Material Characterization of Explosion Welded Clad Plate of Carbon Steel and Alloy 825

International Journal of Scientific Research and Review ISSN NO: 2279-543X

MATERIAL CHARACTERIZATION OF EXPLOSION WELDED CLAD PLATE OF CARBON STEEL AND ALLOY 825

Kamal Kishore Research Scholar, Department of Mechanical Engineering, O.P.J.S. University, Churu, Rajasthan, India, E-mail: [email protected] Dr. Mohammad Israr Professor, Department of Mechanical Engineering, Sur University College, Sur, Sultanate of Oman E-mail: [email protected] Dr. Jai Dev Chandel Senior Vice President – Operations, Jindal Saw Ltd, Samaghogha, Gujarat, India E-mail: [email protected] Abstract

The petrochemical, oil and gas industries are always looking for the economic and best suitable material

for the critical operating atmosphere. The project and operational cost can be reduced by selecting the

suitable material by considering corrosion and temperature of the service. Suitable alloy system can be

used for the operating service. The usage of clad plates is one of the better solutions for the above

statement. In clad plates, two different materials are metallurgically bonded where one material take care

of structural strength whereas other corrosion.

In this work the carbon steel and UNS N08825 (alloy 825) clad plate was investigated for its structural,

corrosion and metallurgical properties. The plate was metallurgically bonded by explosion bonding

(welding) process and a comprehensive testing program is used for characterization of the explosion

bonded clad plate. The plate was investigated for mechanical tests like tensile, impact test, shear bond test

and micro hardness test. The structural steel material grade was API 5L X60M and the grade of CRA was

UNS N08825 (alloy 825). The interface was evaluated by optical microscope and SEM (Scanning electron

microscope). The CRA was tested for corrosion properties as per ASTM G48 and ASTM A262 Practice E.

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During the microscopic investigation, it is observed that the waves formed during explosion welding have

different grain structure at interface. The peak point of carbon steel has finer grains than in rest of the wave

locations. All the tests are compared with the API 5LD specification and found acceptable.

Keywords: CRA, characterization, line pipe, corrosion, clad, SEM, explosion welding

I. Introduction

The clad plates are widely used for their better structural strength and corrosion resistance properties; the

clad plate exhibits the lower weight and cost requirement compared to the whole CRA (corrosion resistant

alloy) material. Clad steel is a composite product developed to provide effective and economic utilisation

of expensive materials. The cladding layer which will be in contact with corrosive environment is made of

corrosion resistant alloy whilst the less expensive backing steel provides the strength and toughness

required to maintain the mechanical integrity. As high strength backing steel can be utilised, the wall

thickness can be reduced relatively to the solid CRA thus reducing fabrication time and cost [1].

Clad plates are used for pressure vessels, heat exchanger, columns and pipeline construction. The

metallurgical bonded clad plates can be manufactured by roll bonding, weld overlay and explosion welding

(bonding) processes. Every process of clad plate manufacturing is having its advantages and disadvantages

in terms of their manufacturing processes, like in weld overlay method of cladding is highly time

consuming process and the dilution from base metal to cladding metal is an issue to achieve a required

chemical composition at lower level of weld metal deposition. The mechanical properties can be greatly

affected in weld overlay due to the heat of welding. The chemical heterogeneity results from the

solidification process and is manifested by dendritic segregation. The intense microsegregation primarily

of such elements as Nb and Mo leads to formation of secondary phases and as a consequence reduces the

corrosion resistance of the overlaid alloy [2-5]. The explosion bonded clad materials do not have the

dilution problem as explosion bonding is a solid state welding (diffusion) process which produces the

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metallurgical bond between similar or dissimilar metals [6]. Moreover, this method can be applied to bond

materials those neither be joined by conventional bonding methods nor they bond in general [7, 8].

Compare to the weld overlay the effect of heat transfer is lesser in explosion bonding.

Explosion driven impact welding is true example of multidisciplinary research as the phenomena

associated with it fall under the various branches of engineering science [9]. The explosion bonding

requires a very high degree of skills. There are two types of explosion welding. The oblique and parallel

configurations are used for manufacturing of clad plates. The oblique configuration is shown in Fig. 1a.

This method came into play when the size of the plate is thin and small but when plate is larger than

parallel method is taken as shown in Fig.1b [10, 11].

(a) (b)

FIG. 1 The view of explosion welding methods oblique (a) and parallel (b)

In parallel method, the plates to be welded are cleaned and polished very gently to achieve the good

bonding. In this process the base plate (parent plate) is kept on the ground, a flyer plate is placed at the top

of it by predefined distance called “standoff” distance. The design of the standoff should be able to bear

and handle the load of the flyer plate and explosive, above this a buffer sheet is kept at the surface of flyer

plate to protect the top surface from damage due to the shock impact of explosion. Now the prepared

explosive is placed in a box structure designed at the perimeter of the flyer plate which is placed at the top

of the flyer/buffer plate [11]. The velocity of the collision point governs the time available for bonding.

The quality of bond depends on careful control of the process parameters. These include material surface

preparation, plate standoff distance, explosive load, detonation energy and velocity [9, 12].

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When explosive is detonated the explosion releases a very high pressure in a violent manner that progress

and propagate with a wave like nature. The detonation velocity of the explosive must be less than 120% of

the sonic velocity of the material [12]. Both materials (flyer and base metal) colloids at an angle with each

other and a jetting action at collision interface occur. This jet is the product of two pieces of metal surfaces

colliding. This clears the metals and allows to pure metallic surfaces to be joined under extremely high

pressure [11]. Therefore, these are not the original surfaces that are put together, but the fresh, unaffected

metals which are below the original surface layers. Also during this process, regions of molten material

may appear in the interface [13]. Even though the heat is not externally applied in making an explosion

weld, it appears that the metal at interface is molten during welding [14-16].

This work is carried out to analyse the material characterization of parallel explosion clad plates of carbon

steel API 5L X60M grade and CRA of UNS N08825 (alloy 825). The clad plate was produced for

manufacturing the CRA clad pipes as per API 5LD, Specification for CRA Clad or Lined Steel pipes [17].

II. Experimental/ Materials and Methods

The material used for this experimental study was a clad plate produced by explosion welding process. The

backing steel was API 5L X60M grade steel and the CRA (corrosion resistance alloy) was UNS N08825

grade. The nominal thickness of the carbon steel plate was 15.88 mm and the CRA was 3.0 mm thick.

The chemical composition of both the materials were analysed by optical spectrometer and the results are

given in Table 1.

TABLE 1

Chemical composition of clad plate

Materials C Si Mn Cr Ni Mo Ti Cu Nb

CS X60M 0.10 0.30 1.52 0.03 0.07 <0.03 0.005 0.04 0.03

Alloy 825 0.01 0.13 0.43 23.0 39.1 3.36 0.62 1.90 --

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The carbon equivalent for base material was PCM 0.19. The steel was produced by TMCP rolling practice.

This grade is widely used for its better weldability and good toughness properties. The UNS N08825 is

having very good corrosion resistance properties in chloride environment whereas normal austenitic

stainless steel grades are not resistant. UNS N08825 is very often used in refineries, chemical processing

units and oil and gas exploration.

The explosion welded clad plate had undergone for various types of test. The tensile properties of carbon

steel and CRA are given in Table 2.

TABLE 2

Tensile properties of clad plate

Material Yield Strength (MPa) Tensile Strength (MPa) % Elongation

CS – X60M 487 567 37

Alloy 825 271 613 48

The CVN impact test values of X60M backing plate was tested at -100C as given in Table 3.

TABLE 3

CVN impact Values of backing plate

Specimen 1 2 3 Average

Values in Joule (J) 390 228 396 338

The clad plate was also tested for its shear bond strength. The sample was prepared in accordance to

ASTM A 265-12 as shown in Fig. 2 and the values are given in Table 4.

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FIG. 2 Shear bond test

TABLE 4

Shear bond strength

Required values Specimen 1 Specimen 2

140 MPa 465 MPa 436 MPa

The Vickers micro hardness test was also performed on clad plate. The profile micro hardness of CRA to

backing plate test was performed at 500 g load and results are shown in Figs. 3a & 3b.

(a)

400 364 350 306 300 270 269 271 269 250 226 229 221 220 222 220 200 150 Load (VPN) Load 100 50 Micro - Hardness at 500 g at 500 Hardness - Micro 0 CRA 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 Layer Distance (μm)

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(b)

450 409 400 374 350 291 294 302 300 285 238 228 250 204 212 207 200 150 Load (VPN) Load 100

Micro Hardness at 500 g at 500 Hardness Micro 50 0 CRA 200 400 600 800 1000 1200 1400 1600 1800 2000 Layer Distance (μm)

FIG. 3 Micro hardness at crest (a) and peak (b)

The guided bend sample of the clad plate was prepared and tested for any discontinuity at the interface.

The clad plate sample was also prepared for the optical microscope and scanning electron microscope

(SEM) where 2% Nital and Marble's reagent was used to reveal the microstructure. The EDS (Energy

Dispersive X-Ray Spectroscopy) analysis of base metal, CRA and interface were also performed.

(a) (b)

CRA layer of Alloy 825 Peak point

Crest point

Backing of CS – API 5LX60M

FIG.4 Macro of explosion welded plate as polished (a) and location marked (b)

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(a) (b)

100X 100X

200X 200X

FIG. 5 Optical microscopic images

(a) base metal microstructure, (b) CRA microstructure,

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(a) (b)

FIG. 6 Scanning electron microscopic images (SEM)

(a) base metal microstructure (b) CRA microstructure,

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(a)

(b)

FIG. 7 EDS analysis at interface CS side (a) and at CRA side (b)

The CRA layer was also undergone for corrosion resistance testing performed according to the ASTM G

48 – 2015, Standard test methods for pitting and crevice corrosion resistance of stainless steels and related

alloys by use of ferric chloride solution [21].

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III. Results and Discussion

The results for various tests shown in Table 1- 3, for the backing plate are meeting the criteria required as

per the API 5LD [17] and ASTM A265 [18]. The values of shear bond test shown in Table 4 exceeded the

requirement of standard (140MPa). The micro hardness test results shown in Figs. 3a and 3b reveals that

interface area between CRA and base material having the different hardness. The peak area is having

higher hardness than the crest area. The indentation was taken at every 200µm distance. As per API 5LD,

the hardness indentation location should be 1.0 mm either side of carbon steel backing to clad alloy weld

interface [17]. In this study, the micro hardness was taken at wavy interface (peak and crest) formed during

explosion bonding. The peak point is having a hardness of 409 HV500 and the crest having the hardness of

364 HV500. The increase in hardness may be caused due to detonation velocity and cold plastic

deformation caused by explosion or sudden (thermal) shock hardening [19].

The bend tests performed on explosion bonded plate do not reveal any crack or discontinuity.

A macro of the clad plate is shown in Fig. 4 which shows the wavy interface. Fig. 5a shows the

microstructure of backing plate (base material) which consist the banded structure of ferrite and pearlite.

The interface was investigated with optical microscope and the differences in grain size were observed.

The peak point in waviness area of carbon steel has the finer grains than in the crest area of the carbon

steel as shown in Figs. 5c and 5d. The microstructure changes significantly at the distance of ≈ 100µm

from the interface and the grain boundary at this region is difficult to reveal. This is possibly due to the

intense plastic deformation close to the interface [7, 19].

Fig. 6 shows the SEM analysis of the clad specimen, the Figs. 6c and 6d shows the peak area of the base

material is having fine microstructure and crest area is having the coarser grain structure. This is because

of plastic deformation and heat generation during the explosion process. The peak area experienced higher

cooling rate than the crest area, due to this grain growth at the crest interface is observed. If we go little bit

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far from the interface into the base metal area, the recrystallized microstructure is observed. One of the

most important features is a pronounced increase of the dislocation density and an extremely strong grain

refinement in the parent sheet near the interface [20]. Fig. 6b shows the CRA area which is the fine grain

nickel based solid solution with twins and strain induced microstructure.

The EDS analysis of clad specimen in different zone is shown in Figs. 7a and 7b. In Fig.7a, the area of

backing steel is having diffusion of nickel and chromium in the matrix. In Fig. 7b, the area at CRA

interface side reveals the diffusion of iron particles in the austenitic reason. Apart from this, the fine

particles of Mn, Si, Cr and Fe are also observed in the interface area. The fine particles are more probably

formed during the explosion process. It is evident that nickel and chromium elements diffused from alloy

825 to carbon steel.

IV. Conclusions

 The study done for material characterization of the explosion welded plate reveals that the

microstructure at peak and crest area are different and the interface has fine particles of diffused

chromium and nickel.

 The mechanical properties are meeting the requirements of the API 5LD. No crack was observed in

guided bend test.

 The shear bond strength exceeded the required values of 140 MPa.

 The corrosion test was conducted and no pitting and cracking was observed under optical

microscope.

V. ACKNOWLEDGEMENT

The authors are extremely thankful to the M/S Jindal Saw Ltd. and its employees for their extremely

appreciable support during the experimental work.

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VI. References

[1] Smith, L., “Engineering with Clad Steel” Nickel Institute Technical Series No 10064,

www.nickelinstitue.org

[2] Rozmus-Gornikowska, M., Cieniek, L., Blicharski, M., and Kusinski, J., “Microstructure and

microsegregation of an Inconel 625 weld overlay produced on steel pipes by the cold metal transfer

technique” Archives of metallurgy and materials, Vol. 59, No. 3, 2014 , pp. 1081 – 1084

[3] DuPont, J.N., “Solidification of an alloy 625 weld overlay” Metallurgical and Materials Transactions

A 27 A, 1996, pp. 3612-3620

[4] Cieslak, M.J., “The welding and solidification metallurgy of alloy 625” Welding Research Supplement,

1991, pp. 49-56

[5] Silva, C.C., Miranda, H.C., Motta, M.F., Farias, J.P., Afonso, C.R.M., and Ramires, A.J., “New insight

on the solidification path of an alloy 625 weld overlay” Journal of Materials Research and Technology

Vol. 2, No. 3, 2013, pp. 228-237

[6] Blazynski, T.Z., “Explosive Welding, Forming and Compaction” Applied Science Publishers LTD,

New York, 1983.

[7] Varavallo,R., Moreira,V., Paes,V., Brito,P., Olivas,J., and Pinto, H.C., “Welding induced residual

stresses in explosion cladded AL-6XN superaustenitc stainless steel and ASME SA516-70 steel

composite plates” Advanced Materials Research , Vol. 996, 2014 , pp. 451- 456

[8] Zdrodowska,K., Wojsyk,K., and Szala.M , “The microstructural properties of explosion welded Ni/Ti

joint” Advances in science and technology research journal, Vol. 8, No. 22, 2014, pp. 71–74

[9] Mousavi, A.A.A., and Al-Hassani, S.T.S., “Numerical and experimental studies of the mechanism of

the wavy interface formations in explosive/impact welding”

Journal of the Mechanics and Physics of Solids, Vol. 53, No. 11, 2005, pp. 2501-2528

Page 13 of 15

Volume 8, Issue 2, 2019 Page No: 453 International Journal of Scientific Research and Review ISSN NO: 2279-543X

[10] Sherpa, B.B., Pal, D.K., Batra, U., Upadhyay, A., and Agarwal, A., “Study of explosive welding

process and applications” Advances in applied physical and chemical Sciences - A sustainable

approach - ISBN: 978-93-83083-72-5, pp. 33-39

[11] Prof. Dr. Cvetkovski. S., “Investigation properties of explosive welded joints between structural steel

and high alloyed materials”. Scientific proceedings xiv International Congress “machines

Technologies materials, Vol. 3, 2017, pp 183-186

[12] Merriman, C., “The fundamentals of explosive welding explosion welding” Welding journal, July

2006, pp. 27-29

[13] Song, J., “Microstructure and properties of interfaces formed by explosion cladding of Titanium to

low carbon steel” Dissertation, Ruhr-Universität Bochum, 2011, pp. 17-18.

[14] Mateša, B., Samardžić,I., and Dunđer ,M., “ Heat treatment influence on clad dissimilar joints

weakness” Tehnički vjesnik , Vol. 21, No. 5, 2014, pp. - 1035-1040.

[15] Crossland, B., “Explosive welding of metals and its application”, Clarendon Press, Oxford, 1982.

[16] Simonov, V. A., “Binding criterion for metals with explosion welding. // Combustion, Explosion, and

Shock Waves. 1991, pp. 127-130.

[17] API 5LD Specification for CRA Clad or Lined Steel pipes – 2015 Edition, API Publishing Services,

1220 L Street, NW Washington, DC 20005

[18] ASTM A265 – 12, Standard specification for nickel and nickel-base alloy-clad Steel plate. ASTM

International, West Conshohocken, PA, 2012, www.astm.org,

[19] Acarer M., Gülenç B., and Findik F., “Investigation of explosive welding parameters and their effects

on microhardness and shear strength” Materials and Design, Vol. 24, 2003, pp. 659-664.

[20] Paul, H., Litynska-Dobrzynska, L., Miszczyk, M., and Prazmowski, M., “Microstructure and phase

transformations near the bonding zone of Al/Cu clad manufactured by explosive welding”. Archives of

metallurgy and materials, vol. 57, No. 4, 2012, pp. 1162 – 2012

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[21] ASTM G 48 – 2015, Standard test methods for pitting and crevice corrosion resistance of stainless

steels and related alloys by use of ferric chloride solution, ASTM International, West Conshohocken,

PA, 2015, www.astm.org,

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