Austenite stability and M2C carbide decomposition in experimental secondary hardening ultra-high strength steels during high temperature austenitizing treatments

Veerababu, R.; Prasad, Kartik; Phani, S Karamched; Balamuralikrishnan, R.; Karthikeyan, S.

doi:10.1016/j.matchar.2018.07.013

Cited by 20 publications

(7 citation statements)

References 55 publications

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“…On the one hand, some alloying elements with a larger radius than Fe (such as W and Mo) cause lattice deformation and increase the lattice constant of α-Fe. On the other hand, these alloying elements can strengthen and improve the stability of austenite, which leads to a decrease in the MS temperature [ 29 ]. Therefore, with the increase in the quenching temperature, the α-Fe peak gradually shifted to the left, and the peak intensity gradually decreased.…”

Section: Resultsmentioning

confidence: 99%

Discussion of the Segregation and Low Hardness of Large-Diameter M3 High-Speed Steel Produced by Spray Forming

Liu

Hongxiao

et al. 2023

Materials

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As an advanced near-net-shape processing method in which directly preformed, semi-finished products are created from liquid metals, spray forming has become popular in the development and application of new materials and is supporting industrialization. However, as investigated in this work, the problems of segregation and low hardness exist in the actual industrialization process, particularly for large-diameter M3 high-speed steel. It was here found that the annual ring segregation morphologies were mostly distributed from the edge to 1/2R, with a large number of stripes primarily enriched in C, Mo, and Cr elements, and the degree of segregation was mild. The ring segregation was located at the 1/2R position, where the main elemental enrichments were C, W, Mo, Cr, and V, and the segregation degree was severe. The formation of segregation during deposition is described based on an equilibrium solidification model. A slow cooling rate and heat dissipation from the surface to the inside were judged to be the main factors causing segregation and changes in the carbide morphology. In terms of hardness, with the increase in the quenching temperature to 1230 °C, the tempering hardness increased significantly. The analysis shows that a faster cooling rate in the atomization stage caused the solidified droplets to exhibit rapid solidification characteristics, and there was a higher proportion of MC carbide in the deposited billet. MC carbides cannot be fully dissolved using the conventional heat treatment process, which decreases the C, Cr, Mo, and V contents in the solution and, thus, reduces the secondary hardening capability. The findings show that, when the spray forming process is used to prepare large-diameter materials, it should not be considered a rapid solidification technology simply because of its atomization stage. Moreover, more attention should be paid to the influence of microstructure transformation during atomization and deposition.

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Section: Resultsmentioning

confidence: 99%

Discussion of the Segregation and Low Hardness of Large-Diameter M3 High-Speed Steel Produced by Spray Forming

Liu

Hongxiao

et al. 2023

Materials

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“…The increase in hardness of AISI 304L after application of DCT cannot be linked to a more effective transformation of retained austenite into martensite [ 11 , 15 , 36 ] or by higher solution annealing temperature [ 37 ], because the control with a higher selected temperature (1080 °C) has lower hardness value compared to tested DCT1. The other possible and more likely explanation suggested by Myeong et al 1997 [ 25 ] and Baldissera 2010 [ 9 ] is the dislocation pinning effect, which is associated with the increased plastic deformation (residual stress) and thus improvement in hardness after the application of DCT.…”

Section: Resultsmentioning

confidence: 99%

Complex Interdependency of Microstructure, Mechanical Properties, Fatigue Resistance, and Residual Stress of Austenitic Stainless Steels AISI 304L

et al. 2023

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Stainless steels are important in various industries due to their unique properties and durable life cycle. However, with increasing demands for prolonged life cycles, better mechanical properties, and improved residual stresses, new treatment techniques, such as deep cryogenic treatment (DCT), are on the rise to further push the improvement in stainless steels. This study focuses on the effect of DCT on austenitic stainless steel AISI 304L, while also considering the influence of solution annealing temperature on DCT effectiveness. Both aspects are assessed through the research of microstructure, selected mechanical properties (hardness, fracture and impact toughness, compressive and tensile strength, strain-hardening exponent, and fatigue resistance), and residual stresses by comparing the DCT state with conventionally treated counterparts. The results indicate the complex interdependency of investigated microstructural characteristics and residual stress states, which is the main reason for induced changes in mechanical properties. The results show both the significant and insignificant effects of DCT on individual properties of AISI 304L. Overall, solution annealing at a higher temperature (1080 °C) showed more prominent results in combination with DCT, which can be utilized for different manufacturing procedures of austenitic stainless steels for various applications.

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“…Steel : Two different secondary hardening ultra-high-strength steels with varying levels of Cr and Mo (table 1) have been chosen for studying the martensitic transformation during in situ cooling in the temperature range from RT (25°C) to −194°C. Further details on the physical metallurgy of the steels are available elsewhere [21]. During the in situ experiment, the as-quenched sample was cooled down from RT to −194°C and cooling was interrupted at regular temperature intervals to record transformations at that particular temperature.…”

Section: Resultsmentioning

confidence: 99%

“…The requirement of an additional driving force in terms of elastic strain energy is attributed to the presence of a higher amount of austenite stabilizing elements (Cr, Mo, etc.) [21]. It is also interesting to note the discrepancy in predicting the M s and M f temperatures from austenite composition [31] or the empirical relation involving fraction of retained austenite [32].…”

Section: Resultsmentioning

confidence: 99%

Study of diffusionless and diffusional transformations usingin situcooling and heating techniques in a scanning electron microscope

Kumar

Sarkar

Singh

et al. 2020

Phil. Trans. R. Soc. A.

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In situ electron microscopy can be an effective tool to investigate the underlying science of many transformation mechanisms in materials science. Useful utilization of these experimentations will provide greater insight into many of the existing theories, as microstructural changes can be visualized in real time under some applied constraints. In this study, we have investigated two basic phase transformation phenomena: diffusionless and diffusional mechanisms with the help of in situ cooling and heating techniques in scanning electron microscope (SEM). In situ cooling experiments have been carried out on secondary hardening ultra-high-strength steels to understand the diffusionless transformation of austenite to martensite. Nucleation and growth of the martensites have been observed with cooling in different steps to −194°C. Details of the formation of different variants of martensites in steel were studied with the help of orientation imaging microscopy. Diffusional transformations were studied in terms of oxidation of pure copper in SEM using in situ heating technique. Different heating cycles were adopted for different samples by in situ heating to a maximum temperature of 950°C for the oxidation study. Nucleation of copper oxides and subsequent growth of the copper oxides at different temperatures were studied systematically. Raman spectroscopy and orientation imaging were done to confirm the formation of oxides and their orientations. The thermal cycling phenomenon was replicated inside SEM with heating and cooling and it has been demonstrated how the nature of copper and its oxides changes with the thermal cycle. This article is part of a discussion meeting issue ‘Dynamic in situ microscopy relating structure and function’.

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Austenite stability and M2C carbide decomposition in experimental secondary hardening ultra-high strength steels during high temperature austenitizing treatments

Cited by 20 publications

References 55 publications

Discussion of the Segregation and Low Hardness of Large-Diameter M3 High-Speed Steel Produced by Spray Forming

Discussion of the Segregation and Low Hardness of Large-Diameter M3 High-Speed Steel Produced by Spray Forming

Complex Interdependency of Microstructure, Mechanical Properties, Fatigue Resistance, and Residual Stress of Austenitic Stainless Steels AISI 304L

Study of diffusionless and diffusional transformations usingin situcooling and heating techniques in a scanning electron microscope

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