1-s2.0-Flash butt welding application on 16MnCr5 chain steel and investigations of mechanical properties-main

Materials

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Materials and Design 27 (2006) 1187–1195

& Design

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Flash butt welding application on 16MnCr5 chain steeland investigations of mechanical properties

Cemil Cetinkaya *, Ugur Arabaci

Gazi Universty, Techical Education Faculty, Metalurgy Department, 06500 Teknikokullar, Ankara

Received 15 October 2004; accepted 1 February 2005Available online 7 April 2005

Abstract

In this study, 16MnCr5 chain steels were welded by flash butt welding and welded samples were annealed. Their microstructureand mechanical properties have been investigated. Upsetting current time was chosen as 1.6 s and build up pressure was chosen as 2,2.5, and 3 bar. It is pointed out that welding parameters and annealing affected the mechanical properties. For all samples, the high-est hardness was measured from weld metal. Non-annealed samples gave the highest tensile strength with the parameter of highestbuild up pressure. It is also found that annealing reduces the tensile strength of all samples.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Flash butt welding; Resistance welding; Mechanical properties; Chain steel

1. Introduction

There are some sorts of welding methods accordingto the materials to weld, processing and aim of the weld-ing. Flash butt welding is a resistance welding methodwhich consists of electrical heating and hydraulic forg-ing [1,2].

Slug residues, porosity and micro strain are disadvan-tages of the fusion welding. Solid state welding methodshave some advantages because no melting occurs andcauses little welding defect [3,4].

Surfaces of sample are not roughened. In the touch-ing surface, there are some areas which have high electri-cal resistance because of not touching areas. This highelectrical resistance causes high heat generation [5,6].Touching points are suddenly melted because of highheat generation. These small melt volumes are thrownto out of welding area by inflating. Then, new craters

0261-3069/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.matdes.2005.02.002

* Corresponding author.E-mail addresses: [email protected] (C. Cetinkaya), uarabaci@

gazi.edu.tr (U. Arabaci).

and touching points are formed. This process is repeateduntil the joining surface is replaced by getting the mobileparts closer. After having the complete surface melted,pressure to the joining surfaces is suddenly increased.At this stage, whole areas in both surfaces touch eachother. Friction between surfaces causes sparkling andconsequently melting. Sparkling time for a metal isdependent on thermal conductivity, geometry of patsand sparkling cycle [7–9].

In this study, the flash butt welding of 16MnCr5 steel,which is used mostly in chains, was studied. By holdingthe build up current time constant, build up pressure isincreased. The effect of build up pressure on welding isinvestigated.

2. Materials and methods

2.1. Materials

The chemical composition of the 16MnCr5 steel is gi-ven in Table 1. The dimensions of the sample are 100 mm

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mailto:uarabaci@ gazi.edu.tr

mailto:uarabaci@ gazi.edu.tr

Table 1Chemical composition of 16MnCr5

Cr (%) C (%) Mn (%) Si (%) Mo (%) Ni (%) Co (%) P (%) Al (%) S (%) Fe (%)

1.04 0.143 1.170 0.188 0.030 0.061 0.020 0.010 0.023 0.019 97.324

1188 C. Cetinkaya, U. Arabaci / Materials and Design 27 (2006) 1187–1195

of length and 18 mm of diameter. For investigative pur-poses, ninety welded samples were cut to work on.

2.2. Experimental procedure

Cleaned samples were welded by using the SCHA-LATTER TYPE flash butt welding machine, which isowned by YAPAS CHA_IN FACTORY located in OS-TIM Ankara. Through the welding process, faces arekept clean to prevent the forming of a film between join-ing surfaces. The welding parameters mentioned beloware kept constant:

VoltageAmpermeterArc heating timeTouching timeVice pressureMachine pressure

Welding parameters were chosen by taking into ac-count the specifications of welding machine. The buildup pressures were chosen as 2; 2.5 and 3 bar, while buildup current time as 1.6 s. Five samples for microstruc-tural investigation and five samples for tensile test wereprepared by using the parameters given in Table 2.

Table 2Applied parameters

Code Buildingpressure(bar)

Building currenttime (s)

Heat treatmentafter welding

Number ofsamples

A 2 1.6 Not applied 15B 2.5 1.6 Not applied 15C 3 1.6 Not applied 15I-A 2 1.6 Applied 15I-B 2.5 1.6 Applied 15I-C 3 1.6 Applied 15

0

160

320

480

640

800

0 4 8 12 16 20 24 28 32 36 40 44

Time (Hour)

Hea

t

Fig. 1. Heat treatment profile applied after welding.

Samples were separated into two groups. One groupis heat-treated and the other one is not heat-treated.The heat treatment profile is given in Fig. 1. The heat-treated samples are coded as ‘‘I’’ (Table 2). Sampleswere heat-treated at 780 �C for 4 h, then left cooled inthe furnace. Standard metallographic method was usedto prepare the samples for microstructural examination.Two percent nital was used as etching media. Prior typeoptical microscope was used to examine the microstruc-ture. Hardness measurement was carried out by usingInstron Wolpert type hardness measurement machine.JSM 500 type JEOL Scanning Electron Microscopewas used to photograph the fracture surface. By usingthe same scanning electron microscope, EDS analysiswas also carried out.

3. Results and discussion

3.1. Hardness results

In Fig. 3, hardness profiles of the welded samplesare given. Samples A, B and C were not heat-treated.Welding of these samples was carried by using 1.6 sbuild up current time. Two bar for A and I-A, 2bar for B and I-B and 3 bar for C and I-C were usedas build up pressures.

100120140160180200220240260280300320340360

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8

Distance to welding center (mm)

Har

dn

ess

Val

ue

(Vic

kers

)

A

B

C

I-A

I-B

I-C

Fig. 3. Hardness profile of heat-treated and not-heat-treated weldedsamples.

7-7 -5 50

Fig. 2. Hardness measurement points from welded samples (0 is weldcenter).

C. Cetinkaya, U. Arabaci / Materials and Design 27 (2006) 1187–1195 1189

It is seen from Fig. 3 that the highest hardness value ismeasured from weld metal of non-heat-treated samples.The highest hardness values of weld metal are 298, 330and 344 Hv for the samples A, B, and C, respectively.

The increase of hardness can be contributed to thedeformation that was caused by increased pressure. Itis reported by Yılmaz [10] that maximum hardnesswas measured from the HSS side of joining line andhardness of joining line and adjacent area was increasedbecause of deformation. It is also reported by Cive-lekoglu [11] that the highest hardness value was mea-sured from the welding zone of flash butt weldeddifferent couples. Hardness was reduced while measur-ing point changing from welding center to base metal.As it is shown in Fig. 2, on the measuring point of #5,250, 248 and 251 Hv hardness values were measured

Fig. 4. Microstructural pictures of sample A (280·): (a) Base metal, (b)HAZ and (c) Weld metal.

for the samples A, B and C, respectively. As schemati-cally shown in Fig. 2, hardness was reduced from mea-suring point of #5 to base metal, however, thisreducing is not as high as it is in the welding zone.

When the hardness graphs of heat-treated samplesI-A, I-B and I-C were examined, it is seen that hardnessof all areas was reduced because of heat treatment, how-ever, hardness of weld zone was higher than that ofother zones. Lamellar cementite in the pearlite wastransformed into granular cementite by heat treatmentof welded sample. This transformation of cementite re-duced the hardness of welded sample. In the weldedzone, hardness values were reduced from 298 to175 Hv, from 330 to 180 Hv and from 340 to 188 Hvfor the samples A, B and C, respectively. The lowesthardness value was measured from measuring point 5

Fig. 5. Microstructural pictures of sample I-A (280·): (a) Base metal,(b) HAZ and (c) Weld metal.


(Fig. 2). The lowest values were 153, 152 and 151 Hv forthe samples A, B and C, respectively. Hardness increases2–3 Hv while going to base metal from weld metal sameas it isfor the non-heat-treated samples.

3.2. Microstructural results

In this section, microstructures of base metal, HAZand weld metal will be examined. Effect of build up pres-sure and heat treatment on the microstructure of weldmetal and HAZ will be discussed.

In the pictures of A and I-A dark, areas represent thepearlite phase and grey areas represent the ferrite phase(Figs. 4 and 5). As it is seen from Fig. 4(a), the micro-

Fig. 6. SEM pictures of fracture surfaces

Fig. 7. EDS results of sample A: (a) From

structure of base metal of the sample A, there are pearlitecolonies among the large ferrite grains. These pearlitecolonies are not distributed homogeneously but gatheredon some areas. The microstructure of HAZ is shown inFig. 4(b). In the HAZ zone, pearlite colonies were smal-ler and distributed homogenously because of heat andpressure. Weld metal microstructure in Fig. 4(c) presentsfine and long grains. These fine and long grains are asic-ular ferrite [12].

Heat treatment effect on welded samples is shown inFig. 5. Lamellar pearlite transformed to sphericalcementite after heat treatment. When both Figs. 4(a)and 5(a) are examined, it is seen that heat treatmentcaused small grains and pearlite colonies are scattered

of: (a) Sample A, (b) sample I-A1.

point 1, (b) from point 2 in Fig. 6(a).


homogenously. The same thing can be said for the HAZzone too. In the weld metal zone, widmanstaten ferritephase was formed and the amount of ferrite was in-creased after heat treatment.

It is seen from Fig. 6(a) that the fracture surface ofsample A is not smooth. There are several craters onthe fracture surfaces.

The fracture surface of annealed sample is rathersmooth (Fig. 6(b)). EDS analysis of point 1 inFig. 6(a) is shown in Fig. 7(a). Elemental analysis ofpoint 1 in Fig. 6(a) shows 57.096% Fe and 42.456%Mn. The other EDS analysis of point 2 in Fig. 6(a)is shown in Fig. 7(b). That point contains 96% Fe,2.2667% Cr and 1.203% Mn. Such a difference canbe contributed to the different distance to the weldingpoint.

Fig. 8. Microstructural pictures of sample B (280·): (a) Base metal,(b) HAZ and (c) Weld metal.

Applied force was increased with increasing build uppressure. The microstructure of base metal, shown inFig. 8(a), is similar to the microstructure shown inFig. 4(a). Ferrite grains are gathered while pearlite colo-nies scattered randomly among ferrite grains of sampleA. After heat treatment, ferrite grains become smallerand are distributed regularly in the HAZ of sample A(Fig. 8(b)). Weld metal of sample A exhibits a mixtureof pin-like and dendiritic grains (Fig. 8(c)).

After heat treatment, base metal of sample A(Fig. 9(a)) has smaller ferrite grains than that of sampleB (Fig. 8(a)). Base metal of sample A exhibits a homog-enous distribution of ferrite grains. Pearlite ratio re-duced in the HAZ zone of heat-treated sample I-B. Inthe zone of weld metal of heat-treated sample, widman-staten ferrite ratio increased more than does in the zone

Fig. 9. Microstructural pictures of sample I-B (280·): (a) Base metal,(b) HAZ and (c) Weld metal.


of not heat-treated weld metal (Fig. 8(c)). Laminarwidmanstaten grain structure is also seen.

SEM micrograph of fracture surface of HAZ ofsamples is shown in Fig. 10(a). EDS analysis of point1 from micrograph in Fig. 10(a) is shown in Fig.11(a). The composition of this point is 77.393 wt%Al, 11.545 wt% Fe and 10.585 wt% Mn. In point 2 ofmicrograph in Fig. 10(a), Fe amount is increased con-siderably (98.153 wt%). Cr, Mn and Si ratios are 0.873,0.621 and 0.353 wt%, respectively. It can be seen fromSEM picture of fracture surface of this sample thatheat treatment reduced the mean grain size of HAZ

Fig. 10. SEM pictures of fracture surface

Fig. 11. EDS results of sample B: (a) From p

(Fig. 10(b)). Black points are cavities on the fracturesurface.

Samples were also welded by increasing the build uppressure to 3 bar from 2.5 bar. Microstructure of thissample, shown in Fig. 12(a), resembles the microstruc-ture shown in Figs. 4(a) and 8(a). The dominant phasehere is the ferrite. Little amount of pearlite phase alsoexists. In the HAZ shown in Fig. 12(b), ferrite grainsare smaller than those in the base metal. Pearlite colo-nies are uniformly located in the grain boundaries offerrite phase. Weld metal area (Fig. 12(c)) has needle-shaped grains. There exist same big ferrite grains locally.

s of: (a) Sample B, (b) sample I-B1.

oint 1 and (b) from point 2 in Figure.

Fig. 12. Microstructural pictures from sample C (280·): (a) Basemetal, (b) HAZ and (c) Weld metal.

Fig. 13. Microstructural pictures from sample I-C (280·): (a) Basemetal, (b) HAZ and (c) Weld metal.

Fig. 14. SEM pictures of fracture surface of HAZ: (a) Sample C, (b) Sample I-C.


Fig. 15. EDS results of sample C: (a) From point 1 and (b) from point 2 in Fig. 14.

Table 3Test parameters and tensile strength of samples

Sample Pressure(bar)

Build uptime (s)

Maximum tensilestrength (N/mm2)

A 2 1.6 670B 2.5 1.6 684C 3 1.6 698I-A 2 1.6 479I-B 2.5 1.6 485I-C 3 1.6 490


It is seen from the picture in Fig. 12(c) that weld metalarea has small amount of dendritic grains.

The annealing affected the shape and size of all the threezones of welded samples. When the annealed and unan-nealed welded samples were compared, it is seen that fer-rite grains are distributed homogenously in the annealedone (Fig. 13(a)). Microstructure of HAZ of annealed sam-ples showed that annealing increased the pearlite amount(Fig. 13(b)). Grain size of HAZ of annealed sample issmaller than that of unannealed sample. Weld metal ofthe annealed sample has mostly nodular ferrite grainsand little amount of laminar grains (Fig. 13(c)).

The widmanstaten ferrite phase ratio is gradually in-creased as seen in Figs. 5(c), 9(c) and 13(c) and conse-quently hardness is increased.

There are several dark points on the fracture surfaceof welded sample C (Fig. 14(a)). EDAX analysis showedthat chemical composition of point 1 is 84.83% Fe,9.583% Mo, 3.651% Mn and 1.003% Cr. SEM micro-graph of the same sample (Fig. 14(b)) showed that thegrain size of this sample got finer after annealing.EDAX analysis of this point in Fig. 14(b) showed thatsamples compositions is 97.591% Fe and small amountof other components. Numerical amounts of elementsare given in Fig. 15.

3.3. Tensile test results

Tensile test parameters are tabulated in Table 3. Pull-ing speed was kept at 2 mm/s. The results are shown inFig. 16.

All fractures were taken place in the HAZ. Thatshows that weld metal has higher strength than HAZdoes. It is seen from the graph in Fig. 16 that, increasingbuild up pressure increases the tensile strength becauseof deformation. Samples A, B and C have the tensilestrengths of 670, 684 and 698 N/mm2, respectively.

Annealing of the welded samples reduced the tensilestrength but the relationship between tensile strengthand build up pressure appears to be like unannealed

400

450

500

550

600

650

700

750

1.5 2 2.5 3

Buildup pressure (Bar)

Max

. Ten

sile

str

eng

ht

(N/m

m2)

unannealed

annealed

Fig. 16. The relationship between tensile strength and build uppressure.


one. Micropictures of the annealed samples suggest thattransforming of pearlite to spherical cementite becauseof annealing reduces the hardness consequently reducingthe tensile strength.

4. Results

The results of flash butt welding of 16MnCr5 steel aregiven as follows:

1. Increasing build up pressure increases the hardness ofweld zone.

2. The highest hardness was measured from the weldmetal for all samples.

3. Full annealing of welded samples reduced the hard-ness of base metal and weld metal reduced the hard-ness difference between base metal and weld metal.

4. Annealing reduced the tensile strength of weldedsamples.

References

[1] Tulbentci K, Yılmaz M. Flash-butt welding, Weldingworld. _Istanbul: Birsen Co.; 1990. p. 14–25.

[2] Cali·s�kan O. Weldability of welding techniques of aluminum andaluminum alloys. M.Sc. Thesis, Marmara University, Institute ofScience and Technology, _Istanbul, Turkey; 1994, p. 5–65.

[3] Suzuki M, Endo Shigero, Yosetso GR. Effect of PWHT on TMCPsteel flash butt welded joint. Q J Jap Weld Soc 1990;8(2):58–64.

[4] Anık S. Handbook for welding: methods and elements, 1. _Istanbul,Turkey: Birsen Co.; 1983. p. 40–50.

[5] Sprow DL. Flash-butt welding – new and future pipelineapplication. In: Proceedings of the pipeline technology confer-ence, Ostend, Belgium. p. 112–8.

[6] Ylmaz M, Karagoz S. Micro analysis application in the fussionwelding. In: XI national electron microscopy symposium, Edrine,Turkey. p. 163–5.

[7] Kuchuk S. Experince of flash-butt welding application in pipelineconstruction in the USSR. In: Proceedings of the PipelineTechnology Conference, Ostend, Belgium. p. 37–9.

[8] Trompler Jr Ruben. Flash butt welding of crane rail. Iron SteelEng 1996;73(10):42–4.

[9] Thomas K, Michailov V, Wohlfahrt H. Toughness investigationson narrow process- affected zones of resistance-butt. Weld Cut2000;52:254–62.

[10] Yılmaz M, Kaluc E, Tulbentci K. Investigation of weld zone offlash-butt welded C45 plain carbon steel and (HSS 6-5-2) highspeed steel. Sci Technol Weld Join 1993:286–8.

[11] Civelekoglu F. Examination of welding parameters and investi-gation of weld zone of flash-butt welded Ck60 plain carbon steeland (S-6-5-2) high speed steel. A thesis for the degree of Assoc.Prof., Istanbul Technical University, Institute of Science andTechnology, _Istanbul. Turkey; 1971, p. 7–59.

[12] Yukler A _Irfan. Weld metal. _Istanbul, Turkey: Erdini Co.; 1979.p. 17–60.

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1-s2.0-Flash butt welding application on 16MnCr5 chain steel and investigations of mechanical properties-main