壳型填铁丸工艺下稀土对凸轮轴用合金铸铁组织和性能的影响

Effect of Rare Earth on Structure and Properties of Alloyed Cast Iron Used for Camshaft Cast in Shell Mould with Iron Shot Backing

对比研究了壳型填铁丸和普通湿砂型两种工艺条件下稀土对凸轮轴用CuCrMoNi多元低合金铸铁组织和性能的影响。研究结果表明,适量的稀土与Mn、S元素相互作用形成富含稀土、Mn、S的复合化合物作为石墨核心,有利于铸铁组织和性能的改善,砂型工艺下较佳的稀土加入量为0.02%～0.04%,而壳型填铁丸工艺下稀土的较佳加入量呈下降趋势。当稀土加入量达到并超过0.06%后,铸铁中出现D、E型石墨,并伴有初生铁素体,性能降低,特别在壳型填铁丸工艺条件下,合金铸铁对稀土的敏感性提高,强度性能的下降幅度比普通湿砂型工艺大。

The effects of rare earth on the structure and properties of low CuCrMoNi-alloyed cast iron used for camshafts cast in shell mould with iron shot backing and in green sand mould was compared and investigated.The result showed that proper amount of rare earth interacted with Mn and S and produced some kind of combined compound rich in RE,Mn and S which,acting as the graphite nuclei,promoted the improvement of structure and properties of the cast iron.For the sand mould castings,the optimum RE addition amount was 0.02%;for the castings cast in shell mould with iron shot backing,the optimum RE addition amount decreased.When RE addition reached 0.06%or higher,there D-and E-type of graphite and primary ferrite appeared in the structure of the cast iron which caused properties decreasing and especially obvious for the castings cast in the shell mould with iron shot backing.In the last case,the sensitivity of the alloyed cast iron to rare earth increased and strength decreasing magnitude was larger than sand mould castings.