Search Results (13)

To manufacture metallic components with high wear resistance, treatments such as nitriding and carburising followed by quenching and tempering (NQT and CQT, respectively) are applied to various types of steel to increase the hardness (H) of the friction surface. However, the wear mechanism of the resulting functionally graded materials has not been fully understood. In this study, specimens of industrial 99.82% pure iron treated with NQT at 913 and 1033 K, and CQT at 1203 K, as well as hot-rolled sheets without heat treatment were examined by performing nanoindentation tests to measure changes in their H, reduced Young’s moduli (E_r), elastic deformation energies (W_e), and plastic deformation energies (W_p) along the depth direction. The relationship between W_p/W_e and the elastic strain resistance (H/E_r) can be expressed for all specimens via the equation W_p/W_e = −1.0 + 0.16 (H/E_r)⁻¹. Furthermore, the obtained H/E_r av measured at 5 µm intervals based on the specimen profile and wear volume has a good correlation depending to the sliding distance, as confirmed by the results of the ring-on-plate sliding tests conducted for the carbon-treated, nitrogen-treated, and hot-rolled specimens. This study provides a new approach, using H/E_r parameters to identify the dominant factors affecting wear resistance at the initial stage of wear that may contribute to the development of wear-resistant materials. Full article

Conventional heat treatment is not capable of converting a sufficient amount of retained austenite into martensite in high-carbon or high-carbon and high-alloyed iron alloys. Cryogenic treatment induces the following alterations in the microstructures: (i) a considerable reduction in the retained austenite amount, (ii) formation of refined martensite coupled with an increased number of lattice defects, such as dislocations and twins, (iii) changes in the precipitation kinetics of nano-sized transient carbides during tempering, and (iv) an increase in the number of small globular carbides. These microstructural alterations are reflected in mechanical property improvements and better dimensional stability. A common consequence of cryogenic treatment is a significant increase in the wear resistance of steels. The current review deals with all of the mentioned microstructural changes as well as the variations in strength, toughness, wear performance, and corrosion resistance for a variety of iron alloys, such as carburising steels, hot work tool steels, bearing and eutectoid steels, and high-carbon and high-alloyed ledeburitic cold work tool steels. Full article

Titanium carbide has attracted widespread attention due to its excellent properties. This study investigates the process of carbon thermally reducing TiO₂ to prepare TiC through a combination of thermodynamic analysis and experiments. The effects of temperature, TiO₂/C molar ratio, and time on the phase transformation and morphology evolution of the products are investigated. The synthesis of titanium carbide involves the main reduction path of TiO₂–Magnéli–Ti₃O₅–Ti₂O₃–TiC_xO_1−x. With the increase in reaction temperature and TiC content, the microstructure transitions from a smooth disc-like structure to a loose and porous layered structure, while the particle size decreases significantly. The carburisation rate of the reduced product is more affected by temperature, according to chemical analysis. The carburisation rate increased from 18.37% to 36.09% for 2 h–10 h of holding time at 1400 °C, and from 51.43% to 77.57% for 2 h–10 h of holding time at 1500 °C. The quantification of the carburisation rate provides a valuable reference for the preparation of titanium carbide by TiO₂. Full article

Seventeen new experimental filler metals from eight different alloy systems based on Fe–P–X and Mn–Fe–P–X (X = B, C, Si in various combinations) were created and experimented with. DSC analyses were performed to determine the solidus and liquidus temperatures and the melting ranges. Hardness measurements of the alloys were performed in the as-cast state. The alloys contain primary and eutectic intermetallic compounds that make them very hard with average hardness values ranging from 590 HV10 to 876 HV10. The wettability was determined at 1000 °C, 1040 °C and 1080 °C on C22 non-alloy steel and 15CrNiS6 low-alloy steel in Ar 4.6 and 78 vol% H₂-22 vol% N₂ atmospheres. The results show good wettability at T = 1080 °C in both atmospheres, as the contact angles were mostly ≤30°. Thirteen alloys exhibit very good wettability with average contact angles of ≤15.5°. Nine alloys exhibit excellent wettability with their average contact angles being ≤10°. Wettability improves at higher temperatures. The liquid alloys are reactive to solid steels and form a diffusion joint. Diffusion of P, B, C, and Si from the filler metal into the base material dealloys the composition of the melt near the joint interface. For the same reason, a continuous layer of solid solution forms on the joint interface. When brazing with filler metals rich in carbon, strong carburisation of steels can be observed near the joint. Full article

Low-pressure carburising (LPC) of steel is an industrially accepted method for improving the properties of a steel surface. LPC is environmentally friendly, does not cause intergranular oxidation and consumes less energy. Its effectiveness depends on the correct choice of process inputs. This paper aims to determine the effect of this type of carboniferous gas, pressure and flow rate on the efficiency of carbon transfer to the surface layer under low-pressure carburisation. A total of 40 disks of 16MnCr5 steel were carburised using pure acetylene or a mixture of acetylene, ethylene and hydrogen as a carboniferous gas, pressures of 2 or 6 hPa and two gas flow rates. The specimens were gravimetrically tested for the increase in the mass of carbon in the carburised layer. The results were analysed with U Mann–Whitney analysis and t-Student test. It was evidenced that carburising with pure acetylene resulted in a higher increase in carbon mass than carburising with the mixture (p < 0.05). Pressure and gas flow rates are important for carburising efficiency (p < 0.05). Full article

Cryogenic treatment as a process that can effectively improve the performance of steel materials is widely used because of its simplicity and speed. This paper investigates the effects of different low temperature treatments on the microstructure and properties of 17Cr2Ni2MoVNb steel. The low temperature treatment range is divided into cryogenic treatment (CT-80), shallow cryogenic treatment (SCT-150) and deep cryogenic treatment (DCT-196), all with a duration of 1 h. The retained austenite content and the change in carbide volume fraction at 0.2 mm in the carburised layer are studied. The microhardness gradient of the carburised layer, as well as the friction coefficient and wear scar morphology at 0.2 mm, was investigated. The results show that the low temperature treatment is effective in reducing the retained austenite content and increasing the volume fraction of carbide. The lowest retained austenite content and highest carbide volume fraction were obtained for DCT-196 specimens at the same holding time. Due to the further transformation of martensite and the diffuse distribution of carbides, the microhardness and frictional wear properties of DCT-196 are optimal. Therefore, low temperature treatment can change the microstructure of the case layer of 17Cr2Ni2MoVNb steel and effectively improve the mechanical properties of materials. Full article

Damages to case-hardened components are often associated with the phenomenon of hydrogen embrittlement due to their specific fracture pattern. In the present work, the effects of the case hardening process on the hydrogen content in the material were investigated and the effects of hydrogen on the mechanical properties were examined. In order to determine not only the influence of the heat treatment process but also the influence of the material, the case-hardening steels EN20MnCr5 (SAE5120) and EN18CrNiMo7-6 (SAE4820) with different degrees of purity were investigated. From the results it can be deduced that the sulphidic and oxidic inclusions have no significant influence on the hydrogen content. When checking the mechanical properties, it was shown in the incremental step loading technique according to ASTM F1624 that a purely case-hardened condition only has a slight tendency to hydrogen embrittlement. However, if the material is additionally loaded with hydrogen, the material fails significantly below the maximum expected load in the incremental step loading test, which is to be interpreted as a clear indication of failure due to hydrogen embrittlement. However, the fracture patterns of these two states do not show any significant differences. Therefore, it does not seem possible to attribute damage to a case-hardened component to hydrogen embrittlement on the basis of the fracture pattern alone. Full article

This article presents a procedure for designing footwear production plants with a Decision Support System combined with an expert system and a simulation approach. The footwear industry has many operations and is labour intensive. Optimisation of plant layout, machinery, and human resources is very important to design the footwear manufacturing system, making adequate investment in space and equipment. In the industry it is essential to reduce the process time, so the research is based on a Decision Support System combined with an expert system and simulation to improve the design of the manufacturing plan. This work contains two case studies, direct injection manufacturing and assembly and carburising methods, which are compared to analyse all the necessary resources to have the best cost–benefit ratio. In each case, a precise knowledge of the type and quantity of machinery and human resources is needed to estimate the production. This comparison has been done through simulations and using a knowledge base of an expert system. The conclusions are presented in which an improvement in production time is obtained by applying the methodology developed in the study. Full article

Consideration of heat treatment in simulations of structural components and its impact on predictions of behaviour during operation is analysed here. An automotive machine element with a complex geometry and dynamic load is analysed rather than a standard laboratory specimen under controlled conditions. The heat treatment analysis of a starter clutch barrel has been performed in DANTE followed by a structural analysis in ANSYS 2019 R3 during operation simulating a load cycle due to the start of an internal combustion engine. The heat treatment simulation consisted of carburisation, quenching and tempering. First, the carbon content and its distribution have been simulated. Next, the hardness of the starter clutch barrel and its distribution have been analysed with respect to the carbon distribution and hardness-dependent material properties of the AISI/SAE 4142 steel. Finally, the stress field after the heat treatment and during the operation of the starter clutch barrel has been thoroughly evaluated and compared to the simulation without the consideration of the heat treatment. Results of the simulation show that the heat treatment introduces favourable compressive stresses at the critical location of the starter clutch barrel and reduces the effective amplitude of the equivalent stress during the operation. Furthermore, the results of the simulation prove that heat treatment should be considered already during the early stages of the R & D process as it can have a decisive effect on the operational behaviour of the structural component. Moreover, a non-consideration of the heat treatment can lead into erroneous conclusions regarding the suitability of machine elements. Full article

The monitoring of the performance of heat treatment equipment has been the subject of a number of studies. This paper proposes and explores a new study on the models—and the monitoring thereof—for predicting the energy intensity of low-pressure carburisation processes using the DeepCaseMaster Evolution soaking furnace. For research purposes, 18 carburising experiments were performed with different carbon layers, at different input parameters, such as the number of cycles, time, temperature and average carburising pressure. Based on the research experiments conducted and statistical analysis, the influence of individual parameters on the energy consumption of the pump and heating systems was determined. Moreover, the models were verified on real data of low-pressure carburising processes. The innovativeness of the proposed solution is a combination of two areas: (1) defining and measurement of the parameters of the low-pressure carburising process; and (2) predicting the energy consumption of low-pressure carburising processes using correlation and regression analyses. The possibilities of using the results of this research in practice are demonstrated convincingly. Full article

In this study, the phase transformation behaviour of the carburised layer and the matrix of 23CrNi3Mo steel was comparatively investigated by constructing continuous cooling transformation (CCT) diagram, determining the volume fraction of retained austenite (RA) and plotting dilatometric curves. The results indicated that Austenite formation start temperature (Ac1) and Austenite formation finish temperature (Ac3) of the carburised layer decreased compared to the matrix, and the critical cooling rate (0.05 °C/s) of martensite transformation is significantly lower than that (0.8 °C/s) of the matrix. The main products of phase transformation in both the carburised layer and the matrix were martensite and bainite microstructures. Moreover, an increase in carbon content resulted in the formation of lamellar martensite in the carburised layer, whereas the martensite in the matrix was still lath. Furthermore, the volume fraction of RA in the carburised layer was higher than that in the matrix. Moreover, the bainite transformation kinetics of the 23CrNi3Mo steel matrix during the continuous cooling process indicated that the mian mechanism of bainite transformation of the 23CrNi3Mo steel matrix is two-dimensional growth and one-dimensional growth. Full article

Titanium use is limited due to its poor tribological properties, and thermal oxidation (TO) and pack carburisation with limited oxygen diffusion (PCOD) are just two of the surface treatments that can be used to enhance the surface properties of Ti. In this study, commercially pure titanium was surface modified using thermal oxidation (TO) and pack carburisation with limited oxygen diffusion (PCOD). Samples were tribological tested in a 0.9% NaCl solution under a contact load of 20 N to investigate the mechanical and electrochemical response of the surface treatments. The tests conducted show that a clear benefit can be obtained in terms of the overall material loss rate using both TO and PCOD. The TO and PCOD treatments generate very different surface structures: TO produces a rutile TiO₂ surface film and the PCOD treatment produces a TiC network structure. Both treatments improve the load bearing capacity with the assistance of an oxygen diffusion zone (ODZ). When subjected to sliding contact in a 0.9% NaCl solution, the results show the PCOD-Ti produced the best overall results, with a material loss rate 7.5 times lower than untreated Ti and 2.4 times lower than TO-Ti. The improved wear rate of the PCOD-Ti is attributed to the TiC network structure. The TO-Ti suffers from rapid film failure and high friction. The reduced material loss rate (MLR) of the TO-Ti is attributed to the hard wearing ODZ. Full article

Tribocorrosion damage is a cause for the premature failure of hip implants made of cobalt-based alloys. Low-temperature carburising can be a plausible solution towards mitigating the tribocorrosion damage of articulating components. This diffusion treatment introduces a supersaturated carbon solid solution, termed S-phase, which hardens the CoCrMo alloy without detriment to the corrosion resistance. This work investigates and compares the tribocorrosion behaviour of untreated and carburised ASTM F1537 CoCrMo alloys tested in Ringer’s solution using a reciprocating sliding configuration against a polycrystalline alumina counterface under different electrochemical conditions. The research shows that whereas the carburised alloy suffered a slightly higher wear loss under a cathodic potential, it was able to reduce the material losses considerably when tested under both open circuit and anodic potential conditions. Under anodic conditions material losses by corrosion due to wear dominated. The better tribocorrosion resistance of the carburised layer was attributed to the better qualities of the passive film for the carburised sample coupled with an increased load support. Full article