呋喃树脂-磺酸自硬砂导致球铁件表层组织异常的原因

An Investigation of the Abnormal Structure at the Surface Layer of Nodular Iron Castings Produced by Furan Resin Bonded and Sulfonic Acid Cured Sand Mold

本实验研究查明,当用甲苯磺酸作催化剂的呋喃树脂自硬砂生产稀土镁球铁件时,通常在其铸件表层出现异常组织。提出导致异常组织产生的原因,是由于甲苯磺酸在铁水浇注和凝固过程中,受热作用分解出SO2气体,并吸附在铸件的表面离解成硫原子后扩散进入铸件表层一定深度,同时同其中的Mg、RE和Mn反应形成硫化物,从而使石墨球化和稳定珠光体的有效元素含量不足,导致铸件表层出现异常组织,并显著降低试件的冲击值(低约44%)。

The abnormal structure usually appears at the surface layer of nodular iron castings produced by furan-sulfonic acid cured sand mold. The sulfonic acid is toluene sulfonic acid （TSA） and the nodulizing agent is Mg-RE alloy, we can reasonably suppose that the abnormal structure （graphite flakes in a ferrite-rich matrix） is caused by the evolution of sulfur dioxide （SO2） combining with TSA during casting and solidification. It is possible that sulfur atoms, dissociated from the adsorbed SO2 at the metal surface, diffuse into certain depth and react with Mg, RE and Mn to form sulfides, which result in a deficiency of corresponding effective elements, and causing a malfunction of nodulizing agent and pearlite-stabilizing effect. The consequence is deteriorated by their mechanical properties such as the impact resistance value decreasing about 44%.