Improving High-Temperature Performance of High Si-Alloyed Ductile Iron by Altering Additions
- PDF / 6,253,906 Bytes
- 15 Pages / 595.276 x 790.866 pts Page_size
- 74 Downloads / 183 Views
Copyright Ó 2020 American Foundry Society, corrected publication 2020 https://doi.org/10.1007/s40962-020-00524-0
Abstract High alloyed Si ferritic ductile irons can offer potential benefits because they combine high strength, ductility at room temperature, and low oxidation rate at high temperature. However, there is one known drawback and that is these cast irons have limited performance during thermal cycling due to a significant drop of ductility at warm temperatures. This decrease in ductility has been linked to poisoning ferrite grain boundaries by Mg. Therefore, thermodynamic simulations were used to identify altering additions which were able to meditate this negative effect by forming intermetallic phases with Mg. To verify thermodynamic predictions, three alloys were cast including a base and two high Si ductile irons with additions of P and
Sb. High-temperature performance of these alloys was experimentally verified including tensile properties at warm temperatures (350–550 °C), oxidation in air at temperatures (700–800 °C), and thermal cycling between 300 and 800 °C. SEM and TEM analyses confirmed that the studied additions reacted with Mg forming different compounds which could prevent poisoning ferrite grain boundaries and improve high-temperature performance of high Si ductile iron.
Introduction
increase tensile strength up to 650–700 MPa, but can significantly decrease the elongation below 1% at room temperature.6.
Silicon (Si) in ductile irons works as a ferrite stabilizer and strengthener in the alloy. Si ranging from 3.5 to 5% has been studied extensively for its solution-strengthening effect and high Si, solution strengthened ferritic (SSF). These ductile irons were introduced in international standards.1,2 In their fully ferritic state, 4% Si alloy concentration can increase the tensile strength up to 550 MPa as compared with 400 MPa which is common for ductile irons with lower Si levels (2.2–2.4% Si). Therefore, increasing the amount of Si in ferritic ductile irons can be attractive because they offer a combination of high strength and ductility at room temperature. Many researchers have shown that increasing Si above 4% improves oxidation resistance at elevated temperatures and these ductile irons alloyed by Mo are suggested for cast exhaust manifolds and other elevated temperature applications.3–5 However, increasing the amount of Si to 5% has been shown to
International Journal of Metalcasting
Keywords: high Si ductile iron, altering P and Sb, high temperature properties
Another problem of high Si ductile iron relates to sudden drops in ductility at warm (400 °C) test temperatures. In the work, 7–9 mechanical properties of the ductile iron were determined by tensile test from room temperature to 500 °C. The ferritic ductile iron exhibited minimum ductility at 500 °C, followed by an increased elongation as the temperature increased to 600 °C. The authors8 reported the embrittlement temperature for a ferritic ductile iron near 400 °C. The combined effects of the metal matrix (ferrite/p
Data Loading...
