Characterization of microstructure,mechanical properties and corrosion resistance of dissimilar welded joint between 2205duplex stainless steel and 16MnR
eurekaShaogang Wang *,Qihui Ma,Yan Li
College of Material Science and Technology,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China
a r t i c l e i n f o Article history:
Received 23March 2010Accepted 10July 2010
哪里学习小儿推拿
Available online 16July 2010Keywords:
A.Ferrous metals and alloys D.Welding
F.Microstructure
a b s t r a c t
The joint of dissimilar metals between 2205duplex stainless steel and 16MnR low alloy high strength steel are welded by tungsten inert gas arc welding (GTAW)and shielded metal arc welding (SMAW)respectively.The microstructures of welded joints are investigated using scanning electron microscope,optical microscope and transmission electron microscopy respectively.The relationship between mechanical properties,corrosion resistance and microstructure of welded joints is evaluated.Results indicate that there are a decarburized layer and an unmixed zone clo to the fusion line.It is also indi-cated that,austenite and acicular ferrite structures distribute uniformly in the weld metal,which is advantageous for better toughness and ductility of joints.Mechanical properties of joints welded by the two kinds of welding technology are satisfied.However,the corrosion resistanc
e of the weldment produced by GTAW is superior to that by SMAW in chloride solution.Bad on the prent work,it is con-cluded that GTAW is the suitable welding procedure for joining dissimilar metals between 2205duplex stainless steel and 16MnR.
nativecodeÓ2010Elvier Ltd.All rights rerved.
1.Introduction
Duplex stainless steel (DSS)consists of approximately equal amounts of austenite and ferrite,which results in the favorable mechanical properties and corrosion resistance.The higher strength properties allow weight savings,which reduce fabrication costs and enable lighter support structures to be ud.The higher corrosion resistance,in particular against stress corrosion cracking,makes them preferably applied in certain environments such as chemical tankers,pressure vesls,pipes to heat exchangers,paper machines and ocean engineering [1–3].With the growing applica-tion of new materials and higher requirements for materials,a great need occurs for component or structure of dissimilar metals.However,the joining of dissimilar metals is generally more chal-lenging than that of similar metals,which is usually due to veral factors such as the differences in chemical compositions and ther-mal expansion coefficients,resulting in different residual stress situation acr
多伦多大学世界排名oss the different regions of weldments as well as the migration of carbon element from the steel with higher carbon content to the steel with relatively lower carbon content.If the welding process is not well controlled,some weld defects such as dilutions and cracks will generate in the weld metal and lead
to great decrea of properties of the welded joint.There are some rearches about failure analysis or mechanical performance for dissimilar metals joints.Ul-Hamid et al.[4]have addresd that carbon diffusion in the dissimilar joint between carbon steel pipe and type 304stainless steel elbows resulted in cracking after a rel-atively short period of usage.Lee et al.[5]have also reported creep–fatigue damage of dissimilar weldment of modified 9Cr–1Mo steel (ASME Grade 91)and 316L stainless steel in a liquid me-tal reactor.In order to overcome the technical problems and take full advantage of the properties of different metals,it is necessary to pay more attention to the joining of dissimilar metals,so as to produce high quality welded joints between them.
At prent,some investigations have been conducted on weld-ing of duplex stainless steel,almost all common fusion welding techniques can be ud to weld duplex stainless steel through lecting appropriate filler metals and parameters such as heat in-put [6,7].Explosive welding can be thought as a feasible method to produce composite plates.Kaçar and Acarer [8]have addresd that explosiv
e welding process can be ud successfully for clad-ding duplex stainless steel on the vesl steels without losing prop-erties such as corrosion resistance and mechanical properties.However,compared to the welding of similar metals,there is lim-ited information about microstructure/property relationships in dissimilar material welds between duplex stainless steel and low alloy high strength steel.Increasing application of the steels will
0261-3069/$-e front matter Ó2010Elvier Ltd.All rights rerved.doi:10.1016/j.matdes.2010.07.012
bogou
*Corresponding author.Tel.:+8602552112901;fax:+8602552112626.E-mail address:sgwang@nuaa.edu (S.G.Wang).
require a better understanding of the mechanics associated with welding of dissimilar metals.Since GTAW and SMAW are widely employed in engineering application,in the current work,a few at-tempts have been made to produce dissimilar material welded joint between DSS and low alloy high strength steel.At the same time,some results are prented as reference for the practical welding of the types of dissimilar metals.
2.Experimental material and procedure
The ba metals employed in this prentation are duplex stain-less steel2205and low alloy high strength steel16MnR.The chem-ical compositions of ba metals andfiller metals are given in
英语四级官方网站3.Results and discussion
3.1.Microstructure of welded joints
The preparation of microstructure samples of dissimilar metals joint is much difficult.Therefore,special operation procedure should be ud.Both of the weld metal(WM)and2205ba metal are etched by aqua-regia.However,the bonding region at the side of16MnR is etched by5%nital solution alone,and16MnR ba me-tal should be prevented from being etched by aqua-regia.The interfacial microstructure of16MnR–WM is shown in Fig.2.It is a region with about30l m width near the fusion line.The existing of this region can be attributed to the thermal conductivity of the
Table1
Chemical compositions of ba metals andfiller metals(wt.%).
Elements C Mn P S Si Cr Ni Mo N
Ba metal SAF22050.0160.820.0240.0010.3622.48 5.46 3.120.16 16MnR0.15 1.380.0160.0140.32––––
chariot
Filler metal ER22090.013 1.540.0180.0070.4922.928.61 3.180.17 E22090.0260.900.0250.0020.9022.1010.00 2.840.18 832S.G.Wang et al./Materials and Design32(2011)831–837
济南新东方英语培训Moreover,some short rod-like carbides,granular carbides and is-land-like carbides are obrved at higher amplification electron microscope,as shown in Fig.4c and d respectively.However,the result shows that no carbides such as M23C6or martensite are ob-rved in the unmixed zone.Therefore,it can be concluded that the development of such a morphology is attributed to decomposition of pearlite at16MnR side and formation of Fe3C at the WM side. The decomposition model is shown in Fig.5.
The optical micrograph of weld metal is shown in Fig.6.From Fig.6,the morphology of acicular ferrite in austenite matrix has been obrved,which is characterized by large amount of austen-ite.However,in terms of ferrite content in the joint,there is not much variation between the two weld metals in welded joints A and B,and the ferrite volume fraction is only17.3%and14.5%(ob-eliminate
improving joint crack resistance and reducing the inhomogeneous distribution of weld structure during multi-pass welding.
Generally,the formation of martensite,M23C6(chromium car-bide),Cr2N and r pha depends on the ba materials joined and welding conditions according to Refs.[15,16].Therefore,X-ray diffraction analysis is carried out on the weld metal and the re-sults are shown in Fig.7.There are only a and c phas in both of the weld metals,and no precipitation of M23C6(chromium car-bide),Cr2N or r pha is found in the weld metal,which is advan-tageous to mechanical properties and corrosion resistance of the joint.
3.2.Mechanical properties
834S.G.Wang et al./Materials and Design32(2011)831–837
si-cleavage fracture,as shown in Fig.9d.
Microhardness profile across the joint interface is shown in
Fig.10.The microhardness distributions of two kinds of welded joints are almost the same.Obviously,the hardness value of weld metal is higher than that of the16MnR ba metal and th
e 16MnR HAZ.With the distance increasing away from interface, the microhardness values vary to a certain extent.The highest hardness values of the two joint interface are approximately 224HV and220HV respectively.It is becau the carbon element migrates from the16MnR side to weld metal during welding due to the difference of chemical compositions between16MnR and weld metal.Similar result is reported by Kaçar and Acarer[8],
studied the explosively welded joint between DSS and
Corrosion behavior
order to evaluate the corrosion resistance of weld
is aled with A/B glue,leaving about10mmÂ10mm area,3.5%NaCl solution is ud as corrosion solution,the sche-
matic diagram is shown in Fig.11.
Electrochemical corrosion test results of2205DSS ba metal and weld metal are shown in Fig.12and Table4respectively. The samples display more or less similar behaviors in terms of In general,the higher the value is,the better corrosion resistance of the material is.Therefore,in3.5%NaCl solution,corrosion resis-tance order of the samples is:2205DSS BM>joint A>joint B.
The pitting corrosion resistance of the DSS BM is much better compared to the two weld metals,as can be en from the polari-zation plot.The DSS BM sample does not display any corrosion in 3.5%NaCl solution and there is no pit in the sample examined after the potentiodynamic cyclic scann
ing.And the good pitting resis-tance behaviors of weld metal are attributed to the addition of Cr,Ni,elements[19].The alloying element Cr could improve the stability of passivefilms,and the Ni would decrea the overall dis-solution rates of Fe and Cr[20].Moreover,the heat input of joint A is different from that of joint B,which affects the weld microstruc-ture and results in the difference of formation condition of metal surface passivefilm.Generally,thefiner the grain is,the more eas-ily the compact passivefilm forms.As a result,the corrosive ions cannot readily diffu through the passivefilm and the metal pre-nts better corrosion resistance,so the joint A has better corrosion resistance compared to joint B.
When welded joint is etched in chloride solution,defects gener-ated in the welding process(such as welding spatter or inclusion) possibly make it lo its ability to protect the surface passivefilm. As a result,a chromium-depleted zone appears around weld metal, which makes the surface activated,and the joint prents an ac-tive–passive behavior.The initiation sites for the pits are located at the ferrite–austenite grain boundaries and once formed they rapidly propagate from ferrite to austenite,as described in Ref.
[21].It can be en from Fig.13that ferrite grains are etched,leav-ing lots of grooves at the ferrite–austenite grain boundaries,and the remaining white strips are austenite.This lective localized corro
吃一堑长一智英文sion is attributed to difference of the electrochemical poten-tial,caud by the ratio of bipha in weld metal.It is concluded that the austenite grains are by far more resistant to the chloride environment than that of the ferrite grains.
4.Conclusions
The investigation of welding between2205DSS and16MnR by GTAW and SMAW respectively reach the following conclusions:
Fig.10.Hardness curves of16MnR–WM interface. Fig.12.Polarization curves of DSS BM and weld metals.
