X-Ray measurement of lattice strains in textured low carbon steel under uniaxial loading
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I.
INTRODUCTION
THE understanding of the deformation behavior of constituent crystals in a polycrystalline aggregate is important for the study of the phenomena accompanying the deformation of metals. However, the mechanisms of elastic and plastic deformation for polycrystalline aggregates are mostly characterized only qualitatively, and only a few experimental investigations have been carried out on the constituent crystals of polycrystals in a strained state, f~ 4t While external strains determined by extensometers or strain gages allow observation of the macroscopic behavior of strained polycrystalline metals, X-ray diffraction techniques provide microscopic information within the diffracting crystals or grains. 13 61 The lattice strains determined from the changes in the position of an X-ray diffraction peak represent the average value of the strains in the direction normal to the lattice planes only in those crystals that are oriented to diffract. This selective nature of X-ray diffraction makes it possible to measure the lattice (elastic) strain of the specified crystals for textured polycrystalline materials. ~61 As has been commonly treated in the literature, the typical rolling texture of iron is such that the majority of crystallites is oriented to the following directions: {211}(01i), {i 11}(2iT), and { 100}(011). lvl The aim of the present study is to examine the effect of relative crystallite misorientations on the inhomogeneous behavior of the elastic and plastic deformation of textured crystallites of cold-rolled low-carbon steel. Lattice strains of the textured crystallites are measured by the X-ray diffraction method under uniaxial loading along the elastic and plastic region in the stress-strain curve. Internal microstresses of the crystallites are also determined from the lattice strains measured along different directions of the crystallites. C.H. CHANG, Research Assistant, and Y.M. KOO, Professor, are with the Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea. Manuscript submitted March 21, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS A
II.
EXPERIMENTAL PROCEDURES
The material examined in this study was hot-rolled low-carbon steel, the chemical composition of which was Fe-0.002C-0.01P (wt pct). After a 3.8-mm-thick steel sheet was cold-rolled to 0.3-ram thick, tensile test specimens having gage length dimensions of 25 mm x 6.25 mm were prepared in the rolling direction. To relieve the residual stresses caused by mechanical treatments, these specimens were annealed inside of a vacuum quartz tube at 470 ~ for 1 hour and then cooled slowly in a furnace. The preferred orientations that exist in the cold-rolled steel sheet do not change by the heat treatment at 470 ~ IS1 From the {200} and {ll0}-pole figures obtained by the Schulz reflection method with Co radiation, the rolling texture of this steel is seen to be three orientation groups; {211}(011), {111}(2iT), and {100}(011). The volume fractions of {211}(01i), {
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