Filtern
Erscheinungsjahr
- 2018 (5)
Dokumenttyp
- Posterpräsentation (3)
- Beitrag zu einem Tagungsband (1)
- Vortrag (1)
Referierte Publikation
- nein (5) (entfernen)
Schlagworte
- Martensitic stainless steels (5) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (1)
Quenching and partitioning (Q&P) heat Treatment increases the 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). The austenitic-martensitic microstructure is gained by an increased austenitization temperature, water quenching and additional partitioning. The partitioning enables local carbon diffusion, which stabilizes retained austenite and leads to partial reversion of martensite to austenite. The influence of partitioning time was studied for the martensitic stainless steel AISI 420 (X46Cr13, 1.4034). In line with these efforts, metallographic, XRD and EBSD measurements were performed to characterize the microstructural evolution. The mechanical properties were tested using tension and compression loading. Additional corrosion investigations showed the benefits of Q&P heat treatment compared to conventional tempering. The reversion of austenite by the partitioning treatment was verified with EBSD and XRD. Furthermore, the results of the mechanical and corrosion testing showed improved properties due to the Q&P heat treatment.
The quenching and partitioning (Q&P) heat treatment enables a higher deformability of high strength martensitic steels. The Q&P heat treatment was applied on the martensitic stainless steel 1.4034 (X46Cr13) to study the influence of partitioning time. Therefore, extensive characterizations of the mechanical properties, focussing on the materials behaviour under different mechanical load scenarios, were performed. A comprehensive analysis of the microstructural evolution was per-formed for different heat treatment and mechanical loading states. A complete solution of chromium carbides was detected to be a first requirement for successful Q&P heat treatment. The comparison of common quenching and tempering with the Q&P heat treatment verifies the extensively enhanced materials strength whereat the formability is still acceptable. The microstructural reason was detected to be an increasing aus-tenite fraction due to austenite reversion at subgrain boundaries of martensite besides the stabilising of retained austenite. Further a distinctive strength differential effect was observed.
Hardness and pitting corrosion resistance are the major quality criteria of cutlery. Both are achieved by the heat treatment (austenitization, quenching and tempering) of the normally used martensitic stainless steels. The established quality control method regarding the pitting corrosion resistance is an alternating immersion test in 1 % NaCl solution at 60 °C according to DIN EN ISO 8442. This standard test shows a high deviation, which limits any optimization of the heat treatment process. New approaches for corrosion testing of martensitic stainless-steels were developed and used in the last years to connect the weak pitting corrosion resistance of martensitic stainless-steels with the phenomenon of chromium depletion. The tempering temperatures used in the industrial heat treatment of cutlery are too low to explain the appearance of chromium depletion. For this reason, a systematic investigation of three heat treatment parameters (austenitization time, cooling speed and tempering temperature) were performed on the martensitic stainless-steels X50CrMoV15 (1.4116) to detect their contribution to chromium depletion. The electrochemical potentiodynamic reactivation (EPR), which is very sensitive to any change of the microstructure, was used to quantify the degree of chromium depletion. The KorroPad indicator-test was applied to correlate low pitting corrosion resistance to the presence of chromium depletion. The results of all investigations allow conclusions about the very small process window, which is necessary to achieve cutlery with high pitting corrosion resistance.
The copper alloyed stainless steel 1.4542 (X5CrNiCuNb16-4) is used in different areas due to its good mechanical properties and corrosion resistance. Strength and corrosion re-sistance can be adjusted by the heat treatment, which is of importance for the application of this alloy. The mechanical properties (strength and hardness) are attributed to the dispersive precipitation of the copper rich ε–Phase. The additional precipitation of chromium carbides can reduce the corrosion resistance. Different ageing states were produced to investigate the precipitation behaviour with various methods. Furthermore, the influence of cold-rolling on the precipitation behaviour was studied in comparison to a solution annealed state without deformation. The microstructure was studied by SEM and the variations of hardness and magnetic proportion were characterised. The electrochemical potentiodynamic reactivation (EPR) was used to determine the corrosion resistance and detect chromium depletion in all heat-treated states. The results show that a work hardening accelerates the precipitation rate, while ageing at 600 °C reduces the corrosion re-sistance due to chromium depletion.
The copper alloyed stainless steel 1.4542 (X5CrNiCuNb16-4) is used in different areas due to its good mechanical properties and corrosion resistance. Strength and corrosion resistance can be adjusted by the heat treatment, which is of importance for the application of this alloy. The mechanical properties (strength and hardness) are attributed to the dispersive precipitation of the copper rich ε–Phase. The additional precipitation of chromium carbides can reduce the corrosion resistance. Different ageing states were produced to investigate the precipitation behaviour with various methods. Furthermore, the influence of cold-rolling on the precipitation behaviour was studied in comparison to a solution annealed state without deformation. The microstructure was studied by SEM and the variations of hardness and magnetic proportion were characterised. The electrochemical potentiodynamic reactivation (EPR) was used to determine the corrosion resistance and detect chromium depletion in all heat-treated states. The results show that a work hardening accelerates the precipitation rate, while ageing at 600 °C reduces the corrosion resistance due to chromium depletion.