The Relationships among Quenching-Tempering Heat Treatment, Metallographic Microstructure and Mechanical Properties of Low Manganese Cast Steel

• Main Authors: Kuo-Chang Lin, 林國璋
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/dn8ekw

碩士 === 逢甲大學 === 機械工程學所 === 90 === This research investigated the effect of heat treatment condition and chemical compositions(carbon or manganese) on mechanical properties, microstructure, and fluidity of low manganese cast steel (SCMn). The results of this study showed that after quenching-tempering heat treatment, the tempered microstructures of low manganese cast steel specimens were consisted of blocky ferrite, acicular ferrite and cementite. Higher tempering temperature made cementite be spheroidal apparently, and led the grains of blocky ferrite growth, reduce the amount of acicular ferrite. The tempering temperature not only changed the microstructure of low manganese cast steel, but also affected the mechanical properties. After quenching-tempering heat treatment, as the tempering temperature increased, the tensile strength and hardness level of low manganese casting steel decreased, but ductility and toughness increased. Increasing carbon and manganese contents generally increased the amount of acicular ferrite and decreased the grain size of blocky ferrite, leading to increase tensile strength and hardness level, but decrease toughness. The effect of carbon content on the tensile strength of low manganese casting steel was more significant than manganese content. As the tempering temperature increased, the rupture mode of rupture surface of the tensile and impact test specimen after ruptured exhibited completely ductile rupture with dimple characteristics. In low tempering temperature there were localized quasi-cleavage rupture of brittle rupture mode facet, in addition to ductile rupture mode. When carbon and manganese contents increased, the brittle rupture mode of rupture surface was more evident. The order of fluidity of low manganese casting steel for chemical composition was that 0.5%C>0.3%C>0.2%C, and 1.0%Mn>1.3%Mn> 1.6%Mn.