微量Sn对灰铸铁组织和性能的影响

Sn作为一种合金化元素,在灰铸铁中既可强烈促进珠光体的生成,又可细化珠光体.在实际生产中,由于某些生铁中含有过量的Sn,铸件易产生裂纹或显微裂纹,导致铸件报废.制备了不同Sn含量的铸件试样,并测定了其抗拉和抗弯强度,用金相显微镜观察不同Sn含量对铸件的石墨形态和基体组织的影响,同时详细考察了其铸造性能.结果表明:适量的Sn会促进珠光体基体的形成、细化共晶团,而对石墨的组织和形态无明显的不良影响.同时微量的Sn溶于奥氏体中,降低了发生先共析铁素体和珠光体的温度范围,使收缩率降低.但过量的Sn增加碳化物和磷共晶的数量,同时使灰铸铁的白口宽度增加,使铸件产生硬脆性,从而导致热裂和冷裂,这是铸件产生裂纹的主要原因.在生产中,应采取措施使铸铁中Sn含量控制在0.102％以下,并结合孕育处理等措施改善铸件的组织,提高力学性能.

Effect of Trace Sn on Microstructure and Properties of Gray Cast Iron

Sn as an alloying element in the gray cast iron not only can strongly promote the formation of pearlite,but also refine the pearlite.When some pig iron was used to produce gray iron casting,crack or micro-cracks will form due to the excess Sn in the pig iron and this resulted in the reject of the castings.Cast iron samples with different Sn content were prepared and their tensile and bending strength were investigated,and the graphite morphologies and microstructure of samples were studied by the metallographical microscope.Also the casting characteristics of the samples were studied in detail.The results show that proper content of Sn can promote the formation of pearlite structure and refine eutectic,while has no adverse effects on the graphite structures and morphologies.That small amounts of Sn dissolved in austenite can lower the temperature range of occurrence of eutectoid ferrite and pearlite,the contraction rate.However,excessive Sn will increase the amount of carbides and phosphorus eutectic,and increase the white width of gray cast iron,which makes the casting hard and brittle,results in hot tearing and cold cracking which are the main reasons of casting crack.Measures must be taken to limit the content of Sn in gray iron ≤0.102% in the production.Also it is necessary to take inoculation measures to improve the structure of casting and strengthen the mechanical properties.