Influence of nickel and cobalt on microstructure of silicon solution strengthened ductile iron

Abstract

‘Second Generation’ ductile iron with a silicon content of up to 4.3 wt- exhibits a fully ferritic matrix, which is solution strengthened by silicon. Outstanding advantages of these ductile iron grades result in their strongly increasing demand. However, due to a presumed formation of a silicon long range order, the maximum strength is limited to 600 MPa at 4.3 wt- silicon. At higher silicon content, the mechanical properties dramatically decrease. In order to increase the maximum achievable strength, the potential of additional solution strengthening elements is subject of present research. Initially, the effects of cobalt and nickel on matrix, graphite shape and nodule count are investigated. Cobalt and nickel are identified as promising candidates for further solid solution hardening.

Effects of cobalt on mechanical properties of high silicon ductile irons

“…Some of the alloys were ferritised by heat-treating at 780°C for 5 h. For comparison purposes only data of fully ferritic structure in the as-cast state are showed in table A2. The works by Fischer et al [22] and Weiss et al [20] were carried out at RWTH-Aachen using the same procedures and indeed report the same results, Weiss et al [20] published the microstructure results and Fischer et al [22] the mechanical properties. The alloys contained 3.8-4.3 wt.% Si and were alloyed with up to 4 wt.% Co.…”

“…UTS, YS and A values, and Si and Co contents of the alloys investigated byFischer et al and Weiss et al[22,20].…”

Effects of high silicon contents on graphite morphology and room temperature mechanical properties of as-cast ferritic ductile cast irons. Part I – Microstructure

“…These cast iron grades have been defined as "solution strengthened ferritic ductile irons" as they are alloyed with silicon contents in the range 3.2-4.3 wto/o. lt has been reported that such high silicon contents promote high nodule count [1][2][3] and thus favor matrices with very high ferrite fractions. Such alloys have much higher strength than standard ferritic cast irons with comparatively low silicon contents though at the expense of lower ductility.…”

Mechanical Properties and Impact Toughness of Nickel and Aluminum Alloyed High Silicon Ductile Iron

“…Lower silicon contents and higher nickel contents are known to promote the nodularity [15]. The lower nodularity of alloy 2 and alloy 3 can therefore only be explained by the addition of aluminum as a ferritizing and solid solution strengthening element.…”

“…In previous studies, it was proven, that cobalt and nickel can be successfully used as additional solid solution strengthening elements in SSF DI [15][16][17]. The mechanical properties of EN-GJS-600-10 were reached at 1.5 wt.% Ni and 3.8 wt.% Si.…”