Modification of Silicon Microsegregation in Solid-Solution-Strengthened Ductile Iron by Alloying with Aluminum

Abstract

In solid-solution-strengthened ferritic ductile iron (SSFDI), a silicon content above 4.3 wt% leads to an abrupt decrease in ultimate tensile strength and elongation at fracture. This phenomenon has recently been proven to be attributed to the formation of iron-silicon long-range orderings that lead to an embrittlement of the material. It is assumed that the local tendency to form silicon superstructures is promoted in particular by the occurrence of silicon microsegregation. During solidification of ductile iron, silicon segregates inversely into the austenite. Thus, the highest silicon concentration is larger than the initial concentration of the melt and is located directly at the graphite nodules. As a straight consequence, the presence of silicon superstructures is expected primarily in these areas. Therefore, the focus is on homogenization of the silicon microsegregation profile in order to avoid the formation of brittle iron-silicon superstructures. For this purpose, in the present study the alloying concept of SSFDI is adapted. Thermodynamic-kinetic simulations as well as experimental investigations indicate that aluminum concentrations of approx. 1.2 wt% lead to an inversion of the silicon microsegregation. The findings provide a promising tool to shift the silicon embrittlement in SSFDI to higher silicon concentrations. This method could be used to increase the maximum strength, to improve toughness properties or to increase the process integrity against deviations in silicon content.

Determination of Corrosion Resistance of High-Silicon Ductile Iron Alloyed with Nb

“…A new DI classification called High-Silicon Ductile Iron (HSDI) has recently been introduced for DI with Si content ranging from 3.2 to 4.3 wt.%. It has been reported that with increasing Si content, hardness, tensile strength, and yield strength properties are promoted, while elongation to failure decreases [8,[12][13][14] and machinability and corrosion resistance improve [15][16][17][18]. These results suggest a potential advantage in the production process and performance over DI with lower Si content [10,11].…”

“…In terms of mechanical properties, Si has a significant effect on the toughness and tensile strength of ferritic DI. As the Si content increases, the yield strength and tensile strength also increase [8][9][10][11]. A new DI classification called High-Silicon Ductile Iron (HSDI) has recently been introduced for DI with Si content ranging from 3.2 to 4.3 wt.%.…”

The effect of silicon microsegregation on the mechanical properties of high silicon alloyed ductile cast iron under monotonous loading

“…This effect can be understood based on the principles of metal physics. Silicon atoms segregate during the solidification of Si-DCI [ 9 ]. Since the diffusion time is too short to homogenize the segregation profile, high Si contents remain in the vicinity of the graphite and decrease towards the interstices of the graphite.…”

“…Promising approaches exist to manipulate the segregation profile, as indicated by Franzen et al [ 9 ], and thereby tailoring the mechanical properties of Si-DCI. However, only little in-depth experimental studies of the influence of the Si-segregation profile on the mechanical properties of Si-DCI were published in the literature [ 14 ].…”

Effect of Niobium on the Microstructure and Mechanical Properties of Alloyed Ductile Irons and Austempered Ductile Irons

“…It is widely acknowledged that combining high ductility with high strength values is essential to produce dynamically loaded parts. Such premise intrigued many researchers to study the effect of small additions of niobium on different types of cast iron alloys [12][13][14][15][16][17][18][19][20][21][22][23][24]. The effect of Nb alloying differs to some extent according to the type of cast irons.…”