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, M 7C3 type carbides were roughly classified into "primary M7C3 carbides" and "eutectic M7C3 carbides" with a 11.2μ m 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 M 7C3 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.

The effect of heat treatment on the microstructure and mechanical properties of Ti-alloyed hypereutectic High Chromium Cast Iron (HCCI) containing Fe-17 mass%Cr-4 mass%C-1.5 mass%Ti was investigated. The size distribution and the volume fraction of carbides (M7C3 and TiC) as well as the matrix structure (martensite) were examined by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). It was found that the number of fine secondary M7C3 carbides with a size below 1 μm increases with lower holding temperatures and shorter holding times during heat treatment. The number of coarse primary M7C 3 carbides with a size above 11.2 μm increases with increasing holding temperatures and longer holding times. In addition, the number of TiC carbides increases with increasing holding times, and martensite units are more refined at longer holding times and lower holding temperatures, respectively. Moreover, the volume fraction of martensite increases with increased holding times. In conclusion, low holding temperatures close to the eutectic temperature and long holding times are the best heat treatment strategies in order to improve wear resistance and hardness of Ti-alloyed hypereutectic HCCI.

In-situ observations on the dynamic precipitation behavior of secondary carbides in Ti-alloyed High Chromium Cast Iron (HCCI) were performed by using a Confocal Laser Scanning Microscope (CLSM). Moreover, the detailed characterization of the microstructure before and after heat treatment was performed by using scanning electron microscopy (SEM). The secondary carbides, which precipitate from the matrix during heat treatment, were identified as M7C3 type carbides by using transmission electron microscopy (TEM). The number, size and volume of secondary carbides during heating, holding and cooling process were quantitatively evaluated based on the in-situ observation and SEM results. It was found that ferrite (alpha) and secondary carbides start to precipitate from the matrix at around 575 degrees C and 840 degrees C, respectively, during the heating process. In addition, the in-situ results showed that the number of secondary carbides increase with an increased heating temperature and time. Moreover, it was found that the size of these secondary carbides increase at higher temperatures and longer holding times. However, the number of secondary carbides increased with a decreased temperature. Finally, it was found that the volume fraction (similar to 5%) of secondary carbides was not changed to a large extent for the different heat treatment conditions being investigated.

In this study, in order to obtain complete size distribution results, the maximum carbide size in a Fe-17 mass% Cr-4 mass% C hypereutectic High Chromium Cast Iron (HCCI) produced with different cooling conditions, titanium additions and heat treatment conditions was determined by using the statistics of extreme values (SEV) method. In addition, the shape factor, circularity, was estimated in order to classify the type of carbides (primary M7C3 carbides, TiC carbides and secondary M7C3 carbides). Compared to the smaller size carbides, such as TiC carbides and secondary M7C3 carbides, it was found that the slope of the extreme value distribution (EVD) regression lines is lower for the large sized carbides such as primary M7C3 carbides than for the smaller carbides. Moreover, it was found that the circularity value for the larger size carbides is higher than for the smaller carbides. Furthermore, the estimated and observed maximum carbide sizes were compared with each other for all carbide types. The characteristic of the different carbide types are summarized and classified based on the shape factor. Finally, the relationship between the carbide size distribution including the maximum carbides size and mechanical properties is discussed based on the combination of a size distribution analysis and a maximum size analysis.