中硅钼耐热蠕墨铸铁排气歧管材料和工艺探讨

Discussion on Material and Production Process of Medium Silicon-Molybdenum Vermicular Iron Exhaust Manifold

对轿车发动机排气歧管而言,蠕化率控制在50%左右可以获得最佳的抗热疲劳性能,因此不能认为我国的蠕铁标准中规定的蠕化率高于50%的要求偏低了,也不能把蠕化率的高低作为衡量工艺水平的依据。中硅钼蠕铁的抗热疲劳性能为普通蠕铁的3倍,因而是制造排气歧管的理想材料。采用成分合适的稀土镁系蠕化剂,能兼顾蠕化率控制和切削加工性能两方面的要求。在自动化造型和自动浇注炉条件下,包内冲入法和槽内喂丝法相结合的蠕化工艺是成功的工艺。

For the manifold of sedan engine, the best thermal fatigue properties can be obtained by keeping the percent of vermicular graphite at about 50%, therefore it shouldn＇t be considered that the lowest v.g. percent limit of 50% specified in Chinese Vermicular Iron Standard is too lower, and it is also not proper to take the v. g. percent as the basis for judging the level of production technology. The thermal properties of medium siliconmolybdenum vermicular iron are about three times of that of normal vermicular iron, so it is an ideal material for producing manifold. By adopting RE-Mg series vermicularizing alloy of proper composition, it is possible to meet both the requirement of vermicularizing c, ontrol and requirement of machinability. Practice showed that, under the conditions of automatic moulding and automatic pouring furnace, a successful vermicularizing process is to adopt pour-over（sandwich） process in ladle as the principal process, and then adupt the cored wire injection in tapping launder as a supplementary process.