Modelling of processes of thermochemical treatment of metals: traditions of Russian scientific school

Abstract

The paper is devoted to 100th anniversary of the outstanding Russian scientist professor Yuriy Mikhailovich Lakhtin – the founder of the world-famous scientific school of surface strengthening of metals and alloys. Lakhtin's scientific school is recognised for its contribution into research of processes of thermochemical treatment of metals and especially of nitriding. Today at the Department of Metal Science and Heat Treatment of MADI his followers continue the traditions of Lakhtin's scientific school. The development of technologies of surface engineering is based on complex modelling of physical processes realised by thermochemical treatment of metals. Thermodynamic models describe the interaction between metals and components of saturating atmosphere and predict phase composition of diffusion layer. Diffusion models of kinetics of saturation of metals allow us to calculate the rate of growth of diffusion layer and regulation of its depth and structure. Structural models determine quantitative dependence between parameters of structure (grain size, dispersed particles, etc.) and mechanical properties. These models allow us to estimate the level of strengthening by control of structural specifics of strengthened layer. On the basis of this complex of models, new efficient technologies of surface strengthening are developed.     

Effect of Periodic High-Voltage Discharge in a Flow of Liquid on the Surface Layers of Structural Steels and Titanium Alloys

Results of a study of the effect of electric pulse treatment with the use of high-voltage periodic discharge in a flow of water on the structure and hardness of surface layers of specimens of steels 45KhN2MFA, 30Kh3NMAF, 12Kh18N10T and titanium alloys OT4-1 and VT6 are described. It is shown that the structure and properties of the surface in the zone of the action of electric discharge change due to the rapid fusion, crystallization, and rapid hardening of microvolumes of specimens subjected to the highly concentrated energy action. The microhardness of the surface of specimens of pearlitic steels after such a treatment is higher than after volume quenching. The microhardness of the surface layers of specimens of austenitic steel 12Kh18N10T decreases. Hardening of the surface layers of titanium alloys under the action of high-voltage discharge is substantially higher than in the case of quenching, which seems to be connected with their saturation with oxygen and nitrogen from the ionized ambient. Some regular features of the influence of the conditions of periodic discharge on the structure and properties of surface layers of the studied materials are described.     

The Influence of Pre-Plating Processes on the Porosity of Electrodeposits on Steel

The electrochemical method of obtaining a numerical index of the porosity of electrodeposits, previously described by the authors, has been applied to a study of the effects of pre-plating preparation of steel. Five different rolled steels and coatings of nickel, tin-nickel, tin and speculum were examined. The validity of the test method has been verified by comparison with laboratory and exposure tests yielding visual indications of porosity. It was found that the depth of steel removed by any method of pre-plating preparation had an influence on the porosity of the coating sufficiently large to obscure, if it were not controlled, effects of difference in preparation method. The removal of the extreme surface layer of steel (about 0·00001 in) influences the porosity of the applied coating for better or worse according to the metal deposited and the conditions of deposition. Evidence was obtained that this effect depends on the form of crystal growth of the deposit. With deeper uniform penetration into the steel, zones were reached which were apparently features of the steel and influenced porosity almost independently of the character of the deposit. These zones are attributed to bands of nonmetallic inclusions. The observed effect of depth of penetration helps to explain the divergent results previously obtained in investigations of surface preparation. It suggests that, in practice, when controlled penetration cannot be expected, no method of surface preparation will give consistent porosity of deposits on a range of steels. The response of an undercoating to the condition of the steel surface was found to govern the porosity of a composite coating. Well-chosen undercoatings may therefore offer the best method of obtaining consistent results and of reducing porosity.     

基于事例推理技术在夹具CAD中应用的研究

通过对夹具在机械加工设备中的作用，夹具的设计过程，现代计算机辅助设计技术在夹具设计中的应用和事例推理技术的分析，提出了基于事例推理（CBR）技术的夹具半智能化设计系统的总体设计和夹具结构设计方案。     

双流法预热条件下铝土矿浆中杂质矿物的反应行为

对我国两个主要矿区的铝土矿进行了双流法预热条件下矿浆中含硅矿物及含钛矿物反应行为的实验研究,考察了矿浆固含不同时含硅和含钛矿物反应行为的变化.在较长的预脱硅时间条件下,随着矿浆固含的增加,预脱硅效率及矿浆液相中的SiO2浓度呈下降的趋势.在矿浆预热过程中,脱硅效率随着矿浆固含的增加而增加,当固含增加到一定程度时,脱硅效率反而下降,脱钛效率随矿浆固含的变化规律和脱硅效率相同;矿浆液相中的SiO2浓度随矿浆固含的增加而下降.在双流法预热条件下,矿浆固含越高,矿浆预热过程中含硅矿物、含钛矿物及含镁矿物的结疤速率越低.     

Modeling of structure of double-phase low-carbon chromium steels

A physical model for determining the relative amount of phase components and the size of ferrite grains after decomposition of austenite in the process of cooling of double-phase steels is suggested. The main products of austenite transformation, i.e., polygonal ferrite, pearlite, bainite, and martensite, are considered. The driving forces of the transformation and the concentration of carbon on the phase surface are determined with the use of methods of computational thermodynamics. The model is based on equations of the classical theory of nucleation and growth. It allows for the structural features of the occurrence of γ → α transformation and contain some empirical parameters. The latter are determined using data of dilatometric measurements of the kinetics of austenite transformation and metallographic measurements of the size of ferrite grains. The model is used for predicting the kinetics of the transformation under the complex cooling conditions implemented by the VOEST-ALPINE STAHL LINZ GmbH rolling mill within the computer system for control of mechanical properties of hot-rolled strip.     

Sensitivity of transfer functions of transport of hydrogen in elastic metals to the uncertainty of their parameters

A comparison of sensitivity of the estimates of bulk elastic modulus of the M–H system and diffusion coefficient of hydrogen, acquired from three alternative transfer functions (TFs) of transport of hydrogen through a thin membrane specimen of metal, was performed with respect to the uncertainty of equilibrium concentration of hydrogen, its partial molar volume and thickness of the specimen. In most cases, the estimate of elastic modulus is more sensitive to these uncertainties than the estimate of diffusion coefficient, and the effects of uncertainty of the partial molar volume are of utmost importance. However, in the case of relatively small concentrations of hydrogen, uncertainty of the specimen’s thickness is most important for the estimate of elastic modulus acquired from one-port flux TF, while the estimates of both parameters acquired from the concentration TF are immune to the uncertainties discussed here. Nevertheless, other factors determine that for practical use the one-port flux TF is the most adequate of the three.     

Partial currents of anodic oxidation of copper in alkaline media according to RRDE data. I. Theory of the method

Anodic oxidation of copper in alkaline media is presented in the form of a sum of concurrent partial processes. An approach to using the method of chronoamperometry on a rotating ring–disk electrode is developed for establishing the kinetics of partial processes of anodic copper oxidation taking into account the possibility of its chemical oxidation by traces of dissolved oxygen. The possibility of implementation of two different cases after switching off anodic disk electrode polarization is shown: prevailing chemical dissolution of oxide Cu(I) or chemical copper postoxidation with formation of this oxide. The conditions of realization of the first or second case are determined by the value of thermodynamic activity of the oxide phase reached at the moment of termination of anodic polarization of the disk electrode.     

Dependence of the rate of steady-state swelling of fuel-element claddings made of ChS68 steel on the characteristics of neutron irradiation

Rate of steady-state swelling of fuel-element sheaths made of the 06Kh16N15M2G2TFR steel in the course of their operation in a BN-600 reactor has been calculated. In the calculations, the diffusion characteristics of point defects and the results of the determination of the characteristics of the irradiation-induced porosity have been used. The dependence of the dose rate of steady-state swelling on neutron-irradiation characteristics has been analyzed. It has been established that the dose rate of swelling at the steady-state stage is independent of the energy of migration of vacancies and the rate of generation of atomic displacements.     

Possibility of Analysis and Prediction of Magnetic Properties of Nanoobjects by Means of Simulation Taking into Account an Implicit Dependence of the Functional of Their Free Energy on the Magnetization Distribution

A short review of the results of a computer simulation of ferromagnets of limited sizes (nanoplatelets, thin films, and rods of rectangular section) using the method of minimizing the functional of the free energy of a magnetic system has been carried out. The implicit dependence of the functional on the magnetization distribution has been taken into account via the potential of the intrinsic field, which made it possible to exclude the points of the labile equilibrium upon minimizing the functional. The efficiency and adequacy of this method for studying micromagnetic properties of nanoobjects have been established. The specific features of the formation of domain structures of nanoobjects, as well as new possibilities of employing them in the magnetic recording of information have been shown.     

合理评估光谱标准样品的均匀性

均匀性是标准样品的基本特性.是标准样品特性值再现的基本保证.标准样品的均匀性水平不仅取决于样品本身的均匀性,还取决于均匀性检验时所采用的方法以及均匀性的统计设计.本文应用方差分析法并结合分析方法的重复性来研究并判断光谱标准样品的均匀性,而不是单一的运用实验数据进行分析统计.合理评价了样品的均匀性.     

Fundamental role of nanoscale structural level of plastic strain in solids

A conceptual substantiation of the necessity to consider the nanoscale structural level of plastic strain in the physics of plasticity and strength of solids is presented. It is inferred that the fundamental mechanism of plastic strain is represented by local structural transformations (of the type of rearrangement of atomic clusters of various configurations) that occur in a loaded solid in local zones of tensile normal stresses. This mechanism determines generality of the nature of all possible kinds of plastic deformation of solids.     

中凸变椭圆活塞横截面车削加工过程分析

通过分析活塞横截面特征,在满足横截面椭圆度公差要求的前提下,从车削加工的特点入手,提出横截面椭圆离散等分点数量必须满足的要求,并给以恰当的数学描述。在此基础上,用相对运动的原理对直线电机在横截面椭圆加工中的运动过程进行了详细的分析,指出了直线电机要满足横截面椭圆车削加工所必须满足的基本条件。并用MATLAB对活塞横截面车削加工的轨迹进行了仿真。     

Crystallographic analysis of the FCC → BCC martensitic transformation in high-carbon steel

Based on the phenomenological crystallographic theory of martensitic transformations, the following crystallographic characteristics of the tetragonal martensite in high-carbon steel have been calculated: orientation relationships between the crystal lattices of the bct martensite and fcc austenite; the magnitude and direction of the macroscopic shear; the habit plane; the angle and the axis of rotation of the crystal lattice of the martensite. The calculation was performed for three variants of lattice deformation: Bain deformation; two-shear Kurdjumov-Sachs deformation; and the deformation we suggested upon the analysis of the fcc-bcc transformation. In the last variant, a minimum rotation of the crystal lattice of martensite is required; consequently, this variant is closest to the real mechanism of the martensitic transformation. An expression has been derived that describes the interrelation between the degree of tetragonality of the crystal lattice of martensite and the magnitude of the shear deformation of the lattice. It has been shown that the 12 crystal-lographically equivalent variants of shear upon the formation of the lattice of the tetragonal martensite form three groups in each of which the martensite has the same tetragonality axis. For each variant of the shear, we have two equivalent variants of deformation of the martensite with invariant lattice. This results in 24 variants of orientation relationships.     

管筒形零件机械扩径工艺过程的成形参数优化

管筒形零件机械扩径最终制品的横断面尺寸精度和形状精度,不同程度地受到各种工艺参数、模具参数、材料性能参数以及摩擦条件的影响。机械扩径工艺设计的重要内容之一,就是针对特定的毛坯规格,合理选择各种成形参数并使其成为一种最优组合,以获得最佳的制品尺寸和形状精度。文章基于MSC.Marc非线性有限元分析软件和遗传优化算法,应用Python语言设计了机械扩径成形参数优化的遗传算法程序,通过对MSC.Marc软件的二次开发,实现了遗传优化算法与MSC.Marc软件的连接,为管筒形零件机械扩径工艺过程的成形参数优化提供了一种新方法。针对大直径管线钢管机械扩径工艺,得到了以最终制品形状精度(横断面圆度误差)为优化目标的扩径率、模具直径和模具边缘圆角半径等成形参数的最优组合。采用最优的成形参数组合,可以显著提高最终制品的横断面形状精度。     

Ar-N2混合气体对奥氏体不锈钢焊缝化学成分的影响

为了验证Ar-N2混合气体对焊缝中各元素含量和焊缝铁素体数(FN值)的影响，对SS304L奥氏体不锈钢进行了4种比例的Ar-N2混合气体GTAW多层多道焊接试验，研究了4种Ar-N2比例对焊缝金属中各元素含量的影响，以及每条焊缝中各元素含量随着焊道层数的变化趋势。结果表明，不同保护气体类型的11种焊缝化学元素中，只有N元素随着保护气体中氮气比例的升高而明显增加，其它元素则没有明显的影响；经过汇总分析，认为由于稀释率的原因，导致各元素含量在同一保护气体焊缝中的规律为：C元素含量随着层数的增加而下降；Si，P，S和Nb元素含量随着层数的增加无明显上升或下降趋势；Mn，Ni，Cr，Mo和Cu元素含量随着层数的增加而上升；而N元素在纯氩气保护SG-A时的含量随着层数的增加而稍微下降，在SG-AN-0.5，SG-AN-1，SG-AN-1.5 3种保护气体中N元素含量随着层数的增加而上升；分析结果也表明,Creq/Nieq值和FN值有相同的变化趋势，都与氮气含量呈现反比关系。 创新点： 采用了阶梯式的多层多道焊，保留了各层焊缝的原始信息，验证了GTAW焊接方法在保护气体中添加氮气对奥氏体不锈钢焊缝各种化学元素成分的影响，为Ar-N2混合气体GTAW焊接奥氏体不锈钢在工程中的应用提供了可参考的试验数据。     

管筒形零件机械扩径工艺过程的多目标优化

管筒形零件的机械扩径成形过程是一个与管坯规格、管坯形状、材料性能、摩擦条件、变形程度、模具直径及其边缘圆角半径等诸多因素相关的塑性变形过程,其最终制品的尺寸和形状精度取决于这些参数的综合影响。在生产实际中,如何根据用户对制品尺寸与形状的精度要求来确定管坯规格、变形程度、模具尺寸等主要工艺参数,是机械扩径工艺设计的一个重要内容。它可以被抽象为一个在满足制品尺寸和形状精度要求条件下,寻求管坯规格等上述主要工艺参数最优组合的多目标优化问题。文章基于MSC.Marc非线性有限元分析软件和遗传优化算法,采用Python语言设计了基于加权组合法的遗传算法程序,实现了在多目标条件下对管筒形零件机械扩径成形工艺参数的优化。     

Effect of Sublimation in Vacuum Annealing on the Limit of Elasticity of Nonferrous Alloys

Results of analytical and experimental studies of the effect of annealing in vacuum on the limit of elasticity of nonferrous alloys are presented. Vacuum annealing changes the chemical composition of the surface layers due to sublimation of the highly volatile component of the alloy, which leads to a decrease in its limit of elasticity due to the accumulation of crystal structure defects. An empirical equation is suggested for predicting the variation of the limit of elasticity of heterophase alloys as a function of the duration of isothermal annealing in vacuum. The results obtained by solving this equation agree satisfactorily with experimental data.     

Evaluation of the heterogeneity of the stress state of welded joints prior to and after heat treatment using the method of the magnetic memory of metal

The results of investigations of the stress state of welded specimens prior to and after heat treatment using the method of magnetic memory (MMM) of the metal are presented. The relationship between the changes of the stress state of the welded joint and the strength of the intrinsic magnetic scattering field, formed in welding in the conditions of a weak geomagnetic field, is described. A method for the efficient determination of the zones of heterogeneity of the stress state of the welded joints by the MMM and the evaluation of the changes of after heat treatment is proposed.     

Effect of reversibility of structure and properties in hydrogen charging of carbon steel and influence of hydrogen on formation of electrodeposited zinc coatings

Specimens of steel 70 are studied before and after alkaline galvanizing and after galvanizing and partial dehydrogenizing. The content of hydrogen and its distribution between the coating and the substrate are estimated. The structures of the substrate metal and of the coating are studied before and after dehydrogenization. Mechanical tests at various rates of deformation of specimens of steel 70 in different initial states are performed. The tests are followed by an analysis of fracture surfaces. The effect of hydrogen on the fracture behavior is evaluated at different rates of deformation of specimens. The effect of reversibility of the structure and properties in “hydrogen charging-dehydrogenization” of the steel is determined and the mechanism of formation of a layered structure of zinc coatings is described.