A Case Study for Predicted Mechanical Properties of Ductile Iron Castings with the Help of Image Analyzer & Spectrometer .Author:-Amitava Sengupta, e-Mail:- [e-mail]

Introduction :-The as-cast microstructure of Ductile Iron typically contains a mixture of Ferrite & Pearlite. In as-cast structure, Ferrite generally appears in the form of concentric Sheels around the Graphite Nodules. The mechanical Properties of as-cast Ductile Iron Strongly depend on the amount & distribution of Ferrite in the Micro Structure. It is known that the Ferrite content of the Matrix depends on the Chemical Composition of Ductile Iron on the rate at which it is cooled through the Eutectoid Transformation range. The Mechanical properties of Ductile Iron can be predicted through the Equation.Ref1 The purpose of the Scope of a Mechanical behavior of Ductile Iron based on Chemical Composition & Micro Structure. It is also the purpose of the Technical write-up for the Topics. "Metal Matrix Composite" of the Mechanical Properties of Ductile Iron should depend on the relationship in between Chemical Composition & Micro Structure of the material.

Experimental Case Study: The Ductile Iron Sample used in the case study were provided Heat No. : R &D-1 was taken, the Melting were carried out in the Induction Furnace Medium Frequency of M/s Inductotherm (India) make 500 kg Capacity crucible in Acid Lining. The S.S.G. Grade of Pig Iron having low 'S', 'P' & 'Mn' content of M/s Tata Metaliks Ltd, Coal cased made D.R.I. (sponge Iron) of M/s Orissa Sponge Iron Ltd. & In-house Foundry returns were the basic charge-mix input. The Desulphurisation & Nodularisation also carried out in Improvised Designed Metal Treatment Converter (BCIRA Rotary Ladle) for 'Mg' Treatment in Pure 'Mg' process. The late Post inoculation were carried out by M/s Elken AS, Norway made Ba-based inoculent the treated Liquid Metal also poured ASTM-Specified 'Y' Block for the test piece attached with the casting as intregral test Bar. The Tapping temperature, the temperature before 'Mg' treatment & the pouring temperature were taken out by the Digital Pyrometer of M/s AJOY SYSCON (INDIA) make, a 'CE' Value also taken of the Liquid Metal by a Carbon Equivalent Meter in thermal analysis process; In order to Study the influence of Cooling rate of different section thickness of Pipe Fittings Castings as per ANSI/AWWA- C-110/21.10.93 were poured in Green Sand mould & examined/observed in the Quality Assurance & Development Department by the author himself in Image Analyser of M/S Metal Power Analytical (India) Ltd for Metallography Evaluation & the Chemical Composition / Analysis also carried out by the Desktop optical Emission Spectrometer of M/s Sepctrolab for the purpose a Chilled Coin Sample was taken in a "Book Mould". The Mechanical properties checked in Electronic Universal Tensile Testing Machine of M/s Blue Star (India) Ltd make of 60 Ton capacity.

Scope of a Case Study: With the help of Image Analyser for Metallographical Evaluation, & Spectrometer for Chemical Analysis, it has became possible to predict the Microstructure of Ductile Iron quantitatively; the Write-up for the purpose of to formulate Tensile strength, Yield Strength, & Elongation Value for Ductile Iron of ASTMA 536; gr 65-45-12, by the help of Image Analyser & Spectrometer for Pipe Fittings Castings & Evaluating & effects on predicated Mechanical properties at a Small 100%. Export Oriented Ductile Iron Foundry at Calcutta, India named M/S Edcons (MKS) Casting Pvt. Ltd.

Equation: The Microhardness data for the individual microstructure can be predict the Ultimate Tensile Strength properties of as -Cast & the Yield Strength & Elongation data with following Equation. Ref 1
Ultimate Tensile Strength (Ksi) = 0.10 x 0.36 x CMMH Ref 2
Yield Strength (Ksi) = 12+0.18 x CMMH Ref 2
Elongation (%) = 37.85 - 0.093 x CMMH Ref 2
The Composite Martix Micro Hardness (CMMH) of Ductile Iron can be expressed as follows Ref 2
CMMH = (Hardness of Ferrite x % of Ferrite) + (Hardness of Pearlite x % of Pearlite) / 100
The Hardness of Ferrite & Pearlite of Ductile Iron can be written as follows Ref 2
Hardness of Ferrite = 66 + 45Si + 12Mn + 10Cu + 7Ni + 21Mo
Hardness of Pearlite = 253 + 27Si + 10Mn + 14Cu + 17Ni + 26Mo

Data of Mechanical Properties Predicted Vs. Actual Achived.
Table -1
Heat U.T.S. (Ksi) Y.S. (Ksi) Elongation (%)
No Predicted (Based / By applying Equation) Actual Achieved data (Machined Test Piece Tested Result) Predicted (Based /By applying Equation) Actual Achieved data (Machined Test Piece Tested Result) Predicted (Based /By applying Equation) Actual Achieved data (Machined Test Piece Tested Result)
R&D-01 72.53 71.38 48.21 47.52 19.13 19.05
Metallographical Evaluation Report & Micro Photograph by Image Analyser.
Table -2
Heat Nodularity Nodule Count Nodule Size Graphite Ferrite Pearlite Carbide
No % Per mm2 50 x ASTM No & Type % % %
R&D-01 93 222 (6-7), (2 to 4) mm at 50 x Type of 1, Graphite Nodules 88 12 Trace










As-Cast Microphotograph of Heat No: R & D -01 of Ductile Iron showing Graphite Nodules Surrounded by Ferrite; Eteched in Colour eteched has been used based on a strong Alkaline Solution Containing Picric Acid which applied at temperature 830C & Etching times were 37min, the composition of Primary Colour Etchant as follows, H2O : 50ml, NaOH: 10gm, KoH: 40gm, & Picric Acid: 10gm Magnification x 50x. (Micro Photograph taken out from Image Analyser)

Spectronetric Chemical Analysis Report :
Table - 3
C Si Mn P S Cr Mo Ni Al Co
% % % % % % % % % %
3.78 2.60 0.110 0.079 0.011 <0.005 <0.001 <0.005 <0.001 <0.0050

Cu Nb Ti V W Pb Sn Mg Te B Fe
% % % % % % % % % % %
0.003 <.002 0.0591 0.0071 0.0063 0.0221 0.0035 0.0584 <0.005 <0.0001 93.3

Prediction based on TABLE: 1, 2 & 3 by applying Equation.
CMMH - (Hardness of Ferrite x % of Ferrite) + (Hardness of Pearlite x % of Pearlite) / 100
Hardness of Ferrite:
66+45Si+12Mn+10Cu+7Ni+21Mo
or 66+45x2.60+12x0.11+10x0.003+7x0.005+21x0.001
or 184.40
Hardness of Pearlite:
253+27Si+10Mn+14Cu+17Ni+26Mo
or 253+27x2.60+10x0.11+14x0.003+17x0.005+26x0.001
or 324.45
Therefore, CMMH = (184.40x88) + (324.45x12)/100
Or 201.20
Ultimate Tensile Strength: 0.10+0.36 x CMMH
Or 0.10+0.36 x 201.20
Or 72.53
Yield Strength: 12+ 0.18x CMMH
Or 12 + 0.18 x 201.20
Or 48.21
Elongation: 37.85 - 0.093 x CMMH
Or 37.85 - 0.093 x 201.20
Or 19.13

Conclusions: The Mechanical properties of Ductile Iron Case Studies in this experimental work including Ultimate Tensile Strength, Yield Strength, & Elongation are mainly dependent on the fraction of Graphite, Ferrite & Pearlite, as well as on the Nodularity of Graphite. If the fraction of each Microstructural Component is known, the Mechanical properties of Ductile Iron can be predicted approximately through the Equation Ref -1 based on the result of Image Analyser & Spectrometer.

References:
Ref-1 A Mechanical properties Model for Ductile Iron - by X. Guo, D.M. Stefaneseu, L. Chuzhoy, M.A. - Pershing, G.L. Biltgen AFS Transactions, AFS Inc, 1997,
page 47
Ref-2 www.ductile.org