The influence of thermal hardening on mechanical properties and microstructural evolutions of as-printed carbon steel

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Additive Manufacturing (AM) is recent concept in fabrication to produce parts with different metallic materialssuch as steels, titanium alloys, superalloys, biocompatible metals as raw, semi-final, or final products for whichmaterial is added layer by layer instead of being formed by conventional shaping processes. In some industriessuch as biomaterials, aerospace, marine; technology readiness level (TRL) has gained enough to producecertified parts that could be competitive with their conventional versions as the process allows adapting eachpart to the specific need. However, the mechanical properties may not meet the expectations in service due tocomplex microstructure formed during AM processes.In the first step of the project, two different types of steels fabricated by two different process parameters werereceived. The main objective was to investigate the possible microstructural modification obtained fromchanging process parameters during printing. Using electron back scattered phase (EBSP) and localmisorientation maps, our first deliverable (2 first months - by end of January 2019) was to identify the strainheterogeneity formed during printing by interpreting data acquired from EBSD analysis. One of the sampleswas a stainless steel and the other one was a carbon steel.For the continuation of research work developed so far, it is necessary to get involved with mechanicalproperties. In this regard, initial hardness measurements were applied on carbon steels after thermal hardeningtreatment. This alloy is prioritized on request of our partner. It was found that changing process parametersduring printing affects the hardness value in carbon steel samples causing severe macro-cracking duringthermal hardening after printing. This confirms the literature talking about premature fracture for thermallyhardened carbon steels after printing [7]. Therefore, for the next step of our collaboration, it is necessary tocontinue the research work in a way to modify the thermal treatment required after printing in order to identifyoptimum thermal hardening process parameters according to the microstructure obtained during printing.