Influence of Melt Holding Time on Microstructure and Mechanical Properties of Ductile Iron

2011 ◽  
Vol 279 ◽  
pp. 16-21
Author(s):  
Zhe Liu ◽  
Wei Ping Chen ◽  
Yu Deng
Keyword(s):  
Cooling Rate ◽  
Ductile Iron ◽  
Average Diameter ◽  
Holding Time ◽  
The Other ◽  
Spheroidal Graphite ◽  
Cooling Rates ◽  
Globular Graphite ◽  
Graphite Morphology ◽  
Nodular Graphite

Six groups of castings which solidified at different cooling rates with or without addition of 0.03%Sb were fabricated. The effects of the melt holding time, cooling rate, and Sb on the microstructure of ductile iron were studied. Results show that as for the other three blocks with addition of 0.03%Sb, reducing the length of eutectic plateau could improve the graphite morphology, and sufficient residual contents of spheroidizing elements REE and Magnesium could also lead to small and diffuse globular graphite particles no matter what the cooling rate is. As for the other three blocks with addition of 0.03%Sb, no matter what the cooling rate is, the nodularity index values are all about 90%. The main difference among the three blocks is just the size of nodular graphite. And even if two of the blocks solidified at different cooling rates, they own nearly identical NI value and globular graphite average diameter value, which is because they both possess the tolerated rare-earth elements/antimony ratio for spheroidal graphite formation.

Graphite Morphology Evolution during Melt Holding of Ductile Iron

2010 ◽  
Vol 457 ◽  
pp. 31-36 ◽  
Author(s):  
Xiao Gang Diao ◽  
Zhi Liang Ning ◽  
Fu Yang Cao ◽  
Shan Zhi Ren ◽  
Jian Fei Sun
Keyword(s):  
Ductile Iron ◽  
Early Stage ◽  
Holding Time ◽  
Spheroidal Graphite ◽  
Morphology Evolution ◽  
Graphite Morphology ◽  
Chunky Graphite ◽  
Long Time ◽  
Prolonged Holding

Evolution processes of graphite morphology in ductile iron were investigated by quenching specimens during a long time holding of iron melt in a Ar atmosphere. Results show that spheroidal graphite is only observed at the early stage of melt holding. There are no evident changes in morphology of spheroidal graphite with increasing holding time up to 180 min. Subsequently chunky graphite precipitates directly after holding for 240 min as spheroidizing ability (Mg residual and RE residual) is insufficient. The number and size of eutectic chunky graphite cells increase with prolonged holding time. It should be noted that vermicular graphite forms around eutectic chunky graphite cells after holding for 360 min. When holding time reaches 420 min, graphite morphology is flake-like together with some chunky graphite. The graphite morphology in ductile iron changes from spherical to chunky, then chunky to vermicular, finally to flake with an increase in melt holding time. Both spheroidizing ability and numbers of effective nucleus decrease with prolonged holding time of melt, which affect graphite morphology.

Influence of Melting Conditions on Graphite Morphology in Spheroidal Graphite Cast Iron Using Ni-C Alloys

2010 ◽  
Vol 457 ◽  
pp. 37-42 ◽  
Author(s):  
Yuji Kato ◽  
Ying Zou ◽  
Hideo Nakae
Keyword(s):  
Cast Iron ◽  
Cooling Rate ◽  
High Purity ◽  
Holding Time ◽  
Spheroidal Graphite ◽  
Graphite Morphology ◽  
Spheroidal Graphite Cast Iron ◽  
Graphite Cast Iron ◽  
Group 2 ◽  
Group 1

The effects of the cooling rate, atmosphere and holding time on the graphite morphology of spheroidal graphite cast iron were studied using Ni-C alloys. Two groups of parent alloys were prepared using high purity materials, i.e., Group 1 containing the spheroidizing element of Ce, Mg or Ca, while in Group 2, S was added as an anti-spheroidizing element. For discussing the influence of the cooling rate on the graphite morphology, 0.5g of the Group 1 samples were melted and held for 15 minutes at 1673K in an Ar atmosphere, then cooled at 1000K/min or 20K/min. The results showed that perfect spheroidal graphite could not be confirmed, while irregular graphite appeared. The atmosphere was changed to Ar+3%H2 for preventing the oxidation, and the holding time was reduced to 10 minutes to prevent fading of the spheroidizing element. These results showed that the formation of spheroidal graphite was confirmed at the cooling rate of 1000K/min in both groups. Nevertheless, at the cooling rate of 20K/min, graphite morphology was only chunky or flake in both groups. In order to investigate which parameter is more important for the formation of spheroidal graphite, the atmosphere and the holding time were independently changed at the cooling rate of 1000K/min. It was found that the addition of the 3%H2 did not significantly affect the spheroidal graphite formation. Moreover, the holding times of 1min and 20min also did not significantly affect the spheroidal graphite area fraction in the Ni-C alloy, while they affected the ones containing the spheroidizing elements like Mg.

Effect of Strontium Addition in Graphite Morphology and Nodularization of Hypoeutectic Cast Iron

2020 ◽  
Vol 1000 ◽  
pp. 454-459
Author(s):  
Rahmadi ◽  
Deni Ferdian
Keyword(s):  
Cast Iron ◽  
Image Data ◽  
Optical Microscope ◽  
Spheroidal Graphite ◽  
Data Processing Software ◽  
Graphite Morphology ◽  
Spheroidal Graphite Cast Iron ◽  
Graphite Cast Iron ◽  
Molten Cast Iron ◽  
Nodular Graphite

Nodular graphite cast iron or known as spheroidal graphite cast iron structurally has a spherical graphite morphology with a matrix consisting of a ferrite-pearlite phase. In general, cast iron has a main alloy consisting of carbon and silicon where both elements have an influence on the potential of graphitization and castability. In this work, the influence of strontium (Sr) added to molten cast iron with a composition of 0, 0.04, 0.06 and 0.08 wt% to graphite morphology were studied. The sample obtained will be carried out a characterization process by observing macro and microstructures using optical microscope equipped with image data processing software that displays graphite fraction, size, form and nodularity. Analysis showed that Sr addition increase in nodularization of graphite from 19.6 % to 31.5% at 0.08 wt% Sr addition.

scholarly journals Effect of Si and Ni Addition on Graphite Morphology in Heavy-Section Spheroidal Graphite Iron Parts

2018 ◽  
Vol 925 ◽  
pp. 70-77 ◽  
Author(s):  
Branko Bauer ◽  
Ivana Mihalic Pokopec ◽  
Mitja Petrič ◽  
Primož Mrvar
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Metallographic Analysis ◽  
Spheroidal Graphite ◽  
Ni Content ◽  
Heavy Section ◽  
Graphite Morphology ◽  
Ni Addition ◽  
Chunky Graphite ◽  
Si Content

Metallographic analysis is applied to the study of the chunky graphite morphology in heavy-section castings of spheroidal graphite cast irons. Three castings with different Si and Ni content were prepared. Three positions in casting from the edge to the centre, with different cooling rates, were chosen for microstructure observation. The effect of the Si and Ni content on the graphite morphology and mechanical properties of heavy-section spheroidal graphite cast iron parts were investigated. Cerium containing commercial inoculant was used for in-stream inoculation. Chunky graphite area was estimated in micro-and macrostructure. Mechanical properties were determined on tensile test bars taken from the centre of the casting. Macro-and microstructure examination showed that the castings with high Si-content and Ni addition had chunky graphite present, while the castings produced by use of low Si and Ni containing charge had no chunky graphite. High Si-content is strong chunky graphite promoter, especially in castings with slow cooling rate. Ni addition also promotes chunky graphite formation, but only in thermal centre of the casting (where the cooling rate is the lowest). The elongation is severely lowered when chunky graphite appears in the microstructure.

Effects of cooling rate and isothermal holding on the characteristics of MnS particles in high-carbon heavy rail steels

2020 ◽  
Vol 117 (1) ◽  
pp. 110 ◽  
Author(s):  
Xuewei Zhang ◽  
Caifu Yang ◽  
Lifeng Zhang
Keyword(s):  
Cooling Rate ◽  
Isothermal Holding ◽  
Average Diameter ◽  
Holding Time ◽  
Area Fraction ◽  
Air Cooling ◽  
Steel Matrix ◽  
Number Density ◽  
3D Morphology ◽  
Holding Temperature

The characteristics of MnS particles were intensively investigated at three different cooling rate of 80.4 K · s−1 (water cooling), 3.8 K · s−1 (air cooling) and 1.8 K · s−1 (furnace cooling) as well as the different isothermal holding temperature and time in laboratory experiments. The three-dimensional (3D) morphology of MnS particles was extracted from steel samples using non-aqueous solution electrolysis. The results showed that the 3D morphology of MnS changed from a nearly spherical into rod-like and the area fraction and average diameter of MnS increased with decreasing cooling rate. During isothermal holding process, the morphology of MnS changed little at 1473 K (1200 °C), but their shape profiles varied from a nearly spherical and spindle-like to irregular at higher holding temperature 1673 K (1400 °C) when the holding time exceeded 60 min. Moreover, the number density and area fraction of MnS decreased with increasing holding time at 1573 K (1300 °C) and 1673 K (1400 °C), respectively. Especially at 1573 K (1300 °C), the 1 ∼ 3 µm MnS inclusions were dissolved and lead to decreasing of number density, but that > 3 µm one occurs growth and resulted in increasing of average diameter. The calculation results show that the starting temperature of precipitation of MnS was about 1627 K (1354 °C) and effect of cooling rate on the segregation of Mn and S is insignificant. Considering the segregation of solutes, MnS formation and growth takes place in the solid/liquid interface of steel when the solid fraction is close to 0.9567 during solidification. It has been found that the increase of cooling rate gives rise to the decreased of MnS diameter because the growth time of MnS is short. Furthermore, thermodynamic calculations of MnS solid solubility product were carried out to reveal the high holding temperature and long holding time favors the dissolution of MnS particles. It is necessary to decrease the sulfur content by less than 16 ppm in order to assure that the larger MnS which formed during solidification redissolves in the steel matrix, rather than relying on increasing the heating temperature which is above 1649 K (1376 °C). Subsequent, the MnS will precipitate again in a finely dispersive state during rolling process, and it can hinder annealing grain growth and finally make for the improvement of the toughness property of the steel.

scholarly journals Effect of Cooling Rate on Hardness and Phase Transformation of a Pd-Ag-Based Metal–Ceramic Alloy with or without Ice-Quenching

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 680
Author(s):  
Hye-Jeong Shin ◽  
Yong-Hoon Kwon ◽  
Hyo-Joung Seol
Keyword(s):  
Phase Transformation ◽  
Cooling Rate ◽  
The Other ◽  
Tetragonal Structure ◽  
Firing Process ◽  
Elemental Distribution ◽  
Cast State ◽  
Cooling Rates ◽  
Other Hand ◽  
Metal Ceramic

The aim of this study was to investigate the effect of cooling rate on the hardness and phase transformation of a Pd-Ag-based metal–ceramic alloy with or without ice-quenching. A total of 28 test specimens, in an as-cast state, were fabricated. A multiple firing simulation was performed on the randomly selected specimens (n = 3/group) in a porcelain furnace; each firing was followed by cooling at the relatively low or high cooling rate. In addition, ice-quenching after oxidation was introduced before the normal firing process (n = 3/group). Microhardness, microstructure, phase transformation and elemental distribution were observed. Oxidation followed by ice-quenching allowed the alloy to be in a homogenized state. On the other hand, the oxidation-treated specimens followed by cooling at relatively high or low cooling speeds showed much higher hardness than the ice-quenched specimen after oxidation, which was resulted from the formation of the metastable precipitates based on the InPd3 phase with tetragonal structure. The hardness of ice-quenched alloy after oxidation was recovered in the very next firing step at both the relatively high and low cooling rates. In all specimens, the Pd-rich matrix and the InPd3-based precipitates were observed. The hardness of a Pd-Ag-based metal–ceramic alloy with and without ice-quenching depended on the cooling rate during the firing process.

scholarly journals Influence of Cooling Rate on Microstructure Formation of Si–Mo Ductile Iron Castings

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1634
Author(s):  
Marcin Górny ◽  
Magdalena Kawalec ◽  
Beata Gracz ◽  
Mirosław Tupaj
Keyword(s):  
Cooling Rate ◽  
Ductile Iron ◽  
Metallic Matrix ◽  
Graphite Nodule ◽  
Microstructure Formation ◽  
Cooling Rates ◽  
Iron Castings ◽  
Cooling Conditions ◽  
Wide Range ◽  
Longitudinal Ultrasonic Wave

The present study highlights the effect of the cooling rate on the microstructure formation of Si–Mo ductile iron. In this study, experiments were carried out for castings with different wall thicknesses (i.e., 3, 5, 13, and 25 mm) to achieve various cooling rates. The simulation of the cooling and solidification was performed through MAGMASOFT to correlate the cooling conditions with the microstructure. The phase diagram of the investigated alloy was calculated using Thermo-Calc, whereas the quantitative metallography analyses using scanning electron microscopy and optical microscopy were performed to describe the graphite nodules and metallic matrix morphologies. The present study provides insights into the effect of the cooling rate on the graphite nodule count, nodularity, and volumetric fractions of graphite and ferrite as well as the average ferritic grain size of thin-walled and reference Si–Mo ductile iron castings. The study shows that the cooling rates of castings vary within a wide range (27 °C–1.5 °C/s) when considering wall thicknesses of 3 to 25 mm. The results also suggest that the occurrence of pearlite and carbides are related to segregations during solidification rather than to cooling rates at the eutectoid temperature. Finally, the present study shows that the longitudinal ultrasonic wave velocity is in linear dependence with the number of graphite nodules of EN-GJS-SiMo45-6 ductile iron.

Microstructure Evolution of Heavy Section Ductile Iron

2010 ◽  
Vol 97-101 ◽  
pp. 1020-1023 ◽  
Author(s):  
Xiao Gang Diao ◽  
Zhi Liang Ning ◽  
Fu Yang Cao ◽  
Shan Zhi Ren ◽  
Jian Fei Sun
Keyword(s):  
Cooling Rate ◽  
Ductile Iron ◽  
Solidification Time ◽  
Cooling Curve ◽  
Eutectic Solidification ◽  
Spheroidal Graphite ◽  
Eutectic Cell ◽  
Cooling Curves ◽  
Iron Castings ◽  
Heavy Section

Ductile iron, Heavy section, Cooling curve, Microstructure, Cooling rate. Abstract. Two 250×250×250 mm cubic ductile iron castings solidified in sand and insulation mould were fabricated. The effect of cooling rate on graphite and matrix microstructure of heavy section ductile iron together with their cooling curves were evaluated. Results show that increasing the cooling rate leads to fine graphitization and favors spheroidal graphite formation. The matrix structure is fully ferrite structure at the edge of both castings, while pearlite can be seen near the eutectic cell boundaries at the center of two castings. Furthermore, the amount of pearlite increases with increasing solidification time. Cooling curves confirm that cooling rate affects solidification time of the eutectic transformation and characteristic temperature points on the cooling curves remain unchanged. Low cooling rate appears to significantly increase the eutectic plateau length. Besides, cooling curves show that eutectic temperature remains constant (about 1160°C), which allows for spheroidal graphite formation. Undercooling and inoculation fading during the long time eutectic solidification lead to pearlite formation in the center of cubic ductile iron castings.

Structural Characteristics of Ductile Iron at Different Rare Earth Contribution from a Magnesium Ferrosilicon Alloy

2014 ◽  
Vol 216 ◽  
pp. 17-22
Author(s):  
Valentin Uta ◽  
Iulian Riposan
Keyword(s):  
Trace Elements ◽  
Rare Earth ◽  
Rare Earth Elements ◽  
High Purity ◽  
Ductile Iron ◽  
Structural Characteristics ◽  
Graphite Morphology ◽  
Nodular Graphite

The structural characteristics of ductile irons were studied using different rare earth elements (REE) in Mg-FeSi treatment alloys (0.005 - 0.025%REEres), in un-inoculated and Ca-bearing FeSi in the mould inoculated irons. In relatively high purity base iron, in terms of anti-nodularising trace elements, (Thielman factor K = 0.7-0.8), increasing REE content after Mg-treatment aggravated the carbides tendency and decreased the nodular graphite compactness, in both un-inoculated and inoculated irons. Graphite parameters improve for lower REE content, and, in both cases, for inoculated irons. A low content of REEres (0.005 to 0.01%) for K < 0.8 is practical and sufficient in a Ca-bearing FeSi alloys inoculated iron to control carbides sensitivity and to sustain acceptable nodular graphite morphology formation.

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