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

钢部件的粉末冶金（PM）一直面临着近净成形工艺的矛盾，该工艺生产的零件中有40%至50%需要机加工操作来最终确定其几何形状。此外，由于在其最终微观结构中存在孔隙，PM钢部件被认为比由锻钢生产的那些部件显著更难加工。对于热处理或烧结硬化的PM部件，这种行为加剧。为了提高机械加工性能，粉末冶金粉末和零件生产商主要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MnS，特别是其混合形式，并不总是产生期望的结果。典型的是观察到含有混合MnS的PM部件的机械性能降低以改善其可加工性。这是由于MnS的吸湿性导致其氧化以及 零件.本提案中总结的工作是基于20多年来对改善粉末冶金钢零件可加工性的研究。最近，拉瓦尔大学开发了一种新方法，以开发新型机械加工性增强添加剂，消除MnS利用所固有的问题。这项研究的目的是建立在最近的成功，以尽量减少粉末冶金和锻钢之间的可加工性方面的差异。显然，为了成功，这种改进不应该以较低的静态和动态机械性能为代价来实现。因此，将进行拉伸和疲劳性能的广泛表征，以优化作为最大机械性能的函数的可加工性。 这些目标的实现将有助于通过显著降低与机加工相关的生产成本来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.