Preliminary Plastic Deformation Research Articles

АНАЛИЗ ВЛИЯНИЯ ПРЕДВАРИТЕЛЬНОЙ И ЦИКЛИЧЕСКОЙ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ НА ХИМИКО-ТЕРМИЧЕСКУЮ ОБРАБОТКУ КОНСТРУКЦИОННЫХ СТАЛЕЙ

The subject of the study was thermodiffusion nitrided and silicified layers on steels obtained after plastic deformation. The influence of preliminary plastic deformation on the low-temperature nitriding process and cyclic plastic deformation on the high-temperature silicification process is studied. The results obtained are of interest for accelerating the production processes of chemical-thermal treatment of steels. It is established that preliminary surface plastic deformation contributes to the intensification of the process of ion-plasma nitriding of structural steel. The presence of high-temperature cyclic plastic deformation ensures the intensification of diffusion processes during the resorption of the diffusion silicified layer on structural steel.

Investigation of influence of ion nitriding in the glow discharge with magnetic field on microstructure and microhardness of steel HSS M2 with preliminary plastic deformation

This work was devoted to the study of the influence of magnetic field on microhardness of HSS M2steel during ion nitriding in the glow discharge. The samples were preliminarily subjected to intenseplastic torsion deformation (IPTD). Standard methods of optical metallography and microhardnessmeasurements were used in the experiments. It was found that IPTD allows creating ultrafine-grained(UFG) structure in the material, and magnetic field allows intensifying the process of ion nitriding byincreasing the number of ionization acts, which leads to an increase in the thickness of the diffusionlayer and microhardness compared to ion nitriding without preliminary IPTD and without magneticfield. The results obtained indicate the importance of using a magnetic field during ion nitridingin the glow discharge. The described effects are of potential interest for improving the mechanicalproperties of high-speed steels.

Evolution of the structure, texture and mechanical properties of a cold-swaged austenitic stainless steel during post-deformation annealing

In this work, we studied the effect of annealing temperature on the structure and texture, as well as the mechanical properties of the austenitic stainless steel AISI 316. Initially, the program material was subjected to cold rotary swaging with a reduction of 95%. Studies showed the formation of the structure and texture gradient during preliminary plastic deformation. Annealing at low temperatures (500-600°C) provoked polygonization, while the intensity of the and texture components remained unchanged. After annealing at 700°С, the onset of recrystallization was observed only in the subsurface layers of the rod. As a result of annealing at 800–900°C, static recrystallization occurred over the entire cross section of the rod, which caused dissipation of the texture gradient. Annealing at temperatures of 400–600°C was accompanied by an increase in the strength and hardness characteristics. Meanwhile, ductility also increased with the annealing temperature. Annealing at 700°C resulted in softening of the program material almost to the level of the initial cold-swaged state and a significant increase in ductility up to 16%.

ВОЗМОЖНОСТИ КОМБИНИРОВАННОГО УПРОЧНЕНИЯ МЕТАЛЛИЧЕСКИХ МАТЕРИАЛОВ ВОЛНОВЫМ ДЕФОРМАЦИОННЫМ ВОЗДЕЙСТВИЕМ И ПОСЛЕДУЮЩЕЙ ТЕРМИЧЕСКОЙ ОБРАБОТКОЙ

Nowadays, industry development requires making new strengthening technologies that allow expanding the rational scope of their application. It is quite promising to use methods of combined hardening that allow changing the physical and mechanical properties of the surface layer during successive external actions having different physical nature: sequential plastic deformation and external thermal effects. Therefore, the objective of the conducted study is to make a complex technology of combined deformation and thermal hardening. Preliminary plastic deformation is proposed to be carried out by the method of wave deformation hardening, in which the improvement of properties is achieved by forming structural imperfections of the crystal lattice of the material under the action of prolonged shock pulses of significant energy and duration. The use of these pulses contributes to a more complete plastic deformation of the hardened metal and the formation of a deeper hardened surface layer than with traditional methods of deformation hardening. The proposed combined technology, consisting in the use of wave deformation hardening before thermal treatment, allows to obtain high hardness and plasticity in the surface layer, provides an additional resource to increase the operational characteristics of the part. The novelty of the work is in the complex development of a method for combined wave deformation and thermal hardening of the surface layer of alloy steels. The conducted studies of the method have shown the high efficiency of the technology of combined deformation wave and thermal hardening for various grades of alloy steels.

Bauschinger effect during alternating deformation

The Bauschinger effect is a phenomenon of a decrease in material resistance to small plastic deformations after preliminary plastic deformation of the opposite direction, discovered in 1881. This effect is of great importance and is used, in particular, in studying the fatigue strength of materials under alternating loads. The Bauschinger effect is inherent in all metals and alloys, although it is most pronounced in steels. Therefore, it is one of the factors affecting the quality of finished metal products subjected to alternating loading during manufacture. This review analyzes the literature data on the problem of the Bauschinger effect in the case of alternating deformation of metals. Various mechanisms explaining the Bauschinger effect are briefly considered. The factors that qualitatively and quantitatively affect the Bauschinger effect are described in detail, namely the degree of preliminary deformation, composition, structure and properties of the material, deformation conditions, the phenomenon of dynamic deformation aging, and temperature. The problem of the Bauschinger effect in the case of alternating deformation of steel products is considered, in particular, in the production of oil and gas pipes of large diameter. Various methods and approaches to the evaluation and quantitative measurement of the Bauschinger effect are described; the dependence of the Bauschinger parameter on the value for residual deformation is shown. It is concluded that the Bauschinger effect plays both a positive and a negative role in the production of metal products, in particular oil and gas pipes. On the one hand, the Bauschinger effect has a negative effect, reducing the level of mechanical properties of the final product below the required one. On the other hand, it creates a certain margin of plasticity of the deformable material in the process of forming and laying pipes.

Mathematical Model for Assessing the Limits of Crack Resistance of Structural Steels of Large-Sized Structures

In metal structures under operating conditions, as well as in emergency situations due to overloads, the presence of stress concentrators, etc., plastic deformations may occur. Such deformation by tensile stresses introduces some damage to the structure of steel, which adversely affects its subsequent operation under cyclic loads. Preliminary relative plastic deformation, ∼ 1-6%, which occurs in structural steels under tension, unambiguously reduces plasticity. It negatively affects the endurance of the material and leads to the early formation of macrocracks. In addition, after unloading, an internal residual stress field at the meso-micro level remains in the structural elements, which also reduces the endurance limit. In causes the decrease of such an important indicator of reliability as fracture toughness, which reflects the resistance of the material to crack propagation. In this regard, designing structures, it seems important to improve the calculation methods for assessing and predicting their fatigue strength, taking into account the listed factors.The article is devoted to the development of a mathematical model that includes dependencies for assessing the fracture toughness of metal structures according to the fracture toughness limit for all sizes of defects in the form of cracks. Analytical dependences have been obtained for calculating the relative limit of crack resistance based on the main mechanical characteristics of the state of the material. The results of the study can be used to assess the crack resistance of structural elements and welded joints pre-deformed by tension.

ON THE EFFECT OF MICROSTRUCTURAL INHOMOGENEITIES ON THE STRENGTH PROPERTIES OF A NICKEL ALLOY CRNI65COMOWALB

The article presents the results of an experimental study of the structure and strength properties of a heat-resistant nickel alloy of the CrNi65CoMoWAlB grade. This alloy is used for the manufacture of rotor blades for turbines of gas turbine plants. Ensuring the reliability of highly loaded parts is an integral part of the production process. For analysis, samples were taken with different structural states, which were cut from two different batches of blanks for the manufacture of rotor blades. Both batches of billets underwent preliminary hot plastic deformation (forging) and heat treatment (austenization and aging). Samples from the first batch had a reference structure with a uniform distribution of hardening phases, the second batch of samples had a defective structure with a pronounced uneven grain size, stitching and uneven distribution of hardening phases. A detailed analysis of the microstructure and mechanical characteristics of the alloy was carried out both using standard methods and non-standard research methods. Conducting microstructural analysis and relaxation tests using microsamples cut from zones with increased inhomogeneity showed that the standard approach recommended by standard does not reflect the real picture with a negative change in the microstructure of the material and is not sensitive to the presence of microdefects in the alloy structure. The study made it possible to establish the influence of the uneven distribution of hardening phases and inequigranularity on the mechanical characteristics. The limit of microplasticity and long-term strength turned out to be especially sensitive indicators. A significant decrease in the value of microplasticity and time to failure was recorded for a sample with a substandard alloy structure. The detected changes in the structural and strength properties in the material can significantly reduce the performance or lead to failures of critical parts.

Investigation of Thermal Stability of Microstructure and Mechanical Properties of Bimetallic Fine-Grained Wires from Al-0.25%Zr-(Sc,Hf) Alloys.

Thermal stability of composite bimetallic wires from five novel microalloyed aluminum alloys with different contents of alloying elements (Zr, Sc, and Hf) is investigated. The alloy workpieces were obtained by induction-casting in a vacuum, preliminary severe plastic deformation, and annealing providing the formation of a uniform microstructure and the nucleation of stabilizing intermetallide Al3(Zr,Sc,Hf) nanoparticles. The wires of 0.26 mm in diameter were obtained by simultaneous deformation of the Al alloy with Cu shell. The bimetallic wires demonstrated high strength and improved thermal stability. After annealing at 450–500 °C, a uniform fine-grained microstructure formed in the wire (the mean grain sizes in the annealed Al wires are 3–5 μm). An increased hardness and strength due to nucleation of the Al3(Sc,Hf) particles was observed. A diffusion of Cu from the shell into the surface layers of the Al wire was observed when heating up to 400–450 °C. The Cu diffusion depth into the annealed Al wire surfaces reached 30–40 μm. The maximum elongation to failure of the wires (20–30%) was achieved after annealing at 350 °C. The maximum values of microhardness (Hv = 500–520 MPa) and of ultimate strength (σb = 195–235 MPa) after annealing at 500 °C were observed for the wires made from the Al alloys alloyed with 0.05–0.1% Sc.

Результаты исследований релаксации напряжений в стали 25Х17Н2Б-Ш и меди М1 с использованием кольцевых образцов равного сопротивления изгибу

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

EXPANSION OF APPLICATION OF AUSTENITE STEEL PRODUCTS IN THE FOOD INDUSTRY

The article considers the increase of machinability of austenitic steels by combining preliminary cold plastic deformation with the use of environmentally friendly lubricating and cooling fluids based on rapeseed oil. It is shown that by fusing plastic steels with a large amount of chromium, nickel and manganese, the Curie point can be reduced to room temperature. State diagrams of Fe - Mn and Fe - Cr - Ni systems after such transformations are considered. In the latter case, steels become suitable for products and technologies of the food industry, but they are difficult to process in mechanical technologies. The study of steels 12Х15G9ND (AISI 201) is given; 08X18H10 (AISI 304); 110G13L (A128). A mathematical model of the object of study was developed, where the process factors were cold plastic deformation (COD), lubricating and cooling fluid (MPC) and cutting speed. The optimization parameters were the shrinkage of the chips and the length of contact of the latter with the front surface of the tool. The equation of the mathematical model is given. A number of modern installations and methods of process research are described. Among the research methods, new ones are noted, in particular, methods of transverse compression, determination of the number of dislocations, spectral analysis, cutting of steels using MPAs of plant origin. The optimal brand of ecologically pure vegetable MPA is determined. It is rapeseed oil together with anti-emergency and anti-wear additives. The main physical and mechanical characteristics of cutting austenitic steels in the context of the impact of HPD together with MPA are presented: friction force, normal force, contact stress, contact pressure, contact length, coefficient of friction, angles of action and shear. It is shown that HPD with coolant reduces the cutting temperature by 30 - 50 ºC, and the components of the cutting forces by 30 – 50%. The effect of selected three main factors of the process on growth is studied. It is shown that the stress-strain state of the system "machined material - tool - chips" from the action of these factors approaches the specified state. That is, the intensity of growth decreases. The relationship between the main phenomena in the cutting of austenitic steels obtained in the study is presented. It is established that medium temperature tempering in a protective environment should be recommended to restore the initial performance properties of austenitic steels. The final finishing operation can be processing with an elastic tool made of superhard materials.

Physicomechanical Characteristics of VT6 Titanium Alloy Subjected to Surface Deformation-Diffusion Treatment

We study the influence of ball burnishing on the surface quality, surface hardening, and structure of the surface layers of Ti–6Al–4V (VT6) titanium alloy. It is shown that the degree of surface hardening of the alloy increases with the load applied in the course of deformation treatment. The degree of hardening and the surface quality after treatment are evaluated. The applied procedure of treatment includes the preliminary cold surface plastic deformation with subsequent thermodiffusion saturation of the surface with nitrogen. It is established that the surface microhardness increases by 2.5 GPa and that the depth of the hardened zone increases by 25 μm.

MULTILEVEL PHYSICAL-ORIENTED MODEL: APPLICATION TO THE DESCRIPTION OF THE INITIAL STAGE OF DYNAMIC RECRYSTALLIZATION OF POLYCRYSTALS

Thermomechanical processing of metals and alloys is accompanied by deep changes of the material structure (including grain structure), which determines physical and mechanical properties and the working characteristics of products made from them. Its change is possible due to mechanical (fragmentation process) and/or temperature (recrystallization process) influences. Because of this, an urgent task is to create mathematical models that allow describing changes in the material structure and the stress-strain state under thermomechanical treatment. For this purpose, the multilevel physically oriented model was developed for researching inelastic deformation of polycrystals. The problem of modeling two stages deformation of a polycrystalline copper sample was formulated. At the first stage, preliminary cold intense plastic deformation under complex loading was investigated. Two variants of preliminary deformation were considered. They were homogeneous deformation corresponding to equal-channel angular compression (ECUP), and deformation with closed deformation trajectory. At the second stage, uniaxial high-temperature deformation was considered prior to the beginning of an intensive dynamic recrystallization. The paper describes the method for estimating the recrystallized material volume fraction within the framework of the multilevel model. The influence of the deformation temperature, the preliminary deformation, the deformation texture, and the average angle of mutual misorientation of neighboring grains on recrystallization was investigated. These parameters determine the development of dynamic recrystallization, since its main physical cause is the difference in stored energy between neighboring grains. It was shown that the developed mathematical model is suitable for describing the thermal activation of dynamic recrystallization at temperatures in the range of 0,4–0,7 homologous temperature. The deformation trajectory complexity determines the type of deformation texture, its “sharpness” or “dispersion”, the angles of neighboring grains mutual misorientation. The results of computational experiments are presented. According to the proposed method, the deformation at the high-temperature stage is determined, at which the intensive migration of new grains begins during recrystallization.

Improving the reliability of metal structures of transport and technological machines during operation in the Arctic

In the course of the study, we analyzed the main factors affecting the brittle fracture of the elements of welded structures made of structural steels, associated with its unexpectedness and the absence of noticeable plastic deformations at metal stresses much lower than the yield point. During experiments, the relationship between the magnetic parameter Hp and the structure of structural steels during thermal cycling was revealed. This became possible due to the high sensitivity of passive magnetic flux leakage testing when monitoring the structural transformations of metal during cyclic heating and cooling. We provide examples of the formation of ultrafine-grain structures in industrial structural steels based on the results of thermal cycling and analyze factors affecting the final grain size. It is shown that the degree of steel microstructure refinement depends on the chemical composition and initial structure of steels as well as the number of thermal cycling cycles. It was established that an increase in the number of thermal cycling cycles and the degree of steel alloying, the presence of a finer-grain initial structure, and preliminary cold plastic deformation during stage-by-stage monitoring using passive magnetic flux leakage testing contribute to the formation of a finer-grain structure. A decrease in the average grain size shifts the temperature of metal transition from ductile to brittle fracture to the region of lower temperatures, which increases the reliability of welded metal structures of transport and technological machines used in the Arctic.

STRUCTURAL CHANGES IN STRUCTURAL STEELS DURING THERMAL CYCLING

Introduction: During experimental studies of structural steels responsible for the reliability of metal structures used, for example, in hoisting and transporting machinery, we established a correlation between the magnetic parameter Hp and characteristic changes in the metal microstructure during thermal cycling. It is shown that the Нр parameter depends on the initial structural state of steel, the amount and mass fraction of alloying elements, and the number of heating/cooling cycles. Methods: We found that an increase in the number of heating/cooling cycles and the amount of alloying elements, as well as preliminary cold plastic deformation with stage-by-stage control of structural changes using passive magnetic flux leakage testing results in a finer-grained structure, which was confirmed by metallographic analysis. Results: The paper considers specifics of structural changes in steels with different initial structures during thermal cycling. It is shown that the final grain size depends on the number of treatment cycles, the amount of alloying elements, and the initial microstructure. It is the fine-grain structure that improves the most important performance characteristics of steels: strength, cyclic strength, and cold brittleness.

Dependence of the preliminary plastic deformation on the curves of chromium-nickel steel deformation

The test results of pre-deformed tubular samples at various values of preliminary deformation are presented. The article describes the chamber of the apparatus, which makes it possible to test tubular samples under conditions of plane and volumetric stress states. Curves built on test results of samples with different levels of preliminary plastic deformation are presented, as well as the test results of samples deformed by the ray α = 0.5. The experiments make it possible to determine the value of the ultimate uniform deformation after preliminary deformation or on the final segment of the multi-link loading path.

Effect of Ion Nitriding on the Structural and Phase Composition and Mechanical Properties of High-Speed Steel R6M5 after SPD

The effect of ion nitriding in glow discharge on the structure and mechanical properties of steel R6M5 after quenching from 1200°C and tempering at 560°C with preliminary severe plastic deformation (SPD) is studied. Application of ion nitriding in glow discharge is shown to be effective for hardening the high-speed steel RM5 after SPD.

Structural Transformations and Tribological Effects in the Surface Layer of Austenitic Chrome-Nickel Steel Initiated by Nanostructuring and Oxidation

Metallography, electron microscopy, and X-ray diffraction are used to study the effect of preliminary plastic deformation in the friction-contact zone on the structural transformations and wear resistance of 12Cr19N9T austenitic stainless steel subjected to subsequent oxidation in air at temperatures of 300–800°C for 1 h. Severe deformation under dry sliding friction produces a two-phase (γ + α) nanocrystalline structure in a ~10-μm-thick surface layer of the steel. The microhardness is 5.2 GPa. Subsequent oxidation at 300–500°C causes an additional increase in the microhardness of the deformed surface layer of steel to the value of 7.0 GPa. This is due to the active saturation of austenite and deformation-induced α'-martensite with oxygen atoms, which rapidly diffuse deep into the metal along the grain boundaries. The oxygen concentration in the surface layer and steel wear products reaches 8.5 wt %. The atoms of the dissolved oxygen efficiently pin dislocations in the γ- and α' phases, increasing the strength and wear resistance of the surface of the 12Cr19N9T steel. Oxidation at 550–800°C results in the formation of a large number of Fe3O4 (magnetite) nanoparticles, which increase the resistance of the steel to thermal softening and its wear resistance.

Shape recovery of the of nickelide titane plate

Shape memory alloys such as titanium nickelide are currently used in different fields of engineering, construction, and medicine, due to their unique ability to recover significant inelastic deformations upon heating. Titanium nickelide plates as structural elements or medical devices are exposed to complex temperature and force impacts during operation, which leads to a change in the stress-strain state of the material. For example, a plate rigidly clamped on one side significantly changes the surface curvature during thermal cycling under load or as a result of heating after preliminary plastic deformation. Similar exposures are implemented in the devices in which the plate is used as a sensitive element, for example, temperature sensors, electrical contacts, smart ailerons, etc. When designing these elements, it is important to take into account changes in such deformation parameters as curvature, deformation, and shape recovery coefficient. The lack of information on those parameters is observed for titanium nickelide plates. We present the results of the experimental study of the shape reduction of a titanium nickelide plate both during isothermal unloading after plastic deformation and during thermal cycling under the impact of a constant bending force. It is shown that plastic deformation of the plate under isothermal conditions with an increase in the initial radius of the curvature by 3.35 times leads to an increase in the curvature by 4.83 times after pseudoelastic unloading. It is shown that the shape memory effect after isothermal bending of a rectangular titanium nickelide plate increases as the prescribed radius of the curvature decreases. Moreover, the curvature under constant load changes during thermal cycling in a complex way. The results of the study can be used in designing devices based on titanium nickelide plates.

Treatment of Titanium Alloys Based on Preliminary Plastic Impact

This paper proposed a new method for processing titanium alloys based on preliminary plastic impact. The reasons for the deterioration of the surface roughness of titanium alloys during machining are considered. This problem lies in the formation of outgrowths on tool cutting wedge, which leads to the cutting process taking place as in the titanium-titanium pair. The adsorption phenomenon leads to the fact that the outgrowth is saturated with gases from the environment, and a thick oxide film is formed. As a result, high temperatures arise during machining from 1100 to 1200°C, increasing the cutting forces P and friction Q, which introduce the technological system into an unstable self-oscillating process. The problem posed eliminated by the method of preliminary plastic deformation, which forms a local inhomogeneous structure. At the stage of processing the titanium billet, the cutting edge enters the region with a heterogeneous structure, destroying the chips and growth with an oxide film. Since most of the temperature, about 80% takes away with the chips, the amplitude of the self-oscillating process decreases, which reduces the surface roughness of the processed titanium alloys.

Fractographic features of technically pure magnesium, AZ31 and ZK60 alloys subjected to stress corrosion cracking

Using quantitative fractography, the present study clarifies the effect of chemical composition and preliminary plastic deformation on the fracture mode of structural magnesium alloys experienced stress corrosion cracking (SCC). It is demonstrated that the fracture surfaces of alloys ZK60 and AZ31 failed during slow strain rate testing (SSRT) under SCC conditions are commonly featured by (i) the close-to-side surface region of typically brittle fracture initiation composing of intergranular and cleavage facets, which gradually transforms to (ii) the region of transgranular fluted facets optionally followed by the regions of (iii) fluted facets with secondary cracks, (iv) flat dimpled rapture and (v) slant dimpled rapture. Counterintuitively, the preliminary plastic strain introduced in air results in the increase of the fraction of the ductile mode on the fracture surface, elongation and stress at fracture of both alloys SSRT tested in corrosive media. The positive effect of pre-straining can be likely explained from the mechanistic viewpoint due to the increase of the yield stress, which has to be overcome to trigger plastic deformation needed to break the surface protective film. Features of the SCC mechanisms affecting the fracture surface appearance are quantified and discussed.