The application of artificial neural networks in optimization of heat treatment processes of steel

This article is dedicated to processes of vacuum carburization, which constitute an alternative method to industrial multi-segment carburization. Special attention has been paid to the possibility of using artificial neural networks to design processes of such type. The following subchapters deal with the essence and purposes of vacuum carburization, the course of research on processes and the possibility of using neural networks to design such processes, and the architecture of a sample neural network which achieves this goal

Influence of Flow and Pressure of Carburising Mixture on Low-Pressure Carburising Process Efficiency

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)

The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

The kinetics of the nitrided layer thickness growth and its structure depend on the nitrogen flux from the atmosphere to the nitrided surface. A nitrogen flux to the surface is more significant than a diffusion flux into the substrate, during forming surface iron nitrides and the internal nitriding zone. For pure iron, nitrided under low pressure, cutting off the nitriding atmosphere creates a flux from the subsurface layer of nitrides to the surface. The purpose of this paper is to determine the direction of the nitrogen flux in a similar situation for steels containing nitride-forming elements, thus answering the question of the stability of the layer nitrided under such conditions. The surface of X37CrMoV5-1 steel was nitrided under low pressure (of 24 hPa) and annealed in a vacuum or nitrogen. The microstructure, thickness of the nitride layers nitrided layers, the thickness of the internal nitriding zone, surface hardness and stresses were examined. The highest values of the nitrided layer properties were observed for the samples saturated only with nitrogen obtained from ammonia dissociation or additionally heated in nitrogen. It has been shown that using a pure vacuum during the annealing stage leads to unfavourable changes in the structure of the nitrided layer formed and, in particular, to the decomposition of the iron nitride layer formed at the saturation stage and occurrence of the tensile stresses—what excludes practical application of such layer. Ultimately, it has been shown that in the low-pressure nitriding process, the stability of the nitride layer of the nitrided surface strongly depends on the annealing atmosphere during the annealing stage, while the stability of the internal nitriding zone remains mainly at the same level

The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

The kinetics of the nitrided layer thickness growth and its structure depend on the nitrogen flux from the atmosphere to the nitrided surface. A nitrogen flux to the surface is more significant than a diffusion flux into the substrate, during forming surface iron nitrides and the internal nitriding zone. For pure iron, nitrided under low pressure, cutting off the nitriding atmosphere creates a flux from the subsurface layer of nitrides to the surface. The purpose of this paper is to determine the direction of the nitrogen flux in a similar situation for steels containing nitride-forming elements, thus answering the question of the stability of the layer nitrided under such conditions. The surface of X37CrMoV5-1 steel was nitrided under low pressure (of 24 hPa) and annealed in a vacuum or nitrogen. The microstructure, thickness of the nitride layers nitrided layers, the thickness of the internal nitriding zone, surface hardness and stresses were examined. The highest values of the nitrided layer properties were observed for the samples saturated only with nitrogen obtained from ammonia dissociation or additionally heated in nitrogen. It has been shown that using a pure vacuum during the annealing stage leads to unfavourable changes in the structure of the nitrided layer formed and, in particular, to the decomposition of the iron nitride layer formed at the saturation stage and occurrence of the tensile stresses—what excludes practical application of such layer. Ultimately, it has been shown that in the low-pressure nitriding process, the stability of the nitride layer of the nitrided surface strongly depends on the annealing atmosphere during the annealing stage, while the stability of the internal nitriding zone remains mainly at the same level

Effect of Ni-Cr Alloy Surface Abrasive Blasting on Its Wettability by Liquid Ceramics

An adequate surface is essential in ensuring a solid bond between the metal and dental ceramics for metal framework wettability. This work is aimed at investigating the effect of variable abrasive blasting parameters on Ni-Cr alloy surface’s ability to be wetted with liquid ceramics at elevated temperatures. One-hundred and sixty-eight samples were divided into 12 groups (n = 14), which were sandblasted using variable parameters: type of abrasive (Al2O3 and SiC), the grain size of the abrasive (50, 110, and 250 µm), and processing pressure (400 and 600 kPa). After treatment, the samples were cleaned in an ultrasonic cleaner and dried under compressed air. Dental ceramics were applied to the prepared surfaces via drops, and the wettability was tested in a vacuum oven at temperatures in the range of 850–1000 °C. The results were statistically analyzed using ANOVA (α = 0.05). For all surfaces, the contact angles were less than 90° at temperatures below 875 °C. For Al2O3, the best wettability was observed for the smallest particles and, for SiC, the largest particles. The ability to wet the surface of a Ni-Cr alloy is related to its sandblasting properties, such as roughness or the percentage of embedded abrasive particles. It should not be the only factor determining the selection of abrasive blasting parameters when creating a prosthetic restoration

Effect of SiC Abrasive Blasting Parameters on the Quality of the Ceramic and Ni-Cr Dental Alloy Joint

The SiC abrasive blasting parameters are vital in ensuring a suitable bond between dental ceramics and the Ni-Cr alloy. The purpose of this in vitro test was to examine the strength of the joint between the Ni-Cr alloy and fused dental ceramics for SiC abrasive blasting at a specific pressure (400, 600 kPa) and particle size (50, 110, 250 µm) in order to determine the optimal treatment parameters. The test also accounted for thermal loads (5000 cycles, 5–55 °C) to which the metal-ceramic joint is subjected during use. One hundred and forty-four Ni-Cr cylinders were divided into six groups (n = 12) and subjected to the airborne-particle abrasion with SiC with various pressure and grit size parameters. After treatment, the specimens were rinsed, dried, fused to dental ceramics, and examined for their shear strength using the Zwick/Roell Z020 machine. The results were statistically analysed using the ANOVA analysis of variance (α = 0.05). The highest metal-ceramic joint strength was obtained for abrasive blasting with 110 and 250 µm SiC grit at a pressure of 400 kPa. This relationship was also observed after the joint was subjected to thermal loads (5000 thermocycles). Additionally, thermal loads did not significantly reduce the joint’s strength compared with non-loaded joints. For small SiC abrasive grit sizes (50 µm) under pressure 400 kPa, the treatment pressure had a significant effect on the strength of the joint (p < 0.05). For larger particle sizes, the pressure had no effect. After abrasive blasting using SiC, the Ni-Cr metal-ceramic joint retained its properties, even under thermal load, ensuring the joint properties’ stability during use

Calculation of the Mixture Flow in a Low-Pressure Carburizing Process

The right selection of carburizing gas flow rates in the low-pressure carburization process is a key factor in terms of its efficiency. However, a correct calculation of the amount of carburizing gas required for uniform carburization of parts, taking into account the process temperature and batch size, is still problematic. For this reason, modern carburizing processes are carried out using an excessive belaying flow of carburizing gases. In this work steel parts (16MnCr5) were carburized in a variable-flow carburizing process (960 °C) individually matched to each segment of saturation. The effect of the variable-flow on the microstructure, surface hardness, and case hardness depth was evaluated and compared to that of a control group. It was proven that the amount of the mixture used in the variable-flow carburizing process can be significantly reduced to 54% of that consumed during the regular constant-flow carburizing without affecting the properties of the hardened layer of the steel parts

LOW PRESSURE CARBURIZING IN A LARGE-CHAMBER DEVICE FOR HIGH-PERFORMANCE AND PRECISION THERMAL TREATMENT OF PARTS OF MECHANICAL GEAR

This paper presents the findings of research of a short-pulse low pressure carburizing technology developed for a new large-chamber furnace for high-performance and precision thermal treatment of parts of mechanical gear. Sections of the article discuss the novel constructions of the device in which parts being carburized flow in a stream, as well as the low-pressure carburizing experiment. The method has been found to yield uniform, even and repeatable carburized layers on typical gear used in automotive industry

Cut-off Value for Thyroglobulin Washout Concentration in the Detection of Cervical Lymph Node Metastases in Patients after Thyroidectomy Due to Differentiated Thyroid Cancer

The aim of this study was to establish the cut-off value for the thyroglobulin (Tg) concentration in washout fluid from fine needle aspiration biopsy (FNA-Tg) in the detection of cervical lymph node metastases of differentiated thyroid cancer (DTC). We evaluated the validity and clinical utility of fine needle aspiration biopsy cytology (FNAB-C), FNA-Tg, and the combined method in detecting DTC recurrences. The study included 82 patients after the total thyroidectomy and elective and, in some cases, also selective cervical lymphadenectomy. The majority of patients also underwent subsequent 131I ablative therapy. The patients presented with 1–6 enlarged and/or ultrasonographically suspicious cervical lymph nodes. One to four aspirates of each lymph node were taken, with a total of 297 samples. An FNA-Tg of 4.34 ng/mL was established as the cut-off value for detecting cervical lymph node DTC metastases for the IRMA Brahms DYNO test, Tg-S. FNAB-C is highly specific (91–99%) but not sensitive enough (53–69%) to be used as a standalone method in the detection of cervical lymph node metastases. FNA-Tg is more sensitive (91%), but caution should be taken when selecting patients for surgery with an FNA-Tg higher than the established cut-off value but lower than the serum Tg concentration. To select patients for lymphadenectomy, we recommend using the combined method (FNAB-C and FNA-Tg) with a sensitivity of 96% and specificity of up to 97%. More than one sample should be taken with each fine needle aspiration biopsy (FNAB) to obtain a representative set of samples