Metal additive manufacturing is a molding method with a high degree of freedom because it can be created from high-strength materials using by CAD, etc. In recent years, there is a demand for metal additive manufacturing due to the demand for more complex mechanisms and shape in industrial products. However, the mechanical properties of metal additive manufacturing materials as metallic materials are not clear compared to metallic materials by melting method. In this study, two types of metal additive manufacturing (AM) materials with different lamination directions are carburized and heat treated to clarify the differences from general metallic materials and to clarify the causes. The carburized AM materials were confirmed to have a surface hardness of 550HV and a total carburization depth of 200 μm, but the amount of carburization differed depending on the orientation. In addition, when analyzed with a SEM, a metal structure was formed in an equiaxed crystal shape, and segregation of metal elements was observed.

Much more steel must be produced from scrap to meet emissions targets, and utilizing this growing resource is a sound economic strategy. However, the presence of contaminating elements restricts the applications in which end-of-life scrap can replace primary steel. The use of low alloyed quenching and tempering steel grade such as 39MnCrB6-2 to reach high mechanical characteristics (around 1000 MPa) obliges often to apply low tempering temperatures for which tempering embrittlement may be observed. In this paper, it is proposed to reduce the hold time and to increase the temperature during conventional tempering to (1) reduce the embrittlement because of segregation of elements like copper, (2) to change the fracture mechanism with finer martensite sub-grains and (3) to promote θ particles with smaller dimensions but higher density.

Advanced characterization techniques and modeling are used to get new insight on the microstructural evolutions occurring during the tempering of low-alloyed steels with initial martensitic microstructure. Tempering temperatures from 150°C to 600°C, are considered to make vary the metallurgical phenomena activated, form carbon segregation to defects to precipitation of different types of carbides (transition, cementite, alloyed). A large range of carbon compositions, from 0.1 to 0.7 wt.% are investigated, with the same main experimental technique: in situ HEXRD at synchrotron beamlines, with complementary post mortem fine-scale characterizations by TEM and 3D-APT. In the middle of this range (~0.3wt.%), the usual sequence is observed: successive precipitation of transition and cementite carbides. New observations concern the carbon concentrations outside this range. For high carbon concentrations (~0.6wt.%), the same sequence occurs but the martensite/ferrite matrix remains highly supersaturated in carbon compared to equilibrium, for a long time and even after the precipitation of cementite. For low carbon concentrations (~0.1wt.%) most of the carbon starts to segregate at defects (dislocations, lath boundaries). This enters in competition with the transition carbides which are almost fully hindered, whereas cementite precipitates afterwards. Two previous models from literature are combined to predict the concomitant kinetics of carbon segregation and precipitation. Segregation puts the transition carbides at a disadvantage with cementite and for this reason, the latter precipitates earlier than usually reported. The effects of nitrogen enrichment (up to ~0.4 wt.%N, context of carbonitriding thermochemical treatments) in austenite domain of stability (before the martensitic quench) are also investigated. In low-alloyed steel considered (23MnCrMo5), nitrides are formed upon enrichment (CrN, MnSiN 2 ). This has a strong impact on the precipitation sequence, compared to model systems previously investigated (Fe-N, Fe-C-N).

The increasing demand for accurate fatigue modeling of powder metallurgy components in automotive, aerospace, and medical industries necessitates improved knowledge of composition-microstructure interactions. Variations in feedstock composition and thermomechanical history can produce unique microstructures whose impact on fatigue performance has not been adequately quantified. When characterizing additively manufactured 316L that is within nominal standard chemistry limits, oxide and nitride species were observed preferentially in the specimen contour region. Thermodynamic simulations provide evidence of segregation of the low manganese and high nitrogen composition driving this precipitation of these phases. When present in the specimen, they promoted brittle fracture mechanisms during fatigue.

Through hardened steel ball fatigue failure is an atypical mode of failure in a rolling element bearing. A recent full-scale bench test resulted in ball spalling well below calculated bearing life. Subsequent metallurgical analysis of the spalled balls found inferior microstructure and manufacturing methods. Microstructural analysis revealed significant carbide segregation and inclusions in the steel. These can result from substandard spheroidized annealing and steel making practices. In addition, the grain flow of the balls revealed a manufacturing anomaly which produced a stress riser in the material making it more susceptible to crack initiation. The inferior manufactured balls caused at least an 80% reduction in rolling contact fatigue life of the bearing.

Samples from forged and heat-treated steel products with known quench crack histories have been mapped in order to study a possible relation between banding segregation and quench cracking. The products were medium carbon low alloy steels produced by ingot and continuous casting. EDS X-ray mapping was used to characterize the banding pattern and tensile testing revealed corresponding properties. The experimental procedures are described in the paper along with test results and conclusions.