Effect of Shear Strain on the Structure and Properties of Chromium-Nickel Corrosion-Resistant Steels

Abstract

The structure and properties of metastable austenitic steel 08Kh18N10T and stable austenitic steel ASTM F138 under shear deformation implemented by torsion under hydrostatic pressure (THP) at T = 300 and 450°C and by equichannel angular pressing (ECAP) at T = 400°C are studied. The THP yields an ultrafine-grain structure in a fully austenitic matrix with grain size 45 -70 nm in steel ASTM F138 and 87 -123 nm in steel 08Kh1810T. The ECAP at 400°C yields a grain-subgrain structure with structural elements 100 -300 nm in size in steel 08Kh18N10T and 200 -400 nm in size in steel ASTM F138. INTRODUCTIONThe processes of shear deformation (SD) attract much interest due to the possibility of formation of an ultrafine-grain (UFG) (nano-and submicrocrystalline) structure responsible for enhancement of the strength and operating properties of metals [1 -4]. One of the methods, i.e., torsion under hydrostatic pressure (THP) [5,6], makes it possible to refine the structure ultimately without fracture of the specimen, to simulate structural and phase transformations in the course of the THP and to recommend deformation modes for massive specimens by the method of equichannel angular pressing (ECAP) [7,8]. In the present work we studied the possibility of refining the structure and elevating the mechanical properties of corrosion-resistant chromium-nickel steels after THP and ECAP under static and cyclic loading. The studied materials were a metastable austenitic steel 08Kh18N10T and a stable austenitic steel ASTM F138, which had been chosen due to the possible applicability in medicine. Cold deformation of steel 08Kh18N10T is accompanied by a martensitic transformation [9 -12], which promotes hardening but decreases the corrosion resistance. One of the tasks was to obtain in steel 08Kh18N10T after SD an ultrafine-grain structure in a completely austenitic state. For comparison we studied a stable austenitic steel ASTM F138 widely applied in medicine.The aim of the present work was to study structure formation in steels 08Kh18N10T and ASTM F138 during THP and ECAP and to determine the mechanical properties under static and cyclic loading of these steels in the ultrafine-grain condition. METHODS OF STUDYSpecimens of steels 08Kh18N10T and ASTM F138 (Table 1) were subjected to quenching from 1050°C for 1 h. After the quenching, the structure of steel 08Kh18N10T was represented by 5% d-ferrite and 95% austenite with grain size 20 mm; in steel ASTM F138 the grain size of the austenite was 60 mm (Fig. 1).Torsional deformation at a pressure of 6 GPa was allied to specimens with a diameter of 20 mm and a thickness of 1 mm. The true strain at the middle of the radius of the specimens was 5.7. The THP deformation was applied at a temperature of 300 and 450°C, which exceeded the temperature of the appearance of strain martensite. ECAP was applied to specimens with a length of 80 mm and a diameter of 20 mm at a temperature of 400°C over path Bc at the angle of intersection of the channels equal to 120°in six passes for steel 08Kh18N10T and...

Microstructure and Mechanical Properties of Austenitic Stainless Steels after Dynamic and Post‐Dynamic Recrystallization Treatment

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Metastable Austenitic Steel Structure and Mechanical Properties Evolution in the Process of Cold Radial Forging

“…Yield strength—elongation to fracture relation of the 321 MASS after different strengthening treatment methods. Note: high pressure torsion (HPT) [45], repetitive cold rolling and reversion annealing (RCR + RA) [46], cold rolling (CR) [1,47], cryogenic rolling (CrR) [48,49], cold radial forging (CRF), fast neutron irradiation (FNI) [50], equal channel angular pressing (ECAP) [15,16], isothermal forging (IF) [49]. …”