Microcracking in multipass weld metal of alloy 690 Part 3 – Prevention of microcracking in reheated weld metal by addition of La to filler metal

Abstract

The effect of addition of La to a filler metal on microcracking (ductility dip cracking) in the multipass weld metal of alloy 690 was investigated with the aim of improving its microcracking susceptibility. The susceptibility to ductility dip cracking in the reheated weld metal could be greatly improved by adding 0·01–0·02 wt-%La to the weld metal. Conversely, excessive La addition to the weld metal led to liquation and solidification cracking in the weld metal. Hot ductility of the weld metal at the cracking temperature was greatly improved by adding 0·01–0·02 wt-%La to the weld metal, implying that the ductility dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of La. The liquation and solidification cracking resulting from excessive addition of La to the weld metal is attributed to the formation of liquefiable Ni–La intermetallic compound. A multipass welding test confirmed that microcracks in the multipass weldment were completely prevented by using a filler metal containing an addition of 0·01 wt-%La.     

Effect of strong carbide forming elements in hardfacing weld metal

To achieve high carbon hard-facing weld metals with both high hardness and crack resistance, strong carbide forming elements Ti, Nb and V were alloyed into the weld metals, and their effect on the formation of carbides and the matrix microstructure were studied. Electron Probe Microanalysis (EPMA), Energy Dispersive Spectroscopy(EDS) and Transmission Electron Microscopy (TEM) were adopted to investigate the microstructure, then thermodynamics of the formation of carbides was calculated and their effect on the matrix was further discussed. It is revealed that Nb, Ti and V influence strongly the distribution and existing state of carbon, inducing precipitation of carbides accompanying with the depletion of carbon in matrix. But when only V are alloyed as carbide forming element, the carbides are scarce and distributed along grain boundaries, and the hard-facing alloy is too hard, while the using of only Nb or Ti could not reinforce the weld metals effectively. The hard-facing alloy reinforced with Nb, V a     

Microstructural changes in weld metal during isothermal process. Study of reheat cracking in flux‐cored arc welding stainless steel weld metal (5th report)

The soiling of the slag, spatter and the fume, etc., which come into contact with the steel sheet surface with welding, is cleaned making use of steel sphere shot material of large particle diameter, high projection pressure with strong peening processing (below, called strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when the surface of a SM490A welded joint was cleaned with strong peening cleaning.

The following experimental results were obtained:

1. The fatigue limit of smooth base metal which received strong peening cleaning at about 320 MPa was remarkably high in comparison with smooth base metal at about 245 MPa.

2. The fatigue limit of a welded joint which received strong peening cleaning at about 300 MPa was remarkably high in comparison with a welded joint at about 170 MPa.

3. The strong peening cleaning was highly efficient and the cleaning state was satisfactory.

4. The cause of the remarkable rise of the fatigue limit (300 MPa) of the welded joint which received strong peening cleaning was because the fatigue limit (about 170 MPa, 57%) of the welded joint was improved (about 130 MPa, 43%) with peening cleaning. It was considered that improvement effects were: a rise (about 68 MPa, 23%) of hardness of the weld toe; relief (about 43 MPa, 14%) of stress concentration; increase (about 136 MPa, 45%) of compressive residual stress; and the decrease (about ? 96 MPa, ? 32%) by increase of surface roughness.

5. The fatigue strength of the hot galvanized welded joint decreased remarkably. This was thought to be due to the decrease (about HV40) of hardness of the surface, the decrease (about 188 MPa) of the compressive residual stress and the influence of many factors which accompanied hot galvanizing.

     

Thermal and metal transfer behaviours in pulsed current gas metal arc weld deposition of Al–Mg alloy

Abstract

The control of pulsed current gas metal arc (GMA) welding is highly critical owing to the simultaneous influence of the pulse parameters on thermal and metal transfer behaviours of the process. An analytical model has been developed to provide a theoretical understanding of the influence of pulse parameters on the behaviour of metal transfer and thermal characteristics in pulsed current GMA welding using Al–Mg filler wire. The variations in thermal and metal transfer behaviours with changes in pulse parameters have been satisfactorily analysed considering a summarised influence of pulse parameters defined by a dimensionless factor &phis; = (I _b/I _p)ft _b, proposed previously. A large number of process parameters have been considered, as a result of using four different GMA welding power sources. The hypothesis has been verified using some previously reported experimental results. The theoretical model may be useful in the control of pulse parameters to achieve desired behaviours of thermal and metal transfer under different conditions of weld fabrication, thereby facilitating more universal application of GMA welding.     

Effect of chemical metallurgical factors on contents of S and P in weld metal during SAW

ＥｆｆｅｃｔｏｆｃｈｅｍｉｃａｌｍｅｔａｌｌｕｒｇｉｃａｌｆａｃｔｏｒｓｏｎｃｏｎｔｅｎｔｓｏｆＳａｎｄＰｉｎｗｅｌｄｍｅｔａｌｄｕｒｉｎｇＳＡＷＸＵＥＳｏｎｇｂａｉ；ＹＥＤｏｎｇｌｉｎ；ＨＡＯＨｅｍｉｎｇａｎｄＬＩＵＷｅｉ（ＨａｒｂｉｎＲｅｓｅａｒ...     

Thermodynamic analysis of inclusion in weld

Ｔｈｅｒｍｏｄｙｎａｍｉｃａｎａｌｙｓｉｓｏｆｉｎｃｌｕｓｉｏｎｉｎｗｅｌｄ￥ＺｈａｎｇＸｉａｏｃｈｅｎｇａｎｄＺｈａｎｇＷｅｉｐｉｎｇ（ＳｏｕｔｈＣｈｉｎａＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏｇｙ．Ｇａｕｎｇｚｈｏｕ）Ａｂｓｔｒａｃｔ：Ｔｈｅｍ...     

New methods of predicting dissimilar steel weld metal microstructures by Schaeffler Diagram

ＮｅｗｍｅｔｈｏｄｓｏｆｐｒｅｄｉｃｔｉｎｇｄｉｓｓｉｍｉｌａｒｓｔｅｅｌｗｅｌｄｍｅｔａｌｍｉｃｒｏｓｔｒｕｃｔｕｒｅｓｂｙＳｃｈａｅｆｆｌｅｒＤｉａｇｒａｍＺＨＡＮＧＨａｎｑｉａｎ；ＷＡＮＧＢａｏａｎｄＺＨＡＮＧＷｅｎｙｕｅ（ＴｈｅＲｅｓｅａｒｃ...     

Effect of weld microstructure on weld properties in A-TIG welding of titanium alloy

1　INTRODUCTIONTheactivatingTIGwelding (A TIG)wasfirstlydevelopedbyPatonWeldingInstitute ,Ukraine ,inthe 196 0s[1,2 ] .Itisnotuntiltheendof 1990sthatA TIGweldinghasbeenwidelyresearchedinEuropeandUS ,forexample ,TWIandEWI[3] .Thefluxes ,whichweredevelopedbyEWI ,havebeenappliedintheUSNavyshipbuildingindustry[4 ] .Theprincipleofthistechniqueisthatathincoatingofactivatingfluxiscoatedonthesurfaceofthebasemetalbeforeweld ing .ComparedwiththeconventionalTIGwelding ,the penetrationca…     

Mechanism of effect of rare earth oxides on high temperature corrosion resistance of weld metal

Through the addition of rare earth oxides into the coming of electrodes, the high temperature oxidation and sulphidation resistance of weld metal were studied. The transfer mechanism of rare earth oxides from coating to the welding pool and the physicochemical reaction during the process were analyzed. With the application of scanning electron microscope and energy spectrometer, the mechanism of weld metal corrosion in air and sulphur environment were studied. The result shows that the addition of rare earth oxides can improve the high temperature resistance of weld metal, especially in sulphidation environment. The electrodes in which La2O3 is added have better performance than the electrodes in which CeO2 is added. The existence form and distribution characteristic of rare earth are defined. It is believed that the marked effect of rare earth oxides in sulphur environment is related to the corrosion mechanism.     

Calculation of AF transformation kinetics in HSLA steel weld

It is of great importance for obtaining the perfect welding properties to control the acicular ferrite (AF)transformation behavior reasonably in steel weld. AF continuous transformation kinetics in the HSLA steel weld was calculated and modeled based on the direct growth on the inclusions inert interface. The simulation results are coincident with the experimental value well.     

Closed-loop control of weld penetration in keyhole plasma arc welding

To improve the penetrating ability and the welding quality of keyhole plasma arc welding, a novel penetration closed-loop control system was established. In the system, welding current and plasma gas flow rate were selected as adjusting variables. The wavelet method was used to detect penetration status from welding arc voltage in real-time. The control strategy of one-keyhole-per-pulse was adapted to fulfill stable and high quality welding process. Experimental results show that the developed system can apparently increase the penetrating force of plasma arc and keyhole plasma arc welding is realized successfully in stainless steel with 10 mm in thickness. Moreover,the disturbances of gradual change and break change from 3mm to 6mm in thickness are come over due to the good response property of the developed system.     

New methods of predicting dissimilar steel weld metal microstructures by Schaeffler Diagram(Part 2)

On the base of the methods of predicting weld metal microstructures of pearlitic dissimilar steel welded joints using austenitic type filler materials by Schaeffler Diagram, the other new methods of predicting and expressing weld metal microstructures of two kinds of dissimilar steel welded joints (pearlite/pearlite and austenite/pearlite) using austenitic filler materials by Schaeffler Diagram are suggested. Those new methods resolve some difficult problems which the microstructure kinds in two heterogeneous mixture zones of weld metal neighbouring two kinds of welded base metals are difficult to be accurately ascertained and the fluctuations of weld metal microstructures across fusion line are difficult to be conveniently expressed according to the traditional predicting method. The new predicting methods are more concise and practical.     

Influence of welding current in plasma–MIG weld process on the bead weld geometry and wire fusion rate

One of the versions of the plasma–metal inert gas (MIG) process is basically a combination of a plasma arc with a MIG/metal active gas (MAG) arc in a single torch. With this association, the advantages of each arc are combined. The main characteristic of this is the independence between the heat input by the process and the deposited material, resulting in greater facility to control bead weld geometry. In the current literature, there is a shortage of information related to the process, and most of this goes back to the 1970s and 1980s when the technology available was not able to make the process viable for industry. However, in recent years, the use of the diffusion of new electronic power sources used in welding has sparked up again the interest in plasma–MIG process. In this context, this paper aims to contribute to the studies related to the influence of the MIG and plasma current balance on the geometry of the bead weld and wire fusion rate. Bead-on-plate welds were carried out with plasma and MIG/MAG current combinations at three levels each, keeping, by welding speed corrections, the bead volume the same. It was observed that the introduction of the plasma current over the MIG/MAG current reduces penetration and dilution and leads to convex beads. On the other hand, the use of plasma current increases the MIG/MAG wire fusion rate. However, it seems that the intensity of the plasma current is not the governing parameter of those changes.     

Investigation on mechanism of reducing diffusible hydrogen in weld using microelements

0IlltroductionRareearthshavethefunctionofreducinghydrogenduringweldingmetallurgy,andhavenotableeflbctonimprovingthecrackingresistanceinweldedjoint.RareelementTealsocangreatlydecreasetheditTusiblehydrogeninweldbead,andimprovethecoldcrackingresistancepropertyinweldedjoint.Inthisthesis,theinfluenceofmicroelementsyttrium(Y)andtclluriunl(Te)ontheditTusiblehydrogeninweldbeadandonthecoldcracldngsusceptibilityofxveldedjointhasbeeninvestigated,andthemechanismofmicroelementshasbeenanalyzed.lTestmethod…     

Investigation on mechanism of reducing diffusible hydrogen in weld using microelements

Ｉｎｖｅｓｔｉｇａｔｉｏｎｏｎｍｅｃｈａｎｉｓｍｏｆｒｅｄｕｃｉｎｇｄｉｆｆｕｓｉｂｌｅｈｙｄｒｏｇｅｎｉｎｗｅｌｄｕｓｉｎｇｍｉｃｒｏｅｌｅｍｅｎｔｓ￥ＤＵＺｅｙｕ；ＤＩＮＧＰｉｎｇａｎｄＺＨＡＮＧＷｅｎｙｕｅ（ＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎ...     

An adaptive thresholding for weld seam image recognition in real time

Ａｎａｄａｐｔｉｖｅｔｈｒｅｓｈｏｌｄｉｎｇｆｏｒｗｅｌｄｓｅａｍｉｍａｇｅｒｅｃｏｇｎｉｔｉｏｎｉｎｒｅａｌｔｉｍｅ￥ＣｈｅｎＱｉａｎｇａｎｄＪｉｎＪｉａｎｍｉｎ（ＴｓｉｎｇｈｕａＵｎｉｖｅｒｓｉｔｙ．Ｂｅｊｉｎｇ）ＪｅｎｓＤｏｅｒｋ（Ａａｃｈｅｎ...     

Numerical analysis of heat transfer process for double sided tungsten inert gas – metal inert gas weld pool

Abstract

Double sided arc welding is a new type of technology developed in recent years. Many experiments show that this technology has great advantages over single arc welding for the joining of intermediate thickness stainless steel and aluminium alloy base metals. In the present work, a three-dimensional transient numerical model is created to reveal the heat transfer process for a double sided tungsten inert gas (TIG) - metal inert gas (MIG) weld pool from the viewpoint of heat transfer literature and hydrodynamics. Considering of the features of the model, effective calculation software using finite element technology is adopted. The temperature fields in the weld pool for double sided TIG - MIG welding are successfully calculated; in addition, the configuration of the weld pool is also calculated.Comparisons show that thecalculatedresults agree approximately with the experimentally measured results. STWJ/310     

Prediction and verification of melting front in GTA weld pool of full-penetration

A thermal conduction model is applied to speed up the numerical analysis of the temperature distribution and the weld pool geometry of full penetration in gas tungsten arc （GTA） welding. With considering both top and bottom flee surface deformation of full-penetrated weld pool, three-dimensional weld pool with melting front and solidification front is predicted. Welding experiments are conducted to measure the melting front curves at the top surface and the longitudinal section of the weld. It shows that the predicted and measured results are in good agreement.     

Relationship between sound signal and weld pool status in plasma arc welding

1　ＩＮＴＲＯＤＵＣＴＩＯＮＰｌａｓｍａａｒｃｗｅｌｄｉｎｇ (ＰＡＷ )ｉｓｃｈａｒａｃｔｅｒｉｚｅｄｂｙｅａｓｙｏｐｅｒａｔｉｏｎａｎｄｌｏｗｃｏｓｔａｍｏｎｇｔｈｅｈｉｇｈ ｅｎｅｒｇｙ ｄｅｎｓｉｔｙ ｂｅａｍ ｐｒｏｃｅｓｓｉｎｇｔｅｃｈｎｉｑｕｅｓ (ｆｏｒｅｘａｍｐｌｅ ,ｅｌｅｃｔｒｏｎｂｅａｍ ,ｌａｓｅｒａｎｄ ｐｌａｓｍａ) .ＰＡＷｉｓｗｉｄｅｌｙｕｓｅｄｉｎｗｅｌｄｉｎｇｏｆｓｔａｉｎｌｅｓｓｓｔｅｅｌ,ｈｉｇｈ ｎｉｃｋｅｌａｌｌｏｙｓ ,ｃａｒｂｏｎｓｔｅｅｌ,ｃｏｐｐｅｒ ,ｃｏｐｐｅｒ …