Numerical Investigation of the Influence of Microstructure on the Residual Stress Distribution and Distortion in DP600 Welds

2011 ◽  
Vol 681 ◽  
pp. 79-84 ◽  
Author(s):  
A.M.Akbari Pazooki ◽  
M.J.M. Hermans ◽  
I.M. Richardson
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Phase Transformations ◽  
Dual Phase Steel ◽  
Ferrite Matrix ◽  
Volume Changes ◽  
Heating And Cooling ◽  
Distortion Level ◽  
Martensitic Phase Transformations ◽  
Cct Diagrams

Dual phase steel consists of martensite embedded in a ferrite matrix. The material experiences high heating and cooling rates during welding, which alter the microstructure significantly. In this work the effects of solid state phase transformations on the prediction of residual stresses and distortion during welding of DP600 steel is investigated. Phase fractions have been calculated implicitly using continuous cooling time (CCT) diagrams. The results of the model are compared with experimental measurements for bead-on-plate welds made on DP600 sheets. It is found that the volume changes and the increase of the strength due to the martensitic transformation have both a significant effect on the residual stress and distortion level although in opposite directions. Martensitic phase transformations in DP600 steel tend to reduce tensile residual stresses in the weld metal.

On the Stress Development in SA508 Autogenous Weld

2014 ◽  
Vol 783-786 ◽  
pp. 2123-2128 ◽  
Author(s):  
Hamidreza Abdolvand ◽  
Mike Keavey ◽  
H. Dai ◽  
Alison Mark ◽  
N. O’Meara ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Phase Transformations ◽  
High Speed ◽  
Elevated Temperatures ◽  
Kinematic Hardening ◽  
Stress Development ◽  
Wide Range ◽  
Martensitic Phase Transformations ◽  
Welding Processes

Considering the significant role that residual stresses play in determining the lifetime-service of materials, it is mandatory to have a good understanding of and a means of predicting those that develop during welding processes. For this purpose, a User MATerial subroutine (UMAT) is developed to study the effects of various parameters that influence solid state phase transformations and residual stress evolution during welding of SA508 ferritic steel. The temperature dependent elastic and kinematic hardening parameters for each of the individual phases that can potentially develop during cooling from elevated temperatures are measured and are used for calculating stress development during low (75 mm/min) and high (300 mm/min) speed gas-tungsten arc welding (GTAW) on SA508 grade 3. These two speeds are selected to cover a wide range of cooling rates in the heat affected zone so that different phase proportions would be present. The results of the numerical simulations for residual stresses are compared against those measured by neutron diffraction. It is shown here that a low speed weld results in bainite formation whereas a high speed weld results in bainitic as well as subsequent martensitic phase transformations where each welding rate results in different residual stress development.

The Prediction of Residual Stresses in an Autogenously Welded Ferritic Beams

2008 ◽  
Author(s):  
A. P. Warren ◽  
I. Symington ◽  
S. K. Bate ◽  
J. A. Francis ◽  
M. Turski ◽  
...  
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Phase Transformations ◽  
Structural Components ◽  
Reliable Operation ◽  
Viable Option ◽  
Heating And Cooling ◽  
Finite Element Package ◽  
Neutron Diffraction Technique

The continued safe and reliable operation of plant invariably has to consider the assessment of defects in welded structural components. This often requires some estimate of the residual stresses that have developed during the welding fabrication process. Increases in the computational power available to finite element analysts have made the prediction of welding residual stresses using finite element methods an increasingly viable option. Consequently recent years have seen many advances in the field of residual stress modelling. However, relatively little work has been conducted on the accurate modelling of welded ferritic components. This is largely due to the added complications associated with the solid-state phase transformations that occur during the heating and cooling of such steels. Against this background, a programme of work has been undertaken in order to investigate the effects that phase transformations have on the development of residual stresses in ferritic components and develop methods for their simulation. To facilitate this, generic components of increasing complexity are being studied. Reported in this paper is the first phase of this programme which considers SA508 beam specimens. These specimens have been subjected to autogenous TIG welds using two different torch travel speeds. In order to predict the resultant residual stresses, simulations have been conducted using the commercial finite element package SYSWELD. These predicted stresses are then compared with residual stress measurements conducted using the neutron diffraction technique.

The Effect of Phase Transformations on Predicted Values of Residual Stresses in Welded Ferritic Components

2006 ◽  
Vol 524-525 ◽  
pp. 827-832 ◽  
Author(s):  
Alex P. Warren ◽  
Steve K. Bate ◽  
Richard Charles ◽  
C.T. Watson
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Phase Transformations ◽  
Welding Process ◽  
Heating And Cooling ◽  
Test Pieces ◽  
Property Data ◽  
Finite Element Package ◽  
Predicted Values ◽  
Welding Processes

The accurate prediction of the residual stresses present in welded structures can be of great importance to the fracture assessment of such components. Therefore, a large amount of benefit can be gained from improving techniques for measuring and numerically analysing these stresses. In recent years many advances have been made in the field of analysing residual stresses using finite element methods. That said, very little work has been conducted on the accurate modelling of welded ferritic components. This is largely due to the added complication of phase transformations that occur during the heating and cooling of such steels. The objective of the work presented in this paper was to improve understanding of the effect that phase transformations have on residual stresses present within welded ferritic structures. This was conducted by simulating such welding processes using the finite element package SYSWELD. An investigation was conducted to determine how phase transformations, and therefore residual stresses, are affected by the welding process used. Phase transformation and material property data available within SYSWELD were used for this analysis. An autogenously welded beam provided a simple basis for this qualitative investigation. In the future the manufacture and measurement of suitable test-pieces will enable these simulations to be validated.

scholarly journals Effect of Phase Transformations on Scanning Strategy in WAAM Fabrication

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7871
Author(s):  
Muhammad Hassaan Ali ◽  
You Sung Han
Keyword(s):  
Residual Stress ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Phase Transformations ◽  
Manufacturing Industry ◽  
Welding Process ◽  
Stress Generation ◽  
Temperature History ◽  
History Of ◽  
Wire Arc Additive Manufacturing

Due to its high production rates and low cost as compared to other metal additive manufacturing processes, wire arc additive manufacturing (WAAM) has become an emerging technology in the manufacturing industry. However, the residual stress generation and part distortion hinder its widespread adoption because of the complex thermal build-histories of WAAM parts. One of the ways to alleviate this problem is to consider the effects of scan strategies as it directly influences the thermal history of the built part. Since WAAM itself is an evolved welding process and even though it is evident from welding studies that phase transformations directly affect the residual stresses in welded parts, it remains unclear how the consideration of phase transformations for different scan strategies will affect the residual stresses and distortions in the WAAMed parts. A FEM study has been performed to elucidate the effects of phase transformations on residual stresses and the distortion for different deposition patterns. The current findings highlight that for the fabrication of low-carbon martensitic steels: The consideration of phase transformations for line-type discontinuous patterns (alternate and raster) do not significantly affect the residual stresses. Consideration of phase transformations significantly affects residual stresses for continuous patterns (zigzag, in–out and out–in). To accurately simulate complex patterns, phase transformations should be considered because the patterns directly influence the temperature history of the built part and will thus affect the phase transformations, the residual stresses and the warpage. During the fabrication of WAAM parts, whenever possible, discontinuous line scanning patterns should be considered as they provide the part with uniform residual stress and distortion. The alternate line pattern has been found to be the most consistent overall pattern.

The Role of Metallurgical Solid State Phase Transformations on the Formation of Residual Stress in Laser Cladding and Heating

2014 ◽  
Vol 777 ◽  
pp. 19-24 ◽  
Author(s):  
Ryan Cottam ◽  
Vladimir Luzin ◽  
Kevin Thorogood ◽  
Yat C. Wong ◽  
Milan Brandt
Keyword(s):  
Residual Stress ◽  
Solid State ◽  
Phase Transformations ◽  
Contour Method ◽  
Second Phase ◽  
Heating And Cooling ◽  
Second Phase Particles ◽  
The Matrix ◽  
Packing Arrangement

There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress.

Residual Stress Profiles of the Laser Surface Remelted Nodular Irons

2005 ◽  
Vol 490-491 ◽  
pp. 460-468 ◽  
Author(s):  
Janez Grum ◽  
Roman Šturm
Keyword(s):  
Residual Stress ◽  
Surface Layer ◽  
Residual Stresses ◽  
Laser Beam ◽  
Stress Measurement ◽  
Laser Surface ◽  
Laser Remelting ◽  
Volume Changes ◽  
Workpiece Surface ◽  
Laser Surface Remelting

Laser remelting process is a very promising hardening method for ferrous and nonferrous alloys, which do not show a homogeneous microstructural state after having been heattreated in a traditional way. Consequently, the alloys concerned do not achieve the required hardness of the surface layer and do not provide the required wear resistance either. The paper deals with residual stresses of thin flat specimens of nodular cast iron 500-7 in the laser remelting process. In the process of gradual remelting of the specimen surface, that is during its heating and cooling, volume changes of the specimen occur due to thermal and microstructural changes. For a better knowledge of volume changes in the thin surface layer of the specimen, the latter were evaluated by residual-stress measurement in the thin modified surface layer after the remelting process. In laser remelting of a workpiece such remelting conditions should be ensured that a uniform thickness of the modified layer could be obtained in spite of several laser-beam passages across the workpiece surface. Because of a multiple laser-beam passage across the workpiece surface, the state of internal stress in the workpiece changes. Optimal laser surface remelting conditions on the basis of knowing the residual stresses were chosen, while the way of guiding the laser beam over the surface of flat samples and degree of overlapping were varied.

Influence of Laser Remelting Process on Strain and Residual Stresses in Nodular Iron

2011 ◽  
Vol 681 ◽  
pp. 188-193 ◽  
Author(s):  
Roman Šturm ◽  
Janez Grum
Keyword(s):  
Residual Stress ◽  
Surface Layer ◽  
Residual Stresses ◽  
Laser Beam ◽  
Stress Measurement ◽  
Specimen Surface ◽  
Thin Surface Layer ◽  
Laser Remelting ◽  
Volume Changes ◽  
Workpiece Surface

The present paper deals with residual stress and strain changes in thin flat specimens of nodular cast iron during laser remelting process. In laser remelting process of a workpiece we have used several laser beam passages across the workpiece surface. The state of internal stress in the workpiece changes because of different ways of guiding the laser beam across the workpiece surface, and consequently strain of the workpiece may occur. In the process of gradual remelting of the specimen surface, i.e. during its heating and cooling, volume changes in the specimen surface layer occur due to thermal and microstructural changes. To find out more about volume changes in the thin surface layer of specimens, the latter were monitored by measuring the strain at the lower side of the specimens during and after the remelting process, and also by residual stress measurement in the thin surface layer. The results obtained confirm that the laser remelting process could be successfully optimised on the basis of knowing the residual stresses and the strain generated during the remelting process.

Residual stresses in a large circular disc caused by local heating and cooling at its centre

1971 ◽  
Vol 6 (2) ◽  
pp. 89-98 ◽  
Author(s):  
T R Gurney
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Temperature Distribution ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Local Heating ◽  
Residual Stress Distribution ◽  
Element Analysis ◽  
Heating And Cooling

By means of a form of finite-element analysis and use of a theoretical, radially symmetrical, temperature distribution, the residual stresses resulting from spot heating at the centre of a large circular plate have been calculated. The investigation was concerned in particular with defining the effect of variations in material yield stress, rate of heat input, and peak temperature on the residual-stress distribution.

scholarly journals Numerical Modelling Of Thermal And Structural Phenomena In Yb:YAG Laser Butt-Welded Steel Elements

2015 ◽  
Vol 60 (2) ◽  
pp. 821-828 ◽  
Author(s):  
M. Kubiak ◽  
W. Piekarska ◽  
S. Stano ◽  
Z. Saternus
Keyword(s):  
Phase Transformations ◽  
Numerical Models ◽  
Welding Process ◽  
Source Model ◽  
Welded Steel ◽  
Heating And Cooling ◽  
Real Distribution ◽  
Classical Models ◽  
Volume Method ◽  
Cct Diagrams

AbstractThe numerical model of thermal and structural phenomena is developed for the analysis of Yb:YAG laser welding process with the motion of the liquid material in the welding pool taken into account. Temperature field and melted material velocity field in the fusion zone are obtained from the numerical solution of continuum mechanics equations using Chorin projection method and finite volume method. Phase transformations in solid state are analyzed during heating and cooling using classical models of the kinetics of phase transformations as well as CTA and CCT diagrams for welded steel. The interpolated heat source model is developed in order to reliably reflect the real distribution of Yb:YAG laser power obtained by experimental research on the laser beam profile.On the basis of developed numerical models the geometry of the weld and heat affected zone are predicted as well as the structural composition of the joint.

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