Experimental validation of error in temperature measurements in thin walled ductile iron castings

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Casting experiments have been performed with eutectic and hypereutectic castings with plate thicknesses from 2 to 8 mm involving both temperature measurements during solidification and microstructural examination afterwards. The nodule count was the same for the eutectic and hypereutectic castings in the thin plates ((4?3 mm) while in the 8 mm plate the nodule count was higher in the hypereutectic than in the eutectic castings. The minimum temperature before the eutectic recalescence (T min ) was 15 to 20uC lower for the eutectic than for the hypereutectic castings. This is due to nucleation of graphite nodules which begins at a lower temperature in the eutectic than in the hypereutectic castings. The recalescence DT rec was however also larger for the eutectic casting and in the thin plates the maximum temperature after recalescence (T max ) was the same in the eutectic and hypereutectic plates. This is because higher undercooling gives a larger driving force for the solidification process and the equal nodule counts therefore give the same T max . However, the higher undercooling before recalescence increases the risk for formation of carbides during the solidification. In the 8 mm plates, the lower nodule count in the eutectic plates also gave a lower T max than in the hypereutectic castings.

Section: Methodsmentioning

confidence: 99%

Undercooling and nodule count in thin walled ductile iron castings

Pedersen¹,

Tiedje²

2007

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“…11,12 As the nucleation of graphite starts at higher temperature in the hypereutectic casting than in the eutectic and hypoeutectic castings, the undercooling will be lower for the hypereutectic castings. 13 It is necessary to minimise the levels of any carbide promoting elements, as carbides will segregate. 14 Variations in the matrix structure will ultimately affect final impact properties due to transition in the crack path mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Solidification behaviour and mechanical properties of ductile iron castings with varying thickness

Shinde

Ravi

Narasimhan

2012

Achieving the desired mechanical properties in thin wall ductile iron castings poured in industrial production foundries is a challenge. In this work, the effect of copper addition (up to 0?74%) and melt processing (Ba based stream inoculation) on the matrix structure, mechanical properties and fracture behaviour of ductile iron castings with varying section thickness (4-16 mm) were investigated in a regular jobbing foundry. It was possible to obtain 80% pearlitic structure without carbides in 4 mm sections, giving a tensile strength of 658 MPa with 2?5% ductility and 264 Brinell hardness. The solidification behaviour represented by the cooling curves helped in checking the effectiveness of the melt treatment by observing the amount of undercooling. Fractography studies of tensile specimens showed the change in fracture mechanisms due to increase in copper content on fracture paths. The increased amount of pearlite in the matrix exhibited brittle fracture with river pattern.

Influence of rare earths on shrinkage porosity in thin walled ductile cast iron

Pedersen¹,

Tiedje²

2009

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Ductile cast iron has been cast in test bars with thickness from 2 to 10 mm. The rare earth elements La and Ce have been added to some of the castings to evaluate their influence on microstructure and shrinkage tendency. Both La and Ce increased the graphite nodule count, especially for thickness of 6 mm and below. La gave the best nodule size distribution with many small nodules. La had less shrinkage tendency than Ce in the 10 mm test bars. This tendency was less pronounced for the 6 and 4 mm test bars and other factors may have a large influence at these thicknesses. Increasing the temperature T 1 , which is controlled by the growth of off-eutectic austenite dendrites, increased the shrinkage tendency.