Effects of heat treatment on wear resistance and fracture toughness of duo-cast materials composed of high-chromium whit
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I. INTRODUCTION
HYPER-EUTECTIC high-chromium white cast irons have excellent wear and corrosion resistance and are inexpensive, and thus have been used for impact coal crusher hammers, pulverizer rings, chute liner, and hardfacing alloys of rolls or molds.[1,2,3] Their excellent abrasive wear resistance is achieved from the high volume fraction of hard M7C3-type chromium carbides having Vickers hardness of 1200 to 1400.[4,5,6] However, these irons are not suitable for wear-resistant components, particularly those exposed to heavy impact. Thus, it is recommended for two parts, one for wear resistance and the other for toughness, to be combined to form one part. Recently, duo-casting in which a high chromium steel having excellent wear resistance and a plain carbon steel (or a low chromium steel) having outstanding toughness are simultaneously cast has been developed.[7,8] In this method, the wearresistant part is first cast, and then inserted into a mold to cast the ductile part, thereby making a mechanical bonding between the two cast parts. The recent study[8] on the wear-resistant alloys has focused on the improvement of microstructure and abrasive wear resistance. To ensure a wider application of duocasting, it is required to extend the life of the wear-resistant part and to further improve its wear resistance. Thus, in this study, the idea of heat treating duo-cast materials was suggested to further improve wear resistance because the austenitic matrix of the wear-resistant part can be hardCHANG KYU KIM, Research Assistant, is with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784, Korea. SUNGHAK LEE, Professor, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, is also with the Materials Science and Engineering Department, Pohang University of Science and Technology. Contact e-mail: [email protected] JAE-YOUNG JUNG, Principal Researcher, is with the New Materials and Components Research Center, Research Institute of Industrial Science and Technology, Pohang, 790-330, Korea. Manuscript submitted July 31, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
ened by forming martensite after the heat treatment. The duocast materials composed of a high-chromium white cast iron having excellent wear resistance and a low-chromium steel having sufficient toughness were fabricated using a duocasting method, and effects of the size, volume fraction, and distribution of chromium carbides on hardness, wear resistance, and fracture toughness were investigated. By varying the chromium content, three wear-resistant alloys having different size, volume fraction, and distribution of chromium carbides were fabricated, and then heat treated to change the volume fraction of austenite and martensite in the matrix. From the correlation of microstructure with wear resistance and fracture toughness, optimum compositions of the wearresistant part and heat-treatment conditions were achieved to improve the performance of the duo-cast materials. II
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