Casting Process Development of the Bimetal Hammer and Its Abrasive Wear Resistance Property

• Main Authors: Pi-Chun Yu, 游弼鈞
• Other Authors: Yung-Ning Pan
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/80315009228749185367

碩士 === 國立臺灣大學 === 機械工程學研究所 === 95 === This study intended to develop the casting method for the production of bimetal hammers which consist of Cr-Ni steel shank and high Cr cast iron head, to establish the optimal heat treatment conditions for achieving the desired microstructures, hardness and wear resistant property, and to analyze the characterizations of carbides precipitated and the interface between the aforementioned two alloys by using SEM and EDAX. The aim of this study is to attain a bimetal hammer which has a tough alloyed steel shank and a high wear resistant head, which can replace the traditional single alloy (high Mn steel) hammer with substantially increased service life. A double-pour technique was employed to cast the bimetal hammer. A bottom-pour gating system with an overflow located at the intended interface between two alloys, together with a top open riser have been designed for this particular casting. Also, the optimal heat treatment conditions have been found to be (900~1000)°C/2hr/ FAC/500°C/2hr. The as-cast microstructures of the hammer head consist of proeutectic austenite dendrites and eutectic phases of M7C3 carbide and austenite. After heat treatment, most of the austenite transformed to martensite after quenching, which subsquently transformed to temper martensite after tempering. In addition, numerous small secondary carbides, which have been identified as M7C3, can also be observed within the original austenite domain. The as-cast microstructure of the hammer shank is martensite, which transformed to temper martensite after heat treatment. Furthermore, the analyses of the interface region reveal that not only a sound fusion between two alloys was achieved, but also little porosity and oxides were observed. The developed bimetal hammer exhibits good combined properties of a tough shank, 21 J/cm2, and a hard head, over 50HRC, which has much better wear resistance than the traditional high Mn steel hammer.