The Experts below are selected from a list of 132 Experts worldwide ranked by ideXlab platform
John G Speer - One of the best experts on this subject based on the ideXlab platform.
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Effect of Mo in Combination with Nb on Austenite Grain Size Control in Vacuum Carburizing Steels
Journal of Materials Engineering and Performance, 2020Co-Authors: John G Speer, David K Matlock, Robert L. CrydermanAbstract:Vacuum Carburizing with high-pressure gas quenching is increasingly employed to reduce near-surface intergranular oxidation and reduce quenching distortion. Vacuum Carburizing can be conducted at higher operating temperatures, as high as 1100 °C, to reduce the processing times and increase furnace productivity. However, processing at elevated temperatures may result in excessive austenite grain coarsening, leading to the degradation of fatigue performance. Microalloying to form small carbo-nitride precipitates is one effective method to limit austenite grain growth during Carburizing. In this study, the effects of microalloying a Carburizing Steel with molybdenum (Mo) and niobium (Nb) on microstructural grain refinement in the core have been investigated. Additions of Nb alone are found to provide some control of abnormal austenite grain growth. Additions of Mo in combination with Nb provide enhanced resistance to austenite grain growth, especially at high Carburizing temperatures up to 1050 °C. The enhanced control is attributed to solute and precipitation effects.
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Austenite Grain Growth and Precipitate Evolution in a Carburizing Steel with Combined Niobium and Molybdenum Additions
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015Co-Authors: Charles M. Enloe, Kip O. Findley, John G SpeerAbstract:Austenite grain growth and microalloy precipitate size and composition evolution during thermal processing were investigated in a Carburizing Steel containing various additions of niobium and molybdenum. Molybdenum delayed the onset of abnormal austenite grain growth and reduced the coarsening of niobium-rich precipitates during isothermal soaking at 1323 K, 1373 K, and 1423 K (1050 °C, 1100 °C, and 1150 °C). Possible mechanisms for the retardation of niobium-rich precipitate coarsening in austenite due to molybdenum are considered. The amount of Nb in solution and in precipitates at 1373 K (1100 °C) did not vary over the holding times evaluated. In contrast, the amount of molybdenum in (Nb,Mo)C precipitates decreased with time, due to rejection of Mo into austenite and/or dissolution of fine Mo-rich precipitates. In hot-rolled alloys, soaking in the austenite regime resulted in coarsening of the niobium-rich precipitates at a rate that exceeded that predicted by the Lifshitz-Slyozov-Wagner relation for volume-diffusion-controlled coarsening. This behavior is attributed to an initial bimodal precipitate size distribution in hot-rolled alloys that results in accelerated coarsening rates during soaking. Modification of the initial precipitate size distribution by thermal processing significantly lowered precipitate coarsening rates during soaking and delayed the associated onset of abnormal austenite grain growth.
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Quantitative analysis of Nb in solution in a microalloyed Carburizing Steel by electrochemical etching
Materials Characterization, 2008Co-Authors: A.l. Rivas, David K Matlock, John G SpeerAbstract:The amount of Nb in solution in a microalloyed Carburizing Steel (Nb-modified SAE 8620) was evaluated in different heat treated conditions. The test procedure involved electrochemical extraction, filtration and Inductively Coupled Plasma Atomic Emission Spectroscopic (ICP-AES) analysis. Characterization by X-ray diffraction of the residues collected in the filters was also performed. Results showed that Nb in solution tends to hydrolyze during electrolysis in a 10 vol.% HCl electrolyte, giving misleading measurements of the amount of Nb that dissolved during high temperature heat treatment. Hydrolysis of Nb is prevented by the addition of tartaric acid to the electrolyte. In the full dissolution condition, coarse (Ti,Nb)CN was the only precipitate present. Finer (Nb,Ti)C precipitates were observed after heat treating at 1050 °C.
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The Influence of Niobium Microalloying on Austenite Grain Coarsening Behavior of Ti-modified SAE 8620 Steel
ISIJ International, 2007Co-Authors: Khaled A. Alogab, John G Speer, David K Matlock, Hans-joachim KleebeAbstract:The potential for suppressing unacceptable austenite grain growth during Carburizing by Nb microalloying additions in the range of 0.02 to 0.11 wt% to a Ti-modified SAE 8620 Carburizing Steel were evaluated. Alloys, were designed based on fundamental equilibrium thermodynamic analyses, as part of an extensive study on the effects of alloy composition, thermomechanical history, and pseudo-Carburizing conditions on austenite grain coarsening behavior. Laboratory samples were produced to simulate both conventional hot rolling and controlled rolling practices designed to produce different initial precipitate distributions. Pseudo-Carburizing heat treatments, i.e. without a Carburizing atmosphere, were performed in the temperature range of 950 to 1100°C for holding times of 30 to 360 min. Precipitate distributions, including size, number density, morphology, distribution, and chemical composition in selected samples from the as-rolled and pseudo-carburized conditions were evaluated with transmission electron microscopy on extraction replicas. Results showed that increasing Nb additions to the Ti-modified SAE 8620 Steel restrained austenite grain coarsening, and increased the grain coarsening time, especially at temperatures below 1050°C. The Nb-free (Ti-modified) Steel yielded either severely duplex grain structures or pseudo-normal grain growth (with very large mean grain diameter). However, holding a Ti–Nb-modified Steel (e.g. 0.06 Nb wt%) at 950°C for 6 h or at 1000°C for 4 h. produced fine and uniform austenite grain structures (with a mean grain diameter less than 20 μm). The finer grain sizes observed in the Ti–Nb-modified Steels were due to the presence of Nb-rich precipitates that hinder austenite grain coarsening, and precipitate distributions and grain growth behaviors are also influenced by the Steel rolling history. The results indicate that Nb can successfully be used to suppress grain growth in Carburizing Steels.
Bin Huang - One of the best experts on this subject based on the ideXlab platform.
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High toughness and multiphase microstructure transition product of Carburizing Steel by a novel heat treatment cooling process
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Bo Jiang, Leyu Zhou, Zhilin Wang, Bin HuangAbstract:Abstract A novel heat treatment cooling process was applied to a Fe-0.27C-1.50Mn-1.7Si-0.35Cr-0.64Mo-1.50Ni-0.10 V (wt%) Carburizing Steel. The cooling process was designed based on the continuous cooling transformation (CCT) and time-temperature-transformation (TTT) analyses of the Carburizing Steel. Mechanical property results of the heat treatment samples show that the Carburizing Steels exhibit excellent toughness (118 J) which is superior to that of the traditional quenching process. Microstructural characterization indicates that high toughness of the Carburizing Steel subjected to the cooling heat treatment process results from a proper multiphase microstructure transition from the surface to the matrix of the Steel. The key factors which greatly improve the toughness are the lower bainite consisting of fine ferrite laths and retained austenite films along the laths at the transition region and the carbide-free lower bainite at the matrix.
Robert L. Cryderman - One of the best experts on this subject based on the ideXlab platform.
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Effect of Mo in Combination with Nb on Austenite Grain Size Control in Vacuum Carburizing Steels
Journal of Materials Engineering and Performance, 2020Co-Authors: John G Speer, David K Matlock, Robert L. CrydermanAbstract:Vacuum Carburizing with high-pressure gas quenching is increasingly employed to reduce near-surface intergranular oxidation and reduce quenching distortion. Vacuum Carburizing can be conducted at higher operating temperatures, as high as 1100 °C, to reduce the processing times and increase furnace productivity. However, processing at elevated temperatures may result in excessive austenite grain coarsening, leading to the degradation of fatigue performance. Microalloying to form small carbo-nitride precipitates is one effective method to limit austenite grain growth during Carburizing. In this study, the effects of microalloying a Carburizing Steel with molybdenum (Mo) and niobium (Nb) on microstructural grain refinement in the core have been investigated. Additions of Nb alone are found to provide some control of abnormal austenite grain growth. Additions of Mo in combination with Nb provide enhanced resistance to austenite grain growth, especially at high Carburizing temperatures up to 1050 °C. The enhanced control is attributed to solute and precipitation effects.
David K Matlock - One of the best experts on this subject based on the ideXlab platform.
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Effect of Mo in Combination with Nb on Austenite Grain Size Control in Vacuum Carburizing Steels
Journal of Materials Engineering and Performance, 2020Co-Authors: John G Speer, David K Matlock, Robert L. CrydermanAbstract:Vacuum Carburizing with high-pressure gas quenching is increasingly employed to reduce near-surface intergranular oxidation and reduce quenching distortion. Vacuum Carburizing can be conducted at higher operating temperatures, as high as 1100 °C, to reduce the processing times and increase furnace productivity. However, processing at elevated temperatures may result in excessive austenite grain coarsening, leading to the degradation of fatigue performance. Microalloying to form small carbo-nitride precipitates is one effective method to limit austenite grain growth during Carburizing. In this study, the effects of microalloying a Carburizing Steel with molybdenum (Mo) and niobium (Nb) on microstructural grain refinement in the core have been investigated. Additions of Nb alone are found to provide some control of abnormal austenite grain growth. Additions of Mo in combination with Nb provide enhanced resistance to austenite grain growth, especially at high Carburizing temperatures up to 1050 °C. The enhanced control is attributed to solute and precipitation effects.
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Quantitative analysis of Nb in solution in a microalloyed Carburizing Steel by electrochemical etching
Materials Characterization, 2008Co-Authors: A.l. Rivas, David K Matlock, John G SpeerAbstract:The amount of Nb in solution in a microalloyed Carburizing Steel (Nb-modified SAE 8620) was evaluated in different heat treated conditions. The test procedure involved electrochemical extraction, filtration and Inductively Coupled Plasma Atomic Emission Spectroscopic (ICP-AES) analysis. Characterization by X-ray diffraction of the residues collected in the filters was also performed. Results showed that Nb in solution tends to hydrolyze during electrolysis in a 10 vol.% HCl electrolyte, giving misleading measurements of the amount of Nb that dissolved during high temperature heat treatment. Hydrolysis of Nb is prevented by the addition of tartaric acid to the electrolyte. In the full dissolution condition, coarse (Ti,Nb)CN was the only precipitate present. Finer (Nb,Ti)C precipitates were observed after heat treating at 1050 °C.
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The Influence of Niobium Microalloying on Austenite Grain Coarsening Behavior of Ti-modified SAE 8620 Steel
ISIJ International, 2007Co-Authors: Khaled A. Alogab, John G Speer, David K Matlock, Hans-joachim KleebeAbstract:The potential for suppressing unacceptable austenite grain growth during Carburizing by Nb microalloying additions in the range of 0.02 to 0.11 wt% to a Ti-modified SAE 8620 Carburizing Steel were evaluated. Alloys, were designed based on fundamental equilibrium thermodynamic analyses, as part of an extensive study on the effects of alloy composition, thermomechanical history, and pseudo-Carburizing conditions on austenite grain coarsening behavior. Laboratory samples were produced to simulate both conventional hot rolling and controlled rolling practices designed to produce different initial precipitate distributions. Pseudo-Carburizing heat treatments, i.e. without a Carburizing atmosphere, were performed in the temperature range of 950 to 1100°C for holding times of 30 to 360 min. Precipitate distributions, including size, number density, morphology, distribution, and chemical composition in selected samples from the as-rolled and pseudo-carburized conditions were evaluated with transmission electron microscopy on extraction replicas. Results showed that increasing Nb additions to the Ti-modified SAE 8620 Steel restrained austenite grain coarsening, and increased the grain coarsening time, especially at temperatures below 1050°C. The Nb-free (Ti-modified) Steel yielded either severely duplex grain structures or pseudo-normal grain growth (with very large mean grain diameter). However, holding a Ti–Nb-modified Steel (e.g. 0.06 Nb wt%) at 950°C for 6 h or at 1000°C for 4 h. produced fine and uniform austenite grain structures (with a mean grain diameter less than 20 μm). The finer grain sizes observed in the Ti–Nb-modified Steels were due to the presence of Nb-rich precipitates that hinder austenite grain coarsening, and precipitate distributions and grain growth behaviors are also influenced by the Steel rolling history. The results indicate that Nb can successfully be used to suppress grain growth in Carburizing Steels.
G. L. Garagnani - One of the best experts on this subject based on the ideXlab platform.
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Tribological Behavior of a Cr_2O_3 Ceramic Coating/Steel Couple Under Dry Sliding and Heavy Loading Conditions
Journal of Materials Engineering and Performance, 2018Co-Authors: C. Soffritti, M. Merlin, R. Vazquez, G. L. GaragnaniAbstract:This work evaluates the effects of heavy loadings on a Cr_2O_3 ceramic coating/Steel couple under dry sliding and in conditions similar to those occurring in heavy-duty diesel engines. Two types of wear tests were performed by a standard pin-on-disc tribometer under high constant and variable loads. Before wear tests, microstructure and mechanical properties of coating and Steel were determined by optical emission spectrometry, optical microscopy, roughness, microhardness and x-ray diffractometry (XRD). The friction coefficient was directly calculated by the tribometer. The wear rate of Cr_2O_3 ceramic coating was evaluated by the wear volume and that of pins by weighing them before and after tests. The wear tracks on pins and coating surfaces were analyzed by XRD and by scanning electron microscopy with energy-dispersive spectroscopy. For all loads except the lowest constant one, the results indicated high friction and wear involving material removal from the coating surface, through a severe-oxidational wear associated with extensive cracking of the surface of the coating, softening of the Carburizing Steel and removal of the carburized layer of pins. The wear mechanism was mild-oxidational under the lowest constant load, which was therefore suggested as the limit for acceptable performance of the sliding couple under study.