灰铁缸体表面突发锈斑的原因分析

Analysis of Reason Causing Rust Spots on Surface of Cast Iron Cylinder Block

对HT250缸体铸件突发锈斑进行了金相、能谱及化学分析,结果表明:锈斑是因铸件浅表面存在CaO和CaS夹渣所致:在铸件存放过程中,由于CaO和CaS渣有较强的吸水能力,使夹渣区域产生电化学反应而生成锈斑并不断扩展。排查发现,采用w(Ca)>1%的高效随流孕育剂是导致出现夹渣的主要原因。指出在铁液充型比较平稳的情况下,不宜选用高钙孕育剂作薄壁灰铁件的随流孕育剂。

The sudden rust spots on the surface of HT250 gray iron cylinder block was investigated by using microstructure inpection,energy spectrometer analysis and chemical analysis.The result showed that the rust spots were caused by the CaO and CaS slag existing in the thin surface layer of the casting as follows：during the conservation process of the castings,since the CaO and CaS slag had quite strong water-absorbing ability that caused electrical-chemical reaction and as the result,the rust spots formed and continually spread.The reasons screening-investigation found that using high effect stream inoculant containing Ca1% was the main reason causing slag formation,and therefore,it was pointed out that,under the condition of stable mold filling,the inoculant with high Ca-content is not suitable to be used as the stream inoculant for the thin wall gray iron castings.