressure distribution under various gas flow rates were measured, and it was consequently demonstrated that melting behaviour was greatly affected by the laser mode in the welding direction and the gas flow rate or pressure. Also the effect of Ar/He gas ratio on melting was investigated, and it was revealed that the use of Ar was beneficial to weld mor...

CO2 laser weldability of aluminium alloys (2nd report) : Defect formation conditions and causes

Abstract: Summary This paper describes the results of a systematic study to clarify the effects of CO2 laser welding conditions on porosity formation in commercial A5052, A5083, A5182, A6061, and A7N01 aluminium alloys. The causes and mechanism of porosity are examined through observations and evaluations of weld beads based on radiographic inspection and analysis of the gas content in pores by Q-mass spectroscopy in a vacuum, and on the amount of hydrogen in base and weld metals. The effects of the welding conditions on the high-temperature (solidification) cracking susceptibility of aluminium alloys are also investigated. The results show that porosity is reduced under the following conditions: a fairly long preflow time of argon shielding gas; polishing of the plate surface to decrease or remove sources of hydrogen and oxygen; a lower welding speed to help gas bubbles float to the surface or a higher welding speed to produce smaller pores; defocusing conditions of moderate power densities; use of nitrogen or hel...

Aluminum alloy sheet for spot welding

Abstract: An aluminum alloy sheet for automotive use is provided which comprises a starting aluminum alloy sheet which has an alloy composition containing from 2 to 6 % by weight of Mg, 0.15 to 1.0 % by weight of Fe and from 0.03 to 2.0 % by weight of Mn, and a surface layer disposed over one surface of the starting alloy sheet to be pressed against electrodes for use in welding, the surface layer containing a particulate intermetallic compound which has a particle diameter of 0.5 µm or more and a density of 4,000 pieces of particles per one mm2 or more. The product alloy sheet ensures least deformation of an electrode and stable weldability by means of continuous resistance spot welding.

Cold-rolled steel sheet suitable for high-density energy beam welding and its production

Abstract: PROBLEM TO BE SOLVED: To improve the weldability and welded formability by hot-rolling, cold-rolling and then annealing a raw steel material contg. specified amts. of C, Mn, S, N, Nb, Ti and V and having specified average crystal grain diameter and area ratio under specified conditions to impart a specified elongation. SOLUTION: A raw steel material contg. 0.001-0.20% C, 0.05-3.5% Mn, ≤0.02% S, ≤0.02% N, at least one kind among 0.005-0.20% Nb, 0.005-0.30% Ti and 0.005-0.20% V and the balance Fe with inevitable impurities and having a parent phase of ≤10 μm average crystal grain diameter or further a second phase of ≤20% area ratio is hot-rolled at a finishing temp. of ≥800°C, then cold-rolled, annealed at 750-850°C, hence recrystallized and cooled at a rate of 5-70°C sec to obtain a cold-rolled sheet having ≥10% uniform elongation and ≥5% local elongation. COPYRIGHT: (C)1999,JPO

Development trends in HSLA steels for welded constructions

Abstract: Costs and time savings in the fabrication of constructions by using steel grades with improved weldability and higher strength lead to an increased realisation of steel structures. But the higher strength can only be used, provided the construction is safe, by avoiding any brittle fracture as well as the propagation of existing flaws by ductile fracture. Besides a high cleanliness of the steel, a low carbon content and the maximisation of grain refinement as strengthening mechanisms are the fundamentals of modem HSLA steel production. As result of the thermomechanical processing of microalloyed steels, high strength levels with a rather low carbon content can be produced. Actually a chemical composition with less than the 0.09% C threshold value is aimed for, in order to avoid the peritectic reaction during solidification, which is responsible for microsegregations and thus a deterioration of the heat affected zone toughness. A finer effective grain size than typical for thermomechanically rolled steels with a ferritic-pearlitic microstructure is achieved with microstructures of acicular bainite or martensite. The alloy design of such steels, which can guarantee yield strength levels of 690 MPa and more, asks for an overall higher alloy content or a faster cooling rate or combinations of both. In any case, austenite processing before transformation adds to the refinement of these microstructures. The industrial verification relies on interrupted accelerated cooling or direct quenching after thermomechanical rolling. Furthermore, the toughness in the heat affected zone is improved with a microstructure of low carbon acicular bainite.

Battery terminal connecting plate

Abstract: PROBLEM TO BE SOLVED: To improve weldability to a battery and reduce electric resistance by composing a battery terminal connecting plate from welded parts each having a single material structure of a nickel material and a conductive part having a multiple material laminated structure of a nickel material and a copper material or aluminum material. SOLUTION: A metal laminated sheet 2 for stamping a terminal connecting plate 1 is formed by pressure-welding a copper material plate 4 to the surface of a nickel material plate 3 such that its end parts are excluded, and the terminal connecting plate 1 is provided by means of stamping from the metal laminated sheet 2. The terminal connecting plate 1 comprises welded parts 1a each having a single material structure of the nickel material and a conductive part 1b having a multiple material laminated structure of the nickel material and the copper material, and a slit 5 is formed in each of the welded parts 1a. The terminal connecting plate 1 is used by being welded to an electrode terminal part of a battery and provided with the conductive part 1b composed by laminating the metal material having lower resistance than that of the nickel material, so that its output loss at the connecting plate part is reduced. COPYRIGHT: (C)2000,JPO

The vibration welding of poly(phenylene oxide)/poly(phenylene sulfide) blends

Abstract: The weldability of three blends of poly(phenylene oxide) and poly(phenylene sulfide), each with a different level or type of impact modifier, is assessed through 120 and 240 Hz vibration welds. The type of impact modifier is shown to have a large effect on the strength and ductility of welds. Weld strength in these blends is shown to be sensitive to the weld frequency; higher weld strengths are attained at the higher weld frequency. In these three blends, maximum relative weld strengths of about 70%, 85%, and 87% have been demonstrated at a weld frequency of 240 Hz. The highest weld strength in each of these three blends is achieved at different weld pressures.

Steel sheet for shipbuilding excellent in laser weldability

Abstract: PROBLEM TO BE SOLVED: To provide a steel sheet for shipbuilding in which the generation of blowholes and porosities which are the representative defects in laser welding and excellent in laser weldability in the case filler wire is not used in particular. SOLUTION: This steel sheet has a compsn. contg., by weight, 0.05 to 0.13% C, 0.1 to 0.5% Si, 0.5 to 1.7% Mn, <=0.02% P, <=0.01% S, 0.002 to 0.05% O, 0.005 to 0.1% Al and <=0.008% N, also satisfying the relationship of 0%+0.5×C%<=0.09%, and the balance Fe with inevitable impurities.