Results of Studying Strain Relaxation in Steel 25Kh17N2B-Sh (25Х17Н2Б-Ш) and Copper М1 Using Annular Samples of Equal Bending Resistance

The paper introduces the research into stress relaxation of corrosion-resistant steel 25Kh17N2B-Sh (25Х17Н2Б-Ш) at temperatures of 20 and 100 °C, annealed copper M1 of two types --- soft and subjected to preliminary plastic deformation --- at a temperature of 20 °C, used in the manufacture of parts for butt joints of high-pressure pipelines. The research was carried out on annular samples of equal bending resistance according to the method of Oding. The study shows the action of temperature on the rate of stress relaxation in steel 25Kh17N2B-Sh (25Х17Н2Б-Ш), as well as the effect of preliminary plastic deformation of annealed copper on its relaxation characteristics, which is especially noticeable in the first hours after loading. As a result of the analysis of experimental data and by means of nonlinear regression, we determined the numerical values of the parameters of the equations used to describe the process of stress relaxation. Using the obtained expressions, we calculated and plotted the curves of stress relaxation in the materials under study. Furthermore, we compared the stress values calculated using the obtained relaxation model for steel 25Kh17N2B-Sh (25Х17Н2Б-Ш) at a temperature of 20 °C with the results of stress relaxation of a control sample from the same material, the test results of which were not used in the development of a mathematical model. The calculated data showed good similarity with the experimental data obtained on the test sample, which indicates the correct operation of the mathematical model

RESEARCH OF PRELIMINARY PLASTIC DEFORMATION VALUE INFLUENCE ON ARTIFICIAL AGEING DYNAMICS

Product quality improvement in the machine manufacturing industryis tightly associated with the introduction of new materialsand technologies. Aluminium alloys are widely used in differentmachine production industries. This paper presents the researchresults of aluminium alloy AD31 (AW 6060). Aluminium alloy isa part of the group subject to deformation and artificial aging. Theintensity of the aging process occurring after the crystallizationdepends on various conditions such as volumetric temperaturegradient during crystallization, alloy overheat temperature, itsduration of exposure, dispensing, and crystallization.

The Effect of Plastic Deformation on Nitrogen Diffusion in α-Fe

The surface diffusion layers formed in preliminary deformed (350 %) -Fe after nitriding at 853 K in ammonia medium were studied by means of metallography, electron microscopy, microhardness test and X-ray powder diffractometry. The preliminary plastic deformation (PPD) effects non-monotonously on the structure, microhardness and thickness of nitride - and -phases layers formed in -Fe. The narrow intervals of deformations of 3-8 % and 20-30 % were found in which the accelerated formation of nitride - and -phases occurs.