有关Si-Mo球墨铸铁的一些问题

Some Questions about Si-Mn Nodular Iron

80多年前,英国开发了含1.8%～2.2%C、5%～7%Si、0.5%～0.8%Mn的西拉尔（Silal）耐热铸铁.20世纪40年代,球墨铸铁问世,含4%～6%Si的球墨铸铁抗氧化性能和抗热生长性能均显著高于Silal铸铁.为了兼顾抗氧化性能和韧性,耐热球墨铸铁的含硅量一般不超过5%.为进一步改善耐热球铁的性能,在提高其硅含量的同时加入少量钼,其最适宜的加入量为0.5%～1.0%.20世纪70年代,Si-Mn球墨铸铁就已成为常用的耐热铸造合金.硅对Si-Mn球铁性能的影响主要是：（1）促进石墨化、抑制渗碳体析出;（2）提高抗氧化性能;（3）减少铸件的热生长;（4）固溶强化铁素体.钼对Si-Mn球铁性能的影响主要是：（1）随着钼含量从0.02%提高至1.93%,Si4球铁的室温和高温（最高650℃）强度,特别是抗拉强度明显提高,塑性下降;（2）提高Si4球铁的抗蠕变强度和断裂强度.碳和碳当量、锰、磷、硫等也对Si-Mn球铁的性能有一定的影响.为此,对于Si-Mn球铁,其碳当量应略大于常规球铁,锰含量一般不超过0.4%～0.5%,磷含量应低于0.05%,硫含量控制在0.010%～0.015%.此外,还论述了Si-Mn球铁在化学成分和力学性能要求等方面的标准,以及熔炼、炉前处理、铸件收缩缺陷的预防、冷隔及其预防、厚壁铸件中的碎块状石墨、铸件的热处理等生产工艺问题.

A Silal heat-resistant cast iron containing 1.8 to 2.2%C, 5 to 7%Si, 0.5 to 0.8%Mn has been developed in Britain above eighty years ago. The nodular iron has came out in the 1940 s. The nodular iron with 4 to 6 % Si is superior to the Silal cast iron in resistance to both oxidation and thermal growth. As a rule, silicon content not exceeding 5 % is advisable for the heat-resistant nodular iron in order to give consideration to its oxidation-resistance and toughness. In order to further improve the performances, while silicon content is increased a small amount of molybdenum （preferably 0.5 to 1.0 %） also is added to the heat-resistant nodular iron. A Si-Mn nodular iron has become commonly used cast alloy in the 1970 s. The effects of silicon on properties of the Si-Mn nodular iron are as follows： （1） to promote graphitization and to restrain precipitation of cementite; （2） to improve oxidation-resistance; （3） to reduce thermal growth of castings; （4） to make ferrite be solution strengthened. The effects of molybdenum on properties of the Si-Mn nodular iron are that： （1） to increase obviously strength （particularly, tensile strength） at room temperature and elevated temperatures（up to 650 ） of Si4 nodular iron with the increase of molybdenum content from 0.02 to 1.93 %; （2） to raise creep strength and fracture strength of Si4 nodular iron. Carbon and carbon equivalent, phosphor, sulfur also exert a certain influence on properties of the Si-Mn nodular iron. For this reason, as to the Si-Mn nodular iron the carbon equivalent should be slightly more than that of common nodular iron, the molybdenum content should not exceed the range of 0.4 to 1.5 %, the phosphor content should be lass than 0.005 %,and the sulfur content is to be controlled within the range of 0.010 to 0.015 %. In addition, the standards on chemical composition and mechanical properties requirements for the Si-Mn nodular iron, and the questions as to production processes, such as smelting, treatment at cast house, casting shrink prevention, cold shut and precaution against it, graphite fragments in thick-wall casting, heat treatment of castings, etc, were described.