The paper considers the possibility of intensifying isothermal holding processes during quenching of high-strength cast irons by using an external source of physical impact in the form of ultrasonic waves. For experimental evaluation of this effect in the laboratory of MiAM of the Physical-Technical Institute of the National Academy of Sciences of Belarus, prototypes of highstrength cast irons were cast in an ISV 0.004 crucible induction furnace. A mixture of NaNO2 and KNO3 salts in a 1:1 ratio was used as a liquid cooling medium during quenching. Ultrasonic treatment of the salt melt during the cooling of the samples was carried out using an UZG-20–15 generator in cooperation with the ITA of NAS of Belarus. The mechanical properties and structure of the treated cast irons were determined both in the cast state and after isothermal quenching.To study the effect of ultrasonic treatment of the quenching bath on the formation of the structure and properties of highstrength cast irons during isothermal quenching, a number of comparative experiments were carried out, consisting in cooling the samples from 910 °C to 350 °C with and without the use of dynamic waves to the bath. With the help of metallographic analysis, measurements of hardness and friction coefficient, the beneficial effect of ultrasonic treatment of the cooling medium on the structure and properties is shown, which is reflected in an increase in the uniformity of the distribution of hardness over the cross section of cast iron and in its wear resistance, as well as a reduction in the isothermal holding time by up to two times.
In this research, ultrasonic melt treatment (UST) was used to produce a new ultrafine grade of spheroidal graphite cast iron (SG iron) and austempered ductile iron (ADI) alloys. Ultrasonic treatment was numerically simulated and evaluated based on acoustic wave streaming. The simulation results revealed that the streaming of the acoustic waves propagated as a stream jet in the molten SG iron along the centerline of the ultrasonic source (sonotrode) with a maximum speed of 0.7 m/s and gradually decreased to zero at the bottom of the mold. The metallographic analysis of the newly developed SG iron alloy showed an extremely ultrafine graphite structure. The graphite nodules’ diameter ranging between 6 and 9 µm with total nodule count ranging between 900 to more than 2000 nodules per mm2, this nodule count has never been mentioned in the literature for castings of the same diameter, i.e., 40 mm. In addition, fully ferritic matrix was observed in all UST SG irons. Further austempering heat treatments were performed to produce different austempered ductile iron (ADI) grades with different ausferrite morphologies. The dilatometry studies for the developed ADI alloys showed that the time required for the completion of the ausferrite formation in UST alloys was four times shorter than that required for statically solidified SG irons. SEM micrographs for the ADI alloys showed an extremely fine and short ausferrite structure together with small austenite blocks in the matrix. A dual-phase intercritically austempered ductile iron (IADI) alloy was also produced by applying partial austenitization heat treatment in the intercritical temperature range, where austenite + ferrite + graphite phases coexist. In dual-phase IADI alloy, it was established that introducing free ferrite in the matrix would provide additional refinement for the ausferrite.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.