AU2021102151A4

AU2021102151A4 - Method to identify the influence of non-metallic inclusions in segregated banded-zone during plate groove butt joint welding

Info

Publication number: AU2021102151A4
Application number: AU2021102151A
Authority: AU
Inventors: D. Jeyasimman; N. Ramasamy
Original assignee: Jeyasimman D Dr
Current assignee: Jeyasimman D Dr
Priority date: 2021-04-22
Filing date: 2021-04-22
Publication date: 2021-07-22
Anticipated expiration: 2029-04-22

Abstract

The present disclosure relates to a method to identify the influence of non-metallic inclusions in segregated banded-zone during plate groove butt joint welding. To analyses the root cause for joint failure, a series of mechanical tests are conducted on prepared samples from production weld. The macro examination is conducted at the failed region and microstructure analysis is carried out by optical microscope and Scanning Electron Microscope on the banded structure of the base metal and at Heat affected zone. The method facilitate to identify the influence of the non-metallic inclusions in the segregated banded zone during welding of plate butt joint and to identify the impurity elements responsible for the weld failure. From this investigation, it is found that the presence of Manganese sulphide, Lead sulphide and Aluminum oxides in the segregated zone, decreased the mechanical properties of the plate groove butt joint weld in terms of failure. 30 100 preparingtwo production test plates of size length 300 mm, width 150 mm and thickness63 mm which is 102 connected on oneend with a production plate groove butt joint welding weld tabs with both ends to get defect-free weld at ends and thereby attaching weld tabs at the ends 104 ofgroove buttjoints toavoid buildup crater crackduringwelding preheatingbase plate to 150degreeCelsiusand welding root pass with electrode diameter 315 mm and 106 subsequentlayersandtherebymakingpasseswithelectrodediameter4and5mm Backgrounding rootweld after completing weld on firstside and thereafter performingDye penetranttest in 108 the rootweld to ensure soundness of the weld metal fillingthe groove with multi-pass layers on firstside and completed on the secondside with the same 110 sequence cleaningslagandotherdebrisandmaintaininginter-passtemperatureof280-300degreeCelsiusforeachlayer 112 duringwelding radio-graphingthe production plate groove buttjoint and test couponand thereafter stress relievedat 4 625degree Celsius subjectingthe processedgroove buttjointtest plate to various tests for processintegrity and quality ofthe 116 jointon further assembly Figure Weld tab Production Test pate A - - -.... - -- " A A t Plate buttjoint weldtb Section A A Figure 2A Figure 2B

Description

preparingtwo production test plates of size length 300 mm, width 150 mm and thickness63 mm which is 102 connected on oneend with a production plate groove butt joint

welding weld tabs with both ends to get defect-free weld at ends and thereby attaching weld tabs at the ends 104 ofgroove buttjoints toavoid buildup crater crackduringwelding

preheatingbase plate to 150degreeCelsiusand welding root pass with electrode diameter 315mm and 106 subsequentlayersandtherebymakingpasseswithelectrodediameter4and5mm

Backgrounding rootweld after completing weld on firstside and thereafter performingDye penetranttest in 108 the rootweld to ensure soundness of the weld metal

fillingthe groove with multi-pass layers on firstside and completed on the secondside with the same 110 sequence cleaningslagandotherdebrisandmaintaininginter-passtemperatureof280-300degreeCelsiusforeachlayer 112 duringwelding

radio-graphingthe production plate groove buttjoint and test couponand thereafter stress relievedat 4 625degree Celsius

subjectingthe processedgroove buttjointtest plate to various tests for processintegrity and quality ofthe 116 jointon further assembly

Figure

Weld tab

Production Test pate A A- - -....- -- "t A

Plate buttjoint

weldtb Section A A Figure 2A

Figure 2B

METHOD TO IDENTIFY THE INFLUENCE OF NON-METALLIC INCLUSIONS IN SEGREGATED BANDED-ZONE DURING PLATE GROOVE BUTT JOINT WELDING FIELD OFTHEINVENTION

The present disclosure relates to a method to identify the influence of non-metallic inclusions in segregated banded-zone during plate of groove butt joint welding.

BACKGROUND OF THE INVENTION

Advances in the plate manufacturing process have enhanced the low level of impurities. In recent years, "clean steel" have been developed and commercialized by plate mill, thereby meeting the demand for steel. The structural steel plates are manufactured with the condition of either normalizing rolled or As Rolled. The modern steel plate manufacturer preferred the normalized rolling for its optimum strength, energy savings and pollution-free environment. Normalized rolling steel plates are widely used for non-alloyed structural steel construction industries such as pressure vessel, boilers, bridges and shipbuilding. Hot rolled medium and high tensile structural (C-Mn) steel with normalizing rolled plate Specification: IS 2062 E 250 BR is used for fabrication of the boiler supporting structure. The boiler supporting structural plate member is designed to different thickness and size to meet out the assembly product. The sizes of the plates are standardized for economic reasons and to satisfy the market demand. To meet the product requirements, the plate groove butt joint is introduced to get the required size.

The normalizing rolling defined by EN 10025:2004 is a rolling process in which the final deformation is carried out in a certain temperature range leading to a material condition and mechanical properties are met and equivalent to normalizing treatment. The mechanical properties and microstructure are determined by the plate rolling process. The microstructure of the normalizing rolled plate includes a combination of ferrite and pearlite phase in the form of banded structure with an alternating band along the rolling direction. Depending upon the cooling condition, the residual interdendritic microstructure occurs, which is mainly responsible for segregation in banding at the mid thickness of the plate. The plate rolling process of steel even if optimized to the required properties; it may still fail to remove the impurities segregation in banding. The rolling temperature, roller pressure, rolling speed and cooling rate are the critical parameters to be maintained during plate rolling.

Inclusions in segregated zones are undesired intermediate products that are further formed depending on their favorable thermodynamic conditions during the production of normalizing rolled steel plate particularly for higher thickness. The type and appearance of these inclusions depends on factors such as steel grade, steel melting, rolling process and secondary metallurgy of steel. Welding of structural steel plates entails certain challenges. Inclusions are non-metallic phases embedded in a metallic matrix and are derived from the chemical reactions of the molten metal with the other elements while processing. The element such as manganese, silicon and aluminum reacts itself and with other non-metallic elements, which lead to forming the non-metallic inclusions. Inclusions are having a detrimental influence on mechanical properties when they found in steel plate. Inclusions are mainly due to insufficient removal of oxygen and other impurities not properly captured by slag. Inclusions are an important source of poor performance in steel. The size and distribution of inclusions beyond the limit may enhance the product failure in service, and it may develop abnormal crack when the component subjected to cyclic stresses. The inclusions in steel are related to the type of equipment which experiences the stains while in service.

The detection of the inclusion by an ultrasonic test is very difficult. Only large inclusions, exceeding the size 1.0 mm can be detected by ultrasonic testing.

The precipitation of carbon, manganese, sulphides and oxides at the segregated banded zone enhance the non-homogenous structure during normalized rolling. The heterogeneity of crystallization while cooling increases the different concentration of impurity elements at the segregated zone is a critical factor that determines the properties of the material. The properties of the banded zone depend on banded fibers and the surrounding matrix. The impurity elements such as Sulphur, Phosphorous, etc., present in carbon steel react with oxygen and with itself, forming oxides and non-metallic compounds. The investigation on the content of non-metallic inclusion is still to improve on the subject of plate rolling. The presences of non-metallic, metallic compounds and oxides may cause an influence on mechanical properties such as yield strength, ductility and toughness of the base metal as well as plate groove butt joint. The compounds and oxides present in the segregation band have a detrimental influence on the deterioration of mechanical properties. It is very difficult to control and determine the segregated elements in a banded structure.

The compounds and inclusions in the segregated zone play the damaging effect against the steel matrix. Rui Feng et al analyzed the formation of abnormal segregation that lowered the toughness and induces the layered fracture. Marcolino Fernandes et al investigated the efficiency of the slag to capture the inclusions and time to float, to get quality steel product. If the impurities are not captured form steel ingot, the impurities could deteriorate the properties of steel. The notching elements such as bubble and cavities which amplify the stress field and pressurized gas, trapped in the cavities could generate stress field around the inclusions. Non- metallic phases generate residual stress due to the different thermal expansion coefficient associated with the metal phase during welding. The mechanical properties are controlled by composition, distribution and precipitation of impurities either in the form of oxides or compounds (sulphides). Inclusions act as a stress raiser and an important source of failures. Failures in terms of cracks caused by metallic, non metallic inclusions can happen when the component is subjected to cyclic stresses. The size of the inclusion and thickness of the fibrous band is the deciding factor on the characteristic of strain on a final product while dynamic loading. Therefore, the steel plate should have the lowest possible level of undesired inclusions. George Krauss analyzed the origins of chemical segregation, the effects of micro-segregation, banding on austenite decomposition, microstructure and properties of carbon and alloy steels. Lifeng et al. investigated and analyzed the chemical characterization of inclusions and morphology of inclusion, using image analysis by an electron microscope to determine the types of inclusions.

Established Shielded Metal Arc Welding (SMAW) is widely employed in structural fabrication field. Carbon steel plate thicknesses ranging from 16 mm to 75 mm are used in fabrication industries. When the steel plate thickness becomes higher, the construction problems get predominant during structural fabrication. Thermal cycles involved during welding, generally alter the mechanical properties of the weld metal when compared to a base metal. The heterogeneity of the microstructure due to segregation at fusion zone can lead to a deficiency of the mechanical properties at heat affected zone (HAZ) of weld metal. The failure analysis helps to identify the impact on potential process or product risk.

In the view of the forgoing discussion, it is clearly portrayed that there is a need to have a method to identify the influence of non-metallic inclusions in segregated banded-zone during plate groove butt joint welding.

SUMMARY OF THE INVENTION

The present disclosure seeks to provide a method to identify the influence of the non-metallic inclusions in the segregated banded zone during welding of plate groove butt joint and to identify the impurity elements responsible for the weld failure.

In an embodiment, a method to identify the influence of non metallic inclusions in segregated banded-zone during plate groove butt joint welding is disclosed. The method includes preparing two production test plates of size length 300 mm, width 150 mm and thickness 63 mm which is connected on one end with a production plate groove butt joint.

The method further includes welding the weld tabs with both ends to get defect-free weld at ends and thereby to avoid build up crater crack during welding.

The method further includes preheating base plate to 150degree Celsius and welding root pass with electrode diameter 3.15 mm and subsequent layers and thereby making passes with electrode diameter 4 and 5 mm.

The method further includes back grounding the root weld after completing the weld on a first side and thereafter performing Dye penetrant test in the root weld to ensure soundness of the weld metal.

The method further includes filling the groove with multi-pass layers which is completed on the second side with the same sequence. The method further includes cleaning slag and other debris and maintaining inter-pass temperature of 280-300degree Celsius for each layer during welding.

The method further includes radio-graphing the production plate groove butt joint and test coupon and thereafter stress relieved at 625degree Celsius. The method further includes subjecting the processed groove butt joint test plate to various tests for process integrity and quality of the joint on further assembly.

In an embodiment, hot rolled medium and high tensile structural steel to low carbon steel specification IS 2062 grade E 250 BR under normalizing rolled condition and ultrasonically tested plate is used for fabrication of boilers supporting structure.

In an embodiment, the 63 mm thick production plate with double V groove butt joint is made with 2 mm root gap as per welding procedure specification (WPS).

In an embodiment, shielded metal arc welding (SMAW) process is employed with electrode preheated to 200degree Celsius and baked to 120degree Celsius (AWS-E 7018) for the welding process.

In an embodiment, eight layers are laid to complete the groove on either side of the plate excluding root pass and 18 layers are deposited to complete the groove butt joint.

In an embodiment, test specimens are prepared from production test plate to identify root cause of failure of production test coupon specimens through various tests including tensile, hardness measurement, macro, micro examination and analysis through the scanning electron microscope.

In an embodiment, side bend test is carried out with the specimen prepared from a butt joint results opening of corner at a bent region measuring up to length 3.0 mm, wherein bend test is carried out on the specimen prepared from the base metal and found that the specimen bent smoothly without opening.

In an embodiment, the hardness (Brinell) measurement is carried out with an indenter diameter of 2.5 mm, and an applied load 187.5 kg at room temperature 23degree Celsius on a segregated zone of base metal and un-affected base metal.

In an embodiment, ASTM E 340-13 method is followed for macro examination on the full section profile of welded test plate results that the crack initiated and propagated to the length of 3 mm from weld metal into base metal at the mid thickness on both sides of the base metal.

In an embodiment, chemical compositions of base metal and in the segregated zone of base metal are examined by using optical emission spectrometer.

An object of the present disclosure is to identify the influence of the non-metallic inclusions in the segregated banded zone during welding of plate groove butt joint.

Another object of the present disclosure is to identify the impurity elements responsible for the weld failure.

Another object of the present disclosure is to prepare production test plates.

Yet another object of the present invention is to deliver an expeditious and cost-effective method to identify the influence of non metallic inclusions in segregated banded-zone during plate butt joint welding.

To further clarify advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings. BRIEFDESCRIPTIONOFFIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a flow chart of a method to identify the influence of non-metallic inclusions in segregated banded-zone during plate butt joint welding in accordance with an embodiment of the present disclosure; Figures 2A and 2B illustrate schematic diagram for production test plate and section AA for production test plate-Double groove joint in accordance with an embodiment of the present disclosure; Figures 3A, 3B and 3C illustrate ductile fracture in base metal, crack at root- Mid thickness and side-bend base metal respectively in accordance with an embodiment of the present disclosure; Figure 4 illustrates hardness at various locations in accordance with an embodiment of the present disclosure; Figure 5 illustrates macro-crack at mid-section of plate butt joint in accordance with an embodiment of the present disclosure; Figure 6 illustrates magnified defect (crack) in accordance with an embodiment of the present disclosure;

Figure 7 illustrates microstructure for base metal in accordance with an embodiment of the present disclosure; Figures 8A, 8B and8C illustrate inclusions and cavities, sulphides and oxides and compound (PbS) and bubbles in accordance with an embodiment of the present disclosure; Figure 9 illustrates selected location in banded zone (EDS) in accordance with an embodiment of the present disclosure; and Figure 10 illustrates abundant elements in banded zone in accordance with an embodiment of the present disclosure.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

Referring to Figure 1, a flow chart of a method to identify the influence of non-metallic inclusions in segregated banded-zone during plate groove butt joint welding is illustrated in accordance with an embodiment of the present disclosure. At step 102, the method 100 includes preparing two production test plates of size length 300 mm, width 150 mm and thickness 63 mm which is connected on one end with a production plate groove buttjoint.

At step 104, the method 100 includes welding weld tabs with both ends to get defect-free weld at ends and thereby to avoid build up crater crack during welding.

At step 106, the method 100 includes preheating base plate to 150degree Celsius and welding root pass with electrode diameter 3.15 mm and subsequent layers and thereby making passes with electrode diameter 4 and 5 mm.

At step 108, the method 100 includes backgrounding root weld after completing weld on a first side and thereafter performing Dye penetrant test in the root weld to ensure soundness of the weld metal.

At step 110, the method 100 includes filling the groove with multi pass layers which is completed on the second side with the same sequence. At step 112, the method 100 includes cleaning slag and other debris and maintaining inter-pass temperature of 280-300degree Celsius for each layer during welding.

At step 114, the method 100 includes radio-graphing the production plate groove butt joint and test coupon and thereafter stress relieved at 625degree Celsius. At step 116, the method 100 includes subjecting the processed groove butt joint test plate to various tests for process integrity and quality of the joint on further assembly.

In an embodiment, side bend test is carried out with the specimen prepared from a test coupon results opening of corner at a bent region measuring up to length 3.0 mm, wherein bend test is carried out on the specimen prepared from the base metal and found that the specimen bent smoothly without opening.

In an embodiment, ASTM E 340-13 method is followed for macro examination on the full section profile of welded test plate and found that the crack initiated and propagated to the length of 3 mm from weld metal into base metal at the mid thickness on both sides of the base metal.

Figures 2A and 2B illustrate schematic diagram for production test plate and section AA for production test plate-Double groove butt joint in accordance with an embodiment of the present disclosure. Hot rolled medium and high tensile structural steel to low carbon steel specification IS 2062 grade E 250 BR under normalizing rolled condition and the ultrasonically tested plate is generally used for fabrication of boilers supporting structure. The production test plate arrangement is shown in Figure 2A and 2B. The production plate 63 mm thick with double V groove butt joint is made with 2 mm root gap as per the Welding Procedure Specification (WPS). Production test plate size length 300 mm, width 150 mm and thick 63 mm, two specimens are prepared with the same material specification and attached on one end with production plate groove butt joint. Weld tabs are welded with both ends to get defect-free weld at ends. The electric arc start and finishing locations are prone to build up crater crack during welding. To avoid such defects, weld tabs are attached at the ends of groove butt joints.

Shielded Metal Arc Welding (SMAW) process is employed with electrode preheated to 200 °C and with baked to 120 C (AWS-E 7018) is used for the welding process as per the electrode manufacturer recommendation. The base plate is preheated to 150 OC and root pass is welded with electrode diameter 3.15 mm and subsequent layers and passes are made with electrode diameter 4- and 5-mm. Root weld is back ground after completing the weld on the first side. The liquid penetrant test is conducted in the root weld to ensure the soundness of the weld metal. The groove is filled with multi-pass layers and completed on the second side with the same sequence. Slag and other debris are cleaned and the inter-pass temperature 280-300 OC is maintained for each layer during welding. Eight layers are laid to complete the groove on either side of the plate excluding root pass and 18 layers are deposited to complete the groove butt joint. The production plate groove butt joint and test coupon are radio-graphed, and stress relieved at 625 °C. The processed groove butt joint test plate is subjected to various tests for its process integrity and quality of the joint on further assembly.

Test specimens are prepared from the production test plate. For plate 63mm thick, the test coupon should be sectioned at top, mid and bottom of the plate as per AWS D1.1 standard requirement. The production test coupon specimen prepared at mid thickness is failed at a low tensile value and corner crack is observed during side bend test. To identify the root cause of failure, different test specimens are prepared from the existing balance welded test coupon according to various test standards for conducting the test such as tensile, hardness measurement, macro, micro examination and analysis through the scanning electron microscope. The test methods had been followed as per the relevant standards and requirements.

Figures 3A, 3B and 3C illustrate ductile fracture in base metal, crack at root- Mid thickness and side-bend base metal in accordance with an embodiment of the present disclosure. Transverse rectangular tensile test (Method ASTM A370-14, test temperature: 23 0 C) specimens are prepared as per the standard AWS D 1.1 from the welded joint and tested. The type of fracture is captured, and it is shown in Figure 3A. Side bend test (4t-1800 ) is carried out (Test method IS 1599) with the specimen prepared from a butt joint and found that the corner is opened at the bent region measuring up to length 3.0 mm. The crack opening is shown in the Figure 3B. Bend test is carried out on the specimen prepared from the base metal and found that the specimen bent smoothly without opening. It is shown in Figure 3C.

Figure 4 illustrates hardness at various locations in accordance with an embodiment of the present disclosure. Hardness (Brinell) measurement is carried out with an indenter diameter of 2.5 mm, and an applied load 187.5 kg at room temperature 23 °C on a segregated zone of base metal and un-affected base metal. Test method ASTM E10/ IS 1500 is followed for hardness measurement. The Brinell hardness values are measured in the cross-section of the butt joint at various locations and average hardness value of banded, non-banded zone of the base metal (BM), at HAZ of the banded zone (BZ) , non-banded zone and weld metal (WM) are plotted in Figure 4.

Figure 5 illustrates macro-crack at mid-section of plate butt joint in accordance with an embodiment of the present disclosure. ASTM E 340 13 method is followed for macro examination on the full section profile of welded test plate and found that the crack initiated and propagated to the length of 3 mm from weld metal into base metal at the mid thickness on both sides of the base metal. Macro examination image is shown in Figure 5. Figure 6 illustrates magnified defect (crack) in accordance with an embodiment of the present disclosure. The micro examination is conducted as per the procedure given in ASTM E407-07 & ASM HANDBOOK VOL 7 on the polished surfaces of the base metal (failed region). The surface is prepared by mechanical polishing with different grades of emery papers and etched with 2 Vol. % Nital solutions. The image captured by optical microscope for the crack at root is shown Figure 6.

Figure 7 illustrates microstructure for banded ferrite and pearlite of the base in accordance with an embodiment of the present disclosure.

Figures 8A, 8B and8C illustrate inclusions and cavities, sulphides and oxides and compound (PbS) and bubbles in accordance with an embodiment of the present disclosure. The morphology of the chemical constituent present in the banded structure at the segregated zone is examined at an appropriate location in HAZ through a scanning electron microscope and its images of oxide and compound are captured at various locations are given in Figure 8A, 8B and 8C.

Chemical compositions of base metal (Test method ASTM E415-14) and in the segregated zone of base metal are examined by using Optical Emission Spectrometer.

Mechanical properties of a plate groove butt joint in equipment, determines the properties which includes tensile strength, ductility, and elastic modulus. This happens when a plate groove butt joint is subjected to mechanical stresses. Such mechanical properties of the groove butt joint are evaluated by production/process qualification test to determine the properties of the consumable, consistency and compatibility. However, structural components in equipments are subjected to tensile, compressive and shear. These basic mechanical properties are ascertained through the respective test. The tensile test is one of the important tests to determine mechanical properties.

Three tensile test specimen samples are prepared across the thickness section (top, mid and bottom) as per the Structural welding code- steel (AWS D1.1-2015). Mechanical tests are conducted on prepared samples and test values are analyzed. The tensile test specimen is failed at 394 N/mm 2 against the required 410 N/ mm 2 at the mid thickness of the welded test plate. From Figure 3A, weld failure is observed in base metal adjacent to the weld metal. The behavior of groove butt joint weld is found critical while loading in the transverse direction of the welds. Higher-strength in the weld metal is associated with alloys constitution in the flux, coated to the electrode. This failure experiences in the base metal, adjoin to the weld metal which is due to lower strength.

As the weld metal cools after welding, weld metal composition has multiple phase transitions and occurs with micro-segregation in liquid solid phase region. Welding electrode manufactures, have to develop the consumable by adding suitable alloying elements with flux and to prevent micro-segregation. Established and proven welding electrode AWS E7018 is used for such process. Hence, the failure is occurred in HAZ and not in the weld metal.

From Figure 3A, the crack is observed at mid thickness of the butt joint on one side of the weld metal and a cup-cone fracture observed on another side of the weld metal adjacent to base metal during the tensile test. From Figure 3B, corner opened to the reasonable length of 3 mm observed on both sides of the base metal at the mid thickness of double groove V butt joint (root weld). The groove butt joint is made with two plates, therefore linear opening is observed on both sides, at the mid thickness of the segregated zone during side bend test. From the tensile and bend test results, the failure is observed at the mid thickness of the plate in the groove joint welded region. During welding, the base metal is heated sufficiently to 1526 0 C and the non-metallic inclusions presented in the banded zone of the base metal is reacted with weld metal. The visible crack is attributed due to differential expansion and contraction of inter-metallic inclusions while heating and cooling during welding.

Depending upon the heating and cooling condition, the formation of residual interdendritic microstructure at the mid thickness of the plate is a responsible for the failure in HAZ.

Separate side bend test is carried out on the specimen prepared from the raw material for full-thickness. From the Figure 3C, there is No significant defect is observed in the bent region and the test result is found to be satisfactory. Even the base metal is banded with the segregation; the mechanical properties are satisfactory to the side bend test requirement. It is apparent that the centerline segregation with inclusions in the base metal had attributed failure; adjoin to weld metal due to repeated heat input during welding.

The hardness test is a mechanical test to assess the mechanical properties such as strength, ductility and resistance to abrasion/wear. Hardness testing is a usual approach to describe the mechanical properties of the material at various zones. Tensile and hardness tests are conducted to measure the resistance of the material in plastic flow.

Hardness values are measured in the base metal (BM), weld metal (WM), banded zone of the base metal and in HAZ of the weld at the banded zone across the section of a butt joint. The hardness is high in transition zone where the differential cooling occurred in HAZ. Therefore hardness in weld metal is considerably low when compared to hardness in HAZ. Steeper raise and drop of welding temperature promote hard structure, if high carbon and other elements are present at the banded zone. Usually, Carbon is controlled 0.05 wt % in the weld metal to get a quality weld joint and to avoid the formation of carbides in weld metal. From the Figure 4, the hardness value is high in HAZ of the banded zone when compared to HAZ of the non-banded zone of the base metal. The measured average hardness value is 209 HBW in HAZ of the banded zone whereas 132 HBW at a non-banded zone of the base metal.

Manganese tends to lower the activity of carbon in austenite. The Mn-rich regions would tend to attract Carbon. During welding, the weld pool temperature is raised to austenite temperature adjacent to weld metal (HAZ). Higher manganese in the segregation zone 1.06 wt% had attributed the formation of manganese carbides. The segregation of carbon 0.28wt% at the banded zone is responsible for the formation of carbides, a hard structure such as Manganese carbide (Mn3C) in HAZ. Therefore, the failure is attributed due to high hardness in the banded zone adjacent to base metal.

The ferrite-pearlite crystal structures are formed by austenite transformation during cooling after the final hot working temperature. The alternative ferrite and pearlite structure of the base metal is shown in Figure 7. Hot rolling process aligns the interdendritic structure and successive transformation on recrystallization during hot rolling. The uniform chemistry is essential for the state-of-the-art steelmaking process. The chemical composition of the steel implies that the compositions of elements are uniformly distributed throughout the sections of the rolled product. The solidification process produces macro and microscopic segregation of chemical elements between liquid and growing solid. The segregation contains with inclusions, and these are residuals from dendrites microstructure, chemical variations and defects produced by solidification shrinkage. The extent of chemical composition and inclusion depends upon the residuals of impurities formed during the solidification process. The undesirable non-metallic inclusions remain in the bath and these inclusions should be captured by the suitable refining process. If the abnormal inclusion found in the solidified ingot, it declines the mechanical properties of the plate after rolling.

The Chemical composition of the base metal and in the segregation, zone is examined through Optical Emission Spectroscopy. From the chemical analysis, the non-metallic low melting point elements such as

Sulphur (S), Phosphorous(P), Lead (Pb) and the metallic elements such as Carbon (C) and Manganese (Mn) are observed on the higher side in the segregated zone. The other traces of elements are captured in the banded zone such as Cr, Ni, Al, V etc. are negligible and not considered for discussion.

Table for chemical composition is not included

According to the modern solidification theory, the mushy zone between liquid-solid phases is a vital region for the formation of Macro segregation. In thermodynamic equilibrium, solubility and chemical potential of elements in solid and liquid phases are different and interdendritic solute elements are redistributed accordingly. Thompson and Howell illustrated the formation of banding process while cooling. The flow of rich interdendritic solute is like a mushy state between liquid and solid. The solute element discharge into liquid results in macro segregation. This mushy state is a vital phenomenon for the formation of macro segregation that leads to the banded zone at the mid thickness of the plate. Manganese and Carbon are considerable variations in substitution of solid solution. Slight variations of Carbon may affect of Manganese on the activity of carbon as proposed by Kirkaldy et al.

Spitzig emphasized in his investigation about banding on the material series with 0.2 wt. % C, 1.0 wt. % Mn with 0.013 wt. % S. He suggested that a high temperature (1315 0 C) heat treatment is required to eliminate the banding. Manganese is a positive segregation element; hence solidification structure contains a higher level of Mn at the banded zone in the continuous rolling slab. According to modern solidification theory, the flow of interdendritic solute rich liquid-solid phase is the vital reason for the formation of macro segregation, because the chemical potential gradient is different in solid-liquid phases.

During cooling, the transformation from molten weld pool to room temperature, any segregation of solute elements precipitate in interdendritic regions and changes in allotropic that occurs at room temperature. The non-metallic inclusion such as Sulphur (0.071 wt. %) is having a greater affinity with manganese and formed manganese sulphide (MnS). Manganese sulphide is a compound which has limited solubility in the weld pool. MnS is one of the non-metallic inclusions compressed in a thin band along the rolling direction resulted in deterioration of tensile properties. In the present investigation, the impurity elements in the base metal are attributed the centerline segregation. This complex constituent formed in the HAZ during welding had influenced the failure in terms of crack and low in tensile value.

On macro examinations of parent material, a dark line of approximately one-millimeter thickness is observed and run through the entire length of the plate in the middle of the plate thickness. The dark band indicates the center line segregation. Crack length of 3 mm is shown in Figure 5 on either side of the butt joint and crack is propagated from weld to parent metal along the center line segregation region. The crack is magnified and shown in Figure 6.

The crack initiated at HAZ and penetrated of base metal is clearly shown in Figure 6. In double V groove joint configuration, the mid thickness of the base metal is prepared as root face for the double groove butt joint. The electric arc is initiated at root face and further layers are followed on the front side and subsequently background and welded on the rear side. The mid thickness of the butt joint is heated localized to austenite temperature repeatedly. From the chemical composition examination at the banded zone, abnormal segregation such as Sulphur (0.071wt.%) and phosphorus (0.036 wt.%) is observed in the banded zone. Sulphur and Phosphorus are on the higher side in the HAZ made weld metal brittle and initiated crack in HAZ, and penetrated into the base metal.

The Scanning electron microscope (SEM) is a useful technique to characterize the morphology, topology, and detailed surface structural elements of various materials. The inclusions in the groove butt joint influence the physical properties of the joint. Therefore, it is decided to investigate the type of inclusions presented in the groove joint and which element attributed the joint failure. SEM image revealed clearly, the true morphology of the inclusions. Several inclusions such as Alumina, Silica, etc., and defects like cavities and bubbles are captured in the segregated zone and these are shown in Figure 8A, 8B and 8C.

From Figure 8B, the A12 03 and MnO are observed as inclusion. Aluminum is added to liquid steel to reduce the oxygen presented in molten steel in ladle. During the steel refining process, the non-metallic inclusions in the form of oxides are captured by the slag. When these oxides are not able to capture by the slag, they remain in steel. These inclusions are segregated at a mid-thickness of the plate during rolling. The A12 03 and MnO are found in the segregated zone had dominated the degradation of mechanical properties rather than banding. Spherical shaped holes are induced by the escape of gases during solidification. Irregularly shaped holes having interdendritic cavities called micro porosity are presented in the banded structure. From Figure 8B and 8C, the manganese sulphide inclusions are observed along the boundary of former bubbles and interdendritic cavities. These inclusions are formed by precipitation within the liquid phase due to the decrease of the solubility of the chemical species contained in the steels. The undesirable compound such as manganese sulphide (Mn), with a melting point of 1620 0C and lead sulphides (PbS) melting point 1114 0 C are showed in the form of thin films along the grain boundaries and at the segregated zone respectively. These inclusions are the major factors which are initiated the crack at a mid-thickness of steel plate.

Figure 9 illustrates selected location in banded zone (EDS) in accordance with an embodiment of the present disclosure. Energy Dispersive Spectroscopy (EDS) analysis is carried out on the prepared surface of the selected segregation zone. The banded zone identified for EDS is indicated in Figure 9. The abundant elements like Sulphur, Aluminum, Silicon and Manganese are captured at the identified zone, where the maximum elements are segregated and reported. The other zone is not considered where inclusions are low. The elements detected at a segregated zone are also aligning with the chemical composition identified using through Optical Emission Spectroscopy. The elements like Carbon 6/2.5 atomic wt./Norm. Wt.%, Sulphur 16/4.8 atomic wt./ Norm. Wt. %, Manganese 25/5.38 atomic wt./ Norm. wt. %, Silicon 14/8.32 atomic wt./ Norm. wt. % and balance Iron (Fe) are captured at the identified banded zone.

Figure 10 illustrates abundant elements in banded zone in accordance with an embodiment of the present disclosure. Heavy atomic weight elements absorbed high eV and proportional with energy counts which are captured through EDS is shown in Figure 10. These abundant harmful elements (S, Si & Al) are segregated in the banded zone and degraded the mechanical properties of the welded groove butt joint. These elements are presented as inclusion in the banded zone and enhanced the formation of oxides, and compounds during welding heat input that resulted in failure.

Normalized rolling is even streamlined for plate rolling processes; it may fail to eradicate the segregation of non-metallic inclusions at a mid thickness of the plate. The precipitation of non-metallic inclusions at the segregated zone is enhanced the non-homogenous structure during welding and resulted in groove butt joint failure.

This extensive investigation concluded that.

1. The cup and cone fracture occurred at lower tensile strength 394 N/ mm2 against 410 N/ mm2 in one side of HAZ and a crack is observed on another side of HAZ. The failure is attributed due to abnormal segregation in the mid thickness of the base metal. The abnormal inclusion decreased the mechanical properties of the plate groove butt joint weld in terms of failure. The reduction of tensile strength is 3 .9 % when compared to base metal strength.

2. The weld metal had not experienced the failure due to the addition of the alloying element in the coated flux to the core wire of an electrode. The coated flux enhances the removal of impurities and to prevent the formation of segregation in the weld metal.

3. Corner opened to the length of 3 mm on both sides of the root at a mid-thickness of HAZ during side bend test. Double groove butt joint is experienced by repeated localized heating at the root during welding as the process sequence warranted. Therefore root is heated to austenite temperature repeatedly. Low melting elements Sulphur (0.071 wt %) and Phosphorus (0.036 wt %) are on the higher side in the HAZ. The difference in solidification temperature between metallic and non-metallic compounds created micro voids and developed brittle, which initiated crack in HAZ and penetrated into the base metal.

4. Hardness value (Brinell) remains 209 HBW in the HAZ with the banded zone against 132 HBW at the non-banded area of the base metal. The segregation of carbon (0.28 wt %) in the banded zone is mainly attracted by Mn-rich (1.06 wt %) banded zone and therefore the formation of Manganese carbide (Mn3C). High hardness in the banded zone is due to segregation of carbon and manganese and hardness is 3 9 .3 9 % higher than that of the non-banded zone.

5. The chemical composition like Sulphur (0.071 wt%), Lead (0.011 wt%) and Manganese (1.067 wt%) captured using Optical Emission Spectrometer are observed on the higher side. Sulphur reacted with Manganese and Lead, together formed Manganese sulphide (MnS) and Lead sulphide (PbS) in the weld zone.

6. The segregated surface is scanned using Scanning electron microscope and EDS analysis. The abundant elements such as Mn, Si, S, Al are captured through EDS. These elements are mainly responsible for the formation of compounds (MnS, PbS) and oxides (A1 20 3 , MnO) in HAZ.

7. The oxides (A1 2O3 ,MnO) and non-metallic compounds (PbS, MnS) developed in HAZ during welding had degraded the weld joint. The non- homogenous structure constituted due to segregation in the mid section of the base metal is responsible for failure during tensile and side bend test of the welded test specimen.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims

WE CLAIM

1. A method to identify the influence of non-metallic inclusions in segregated banded-zone during plate groove butt joint welding, the method comprises:

preparing two production test plates of size length 300 mm, width 150 mm and thickness 63 mm which is connected on one end with a production plate groove joint; welding weld tabs with both ends to get defect-free weld at ends and thereby attaching weld tabs at the ends of groove butt joints to avoid build up crater crack during welding; preheating base plate to 150degree Celsius and welding root pass with electrode diameter 3.15 mm and subsequent layers and thereby making passes with electrode diameter 4 and 5 mm; backgrounding root weld after completing weld on a first side and thereafter performing liquid penetrant test in the root weld to ensure soundness of the weld metal; filling the groove with multi-pass layers which is completed on the second side with the same sequence; cleaning slag and other debris and maintaining inter-pass temperature of 280-300degree Celsius for each layer during welding; radio-graphing the production plate groove butt joint and test coupon and thereafter stress relieved at 625degree Celsius; and subjecting the processed groove butt joint test plate to various tests for process integrity and quality of the joint on further assembly.

2. The method as claimed in claim 1, wherein hot rolled medium and high tensile structural steel to low carbon steel specification IS 2062 grade E 250 BR under normalizing rolled condition and ultrasonically tested plate is used for fabrication of boilers supporting structure.

3. The method as claimed in claim 1, wherein the 63 mm thick production plate with double V groove butt joint is made with 2 mm root gap as per welding procedure specification (WPS).

4. The method as claimed in claim 1, wherein shielded metal arc welding (SMAW) process is employed with electrode preheated to 200degree Celsius and baked to 120degree Celsius (AWS-E 7018) for the welding process.

5. The method as claimed in claim 1, wherein eight layers are laid to complete the groove on either side of the plate excluding root pass and 18 layers are deposited to complete the groove butt joint.

6. The method as claimed in claim 1, wherein test specimens are prepared from production test plate to identify root cause of failure of production test coupon specimens through various tests including tensile, hardness measurement, macro, micro examination and analysis through the scanning electron microscope.

7. The method as claimed in claim 6, wherein side bend test is carried out with the specimen prepared from a groove butt joint test coupon results opening of corner at a bent region measuring up to length 3.0 mm, wherein bend test is carried out on the specimen prepared from the base metal and found that the specimen bent smoothly without opening.

8. The method as claimed in claim 6, wherein the hardness (Brinell) measurement is carried out with an indenter diameter of 2.5 mm, and an applied load 187.5 kg at room temperature 23degree Celsius on a segregated zone of base metal and un-affected base metal.

9. The method as claimed in claim 6, wherein ASTM E 340-13 method is followed for macro examination on the full section profile of welded test plate results that the crack initiated and propagated to the length of 3 mm from weld metal into base metal at the mid thickness on both sides of the base metal.

10. The method as claimed in claim 6, wherein chemical compositions of base metal and in the segregated zone of base metal are examined by using optical emission spectrometer.