Papers by Keyword: Steel

Abstract: To increase the safety of steels in high performance cases like crash energy absorption, even better properties of the materials are necessary. To advance this research, a TWIP and a TRIP steel were combined in a laminated composite via roll bonding at 450 °C with the goal of using accumulative roll bonding (ARB) in later research to further enhance the properties reaching an ultra-fine-grained material. Two different TWIP layer thicknesses (2 mm and 3 mm) were experimentally roll bonded with a 3 mm thick TRIP layer each using a 4-high rolling mill. A modular Python-based simulation incorporating coupled solving of ordinary differential equations of the temperatures and the horizontal stress changes of the layers were implemented to predict deformation and bonding behavior. Simulated results matched well with experimental data in terms of final geometry and temperature, while roll force deviations indicated the need for the refining of the used model. Furthermore, experimentally asymmetric layer relationships at the beginning and the addition of a thin (10 µm) Ni interlayer were found to enhance bond strength in high-strength steel laminates.

Abstract: In this study, the electromagnetic heating of a steel sample in dilatometer was modeled with finite element method. The model was developed to simulate electromagnetic heating process of Linseis DIL L78 DQT/RITA Quenching & Deformation dilatometer, using the dimensions, current and frequency measured from the dilatometer for model validation. Thermophysical and electromagnetic behaviour of a steel is highly temperature-dependent, necessitating the temperature dependent material properties of the test material. The goal of this study was to replicate the behaviour of the electromagnetic heating in the dilatometer as accurately as possible. In electromagnetic heating the material properties have a significant impact on the efficiency of the heating process. The material must be electrically conductive to allow generating the electric current caused of a changing magnetic field which forms the electric field on the surface of the heated material. Material properties, which vary with temperature, were defined in the model as a function of temperature to ensure realistic thermophysical behaviour of the simulated part. Two different analysis solvers were used for electromagnetic and heat transfer analysis. The model was validated using measured data from the dilatometer.

Abstract: In the production of layered steel-based composite materials by the liquid-phase method, an importance is attached to preserving the structural and physical-mechanical characteristics of the steel sheet serving as the middle layer. The temperature field in such a steel layer contacting with aluminum melt at a temperature of ~700°C in a roller-crystallizer is analyzed. A formula is obtained that can be used to determine the temperature distribution in the middle layer of steel at the initial stage of the technological process. A comparison of the theoretical results with experimental studies of the thermal modes of obtaining a layered steel–aluminum composite by the liquid-phase method is carried out.

Abstract: A computer program in Python was developed based on the mathematical model, which allows obtaining preliminary calculations of the diffusion coefficient and nitriding time of a punch part. As a result of a numerical experiment, the process of nitrogen diffusion into the depth of the part was studied. The redistribution of nitrogen occurs as a result of diffusion due to the nitrogen concentration gradient in the volume of the part and the high quenching temperature. The numerical experiment confirms the full-scale experiment. Nitrogen penetration into the depth of the metal occurs precisely at the quenching temperature. The nitrogen content in the internal nitriding zone due to the nitrogen released from the surface layer increases and decreases on the surface with the exposure time of the part. Computer modeling and research of the diffusion coefficient in the process of heat treatment after ion nitriding made it possible to establish that for tool steels, diffusion along grain boundaries occurs. Thus, the use of complex ion nitriding (CIN), i.e. ion nitriding and subsequent heat treatment of nitrided parts allows you to change the phase composition and increase the depth of the nitrided layer due to nitrogen doping, control the nitrogen concentration and hardness along the depth of the nitrided layer due to selected modes.

Abstract: Mechanical tests and electron microscopic structural studies of low-carbon copper-steels quenched after austenitization and tempered at different temperatures are carried out to clarify the decomposition mechanism of α-Fe based substitution solid solutions. With the onset of decomposition, limited nanosize (4–7 nm) precipitates of so-called ε-phase (solid solution of iron in copper with fcc structure) appear on dislocations. The substructure formed from the austenitic region during quenching determines the nature of such decomposition. In alloys with martensitic structure, the decomposition is heterogeneous. Both the formation of precipitates of the copper-rich ε-phase and their growth primarily occur on dislocations and grain boundaries. In supersaturated alloys with polyhedral ferrite structure, on the contrary, the decomposition is homogeneous, and the growth of the copper-rich phase occurs mainly in the defect-free part of the bcc matrix. Supersaturated iron begins to decompose, forming copper-rich zones isomorphic α-Fe. When a sufficiently high copper concentration is reached, these zones create mechanical stresses that cause local tetragonal distortions of the crystal lattice leading to its reconstruction. When a dislocation loop is formed around this zone, compensating for the elastic deformation, the coherence of the structure is destroyed and fcc precipitates are formed in the matrix. Satisfactory agreement between the theoretical estimate of 8 nm of the critical displacement required for the formation of a dislocation of inconsistency and the initial incoherent precipitates size determined experimentally – by electron microscopy, confirms the proposed mechanism based on the nucleation of nanoinclusions of the ε-phase copper in the bcc iron matrix.

Abstract: The efficiency, precision, and expected lifespan of mechanisms and machine components (such as ball bearings, couplings, and gauges) are significantly influenced by the quality of the materials used. Thus, it is essential to select materials that offer well-defined hardness and stability throughout the product's lifetime. This paper examines the heat treatment applied to 100Cr6 steel to achieve precise hardness in the range of 230–390 HV10, while also meeting requirements for stability and uniformity over the product's lifespan.

Abstract: Steel construction is one of the main constructions for building and bridge structures because it has great tensile strength. However the main drawback is its resistance to corrosive environments which makes steel very corrosion prone. So that the use of steel construction must pay attention to the corrosion rate in the environment of use. So we try to do research on the level of corrosion rates in the tropics. This study aims to determine the atmospheric corrosion rate on steel plates in the city of Palu which is in the tropical region and the effect of the angle of installation of the steel plates. In this study there were 27 specimens and each variation of specimens totaled 9 consisting of PL45, PL90 and PL180 plates with a size of 160x80x5 mm. The results showed that the highest corrosion rate occurred in the first month and at an angle of 180⁰ with a corrosion rate value of 2.03 mpy and the lowest corrosion rate occurred in the third month and at an angle of 90⁰ with a corrosion rate value of 1.01 mpy. From this study it can be concluded that the corrosion rate that occurs in Palu City in the tropics is still in the very slow category for all test specimens based on corrosion engineering books.

Abstract: This paper presents an experimental study on the influence of solidification cooling rate on the evolutions of microstructural morphologies of a high strength low alloy steel. To this end, solidification samples (cylindrical form with 10 mm diameter and 120 mm length) were prepared from 30 cm below the ingot/hot-top interface, at the center, of a 40 MT (Metric Ton) ingot. Solidification experiments were carried out by using Gleeble^® 3800 thermo-mechanical simulator. Two solidification cooling rates of 1 and 50°C/s were chosen. For microstructural characterization, samples were prepared by mounting, polishing and etching with 3% Nital solution. Also, an optical microscope was employed for microstructural observations. The obtained results showed that for 1°C/s, the microstructure is composed with dendrites and grains. Here, the grain morphology is the dominant one. In the case of 50°C/s, the dendrites were localized at the sample surface and the grains were present more into the depth of the sample. Moreover, the increase of solidification cooling rate results in finer dendrites. The results are discussed in the framework of solidification mechanisms.

Abstract: In this paper, the steels used in MN knife mills, which are used for plastic recycling, are investigated. 90MnCrV8 steel is commonly used in these mills, which will be replaced by X153CrMoV12 steel. The main goal of the presented contribution is to perform tribological tests and verify the wear rate of both steels experimentally with subsequent practical verification in the knife mill MN. Partial results relate to the analysis of hardness, roughness, and overall wear mechanism. A hardened steel ball of material G40 with a diameter of 4.76 mm was used as the contact material. The steel ball performed reciprocal linear motion on the surface of the experimental materials at room temperature and without the use of lubrication. The measurements were carried out in three-time intervals of 20, 30 and 40 min. The experimental material X153CrMoV12 can fully replace the material 90MnCrV8 in processes where its degradation occurs due to the friction mechanism. The material X153CrMoV12 showed significantly better results in all the values ​​we measured. It can be expected that the knife in the MN knife mill made of X153CrMoV12 steel will last several times longer in the working environment, which was also proven by practical verification in production.

Abstract: Improved understanding of friction during cold rolling is crucial to further optimize the rolling process, to accurate analyse cold rolling defects and to increase model accuracy enabling an improved mill setup during industrial operation. Classical slab rolling models make use of the Coulomb friction law, assuming a constant coefficient of friction in the roll bite. In the last decades, mixed-lubrication models have been developed that explicitly take the lubricant action into account. These models have greatly increased the understanding of factors that influence friction during cold rolling, but quantitatively the model results should still be further improved before such models can be used as an online tool for setting up the cold rolling mill. This article describes a mixed-lubrication model to simulate cold rolling of low-carbon steel. Especially the tribological core of the model is extended and improved compared to state-of-the-art models. Friction mechanisms now also include a viscous shear stress and ploughing friction. The quantification of viscous shear stress was reported in a previous work [1], this work focuses on the quantification of ploughing friction. Material Point Method (MPM) simulations were carried out to determine the work piece strain-hardening and strainrate-hardening under a ploughing indenter. These simulations result in an ‘Surface Ploughing Resistance’ and finally in a quantification of the contribution of ploughing friction to the overall friction in the roll bite. The description of the various friction mechanisms (ploughing, adhesive and viscous shear) is implemented in the mixed-lubrication model. This article concludes by presenting typical results of the developed model. One of the main conclusions is that the contribution of ploughing friction in a cold rolling process cannot a priori be neglected.