Showing papers on "Weldability published in 2001"

The laser welding technique applied to the non precious dental alloys procedure and results.

Abstract: Aim The laser welding technique was chosen for its versatility in the repair of dental metal prosthesis. The aim of this research is to assess the accuracy, quality and reproducibility of this technique as applied to Ni-Cr-Mo and Cr-Co-Mo alloys often used to make prosthesis Method The alloy's ability to weld was evaluated with a pulsed Nd-Yag Laser equipment. In order to evaluate the joining, various cast wires with different diameters were used. The efficiency of the joining was measured with tensile tests. In order to understand this difference, metallographic examinations and X-Ray microprobe analysis were performed through the welded area and compared with the cast part. Results It was found that a very slight change in the chemistry of the Ni-Cr alloys had a strong influence on the quality of the joining. The Co-Cr alloy presented an excellent weldability. A very important change in the microstructure due to the effect of the laser was pointed out in the welding zone, increasing its micro-hardness. Conclusion The higher level of carbon and boron in one of the two Ni-Cr was found to be responsible for its poor welding ability. However for the others, the maximum depth of welding was found to be around 2mm which is one of the usual thicknesses of the components which have to be repaired.

Considerations for the weldability of types 304L and 316L stainless steel

Abstract: The susceptibility of austenitic stainless steels to the formation of two distinct weld defects, solidification cracking and lack of penetration, is related to the chemical composition of the base and filler material. The propensity for cracking is determined primarily by the solidification mode and the amount of residual tramp elements such as phosphorous and sulfur. High sulfur levels can lead to weld centerline cracking and heat affected zone (HAZ) cracking while very low sulfur levels (less than ∼50 ppm) in types 304L and 316L are associated with lack of penetration weld defects and a distinct loss in puddle control during fusion welding. A calculated Creq to Nieq ratio of 1.52 to 1.9 is recommended to control the primary mode of solidification and prevent solidification cracks in type 304L while the Creq/Nieq ratio of 1.42 to 1.9 is recommended for type 316L stainless steel. A lower limit of 50 ppm sulfur is recommended to avoid possible lack of penetration. These ranges should be validated by welding trials for specific weld processes and applications.

Microwave welding of thermoplastics

Abstract: The aim of this work was to develop a new and versatile method for welding thermoplastics using microwave energy. A multimode cavity applicator was developed including features designed to deliver an even energy density and to apply weld pressure. A review of possible microwave susceptible implant materials was undertaken and results of welding trials using several candidate materials showed that this is a feasible welding technique.

Physical Metallurgy of Steel Weldability

Abstract: The concept of hardenability used in the welding field differs from that used in the heat treatment. It represents the hardened depth after quenching in the heat treatment while it is related with the welding condition for fully hardened heat-affected-zone (HAZ) in the welding. The effect of steel chemical composition on hardenability is expressed by a multiplying factor for the former and by carbon equivalency for the latter. The metallurgical relation between these two factors can be clarified by a heat conduction analysis of a quenched round bar. Steel weldability means susceptibility to hydrogen-assisted cold cracking which mostly occurs in the welding of high strength steels. Many carbon equivalents with different coefficients have been proposed to assess the cold cracking susceptibility which is affected greatly by the hardness at HAZ. Since the HAZ hardness is interactively determined by the carbon content and hardenability, carbon equivalency for assessing susceptibility to cold cracking must consider this interactive effect. Toward the international standardization of the guideline for the avoidance of cold cracking, the methods based on different carbon equivalency are discussed.

Duplex stainless steel

Abstract: The present invention relates to a duplex stainless steel alloy with austenite-ferrite structure, which in hot extruded and annealed finish shows, high strength, good corrosion resistance and good weldability, which is characterized in that the alloy contains in weight-% max 0.05 % C, 0-2.0 % Si, 0-3.0 % Mn, 25-35 % Cr, 4-10 % Ni, 2-6 % Mo, 0.3-0.6 % N, as well as Fe and normally occurring impurities and additions, whereby the content of ferrite is 30-70 %.

Weldability of friction stir welding of AZ91D magnesium alloy thixomolded sheet.

Abstract: Weldability of Friction Stir Welding (FSW) of AZ91D magnesium alloy thixomolded sheet with 2 mm in thickness was evaluated by changing joining parameters of tool rotating speed and specimen travel speed. Square butt joint with good quality was obtained at the optimum FSW conditions of 50 mm/min of travel speed with 1240 to 1750 rpm of tool rotating speed by using a tool with 12 mm of shoulder diameter, 3 mm of pin diameter and 2 mm of pin length. Higher travel speed or lower rotating speed made a lack of bonding in the joint. Stir zone in a central part of the joint consisted of very fine recrystallized structure with 2∼5 μm in mean grain size. Hardness of stir zone increased slightly with decreasing mean grain size. Transverse tensile test of FSW joint resulted in the fracture at base metal. The tensile strength of stir zone showed 330∼360 MPa, much higher than that of base metal, about 250 MPa.

Colored thermoplastic resin compositions for laser welding, specific neutral anthraquinone dyes as colorants therefor, and molded product therefrom

Abstract: Thermoplastic resin compositions suitable for laser welding are disclosed, which include a mixture of neutral anthraquinone dyes and at least one other red dye to absorb and transmit select regions of visible light and to enhance weldability.

High strength steel sheet having excellent weldability, hole expansibility and ductility and production method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a high strength steel sheet in which the weldability, hole expansibility and ductility of a high strength steel sheet having a tensile strength of ≥800 MPa are simultaneously improved, and to provide a production method therefor. SOLUTION: The high strength steel sheet having excellent weldability, hole expansibility, and ductility, and having a tensile strength of ≥800 MPa has a microstructure containing bainite or bainitic ferrite as the main phase of 50 to 97% by an area fraction, and containing austenite as a second phase of 3 to 50% in total by an area fraction. COPYRIGHT: (C)2003,JPO

Electropolishing of 316L stainless steel for anticorrosion passivation

Abstract: 316L stainless steel is deemed an indispensable material in the semiconductor industry. In many instances, the surface of the production equipment needs to be treated for low-corrosion passivation, good finish, weldability, and cleanliness. The process characteristics of electropolishing meet these requirements well. The current study investigates the effects of the major processing parameters on the anticorrosion performance and the surface roughness. The electrolyte with 10% water content and a ratio between H2SO4 and H3PO4 of 4 and 6 has been proven to be successful, showing no corrosion pitting points on the specimen surface. The electrolyte temperature of 85±10 °C and the electrical current density of 0.5 to 1.0 A/cm2 are found to be optimal. The processing time beyond 3 to 5 min produces no further improvement. The addition of 10% glycerin provides a very fine surface (maximum roughness of 0.05 µm), while the anticorrosion performance is deteriorated. The results obtained are useful for the manufacture of the semiconductor equipment.

Welding of ferritic and martensitic 11-14% Cr steels

Abstract: This paper reviews the development of 11-13%Cr ferritic and martensitic stainless steels,_from the low carbon ferritics, through the mature martensitic steels up to the recently developed "supermartensitics" (much of the information included in this review is taken from the proceedings of the first international conference on Supermartensitic Stainless Steels held in Brussels in May 1999). Although key aspects of the review are welding and weldability, these are so intimately connected with the basic metallurgy of this group of steels that a significant part of the document is devoted to a metallurgical overview. This deals with solidification behaviour and transformation control, not only in standard alloys, but also in the 12%Cr ferritics and the low carbon martensitics. In order to put the metallurgical overview into perspective, the 13%Cr steels have been classified in four groups, which provides an opportunity to bring together steels of similar composition and fields of application. Each group contains examples of both generic and proprietary steels (and in some cases steels still under development) and is supported by a commentary which provides basic data on mechanical properties, welding and weldability, structural integrity and corrosion resistance. Also included is a significant bibliography (over 90 references).

Impact of new rolling and cooling technologies on thermomechanically processed steels

Abstract: At the hot strip mill, two different important trends are being observed: the development of thinner hot strips for direct applications as a substitute for cold rolled and annealed sheets; and the production of strip of increased strength, for various applications, which requires an adequate balance of ductility, formability, weldability, fatigue resistance, toughness, and/or crash resistance. In these grades the absence of internal stresses is also often required. The development of new rolling and cooling technologies that allow the production at low cost of new grades with better reproducibility and consistency of the mechanical properties is reviewed.

High Strength Bainitic Steel Rails for Heavy Haul Railways with Superior Damage Resistance

Abstract: NKK has developed high strength bainitic steel rails with superior flaking resistance for heavy haul railways. In this paper, rolling contact fatigue and wear behavior in bainitic and pearlitic rail steels with various tensile strengths were studied. Emphasis was placed on examining the formation behavior of the WEL(White Etching Layer) in bainitic and pearlitic steels, and its effect on flaking resistance. Advantages of the newly developed high-strength bainitic steel with superior flaking resistance, good wear resistance and excellent weldability have been also discussed.

Galvanized high strength steel sheet having excellent weldability, hole expansibility and corrosion resistance and production method therefor

Abstract: PROBLEM TO BE SOLVED: To provide a galvanized high strength steel sheet which has a tensile strength of ≥800 MPa, and excellent weldability, hole expansibility and corrosion resistance, and to provide a production method therefor. SOLUTION: The steel sheet has a composition containing, by mass, 0.01 to 0.20% C, ≤1.5% Si, 0.01 to 3% Mn, 0.0010 to 0.1% P, 0.0010 to 0.05% S, and 0.005 to 4% Al, and further containing one or two kinds selected from 0.01 to 5.0% Mo and 0.001 to 1.0% Nb in the ranges so as to simultaneously satisfy the following inequalities (A) and (B), and the balance Fe with inevitable impurities, and has a microstructure containing bainite or bainitic ferrite by ≥70% in an area ratio, and has a tensile strength of ≥800 MPa: 3.0Nb+2.5Mo+Mn-5C 0.5 >0 (A), and Al+15.0Si 2 +1.5Si-1.8<0 (B). COPYRIGHT: (C)2003,JPO

Hot press formed product with high corrosion resistance

Abstract: PROBLEM TO BE SOLVED: To provide a hot press formed product which restrains occurrence of scales with high corrosion resistance and weldability. SOLUTION: This product is characterized in that an iron-zinc solid soluble phase exists in the plated layer on a steel surface, its thickness is 1 to 50 μm, and the total zinc quantity in the plated layer is 10 to 90 g/m .

The Behaviour of Structural Steels at Elevated Temperatures and the Design of Fire Resistant Steels

Abstract: This paper reviews the current understanding of the characteristics of structural steels at elevated temperatures typical of those experienced in a fire and the design of fire-resistant steels for building construction. Following a commercial view of the requirements and market for steels with enhanced properties at elevated temperatures, the microstructure/property relationships and the influence of these upon high temperature strength are discussed in detail. Steel composition and processing variables can be controlled to modify grain size, the presence of second phases and precipitation, ferrite/austenite transformation temperature, dislocation density and weldability. These are reviewed as well as the important issues concerning structural aspects that determine the fire resistance of steels. The microstructure and property requirements of fire resistant steels are outlined and the ways in which these may be achieved are discussed including those that have already been developed.

Comparison of Impact Property of Japanese and US Reference Heats of V-4CR-4TI After Gas-Tungsten-ARC WELDING

Abstract: Charpy impact tests of Japanese and US reference V-4Cr-4Ti alloys, NIFS-HEAT- 1 (180 wppm oxygen) and US832665 (310 wppm Oxygen), were examined after gas-tungsten-arc (GTA) welding in a purified argon atmosphere. To investigate the effects of further reduction of oxygen level in the fusion zone, filler wires made of HP (high-purity V-4Cr-4Ti, 36 wppm oxygen) were used as well as those made of the reference alloys. Charpy impact property of NIFS-HEAT-1 in as-GTA-welded condition was superior to that of US832665. Use of the high-purity filler wires improved the impact property further. Good correlation was obtained between ductile-brittle-transition temperature (DBTT) and the oxygen level in the fusion zone. Since oxygen contamination from the atmosphere is avoidable by controlling its impurity level, oxygen reduction in weld materials, such as plate and wire, is crucial to obtain good weldability. Only contamination element detected in this study was hydrogen. Contamination occurred not only in fusion zone but also in base metal. Degassing of hydrogen after the welding may improve the impact property further.

Electron Bean Weldability of Pure Magnesium and AZ31 Magnesium Alloy

Abstract: Pure magnesium and AZ31 magnesium alloy plates 4 mm in thickness were butt welded without addition of filler wire using a high voltage electron beam welding machine. Mechanical properties and microstructures of the welded joints were investigated. Regardless of the materials, the welded joints were almost free from welding defects and showed good bead appearance under appropriate welding conditions. The arcing phenomena tend to appear at low welding speed. Optimum beam current and welding speed were smaller than those for electron beam welded joints of aluminum alloys. Hardness in the fusion zone of the joints are nearly equal to those of the base metals. Microstructure on the fusion zone of pure magnesium joints was remarkably coarse, although the weld interface could not unambiguously detected. The fine crystal grains observed on the fusion zone of AZ31 alloy joints. Regardless of the welding conditions, both tensile strength and ductility of the joints show same value to those of the base metals, but the elongation of the joints are inferior to those of the base metals. From the tension test and impact test, pure magnesium joints fractured at the center of the fusion zone, but in case of AZ31 alloy joints, crack occurred at weld interface and it propagated through the fusion zone.

Microfocused X-ray transmission real-time observation of laser welding phenomena

Abstract: The laser welding process benefits from huge advantages such as automatisation, energy preservation, robotisation, systématisation etc; it invites maximum attention and is forecast to provide high quality, high precision, high flexibility and high speed joining for various industrial products and structures. However, depending upon the welding conditions, weld defects, such as porosity and hot cracking are likely to develop in the deep penetration laser weld metal zone. Consequently, in order to produce high quality laser welds it is necessary to understand the initiation mechanisms for welding phenomena and weld defects and to develop and establish preventive measures. In particular, it is essential to observe the keyhole behaviour during laser welding and the circumstances for the formation of bubbles and porosity in order to explicate the pore initiation mechanism and to establish preventive measures. Accordingly, the authors and others\" have developed the microfocused X-ray transmission system in order to explicate the pore formation mechanism during CO2 laser or YAG laser welding of various metallic materials; consequently, high speed real-time observation was made of the keyhole behaviour within the molten pool, of bubble formation and flow, and of the state of the pore formation during continuous or pulsed laser welding of stainless steel, aluminium alloy and galvanised sheet iron. In addition, the molten pool configuration and the liquid flow during laser welding were observed using molten type and non-molten type markers of a high density; the bubble surfacing behaviour and the flow position during welding were also defined. Furthermore, penetration welding, drag angle welding, pulse modulated welding, welding with nitrogen shielding gas and vacuum welding were carried out with the aim of achieving porosity reduction measures; X-ray transmission real-time observation was performed for the behaviour of bubbles and porosity reduction during laser welding; thus, the efficacy of the reduction measures and the reduction mechanisms were identified. These results of observation are also expected to facilitate information acquisition for the development of modelling and simulation of welding phenomena and of monitoring techniques during welding.

An investigation of the repair weldability of Waspaloy and alloy 718

Abstract: Nickel-base superalloys are extensively used for elevated temperature components o f the aircraft gas turbine engine such as disks, nozzle vanes, blades, shafts and casings owing to their excellent high temperature properties. Gas turbine engines are subject to frequent inspection, repair and replacement owing to the severe service conditions under which they operate. Welding repair o f turbine engine components plays an important role in aircraft maintenance and overhaul. Generally, post weld heat treatment!PWHT) is needed to restore the properties o f these components for the designed service performance. Engine components subject to multiple repairs over their lifetimes w ill also be exposed to multiple cycles o f PWHT. It has been observed that the weldability o f some superalloys degrade after an accumulation o f repair/PWHT cycles, making further repair difficult or impossible. Two popular Ni-base superalloys, Waspaloy and A lloy 718, were selected for this investigation. Time-efficient and effect-equivalent long term isothermal solution heat treatments were used to simulate the metallurgical “ damage" incurred by multiple weld repair/PWHT cycles. A GeelbleTM thermo-mechanical simulator was used to perform hot ductility testing to quantify the repair weldability in terms o f susceptibility to heataffected-zone(HAZ) liquation cracking. Hot ductility testing successfully quantified the degradation o f weldability in the two alloys subjected to simulated multiple repair/PWHT cycles. HAZ liquation was the mechanism for the short time high temperature grain boundary(GB) weakening leading to intergranular(IG) failure. Degradation o f Waspaloy was correlated with carbide constitutional liquation and GB liquation. Constitutional liquation o f MC-type carbides is responsible for the onset o f on-heating ductility drop. Penetration o f liquid, the liquation product o f MC carbides, into GBs initiates the GB liquation. The severity o f GB liquation depends on both carbide constitutional liquation and GB boundary segregation-related general and local liquation. The latter is mainly dependent on boron (B) segregation. The effect o f grain size and special grain boundaries was evaluated based on a GB engineering concept to explain the weldability performance o f Waspaloy after simulated multiple repair/PWHT cycles. The weldability degradation from 1079°C/40hr(equivalent 10 cycles) treatment is associated to the coarsened grain size and a lower fraction o f special GBs. The restored weldability by 1079°C/100hr (equivalent 25 cycles) is attributed to the increase o f the fraction o f special GBs, even though a coarse-grained microstructure existed. Based on this result, a short time rejuvenation heat treatment)RHT) was devised to increase fraction o f special GBs and was proved to be experimentally practical for improvement o f the weldability o f Waspaloy after multiple PWHT cycles. .■\lloy 718 was plagued by excessive precipitation o f needle-shaped and plate­ shaped Ô phase in the y-nickel matrix, which is the major metallurgical damage from simulated multiple repair/PWHT cycles (954°C/40hr-100hr, equivalent 20-50 cycles). Grain size did not increase during this exposure due to the pinning effect o f the Ô phase. The degradation o f weldability is owing to the short time high temperature GB weakening caused by the combined effects o f 6 phase dissolution-promoted liquation, boron carbide constitutional liquation, and grain boundary(GB) liquation. 6 phase dissolution-promoted liquation effects over a wide temperature range, which is responsible for the onset o f the on-heating ductility drop, severe GB liquation from N'DT to NST and associated intergranularfIG) degradation extended to the DRT. 5 dissolution results in Mb enrichment o f the GB, promoting the formation o f complex Brich. Nb-containing eutectics hence aggravating the GB liquation.

Chromate-free treated hot dip zinc - aluminum alloy plated steel sheet having excellent weldability and corrosion resistance

Abstract: PROBLEM TO BE SOLVED: To provide a chromate-free hot dip zinc - aluminum alloy plated steel sheet subjected to post-treatment which has excellent weldability and corrosion resistance. SOLUTION: A galvannealed layer having a composition containing, by mass, 1 to 10% Mg, 2 to 19% Al and 0.01 to 2% Si, and in which Mg and Al satisfy the inequality of Mg (mass%)+Al (mass%) as coating weight.