Study On Microstructures And Mechanical Properties Of Heavy Section Low-temperature Ferrite Nodular Cast Iron

Low-temperature ferrite nodular cast iron of heavy section is the emergingproducts in nodular cast iron industry in recent years. Compared with normal ferritenodular cast iron, the low-temperature ferrite nodular cast iron on the compositioncontrol, spheroidizing inoculation process and the organization controlrequirements are stricter. In order to acquire the requirements of low-temperatureimpact properties and elongation, the castings of heavy section ferrite nodular castiron present the ferritic matrix, cannot appear chunky graphite. In recent years,some achievements has been made on the low-temperature ferrite nodular cast ironin our country,but most of the domestic manufacturers still fail to grasp keytechnology, the production of castings which they produced are small, thickness,and simple, the growing market demand of ductile iron cannot be satisfied.In the present paper, the heavy section low-temperature ferrite ductile castiron was prepared by sand mould process. We studied the functions of Si, Ni, Sband other alloy elements which affected quality of heavy section ductile iron; Theeffects of technology factors (like nodularizer, inoculation, pouring temperatureand wall thickness) on heavy section ductile iron be analysed; Observed thegraphite and matrix organization by optical microscopy and analysed the elementswhich around the graphite ball and chunky graphite by scanning electronmicroscopy (SEM) and (EDS).The results showed that:1, For the heavy section low-temperature ferriteductile cast iron, the chunky graphite can be restrained by both increasing pouringtemperature and adding defined amount Sb, but the latter effect more powerful.When Si content in1.8%-2.0%and2.0%-2.2%,add0.005%and0.008%Sbrespectively, chunky graphite can be fully restrained, and no pearlite be promoted;2, The content of C, Si around chunky graphite was obviously higher than whicharound nodule graphite, and the content of La, Ce, Sb around nodule graphite washigher than which around chunky graphite;3, The tensile strength, yield strengthand hardness could be improved and－40℃low-temperature impact toughness isdeclined by improved Si content or added0.6%Ni, when Si content at2.0%-2.2%or adding0.6%Ni,－40℃low-temperature impact energy still can be guaranteed atthe level of individual value≥10J, average value≥10J;4, The graphitemorphology could be evidently improved by used yttrium base heavy rare-earth spheroidizing and choosed efficient inoculation method;5, As the thicknessincreased, the eutectic freezing time and diameter of nodule graphite be increased,and the synthesis mechanical properise be decreased.