Zhifu Huang

Effect of Ti addition on morphology and size of primary M7C3 type carbide in hypereutectic high chromium cast iron

Abstract Effect of Ti addition on the morphology and size of primary M7C3 type carbide in hypereutectic high chromium cast iron was investigated. The results indicated that the carbide is refined gradually, and its morphology becomes more equiaxed as titanium addition increases, but rather slowly when Ti addition exceeds 0·95%. The qualitative measurement result indicated that value shape factor K increases clearly first and then changes little, and the average equivalent diameter D changes against K exactly. Furthermore, by TEM analysis and Brammit’s theory calculation, the results also indicated that there are orientation relationships of TiC||M7C3 and [011]TiC||[0001]M7C3 between M7C3 type carbide and TiC, and the lattice misfit δ between TiC and M7C3 is 1·32%, explaining that TiC may provide the effective substrate plane for M7C3 nucleation to ameliorate morphology and size of primary M7C3 type carbide.

Effect of titanium on the as-cast microstructure and impact toughness of hypereutectic high-chromium cast iron

Abstract The effect of titanium on the as-cast microstructure of a hypereutectic high-chromium cast iron was investigated by means of optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results indicate that the primary M7C3 carbides are refined and spheroidized with the addition of a suitable amount of titanium. TiC is found in the primary carbide by energy dispersive spectroscopy analysis. The mechanism of titanium modification on the microstructure of the alloy is also discussed. In addition, the impact test result indicates that, compared with the hypereutectic high-chromium cast iron without titanium addition, the impact toughness value of hypereutectic high-chromium cast iron with titanium additions is improved and approximately reaches 6.4 J · cm−2.

Effect of chromium content on cementite – pearlite interaction of white cast iron during three-body abrasive wear

Purpose This paper aims to demonstrate the effect of varying chromium content on the wear behavior of white cast iron, to study the interaction relationship between cementite and pearlite in white cast iron, while estimating their contribution rate in abrasive wear. Design/methodology/approach To study interaction of cementite-pearlite of white cast irons with different chromium content in three-body abrasive wear, three kinds of chromium white cast iron, bulk single-phase cementite, pure pearlite samples and the white cast iron (WCI), were prepared using the melting and casting technique. The so-called pure pearlite samples have the same chemical composition, microstructure and properties as the pearlite matrix in white cast iron. Findings Results indicated that the interaction has a negative value. Its absolute value decreased with increasing chromium addition. Meanwhile, a high load resulted in an increased interaction value. The contribution rate of cementite to interaction, which was higher than that of pearlite, increased with increasing chromium addition. This indicated cementite was a main phase. Besides, the reductive size of abrasive has a significant effect on the contribution rate at the high load. These prominent cementite occurred fracture, when small size abrasive indented the matrix. These result in the absence of a protective effect of cementite during wear process. Eventually, the contribution rate of cementite decreased significantly. Originality/value This paper demonstrates the effect of varying chromium content on wear behavior of white cast iron, to study the interaction relationship between cementite and pearlite in white cast iron while estimating their contribution rate in abrasive wear.

Effects of Chromium Addition on Preparation and Properties of Bulk Cementite

Bulk cementites with the Cr contents of 0, 3. 01, 6. 03, 8. 22, and 11. 51 mass% were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The results indicated that when the Cr content was low (3. 01 mass%), the phases were composed of cementite with a small amount of α-Fe at a sintering temperature of 1173 K, but the microstructure became single-phase alloyed cementite as the Cr content was further increased. It showed that micro-addition of Cr was beneficial for promoting the formation of cementite. Furthermore, the mechanical performance of cementite can be greatly affected by the variation of Cr content. The hardness, elastic modulus and elastic recovery presented a remarkably increasing tendency with the addition of Cr, and the maximum micro-hardness and elastic modulus values reached 1070. 74 HV and 199. 32 GPa, respectively, which were similar to the precipitation phase (cementite) obtained by melting and casting techniques. Moreover, when the Cr content was below 11. 51 mass%, the crystal structure of Fe3 C-type cementite would not change with increasing the Cr content. A Cr atom replaced an Fe atom in the lattice of the cementite, and voids appeared when Cr was doped into the cementite at content of about 11. 51 mass%, causing the relative density to decrease.