Effect of microstructure evolution on strength and impact toughness of G18CrMo2-6 heat-resistant steel during tempering

Self Cite

The precipitation, dissolution, and coarsening of different carbides at 680 °C in G18CrMo2–6 steel was investigated experimentally combined with Jmatpro simulation. The G18CrMo2–6 steel was normalized at 940 °C, followed by tempering at different times at a constant temperature of 680 °C. During the tempering process, there are mainly two kinds of carbide, namely M3C and M23C6. Through characterization of microstructural evolution, thermodynamic calculation, and kinetic simulation, it was observed that during the tempering process, the stable M23C6 carbide was growing, whereas the metastable M3C carbide was disappearing. At the end, the M3C carbide was dissolved and the M23C6 carbide was in equilibrium with the matrix.

Section: Phase Diagram Calculationmentioning

confidence: 86%

“…Figure 4. Patterns of precipitate extracted from samples tempered at 680 °C for 2 h and 250 h, reproduced from [19], with copyright permission from Elsevier, 2014. Figure 5a,b shows the TEM images of the precipitates in the bainite grains.…”

Section: Characterization Of Microstructural Evolution By Sem and Xrdmentioning

confidence: 99%

Carbide Precipitation, Dissolution, and Coarsening in G18CrMo2–6 Steel

Jia

Liu

et al. 2019

Self Cite

“…As we all know, in steel, the main factors affecting impact toughness are microstructure, grain boundary segregation of impurity elements, prior austenite grain size, and grain boundary precipitation [19][20][21][22]. Therefore, this article will explain the evolution of impact toughness from the above aspects.…”

Section: Discussionmentioning

confidence: 99%

Effect of Trace Mg on Impact Toughness of 2.25Cr1Mo Steel Doped with 0.056% P at Medium Temperature Aging Process

Dong

Xing

et al. 2020

In order to investigate the effect of Mg addition on the embrittlement of Cr-Mo steels, the 2.25Cr1Mo steel plates containing Mg, P contents were refined with vacuum induction furnace and rolled with double-stick reversible rolling mill. The impact toughness evolution and microstructural characteristics of these steels after aging at 580 °C for up to 5000 h were systematically investigated. The grain boundary segregation behaviors of P, S, and Mg before and after aging were analyzed with auger electron spectroscopy (AES), and the microstructure characteristics of the steels were detected with optical electron microscope (OM) and transmission electron microscope (TEM). The research results show Mg addition can improve the impact toughness of the 2.25Cr1Mo steel to a certain extent even with 0.056 wt.% P doping. It was clarified that Mg can segregate to grain boundary during the aging process, and its strong segregation tendency can reduce the grain boundary segregation of P to some degree. The effects of Mg on the impact toughness after subjecting to 580 °C ageing, including element segregation behaviors at grain boundary, ferrite formation, prior austenite grain characteristics, and carbides at grain boundary were also identified and discussed.

“…The existing small carbides can coalesce and grow up under the interaction of cyclic mechanical and thermal loads during the service process [12]. Especially, the fatigue loads can accelerate the growth of M 23 C 6 carbides [17][18][19]. In region 4, plenty of large size M 23 C 6 carbides that are formed along the martensitic lath boundaries can decrease the impact toughness.…”

Section: Discussionmentioning

confidence: 99%

Brittle Fracture Behaviors of Large Die Holders Used in Hot Die Forging

Zhang

Wang

Zhang

et al. 2017

Brittle fracture of large forging equipment usually leads to catastrophic consequences. To avoid this kind of accident, the brittle fracture behaviors of a large die holder were studied by simulating the practical application. The die holder is used on the large die forging press, and it is made of 55NiCrMoV7 hot-work tool steel. Detailed investigations including mechanical properties analysis, metallographic observation, fractography, transmission electron microscope (TEM) analysis and selected area electron diffraction (SAED) were conducted. The results reveal that the material generated a large quantity of large size polyhedral M 23 C 6 (M: Fe and Cr mainly) and elongated M 3 C (M: Fe mainly) carbides along the martensitic lath boundaries when the die holder was recurrently tempered and water-cooled at 250 • C during the service. The large size carbides lead to the material embrittlement and impact toughness degradation, and further resulted in the brittle fracture of the die holder. Therefore, the operation specification must be emphasized to avoid the die holder being cooled by using water, which is aimed at accelerating the cooling.