EBSD анализ микроструктуры аустенитной стали после прокатки в криогенных условиях

This work is based on the use of electron backscatter diffraction (EBSD) methods to investigate the microstructure of metastable austeniticsteel 12X18H10T (321) after cryogenic rolling. Cryogenic deformation was accompanied by martensitic transformations, and the martensitic phase nucleation mainly in deformation bands. It is assumed that the proceeding of the martensitic transformation in the most deformed parts of the microstructure should prevent the evolution of deformation-induced boundaries in the austenite and, thus, inhibit the process of fragmentation of this phase. Mechanical twinning was the primary (or even sole) mechanism providing HAB formation in the austenite

EBSD investigation of microstructure evolution during cryogenic rolling of type 321 metastable austenitic steel

Electron backscatter diffraction (EBSD) was employed to establish microstructure evolution in type 321 metastable austenitic stainless steel during rolling at a near-liquid-nitrogen temperature. A particular emphasis was given to evaluation of microstructure-strength relationship.As expected, cryogenic rolling promoted strain-induced martensite transformation. The transformation was dominated by the γ→α′ sequence but clear evidence of the γ→ε→α′ transformation path was also found. The martensitic reactions were found to occur almost exclusively within deformation bands, i.e., the most-highly strained areas in the austenite. This prevented a progressive development of deformation-induced boundaries and thus suppressed the normal grain-subdivision process in this phase. On the other hand, the preferential nucleation of martensite within the deformation bands implied a close relationship between the transformation process and slip activity in parent austenite grains. Indeed, the martensite reactions were found to occur preferentially in austenite grains with crystallographic orientations close to Goss {110} and Brass {110}. Moreover, the martensitic transformations were governed by preferential variant selection which was most noticeable in ε-martensite. The sensitivity of the martensitic reactions to the crystallographic orientation of the austenite grains resulted in re-activation of the transformation process after development of a deformation-induced texture in the austenitic phase at high strains. Both martensitic phases were concluded to experience plastic strain which resulted in measurable changes in misorientation distributions. Cryogenic rolling imparted dramatic strengthening resulting in a more-than-sixfold increase in yield strength. The main source of hardening was the martensitic transformation with lesser contributions from dislocations and subboundary strengthening of the austenite

СВЕРХПЛАСТИЧЕСКОЕ ПОВЕДЕНИЕ АЛЮМИНИЕВОГО СПЛАВА 1420 С МЕЛКОЗЕРНИСТОЙ СТРУКТУРОЙ

The superplastic behavior of fine-grained 1420 Al-Mg-Li alloy was investigated using a modern electron microscopy technique based on automatic analysis of electron backscattered diffraction patterns (EBSD analysis). The generally accepted idea that grain boundary sliding is dominant during superplastic flow suggests the preservation of an equiaxed fine-grained structure with predominantly high-angle grain boundary misorientation in the material. The present study revealed that heating prior to the onset of deformation leads to some grain growth due to static recrystallization, and superplastic deformation is accompanied by dynamic grain growth and continuous dynamic recrystallization. Continuous recrystallization has a more significant effect on microstructural changes. This mechanism involves the transverse division of pre-elongated grains into subgrains that ultimately transform into chains of nearly equiaxed small grains, resulting in a bimodal grain structure. The data obtained, including significant strain hardening, noticeable grain elongation, the formation of a well-defined dislocation structure and subboundaries within grains, as well as the development of a pronounced crystallographic texture, provide convincing evidence of the occurrence of intragranular slip during superplastic flow throughout the entire volume of the material..

EBSD characterization of cryogenically rolled type 321 austenitic stainless steel

Electron backscatter diffraction was applied to investigate microstructure evolution during cryogenic rolling of type 321 metastable austenitic stainless steel. As expected, rolling promoted deformation-induced martensitic transformation which developed preferentially in deformation bands. Because a large fraction of the imposed strain was accommodated by deformation banding, grain refinement in the parent austenite phase was minimal. The martensitic transformation was found to follow a general orientation relationship, {111}γ||{0001}ε||{110}α′ and 〈110〉γ||〈11-20〉ε||〈111〉α′, and was characterized by noticeable variant selection

EBSD study of superplasticity : new insight into a well-known phenomenon

Electron backscatter diffraction (EBSD) was applied to investigate the superplastic behavior of a fine-grain Al-Mg-Li alloy. It was found that microstructural changes were noticeably influenced by the occurrence of continuous dynamic recrystallization. This mechanism involved a transverse subdivision of pre-elongated grains which eventually transformed into chains of nearly-equiaxed grains. A body of experimental observations, including extensive strain hardening, marked grain elongation, the formation of pronounced substructure in interior regions of grains, and the development of crystallographic texture, provided strong evidence of large amounts of intragranular slip operating during superplastic flow