AISI4140 processed by powder bed electron beam melting with subsequent surface layer treatment - From process strategy to material properties

调质钢是广泛应用于机械工程的材料。由于其化学成分，这些钢适合硬化，并且在淬火和回火状态下具有相对较高的抗拉强度。适合预期用途的热处理，即淬火和回火，通常由淬火和随后的单步回火组成，能够有针对性地适应技术要求。在过去的几年里，增材制造和生成制造工艺（AM）已经成为传统制造和成型工艺的一个有前途和有竞争力的替代方案。粉末增材制造工艺，即激光金属沉积，激光金属粉末床熔合（PBF-LB/M），也称为选择性激光熔化（SLM），以及电子束金属粉末床熔合（PBF-EB/M），也称为选择性电子束熔化（EBM），已经证明自己已经成熟，可以在不同长度尺度上制造最高几何复杂性的部件。特别是，包括粉末床的工艺可以生产丝状结构，因此，通过在屏蔽建筑外壳中加工，可以保证对工艺条件的良好控制。与PBF-LB/M工艺相比，PBF-EB/M工艺具有在真空和高温下制造组件的优点，后者与粉末材料所需的预热有关。迄今为止发表的研究结果表明，PBF-EB/M工艺中适当的暴露策略允许加工不同的材料，例如不锈钢，工具钢，Ni和co基高温合金，硬质金属，金属间化合物，铝，铜，铍和铌。这些材料的加工质量非常高。尽管如此，PBF-EB/M技术仍然专注于钛合金。因此，迄今为止，通过PBF-EB/M工艺对传统钢材进行增材制造一直不受关注。本项目解决了热处理钢增材制造领域的基本问题，同时考虑了一种资源和成本效益高的表面层工艺，这在国际社会尚未在这方面进行彻底研究。其目的是增加相关载荷条件下的使用寿命，并最终提高加工合金的结构完整性。

Quenched and tempered steels are materials widely employed for mechanical engineering applications. These steels are suitable for hardening due to their chemical composition and, in the quenched and tempered state, have a relatively high tensile strength. A heat treatment adapted to the intended use, i.e. quenching and tempering, which usually consists of hardening and the subsequent single step tempering, enables a targeted adaptation to technical requirements. In the past few years, additive and generative manufacturing processes (AM) have become a promising and competitive alternative to conventional manufacturing and shaping processes. Powder based AM processes, i.e. laser metal deposition, laser-based powder bed fusion of metals (PBF-LB/M), also referred to as selective laser melting (SLM), and electron-beam powder bed fusion of metals (PBF-EB/M), also referred to as selective electron beam melting (EBM), have proven themselves to be mature to manufacture components of highest geometric complexity on different length scales. In particular, the processes comprising a powder bed enable the production of filigree structures, whereby good control of the process conditions can be guaranteed by processing in shielded build envelopes. In contrast to PBF-LB/M, the PBF-EB/M process offers the advantages of manufacturing components under vacuum and elevated temperature, the latter being related to the required preheating of the powder material. Research results published to date have shown that suitable exposure strategies in the PBF-EB/M process allow processing of different materials, e.g. stainless steels, tool steels, Ni and Co-based superalloys, hard metals, intermetallic compounds, aluminum, copper, beryllium and niobium. These materials can be processed in very high quality. Nevertheless, the PBF-EB/M technology continues to focus on titanium alloys. Thus, additive manufacturing of conventional steels via the PBF-EB/M process has so far been out of focus. The present project addresses elementary questions in the field of additive manufacturing of heat-treatable steels and at the same time considers a resource- and cost-efficient surface layer process, which has not yet been studied thoroughly in this context in the international community. The aim is to increase the service life under relevant loading conditions and, eventually, to improve the structural integrity of the alloys processed.