Effect of Strain Aging on Stages of Plastic Strain and Tensile Fracture of Specimens of Steel 08G2B. Part I. Yield Plate
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EFFECT OF STRAIN AGING ON STAGES OF PLASTIC STRAIN AND TENSILE FRACTURE OF SPECIMENS OF STEEL 08G2B. PART I. YIELD PLATEAU AND THE STAGE OF STRAIN HARDENING V. M. Farber,1 V. A. Khotinov,1 O. N. Polukhina,2 O. V. Selivanova,1 A. N. Morozova,3 and D. I. Vichuzhanin4 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 38 – 45, July, 2020.
Mechanisms of Luders deformation in tensile tests of specimens of steel 08G2B with ultrafine ferrite-bainite structure are studied by the method of digital image correlation. The fields of displacements of eyy and exy and their distribution over the length of a specimen are determined. Two kinds of Luders deformation differing in the behavior of the Chernov–Luders bands are detected. The results of the measurement of microhardness in Chernov–Luders bands and of the EBSD analysis are used to determine the interrelation between the strain aging effect and the variation of the characteristics of strength (sy , sr ) and ductility (dpl , du , d, n ) at tension.
Key words: strain aging, stress–strain curve, Luders deformation, digital image correlation, displacement components, Chernov–Luders bands.
The degree of the influence of SAE on the mechanical properties of the steel depends on the intensity of the effect, which may vary in a wide range upon variation of the ratio rd /Nst , where rd is the dislocation density and Nst is the density of the particles blocking the dislocations, i.e., stoppers. Parameter D introduced in [11 – 13] characterizes the value of SAE for the given sample (article). It is important that this parameter is a relative characteristic describing the intensity of the strain aging effect on the mechanical properties of steels of the same alloying system. In addition to the application significance, investigation of SAE of steels of type 07G2B gives ample data on the nature of this phenomenon, because these steels have a small grain size, which intensifies the SAE [14], and enhanced dislocation density in bainite or martensite where the dislocations are fixed by fine particles of various carbides [15]. Such characteristics are used for varying the values of rd , Nst and D in a wide range, as well as the combination of the mechanical properties, by heat treatment. The methods of correlation of digital images (CDI) [16 – 19] and speckle video shooting [20, 21] permit a detailed study of SAE. However, most of the works are reduced to the strain on the yield plateau and sometimes to sr , though assessment of the influence of SAE on the viscoplastic properties and on the fracture behavior also requires data on the stage of concentrated strain.
INTRODUCTION The circle of alloys and their structural and phase states exhibiting strain aging effect (SAE) has widened substantially due to recent researches. Despite the development of quite successful models of SAE, detailed studies of the influence of strain aging on the mechanical and functional properties of articles remain urgent. Such studies should provide purposeful control of SAE aime
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