Mechanism and Kinetics of Thermal Embrittlement of Austenitic Chromium-Nickel Steel during Long-Term High-Temperature Holding

This article describes a model of structural changes in austenitic chromium-nickel steel during long-term thermal soakings. The time for reaching equilibrium content of Cr23C6 carbide at a temperature of 600 °C is calculated. The calculation results are compared with experimental data on the kinetics of thermal embrittlement of steel at a temperature of 600 °C after thermal holding for up to 15000 hours.

Effect of different core materials in very low voltage induction motors for electric vehicle

The use of squirrel cage induction motor for electric vehicle (EV) has been increasingly popular than permanent magnet and brushless motors due to their independence on rare materials. However, its performance is significantly affected by the core materials. In this research, induction motors performance with various core materials (M19_24G, Arnon7, and nickel steel carpenter) are studied in very low voltage. Three phases, 50 Hz, 5 HP, 48 V induction motor were used as the propulsion force testbed applied for a golf cart EV. The aims are to identify loss distribution according to core materials and compare power density and cost. The design process firstly determines the motor specifications, then calculates the dimensions, windings, stator, and rotor slots using MATLAB. The parameters obtained are used as inputs to ANSYS Maxwell to calculate induction motor performance. Finally, the design simulations are carried out on RMxprt and 2D transient software to determine the loss characteristics of core materials. It is found that the stator winding dominates the loss distribution. Winding losses have accounted for 52-55 % of the total loss, followed by rotor winding losses around 25-27 % and losses in the core around 1-7 %. Based on the three materials tested, nickel steel carpenter and M19_24G attain the highest efficiency with 83.27 % and 83.10 %, respectively, while M19_24G and Arnon7 possess the highest power density with 0.37 kW/kg and 0.38 kW/kg whereas, in term of production cost, the Arnon7 is the lowest.

Experimental Study on Bead on Plate (BOP) Welding of 6 mm Thick 9% Nickel Steel by Fiber Laser Welding

Nine percent nickel steel has excellent properties in a cryogenic environment, so it has recently been used as a tank material for most LNG fuel-powered ships. However, 9% nickel steel causes arc deflection due to its tendency of magnetization during manual FCAW welding and the currently used filler metal is 10–25 times more expensive as a base metal compared to other materials, depending on manufacturers. Furthermore, the properties of its filler metal cause limitation in the welding position. To overcome these disadvantages, in this study, the tendency of penetration shape was analyzed through a fiber laser Bead on Plate (BOP) welding for 9% nickel steel with a thickness of 6 mm and a range of welding conditions for 1-pass laser butt welding of 6 mm thick 9% nickel steel with I-Groove were derived. Through this study, basic data capable of deriving optimal conditions for laser butt welding of 9% nickel steel with a thickness of 6 mm were obtained.

A Study on Welding Deformation in Fiber Laser Welding of 9% Nickel Steel through Finite Element Analysis Part I: Implementation of Welding Heat Source Model

Due to various environmental regulations, the demand for natural gas, i.e., a clean energy, is expected to increase continuously. In terms of efficient storage and transportation of natural gas, liquefied natural gas has an advantageous volume of 1/600 compared to natural gas, but the materials that can be used at a cryogenic temperature of −163 °C are limited. A 9% nickel steel is a material recommended by IMO through IGC. It has excellent mechanical properties compared to other cryogenic materials, but its use has been limited due to its disadvantages in arc welding. Therefore, the main topic of this study is the automatic welding of 9% nickel steel using fiber laser and its purpose is to predict the welding deformation during fiber laser welding. First, an investigation was conducted to find the fiber laser welding heat source. A model that can cover all the models in prior studies such as curve, exponential, conical, conical-conical combination, and conical-cylinder combination models was proposed and the heat source model was constructed in a multi-layer format. Heat transfer analysis was performed using the ratio of a heat source radius and heat energy of each layer as a variable and the pass or failure of a heat source was determined by comparing the analysis results to the experimental results. By changing the variables in conjunction with the optimization algorithm, the main parameters of a passed heat source model were verified in a short period of time. In addition, the tendency of parameters according to the welding speed was checked.

Wear Analysis of Forging Tools Used in an Industrial Production Process—Hot Forging in Closed Dies of the “Head-Disk” of an Engine Valve Forging

The article performs an analysis of the durability of punches applied in the process of producing a valve forging from chromium-nickel steel. A forging of this type is made in two operations: coextrusion of a long shank, followed by finishing forging in closed dies of the valve head. The product obtained in this way (after other additional finishing procedures) constitutes the key element of the combustion engine (resistant to high pressures and temperatures) in motor trucks. Unfortunately, a significant problem in this production process is a relatively low durability of the forging tools, especially the punch used in the second forging operation. The key element at this stage, deciding about the punch’s further operation, is the area of the so-called “calotte”. The short-term life of the tools results from very hard performance conditions present during the forging process (periodical high mechanical and thermal loads, long path of friction). The latter cause intensive abrasive wear as well as high adhesion of the forging material to the tool surface. Based on the performed studies, including the following: technology analysis, numerical modelling, macro analyses combined with 3D scanning of tool sections as well as microstructural tests and hardness measurements, it was established that it is crucial to properly select the process parameters (charge and tool temperature, tribological conditions), as even slight changes introduced into them significantly affect the operation time of the forging tools. Mastering and proper implementation of the analyzed forging technology requires numerous further studies and tests, which will enable its perfection and thus increase the durability of the tools as well as the quality of the produced items.

Investigation of the Structural, Mechanical and Tribological Properties of Plasma Electrolytic Hardened Chromium-Nickel Steel

This paper investigates how electrolytic plasma hardening (PEH) bears upon the changes in the phase structural and tribological properties of steel 0.34C-1Cr-1Ni-1Mo-Fe, which is widely used in manufacturing highly stressed gears. The samples of steel 0.34C-1Cr-1Ni-1Mo-Fe went through the PEH in an electrolyte containing an aqua solution of 20% calcined soda (Na2CO3) and 10% carbamide ((NH2)2CO). The initial steel 0.34C-1Cr-1Ni-1Mo-Fe is stated to have the following structural components: a lamellar pearlite with volume share of 35%, a ferrite-carbide mixture of ~45% and a fragmented ferrite of ~20%; after the PEH it contains lath-lamellar martensite, fine particles of cementite and M23C6 carbide. The durability of steel 0.34C-1Cr-1Ni-1Mo-Fe was found to rise by 3.4 times after the PEH and its microhardness increased in 2.6 times. The curve-tension of the crystal lattice was established to be like plastic (χ = χpl) and does not cause the formation of microcracks in the material.

Using of the Tape Extensometer for Possibilities of Landslide Monitoring or another purposes

The main goal of this article is to analyze the possibility of using tape extensometry. It is one of the methods of evaluating the development of slope deformation. Tape extensometry is used to monitor the movement of the slope on the surface. Tape extensometry is used for fast and accurate measurement of relative distances between pairs of reference points on the surface of structures, including radial movements and convergence of tunnels, linings, shafts and caves. Then deformations of excavations in underground caves and displacements of retaining walls, bridge piers and arches. The digital tape extensometer is a portable device used to measure the displacement between pairs of eye bolts. The principle of measuring on a slope consists in directly measuring the distance between the stabilized measuring points. The measuring points are located in both stable and unstable parts. The measuring points are concreted into boreholes drilled to a non-freezing depth, which in the Czech Republic is about 0.8 m below the ground. The direction of movement can be determined by measuring the change in distance between several points located in the stable part and points in the unstable part. If we also measure in time intervals, we can also find out the approximate speed of movement. The tape extensometry method is performed using a tape extensometer. It is a specially adapted zone in which emphasis is placed on the material from which the meter is made, because it is important that the material has a low thermal expansion, for example nickel steel is suitable.

Influence of titanium and zirconium on structure and heat-resistance of low-carbon iron-aluminium alloys

The paper considers the effect of introducing ferroalloys containing titanium and zirconium on the structure and heat-resistance of low-carbon ferroalloys. Theoretically and experimentally, it has been proven that addition of 1.0 mass. % of titanium and 0.1 mass. % of zirconium to a low-carbon iron-aluminum melt containing 12 – 14 mass. % of aluminum, grinds its structure increasing temporary resistance and heat-melting. Titanium and zirconium are strong carbide-forming elements. When introduced into a low-carbon iron-aluminium alloy, they form a large number of crystallization centers, thus affecting its microstructure, allowing to get shredded and more equal grain compared to an alloy without additive. This in turn increases the strength limit of processed alloy. In addition, the use of titanium as a modifying additive in a low-carbon ferroalloy allows increasing its heatresistance, which exceeds several times the heat-resistance of famous chrome-nickel steel of 20Kh23N18 grade. As a result, a new technology for obtaining titanium and zirconium was developed based on research of the effect of their modifying additives on the structure and heat-resistance of low-carbon iron-aluminum alloys.