Papers by Keyword: Quench

Abstract: In-situ high-energy synchrotron X-ray diffraction was employed to track phase evolution in a medium-carbon (0.4 wt.% C) advanced high-strength steel processed via quench-and-partitioning (Q&P). Real-time diffraction data, captured during quench stop temperatures of 200 °C (QT200) and 240 °C (QT240), followed by a 1000 s holding time at the partitioning temperature of 300 °C, revealed precise phase fractions during the Q&P. However, the retained austenite in both process routes produced comparable retained-austenite fractions at room temperature —23% for QT200 and 21% for QT240—the higher quench-stop temperature generated three times more fresh martensite (15% vs. 5%). The mechanical properties were examined by tensile tests, showing that the lower fresh-martensite content in QT200 promotes progressive, strain-induced austenite transformation, delays necking, and yields a uniform elongation of 6.9%. By contrast, QT240 reaches a higher ultimate tensile strength (around 2023 MPa vs. 1984 MPa) and yield strength (about 983 MPa vs. 938 MPa) at the expense of ductility (around 4.7% uniform elongation). In both conditions, the TRIP effect is active, but its contribution is curtailed by the presence of fresh martensite. The present study thus establishes a quantitative link between in-situ phase evolution pathways and the resulting strength–ductility balance, providing guidance for tailoring Q&P processing route in medium-carbon advanced high-strength steel for crash-critical automotive applications.

Abstract: The temperature of polymorphic transformation (Tpt) has been determined for accurate composition of two-phase titanium alloy which has been marked like VT8 through different ways: the method of trial quench and with the help of dilatometric and differential thermal analyzes. The close values of Tpt have been received. Herewith the phase composition has been estimated qualitatively and quantitatively for the hardened samples of alloy VT8 using optical and scanning electron microscopes and the chemical composition with the help of the micro X-ray spectral analysis. The influence of the quenching temperature on the hardness has been investigated. Also, the hardness of the individual structural components and alloy VT8 as a whole unit has been measured. Hardness curves are based depending of the quenching temperature; the results are displayed in tabular and graphical form. The coefficient k has been found for the calculation of allotropic transformation temperature for this alloy using the known temperature of hardening and quantity of preserved α-phase of hardened structure. The album of the microstructures after quench with different temperatures has been created, this album will allow to reduce the duration of preliminary works for finding specific temperature of polymorphic transformation in production conditions for each new batch of alloy VT8 with another chemical composition (but within the vintage), knowledge of which is necessary for setting the temperature regime of treatment.

Abstract: Third-Generation advanced high strength steels are being developed with the goal of reducing the body-in-white weight while simultaneously increasing passenger safety. This requires not only the expected increase in strength and elongation, but also improved local formability. Optimizing elongation and formability were often contradictory goals in dual-phase steel developments. Recent results have shown that so-called "quench and partitioning" (Q&P) concepts can satisfy both requirements [1]. Many Q&P-concepts have been studied at thyssenkrupp Steel Europe. Thorough investigation of the microstructure has revealed relationships between features such as the amount, morphology and chemical stability of the retained austenite and the obtained mechanical properties. An evaluation of the lattice strain by means of electron-back-scattering-diffraction has also yielded a correlation to the obtained formability. The aim of this work is to present the interconnection between these microstructural features and propose hypotheses for the explanation of how these features influence the macroscopically observed properties.

Abstract: Extensive efforts are underway worldwide to develop new steels with substantial fractions of retained austenite, for lightweight automobile manufacturing and other applications requiring improved combinations of strength and formability. It is likely that microalloying can provide product enhancements in these emerging products, such as Q&P, TBF, medium-Mn TRIP, etc. and this paper examines the expected behavior of niobium using inferences based on published AHSS literature and principles of Nb microalloying. Some benefits of Nb in terms of microstructure refinement and precipitation strengthening have been reported. The potential influences of Nb are complex due to the sensitivity of Nb dissolution and precipitation to chemical composition and processing; differences in the expected role of Nb are pointed out with respect to different product forms produced via hot-rolling or annealing after cold-rolling, and microstructures with or without substantial quantities of primary ferrite. Some issues that warrant further examination are identified, as a deep understanding of Nb microalloying and other fundamental behaviors will be needed to optimize the performance of these next-generation steels.

Abstract: Two important objectives of the automotive industry are the decrease of the body-in-white weight and the improvement of the passenger safety. High strength steels (HSS) are widely used to achieve these objectives. Quenching and partitioning (Q&P) has recently been proposed to achieve high strength steel grades for the third generation of advanced high strength steels (AHSS), which contain a considerable amount of retained austenite. Due to their microstructure these new steel grades combine a high tensile strength with good elongation values, as long as cementite precipitation is avoided. A model describing the involved phase transformations is presented. Special focus is put on the cementite precipitation and how it is influenced by silicon and aluminum additions.

Abstract: The quenching process of 20 steel and 45steel is investigated in the paper and the changing law of martensite in carbon steel is discussed. The carbon content in 20steel and 45steel is both less than 0.77%,which means they are hypoeutectoid steel. The microstructure of 20 steel after quench shows lath shape while martensite in that of 45steel exhibits both lath shape and flake which occupies approximately 80%. The plasticity and toughness of martensite depend on the substructure, that is, the toughness of dislocation martensite is better than that of twin martensite under the same condition.

Abstract: We conduct the process experiment on the shaft of the 40MnB steel after forging, and propose the scheme of heat treatment by using residual heat after forging process. According to the experiment results, the internal structure of 40MnB was improved, the metal grain was refined, the mechanical properties was better and the quality was guaranteed. At the same time, it improved production efficiency, shortened the production cycle and reduced the cost.

Abstract: A Standing Contact Fatigue (SCF) test set up has been developed in order to facilitate quick testing of contact fatigue resistance of material surfaces. In this method the sample is pressed against a hard ball rapidly and the resulting crack formation is studied in order to evaluate the SCF resistance. Induction hardened surfaces of cam-ring steel and steels with pearlitic, martensitic, bainitic, ausferritic and quench and tempered microstructures have been studied. Characterization was performed by optical microscopy, scanning electron microscopy and hardness measurements. Ring-cone cracks were found at the edge of the indentations but inside the indent in the surface hardened cam-ring steel samples. Sectional views revealed that these cracks also grow underneath the indentation. Radial cracks were found in non-surface hardened samples. The test of the SCF resistance of steels with different microstructures showed that the ausferritic microstructures tested shoved better SCF resistance than the quench and tempered samples with similar hardness. A comparison between different tempering temperatures of surface hardened steels showed that samples tempered at the higher temperature 240 °C resulted in better SCF resistance.

Abstract: In order to limit the short-circuit current, and to prevent the power grid and its equipment from the shock of the short circuit, the fault current limiter with detection, trigger and limiting was introduced. A small resistive type superconducting fault current limiter prototype based on MgB2, cooled by liquid helium and heliumgas, was developed and tested by a test system. The test result showed that the prototype based on MgB2 produced superior limiting performance, the short-circuit current suppressing ratio was up to more than 45%, and with the rise of the voltage level, the current limiting capability was also gradually increased, up to 56%.

Abstract: The heat transfer coefficient during the aluminum thin plate quenching is difficult to measure experimentally. In this paper, according to the warping deformation characteristics of the 2024 honeycombed aluminum thin plate quenching, the heat transfer coefficient is obtained using finite element software ABAQUS. During the calculation process of the heat transfer coefficient, the sheet practical quenching process of immersion and the air-cooling has been considered. Using the heat transfer coefficient above, the quenching temperature field is solved through the simulation. Based on the temperature field, the residual stress field is simulated. Depending on the simulation results, the magnitude and the distribution of the residual stress is obtained. By X - ray diffraction method, the simulation results have been compared to the experiment results and they are in better agreement. It proves that the simulation method is available and effectively.