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The novel heat treatment concept, “quenching and partitioning” (Q&P) has been devel-oped for high strength steels with enhanced formability. This heat treatment involves quenching of austenite to a temperature between martensite start and finish, to receive a several amount of retained austenite. During the subsequent annealing treatment, the so called partitioning, the retained austenite is stabilized due to carbon diffusion, which results in enhanced formability and strength regarding strain induced austenite to mar-tensite transformation. In this study a Q&P heat treatment was applied to a Fe-0.45C-0.65Mn-0.34Si-13.95Cr stainless martensite. Thereby the initial quench end temperature and the partitioning time were varied to characterize their influence on microstructural evolution. The microstructural changes were analysed by dilatometer measurements, X-ray diffraction and scanning electron microscopy, including electron back-scatter diffrac-tion. Compression testing was made to examine the mechanical behaviour. It was found that an increasing partitioning time up to 30 min leads to an enhanced formability with-out loss in strength due to a higher amount of stabilized retained and reversed austenite as well as precipitation hardening.
The quenching and partitioning (Q+P) heat treatment enables a higher deformability of high strength martensitic steels. Therefore, it is necessary to have some metastable austenite in the microstructure, which transforms in martensite during plastic deformation (TRIP-effect). This condition is guaranteed by the quenching and the additional partitioning treatment. Due to local carbon diffusion retained austenite is stabilized and a partial reversion of austenite from martensite occurs. The Q+P heat treatment was investigated for the martensitic stainless steel 1.4034 (X46Cr13) concerning the influence of partitioning time. In line with these efforts metallographic, XRD- and EBSD-measurements were performed to characterize the microstructural evolution. The mechanical experiments included mechanical testing with different strain rates. The reversion of austenite by the partitioning treatment could be detected with EBSD- and XRD-measurements. Further-more the results of the mechanical testing showed improved values of strength and de-formability because of the Q+P heat treatment.
Electrochemical tests, hardness measurements, and microstructure analysis are performed to study the influence of austenitizing, quenching, and tempering parameters on the corrosion resistance of the martensitic stainless steel grade X50CrMoV15 (1.4116). Different heat treatment states were studied using an adapted EPR-Test to evaluate the chromium distribution and depletion caused by the formation and dissolution of chromium rich carbides. The EPR results were correlated with pitting corrosion behavior, demonstrating the strong effect of heat treatment parameters on the susceptibility of martensitic stainless steels to corrosion phenomena.
Iron aluminides depict a sustainable and light-weight material class which could be employed in many applications requiring high strength at intermediate to high temperatures. According to first results, the alloy Fe-26Al-4Mo-0.5Ti-1B surpasses conventional materials in wet corrosion resistance and creep resistance up to 650 °C. For these reasons, the AiF research project “WAFEAL – Materials applications for iron aluminides” was initiated to transfer these findings into a standardised materials dataset and to derive best practices for processing. In the first place, a set of different microstructures adjusted by varying casting methods, wall thicknesses and heat treatments was investigated and correlated with hardness on macro and micro scale. Correlations were drawn between solidification rates and resulting grain sizes and hardness. The effect of vacancy hardening was only verified for wall thickness as low as 2.5 mm. Moreover, a common decrease of macrohardness after a heat treatment at 1000 °C for 100 h was observed irrespective of casting process or wall thickness. This effect was linked with an unexpected decrease of the complex boride phase fraction which acts as a hardening phase.