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A study on low magnetic permeability gastungsten arc weldment of AISI 316LN stainless

steel for application in electron accelerator

ARTICLE in MATERIALS AND DESIGN · JANUARY 2014

Impact Factor: 3.5 · DOI: 10.1016/j.matdes.2013.06.029

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Abhay Kumar

Raja Ramanna Centre for Advanced Techno…

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Rakesh Kaul



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Jishnu Dwivedi



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Accepted Manuscript

A Study on Low Magnetic Permeability Gas Tungsten Arc Weldment of AISI

316LN Stainless Steel for Application in Electron Accelerator

Abhay Kumar, R.K. Soni, P. Ganesh, Rakesh Kaul, V.K. Bhatnagar, Jishnu

Dwivedi, L.M. Kukreja

PII: S0261-3069(13)00563-3

DOI: http://dx.doi.org/10.1016/j.matdes.2013.06.029

Reference: JMAD 5569

To appear in: Materials and Design

Received Date: 31 March 2013Accepted Date: 12 June 2013

Please cite this article as: Kumar, A., Soni, R.K., Ganesh, P., Kaul, R., Bhatnagar, V.K., Dwivedi, J., Kukreja, L.M.,

A Study on Low Magnetic Permeability Gas Tungsten Arc Weldment of AISI 316LN Stainless Steel for Application

in Electron Accelerator, Materials and Design (2013), doi: http://dx.doi.org/10.1016/j.matdes.2013.06.029

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers

we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, andreview of the resulting proof before it is published in its final form. Please note that during the production process

errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

http://dx.doi.org/10.1016/j.matdes.2013.06.029http://dx.doi.org/http://dx.doi.org/10.1016/j.matdes.2013.06.029http://dx.doi.org/http://dx.doi.org/10.1016/j.matdes.2013.06.029http://dx.doi.org/10.1016/j.matdes.2013.06.029


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A Study on Low Magnetic Permeability Gas Tungsten Arc Weldment of AISI

316LN Stainless Steel for Application in Electron Accelerator

Abhay Kumar, R. K. Soni, P. Ganesh, Rakesh Kaul*, V. K. Bhatnagar, Jishnu Dwivedi and

L. M. Kukreja

Raja Ramanna Centre for Advanced Technology, Indore - 452 013, INDIA

(*Email: [email protected], Phone: +91 731 2488381)

Abstract

Low magnetic permeability is an important criterion in selection of the material of construction

of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the

magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing

synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as

the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with

conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3-

8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has

demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler

produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI

316LN stainless steel is not required to be solution annealed after the final forming operation for

obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber

in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector

Microtron, the study also provides useful input for design of future indigenous accelerators with

vacuum chambers of austenitic stainless steel.

Keywords: Accelerator, austenitic stainless steel, non-magnetic weld, delta ferrite free weld, high Mn

filler, solidification cracking.

1.0 Introduction

Austenitic stainless steel (SS), because of its good mechanical and corrosion properties, finds

wide ranging applications in a variety of industries. However, use of austenitic SS in certain important

applications requires that the fabricated components must meet the stringent requirement of low

http://ees.elsevier.com/jmad/viewRCResults.aspx?pdf=1&docID=20457&rev=2&fileID=809121&msid={AD632F8F-6EBA-40C9-B8F9-E947A3568F8C}


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residual magnetic permeability. Some of such critical applications include components of particle

accelerators for suppressing distortion of applied magnetic field [1], naval submarines for providing

protection against airborne surveillance as well as against undersea mines [2] and coronary stents for

suppressing unwanted artifacts in magnetic resonance imaging (MRI) [3]. Putatunda et al reported

development of a new austenitic structural steel for potential applications in power generation deviceslike components of turbine, generators etc. [4]. Low residual magnetic permeability is one of the major

requirements involved in the design of 20 MeV/30 mA injector microtron operating in authors‟

laboratory. The injector microtron is the primary source of electrons for two major electron

accelerators 450 MeV Indus-1 and 2.5 GeV Indus-2 [5, 6].

A cylindrical vacuum chamber is contained within the dipole magnet of the Injector Microtron.

The two ends of the vacuum chamber are the pole faces of the dipole magnet. The vacuum chamber

houses the sub-systems for emission, acceleration, bending and extraction of the electron beam. For

achieving good cathode life, the vacuum chamber is maintained at high vacuum level (pressure = 10-5

Pa). The size of the vacuum chamber is primarily determined by the dimensions of the electron beam

extraction orbit, with some extra radial allowance for minimizing the effect of residual magnetic

permeability (introduced as a result of forming, machining and welding) on the applied magnetic field

distribution. The vacuum chamber of existing injector microtron has multiple ports for its interfacing

with various diagnostic probes, microwave powering, beam probing, evacuation, extraction systems

etc. All these openings are provided with knife-edged flanges for their sealing with copper gaskets.

Important factors governing the choice of material of construction for the vacuum chamber are low

relative magnetic permeability, mechanical strength and manufacturability. The basic requirement of

low magnetic permeability limits the choice of material to either aluminium alloys or austenitic

stainless steels (ASS). The use of aluminium alloys as the material of construction of the vacuum

chamber introduces several complications in its design, necessitating either (i) hard coating of

aluminium knife edge flanges with TiN, CrN or electroless nickel to protect the knife edge from

associated wear effects or (ii) Al/austenitic SS transition joints (achievable through explosion/friction

welding) with the knife edge machined in the austenitic SS part. Moreover, lack of well-versed

vendors in the field of manufacturing of aluminium high vacuum chambers with knife-edged flanges,

introduces practical complications in the fabrication of vacuum chamber. On the other hand, due to

simplified design and availability of established fabrication technology of austenitic SS, AISI 304L SS

was selected as the material of construction of the vacuum chamber of existing Injector Microtron and

welding of the vacuum chamber was carried out by gas tungsten arc welding (GTAW) using ER 308L

https://www.researchgate.net/publication/10932623_Comparative_MRI_Compatibility_of_316L_Stainless_Steel_Alloy_and_NickelTitanium_Alloy_Stents?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/248464768_Development_of_an_austenitic_structural_steel?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/10932623_Comparative_MRI_Compatibility_of_316L_Stainless_Steel_Alloy_and_NickelTitanium_Alloy_Stents?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/248464768_Development_of_an_austenitic_structural_steel?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUz


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SS filler. According to WRC-1992 diagram [7], such a WM (considering about 30% dilution from the

base metal) should carry ferrite number (FN) in the range of 4-18. Magnetic permeability

measurements, performed on the existing Injector Microtron, exhibited asymmetric distribution of

magnetic field across the diameter of the vacuum chamber, as shown in Fig.1.

A project is currently underway to replace the existing 20 year old injector microtron with anupgraded one. With ASS as the material of construction of the vacuum chamber, the most critical

factor influencing the performance of the Injector Microtron is its residual magnetic permeability

which must be very close to 1 to minimize the distortion of the magnetic field. Possible sources of

residual magnetic permeability in ASS are: formation of (i) strain-induced martensite during machining

and forming [8,9] and (ii) ferro-magnetic -ferrite in the WM [8]. Takemoto [10] found that for

complete suppression of magnetism during cold deformation of ASS, its Ni equivalent (Nieq = Ni +

0.6Mn + 9.69(C+N) + 0.18Cr - 0.11Si2) should be more than 19. Small and Pehlke [11] proposed an

adapted factor (A = Ni + 42.7C + 18.9N - 1.21Cr - 0.18Mn - 0.95Si2) to quantify the stability of

austenite vs. precipitated -ferrite in the stainless steel (SS) welds. For complete suppression of -

ferrite, A ≥ -8.5.

In the modified design of the new Injector Microtron, AISI 316LN SS has been identified as the

material of construction of its vacuum chamber. The selection of AISI 316LN SS is based on the fact

that the magnetic permeability of this alloy in the solution annealed condition (1.003) is not only

among the lowest offered by any ASS, but it also remains largely unaltered by machining and forming

operations [12]. Welding of AISI 316LN SS with conventional filler alloys like ER316L and ER317L

of AWS A5.9 produces WM compositions that are not fully non-magnetic. This arises from the need

to maintain 3-8% -ferrite in the room temperature microstructure of the WM, which is considered

necessary for controlling WM solidification cracking [13,14]. This small -ferrite content is sufficient

to introduce distortion in the magnetic field. It is reported that GTAW of vacuum chambers and

antechambers of Shanghai Synchrotron Radiation Facility (SSRF) made of AISI 316LN SS, brought

about a significant increase in magnetic permeability (from 1.01 to 2.5) and the welded structure was

subjected to a post weld heat treatment in vacuum above 1173 K to bring down magnetic permeabilityvalue to 1.02 [15, 16]. Post-weld vacuum heat treatment of vacuum chamber not only adds to the cost

but also introduces considerable distortions in the fabricated structure. Lee et al has reported no

significant change in magnetic permeability of AISI 316 LN SS during its entire fabrication process,

involving vacuum annealing, machining, forming, GTAW and final machining [12]. Kaan et al also

reported that with respect to AISI 304L SS and 316L SS, magnetic permeability of the weld of AISI

https://www.researchgate.net/publication/222347678_Characterization_of_strain-induced_martensitic_transformation_in_a_metastable_austenitic_stainless_steel?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/229037760_Magnetic_Properties_of_Undulator_Vacuum_Chamber_Materials_for_the_Linac_Coherent_Light_Source?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/236505576_Prediction_of_austenitic_weld_metal_microstructure_and_properties?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/229037760_Magnetic_Properties_of_Undulator_Vacuum_Chamber_Materials_for_the_Linac_Coherent_Light_Source?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/229037760_Magnetic_Properties_of_Undulator_Vacuum_Chamber_Materials_for_the_Linac_Coherent_Light_Source?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/229037760_Magnetic_Properties_of_Undulator_Vacuum_Chamber_Materials_for_the_Linac_Coherent_Light_Source?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/222347678_Characterization_of_strain-induced_martensitic_transformation_in_a_metastable_austenitic_stainless_steel?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/236505576_Prediction_of_austenitic_weld_metal_microstructure_and_properties?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUz


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316LN SS was much lower (< 1.01) and a post-weld annealing further brought down its magnitude to

1.004 [17]. Both the reports did not provide details of filler used in their respective studies. European

Organization for Nuclear Research (CERN) has reported development of a special high Mn, high N

ASS P506 (C: 0.03%; Cr: 19-19.5%; Ni: 10.7-11.3%; Mn: 11.8-12.4%; Mo: 0.8-1%; Si: 0.5%; N:

0.3-0.35%; Fe: Bal) capable of maintaining low relative magnetic permeability ( 1.005) in the basemetal as well as in its welds down to cryogenic temperatures [1,18]. The alloy exhibits complete

austenite stability against -ferrite precipitation in autogenous welds as well as against its

transformation to strain-induced martensite during deformation at low temperatures.

2.0 Role of Delta Ferrite in Welding of ASS

As explained above, solidification cracking (or hot cracking) is one of the major problems

associated with welding of ASS is solidification cracking. Sulphur, phosphorus, boron, niobium,titanium and silicon have been identified as the most harmful alloying elements responsible for

enhancing cracking sensitivity of stainless steel welds [19,20]. These elements strongly partition

themselves into the liquid metal and form low melting point eutectics with Fe, Cr and Ni. During the

course of solidification, solidifying grains reject S and P into the remaining melt and as a result of this,

the remnant liquid metal is enriched with S and P, leading to formation of low melting point eutectics.

Towards the end of solidification, solidifying grains are separated by a thin melt layer and under the

influence of welding-induced thermal stresses, cracking occurs along the grain boundaries [20].

Although, B content in stainless steel welds are recommended to be limited to very small quantities

[21], the element displays an interesting influence on solidification cracking susceptibility of the

austenitic stainless steel welds. An experimental study performed by Shinoda et al [22] on the welds of

boron-modified 304 stainless steel has demonstrated that the hot cracking susceptibility is high for

boron additions of about 0·2%, but is decreased when the boron content is increased to ≥ 0·5%.

Solidification cracking at 0.2% B is attributed to the suppression of ferrite precipitation and formation

of low melting point grain boundary films whereas reduced solidification cracking susceptibility at

higher B content (B ≥ 0·5%) is mainly caused by healing of cracks by the abundant amount of low-

melting-point eutectic liquid of (Cr, Fe)2B and -Fe [23].

Important factors controlling solidification cracking susceptibility of ASS weld are:

concentration of crack promoting elements, particularly S and P [24, 25], restraint, chemical

composition and microstructure of the WM. Scherrer et al, in their path-breaking patent, claimed that

crack-resistant weld deposits would be produced if the chemical composition of the WM is adjusted to

https://www.researchgate.net/publication/252382483_Mechanical_design_philosophy_and_construction_of_the_Amsterdam_Pulse_Stretcher_ring_AmPS?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226695012_Solidification_cracking_in_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226695012_Solidification_cracking_in_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/233524510_Hot_cracking_susceptibility_of_boron_modified_AISI_304_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/255033129_Effect_of_low-melting-point_eutectic_on_solidification_cracking_susceptibility_of_boron-added_AISI_304_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226311978_The_relationship_between_solidification_and_microstructure_in_austenitic_and_austenitic-ferritic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/233524510_Hot_cracking_susceptibility_of_boron_modified_AISI_304_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/252382483_Mechanical_design_philosophy_and_construction_of_the_Amsterdam_Pulse_Stretcher_ring_AmPS?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226311978_The_relationship_between_solidification_and_microstructure_in_austenitic_and_austenitic-ferritic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/255033129_Effect_of_low-melting-point_eutectic_on_solidification_cracking_susceptibility_of_boron-added_AISI_304_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/274692628_Correlation_Between_Solidification_Cracking_and_Microstructure_in_Austenitic_and_Austenitic-Ferritic_Stainless_Steel_Welding_Research_International_9255-76?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226695012_Solidification_cracking_in_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226695012_Solidification_cracking_in_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUz


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form 5 - 35 % -ferrite in the WM [26]. Since then, the presence of -ferrite in the WM is considered

essential to avoid solidification cracking in the austenitic SS welds. Chemical compositions of

commercial ASS fillers are usually engineered to obtain 3-8% -ferrite in the room temperature

microstructure of the resultant WM [13,14]. Many reasons have been proposed to account for the

enhanced solidification cracking resistance of the duplex microstructure of austenitic SS welds. Someof the important factors are [20,27,28]: (i) higher solubility of S and P in delta ferrite (than in austenite)

leaving little segregation of S and P in the grain boundary region, (ii) irregular path offered by duplex

/-ferrite structure helps in arresting the crack, (iii) lower surface energy of /-ferrite causes its

reduced wettability by eutectic films as compared to / or / interface, (iv) presence of -ferrite

results in larger interface area due to its solid-state transformation to austenite resulting in a reduced

concentration of impurity elements at grain boundaries, (v) greater ductility of -ferrite at high

temperature (as compared to austenite) facilitates stress relaxation, (vi) lower coefficient of thermal

expansion of -ferrite (with respect to austenite), leading to reduced shrinkage stress, (vii) narrower

solidification temperature range for primary ferrite welds (with respect to primary austenite welds),

(viii) presence of ferrite refines grain size of the solidified WM resulting in improved mechanical

properties and cracking resistance, (ix) higher coefficient for impurity diffusion in ferrite (with respect

to austenite) allows faster homogenization in ferrite, (x) volume contraction associated with -ferrite to

transformation reduces tensile stresses close to the crack tip. In this respect, many diagrams have

been proposed for predicting room temperature weld microstructure [19]. These diagrams have been

found extremely useful in identifying the chemical composition of weld fillers for controlling resultant

WM microstructure with desired amount of -ferrite, which in turn, governs solidification cracking.

The diagrams developed by Schaeffler, Delong and Welding Research Council are some of the most

prominent diagrams widely used for estimating the room temperature -ferrite content of the WM [19].

However these diagrams do not take into account the effect of solidification rate on the primary mode

of solidification which is considered essential to identify the risk of solidification cracking in various

compositions.

Since, the solidification cracking in ASS welds occurs before its complete solidification, the

cracking resistance of the WM is primarily influenced by the sequence of micro-structural evolution

during the course of solidification and not by its room temperature microstructure. Masumoto et al

reported that primary ferrite mode of solidification, rather than residual ferrite content after welding, is

essential to suppress cracking in ASS welds [29]. It is now well known that welds made with primary

austenite mode of solidification are prone to the solidification cracking whereas those solidifying with

https://www.researchgate.net/publication/236505576_Prediction_of_austenitic_weld_metal_microstructure_and_properties?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226695012_Solidification_cracking_in_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/274288829_Weld_Cracking_of_Austenitic_Stainless_Steel?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/274288829_Weld_Cracking_of_Austenitic_Stainless_Steel?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/226695012_Solidification_cracking_in_austenitic_stainless_steel_welds?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/236505576_Prediction_of_austenitic_weld_metal_microstructure_and_properties?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUz


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primary ferrite mode exhibit enhanced resistance against solidification cracking [27]. Control of

primary mode of weld solidification is obtained by controlling the chemical composition of the filler.

Kujunpaa et al reported an abrupt increase in cracking propensity in duplex SS WM as its Cr eq/Nieq

ratio (where Cr eq and Nieq are defined according to Schaffler diagram) drops below 1.5 [25]. The

observed effect is attributed to the transition in primary mode of solidification from ferrite to austenite.Based on the research work carried out to review the role of -ferrite in suppressing

solidification cracking, it has been suggested that a higher Mn content in the WM is an effective way to

obtain completely austenitic sound welds [30]. The beneficial effect of Mn is attributed to the fact that

it encourages ferrite solidification at high temperatures while promoting its rapid transformation to

austenite at lower temperatures [31,32]. In addition, high Mn content of the ASS weld also serves to

tie up S to form higher melting MnS- eutectic, in place of crack-promoting iron/nickel sulphide

[19,33,34]. Dixon demonstrated that ferrite-free welds with exceptionally low sensitivity to the

solidification cracking can be obtained with high Mn electrode (Fe-20Cr-15Ni-7.6Mn-2Mo) [32].

Kane et al reported development of low -ferrite high Mn welding consumable for cryogenic

application (4 K) [35]. Use of this kind of SS fillers should result in the formation of completely non-

magnetic welds while suppressing solidification cracking. The present experimental study was

undertaken with an objective to evaluate high Mn filler for obtaining crack-free non-magnetic ASS

weldments of AISI 316LN SS by GTAW. The scope of the study also included effects of machining

and forming operations on the magnetic permeability of AISI 316LN SS and its comparison with AISI

316L SS, another candidate material for the construction of vacuum chamber of particle accelerators.

3.0 Experimental study

The experimental study was performed a plate of AISI 316 LN SS. Table-1 presents chemical

composition of the substrate (in wt%), as determined by chemical analysis. The chemical composition

of the substrate conformed to nominal chemical composition of AISI 316 LN SS [36]. The substrate

was subjected to magnetic permeability measurements in different processing conditions, including

untreated, machined, plastically deformed and welded conditions. In order to introduce effect of

machining a 10 mm thick piece of AISI 316 LN SS was machined down to 8 mm thickness. The

machined specimens were subsequently subjected to bending with machined tools of different radii of

curvature to generate controlled plastic strains of 4%, 5.3%, 8%, 10% and 40%. On the other hand,

weld specimens were prepared by machining a V-notch in a 40 mm thick plate of AISI 316 LN SS. A

higher Mn adaptation of W 18 16 5 N L was selected as the filler for GTAW of AISI 316LN SS [37,

https://www.researchgate.net/publication/274692628_Correlation_Between_Solidification_Cracking_and_Microstructure_in_Austenitic_and_Austenitic-Ferritic_Stainless_Steel_Welding_Research_International_9255-76?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/29677412_Solidification_Crack_Susceptibility_in_Weld_Metals_of_Fully_Austenitic_Stainless_Steels_Report_VII_Effect_of_Mn_and_N_on_Solidification_Crack_ResistanceMaterials_Metallurgy_Weldability?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/241928317_Welding_consumable_development_for_a_cryogenic_4_K_application?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/29677412_Solidification_Crack_Susceptibility_in_Weld_Metals_of_Fully_Austenitic_Stainless_Steels_Report_VII_Effect_of_Mn_and_N_on_Solidification_Crack_ResistanceMaterials_Metallurgy_Weldability?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/241928317_Welding_consumable_development_for_a_cryogenic_4_K_application?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUzhttps://www.researchgate.net/publication/274692628_Correlation_Between_Solidification_Cracking_and_Microstructure_in_Austenitic_and_Austenitic-Ferritic_Stainless_Steel_Welding_Research_International_9255-76?el=1_x_8&enrichId=rgreq-5444d599-871c-458c-897a-ec37bc5176b9&enrichSource=Y292ZXJQYWdlOzI1NTkxMDc5NztBUzo5OTEwMzMzMzY4MzIzMEAxNDAwNjM5NDg0ODUz


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38]. The said filler is an adaptation of ER317L with higher Mn content. The chemical composition of

filler wire (in wt%) is presented in Table 2, while Table 3 summarizes experimental welding

parameters used for the study. Welded specimens were characterized by radiographic examination,

magnetic permeability measurements, -ferrite measurements and chemical analysis by vacuum arc

emission spectroscopy, optical and scanning electron microscopy, tensile and guided bend tests.

4.0 Results and Discussion

4.1. Non-destructive testing

Visual and macroscopic examination of the weldment revealed no surface defects. The SS

weldment was subjected to different non-destructive tests, including dye penetrant test and X-ray

radiographic examination. Dye penetrant test, performed on the top surface of the weld, exhibited no

surface cracks. X-ray radiographic examination was performed in single wall single image mode with

DIN 6-ISO-12 image quality indicator (IQI). The resultant radiograph, with the sensitivity of 250 µm,

did not bring out any internal defects in the weld metal.

4.2. Chemical analysis

Local chemical analysis measurements were conducted by vacuum arc emission spectrometry

on the machined transverse cross-section of the weldment. Table 4 presents the chemical composition

(in wt%) at different locations in WM as well as in the base metal. Chemical composition of the base

metal and WM largely corresponded to reported compositions of the AISI 316 LN SS and filler alloy

W Z 18 16 5 N L, respectively. For the WM compositions presented in Table-2, Schaffler diagram

[19] predicts a completely austenitic room temperature microstructure with 0% ferrite. On the other

hand, in Delong, WRC-1988 and WRC-1992 diagrams [19,7], WM compositions fell beyond the

limiting value of Nieq. Moreover, the magnitude of Nieq [10], estimated for base metal and WM (refer

Table 4), suggest complete stability of magnetic permeability during cold working at room temperature

(as Nieq >19). On the other hand, value of adapted factor A (as defined by Small and Pehlke [11]) for

AISI 316 LN SS, worked out to be -6.45 and -6.61 (> -8.5), thereby indicating no -ferrite formation in

its autogenous weld. The value of adapted factor A [11] for the WM worked out to be in the range of -

3.51 to -3.91 which precludes -ferrite formation in WM as well as in inter-mixing zone where value of

A is likely to lie in between the two extremes of -6.61 and -3.51.


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4.3. Magnetic permeability measurements

In-order to evaluate the effect of plastic deformation on the relative magnetic permeability of

AISI 316LN SS, measurements were performed on (i) 10 mm thick base metal in solution annealed

condition, (ii) machined specimen - after machining 2 mm surface layer, (iii) pre-deformed specimenswith total plastic strain of 4%, 5.3%, 8% and 40% (achieved by bending the specimen) and (iv) welded

specimens. Similar measurements were also made on equivalent specimens of AISI 316L SS. These

measurements were made with Ferromaster Permeability meter. The text “relative magnetic

permeability” is termed as “magnetic permeability” in the following text. The results of magnetic

permeability measurements are summarized in Fig. 2. AISI 316 LN SS specimen, in solution annealed

condition, displayed a magnetic permeability of 1.004. A small decrease in relative magnetic

permeability was noticed after machining of a thin surface layer which is attributed to the removal of

temper rolled layer with possible presence of small amount of strain-induced martensite. Similar effect

was also displayed by AISI 316L SS specimen. Formation of significant amount of stain-induced

martensite is reported on the machined surface of AISI 304L and 304 stainless steel specimens [39,40].

Absence of any adverse effect of machining on the magnetic permeability of AISI 316L and AISI

316LN SS specimens is attributed to enhanced stability of austenite in these alloys. Related literature

on the subject also reports little effect of grinding/machining on magnetic permeability of 316L [41]

and 316 LN SS [12]. On the other hand, AISI 316L and 316 LN SS specimens displayed different

response against plastic deformation. In the case of AISI 316 LN SS, it was noticed that after 4%

plastic strain, the decrease in magnetic permeability is regained to „solution annealed‟ condition and

subsequent straining upto 40% did not bring about any further change in its magnetic permeability,

which remained confined in the range of 1.0025 - 1.0035. This is in sharp contrast to about 4.6 % rise

in the magnetic permeability of AISI 316L SS from 1.073 (in solution annealed condition) to 1.122

after 10% plastic strain. Manjaana et al [42] reported formation of ferro-magnetic α‟ martensite phase

after a deformation of about 25% true strain in AISI 316 LN SS. However, the amount of α‟ was very

small (0.18 volume% at a true strain of 60%) when compared to the reported data for AISI 304, 304L,

316 and 316L stainless steels. A related study in this regard also reported little effect of machining and

forming on magnetic permeability of AISI 316 LN SS [12]. On the other hand, magnetic permeability

value of the WM of AISI 316 LN SS remained below 1.005 (magnetic permeability of base metal in

solution annealed condition) at all locations in the weld, although a marginal rise in magnetic

permeability was noticed towards the fusion boundary region. Since, magnetic permeability of an


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austenitic SS weldment is primarily controlled by chemical composition of the filler used, there are

widely different reports on magnetic permeability of AISI 316 LN SS weldment. On one hand, Jiang et

al [16] reported large increase in magnetic permeability of AISI 316 LN SS weldment, while many

other researchers reported significantly lower magnetic permeability (< 1.01) [12,17], although these

literature did not make mention o the chemical of the filler used. Past studies have reporteddevelopment of completely austenitic and yet crack-free SS welds [32,35,43], although with fillers of

different chemical compositions than used in this study. In spite of difference in chemical

compositions, fillers used in all these studies (including the present one) carried higher Ni, Mn and N

contents than used in conventional austenitic SS alloys.

4.4. Delta ferrite measurements

Delta ferrite measurements were carried out on the transverse cross-section of WM using Fisher

Ferrite Scope M-0701. Ferrite measurements, taken at four different sites in the WM exhibited zero

ferrite number (FN), indicating completely austenitic non-magnetic WM.

4.5. Metallographic examination and micro-hardness measurements

Metallographic examination and micro-hardness measurements were performed on the

transverse cross-section of the welded specimen. Figure 3 presents macro-etched cross-section of the

welded specimen. Cross-section of the multi-pass weld did not reveal any defects. Micro-hardness

measurements, carried out with a load of 0.98 N, showed that the micro-hardness of WM (181 - 201

VHN) was quite similar to that of the base metal in solution-annealed condition (184 - 214 VHN). For

metallographic examination, welded specimens were electrolytically etched with 10% oxalic acid.

Base metal exhibited an equi-axed austenite microstructure without any carbides, as shown in Fig. 4.

No cracks were observed in the weld region, although a few isolated lack of fusion regions were

noticed between successive weld passes. The WM exhibited typical cellular/dendritic microstructure.

Due to the absence of remnant delta-ferrite in the room temperature weld microstructure, WM did not

display typical signatures of primary ferrite mode of solidification in the form of a lathy or vermicular

ferrite, as shown in Fig. 5. However, vermicular ferrite microstructure, representing primary ferrite

mode solidification, was noticed in small localized regions of WM, as shown in Fig. 6.


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4.6. Mechanical testing

Welded SS plate was characterized by tensile and guided bend tests under different

configurations, including face, root and side bend. The test specimens were fabricated as per Section

IX of ASME Boiler and Pressure Vessel Code [44]. Figure 7 presents stress-strain curve of the tensile

test performed on the welded specimen. The results of tensile test were: tensile strength = 613 MPa;

yield strength = 406 MPa and % elongation (50 mm gauge length) = 34. Failure of these specimens

occurred in the WM. A closer examination of the fracture surface of tensile tested specimen under

scanning electron microscope revealed typical dimpled appearance (Fig. 8), indicating extensive plastic

deformation preceding failure. In order to determine the effect of plastic deformation introduced during

the tensile test on magnetic permeability of the WM, one of the fractured tensile specimens was

subjected to magnetic permeability measurements at four different places on the gauge length of

fractured welded specimen. At all the four places magnetic permeability values were found to be

1.005, indicating no effect of plastic deformation on magnetic permeability of the WM. Keeping in

view the high value of Nieq (as proposed by Takemoto [10] of WM (24.27 - 24.88), the results of

magnetic permeability measurements are on the expected lines. Guided bend tests, in longitudinal face

and root bend, transverse face bend and side bend configurations, were performed on the welded

specimens as per Section IX of Boiler and Pressure Vessel Code [44]. The specimens were tested with

a 150 kN servo-hydraulic universal testing machine in stroke-control mode at the rate of 10 mm/min.

Macroscopic examination of the convex surface of the bend tested specimens revealed that except for

the longitudinal face bend specimen, all other bend tested welded specimens did not exhibit any

defects. Moreover, in the longitudinal face bend specimen, length of linear defect (2 mm) noticed on

the convex surface of welded specimen was found to be within the specified acceptance limit of 3.2

mm. Figure 9 presents photo-macrographs of convex surface of the guided bend specimens tested in

different configurations. The results of bend test demonstrate soundness and ductility of gas tungsten

arc welds made with the high Mn filler.

5.0 Conclusions

In the light of the results of the present investigation, it is inferred that AISI 316LN SS, in the

solution annealed condition, is a suitable choice for fabrication of vacuum chamber of upgraded

Injector Microtron. The formed component made of AISI 316LN SS is not required to be solution

annealed after the final forming operation to obtain low magnetic permeability, thereby greatly


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11

simplifying the fabrication process. Gas tungsten arc welding of AISI 316LN SS with a high Mn

adaptation of W 18 16 5 N L filler produced a crack-free non-magnetic welds with acceptable

mechanical properties. Magnetic permeability of the material remained unaltered after welding.

Besides Injector Microtron, the output of the study also provides useful inputs for the design of

austenitic SS vacuum chambers for future indigenous accelerators, which was primarily hampered bythe need to maintain 3 - 8 % ferro-magnetic -ferrite in the WM to avoid solidification cracking.

Acknowledgement

Authors are thankful to Mr. V. K. Lal for his contribution in welding the test coupons. Authors

also thank Mr. D. C. Nagpure and Mr. Ram Nihal Ram for their assistance during various stages of the

investigation. They express their sincere thanks to Mr. R S Sandha, Mr. Brahmanand Sisodia and Mr.

Ravi Choudhary for procurement of raw materials and characterization equipment used in thisinvestigation.

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http://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-UShttp://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-UShttp://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-UShttp://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-UShttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Ozaki,%20Y..QT.&searchWithin=p_Author_Ids:37338588100&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Furukimi,%20O..QT.&searchWithin=p_Author_Ids:37329059200&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Shiraishi,%20M..QT.&searchWithin=p_Author_Ids:37325626300&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Nohara,%20K..QT.&searchWithin=p_Author_Ids:37329063300&newsearch=truehttp://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=77http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=77http://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Nohara,%20K..QT.&searchWithin=p_Author_Ids:37329063300&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Shiraishi,%20M..QT.&searchWithin=p_Author_Ids:37325626300&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Shiraishi,%20M..QT.&searchWithin=p_Author_Ids:37325626300&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Furukimi,%20O..QT.&searchWithin=p_Author_Ids:37329059200&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Furukimi,%20O..QT.&searchWithin=p_Author_Ids:37329059200&newsearch=truehttp://ieeexplore.ieee.org/search/searchresult.jsp?searchWithin=p_Authors:.QT.Ozaki,%20Y..QT.&searchWithin=p_Author_Ids:37338588100&newsearch=truehttp://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-UShttp://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-UShttp://www.mip-co.com/Welding/DatasheetsView.aspx?SubgroupID=d1174590-a4c7-4916-a6f7-ef2bb88c176f&Locale=en-US


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Table-1: Nominal and actual chemical composition of substrate (in wt%)

C Cr Ni Mn Si Mo S P N Fe

Nominal < 0.03 16-18 10-14 < 2.0 < 0.75 2-3 < 0.03 < 0.045 0.1-0.16 Bal

Actual 0.026 17.727 12.3 1.625 0.385 2.492 0.0002 0.019 0.1249 Bal

Table-2: Chemical composition (in wt%) of filler wire

C Cr Ni Mn Si Mo S P N Fe

< 0.01 18.7 17 5.1 0.4 4.0 < 0.01 0.01 0.15 Bal

Table-3: Parameters of GTAW of 40 mm thick AISI 316 LN stainless steel plate

Welding groove Diameter of filler

wire

Polarity Current Ar flow

rate

Welding

speed

V-groove

Included angle: 90

Root face: 2 mmRoot gap: 2.5 mm

2.5 mm DCEN 90-140 A 6 lpm 25 mm/min

Table-4: Chemical composition (in wt.%), as determined by vacuum arc emission spectrometer

at different locations in weld metal (WM) and base metal (BM)

C Cr Ni Mn Si Mo N B S/P Fe Nieq* A**

BM:

Site1

0.03 17.82 12.35 1.66 0.399 2.55 0.102 0.0015 S: 0.0010

P: 0.023

Bal 26.62 -6.45

BM:

Site2

0.024 17.75 12.35 1.65 0.401 2.54 0.103 0.0015 S: 0.0017

P: 0.023

Bal 26.54 -6.61

WM:Site1

0.0081 18.49 17.43 5 0.36 4.06 0.112 0.0021 S: 0.0099P: 0.013

Bal 33.62 -3.50

WM:

Site2

0.01 18.39 17.04 4.76 0.36 3.98 0.109 0.0022 S; 0.0090

P: 0.015

Bal 33.09 -3.71

WM:

Site3

0.0082 18.47 16.99 4.75 0.365 3.97 0.11 0.0022 S: 0.0092

P: 0.015

Bal 33.03 -3.91

*As defined by Takemoto [5]; **As defined by Small and Pehlke [6].


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16

List of Table Captions

Table 1: Nominal and actual chemical composition of substrate (in wt%).

Table 2: Chemical composition (in wt%) of filler wire.

Table 3: Parameters of GTAW of 40 mm thick AISI 316 LN stainless steel plate.

Table 4: Chemical composition (in wt.%), as determined by vacuum arc emission spectrometer at

different locations in weld metal (WM) and base metal (BM).

List of Figure Captions

Fig. 1: Magnetic field profile across the diameter “XY” (shown as blue line in the photograph) of the vacuum chamber of 20 MeV/30 mA Injector Microtron.

Fig. 2: Magnetic permeability of AISI 316L and 316 LN stainless steels in different conditions ( -strain).

Fig. 3: Transverse cross-section of gas tungsten arc weldment of AISI 316 LN stainless steel.

Fig. 4: Equi-axed austenite microstructure of base metal in solution-annealed condition.

Fig. 5: Microstructure of weld metal.

Fig. 6: Vermicular ferrite microstructure in localized region of weld metal.

Fig. 7: Stress-strain curve of welded specimen of AISI 316LN stainless steel.

Fig. 8: Scanning electron fractograph of tensile tested welded specimen of AISI 316 LN stainless steel.

Fig.9: Photo-macrographs of convex surface of (A) longitudinal root bend, (B) longitudinal face bend,

(C) transverse face bend and (D) side bend tested welded specimens of AISI 316 LN stainless

steel.


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ure1

http://ees.elsevier.com/jmad/download.aspx?id=809123&guid=fbadc276-86c9-410d-b05b-781651c7214a&scheme=1


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ure2

http://ees.elsevier.com/jmad/download.aspx?id=809277&guid=09f98db2-2a68-4620-8e42-a048f619afa1&scheme=1


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ure3

http://ees.elsevier.com/jmad/download.aspx?id=809278&guid=7aa3c9dc-46e9-447f-99fa-fb1ea6a93bbd&scheme=1


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ure4

http://ees.elsevier.com/jmad/download.aspx?id=809279&guid=842e6e46-ab21-43ac-9f48-28af58755cc8&scheme=1


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ure5

http://ees.elsevier.com/jmad/download.aspx?id=809280&guid=73508dcb-4dc9-4571-a0e9-2f4ecb081089&scheme=1


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ure6

http://ees.elsevier.com/jmad/download.aspx?id=809281&guid=a814d572-8ca8-4106-a6e9-963899e241f4&scheme=1


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http://ees.elsevier.com/jmad/download.aspx?id=809282&guid=2040ed8b-2a0e-4257-96d7-b981baa71bd4&scheme=1


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http://ees.elsevier.com/jmad/download.aspx?id=809283&guid=674a41b0-1783-447f-9d3a-6467ed40b197&scheme=1


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http://ees.elsevier.com/jmad/download.aspx?id=809286&guid=942d7472-c3df-4cca-bcdc-613594b8e030&scheme=1


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Highlights

AISI 316LN is a suitable material for vacuum chamber of Injector Microtron.

Formed component need not be annealed to obtain low magnetic permeability.

GTAW with high Mn filler produced a crack-free non-magnetic weld.

The weld exhibited acceptable mechanical properties.

Results are also important for future indigenous accelerators.

a study on low magnetic permeability

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