Studying a series of near eutectic spheroidal graphite cast irons with various amounts of silicon up to 9.12 wt% confirmed that: 1. silicon stabilizes ferrite to such an extent that ferrite is the Fe-rich phase appearing during solidification at the highest silicon contents; 2. silicon triggers graphite degeneracy such as chunky graphite. As well-known, cerium and magnesium do also increase the risk of chunky graphite formation while antimony counteracts cerium. Based on the metallographic observations of the present work, an index is proposed to evaluate the risk of chunky graphite appearance from the silicon, magnesium, cerium and antimony contents. Above a critical value of this index, the risk for chunky graphite formation increases steadily. Using data from previous studies, it is further demonstrated that the critical value decreases with increase in casting modulus as expected. The evolution of mechanical properties of the prepared cast irons will be presented in a second part of this study.

对一系列含9.1％（重量）多种硅的近共晶球墨铸铁的研究证实：1.硅使铁素体稳定到一定程度，使得铁素体是在最高硅含量下凝固过程中出现的富铁相；2.硅会触发石墨的简并性，例如块状石墨。众所周知，铈和镁的确会增加形成块状石墨的风险，而锑会抵消铈。基于本工作的金相观察，提出了一种指标，用于从硅，镁，铈和锑含量中评估块状石墨外观的风险。超过该指标的临界值，形成块状石墨的风险稳步增加。使用以前的研究数据，进一步证明，临界值随铸造模量的增加而降低。制备的铸铁的机械性能的演变将在本研究的第二部分中介绍。