球墨铸铁中的石墨在光学显微镜下观察为一近似的圆球形状,中心有一亮点呈辐射状,其色彩为灰色,硬度很低,只有 H_(Rc)2～3,结构疏松,由于石墨的强度低,结构松,因此试样的磨制过程易于剥落,这样往往在抛磨时给金相工作者带来了较大的困难。目前各厂矿企业中对小直径的铸件中石墨的抛磨积累了丰富的经验,且掌握了一套磨制的方法。对大厚度铸件的试 Graphite in ductile iron is observed as an approximately spherical shape under an optical microscope. The center of the graphite has a bright spot with a gray color and a low hardness. Only H_ (Rc) 2~3 has a loose structure. Since the graphite strength Low, loose structure, so the sample grinding process is easy to peel off, so often in polishing the metallographic workers have brought greater difficulties. At present, factories and mines in the small diameter of the castings of graphite polishing has accumulated rich experience, and mastered a set of grinding methods. The test of large thickness castings