Available online at www.sciencedirect.com *- @# . * ; @ ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2011, 18(11): 31-39 Effect of Boron and Heat Treatment on Mechanical Properties of White Cast Iron for Mining Application Havva Kazdal Zeytin' , Hakan Yildirim2, Banu Berme', Selim Duduoglu' , Giirkan Kazda13 , Adem Deniz' (1. TUBITAK MRC, Materials Institute, Kocaeli 21-41470, Turkey; and Trade Inc Co, Corum 13, Turkey; Istanbul 34469, Turkey) 2. Duduoglu Steel Casting Industry 3. Chemistry Metallurgy Faculty, Istanbul Technical University, Abstract: Heat treatment methods were applied to white cast iron for improving the impact and wear resistance. Ad- ditionally, chemical composition optimization was made. Furthermore, the effect of boron addition on such applica- tions was investigated. Samples were investigated by using optical and electron microscope methods. Hardness, wear and impact tests were conducted. The results showed that the secondary carbides in the standard alloy were iron-en- riched, needlelike carbides M3C when the boron-added alloy contained FeZ3 (C, B)d type, globular secondary car- bides. It was concluded that heat treatment B provided higher wear and hardness properties, compared to the stand- ard heat treatment. Optimum mechanical properties were obtained by lower destabilisation temperatures and increas- ing temperature reduced the wear resistance and hardness. Key words: white cast iron; mining application; impact resistance; wear; toughness High strength impact and wear resistant white cast irons are used for the mining applications. These cast irons are heat treated to provide the de- sired impact and wear resistance. These heat treat- ments are chosen according to the service condi- tions. However, it is difficult to increase the wear resistance of a white cast iron without decreasing the toughness. They have high wear resistance owing to their microstructural properties. Fe-Cr-C system is the basis of the most widely used wear resistant ma- terials in the presence of the chromium carbides in the microstructure. In the F e C r C system, chromium can substitute iron in cementite up to a content of 15 %. However, for higher chromium concentrations, cementite becomes unstable and is replaced by M7 C, hexagonal carbide. The HV hardness of chromium carbide is in the range of 1 500 - 1 800, whereas the HV hardness of cementite is in the range of 1000- 1200. Although white cast irons have excellent wear resistance, their toughness is too low owing to the high carbide concentration. The selection and amount of the alloying element depend on the composition of chromium carbides, the controlled precipitation of primary and secondary carbides, the retardation of pearlitic transformation and the effect of martensitic transformation temperat~re['-~'. The most impor- tant alloying element was molybdenum. It is usually added in the range of 0.5%-4%. The formation of molybdenum carbide depended on the chromium to carbon mass ratio. When the chromium to carbon mass ratio was 5 and 10, MozC and M6C carbides were formed, respectively. Molybdenum is parti- tioned between MozC (50x1, M7C3 (25%) and the matrix (25%). The most specific property of mo- lybdenum was to stabilize the austenite phase during ~asting[~-~'. The aim of boron addition was to increase wear resistance without lowering the toughness by form- ing borides instead of carbides. As known, boron can greatly increase the hardenability of steels with a lit- tle amount, but this effect is decreased quickly with the increase of carbon content. The boride morphol- ogy of high boron white cast iron much likes that of carbide in high chromium white cast iron, but the Biography: Havva Kazdal Zeytin( 1962-), Female, Post-Doctor, Associate Professor; Received Date: August 20, 2010 E-mail: banubermeBgmai1. com;