| 摘要 |
A method for producing austempered spheroidal graphite iron having a microstructure comprising bainite, ferrite and austenite. A nodular-iron casting containing 2-3.5% Si, 0-2% Mn, 0-5% Ni 0-0.3% Sn, 0-03% Cr, 0-3% Mo, 0-1.5% Cu, and 3.3-3.8% C and at most 0.08% P and 0-015% S is partially austenitized by heat treatment at a temperature beneath the temperature at which austenite and graphite or austenite are in equilibrium, but within the temperature range in which ferrite, austenite and graphite are in equilibrium. The temperature of the casting is then rapidly lowered by at least 100 K min<-><1>, and is held at a constant temperature within a range of 235 and 425 DEG C, wherewith part of the austenite formed is converted to bainite to provide a casting that includes a bainite structure with a residual austenite content of 5-40%, preferably 15-20%, and a ferrite content of 10-15%, preferably 20-40%. |
