High-Speed Erichsen Testing of Grain-Refined 301LN Austenitic Stainless Steel Processed by Double-Reversion Annealing (original) (raw)
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Materials Science and Engineering: A, 2021
A novel processing route comprising double reversion annealing (DRA) was designed for developing bulk nanograined (NG) structure of an austenitic stainless steel (Type 301LN). The new processing concept of DRA comprised two subsequent intrinsic type processes i.e., two times cold reductions (~53% and 63%) followed by fast induction heating (~200 • C/s) and short duration annealing at different temperatures (first at 690 • C/60s and second at 750-900 • C/0.1-1s). The NG structure revealed a remarkable improvement of the mechanical properties compared to the counterparts processed by single reversion annealing. Furthermore, outstanding combination of strength and formability is achieved for the DRA structures, significantly higher than those of high-Mn TWIP steels, low-alloy TRIP steels and 304 stainless steel. For instance, a superior combination of yield strength (~950-1030 MPa) and formability index (11.8-12.5 mm) obtained after DRA at 750 • C/0.1s and 800 • C/1 s, respectively. However, the corresponding values are 300 MPa and 12 mm for TWIP steels, 500 MPa and 10 mm for TRIP steels, and 270 MPa and 12 mm for 304 stainless steel. In order to reveal the effect of DRA on the stretch formability, Erichsen cup testing was conducted of both the initial and DRA steel specimens. Moreover, Erichsen cup testing also simulated by the finite element method (FEM) to survey further details of their deformation.
Controlled martensitic reversion annealing was applied to a heavily cold-worked metastable austenitic low-Ni Cr-Mn austenitic stainless steel (Type 201) to obtain different ultrafine austenite grain sizes to enhance the mechanical properties, which were then compared with the conventional coarse-grained steel. Characterization of the deformed and reversion annealed microstructures was performed by electron back scattered diffraction (EBSD), X-ray diffraction (XRD) and light and transmission electron microscopy (TEM). The steel with a reverted grain size $ 1.5 μm due to annealing at 800 1C for 10 s showed significant improvements in the mechanical properties with yield stress $ 800 MPa and tensile strength $ 1100 MPa, while the corresponding properties of its coarse grained counterpart were $ 450 MPa and $ 900 MPa, respectively. However, the fracture elongation of the reversion annealed steel was $ 50% as compared to $ 70% in the coarse grained steel. A further advantage is that the anisotropy of mechanical properties present in work-hardened steels also disappears during reversion annealing.
2020
The notable contributions of Iranian scientists in the field of formation and reversion of strain-induced martensite for grain refinement and enhanced mechanical properties of Fe-Cr-Ni austenitic stainless steels are reviewed. Accordingly, the processing of ultrafine grained (UFG) structure via cold rolling and reversion annealing is summarized for AISI 301, 304, 309Si, 316, and 321 stainless steels, as well as their variants. The repetitive and innovative thermomechanical processing routes are introduced as well. The understanding of the stages of annealing (reversion of strain-induced martensite to austenite, primary recrystallization of the retained austenite, and grain growth) and the underlying reversion mechanisms (diffusional-type and martensitic shear-type) constitute the subsequent part of this overview. Finally, the transformation-induced plasticity (TRIP) effect in the reversion-treated metastable austenitic stainless steels is discussed. The present review paper summariz...
Materials Science and Engineering: A, 2011
ABSTRACT The formation of nano/ultrafine grain structure in a 201 austenitic stainless steel was investigated by the martensite thermomechanical treatment. Cast ingots were first homogenized, then hot-forged and solution-annealed to reduce the initial grain size. Cold rolling was then conducted down to 90% reduction in thickness, followed by reversion annealing at a temperature in the range of 1023–1173K for 15–1800s. The effect of reversion parameters on grain refinement was investigated. The resulting microstructures were characterized by a scanning electron microscopy equipped with X-ray energy-dispersive spectrometer, an X-ray diffractometer and a Feritscope. The hardness was measured by the Vickers method. The results show that a nano/ultrafine-grained structure formed in the initial stages of the reversion, but significant grain growth took place during the entire course of reversion. Initially lowered, the volume fraction of martensite increased again during the reversion treatment due to carbide precipitation. A fully austenitic nano grained 201 stainless steel with the average grain size of 100nm was produced, possessing a yield strength of about 1370MPa.
Advanced Engineering Materials, 2016
The effect of a new severe plastic deformation method, "repetitive corrugation and straightening by rolling (RCSR)" on AISI 304 stainless steel is investigated. A thermo-mechanical treatment based on the reversion of a 0-martensite is applied to produce fine-grained structure. Microstructural characterizations are conducted by X-ray diffraction and electron backscattered diffraction. Mechanical properties are investigated by measuring uniaxial tensile properties. It is found that the amount of strain-induced martensite increases monotonically with increasing of applied strain, yielding up to 90 vol% of martensite after 30 cycles of the RCSR process. By applying a subsequent annealing, austenite grain size is decreased considerably, which leads to substantial strengthening.
Austenite stability in reversion-treated structures of a 301LN steel under tensile loading
Materials Characterization, 2017
Ultrafine-grained austenitic stainless steels can be produced by the martensitic reversion process, but the factors affecting the stability of refined austenite in subsequent deformation are still unclear. To clarify this, fully and partially austenitic reversed structures with the average grain size between 24 and 0.6 µm were created in a 60% cold-rolled 301LN type (18Cr-7Ni-0.16N) austenitic stainless steel by varying the annealing conditions. The amount of strain-induced α'-martensite (SIM) during tensile loading was determined by magnetic measurements and the microstructure evolution and texture examined by electron backscatter diffraction and X-ray diffraction methods. The extensive experimental data evidenced firmly that in completely austenitic structures the austenite stability increases with decreasing grain size down to about 1 µm, obtained at 900°C, but the stability decreases drastically in the ultrafine-grained and partially reversed structures, with the average grain size of 0.6-0.7 µm obtained at 800-700°C. However, these structures are nonuniform also containing larger micron-size grains transformed from slightly deformed SIM. The low stability of austenite is not a result from the ultrafine grain size, neither due to retained phases nor texture, but the main reason is concluded to be the precipitation of CrN during the reversion at low temperatures of 800-700°C. Due to this precipitation, micron-size grains in the ultrafine and partially reversed structures show most unstable behavior under tensile deformation.
Cyclic deformation behaviour and stability of grain-refined 301LN austenitic stainless structure
MATEC Web of Conferences
Low cycle fatigue (LCF) behaviour of metastable austenitic 301LN stainless steel with different grain sizes – coarse-grained (13 μm), fine-grained (1.4 μm) and ultrafine-grained (0.6 μm) – produced by reversion annealing after prior cold rolling was investigated. Fully symmetrical LCF tests with constant total strain amplitudes of 0.5% and 0.6% were performed at room temperature with a low constant strain rate of 2×10-3 s-1. Microstructural changes in different positions within the gauge part of the specimens were examined by optical microscopy (polarized light) and electron backscatter diffraction (EBSD) technique; for quantitative assessment of the volume fraction of deformation induced martensite (DIM) a Feritscope FMP 30 was adopted. The cyclic stress-strain response and specific changes of hysteresis loop shapes in the very early stage of cycling are confronted with the character of DIM formation and its distribution in the whole volume of the material. A possible effect of str...
Metallurgical and Materials Transactions A, 2010
We describe here an electron microscopy study of shear reversion-induced nanograined/ultrafine-grained (NG/UFG) structure and evolution of tensile strained microstructure in metastable type 301 austenitic stainless steel. The NG/UFG structure with grain size in the range of 200 to 500 nm was obtained by severe cold deformation and controlled annealing in the narrow temperature range of 973 to 1073 K (700 to 800°C). The different stages of annealing involve the following: (a) transformation of strain-induced martensite to highly dislocated lath-type austenite, (b) formation of dislocation-cell structure and transformation to recovered austenite structure with defect-free subgrains, and (c) coalescence of subgrains to form a NG/UFG structure concomitant with a completely recrystallized structure, and consistent with martensitic shear-type phase reversion mechanism. The optimized cold working and annealing treatment resulted in NG/UFG material with a high yield strength (~1000 MPa) and high ductility (~30 pct) combination. Multiple deformation mechanisms were identified from postmortem electron microscopy examination of tensile strained NG/UFG 301 austenitic stainless steel and include dislocation glide and twinning. The evidence of heterogeneous nucleation of overlapping stacking faults and partial dislocations points toward deformation
2013
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with considerably enhanced mechanical properties. Two different conditions of the thermomechanical treatment were adopted and resulting microstructures with different grain sizes were characterised by optical and high resolution scanning electron microscopy (FEG SEM). Hardness measurements and tensile tests were performed to characterize mechanical properties. To reveal structural changes induced during thermomechanical treatment and during tensile tests a magnetic induction method was additionally applied. Experimental study validated the ability of the treatment to produce an austenitic stainless steel with the grain size of about 1.4 m which exhibits tensile strength of around 1000 MPa while ductility remains close to 60 %. The results obtained for both thermomechanical conditions are comp...
Journal of Materials Science, 2010
Metastable austenitic stainless steel of type AISI 304L was cold rolled to 90% with and without interpass cooling. Inter-pass cooling produced 89% of straininduced martensite whereas no inter-pass cooling resulted in the formation of 43% of martensite in the austenite matrix. The cold-rolled specimens were annealed at various temperatures in the range of 750-1000°C. The microstructures of the cold-rolled and annealed specimens were studied by the electron microscope. The grain size and low angle boundaries were determined from the orientation maps recorded by the scanning electron microscope-based electron backscattered diffraction technique. The observed microstructural changes were correlated with the reversion mechanism of martensite to austenite and volume fraction of martensite. It was noted that large volume fractions of martensite at low annealing temperatures, below 900°C, were most suitable for the formation of fine grains. On the contrary, reversion of small volume fractions of martensite at critical annealing temperature of 950°C resulted in grain refinement.