Pinning effect of strain induced Nb(C,N) on case hardening steel under warm forging conditions

Springer, Phillip; Prahl, Ulrich

doi:10.1016/j.jmatprotec.2017.11.008

Cited by 8 publications

(4 citation statements)

References 27 publications

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“…21 also shows that increasing the volume fraction of precipitates and reducing the precipitates' radius would both increase the Zener pinning force and, therefore, increase the grain boundary pinning process. The above analyses are in agreement with those reported by Singh et al and Springer et al, who found that Z p increased with deformation and related it to a more homogeneously distributed precipitation under deformation (Springer and Prahl, 2018;Singh et al, 2019).…”

Section: Interaction Between Dynamic Recrystallization and Precipitatessupporting

confidence: 93%

Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

et al. 2021

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Open-die forging is a critical step in the manufacture of large numbers of components used in the transportation and energy industries. Dynamic recrystallization, dynamic transformation, and dynamic precipitation take place during the hot deformation process and significantly affect microstructure conditioning, which ultimately influences the service properties of the component. In the present work, using a Gleeble 3800 thermomechanical simulator, the open-die forging of a large-size ingot made of a modified AISI 6140 medium carbon high-strength steel is investigated. Deformation temperatures ranging from 950°C to 1,250°C and strain rates ranging from 0.01 to 1 s−1, representative of the actual process, are considered in the analysis. The generated true stress–true strain curves are used as a basis for the development of a constitutive model predicting the occurrence of softening and strengthening phenomena as a function of thermomechanical conditions. The corresponding activation energy is determined to be about 374 kJ mol−1 and is compared against the values reported in the literature for other high-strength steels. Dynamic recrystallization kinetics is studied using the t50 model, and the influence of temperature and strain rate is quantified and discussed. The interaction between dynamic precipitation and dynamic recrystallization is discussed, and the deformation conditions under which such interactions occur are determined. The thermomechanical results are validated by microstructure examination, including laser confocal microscopy, field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy. The present study focuses on reproducing the deformation cycle applied during the open-die forging process of a vanadium-containing high-strength steel used in the industry with special attention to the interaction between dynamic recrystallization and precipitation processes.

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Section: Interaction Between Dynamic Recrystallization and Precipitatessupporting

confidence: 93%

Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

et al. 2021

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“…The microalloying strategy of Nb and Ti was taken into consideration because of its potential to form more stable grain refiner (Nb, Ti)C precipitates to provide grain coarsening resistance. [ 3 ] The experimental material of this work was Nb–Ti microalloyed 18CrNiMo7‐6 steel which was designed for high‐temperature carburizing. According to the previous work and thermodynamic calculation results, additions of 0.06 wt% Nb and 0.02 wt% Ti appear to provide the best potential to limit unacceptable austenite grain growth of gear steels during high‐temperature carburizing without generating excessive large TiN particles.…”

Section: Methodsmentioning

confidence: 99%

“…[ 1 ] 18CrNiMo7‐6 steel has been an essential material of choice for manufacturing heavy‐duty gears, especially transmission gears in heavy trucks and coastal machines. [ 2,3 ] The large or heavy‐duty gears typically require deep carburization, which takes a long time and consumes a large amount of energy. Increasing the carburizing temperature could greatly shorten the carburizing process and significantly improve the production efficiency.…”

Section: Introductionmentioning

confidence: 99%

Effect of Preheat Treatment on Microstructure and Properties of a Gear Steel for High‐Temperature Carburizing

Tian

Wang

et al. 2020

steel research int.

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Preheat treatment affects not only the microstructure and machinability of the gear steels, but also the final distortion after carburizing and quenching. The effects of preheat treatments of normalizing, tempering, isothermal normalizing, normalizing and tempering, and quenching and tempering on the microstructure and properties of the Nb–Ti microalloyed 18CrNiMo7‐6 gear steel for high‐temperature carburizing are systematically studied herein. The results show that preheat treatment has a significant influence on microstructure evolution, austenite grain coarsening behavior during pseudocarburizing, hardness distribution, and impact toughness of the experimental steel. The microstructure of experimental steel after quenching and tempering is typical tempered martensite with a large number of fine Cr‐rich carbides and Nb–Ti precipitates uniformly distributed. Compared with the pretreatments of simple normalizing, tempering, isothermal normalizing, and normalizing and tempering, the steel after quenching and tempering exhibits the best microstructure uniformity, austenite grain coarsening resistance, machinability, and impact toughness. For the Nb–Ti microalloyed 18CrNiMo7‐6 gear steel, quenching and tempering is the optimum preheat treatment prior to carburizing. In addition, the tempering temperature is selected in the range of 600–650 °C due to the effect of secondary hardening and phase transformation behavior.

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“…These smallsized precipitates were identified as Nb(C,N), which may be the strain-induced precipitates on the dislocations. [39][40][41] A few isolated large spherical precipitates also exist in steel 3, as presented in Figure 4g, which exhibits face centered-cubic lattice (FCC) structure, as shown in Figure 4h, and is rich in Nb with negligible Ti content, as shown in Figure 4i. This precipitate was also identified as Nb(C,N), and its coarser size suggests that it could form during the heating process at high temperatures before hot deformation.…”

Section: Microstructures and Precipitates In The As-received Steelmentioning

confidence: 99%

AlN and Nb(C,N) Composite Precipitation Behaviors and Their Effects on Austenite Grain Growth in SCr420H High‐Temperature Carburized Gear Steel

Gong,

Wang,

Chen

2024

steel research int.

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The effects of nitrogen (N) and niobium (Nb) contents on the precipitation behaviors of AlN, Nb(C,N), and AlN‐Nb(C,N) precipitates and austenite grain growth during the pseudo‐carburizing process are investigated for the carburized steel SCr420H. The results indicate that an increase of N content from 0.011% to 0.019% leads to the emergence of fine and uniform austenite grain structure in the sample while being held at 930 °C for 6 h, which is attributed to a notable rise in the number density of AlN and a decrease in the coarsening rate of AlN. In the steel containing 0.023% Nb, the composite precipitates AlN‐Nb(C,N) play a primary role in the pinning effect on austenite grains growth. The isolated Nb(C,N) and AlN precipitates have minor pinning effects due to their very low volume fractions. Nb(C,N) cap forming on AlN substrate obeys the Shoji–Nishiyama orientation relationship. The favorable lattice matching between AlN and Nb(C,N) and accelerated coarsening rate of Nb(C,N) cap decrease hindrances to the nucleation, growth, and coarsening of Nb(C,N) on AlN substrate. Meanwhile, these simultaneous effects also suppress the same processes for the isolated Nb(C,N) in the matrix.

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Pinning effect of strain induced Nb(C,N) on case hardening steel under warm forging conditions

Cited by 8 publications

References 27 publications

Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

Interactions Between Dynamic Softening and Strengthening Mechanisms During Hot Forging of a High-Strength Steel

Effect of Preheat Treatment on Microstructure and Properties of a Gear Steel for High‐Temperature Carburizing

AlN and Nb(C,N) Composite Precipitation Behaviors and Their Effects on Austenite Grain Growth in SCr420H High‐Temperature Carburized Gear Steel

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