Formation of Ultrafine-Grained Structures in 304L and 316L Stainless Steels by Recrystallization and Reverse Phase Transformation

2016 ◽  
Vol 838-839 ◽  
pp. 410-415 ◽  
Author(s):  
Marina Odnobokova ◽  
Andrey Belyakov ◽  
Alla Kipelova ◽  
Rustam Kaibyshev
Keyword(s):  
Stainless Steels ◽  
Cold Working ◽  
Large Strain ◽  
Austenitic Stainless Steels ◽  
Mechanical Twinning ◽  
Subsequent Annealing ◽  
304L Stainless Steel ◽  
Reverse Phase ◽  
Bar Rolling ◽  
Ultrafine Grained

The microstructure evolution and mechanical properties of 316L and 304L austenitic stainless steels subjected to large strain cold bar rolling and subsequent annealing were studied. The cold working was accompanied by mechanical twinning and strain-induced martensitic transformation. The latter was readily developed in 304L stainless steel. The uniform microstructures consisting of elongated austenite and martensite nanocrystallites evolved at large total strains, resulting in tensile strength above 2000 MPa in the both steels. The subsequent annealing at temperatures above 700°C was accompanied by the martensite-austenite reversion followed by recrystallization, leading to ultrafine grained austenite.

scholarly journals Development of Ultrafine Grained Austenitic Stainless Steels by Large Strain Deformation and Annealing

2014 ◽  
Vol 783-786 ◽  
pp. 651-656 ◽  
Author(s):  
Andrey Belyakov ◽  
Alla Kipelova ◽  
Marina Odnobokova ◽  
Iaroslava Shakhova ◽  
Rustam Kaibyshev
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Stainless Steels ◽  
Cold Working ◽  
Subgrain Size ◽  
Large Strain ◽  
Austenitic Stainless Steels ◽  
Mechanical Twinning ◽  
Transverse Size ◽  
Ultrafine Grained

The development of ultrafine grained structures in 316L and 304-type austenitic stainless steels subjected to large strain cold working and subsequent annealing and their effect on mechanical properties were studied. The cold rolling was accompanied by a mechanical twinning and a partial martensitic transformation and resulted in the development of elongated austenite/ferrite grains with the transverse size of about 50 nm at a strain of 4. The grain refinement by large strain cold working resulted in an increase of tensile strength above 2000 MPa in the both steels. Annealing at temperatures above 500°C resulted in ferrite-austenite reversion. However, the transverse grain/subgrain size remained on the level of about 100-150 nm after annealing at temperatures up to 700°C.

Hydrogen Embrittlement of Ultrafine-Grained Austenitic Stainless Steels

2018 ◽  
Vol 54 (1) ◽  
pp. 25-45 ◽  
Author(s):  
E. G. Astafurova ◽  
S. V. Astafurov ◽  
G. G. Maier ◽  
V. A. Moskvina ◽  
E. V. Melnikov ◽  
...  
Keyword(s):  
Martensitic Transformation ◽  
Hydrogen Embrittlement ◽  
Stainless Steels ◽  
Subgrain Size ◽  
Austenitic Stainless Steels ◽  
Mechanical Twinning ◽  
Coarse Grained ◽  
Flow Strength ◽  
Hydrogen Charging ◽  
Ultrafine Grained

Abstract The effect of electrochemical hydrogen-charging on tensile properties, mechanisms of plastic deformation and fracture micromechanisms was studied using two ultrafine-grained (UFG) Cr-Ni austenitic stainless steels. UFG austenitic structures with an average subgrain size of 200 nm for CrNiMo (316L-type) and 520 nm for CrNiTi (321-type) steel were produced using hot-to-warm ABC-pressing. Hydrogen-charging up to 100 hours weakly influences stages of plastic flow, strength properties and elongation of the UFG steels. TEM analysis testifies to hydrogen-assisted partial annihilation and rearrangement of dislocations into dislocation tangles, and to hydrogen-induced variation in ratio of low- and high-angle misorientations in UFG structure of both steels. Hydrogen-alloying promotes mechanical twinning and deformation-induced γ ® e martensitic transformation in the UFG steels under tension. Ultrafine-grained CrNiTi steel with lower stacking fault energy (SFE) is more susceptible to mechanical twinning and deformation-induced γ ® e martensitic transformation in comparison with CrNiMo steel with higher SFE. The micromechanism of the fracture in hydrogen-assisted surface layers of the steels is compositional, grain-size and hydrogen content dependent characteristic. The present results demonstrate that the steels with UFG structure possess higher resistance to hydrogen embrittlement compared to coarse-grained analogues.

Annealing behavior of a ferritic stainless steel subjected to large-strain cold working

2007 ◽  
Vol 22 (11) ◽  
pp. 3042-3051 ◽  
Author(s):  
A. Belyakov ◽  
K. Tsuzaki ◽  
Y. Kimura ◽  
Y. Mishima
Keyword(s):  
Stainless Steel ◽  
Ferritic Stainless Steel ◽  
Cold Working ◽  
Large Strain ◽  
Recrystallization Behavior ◽  
Bar Rolling ◽  
Annealing Behavior ◽  
Ultrafine Grained ◽  
Continuous Recrystallization ◽  
Cold Strain

Mechanisms of microstructure evolution during annealing after cold working were studied in an Fe-15%Cr ferritic stainless steel, which was processed by bar rolling/swaging to various total strains ranging from 1.0 to 7.3 at ambient temperature. Two types of recrystallization behavior were observed depending on the cold strain. An ordinary primary (discontinuous) recrystallization developed in the samples processed to conventional strains of 1.0–2.0. On the other hand, rapid recovery at early annealing resulted in ultrafine-grained microstructures in the larger strained samples that continuously coarsened on further annealing. Such annealing behavior was considered as continuous recrystallization.

Regularities of Microstructure Evolution and Strengthening Mechanisms of Austenitic Stainless Steels Subjected to Large Strain Cold Working

2016 ◽  
Vol 879 ◽  
pp. 224-229 ◽  
Author(s):  
Andrey Belyakov ◽  
Marina Odnobokova ◽  
Iaroslava Shakhova ◽  
Rustam Kaibyshev
Keyword(s):  
Martensitic Transformation ◽  
Yield Strength ◽  
Cold Rolling ◽  
Stainless Steels ◽  
Cold Working ◽  
Large Strain ◽  
Austenitic Stainless Steels ◽  
Nanocrystalline Structures ◽  
Stable Austenite ◽  
Dislocation Strengthening

The deformation microstructures and their effects on mechanical properties of austenitic stainless steels processed by cold rolling at ambient temperature to various total strains were studied. The cold working was accompanied by the development of strain-induced martensitic transformation because of meta-stable austenite at room temperature. The strain-induced martensitic transformation and deformation twinning promoted the grain refinement during cold rolling, leading to nanocrystalline structures consisting of a mixture of austenite and martensite grains with their transverse grain sizes of 50-150 nm containing high dislocation densities. The rolled samples experienced substantial strengthening resulted from high density of strain induced grain/phase boundaries and dislocations. The yield strength of austenitic stainless steels could be increased to 2000 MPa after rolling to total strains of about 4. The martensite and austenite provided almost the same contribution to overall yield strength. The dislocation strengthening was much higher than the grain boundary strengthening at small to moderate strains of about 2, whereas the latter gradually increased approaching the level of dislocation strengthening with increasing the strain.

Hydrogen-Assisted Fracture Mechanisms in Ultrafine-Grained CrNi Austenitic Stainless Steels with Different Initial Microstructures

2018 ◽  
Vol 941 ◽  
pp. 370-375
Author(s):  
Sergey Astafurov ◽  
Elena Astafurova ◽  
Valentina Moskvina ◽  
Galina G. Maier ◽  
Eugene Melnikov ◽  
...  
Keyword(s):  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Fracture Mechanisms ◽  
Flow Strength ◽  
Hydrogen Charging ◽  
Ultrafine Grained ◽  
Electrolytic Hydrogen ◽  
Cold Rolling And Annealing ◽  
Abc Pressing ◽  
Assisted Fracture

We investigated the effect of electrolytic hydrogen-charging on regularities of plastic flow, strength and fracture mechanisms of AISI 316L and 321 austenitic stainless steels. In the steels, an ultrafine-grained structure of various morphologies was formed using methods of warm abc-pressing and thermomechanical treatment (cold rolling and annealing). Hydrogen-charging of ultrafine-grained steels reduces their yield strength and elongation. The high dislocation density and low-angle boundaries inhibit the effects of hydrogen embrittlement in 316L and 321 steels.

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