| 摘要 |
PURPOSE:To inexpensively manufacture a tough vehicle engine mounting member having required strength and impact resistance, by incorporating respectively specific percentages of C, Si, Mn, P, S, Cu, Ni, and Mg into Fe and also by forming a mixed structure of bainite and retained austenite. CONSTITUTION:A spheroidal graphite casting which has a composition consisting of, by weight, 2.5-4.1% C, 1.5-3.0% Si, 0.3-0.5% Mn, <=0.15% P, <=0.03% S, 0.3-0.7% Cu, 0.1-0.5% Ni, 0.005-0.08% Mg, and the balance essentially Fe is machined in an as-cast state. Subsequently, this casting is heated and held at 830-920 deg.C for 0.5-3hr to undergo austenitizing treatment and is then subjected to isothermal transformation treatment consisting of heating and holding at 360-400 deg.C for 0.2-2.5hr so as to be formed into a structure in which bainite and retained austenite (about 25-45vol.%) exist as a mixture in the matrix of spheroidal graphite cast iron. In this way, the engine mounting member securing required strength, toughness, and fatigue strength and improved in machinability can be manufactured.
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