Temperatur-Abhängigkeit der mechanischen Eigenschaften in martesitisch-austenitischen nichtrostenden Stählen erzielt durch "Quenching and Partitioning" (Q&P)-Wärmebehandlungsverfahren
Mechanische Eigenschaften von metallischen Werkstoffen und ihre mikrostrukturellen Ursachen
Zusammenfassung der Projektergebnisse
Quenching and Partitioning (Q&P) processing was applied to stainless steels containing C contents exceeding 0.45 mass-%. Successful application of Q&P processing requires sufficient C enrichment of austenite to prevent the occurrence of deformation-induced martensite at low strains. Because of the brittle nature of martensite in the present high C steels, suppression of deformation-induced martensite was of special importance. In spite of the partitioning of C between martensite and austenite, as confirmed by X-ray diffraction measurements, deformation-induced martensite formation still occurred during tensile tests at RT. The raised stability of austenite and delayed formation of martensite enhanced the tensile elongation as the test temperature was raised to 200 °C. In-situ and ex-situ X-ray diffraction measurements indicated that only a small fraction of the C present in the martensite successfully migrated to the austenite. Based on detailed dilatometry investigations, C in the martensite is expected to have quickly diffused to the boundaries with austenite. This results in pinning of dislocations near the boundaries and disables the reactions required for the formation of athermal martensite. Pinning of dislocations by the C diffusing out of the martensite was supported by the occurrence of dynamic strain aging aided by deformation-induced martensitic transformation. Dynamic strain aging occurred during RT tensile testing of one of the steels which retained an almost fully austenitic microstructure after quenching to RT. On this basis, the C partitioned into the austenite during Q&P processing is expected to be mainly supplied by that accumulated at the martensite-austenite boundaries. To enhance the extent of C partitioning, strategies such as the suppression of cementite formation in martensite and the application of tensile stresses during partitioning were examined. Paraequilibrium cementite formation, as a major tempering reaction competing with the partitioning of C, was effectively opposed by alloying with Si. Nevertheless, changes in the C enrichment of austenite caused by Si addition remained negligible. Similarly, experiments involving partitioning under external uniaxial tensile stress indicated no measurable enhancement of the C enrichment. This implies a rapid consumption of C by tempering reactions in the martensite. In this case, only C atoms preexisting at martensite-austenite boundaries contribute to the partitioning. Another factor which might have counteracted the expected beneficial effect of uniaxial tensile stress is the non-hydrostatic nature of the internal stresses induced by uniaxial tensile loading. Using the austenitic steel exhibiting ready deformation-induced martensite formation at RT, the effect of pre-straining at temperatures above Mdd→α temperature on the deformationinduced martensite formation at RT was studied. Tensile pre-straining by 20% did not influence the strain dependence of deformation-induced martensite fraction; only serrations on the stress-strain curves became more pronounced. Amplification of serrations was justified by changes in the spatial distribution of deformation-induced martensite due to pre-straining. These changes should have facilitated interactions between the C atoms diffusing out of the martensite and dislocations in the surrounding austenite.
Projektbezogene Publikationen (Auswahl)
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Influence of Martensite Fraction on Tensile Properties of Quenched and Partitioned (Q&P) Martensitic Stainless Steels, Steel Res. Int. 2016, 87 (8), 1082–1094
Huang, Q.; Schröder, C.; Biermann, H.; Volkova, O.; Mola, J.
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Influence of Martensite Fraction on the Stabilization of Austenite in Austenitic–Martensitic Stainless Steels, Metall. Mater. Trans. A 2016, 47 (5), 1947–1959
Huang, Q.; De Cooman, B. C.; Biermann, H.; Mola, J.
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Austenitic Nickel- and Manganese-Free Fe-15Cr-1Mo-0.4N-0.3C Steel: Tensile Behavior and Deformation-Induced Processes between 298 K and 503 K (25 °C and 230 °C), Metall. Mater. Trans. A 2017, 48 (3), 1033–1052
Mola, J.; Ullrich, C.; Kuang, B.; Rahimi, R.; Huang, Q.; Rafaja, D.; Ritzenhoff, R.
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Dilatometry Analysis of Dissolution of Cr-Rich Carbides in Martensitic Stainless Steels, Metall. Mater. Trans. A 2017, 48 (12), 5771–5777
Huang, Q.; Volkova, O.; Biermann, H.; Mola, J.
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Tensile Elongation of Lean-Alloy Austenitic Stainless Steels: Transformation-Induced Plasticity versus Planar Glide, Mater. Sci. Technol. 2017, 33 (10), 1224–1230
Huang, Q.; Volkova, O.; Biermann, H.; Mola, J.
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Effect of tensile stresses on the partitioning of carbon during quenching and partitioning (Q&P) of stainless steels, 6th International Conference on Advanced Steels (ICAS), Jeju, South Korea, 2018
Q. Huang, X. Feng, J. Mola
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Influence of Si addition on the carbon partitioning process in martensitic-austenitic stainless steels, in: IOP Conference Series: Mater. Sci, Eng., WTK 2018, Chemnitz, Germany, 2018
Q. Huang, O. Volkova, B.C. De Cooman, H. Biermann, J. Mola
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Tempering Reactions and Elemental Redistribution During Tempering of Martensitic Stainless Steels, Metall. Mater. Trans. A 2019, 50 (8), 3663– 3673
Huang, Q.; Yao, M.; Timokhina, I.; Schimpf, C.; Biermann, H.; Volkova, O.; De Cooman, B. C.; Mola, J.
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Neutron Diffraction Analysis of Stress and Strain Partitioning in a Two-Phase Microstructure with Parallel-Aligned Phases, Sci. Rep. 2020, 10 (1), 13536
Huang, Q.; Shi, R.; Muránsky, O.; Beladi, H.; Kabra, S.; Schimpf, C.; Volkova, O.; Biermann, H.; Mola, J.
