RU2541388C1 - Procedure for prognosis of wear resistance of hard alloy cutting tools - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: distinctive feature of the method of forecast of wear resistance of hard alloy cutting tools of the K usability group consists in close correlation between the properties of hard alloys of the K usability group to accumulate hydrogen with the surface and near surface structure and their wear resistance. With decrease of capacity of the structure of hard alloy cutting tools to accumulate the hydrogen their wear resistance increases.

EFFECT: improved accuracy of wear resistance forecast.

2 dwg

Description

The invention relates to the field of metal cutting and can be used to predict - control the wear resistance of carbide cutting tools in their manufacture, use or certification.

A known method for determining the wear resistance of hard alloys is that the test material is placed in an alternating magnetic field with an intensity of about 5 Oersted, the magnetic permeability of the material is measured, and the magnitude of the material’s wear resistance is determined from the magnetic permeability - resistance graph plotted for the reference sample [ SU AC 268720, IPC G01N 3/58, BI 1970, No. 14].

One of the disadvantages of this method is that the measurement does not take into account the influence of the mass and demagnetizing factor of products, which often have different shapes and dimensions on the value of magnetic permeability, which reduces the accuracy of the measurements. In addition, the operational characteristic - wear resistance is controlled by this method by assessing the physical condition using relative magnetic permeability in only one of the components of the hard alloy - cobalt bond. This is because tungsten carbide is a paramagnet and its contribution from magnetization to the total relative magnetic permeability is small. Therefore, using this method, essentially, the relative magnetic permeability of cobalt, its quantity and deformation state are evaluated. Moreover, other properties of the surface and volume of the hard alloy are not taken into account at all, including the cohesive and adhesive state at the phase boundaries and in the volume of the components of the hard alloy, etc. Due to the reasons considered, this method is characterized by low accuracy in assessing the wear resistance of hard alloys.

A known method of controlling the cutting properties of a batch of carbide tools, according to which first they act on each tool (carbide plate) from the batch, a control parameter is recorded, then several tools from the batch are selectively subjected to mechanical wear and the cutting properties of the tools of the entire batch are determined. The impact on each tool is carried out by uniformly distributed pulse heating, a chronological thermogram is recorded, the thermal diffusivity of each instrument is determined as a control parameter, according to the results of a selective wear mechanism depending on the thermal diffusivity, and the cutting properties of the instruments of the entire batch are determined using the obtained dependence [SU AC 1651155, IPC G01N 3/58, BI 1991 No. 19]. The selected initial parameter in this method is the thermal diffusivity. The main disadvantage of this method is that it is very difficult, more or less accurately, to determine the rate of heat propagation in materials in which free electrons are the heat carriers. Hard alloys are such materials, and their heat transfer is ensured by the movement of electrons. The thermal diffusivity of all hard alloys differs by an insignificant amount. Therefore, it is very difficult to determine the fluctuations (changing the wear resistance) of the thermal diffusivity for one particular grade of hard alloy (they are almost invisible). The latter is fraught with great technical difficulties. The proper provision in this situation of control operations with precise - acting, recording and auxiliary instruments and devices guaranteeing the necessary accuracy will entail a significant increase in the cost of control operations. As a result of this, this control method is not very promising for use in both laboratory and production conditions.

A known method for predicting the wear resistance of a cutting tool, selected as a prototype and consisting in the following. Carry out benchmark tests of cutting tools at an optimum or close cutting speed, conduct tests to change the value of the initial parameter on the properties of the surface polyoxide structure of the hard alloy formed during its heating, build the reference correlation “initial parameter - wear resistance”, perform statistical monitoring only initial parameter values for the current batch of carbide cutting tools. After that, wear resistance is predicted for the current batch of tools based on the relationship:

,

,

where T (current), min - wear resistance in minutes - the average predicted time of trouble-free operation of carbide cutting tools undergoing tests from the current batch of samples;

T (reference), min - average wear resistance in minutes for carbide cutting tools from a reference batch of carbide products;

τ (reference), ps - the average value of the selected initial parameter obtained by measuring the characteristics of the surface polyoxide structure of carbide cutting tools from a reference batch of carbide products;

τ (current), ps - the average value of the selected initial parameter obtained by measuring the characteristics of the surface polyoxide structure of carbide cutting tools from the current - controlled batch. In this case, the value of the positron lifetime embedded in the surface and near-surface layers of hard alloys and estimating the electron density of their structure is used as the initial parameter. The magnitude of the electron density predict the wear resistance of the manufactured cutting tools [SU AC 2251095 IPC G01N 3/58, BI 2005 No. 12]. The main disadvantage of this method is the high organizational complexity in its implementation. To implement this method, a radioactive source is required. In accordance with the standards for its maintenance, there are high requirements. It is necessary to have a special room for its storage. The measurement of the relevant parameters and the processing of the results obtained can only be done by specially trained and trained personnel. Using this method, the structure is evaluated at the atomic level, and not always comparing these results with the results obtained by wear resistance leads to an accurate forecast. This method allows you to sort - to predict the wear resistance of hard alloys similar in appearance and degree of defective structure. A comparison of structures that differ greatly in appearance and degree of defectiveness gives quite noticeable errors in predicting the wear resistance of carbide cutting tools. As a result of this, this method for predicting wear resistance does not exactly characterize the operational properties determined by the degree of defective structure, which ultimately reduces the degree of tightness of the correlation between the initial parameter and the wear resistance of cutting tools. Nevertheless, this control method informatively reflects the operational state of the surface structure of the tool material, which is important for establishing a relationship between this characteristic and adhesive wear, which largely depends on the type and degree of imperfection of the surface layer and we choose it as a prototype.

The objective of the proposed method is predicting the wear resistance of carbide tungsten - cobalt (group K) cutting tools is to increase accuracy and reduce the complexity in predicting the wear resistance of carbide cutting tools. Prediction is based on the close correlation between wear resistance and the concentration of hydrogen contained in the surface and near-surface structure of the hard alloy. With a decrease in the concentration of hydrogen in the surface and near-surface structure of hard alloys of the applicability group K, the wear resistance of steel and alloys that cause intensive adhesive wear increases when they are made of these hard alloys of cutting tools.

The task in predicting the wear resistance of carbide cutting tools of the applicability group K in the proposed method is solved by using the selected initial parameter and includes: testing for changing the value of the initial parameter from the properties of the surface and surface structures formed in the manufacturing process of carbide cutting material, conducting reference tests of cutting tools on wear resistance in the process of cutting materials that cause intense hezing wear at an optimum or close cutting speed, building a reference - correlation dependence "wear resistance - initial parameter", statistical control of only the value of the initial parameter for the current (incoming to the consumer) batch of carbide cutting tools, predicting wear resistance for the current batch of carbide tools based on dependencies:

where a _E and b _E are constant coefficients:

of them:

T _PT - the current wear resistance in minutes for carbide cutting tools that have been tested, from the projected current batch of carbide products;

S _PT - the current value of the selected initial parameter, obtained by monitoring the surface and near-surface structure of carbide replaceable cutting inserts from the current-predicted current batch of carbide products;

и

- износостойкость в минутах для двух независимых выборок сменных твердосплавных режущих инструментов (пластин) из эталонной (предыдущей) партии твердосплавной продукции;

and

- wear resistance in minutes for two independent samples of interchangeable carbide cutting tools (inserts) from the reference (previous) batch of carbide products;

S _E1 and S _E2 are the average values of the selected initial parameter obtained by monitoring the surface and surface structures for two samples of carbide cutting tools (plates) from the reference (previous) batch of products, characterized in that in order to improve the accuracy of predicting wear resistance in as the initial parameter, the value of the concentration of hydrogen contained in the surface and near-surface structure of the hard alloy is used, with a decrease in which the wear resistance of carbide x cutting tools, a group of applicability of K increases.

The surface and near-surface structure of the carbide cutting tool of the applicability group K, which is formed in the process of manufacturing a hard alloy, has a great influence on its wear resistance. One of the most important characteristics of the surface and near-surface structure, which determines the most important physical, mechanical and operational properties of carbide cutting tools of this group, is its ability to store the main concentration of hydrogen absorbed by the hard alloy. Using various control methods, it was found that the main concentration of the accumulated structure of the hard alloy of the applicability group K of hydrogen is contained on the surface and in the surface layers. As a result, the proposed method for predicting the wear resistance of cutting tools is reasonable, sufficiently reliable and accurate.

Hydrogen has a great influence both on the formation of the surface and near-surface structure of the hard alloy, and on the processes developing in the zones of interaction of the tool and the processed materials during the cutting process. Saturation of a solid alloy with hydrogen occurs both at the stage of preparation of its constituent components (carbide grains and cobalt powder), and at the stage of sintering of the composite carried out in a hydrogen-containing medium. Moreover, the bulk adsorbed by the hard alloy of the group of applicability To hydrogen accumulates on the surface and in the surface layers of the structure. Initially, hydrogen molecules are adsorbed by the chemically most active regions of the surface topography and the surface region of the hard alloy, including carbide grains, cobalt interlayer, and interphase boundaries. Then, due to diffusion, hydrogen penetrates into the surface layers of the hard alloy. Subjects of the surface and near-surface structure of hard alloys, on which significant adsorption of hydrogen molecules primarily occurs, include the space of communicating and closed pores, as well as the cavities formed by a system of short branching cracks, which in turn belong to carbide grains and cobalt particles. The highest concentration of pores and cracks is contained in the structure of carbide grains and interfacial space. The cobalt layer contains mainly a high concentration of short branching cracks. The porous system in the carbide structure is formed during the high-temperature treatment of tungsten powder in the process of saturation with its carbon component. A system of cracks in carbide and cobalt particles is formed at the stages of their grinding in a ball mill. The process of saturation with hydrogen during sintering can be accompanied by the formation of new systems of pores and cracks, as well as their annihilation. The processes of decomposition of molecules into atoms during hydrogen adsorption, the diffusion of hydrogen atoms into the deep layers of the structure, the formation of solid solutions and hydride compounds are greatly influenced by the electric field of the adsorbed surface. The electric potential of the surface of the powders is evolving, simultaneously with the transformation of the surface structure from the preparation of mixtures and their grinding to sintering of the manufactured moldings. The formation of an electric field on the surface and in the near-surface region of carbide materials is due to the heterogeneity of the properties of structural components (carbide grains and cobalt interlayers), as well as the presence of many dangling valence bonds on their surface atoms. Along with the change in the state of the components and their chemical, physical and mechanical properties, the electrical properties of the surface also change. Hydrogen molecules are adsorbed by carbide grains and a cobalt layer of the surface of the hard alloy, both unchanged and as a result of their dissociation into atoms. At the same time, the strength of the resulting hydrogen compounds with the surface of both tungsten carbide and the cobalt interlayer is not significant. In this case, hydrogen molecules, as a rule, remain on the surface, and atoms due to diffusion can move into the deeper layers. A large effect on the penetration of hydrogen into the surface layers of the hard alloy is provided by counter diffusion from the deep structure of oxygen impurities and low-melting elements. The latter, during movement, maintain and strengthen the electric field, which promotes the movement of hydrogen atoms into the deep layers of the structure of hard alloys. Hydroxyl groups and complexes formed as a result of the interaction of hydrogen and oxygen atoms increase the volumetric heat capacity of carbide grains and the cobalt interlayer and, accordingly, increase the temperature of the onset of active oxidation of the hard alloy of the applicability group K, which is an undesirable fact when cutting materials that cause intense adhesive wear. In the case of adhesive wear of a cutting tool, on the contrary, it is important to reduce the temperature of the onset of intense oxidation for the hard alloy material, to ensure the formation of oxide films on the contact surfaces that reduce the activity of adhesive interactions and the friction coefficient, which, in general, reduces the wear rate of contact surfaces. The ratio of hydrogen adsorption in the form of molecules and atoms determines its concentration on the surface and diffusing into the deeper layers. The nature of hydrogen adsorption by the surface of a hard alloy is influenced by many factors, primarily, the type and degree of vacancy defects in the components of this tool material, the stoichiometric composition of carbide grains, the presence of various impurities in the components, etc. Hydrogen adsorbed on the surface and penetrated into the deep structure does not form hydride compounds with the components of the hard alloy, the group of applicability K is hydride compounds and to a small extent is involved in the formation of solid solutions. The presence of certain impurities, for example, oxygen, alkali and alkaline earth metals, has a great influence on the kinetic and thermodynamic properties of the tool material when they interact with hydrogen. Impurities can also change the capacity of the hydrogen alloy placed in the structure of the solid alloy, reduce or decrease the temperature at which the effective filling of the structure with hydrogen begins, reduce or increase the temperature at which the effective desorption of hydrogen starts from the structure, and change the rate of hydrogen absorption and its release rate. The desorption of hydrogen accumulated by the structure, for example, can occur during the operation of cutting tools into a space with reduced pressure. This object is placed between the contact surfaces of the cutting tool and the processed material (intercontact space). Hydrogen desorbed into the intercontact space can take part in deoxidation and reduce the likelihood of the formation of dissipative oxide structures on the contact surfaces of the cutting wedge. At the same time, dissipative oxide structures, if any, effectively shield the intermolecular interaction with the material being processed and protect the cutting wedge from adhesive wear.

The presence of a thin oxide film on the components (carbide grains and cobalt particles) has a large effect on the adsorption of hydrogen by a solid alloy and its diffusion into the surface layers. The oxide film, depending on the composition of carbide grains and cobalt particles and their thermodynamic state, can both contribute to the subsequent process of hydrogen saturation during sintering in a hydrogen-containing medium, and also hinder this process. In the presence of impurities that form strong bonds with oxygen, the oxide film prevents the saturation of the structure with hydrogen. In the presence of hydride-forming impurities, the oxide film helps to saturate the structure with hydrogen.

The formation of an oxide film on the surface of carbide grains and cobalt particles occurs mainly at the stages of their grinding. Oxide films of nanosized thickness on these components are formed under the action of high, pulsed temperature effects resulting from the implementation of various types and degrees of elastic and plastic deformations occurring in their surface layers and in the volume during grinding in special ball mills. The grinding is realized as a result of periodic impacts of metal balls on particles in a confined space. The formation of oxide films on carbide grains and the cobalt layer during grinding is preceded by surface reconstruction (changing the arrangement of surface and surface atoms belonging to the substrate and oxygen) with the participation of adsorbed oxygen or the formation of island oxygen formations on the surface. The relationship between reconstruction processes and the formation of islands on the surface can be different and depends on many factors. As a result of the reconstruction, there is a general decrease in the chemical potential of the surface, but at the same time, depending on the initial crystallographic relief, particle composition, and the presence of impurities, mechanical stresses between structural elements of these carbide components can increase or decrease. The latter can lead to an increase in surface energy and intensification of adsorption, or, conversely, to a decrease in energy and adsorption. Due to the formation of islet formations on the surface, a local decrease or increase in surface energy occurs in the components of the hard alloy.

The driving force for the reconstruction of the surface of carbide grains is the presence of dangling atomic bonds on the surface and the strong electrostatic interaction of adsorbed oxygen atoms with tungsten and carbon atoms. The driving force for reconstructing the surface of the cobalt component is the strong electrostatic interaction of the adsorbed oxygen atoms with cobalt atoms. The specific gravity of the reconstruction of the surface of carbide grains (the arrangement of surface and subsurface atoms of tungsten, carbon, and oxygen) depends on the initial stoichiometry of carbide grains. With an increase in the stoichiometry of carbide compounds, the proportion of reconstruction processes in comparison with the processes of formation of islet formations increases. The impurities that make up the carbide grains influence the processes of reconstruction and the formation of islet formations. Carbide-forming impurities increase the stoichiometry of carbide grains and, accordingly, the reconstruction of their surface with the participation of oxygen. Impurities of alkali and alkaline earth metals, on the contrary, contribute to the formation of islet formations from oxygen atoms on the surface of carbide grains.

Subsequent oxidation of the carbide component and the formation of a surface oxide structure to a large extent depends on the type of crystallographic relief formed during reconstruction or during the formation of islet formations. The formation of an oxide film of nanoscale thickness with a higher intensity occurs when high-index tungsten faces exit onto the surface.

The specific gravity of the surface reconstruction of the cobalt component (the arrangement of surface and near-surface cobalt and oxygen atoms) depends on the ratio of the processes of hardening (hardening) and relaxation arising in the cobalt particle of stresses during their grinding - activation. When the hardening processes exceed relaxation processes, the proportion of reconstruction processes in comparison with the processes of formation of islet formations increases. The impurities that make up cobalt can have a great effect on both the hardening process and the relaxation process. The predominance of impurities that contribute to the strengthening of the cobalt structure will initiate surface reconstruction, both due to the interaction of own atoms, and during the interaction of surface atoms with oxygen, and, conversely, the predominance of impurities that contribute to the relaxation of the cobalt structure will promote the formation of island structures on the surface. Impurities that do not form compounds with cobalt contribute to hardening during grinding of powder cobalt. Impurities that form compounds with cobalt, on the contrary, hinder the hardening processes. Subsequent oxidation of the cobalt component and the formation of a surface oxide structure to a large extent depends on the type of crystallographic relief formed during reconstruction or during the formation of islet formations. The formation of an oxide film of nanoscale thickness with a higher intensity occurs when low-index faces emerge on the surface.

Preliminary reconstruction of the surface, the formation of island oxide formations, and surface oxidation during sintering of hard alloys provide general and local processes of internal oxidation of the structure of tool materials — oxygen accumulation in deep layers. The degree of oxygen dissolution in the structure of instrumental materials and the formation of solid solutions depend on the rate of surface and volume diffusion. With an increase in the sintering temperature, the rate of oxygen diffusion into the deep layers first increases and then decreases. The decrease is caused by the processes of sublimation of oxide compounds from the surface of both components. The latter leads to depletion of the internal structure of the solid alloy with oxygen. In order to avoid this, it is necessary to optimize the range of the most favorable sintering temperatures. Subsequently, at the stages of operation of carbide applicability groups of K cutting tools, the oxygen accumulated by the internal structure forms dissipative structures on the contact surfaces, which effectively shield intermolecular interactions with the material being processed and reduce intensive adhesive wear. The wear resistance of cutting tools therefore increases.

The adsorption of oxygen by the surface of tungsten carbide is accompanied by its significant reconstruction. This is due to the high strength of the formed bonds between oxygen and tungsten carbide. With a uniform distribution of oxygen on the surface during the reconstruction process and with its uniform diffusion into the surface layers, the best results can be achieved by shielding intensive adhesive wear due to the reliable formation of dissipative oxide film on contact surfaces during operation of carbide cutting tools.

The accumulation of oxygen on the surface of carbide grains in the form of islands creates a high local concentration gradient, and the probability of intense local diffusion of oxygen into the surface layers. However, the insular nature of the distribution of oxygen on the surface of carbide grains of the hard alloy only partially shields the adhesive interaction of the working surfaces of the cutting tool with the material being processed.

The processes of surface reconstruction and the formation of island structures on the surface of tungsten carbide contribute to the internal oxidation of hard alloys and have a beneficial effect on the wear resistance of cutting tools when they process materials that cause intense adhesive wear.

The processes of surface reconstruction and the formation of island structures on the surface of the cobalt component also contribute to the internal oxidation of hard alloys and have a negative impact on the wear resistance of cutting tools when they process materials that cause intense adhesive wear. This is due to the loss of the plastic properties of the cobalt binder and a decrease in its ability to retain carbide grains in the composition. The cobalt component must contain a limited amount of oxygen in order to maintain a sufficiently high yield strength for a given material. It is the high yield strength of cobalt that provides a strong and reliable retention of carbide grains in the composite without the formation of cracks at the interfaces.

Sintering of hard alloys of the applicability group K is carried out in a hydrogen-containing medium at sufficiently high temperatures. In this case, the process is accompanied by the adsorption of hydrogen to the surface of carbide grains and the cobalt interlayer, and its diffusion into the surface layers. The nature of the distribution of hydrogen atoms on the surface of carbide grains and cobalt particles, in the form of reconstruction or the formation of island structures, is exerted, like in the case of oxygen adsorption, by the ratio of the interaction forces between the particles of the adsorbate, as well as between the particles of the adsorbate and the substrate. In this case, depending on the structural state of the constituent components of the hard alloy, hydrogen adsorption can be accompanied either by reconstruction of the surfaces of carbide grains and cobalt bonds, or the formation of local islet formations on their surface.

Surface reconstruction (changing the arrangement of surface and surface atoms of the substrate and hydrogen) with the participation of hydrogen becomes possible when the interaction between the particles of the adsorbate (hydrogen) is repulsive, and the interaction between the adsorbate and the adsorbent (substrate) is quite strong. During reconstruction, hydrogen particles as a result of diffusion move along the surface at distances not exceeding several lattice constants.

The formation of an island landscape from adsorbed hydrogen becomes possible when the interaction between the adsorbate particles is strong and attractive, and the interaction between the adsorbate and adsorbent is weak. During the formation of islands, hydrogen particles, as a result of diffusion, move along the surface at distances significantly exceeding the constant value of the lattice.

The stoichiometric composition of carbide grains, the stress-strain state of the cobalt binder, the presence of impurities in their composition, the composition and structure of oxide films on these components of the hard alloy strongly influence the relationship between the hydrogen particles on the one hand and the hydrogen particles and the substrate (adsorbent). applicability groups K and other factors.

Hydrogen does not form hydride compounds or solid solutions with tungsten carbide. The relationship between reconstruction and the formation of islet formations on the oxide surface of tungsten carbide depends on the degree of stoichiometry of carbide grain, the presence of oxide formations on the surface, the degree of coherence of the oxide film and substrate, the presence of an oxycarbide layer, and the presence of certain impurities.

With an increase in the initial stoichiometry of carbide grain, uniformity of the thickness of the oxide film, an increase in carbide-forming impurities, for example, iron, manganese, and molybdenum, an increase in the coherence of the oxide film with the substrate, the specific gravity of surface reconstruction processes involving hydrogen increases. Moreover, due to the uniform diffusion of hydrogen into the surface layers, the diffusion of oxygen from the deep layers to the surface is intensified. That at the stages of sintering is an inappropriate effect. Only with the operation of cutting tools is oxygen diffusion to the surface desirable. The presence of oxygen in the surface layers, during the operation of cutting tools, effectively provides oxidation of the contact surfaces. As a result, the effect of intense adhesive wear is shielded by oxide films, which leads to an increase in the wear resistance of cutting tools.

With a low degree of stoichiometry of carbide grains and the presence of hydride-forming impurities in their composition between adsorbed hydrogen particles, mainly attractive forces act on the surface. In this case, mainly local hydrogen islet regions are formed on the surface of the carbide grain. Islands usually form near some active centers in which, for example, sodium, magnesium, potassium, and calcium act as the nucleus. In the force field of action of these impurities, not only single-layer, but also multilayer hydrogen island formations are formed. From these initial positions, hydrogen, due to the high concentration gradient due to diffusion, penetrates through the carbide grain into the deep layers of the hard alloy structure. Both on the surface and in the surface layers, hydrogen is located in the unfilled, first, tetrahedral and then in the octahedral pores of the crystal lattice of tungsten carbide.

The insular nature of the distribution of hydrogen on the surface of carbide grain and its subsequent diffusion into the near-surface region forms a kind of so-called columnar structures. Areas of the structure with an islet character of hydrogen distribution on the surface and in depth of the hard alloy components during the operation of carbide cutting tools of applicability group K, during the cutting of materials that cause intense adhesive wear, are difficult to oxidize and are, therefore, areas with increased adhesive activity, which, in in general, it leads to their intensive wear. Various facets of tungsten carbide grains formed as a result of carbidization, sintering, reconstruction, or the formation of island structures on the surface and in the volume variously participate in the accumulation of hydrogen. The most active hydrogen is located on low index faces. With a high initial degree of stoichiometry of carbide grain and in the presence of carbide-forming impurities, for example, iron, manganese, molybdenum, the probability of the absence of impurities, for example, sodium, magnesium, potassium, calcium, increases their yield to the surface, and the proportion of absorbed hydrogen increases.

Hydrogen interacts with cobalt only at high temperatures. However, the solubility of hydrogen in cobalt, even at high temperatures, is small. Hydrogen adsorbed during sintering of hard alloys with cobalt oxide surface can both reconstruct the surface and form island formations on it. If cobalt contains impurities that reduce the chemical bond strength of cobalt with the oxide film (reduce coherence between the oxide film and the substrate), for example, nickel, manganese, and iron, the interaction of hydrogen at local points and their environs on the surface becomes quite strong, and surface diffusion propagates only at distances comparable to the lattice constant. In this case, the surface is reconstructed with the participation of cobalt, oxygen, and hydrogen atoms. As the cobalt content of hydride-forming elements, such as sodium, potassium, magnesium, calcium, increases, the coherence between the oxide film and the substrate increases, and the interaction of the oxide film with the cobalt surface increases. In this case, hydrogen atoms freely diffuse over the surface of the oxide film over long distances and are actively involved in the formation of island structures. We can assume that hydrogen on the surface of cobalt particles is involved both in surface reconstruction and, simultaneously, in the formation of the island landscape. The result of the reconstruction of the surface with the participation of hydrogen can be increased adhesive activity of the cobalt surface to the processed material in the initial period of operation of the cutting tool. As a result of this, increased wear of the cobalt binder and an intensive character of the removal of carbide grains from the structure of the hard alloy occur. In this case, the destruction of the cutting wedge occurs due to weakening of the bond between the carbide grain and the cobalt layer, caused by the predominant destruction of the cobalt matrix. When removed during the cutting process, reconstructed with the participation of the hydrogen layer on the cobalt component, the wear rate is significantly reduced.

Islands of hydrogen on a cobalt matrix are usually formed near some active centers, the nucleus of which are, for example, sodium, potassium, magnesium, calcium. In the force field of action of these impurities, not only single-layer, but also multilayer island formations are also formed. From these initial positions, hydrogen due to the high concentration gradient due to diffusion penetrates through the cobalt matrix into the deep layers of the hard alloy structure. Both on the surface and in the surface layers, hydrogen is located in the unfilled, first, tetrahedral, and then in the octahedral pores of the cobalt crystal lattices. The insular nature of the distribution of hydrogen on the surface of cobalt and its subsequent diffusion into the near-surface region forms, as in adsorption on carbide grains, some varieties of columnar structures. Areas of the structure with an insular nature of the distribution of hydrogen on the surface and in depth of the cobalt component during the operation of carbide cutting tools of the applicability group K, are difficult to oxidize during the cutting of materials that cause intense adhesive wear and are therefore areas with increased adhesive activity. This leads to accelerated destruction of the cobalt matrix and a decrease in the retention strength of carbide grains in the structure of the hard alloy. The wear resistance of carbide cutting tools of the applicability group K when cutting materials that cause intense adhesive wear, decreases sharply. Individual faces of the cobalt component that emerge as a result of reconstruction or the formation of island structures on the surface are involved in various ways in the saturation of the surface and subsurface structures of the cobalt hard metal component with hydrogen. The most active in the accumulation of hydrogen are high-index facets. With an increase in the degree of hardening of the cobalt structure at the grinding stage, the specific gravity of the fine-grained structure both on the surface and in the surface layers increases. This circumstance is the main factor in the appearance of these faces on the surface and an increase in the amount of accumulated hydrogen. To reduce the intensity of filling the structure of local surface areas and the volume of cobalt with hydrogen, it is necessary to exclude the limiting hardening of cobalt particles during their grinding in ball mills. In the absence of hydride-forming impurities in the composition of cobalt particles, for example, sodium, potassium, magnesium and calcium, the probability of island formation and the amount of hydrogen absorbed are reduced. The latter ultimately leads to an increase in the wear resistance of cutting tools.

In general, with a decrease in the hydrogen content in the carbide components of the applicability group K of cutting tools, their wear resistance increases when cutting materials that cause intense adhesive wear. In the preparation of carbide components, it is thus necessary to influence the composition of particles and technological methods in order to ultimately ensure the optimal combination between surface reconstruction and the formation of island structures, which ultimately can guarantee the maximum allowable saturation of carbide grains with oxygen and minimal saturation of both carbide grains and cobalt interlayer with hydrogen. This provides the highest performance characteristics for carbide cutting tools of the applicability group K, when they process materials that cause intense adhesive wear.

A significant feature of the proposed method is that in accordance with its methods - without additional costs and technical difficulties - it seems possible to conduct a more objective and accurate assessment of wear resistance - due to the operational analysis and comparison of current controlled and reference parameters obtained in a wide range of cutting conditions and cutting temperatures. The properties of carbide cutting tools of the applicability group K are greatly influenced by wear-resistant coatings. A stable correlation is also observed between the hydrogen content on the surface and in the surface layers of these hard alloys and their operational characteristics. And for these tool materials, the rule is observed: with the increase of hydrogen accumulated by their surface and near-surface region, the wear resistance of cutting tools increases. Accordingly, the proposed forecasting method for evaluating their operational characteristics is also applicable.

The implementation of the method is carried out through several stages. First, carbide cutting tools (cutting inserts) are tested during cutting of materials that cause intense adhesive wear. After wear resistance tests, the cutting inserts are thoroughly cleaned, one of the surfaces is polished (for example, landing or side), thoroughly washed in an alcohol solution, dried and, finally, tested for the hydrogen content on the surface and in the surface area. Control can be attributed to non-destructive methods, because the cutting inserts, if they have left unused cutting edges (multifaceted cutting inserts) can be continued to operate.

Due to the large influence exerted by the accumulated hydrogen on the operational characteristics of hard alloys of the applicability group K, as well as due to its location mainly on the surface and in the surface structure, the wear resistance of cutting tools of the applicability group K was predicted by comparing the wear resistance with the total hydrogen content on the surface and in the near-surface region data structures of hard alloys.

The process of diagnosing the surface and near-surface region of a hard alloy with a depth of 0.15 mm for the hydrogen content was carried out using an atomic emission spectrometer operating in the glow discharge mode of the GD-Profiler - 2 model of HORIBA. The instrument is tuned to the process of identifying hydrogen in carbide cutting inserts of the applicability group K using standard samples. The work was carried out in the following sequence: First, prepare the surface of the sample of the hard alloy of the applicability group K - samples for measurements on it. The surface is pre-polished to R _A = 0.32-0.63 μm. After cleaning the surface in an ultrasonic bath and drying for 2-4 minutes at room temperature, the sample - sample is applied to the exit window of the hollow anode of the spectrometer and the vacuum pump is turned on, creating a high vacuum in the measuring chamber - the internal cavity of the anode. The retention of the sample cathode at the exit window is due to the formation of a vacuum of about 10 ^-4 -10 ^-3 mm Hg in the inner cavity of the anode. After creating a high vacuum in the measuring chamber, its internal space is filled with high purity argon and, at the same time, a high ripple voltage with a frequency of 13.56 MHz is created between the sample - cathode and anode. This voltage is created by a special radio frequency generator. Under the influence of high-frequency voltage, ionization of argon atoms occurs and their directed motion to the cathode - carbide sample. At low argon pressure in the discharge cell, the hollow anode, there is always a certain concentration of positively charged ions and electrons. Under the action of the potential difference between the cathode and the anode, electrons rush to the anode, and positively charged argon ions to the cathode - to the sample. Due to the high kinetic energy, argon ions knock out the atoms of the cathode, a hard alloy, and contribute to the formation of secondary electrons. In the process of burning a glow discharge plasma, a continuous process of excitation of atoms of the sample surface and relaxation of the excited state occurs. The transition to a higher energy level of atomized atoms of the sample occurs both due to atoms and argon ions, and due to secondary electrons. Secondary electrons are accelerated from the cathode and experience various collisions in their path, including with atoms and ions of the sample. As a result of relaxation of the excited state, during the transition of atomic electrons of the sample from high to low energy levels, quantum energy is emitted. Light radiation is recorded and processed by special receivers and photomultipliers. The hydrogen concentration in the structure (including in depth) is identified with the intensity of the appearance of characteristic lines in its spectrum. The depth spectral analysis of hydrogen is compared with the duration of the glow plasma discharge and is entered in advance into the spectrometer program. The data on the processing of the obtained spectra are transmitted to an analog-to-digital converter, and then to a computer processor and, finally, to a computer display. The entire control process is displayed on the screen of the processor unit. Typically, the measurement time is not more than 5 minutes. The measurement is characterized by high reproducibility of the results, because eliminates errors associated with the selection, preparation and analysis of individual samples of hard alloy, characteristic of traditional methods of analysis.

The prediction of the wear resistance of carbide cutting tools of the applicability group K when they process materials that cause intense adhesive wear is that they first conduct resistance tests of carbide cutting inserts from two samples of a batch of carbide products, determine the wear resistance of each cutting insert, determine the average wear resistance for cutting inserts for each sample, prepare the images (polishing, cleaning, drying), place the samples in turn with ektrometr, the concentration of accumulated surface and near-surface region of a hydrogen in each sample, determining the average values for samples of released hydrogen - samples for each sample, plotted wear resistance on the hydrogen concentration. Then, the prediction of the wear resistance of the supplied batch of carbide cutting inserts of the applicability group K is performed without testing them during the cutting process, but only if they have a concentration of hydrogen in their surface and near-surface structure. With a decrease in hydrogen concentration in the surface and near-surface structure of carbide cutting inserts of the applicability group K, their wear resistance increases when cutting materials that cause intense adhesive wear. Moreover, to predict the wear resistance, dependence (1) is used, and they also use the graph of the dependence “wear resistance - hydrogen concentration”, obtained earlier in the test - forecasting the wear resistance of the first (reference) batches of carbide cutting inserts.

Figure 1 shows the reference relationship "wear resistance - hydrogen concentration", on the basis of which a forecast is made of the wear resistance of carbide applicability groups K of cutting inserts when they cut materials that cause intense adhesive wear.

Figure 2 presents the integral dependence of the hydrogen content in the surface structure of the hard alloy during a given duration of combustion of a glow discharge.

The saturation of the structure of carbide cutting tools of the group of applicability to hydrogen occurred during the manufacturing of individual components and subsequent sintering of the composite. The concentration of hydrogen accumulated by the structure reflects the chemical composition and the nature of the manufacture of constituent components and the hard alloy as a whole.

Taking into account the peculiarities of the interaction of carbide tool materials of the applicability group K with hydrogen, it can be stated that a large number of controlled factors, such as the main ones: the composition of the starting materials intended for the production of tungsten, cobalt, graphite, the presence of these or those impurities, the technology for producing these powders, the technology for producing carbides, especially grinding mehanoaktivatcii powders, especially hard metal sintering process components, the composition of the gas medium used in the preparation of powders and sintering them. By targeted control and regulation of these factors, it is possible to create conditions under which the surface and surface structure of hard alloys will accumulate the smallest possible amount of hydrogen. This approach will ensure the formation of the most optimal structure of hard alloys in their manufacture. In this case, with a decrease in the structure of hard alloys of the applicability group K of hydrogen, their wear resistance increases when cutting materials that cause intense adhesive wear.

An example of a method for predicting the wear resistance of carbide cutting tools. At first, two batches (accepted as reference) obtained in the sampling, in the amount of 10 pieces each, carbide cutting inserts of the applicability group K of the VK8 grade were tested for wear resistance on a model 163 screw-cutting lathe. The nickel-chromium austenitic steel 12X18H10T was used as the processed material . The cutting speed during the tests was chosen equal to 74 m / min. The feed rate and depth of cut were respectively 0.23 mm / rev and 1.5 mm. Cutting was carried out without cooling. As a blunting criterion, the wear of the insert along the rear surface, equal to 0.6 mm, was taken.

Resistance (T _1i ) for samples of 10 pieces of the first reference batch was: 18.5; 20.1; 21.4; 22.2; 23.6; 24.9; 25.8; 27.8; 30.1; 31.6 minutes The average value of resistance was 24.6 minutes

Resistance (T _2i ) for samples of 10 pieces of the second reference batch was: 19.6; 20.2; 22.5; 24.3; 25.2; 26.1; 28.2; 29.0; 30.2; 31.7 minutes The average resistance value was 25.7 minutes.

Then, the tested carbide inserts after polishing chemical cleaning in an ultrasonic bath and drying were examined to determine the surface accumulated by the structure and the surface region of hydrogen. The optimal roughness of the surface prepared during polishing is R _A = 0.32-0.63 μm.

The carbide plates thus prepared are installed as a cathode at the outlet of the hollow anode and, when the spectrometer is turned on, the hydrogen content monitoring process begins. The process of determining the hydrogen concentration on the surface and in the near-surface region based on measuring the intensity of the characteristic line in the optical spectrum of a glow discharge was determined using a HORIBA GD-Profiler - 2 atomic emission spectrometer. The accuracy of the recorded intensities of the appearance of the characteristic lines of hydrogen in the spectrum is ± 0.01 V. The burning time of the glow discharge is set constant and is 180 seconds for monitoring each plate.

In the process of monitoring to determine the hydrogen content on the surface and in the near-surface region, at a specified glow discharge duration of 180 sec (the depth was approximately 100-120 μm), the dependency graphs were obtained “intensity of the characteristic lines of hydrogen in the glow discharge spectrum in volts is the glow discharge burning time in seconds. " Graphs of typical dependencies are presented in figure 2. Using a standard computer program, at the same time, we determined the area under each graphical dependence obtained for each specific insert and characterizing the integral, relative hydrogen content on the surface and in the near-surface region for 180 sec of burning glow discharge. This time corresponds approximately to the propagation of the crater (plasma action) to a depth of approximately 100-120 microns. Area S, characterizing the relative integral hydrogen content over the scanning depth, was measured by the product (Volt × sec) - (V · s). For the first batch of cutting inserts, the following data were obtained on the integral parameter S _1i (the area under a particular curve characterizing the relative integral hydrogen content on the surface and in the near-surface region) for the cutting inserts, in the order, respectively, with their previously obtained during wear resistance tests: 5,280 ; 5.125; 4,875; 4,670; 4,375; 4,110; 3,880; 3,500; 3,110; 2.610 (V s). The average value of the parameter of hydrogen concentration on the surface and in the near-surface region was: 4.150 (V s).

For the second batch of cutting inserts, the following data were obtained on the parameter S ₂ i (the area under a particular curve characterizing the relative integral hydrogen content on the surface and in the near-surface region) for the cutting inserts, in the order, respectively, also with their wear resistance previously obtained during testing: 5.225; 5,000, 4,500; 4.225; 4,000; 3,725; 3,450; 3,110; 2,890; 2.775 (V s). The average value of the hydrogen concentration parameter on the surface and in the near-surface region was: 3.890 (V · s).

Based on the results obtained earlier on determining the wear resistance of carbide cutting inserts (T _min ) and the values of the parameter characterizing the hydrogen content on the surface and in the near-surface layers (S _{B · s} ), a graph of the dependence “wear resistance-T - an integral parameter of hydrogen concentration on the surface and in the near-surface area - S ”.

Figure 1 shows the dependence of the wear resistance of cutting inserts from VK8 of the applicability group K, respectively, for samples 1 and 2 during their processing of austenitic chromium-nickel steel 12X18H10T on the concentration of hydrogen accumulated by their surface and the surface structure of hydrogen. To predict the wear resistance of carbide cutting inserts in the subsequent current (manufactured or obtained) and intended for consumption batch of tool samples, only the concentration values of the hydrogen accumulated by their surface and near-surface region are tested. So, for example, when predicting the wear resistance of the next batch of carbide cutting inserts of the applicability group P on the GD-Profiler - 2 atomic emission spectrometer, the following values of the integral parameter of hydrogen concentration (S) on the surface and in the near-surface region for carbide inserts were obtained: 5.225; 5,000; 4,850; 4,650; 4,500; 4,375; 4,000; 3,850; 3,500; 3.110 (V s). The average value from the obtained data was 4,300 (V · s). In accordance with the above formulas, a _e and b _{e are} determined.

a _e = 4.23; b _e = 42,157

then determine T _pt

T _pt = 23.97 min.

Thus, the predicted average wear resistance of the current batch of carbide cutting inserts was 23.97 minutes.

Control tests of wear resistance during cutting on a metal cutting machine showed the following wear resistance results: 18.8; 19.8; 20.6; 22.8; 23.6; 24.8; 25.8; 26.4; 27.2; 28.4 minutes The average value was 23.82 minutes.

When predicting wear resistance for the current batch of carbide tools, there is no need for expensive and time-consuming wear tests conducted on metal cutting machines. The method has a high forecast accuracy. This is due to the close correlation between the ability of carbide cutting tools of the applicability group P to accumulate hydrogen in their structure and their wear resistance when cutting materials that cause intense adhesive wear. The degree of correlation between the concentration of hydrogen contained in the structure of the carbide group of applicability P of cutting tools and their wear resistance was r = 0.92. The degree of correlation between the initial parameter and the wear resistance of the cutting inserts in accordance with the prototype was r = 0.74. When comparing the data on the forecast of wear resistance, obtained in accordance with the prototype, according to the proposed method, as well as as a result of control experimental studies of wear resistance, performed in the process of cutting chromium-nickel steel of the austenitic class, it was found that the results obtained in accordance with the prototype differ from control tests on 15-20%, while the results obtained by the proposed method differ by only 5-10%.

Thus, the proposed control method - predicting the wear resistance of carbide cutting tools can be used with sufficiently high economic efficiency in enterprises manufacturing or consuming carbide products.

Claims (1)

A method for predicting the wear resistance of carbide applicability group K of cutting tools, according to the selected initial parameter, including testing for changing the value of the initial parameter from the properties of the surface and surface structures formed during the manufacture of carbide cutting material, carrying out benchmark wear tests in the process of cutting materials that cause intense adhesive wear at an optimal or close cutting speed, construction is standard d - correlation dependence “wear resistance - initial parameter”, statistical control of only the value of the initial parameter for the current batch of carbide cutting tools, prediction of wear resistance for the current batch of carbide tools based on the relationship:

where a _E and b _E are constant coefficients:

of them:
T _PT - the current wear resistance in minutes for carbide cutting tools that have been tested, from the projected current batch of carbide products;
S _pt is the current value of the selected initial parameter obtained by monitoring the surface and near-surface structure of carbide replaceable cutting inserts from the current-predicted batch of carbide products;

and

- wear resistance in minutes for two independent samples of interchangeable carbide cutting tools (inserts) from the reference (previous) batch of carbide products;
S _E1 and S ₂ - the average values of the selected initial parameter obtained by monitoring the surface and surface structures for two samples of carbide cutting tools (plates) from the reference (previous) batch of products, characterized in that in order to improve the accuracy of prediction of wear resistance in as the initial parameter, the concentration of hydrogen contained in the surface and in the surface structure of the hard alloy is used, with an increase in which the wear resistance of carbide cutting tools, a group of applicability of K increases.

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