几年前,我们为北京某机床厂干型生产了Z30-40铸铁钻床空心立柱。立柱件重500kg,壁厚40～55mm,材料为HT15～33。由于我厂执行的标准是GB976-67,即铸件以抗弯(或抗拉)强度作为验收的标准,而硬度不作为验收的依据,因而造成第一批铸件未能满足用户对硬度值(HB170～241)的要求。后来我们采用正火工艺挽救 A few years ago, we produced the Z30-40 cast iron hollow drill post for the dry type of a machine tool plant in Beijing. Column weight 500kg, wall thickness 40 ~ 55mm, the material is HT15 ~ 33. Since the standard of our factory is GB976-67, that is, the strength of the castings is accepted as the standard of acceptance (bending strength), and the hardness is not accepted as the basis of acceptance. As a result, the first batch of castings failed to meet the users’ ~ 241) requirements. Later, we use normalizing process to save