International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 14 (2017) pp. 4675-4686 © Research India Publications. http://www.ripublication.com 4675 Microstructural Characteristics and Mechanical Properties of Heat Treated High-Cr White Cast Iron Alloys Kh. Abdel-Aziz 1a , M. El-Shennawy 1b* and Adel A. Omar 1c 1 Taif University, Engineering College, Mechanical Engineering Department, Taif, Post Code 888, KSA. a On leave from Zagazig University, Faculty of Engineering, Materials Engineering Department, Zagazig, Egypt. b On leave from Helwan University, Faculty of Engineering, Mechanical Engineering Department, Helwan, Egypt. c On leave from Benha University, Faculty of Engineering, Mechanical Engineering Department, Benha, Egypt. Abstract High Cr white cast irons are an important class of wear resistant materials currently used in a variety of applications that requires high wear resistance and reasonable toughness. The outstanding performance of these alloys is due to the presence of large amounts of chromium carbides which exhibit high hardness. The size, type and morphology of these carbides control the wear resistance and toughness. The microstructural characteristics of these alloys, and consequently their wear resistance, can be extensively changed by varying the chemical composition or the solidification rate or by specific heat treatment after casting. Heat treatments for all high-Cr WCI alloys are essential to change their microstructure and therefore, to improve their wear resistance to suit the individual application requirements. Changing in chemical composition and heat treatment carried out to this alloy related to microstructural characteristics and mechanical properties of high Cr white cast iron alloys are oresented. Keywords: High-Cr WCI alloys, microstructural characterization, abrasive wear resistance, alloying additions, heat treatment, mechanical properties. INTRODUCTION The high alloy white irons are primarily used for abrasion resistant applications and are readily cast in the shape needed in machinery used for crushing, grinding and general handling of the abrasive materials. The presence of M7C3 eutectic carbides in the microstructure provides high hardness needed for abrasion resistant applications. The metallic matrix supporting the carbide phase in these irons can be adjusted by the alloy content and heat treatment to develop the proper balance between resistance to abrasion and toughness. All high alloy white irons contain chromium to prevent the formation of graphite on solidification, stabilize the carbide and to form chromium carbides which are harder than iron ones. Most of them also contain nickel, molybdenum, copper or combinations of these alloying elements in order to prevent the formation of pearlite in the microstructure [1,2]. The chromium-molybdenum white irons (class II of ASTM A532) contain 11 to 23% Cr and up to 3% Mo and some Ni and Cu and can be supplied; either as-cast with an austenitic or austenitic-martensitic matrix, or heat treated with a martensitic matrix microstructure for maximum abrasion resistance and toughness. These irons provide the best combination of toughness and abrasion resistance of all white irons and are used in hard rock mining equipment, slurry pumps, coal grinding mills, and brick molds [3]. MECHANICAL PROPERTIES AND APPLICATIONS OF HIGH CR IRON ALLOYS The tensile strength of pearlitic white irons normally ranges from about 205 MPa for high-carbon grades to about 415 MPa for low carbon grades. The tensile strength of martensitic irons with M3C carbides ranges from about 345 to 415 MPa, while high chromium irons, with their M7C3 type carbides, usually have tensile strengths of 415 to 550 MPa [4]. Limited data indicate that the yield strengths of white irons are about 90% of their tensile strengths. These data are extremely sensitive to variations in specimen alignment during testing. The elastic modulus of a white iron is considerably influenced by its carbide structure [4]. An iron with M3C eutectic carbides has a tensile modulus of 165 to 195 GPa, irrespective of whether it is pearlitic or martensitic, while an iron with M7C3 eutectic carbides has a modulus of 205 to 220 GPa. MICROSTRUCTURAL CHARACTERISTICS OF HIGH CR WHITE CAST IRONS As-cast austenitic and pearlitic microstructures High Cr white cast irons are ferrous alloys containing chromium between 12 and 30%. It is well documented that the microstructure of all hypoeutectic high Cr white iron alloys in the as cast condition consists of a network of M7C3 eutectic