| 摘要 |
PURPOSE:To manufacture spheroidal graphite cast iron with high strength and toughness by austempering spheroidal graphite cast iron and forming a mixed structure consisting of semi-austenite, bainite and martensite by surface working. CONSTITUTION:Spheroidal graphite cast iron is austempered by heating at 800- 950 deg.C austenitizing temp. for 0.5-3hr and quenching to 350-450 deg.C. By the austempering, a mixed structure consisting of about 10-70vol% residual semi- austenite which causes martensitic transformation by working and the balance bainite or bainite and martensite is formed. Surface working is then carried out by cutting, shot peening or other method to cause martensitic transformation. Part of the structure is converted into martensite, the residual compressive stress is increased, and the fatigue strength is remarkably improved by work hardening, thus obtaining spheroidal graphite cast iron with high strength and toughness.
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