Effect of Casting Design on Microstructure and Mechanical Properties of 3 mm TWDI Plate

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Effect Of Casting Design To Microstructure And Mechanical Properties Of 3 Mm Twdi Plate

Article in Advanced Materials Research · October 2011

DOI: 10.4028/www.scientific.net/AMM.110-116.3301

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Effect Of Casting Design To Microstructure And Mechanical Properties Of 3 Mm Twdi Plate

Johny Wahyuadi Soedarsono

^{1,2, a}

, Bambang Suharno

^1,b

, Rianti Dewi Sulamet-Ariobimo

^3,4,c

1 Department of Metallurgy and Materials, Faculty of Engineering, Universitas Indonesia, Jakarta, Indonesia.

2 Politeknik Negeri Jakarta, Jakarta, Indonesia.

3 Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Jakarta, Indonesia

4 Mechanical Engineering Department, Faculty of Industrial Technology, Universitas Trisakti, Jakarta, Indonesia

a [email protected], ^b[email protected], ^c[email protected]

Keywords: casting design, TWDI, 3 mm plate, middle level

Abstract. The problem occurs in producing thin wall ductile iron (TWDI) is high cooling rate due to its thickness. Cooling rate must be strictly maintained to prevent carbide formation. There are many ways to control cooling rate. Casting design is one of these, especially gating system design.

This parameter is often chosen because of its independence. Major changes in equipment and raw material used in the foundry are not needed when a casting design is chosen to deal with cooling rate. This paper discusses the effect of gating system design on microstructure and mechanical properties of 3 mm TWDI plate. A casting design based on gating system design is made to produce 1, 2, 3, 4, and 5 mm TWDI plates. There are three designs coded as T1, T2, and T3. These three designs were also used in making 1 mm TWDI plates of which the result has been published. The plate with thickness of 3 mm will be used for automotive component like the crankshaft made by Martinez. The moulds used were furan sand. Beside the experiment, casting design simulation with Z-Cast was also conducted to see the behaviour of solidification in 3 mm TWDI plate. Simulation result showed every design has its own solidification behaviour for 3 mm TWDI plate, especially for T2. Experiment result showed that all the designs have microstructure consisting of nodule graphite in ferrite matrix, no trace of carbide and skin effect are formed. Skin effect length is various for all designs. Nodularity exceeded 75% and nodule count exceeded 900 nodules/mm². Brinell hardness number for all design is beyond standard given by JIG G5502. As for UTS and elongation none of the designs exceed the minimal standard. Experiment results confirmed simulation result. Compared to the previous result nodularity and nodule count decrease and curve trends for every result are not the same.

Introduction

Ductile Iron (DI) has many superior characteristic compared to aluminium but cannot compete in weight problem. Aluminium is a light weight material. Thin wall ductile iron (TWDI) is produced due to lighter the weight of DI. TWDI makes ductile iron possible to compete with aluminium in terms of weight. The standard of casting thickness classified as thin wall ductile iron casting (TWDI) has not been established. Caldera describes it as equal or less than 5 mm [1] but Martinez takes it to be equal or less than 4 mm [2]. Stefanescu describes it as equal or less than 3 mm [3]. The thinnest part ever made in TWDI is 1.4 mm [4]. The thickness of TWDI is the main problem during casting process. As described above the thickness of TWDI is below 5 mm, it is below a normal casting thickness. As the thickness decreases the cooling rate will increase and will tend to promote the formation of carbides during solidification [5]. To overcome this, the cooling rate should be maintained. There are many ways to control cooling rate and one of these is through casting design especially in gating system designs.

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 114.79.53.175-14/12/11,23:16:52)

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Many designs were made to produce quality TWDI. A step block casting design was used by Javaid [5]. Modified step block casting designs were used by Showman with a horizontal groove step block[6]. Pedersen et al. with a horizontal stepped block with feeder [7]. Specific casting designs have been introduced in making TWDI. Stefanescu and his research group [3,8] used special horizontal and vertical gating designs. Another horizontal casting design was created by Schrems et al. [9]. INTEMA researchers developed special horizontal and vertical gating system designs for their research on TWDI[1,6,10]. Labrecque and his associates [11] created their own casting design. Special vertical casting designs were developed by Soedarsono et al. [12].

The designs made by Soedarsono et al. [12] were modified and developed from Stefanescu vertical casting design [8]. Modifications were made in dimension, thickness, and arrangement of the plates. The arrangement of plates cast contradicted the general principle of casting and may cause the failure of the filling process by positioning the thinnest plate near ingate. The result showed that filling process was successful. There was no trace of premature solidification and all the plate was fully cast. After the modification, development was made in gating system design.

The original design only used the bottom gating principle. The modified design used 3 variations of gating system: bottom gating, bottom gating with supporting gates and top gating gravity.

This paper discusses the effect of microstructure and mechanical properties of 3 mm TWDI plate resulted from 3 various designs.

Experimental Methods

The research was done on the foundry scale. The casting designs used in this work can be seen in Figure 1. There are 3 designs and coded as T1, T2, and T3. Dimensions of the plates were (75 X 150 mm) with thicknesses of (1, 2, 3, 4, and 5 mm). Every mould produced five plates. The plates were arranged parallel to each other. The 1 mm thick plate was closest to the ingate followed by the 2, 3, 4, and 5 mm thick plates.

T1 T2 T3

Fig. 1. Casting Design a. T-1 b. T-2 c. T-3

1. down sprue – 1a. supporting gate - 2. runner – 3. ingate – 4. riser – 5. plate – 6. gas tunnel The moulds were made from furan sand. The metal cast was Ferro Casting Ductile (FCD) grade 450 (JIS 2000). The chemical composition used was examined before the liquid treatment process. The result can be seen in Table 1. The liquid treatment used 12 kg Fe-Si-Mg with 6%Mg as the nodularising agent in the sandwich method with a tapping temperature of 1500ÔC. Inoculants were also placed in the ladle. The inoculant used in this research was S70 with the composition 1.5%Ca; 72.95%Si; 0.86%Al; 2.1%Ba. Pouring temperature were 1393ÔC, 1398ÔC, and 1379ÔC.

The observations made included carbides appearance, nodule count, nodularity and nodule diameter

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uniformity. The calculations of nodular graphite characteristics were made by using manual calculation based on American Standard Testing Material (ASTM) A427 and also by using Cyuuzou Kun. Cyuuzou Kun is an imagine analyses software used in Iwate University.

Beside the experiment, simulation on casting designs using ZCast was also done.

Results and Discussion

Chemical composition of molten metal used can be seen in Table 1.

Table 1. Chemical Composition – weight, [%].

Element/Pouring C Si Mn P S Cu Ni Cr Mg

P1 3.8 2.6 0.37 0.02 0.02 0.04 0.03 0.04 0.04

The chemical composition of molten metal used was all in range. There is no significant difference.

Solidification stimulation showed that the solidification process for every design is different one to the other. 3 mm TWDI plat has begun to solidify in 2 s, while T1 and T3 have not. The colour scheme show that temperature in T1 is lower than T2. T1 has begun to solidify at 4 s and T2 at 6 s, (refer with Fig. 2). Solidification in T1 starts from 1 mm plate with 1 and 2 mm followed by 3, 4, and 5 mm. In T2, solidification starts from 1 and 2 mm plate and followed by 5, 4, and 3 mm.

Last to freeze in T2 is on 3 mm plate. Solidification process in T3 happen the same as T2. The major difference lies in the temperature. Colour scheme showed that temperature condition in T3 is lower than T2. The highest solidification rate for 3 mm plate is T3 and the lowest is T2.

2 s

4 s

6 s

T1 T2 T3

Fig. 2. Solidification

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T1 T2 T3 Fig. 3. Non Etched Microstructures

Un-etched microstructures from all designs (refer with Fig. 3) show that all designs have similar nodule counts but the nodularity in T2 is higher than T1 and T3. Primary graphite is formed in T2 although the diameter is not too big. Homogenized distribution is shown by T3.

T1 T2 T3

Fig. 4. Etched Microstructures - Outside

T1 T2 T3

Fig. 5. Etched Microstructures

The etched microstructures for all designs (refer with Fig. 4 and Fig. 5) show that the matrix is ferrite. No trace of carbides formation in all sites. This condition shows that the cooling rate of 3 mm is the cooling rate needed to produce TWDI. Microstructures also show appearance of skin effect, (refer with Fig. 4 and Fig. 6). Skin effect is a rim of flakes and vermicular graphite. Skin effect is normal if found in sand casting. Usually they are removed with machining process. Skin effect becomes a problem to thin wall casting due to thickness of casting product. The widest skin effect is in T3 and the lowest one is in T1. T3 got the widest skin effect because based on simulation it has the highest cooling rate. Although skin effect will lower mechanical properties, to a certain point they homogenise formation of middle part [12].

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Skin Effect

0 2 4 6 8 10 12

T1 T2 T3

Design Skin Effect Thickness to Thinkness of the Plate - %

Fig. 6. Comparison of Skin Effect

Nodularity

78 78.5 79 79.5 80 80.5 81 81.5

T1 T2 T3

Design

nodularity - %

Nodule Count

860 880 900 920 940 960 980 1000

T1 T2 T3

Design Nodule Count - nodule/mm2

Fig. 7. Comparison of Nodule Graphite Characteristic

Nodularity of T1 and T3 are 79, while T2 is 81. The highest nodularity is gained by T2 (refer with Fig. 7). As for nodule count, T1 is 941 nodule/mm², T2 is 907 nodule/mm², and T3 is 988 nodule/mm². The highest nodule count is T3 while the lowest is T2 (refer with Fig. 7). T2 has the highest nodularity due to low nodule count and longer cooling rate. The presences of primary graphite in T2 are also causing lower nodule count. T3 has the highest nodule count because of higher cooling rate and skin effect. The nodule count achieved by 3 mm TWDI plate from all design is differing from one to another. But the differences are not significant; all differences are below 10%. This showed that the differences in cooling rate for 3 mm plates are not wide. Nodule diameter of T1 is 14.7 µ, T2 is 14.4 µ and T3 is 14.5 µ. This result confirmed the prediction made before. There is no significant difference in average nodule diameters.

Brinell Hardness Number (BHN) of T2, 171, is the highest while BHN of T3, 155 is the lowest one (refer with Fig. 8). T2 is highest due to high nodularity and presence of primary graphite.

The range of BHN for 3 mm plate is not wide, only 10%. All of the results lie beyond the standard given by JIS G5502, BHN (140 – 210). This confirms that the microstructure gain is free of carbide.

Ultimate tensile strength (UTS) of 3 mm plate thickness from all design has not passed the minimum limit of UTS given by the JIS G5502, min. 45 kgf/mm² (refer with Fig. 8). T3 has the highest UTS. This happens because T3 has the highest nodule count. Generally, high nodule count indicates good metallurgical metallurgy although not as strong as nodularity. Elongation in all design has not passed the minimum limit too, that is of 10% minimum. T2 has the highest elongation as a result of highest nodularity. Range of UTS gain in this work is not significant, 9%, but for elongation is significant, 275%.

When all the result compare to the result of 1 mm plate thickness [12], it is obvious that the behaviours of 1mm and 3 mm plate thickness are not the same. This is also valid for the range of the result. Generally, in 3 mm plate thickness, the results of all designs are not significant but in 1 mm plate thickness the results are generally significant.

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Brinell Hardness Number

145 150 155 160 165 170 175

T1 T2 T3

De sign

BHN

Ultimate Tensile Strength

31 32 33 34 35 36 37

T1 T2 T3

Design

UTS - Kg/mm2

Elongation

0 1 2 3 4 5 6 7 8

T1 T2 T3

Design

e - %

Fig. 8. Comparison of Mechanical Properties

Result of this work does not confirm the statement about skin effect made by Wooley [13] . T3 has the thickest skin effect but the nodule count and UTS is also the highest. While T1 and T2 have similar thickness of skin effect but UTS and elongation of T1 is the lowest [refer with Fig. 6, 7, and 8].

Nodularity for 3 mm Thickness

0 20 40 60 80 100

Martinez, 2003 Labreque, 2005 Soedarsono, 2009 (T1) Soedarsono, 2009 (T2) Soedarsono, 2009 (T3)

nodule count - nodule/mm2

Nodule Count for 3 mm Thickness

0 200 400 600 800 1000 1200 1400 Martinez, 2003

Labreque, 2005 Soedarsono, 2009 (T1) Soedarsono, 2009 (T2) Soedarsono, 2009 (T3)

UTS for 3 mm Thickness

0 5 10 15 20 25 30 35 40

UTS for 3 mm Thickness

0 1 2 3 4 5 6 7 8

Fig. 9. Designs Compare to Other Designs

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When comparing results of this work to other designs, nodule counts resulted from this worked are higher than Martinez [2] but lower than Labreque [14] (refer with Fig. 9). As for nodularity, UTS and elongation, there is no data record from either Martinez or Labreque (refer with Fig. 9).

Conclusion

Solidification simulation by Z-Cast showed that all the designs have different cooling rate In all plates were found nodule graphite in ferrite matrix, and skin effect. The highest nodularity is 81 reached by T2. The highest nodularity is 988 nodule/mm² reached by T3. The highest UTS is 36 kg/mm² reached by T3 while the highest elongation is 7.5 reached by T2. All the designs showed their own speciality behaviour for 3 mm plate thickness.

Experiment result confirmed simulation result. According to experiment the highest cooling rate is reached by T3. This conclusion is based on width of skin effect, nodule count and approved by UTS. Simulation result also showed the highest cooling rate is T3.

Experiment results contradict the statement made by Wooley.

Acknowledgment

The authors wish to thank The Goverment of The Republic of Indonesia for the research grants No. 346/SP2H/PP/DP2M/VI/2009 and PT. Geteka Founindo for permission to use their foundry. The authors also wish to thank Prof. Hiratsuka and Mr. Bimo from Iwate University for their helped in measuring the graphite nodule properties. The authors would also wish to thank Mrs.

R. Tjokroadiredjo for lingual corrections.

References

[1] M. Caldera, M. Chapetti, J.M. Massone, and J.A. Sikora: Mater. Sci. Technol, Vol. 23 No. 8 (2007), pp. 1000.

[2] R.A. Martinez, R.E. Boeri, and J. A. Sikora in: Proceeding of 2002 world conference on ADI, AFS, 2002.

[3] D.M. Stefanescu, L.P. Dix, R.E. Ruxanda, C. Corbitt-Coburn, and T.S. Piwonka: AFS Trans, Vol. 110 (2002), pp. 1149.

[4] R. E. Ruxanda, D.M Stefanescu, and T.S. Piwonka: AFS Trans, Vol. 110 (2002), pp. 1131.

[5] A. Javaid, K. G. Davis, and M. Sahoo: Mod. Cast., 90(2000), pp. 39.

[6] R. E. Showman, R. C. Aufderheiden and N. Yeomans: Mod. Cast., 96(2006), pp. 29.

[7] K. M. Pedersen, N. S. Tiedjen: Mater. Charact., 09(2007).

[8] L. P. Dix, R. Ruxanda, I. Torrance, M. Fukumoto, and D. M. Stefanescu: AFS Trans, Vol.

111 (2003), pp. 895.

[9] K. K Schrems, J. A. Hawk, Ö. N. Dogan and A. P. Druschitz: SAE Tech. Paper Doc. No.

2003-01-0828 (2003).

[10] C. Labreque, M. Gagné, A. Javaid and M. Sahoo: Int. J. Cast Metal Res., 16(2003), pp. 313.

[11] C. Labreque, M. Gagné: AFS Trans, Vol. 108 (2000), pp. 31.

[12] J.W. Soedarsono and R. D Sulamet-Ariobimo: Adv. Mat. Res., (2011), in press.

[13] J.W. Woolley, D.M. Stefanescu: AFS Trans, Vol. 113 (2005), pp. 637.

[14] C. Labreque, M. Gagné and A. Javaid: AFS Trans, Vol. 113 (2005), pp. 677.

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Effect of Casting Design to Microstructure and Mechanical Properties of 3 Mm TWDI Plate

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