National Conference on Advancements and Futuristic Trends in Mechanical Engineering (February 19-20, 2010)

INFLUENCE OF SLAG FLUX MIXTURE ON MECHANICAL PROPERTIES OF WELDS IN SUBMERGED ARC WELDING
Kulwant Singh , Jagtar Singh
a* a

aDepartment of Mechanical Engineering, Sant Longowal Institute of Engineering and Technology, Longowal, Punjab 148106, India *Corresponding author e-mail: engrkulwant@yahoo.co.in

ABSTRACT
Slag generated during conventional submerged arc welding has been recycled by mixing various percentages of crushed slag in fresh flux to use in subsequent runs. The mechanical properties of weld metal prepared using various slag mix have been evaluated. Tensile strength of weld metal using slag-flux mix up to 60% slag in fresh flux was found to be within the acceptable range of AWS (American Welding Society) specifications. The test plates were subjected to visual inspection, dye penetration test and radiography before removing specimens meant for mechanical testing. Test plate prepared using 20% slag mixed in fresh flux cleared radiographic test. Slag detachability and arc stability both were found to be satisfactory. Keywords: Submerged arc welding, Slag-flux mixture, Recycling, Mechanical properties.

1. Introduction
Since the development of the submerged arc welding process (SAW) there have been attempts by technologists and researchers to increase its productivity and to decrease the welding cost. Flux contributes a major part towards welding cost in submerged arc welding process. Weisman [1] has estimated that, in general, one kg of flux is consumed for every kg of weld metal deposited. About 2500 tonnes of flux was consumed in India alone in year of 1982, Visvanath [2] which have risen to 10000 tonnes in the year of 2006, Honavar [3]. Such a large quantity of flux, after welding, becomes slag waste and has to be disposedoff. Attempts have been made by researchers and engineers to process fused slag in such a manner that allow it to be used as a flux in submerged arc welding for shielding. Eagar et al. [4] investigated that the reuse of fused slag is economical in submerged arc welding of titanium. Beck and Jackson [5] found that if it is processed properly and according to the code requirements, recycled slag can be reliably used as an alternative to fresh flux. They further claimed a saving up to 50% of the total cost of purchased flux by recycling the slag. Motivated by their concept, Singh et al. [6] attempted to recycle the slag and observed that recycled slag can produce acceptable bead geometry. As a continuation of the study, Singh et al. [7] recycled the fused slag by replenishing it with suitable alloying elements and deoxidizers and by agglomeration process. They carried out experiments using recycled slag. The performance of weldment was evaluated by chemical analysis, radiography, mechanical and metallurgical tests. They observed favourable results.

Simultaneously some researchers have also been explored the possibility of using a mixture of fresh flux and fused slag. Experiments carried-out by Livshits et al. [8] have shown the possibilities of using pulverized slag crust mixed with iron filings for hardfacing applications. They further claimed that this process is efficient and economical. Moi et al. [9] found that the use of fused slag does not affect the weld metal and HAZ microstructure harmfully. Datta et al. [10] obtained favourable bead geometry and HAZ using slag-mix up to 20%. They further optimized the process parameters using Taguchi method [11]. As a continuation of the study, Dutta et al. [12, 13] developed mathematical models for prediction of bead geometry in submerged arc welding using slag -mix for shielding. Research related to slag recycling and subsequently reuse in submerged arc welding is not rich. Very few weld researchers so far have been attracted to this field, but the scope of work and its significance is vast and bright. It is felt that there exist enough prospects to elaborate the research in this particular direction. If it can be experimentally proved successfully that the use of slag is possible instead of fresh flux, without producing any harmful / adverse effect on weld quality then this technique can be adopted in practical field resulting waste to wealth, because its time to employ zero waste concept. Motivated by this concept, the present work has been aimed with an objective to carry out investigations using slag-mix for shielding in submerged arc welding. The motive of this work is to check the application feasibility of recycled slag in the form of a mixture consisting fresh flux and fused slag. The influence of using slag mix on mechanical properties of weld metal has been investigated. Visual inspection, dye penetration test and radiographic tests have also been

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National Conference on Advancements and Futuristic Trends in Mechanical Engineering (February 19-20, 2010)

carried out to check the soundness of weldment. Arc stability and slag detachability have also been adjudged.

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2. Experimentation
The slag generated by Mukat Pipes, Rajpura, Punjab, an industry producing large diameter cross country pipes by submerged arc welding, was collected. It is available in abundance at their dump yard, free of cost. This slag was crushed and meshed to the granular size of the original flux and then mixed with the fresh flux in varying proportions (0%, 20%, 40%, 60, 80% and 100%). Slagmix in combination with EL-8 filler wire was used in these investigations. The chemical composition of filler wire and base plate has shown in Table 1.
Table 1: Chemical composition of electrode and base metal C 0.069 0.165 Mn 0.48 0.40 Si 0.02 0.17 S 0.02 0.05 P 0.0184 0.046
9 7 5 1 3 2 10 8 6 4

25

12

Backing plate
Figure 2: Detail of weld groove Table 2: Welding conditions

Electrode Base plate

S. No. 1 2 3 4

Parameter Welding Current Arc voltage Travel speed Contact tip-to-work distance Inter pass temp.

Unit Ampere Volts mm /min mm

0

Magnitude 500 32 330 24 150

25

125 25 30

Figure 1: Dimensions of test assembly

Test assemblies as shown in Fig. 1 were prepared. Mild steel plates (AISI-1018) having 25mm thickness, 275 mm length and 125 wide were used. Weld groove as shown in Fig. 2 was prepared by a shaping machine. These plates were clamped in a welding fixture designed for this purpose to avoid any distortion during welding. As stated in the ASME Sec-II SFA 5.17 code, inter pass temperature was maintained as 150 0C. The inter pass temperature was measured with the help of a themostick. A constant potential transformer-rectifier type power source having current capacity of 600 amperes at 100% duty cycle and open circuit voltage ranging 12-48 volts was used. Fully mechanized submerged arc welding system of carriage type was employed to conduct the experiments. DCEP polarity was used throughout the experimentation. Slag mixture having various proportions of slag mixed in fresh flux in combination with EL-8 filler wire was used for protection of molten pool.

Welding parameters and other conditions for these test assemblies were as dictated by ASME SFA 5.17 and have been presented in Table 2. These assemblies were subjected to visual inspection, dye penetration test and radiographic test before cutting for specimens meant for mechanical testing. Three tensile and five impact specimens were removed from each test assembly. The dimensions of these specimens were in accordance with ASME SFA 5.17. Tensile test was performed on Hounsfield Tensometer. The axial loading rate was maintained approximately 200 kg/min. The results of mechanical test are recorded in Table 3. Locations and dimensions of all weld specimens are shown in Fig. 3 and 4 respectively. Location of charpy impact specimen is shown in Fig. 5. Arc stability was observed from the pointer of voltmeter fitted on the control panel of the equipment. Slag detachability was observed during cleaning of the weld for each run.

Figure 3: Location of all weld tensile specimens

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National Conference on Advancements and Futuristic Trends in Mechanical Engineering (February 19-20, 2010)

19.9 8.1 5.06 - 5.04 1R

Figure 4: Dimensions of tensile specimen

4.0-6.0

Stable arc was indicated by the pointer of voltmeter fitted on the control panel of the equipment. Fluctuations of the pointer of voltmeter indicate fluctuations in the arc voltage which depends on arc length during welding. Evenly distributed ripples further support the stable arc during welding. 3.3 Radiography After flushing out the reinforcement by a shaper and subsequently grinding, all the test assemblies were subjected to radiographic test. Test assemblies prepared with 40% to 100% slag in flux slag mix failed in radiography. Porosity, slag inclusions and lack of fusion were indicated by the radiographs of the test assemblies. Porosity may be due to carbon dioxide gas formed in the molten pool by oxidation of carbon, as deoxidizers have already been exhausted. Slag inclusions may be due to entrapment of slag in under cuts as slag detachability was poor for first three runs. Slag entrapment in side walls under cuts may also lead to the porosity. Addition of fresh flux (reduction of slag) in flux slag mixture increased the amount of deoxidizers through fresh flux and above defects got eliminated from the test assemblies prepared with 0% and 20% slag. Evaluations of the weld radiographs were as per 9.25.2 of AWS D1.1-88 structural code of dynamic loading. 3.4 Tensile strength The results of all weld tensile and impact tests of all the test assemblies as well as AWS requirements are shown in Table 3. According to AWS specifications, minimum tensile strength and percentage elongation required is 420 N/mm and 24% respectively which were achieved using slag-mix containing slag up to 60%. Tensile strength of weld metal prepared using slag-mix containing slag 80% and 100% is 392 and 370 N/mm2 respectively which is below the acceptable range. However percentage elongation increased with increasing the amount of slag in flux-slag mix, which further supports the use of flux-slag mix instead of fresh flux. 3.5 Impact strength Five impact specimens were removed from each test assembly. The dimensions of impact specimen have been shown in Fig.6. In evaluating the test results, the highest and the lowest values obtained have been discarded as dictated by ASME codes, According to this code two of the remaining three values should be equal, or exceed, the specified (90J) and average of three should not be less than the required (90 J) at 0OC. This condition was satisfied in case of fresh flux. The weld metal prepared with slag-mix having slag 20% and 40% in flux-slag mix indicate 96.6 and 105 J respectively which is within the acceptable range of AWS specifications. The impact strength of weld metal prepared with slag mixture having percentage of slag 60% or more do not satisfy AWS requirements. However tensile strength and percentage elongation is within the acceptable range of AWS and have been presented in Table 3.

Figure 5: Location of impact specimen

Figure 6: Dimensions of impact specimen

3. Results and Discussion

3.1 Surface appearance Smooth beads with good surface finish were obtained. Top surface of the bead was shining with light blue in colour, may be due to oxidation. No undercuts, slag entrapments and pockmarks were observed. However scattered porosity was revealed by dye penetration test. Ripples were evenly distributed. 3.2 Slag detachability and arc stability Slag detachability was observed for each pass during cleaning. For first three runs in groove welds, slag detachability was poor and then after was self-lifting. Under cuts along the side wall of groove were observed which were removed by grinding before depositing subsequent run. Slag sticking in the undercuts was also removed by grinding. This happened for first three runs and then after no undercut was observed and slag was self detaching. It was further observed that slag detachability decreased with increasing the amount of slag in flux-slag mix. No pock marks on the bead surface were observed that indicate good permeability of flux-slag mixture for easy escape of gases generated in the molten pool.

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National Conference on Advancements and Futuristic Trends in Mechanical Engineering (February 19-20, 2010)

Table 3: Results of mechanical tests

UTS N/mm2
AWS Requirement With 0% slag mix With 20% slag mix With 40% slag mix With 60% slag mix With 80% slag mix With 100% slag mix 420 455.6 430 433 434 392 370

% Elong.
24 30.5 30 32 35 35 32.7

Charpy Impact, J
90 116.7 96.6 105 70 75 72.9

Radiography
Must Pass Passed passed Failed Failed Failed Failed

6. Singh K, Pandey S, Arul Mani R (2006) Recycling of Submerged Arc Welding Slag, Australasian Welding Journal, Vol. 51(2), pp 34-38. 7. Singh K, Pandey S (2007) Utilization of Slag as a Useful Flux in Submerged Arc Welding, Indian Welding Journal, Vol. 40(3), pp 31-38. 8. Livshit LG, Shiryaev AI (1960) A New Ceramic Flux for Hard facing, Welding Production, January, pp 25-29. 9. Moi SC, Bandyopadhyay A, Pal PK (2001) Submerged Arc Welding with a Mixture of Fresh Flux and Fused Slag, Proceedings of National Seminar on Advances in Materials & Processing, IIT, Roorkee, India, pp 98-102. 10. Datta S, Bandyopadhyay A, Pal PK (2008) Solving Multicriteria Optimization Problem in Submerged Arc Welding Consuming a Mixture of Fresh Flux and Fused Slag, International Journal of Advanced Manufacturing Technology, Vol. 35(11), pp 935-942. 11. Datta S, Bandyopadhyay A, Pal PK (2008) Modeling and Optimization of Features of Bead Geometry including Percentage Dilution in Submerged Arc Welding using Mixture of Fresh Flux and Fused Slag, International Journal of Advanced Manufacturing Technology, Vol. 36(3), pp 1080-1090. 12. Datta S, Bandyopadhyay A, Pal PK (2008) Application of Taguchi Philosophy for Parametric Optimization of Bead Geometry and HAZ Width in Submerged Arc Welding using A Mixture of Fresh Flux and Fused Flux, International Journal of Advanced Manufacturing Technology, Vol. 36(1), pp 689-698. 13. Datta S, Bandyopadhyay A, Pal PK (2008) Slag Recycling in Submerged Arc Welding and its influence on Weld Quality leading to Parametric Optimization, International Journal of Advanced Manufacturing Technology, Vol. 39(10), pp 229-238.

Conclusions
Slag mixed with fresh flux can be applied for shielding of molten pool in submerged arc welding. Slag detachability and arc stability both were satisfactory. Slag mixture containing slag up to 60% can produce welds having tensile strength 643 N/mm which is within the acceptable range of AWS (American Welding Society).

Acknowledgement
Authors would like to thank Late Mr. Mahender Singh, Technician, Welding Research Laboratory, Indian Institute of Technology Delhi for extending help during the experimental stage of this research work.

References
1. Weisman C (1976) AWS Welding Hand Book, 7TH Edition,
Miami, USA, American Welding Society 2. Visvanath PS (1982) Submerged Arc Welding Fluxes, Indian Welding Journal, Vol. 15(1), pp 27-30. 3. Honavar DS (2006) Cost Effective Productivity in Welded Fabrication, Technology Trends, October, 2006. 4. Eagar TW (1980) Oxygen and Nitrogen Contamination during Submerged Arc Welding of Titanium. Proceedings of International Conference of Welding Research, in the 1980s. Osaka University, Osaka, Japan. 5. Beck HP, Jackson AR (1996) Recycling SAW slag Proves Reliable and Repeatable, Welding Journal, Vol. 75 (6), pp 51-54.

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