我厂生产的地下电动客车运行六年多后返厂检修。发现低合金(20SiMn)铸造架都有裂纹,少者二处,多者达15处。据分析观察,裂纹多分布在构架上平面,横梁和各种吊座凸台的附近,长度15～100毫米。有的裂纹穿透构架壁厚,尤其是Ⅳ区的裂纹(见图)按原设计规定,不得有裂纹,不准焊修。 I plant the underground electric bus to run more than six years after the plant maintenance. Found that low alloy (20SiMn) casting frame has cracks, the less two, more than 15. According to the analysis and observation, cracks are distributed in the framework of the plane, beams and bosses near the various abutments, the length of 15 to 100 mm. Some cracks through the wall thickness of the framework, in particular, the cracks in Section IV (see photo) according to the original design requirements, no cracks, not allowed to repair welding.