Papers by Keyword: Surface Hardening

Abstract: The work investigated the nature and features of surface strengthening of steel products during friction thermomechanical processing (FTMP) of the surface. For this purpose, changes in the structure and properties occurring under the influence of FTMP in test samples were studied, and the influence of energy parameters during FTMP on the amount of surface strengthening of the samples was also evaluated. As a result of the research work, the factors affecting the preliminary thermal strengthening and additional strengthening of 65G steel samples using FTMP were identified, which allowed to increase the microhardness of the steel in the processing zone by more than 2 times. At the same time, the microhardness was increased thermally to the level of about 580 kgf/mm², which is equivalent to 5800 MPa, and after FTMP, the microhardness increased to 1300 kgf/mm², which corresponds to 13000 MPa. It is also shown that the strengthened "white" layer formed during FTMP and located along their entire processing length is continuous, which characterizes the homogeneity and uniformity of the strengthening of the surface of the samples. The load distribution at FTMP was determined using a dynamometer and the circumferential force of friction processing was calculated, which made it possible to establish dependencies that show the strengthening characteristics taking into account the thickness of the friction disc. Taking these data into account, recommendations are offered regarding the optimal thickness of the reinforcing disc.

Abstract: This study deals with the hardening of titanium surface by carburising of CP Ti Gr 2 substrate by using laser sintering process. The objective of this project is to harden the surface to improve surface wear resistance of titanium. In this study graphite powder is used as source of Carbon. Carbon from graphite reacts with titanium and TiC layer of 109 micron was measured on the titanium surface. The microstructure and phase analysis results show that presence of only TiC phase on the surface of the titanium substrate. TiC grains are nearly 5 times finer than titanium substrate grains. Grain refinement of TiC phase all over the surface of the substrate resulted in increase in hardness and development of significant wear resistance surface in titanium substrate. Hardness of TiC layer was found to be 2191Hv which is nearly ten times higher than the substrate titanium. Wear test results of pin and disc type shows negligible wear rate as compared to CP Ti substrate. TiC grains are nearly 5 times finer than titanium substrate grains.

Abstract: The present research shows the possibility of using an ytterbium nanosecond pulsed fiber laser for wear resistance improvement of carbon and alloy steels. The wear test was performed in accordance with the block-on-ring scheme with dry sliding friction on a friction machine. Surface dispersing/alloying was carried out from a boron carbide paste. This leads to a significant wear resistance improvement of steels. It was revealed that the mass loss during wear test reduced by several times after laser treatment compared to the non-treated samples. The wear mechanism differs depending on the type of steel and largely refers to their microstructure and composition. The tribo-oxide layer forms during the wear test.

Abstract: Two types of graphite cast iron are evaluated. The effect of laser surface hardening is compared using metallographic analysis of the microstructure and measurement of hardness profile. Conditions of the hardening were the same for both analyzed materials. The alloys that were compared are: cast iron with lamellar graphite EN GJL-200 and cast iron with nodular graphite EN GJS-700 CuNi. Microstructure of tested cast irons was pearlitic-ferritic. Laser surface heat treatment caused formation of martensitic layer. The depth and structural compositions of hardened layers do differ. In the case of gray cast iron the higher hardened depth was achieved and in the case of ductile cast iron the higher hardness was observed.

Abstract: Two new parameters – reduced wear and reduced integral microhardness of the modified surface layer was used to evaluate the effectiveness of surface hardening technologies. The existence of a correlation between the entered parameters is shown, the regression equation is obtained based on the analysis of experimental data of the wear of a tool made of steel CrWMn and U10 treated with a laser with coatings in the reflow mode. We construct the functional dependence of tool wear on this parameter.

Abstract: The new method for a comprehensive assessment of the strength, durability and material capacity of the critical elements of the main gas pipelines, taking into account the combined impact of factors causing damage (environment, corrosion, random loading, geometry variation, material defects, etc.), which are changing the bearing capacity and material capacity of these structures, is proposed. As the main damaging factor, the process of corrosion fatigue is accepted, the qualitative and quantitative assessment of which are realized by applying a set of equations of comparable fatigue lines obtained by fatigue tests carried out in air and in corrosive environment. By the joint solution of these equations, the functions of the corrosion action coefficients are obtained in a wide range of cyclic strength and durability, which in standard calculation procedures are performed only for cyclic strength and only at the inflection point of the fatigue lines (N_G  5  10⁶ cycles).The issues of reducing the material consumption and ensuring the cost-effectiveness of structures, by using relatively cheap materials for pipelines - low-carbon and low-alloy structural steels subjected to surface hardening in stressed sections of pipes (edge welds) in order to significantly increase the physical and mechanical characteristics of the used steel grades are considered. In order to increase the corrosion resistance of these sections, contemporary polymer anticorrosive coatings are used.

Abstract: The paper focuses on a combined processing method developed to control the properties of the surface layer of parts. A regular micro-relief was obtained on the surface, with oil pockets to hold the lubricant during the friction process. Profilograms of samples processed by different modes and a model of the process of obtaining regular micro-relief are presented. We carried out comparative endurance tests of the samples processed by various methods. For the study the samples of steel 5140 (41Cr4) were selected. The results obtained allow us to recommend combined processing for the parts operating under conditions of intense friction with lubrication.

Abstract: An elastic-plastic contact stress analysis is presented to study cyclic plastic deformation of surface hardened rolling elements under repeated contacts. The rolling contact is simulated by a Hertz contact loading moving across an elastic-plastic half-space. An exponential model with hardness varying with depth is employed for the surface hardened components, and the Chaboche nonlinear hardening rule is used to model cyclic plastic behavior of contact elements. Numerical results show that the hardened layer can effectively reduce the plastic deformation near contact surface. The contact elements with sufficient surface hardness may reach elastic shakedown state under repeatedly rolling contact. As the hardened layer reaches a certain depth, e.g. two times of half contact length, however, the effects of case depth on plastic strain and residual stress become negligible after hundred contact cycles.

Abstract: A combined processing method for improving the performance features of machine parts (durability), that works under intense wear and high lubricated or boundary friction has been developed; a working installation based on a CNC lathe has been developed. The research on resulting surface hardness material of steels: С45Е; 1.1191 (1 option); SA-240 TP 310S (2 option); 34CrNiMo6, 36CrNiMo4, 40NiCrMo4KD (3 option) and hardening depth variation under different combined processing conditions has been carried out. Surface roughness parameters have been calculated. The suggested method can increase the operational life of a machine part due to improving features, such as surface hardening, creating a favorable surface topography.

Abstract: The paper studies the surface structure and microhardness of the coating modified by the pulsed laser irradiation. The coating is obtained by plasma-jet hard-facing of the AISI (American Iron and Steel Institute) М2 high speed steel powder. The modes of the laser irradiation differ in peaking capacity, pulse duration and diameters of the focused laser beam. It is demonstrated that the weld penetration shape factor depends on the laser beam fluence and the pulse duration. In its turn, the weld penetration shape factor effects the quality of obtained irradiation zones.