Strain hardening of metastable austenitic steel under repeated simple loading at different temperatures

The industrial application of stainless steels is of high importance because of their high corrosion resistance and forming behaviour. The evolution of martensite during the deep drawing processes leads to an increasing strain hardening of the material. In the collaborative research centre 675 “Erzeugung hochfester metallischer Strukturen und Verbindungen durch gezieltes Einstellen lokaler Eigenschaften” (Creation of high strength metallic structures and joints by setting up scaled local material properties), metal forming processes is being researched. Emphasis on this part of the project is the stress-induced formation of martensite in sheet metal and bulk metal components in metastable austenitic steel. The aim of the investigations is to develop partial structure fields of martensite in sheet metal components in order to construct a lightweight structure. Therefore, components are divided into stretched and non-stretched parts. This leads to a defined buckling of components, for example in case of a crash. Furthermore, the effect of the transformation induced formation of martensite in metastable austenitic steel should be utilised on bulk metal forming components. Thereby special load adapted components with locally optimized properties are producible, like austenitic ductile regions and martensitic high-strength areas.

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Microstructure and properties of violin strings made of metastable austenitic steel

International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) ◽

10.3139/146.110215 ◽

2009 ◽

Vol 100 (11) ◽

pp. 1557-1565 ◽

Cited By ~ 3

Author(s):

Rüdiger Haas ◽

H. Peter Degischer ◽

Peter Pongratz ◽

Anke R. Pyzalla

Keyword(s):

Austenitic Steel ◽

Microstructure And Properties ◽

Metastable Austenitic Steel

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Structural Transformations and Mechanical Properties of Metastable Austenitic Steel under High Temperature Thermomechanical Treatment

Metals ◽

10.3390/met11040645 ◽

2021 ◽

Vol 11 (4) ◽

pp. 645

Author(s):

Igor Litovchenko ◽

Sergey Akkuzin ◽

Nadezhda Polekhina ◽

Kseniya Almaeva ◽

Evgeny Moskvichev

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

High Temperature ◽

Austenitic Steel ◽

Structural Transformations ◽

Initial State ◽

Twin Boundaries ◽

Metastable Austenitic Steel ◽

Average Grain Size ◽

Heating Up

The effect of high-temperature thermomechanical treatment on the structural transformations and mechanical properties of metastable austenitic steel of the AISI 321 type is investigated. The features of the grain and defect microstructure of steel were studied by scanning electron microscopy with electron back-scatter diffraction (SEM EBSD) and transmission electron microscopy (TEM). It is shown that in the initial state after solution treatment the average grain size is 18 μm. A high (≈50%) fraction of twin boundaries (annealing twins) was found. In the course of hot (with heating up to 1100 °C) plastic deformation by rolling to moderate strain (e = 1.6, where e is true strain) the grain structure undergoes fragmentation, which gives rise to grain refining (the average grain size is 8 μm). Partial recovery and recrystallization also occur. The fraction of low-angle misorientation boundaries increases up to ≈46%, and that of twin boundaries decreases to ≈25%, compared to the initial state. The yield strength after this treatment reaches up to 477 MPa with elongation-to-failure of 26%. The combination of plastic deformation with heating up to 1100 °C (e = 0.8) and subsequent deformation with heating up to 600 °C (e = 0.7) reduces the average grain size to 1.4 μm and forms submicrocrystalline fragments. The fraction of low-angle misorientation boundaries is ≈60%, and that of twin boundaries is ≈3%. The structural states formed after this treatment provide an increase in the strength properties of steel (yield strength reaches up to 677 MPa) with ductility values of 12%. The mechanisms of plastic deformation and strengthening of metastable austenitic steel under the above high-temperature thermomechanical treatments are discussed.

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