Improving the machining behaviour of powder metallurgy steels through development and optimized utilization of machinability enhancing additives

钢铁零件的粉末冶金(PM)一直面临着一个悖论，即生产出40%到50%的零件需要经过机械加工才能最终确定其几何形状的近净成形过程。此外，由于最终组织中存在孔洞，粉末冶金钢组件的可加工性明显低于锻钢组件。对于热处理或烧结硬化的粉末冶金零件，这种行为会加剧。为了改善机械加工性能，粉末冶金和零件生产商在很大程度上依赖于最初为锻钢开发的策略，即利用硫化锰(MnS)。然而，PM中的MN，特别是其混合形式，并不总是产生令人满意的结果。在含有混合MnS的粉末冶金零件中观察到机械性能的下降是典型的，以改善其可加工性。这是由于MnS的吸湿性导致其氧化和生锈。 零件。本方案总结的工作是基于20多年来对提高粉末冶金钢件可加工性的研究。最近，拉瓦尔大学开发了一种新的方法来开发新型的可加工性增强添加剂，以消除使用MnS所固有的问题。这项研究的目的是在最近的成功基础上，将粉末冶金钢和锻造钢在可加工性方面的差异降至最低。显然，要取得成功，这种改进不应以降低静态和动态机械性能为代价。因此，将对拉伸和疲劳性能进行广泛的表征，以优化作为最大机械性能函数的加工性。 通过显著降低与机械加工相关的生产成本，这些目标的实现将有助于提高粉末冶金工艺的竞争力。

Powder metallurgy (PM) of steel components is continually facing the paradox of being a near net shape process that produces parts of which 40 to 50% require a machining operation to finalize their geometry. Moreover, due to the presence of porosity in their final microstructure, PM steel components are recognized as being significantly less machinable than those produced from wrought steels. This behaviour is exacerbated for heat-treated or sinter-hardened PM parts. In order to improve machinability, PM powder and parts producers largely rely on strategies initially developed for wrought steels, i.e. the utilization of manganese sulphide (MnS). Nevertheless, MnS in PM, especially in its admixed form, does not always yield desirable results. It is typical to observe a decrease of mechanical properties in PM parts containing admixed MnS to improve their machinability. This is due to the hygroscopic nature of MnS that leads to its oxidation as well as rusting of parts. The work summarized in this proposal is based on 20+ years of research on improving machinability of PM steel parts. Recently, a new approach was developed at Université Laval to develop novel machinability enhancing additives that eliminate the problems inherent to the utilization of MnS. This research aims at building on recent successes to minimize the differences in terms of machinability between PM and wrought steels. Obviously, to be successful such improvement should not be achieved at the expense of lower static and dynamic mechanical properties. Therefore, extensive characterization of tensile and fatigue properties will be carried out to optimize machinability as a function of maximum mechanical properties. Achievement of these goals will help increase the competitiveness of the PM process by significantly reducing production costs related to machining.