Effect of Cooling Rate and Ti Addition on the Microstructure and Mechanical Properties in As-cast Condition of Hypereutectic High Chromium Cast Irons

Abstract

The effect of cooling rate and Ti additions on the mechanical properties and carbides characteristics such as morphology, size distribution and composition was studied in high-chromium cast irons containing Fe-17 mass%Cr-4 mass%C. Based on the size distribution, composition and morphology, M7C3 type carbides were roughly classified into "primary M7C3 carbides" and "eutectic M7C3 carbides" with a 11.2 μm border size. Thereafter, the change of the solidification structure and especially the refinement of carbides size were determined. It was found that both the size and number values should be summarized systematically for primary M7C3 carbides and eutectic M7C3 carbides, respectively. Also, TiC carbides with a high formation temperature can not only act as a nuclei of M7C3 carbides, but they also contain a Ti(C, N) core. In the as-cast condition, the bulk hardness of the cast irons increases with an increased Ti content. In addition, the wear loss increases with an increased Ti content. Neither the bulk hardness nor the wear loss did change too much with an increased cooling rate.

Partial Equilibrium Prediction of Solidification and Carbide Precipitation in Ti-added High Cr Cast Irons

“…Our previous study by Liu, et al, 1) and other studies by Zhi, et al, 2) Chung, et al 3) and Bedolla-Jacuinde, et al 4) have reported the experimental results on Fe-4wt%C-17wt%Cr, Fe-4wt%C-20wt%Cr, Fe-4wt%C-25wt%Cr and Fe-2.5wt%C-16wt%Cr high chromium cast irons with different Ti-additions, as shown in Table 1. They found that, besides the refinement of M7C3 carbides, the volume fraction of M 7 C 3 carbide also decreases with Ti addition, as shown in Fig.…”

“…4 in our previous work [1]), it is clarified that the eutectic transformation in multicomponent alloy system is different from that in binary alloy system. That is, in multicomponent alloy system, the eutectic transformation does occur within a temperature range but not under a constant temperature.…”

“…et al 1) The raw materials were melted inside a medium frequency induction furnace (45 kW, 7 kHz) with Ar gas atmosphere. Then, the molten alloy was poured into three kinds of moulds (metal, silica sand and graphite, respectively) with 120 mm length × 84 mm width × 55 mm height.…”

“…It is helpful to make clear the effects of carbide composition variation on its hardness. Then, for all the alloys in Table 1, the effects of carbon, titanium and chromium on the precipitation sequence, the amount and the composition of carbides are discussed in details with the help of previous experimental results, [1][2][3][4] from the viewpoint of hardness © 2014 ISIJ control by carbides. Finally, it is confirmed that PE approximation clearly presents its versatile application up to the case of large amount of precipitated carbides.…”

“…First, the carbide precipitation mechanism during solidification is carefully analyzed on Fe-4wt%C-17wt%Cr-1.5wt%Ti based alloys. At that time, the predicted precipitation sequence is compared with those in DSC thermal analyses and the predicted micro-segregation in each phase is compared with the measured composition of M 7 C 3 carbide using the experimental samples made in our previous study by Liu, et al 1) The composition variation in primary and eutectic M7C3 carbide can be distinguished both in prediction and measurement. It is helpful to make clear the effects of carbide composition variation on its hardness.…”