Showing papers on "Weldability published in 2003"

Improved weldability diagram for pulsed laser welded austenitic stainless steels

Abstract: Pulsed Nd:YAG laser welds were produced on 23 different austenitic stainless steel alloys of known composition. The primary solidification mode (PSM) and solidification cracking susceptibility of individual welds on each alloy were identified and correlated with their compositions. Single phase austenite solidification occurred in alloys with Cr equivalent to Ni equivalent ratios (Creq/Nieq) below approximately 1.59 (Hammar and Svennson equivalency relations). Alloys having a Creq/Nieq value above approximately 1.69 exhibited single phase ferrite PSM, whereas alloys for which Creq/Nieq was between 1.59 and 1.69 displayed either single phase ferrite PSM or a dual PSM with grains of single phase austenite adjacent to grains of single phase ferrite. The results of the present work were combined with those of a previous study to construct an improved weldability diagram for pulsed Nd:YAG laser welding of austenitic stainless steels. Consistent with previous observations, alloys that solidified as prim...

Joint properties of friction stir welded AZ31B– H24 magnesium alloy

Abstract: The weldability of friction stir welded hot rolled AZ31B-H24 magnesium alloy sheet, 4 mm in thickness, was evaluated, varying welding parameters such as tool rotation speed and travel welding speed. Sound welding conditions depended mainly on sufficient heat input during the welding process. Insufficient heat input, which was generated in the case of higher travel speed and lower rotation speed, caused an inner void or lack of bonding in the stir zone. The microstructure of the weld zone was composed of five regions: base metal, heat affected zone, thermomechanically affected zone, stir zone I and stir zone II. Unlike the general feature of friction stir welded aluminium alloys, the grain size of the weld zone was larger than that of the base metal. Stir zones I and II were characterised by partial dynamic recrystallisation and full dynamic recrystallisation, respectively. The hardness of the weld zone was lower than that of the base metal owing to grain growth. A wider range of defect free weldin...

Examination of the effect of Sc on 2000 and 7000 series aluminium alloy castings: for improvements in fusion welding

Abstract: It has been reported that small additions of scandium (Sc) can improve the weldability and mechanical properties of some aluminium aerospace alloys that are normally considered to be ‘unweldable’. In order to determine the mechanisms by which these improvements occur, and more rapidly arrive at optimum Sc addition levels, small wedge-shaped castings have been used to simulate the cooling rates found in MIG/TIG welds. Using this technique, a range of Sc addition levels have been made to two typical Al-aerospace alloys, 2024 and 7475. It has been found that when the Sc level exceeds a critical concentration, small Al 3 Sc primary particles form in the melt and act as very efficient grain nucleants, resulting in simulated fusion zone grain sizes as fine as 15 μm. This exceptional level of grain refinement produced an unusual grain structure that exhibited no dendritic, or cellular, substructure and a large increase in strength and ductility of the castings. Sc also produced changes in the alloy's freezing paths, which cannot yet be fully explained, but led to the appearance of the W phase in the 2024 alloy and, in both alloys, an overall reduction in the amount of eutectic formed during solidification. When coupled with the high level of grain refinement, this behaviour could be used to explain the increased strength and ductility of the castings. In 2000 and 7000 series aluminium alloys, it is therefore, anticipated that optimised Sc bearing filler wires will significantly improve the mechanical properties of the weld metal, as well as reducing the tendency for solidification cracking.

Microstructural evolution and weldability of dissimilar welds between a super austenitic stainless steel and nickel-based alloys

Abstract: Microstructural evolution and solidification cracking susceptibility of dissimilar metal welds between AL-6XN super austenitic stainless steel and two nickel-based alloys, IN625 and IN622, were studied using a combination of electron microscopy, differential thermal analysis, and Varestraint testing techniques. Welds were prepared over the entire dilution range (where dilution was determined with respect to AL-6XN as the base metal). The effect of processing parameters and filler metal chemistry on the fusion zone composition, microstructure, and resultant weldability was investigated. Iron additions to the weld (which occur with increasing dilution) increased the segregation potential of Mo and Nb. This behavior was attributed to a reduction in the solubility of Mo and Nb in austenite with increasing iron additions. as inferred from available binary phase diagrams. Welds prepared with IN622 formed a single interdendritic a phase at the end of solidification, and the amount of this secondary phase was not sensitive to changes in dilution. The a phase formed at a relatively high temperature and led to a relatively narrow solidification temperature range for welds prepared with IN622. In contrast, welds prepared with IN625 exhibited NbC and Laves phases in the interdendritic regions, and the total amount of secondary phase decreased with increasing dilution. Solidification of welds prepared with IN625 terminated with formation of the Laves constituent at relatively low temperature and, thus the solidification temperature range of welds involving IN625 was relatively wide. The solidification cracking sensitivity of welds prepared with IN622 was relatively low and independent of weld metal dilution level, while the cracking susceptibility of welds produced with IN62,5 was relatively high and increased with decreasing dilution. The dilution/cracking relation is controlled by the solidification temperature range and amount of secondary phase that forms at the terminal stages of solidification. The good cracking resistance of welds prepared with IN622 is attributed to the small amount of secondary phase and narrow solidification temperature range. The relatively poor cracking resistance of welds prepared with IN625 is attributed to a wide solidification temperature range and increasing amount of secondary phase that forms with decreasing dilution.

Laser welding and surface treatment of a 22Cr-5Ni-3Mo duplex stainless steel

Abstract: A study on improved laser weldability of a type 22Cr–5Ni–3Mo (UNS S32205) duplex steel is presented. To counterbalance the excess of δ-ferrite formed in the as welded joint, samples were surface treated by using the same laser source adopted during welding. An analytical description of the thermal field generated during welding and surface treatment by a CO2 laser source was developed and allowed optimal process parameters to be stated for the experimental investigation. Experimental results demonstrated that both microstructure and elemental distribution between δ-ferrite and γ-austenite could be restored to values close to those of the solution treated parent metal. The capability of achieving a good structural control of the weld bead microstructure by an optimized selection of laser parameters for the post-weld surface treatment was thus demonstrated.

Optimization of mechanical properties of an HSLA-100 steel through control of heat treatment variables

Abstract: HSLA-100 steel is widely used in Navy vessels, where the requirement is a steel with good weldability possessing a high strength together with a high degree of low-temperature toughness property. However, an increase in strength is usually accompanied by a decrease in toughness. Hence there is a need for optimization of the properties. The present work attempts to optimize the mechanical properties of an HSLA-100 steel through control of heat treatment process parameters. Initially single factor experiments are carried out over a wide range of tempering time/temperature combinations to identify the heat treatment zone where the optimum combination of properties is likely to be obtained. Further experiments are done in this zone through statistical design of experiments. The present work involves quantification of properties by: (i) classical curve fitting technique with data obtained from single factor experiments; and (ii) forming regression equations from 2 2 factorial design of experiments. Subsequently maximization of low-temperature impact property has been done within the experimental region by Steepest Ascent method, and finally optimum combination of the properties of the present steel has been obtained by Grid Search technique with a constraint on yield strength. Transmission Electron Microscopy studies are made with a view to understanding and correlating the mechanical properties with the microstructures. # 2002 Elsevier Science B.V. All rights reserved.

Properties of Aluminum-coated Steels for Hot-forming

Abstract: Production of parts with high strength by means of hot-forming process has been receiving considerable attention lately. Application of aluminized steel with good hardenability for this process has been investigated*. Tensile strength over than 1,500MPa was obtained with steel containing around 0.2mass% C. Surface coated layer changed from Al-10% Si to Fe-Al(-Si) phases through the hot-forming proc- ess. The steel with Fe-Al(-Si) surface layer showed good paintability even without phosphatized treatment. After painting, they showed good corrosion resistance in JASO-CCT as galvanized steel did. The steel showed good spot weldability due to the stable surface layer at high temperature. (*license product within the frame of glob- al strategic alliance with Arcelor (USIBOR1500))

Review of the performance of high strength steels used offshore

Abstract: High strength steels (yield strength > 500MPa to typically 700MPa) are increasingly being used in offshore structural applications including production jack-ups with demanding requirements. They offer a number of advantages over conventional steels, particularly where weight is important. This review considers the types of steel used offshore, their mechanical properties, their weldability and their suitability for safe usage offshore in terms of fracture, fatigue, static strength, cathodic protection and hydrogen embrittlement performance. It also addresses the performance of high strength steels at high temperatures and at high strain rates and outlines the difficulties in working with the very limited published codes and standards discussing performance in the field. Current design restrictions such as limits on yield ratios, susceptibility to hydrogen cracking including the influence of sulphate reducing bacteria (SRBs) and the management of the behaviour of such steels in seawater undercathodic protection conditions are discussed. Makes recommendations to encourage the wider use of high strength steels in the future and identifies areas where further study is required. (author)

Effect of nitrogen addition on microstructure and fusion zone cracking in type 316L stainless steel weld metals

Abstract: Nitrogen is known to have a significant effect on cracking behaviour of austenitic stainless steel during welding, although reports on its effects have often been controversial. A study was therefore undertaken to examine the effect of nitrogen on the weldability of two type 316L weld metals. Weldability was assessed using the longitudinal moving torch Varestraint test. The brittleness temperature range during solidification was calculated from crack length data. Nitrogen was added through the shielding gas to 316L (base N-0.036%) and 316LN (base N-0.073%) to produce weld metal nitrogen contents in the range 0.04–0.19%. In the primary austenitic solidification mode, nitrogen addition had little effect when the P+S levels were relatively low (316LN with 0.031%P, 0.001%S) while cracking increased for higher impurity levels (316L with 0.035%P, 0.012%S). Nitrogen additions also produced significant coarsening of the primary solidification structure. The study indicates that weldability effects of nitrogen may be influenced by the impurity levels, particularly S. The cracking data showed good correlation with the WRC Cr eq /Ni eq ratio.

High-strength thin steel sheet superior in hydrogen embrittlement resistance, weldability, hole-expandability, and ductility and manufacturing method therefor

Abstract: PROBLEM TO BE SOLVED: To simultaneously improve hydrogen embrittlement resistance, weldability, hole-expandability, and ductility of a high-strength steel sheet having a tensile strength of 800 MPa or higher. SOLUTION: This steel sheet comprises, by mass%, 0.05-0.3% C, 0.01-3.0% Si, 0.01-4.0% Mn, 0.0001-0.020% P, 0.0001-0.020% S, 0.01-3.0% Al, 0.0001-0.01% N, and one or more elements of 0.001-5.5% Ni, 0.001-3.0% Cu, 0.001-5.0% Cr and 0.005-5% Mo, and the balance being iron with unavoidable impurities; has a microstructure comprising the main phase consisting of one or both of bainite and bainitic ferrite, the secondary phase consisting of austenite which occupies an area rate V γ of 3 to 30%, and the balance being ferrite and/or martensite; has a tensile strength TS of 800 MPa or higher; and satisfies the following expressions (1-1) and (1-2): 0≤0.8×{2Cu+20Mo+3Ni+Cr}-{0.1-3.5×10 7 ×(TS) -3.1 }-0.3V γ --- (1-1) and 0≤Si+Al+7.67C-1.78 --- (1-2). COPYRIGHT: (C)2005,JPO&NCIPI

Typical failures in pyrolysis coils for ethylene cracking

Abstract: Publisher Summary This chapter mentions that pyrolysis coils in ethylene cracking furnaces are exposed to very severe conditions, for instance, high temperatures up to 1150 °C, severe start/stop and de-coke cycles, oxidizing and nitriding flue gases at the outside, and carburizing atmospheres at the tube inside surface. Therefore, high-alloyed centrifugal cast Ni–Cr–Fe alloys with adequate high-temperature corrosion resistance, good high-temperature strength, and good machinability and weldability (even after years of service) are required. The chapter highlights the principal alloys for ethylene cracking furnaces. It focuses on the typical failures in pyrolysis coils for ethylene cracking. The dominant failure mechanisms for radiant tubes are: (a) the combined action of carburization and creep ductility exhaustion, and (b) brittle fracture during furnace trips. The first mechanism results in bulging, bending, and ovalization of the tubes. The second mechanism results in large, longitudinal cracks.

Effects of magnesium content on dual beam Nd : YAG laser welding of Al – Mg alloys

Abstract: The effects of Mg content on the weldability of aluminium alloy sheet using the dual-beam Nd:YAG laser welding process have been studied by making bead-on-plate welds on 1.6 mm thick AA 1100, AA 5754 (3.2 wt-%Mg) and AA 5182 (4.6 wt-%Mg) alloy sheets. Whereas all full-penetration laser welds made in 1100 aluminium were of excellent quality,many of the welds produced in the aluminium–magnesium alloys exhibited rough, spiky underbead surfaces with drop-through and undercut. A limited range of process variables was found, however, that allowed welds with acceptable weld bead quality to be produced in the 5754 and the 5182 alloy sheet. Goodwelds were only produced in these alloys if the lead/lag laser beam power ratio was ≥1. Weld penetration and the maximum welding speed allowing full penetration keyhole-mode welding were observed to increase with Mg content. This was attributed to the effect of Mg on the vapour pressure within the keyhole and the surface tension of the Al–Mg alloys. Significant occl...

Effect of dual torch technique on duplex stainless steel welds

Abstract: Duplex stainless steels are characterized by balanced ferrite/austenite microstructures and are well known for their superior corrosion resistance and higher strength compared with the common austenitic stainless steels. One major concern, however, is that welding might degrade the corrosion resistance by producing unbalanced phase content, detrimental precipitates, and possible embrittlement of the weldment. In this paper, a dual-torch arc welding technique (plasma torch followed by a gas tungsten arc (GTA) torch) was proposed. Effects of the dual-torch technique on the microstructural changes and corrosion properties were investigated. The preliminary study indicated that a correlation between the welding parameters and the microstructural changes and corrosion resistance existed. It was found that the corrosion rate increases with increasing torch pitch and/or decreasing GTA welding current. By adjusting the distance between the torches, modification of weld microstructure may be realized. Although further studies are required to fine-tune the technique, the present study demonstrated the potential of using dual torch technique to improve weldability of duplex stainless steels.

The effect of rejuvenation heat treatments on the repair weldability of wrought Alloy 718

Abstract: Extensive precipitation of needle- and plate-shaped δ-phase in the γ-nickel matrix of wrought Alloy 718 is the major microstructural change resulting from multiple weld repair/post weld heat treatment (PWHT) cycles. Isothermal heat treatments at 954 °C for times up to 100 h were used to simulate the multiple PWHTs in laboratory samples. Grain size did not change appreciably during these heat treatments owing to δ-phase pinning of the grain boundaries (GBs). The susceptibility of Alloy 718 to heat-affected-zone (HAZ) liquation cracking degraded as a result of these heat treatments. This degradation is due to the short time, high temperature GB liquation caused by the combined effects of δ-phase dissolution, boron carbide constitutional liquation, and GB segregation. A rejuvenation treatment (1010 °C/2 h) effectively restored the degraded weldability by removing the adverse influence of δ-phase through dissolution above the δ-phase solvus. This heat treatment also promoted a spontaneous grain refinement and increase in the fraction of special GBs owing to the elimination of δ-phase pinning of GBs. The combined effects of δ-phase, grain size and fraction of special GBs are discussed in the context of HAZ liquation cracking that occurs during repair welding of Alloy 718.

High yield ratio and high strength cold-rolled steel plate and high yield ratio and high strength galvanized steel plate excellent in weldability and ductility, and high yield ratio and high strength alloyed galvanized steel plate and its manufacturing method

Abstract: PROBLEM TO BE SOLVED: To provide a high yield ratio and high strength hot rolled steel plate and a high yield ratio and high strength galvanized steel plate, both having excellent weldability and ductility, and to provide a high yield ratio and high strength alloyed galvanized steel plate and its manufacturing method. SOLUTION: The high yield ratio and high strength hot rolled steel plate having excellent weldability and ductility is a steel containing, by mass%, over 0.030 to less than 0.10 of C, 0.35 to 0.80 of Si, 1.7 to 3.2 of Mn, 0.001 to 0.02 of P, 0.0001 to 0.006 of S, ≤0.060 of Al, 0.0001 to 0.0070 of N, 0.01 to 0.055 of Ti, 0.012 to 0.055 of Nb, 0.07 to 0.55 of Mo, 0.0005 to 0.0040 of B and the balance of iron and inevitable impurities, and the steel has the yield ratio of 0.68 or more and less than 0.92, ≥1.0 X-ray intensity ratio on a {110} plane in a layer at a depth corresponding to 1/8 thickness of the steel plate and parallel to the plate face, and ≥780 MPa highest tensile strength (TS). COPYRIGHT: (C)2005,JPO&NCIPI

High-strength steel excellent in low temperature toughness and toughness at weld heat-affected zone, method for producing the same, and method for producing high-strength steel pipe

Abstract: The present invention provides an ultra-high- strength steel pipe excellent in weldability on site and a method for producing the steel pipe by improving the reliability of the low temperature toughness of a steel to which elements to enhance hardenability are added for furthering high-strengthening and also improving toughness at a weld heat affected zone subjected to double or more layer welding and, in the method, the steel is made to consist of a structure composed of bainite and/or martensite by containing prescribed amounts of C, Si, Mn, P, S, Ni, Mo, Nb, Ti, Al and N, and, as occasion demands, one or more of B, V, Cu, Cr, Ca, REM and Mg, and regulating C, Si, Mn, Cr, Ni, Cu, V and Mo, those being elements to enhance hardenability, by a specific relational expression. The diameter of prior austenite grains may be regulated in a prescribed range. The method includes the steps of heating a casting to a temperature not lower than the Ac3 point, hot rolling it, and thereafter cooling the resulting hot-rolled steel plate at a prescribed cooling rate.

High temperature corrosion in molten salts

Abstract: Numerous commercial processes operate at temperatures exceeding 500 degrees Celsius. The materials used in high-temperature structures have design constraints which are in addition to those on materials used at, or near to, room temperature. These important additional constraints include time-dependent inelastic strain (creep), thermal stability of the microstructure and high-temperature corrosion. The addition of these constraints to those of low cost, strength, toughness, machinability, formability, weldability, and combinations of these, has led to the intensive development since the mid-20th century, of an extensive group of metallic materials: generally referred to as "high-temperature alloys". The purpose of the book is to provide chemical, metallurgical and materials scientists and engineers with up-to-date corrosion data pertinent to academic studies and industrial problems resulting from the effects of pure molten salt and ash/salt deposit environments. The book covers key aspects of corrosion reactions in molten deposits, and provides a wealth of engineering data to help in making a shortlist of candidate materials for high-temperature service under such conditions.

Weldability of 1.6 mm thick aluminium alloy 5182 sheet by single and dual beam Nd: YAG laser welding

Abstract: The weldability of 1.6 mm thick 5182 Al–Mg alloy sheet by the single- and dual-beam Nd:YAG laser welding processes has been examined. Bead-on-plate welds were made using total laser powers from 2.5 to 6 kW, dual-beam lead/lag laser beam power ratios ranging from 3:2 to 2:3 and travel speeds from 4 to 15 m min-1. The effects of focal position and shielding gas conditions on weld quality were also investigated. Whereas full penetration laser welds could be made using the 3 kW single-beam laser welder at speeds up to 15 m min-1, the underbead surface was always very rough with undercutting and numerous projections or spikes of solidified ejected metal. This 'spikey' underbead surface geometry was attributed to the effects of the high vapour pressure Mg in the alloy on the keyhole dynamics. The undesirable 'spikey' underbead geometry was unaffected by changes in focal position, shielding gas parameters or other single-beam welding process parameters. Most full penetration dual-beam laser welds exhibit...

Conductive sizing agent and its producing process for high-power thick-film circuit based on stainless steel substrate

Abstract: An electrically conductive slurry for the high-power thick-film circuit on stainless steel substrate is composed of the solid-phase component (composite Ag-Pd powder and microcrystal glass powder) and the organic adhesive in Wt ratio of (70-90):(10-30). Its preparing process includes such steps as preparing microcrystal glass powder, preparing composite Ag-Pd powder, preparing organic adhesive, proportional mixing, stirring and rolling. Its advantages are high weldability and high compatibility.

Laser weldability of high-strength steel sheets in fabrication of tailor welded blanks

Abstract: Tailor welded blanks (TWBs) – pressing blanks arranged to combine, by welding, multiple steel sheets of different thicknesses and properties, and which may or may not have been surface-treated – are now extensively used in the automotive industry for fabrication of car body panels. TWBs were initially used at mass production level in Germany in the early 1980s and have since seen rapidly increasing engineering applications worldwide.1, 2 TWBs were originally viewed as a way of boosting material yields through reuse of pressed-off edge material as well as of cutting manufacturing costs by reducing the number of component spot welds, number of welding operations, and number of pressing dies through integral forming of multiple pressings after pre-welding of blanks from conventional spot welding production.

High titanium/zirconium filler wire for aluminum alloys and method of welding

Abstract: A weld filler wire chemistry has been developed for fusion welding 2195 aluminum-lithium. The weld filler wire chemistry is an aluminum-copper based alloy containing high additions of titanium and zirconium. The additions of titanium and zirconium reduce the crack susceptibility of aluminum alloy welds while producing good weld mechanical properties. The reduced weld crack susceptibility enhances the repair weldability, including when planishing is required.

High strength hot rolled steel strip with excellent low-temperature toughness and weldability for resistance welded pipe, and its manufacturing method

Abstract: PROBLEM TO BE SOLVED: To inexpensively provide a hot rolled steel strip having excellent low-temperature toughness and weldability and suitably used as a stock for resistance welded pipe without construction of a new manufacturing line and cost increase. SOLUTION: The high strength hot rolled steel strip with excellent low-temperature toughness and weldability for resistance welded pipe has a composition in which, in particular, one or more selected from ≤0.5% Cu, ≤0.5% Ni and ≤0.5% Mo are contained in low carbon steel within the range satisfying that the value of Pcm represented by Pcm=[%C]+[%Si]/30+([%Mn]+[%Cu])/20+[%Ni]/60+[%Mo]/7+[%V]/10 is ≤0.17 and the balance consists of Fe and inevitable impurities. Further, bainitic ferrite as a main phase comprises ≥95 vol.% of the whole structure. COPYRIGHT: (C)2005,JPO&NCIPI

Development of new high strength Al – Sc filler wires for fusion welding 7000 series aluminium aerospace alloys

Abstract: It has been reported that the transition metal scandium (Sc) can improve the weldability and mechanical properties of aluminium aerospace alloys that are normally considered to be 'unweldable'. However, little is currently known about the mechanisms by which Sc leads to such improvements. Here, the effect of the Sc concentration in the fusion zone of metal inert gas (MIG) welds in a typical 7000 series Al aerospace alloy has been investigated in detail. It was found that at a critical Sc level (~ 0.4 wt-%) a dramatic level of grain refinement occurs, leading to a highly uniform, ultrafine (~ 10 μ m) grain structure across the entire the fusion zone. Grain refinement was accompanied by an increase in the concentration of solute that was retained in solid solution after solidification, which led to a reduction in the volume fraction of eutectic per unit grain boundary area, and a significant age hardening response in the fusion zone. The tensile properties of single pass MIG welds, produced with an ...

High strength galvanized steel sheet having excellent hydrogen embrittlement resistance, weldability and hole expansibility, and its production method

Abstract: PROBLEM TO BE SOLVED: To provide a high strength galvanized steel sheet in which the weldability and hole expansibility of a high strength steel sheet having a tensile strength of ≥900 MPa are simultaneously improved, and to provide its production method. SOLUTION: The high strength galvanized steel sheet having excellent hydrogen embrittlement resistance, weldability and hole expansibility has a composition comprising, by mass, ≤0.25% C, ≤2.0% Si, ≤4.0% Mn, ≤0.05% P, ≤0.05% S, ≤3.0% Al and ≤0.01% N, and comprising one or more kinds of metals selected from ≤5.5% Ni, ≤3.0% Cu, ≤5.0% Cr, ≤5% Mo and ≤1.0% Nb, and the balance iron with inevitable impurities, has a structure comprising bainite and/or martensite of ≥70% in total by area and 0, inequality (1-2): 0≤0.8×{2Cu+20Mo+3Ni+Cr}-{0.1-3.5×10 7× (TS) -3.1 }-0.3Vγ, and inequality (1-3): 0>Si+Al+2-(Mn+Ni+1.5Mo). COPYRIGHT: (C)2005,JPO&NCIPI

Factors affecting flash weldability in high strength steel – a study on toughness improvement of flash welded joints in high strength steel

Abstract: (2004). Factors affecting flash weldability in high strength steel – a study on toughness improvement of flash welded joints in high strength steel. Welding International: Vol. 18, No. 6, pp. 436-443.