Characteristics of Retained Austenite in Quenched High C-High Cr Alloy Steels

Yaso, Muneo; Hayashi, Shuhei; Morito, Shigekazu; Ohba, Takayoshi; Kubota, K.; Murakami, Kouji

doi:10.2320/matertrans.mra2008161

Cited by 29 publications

(17 citation statements)

References 13 publications

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“…The retained austenite can be classified into block-like or film-like; 5) the former is formed at packet boundaries while the latter is located along lath boundaries. Typically, they are distinguished by their thickness-in Fe-high Cr-high carbon steels, blocks are approximately 0.5-1 μ m thick and films are less than 50 nm thick.…”

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Carbon Enrichment in Retained Austenite Films in Low Carbon Lath Martensite Steel

et al. 2011

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KEY WORDS: lath martensite; 3-DAP; TEM; retained austenite films; carbon concentration.Bainite and martensite low alloying steels contain stable austenite phase called 'retained austenite '. 1,2) The retained austenite phase is stabilized by austenite stabilizing elements (austenite formers) such as carbon, nickel and manganese. Retained austenite has been used for improving the ductility of tool steels 3) and for transformation-induced plasticity steels.4) However, retained austenite causes secular change, which is an unfavourable volume change distortion by martensitic transformation during practical utilization and ageing.3)The retained austenite can be classified into block-like or film-like; 5) the former is formed at packet boundaries while the latter is located along lath boundaries. Typically, they are distinguished by their thickness-in Fe-high Cr-high carbon steels, blocks are approximately 0.5-1 μ m thick and films are less than 50 nm thick. Because the retained austenite films are sufficiently thin and are found between laths, great effort is required to observe them. Therefore, the film-like retained austenite has not been investigated in many studies.In this study, we focus on the film-like retained austenite in the lath martensite of a low carbon steel. Quenched low carbon steels contain retained austenite, whose morphology is thin film-like, exists between martensite laths. 6) Thomas et al., using high resolution electron microscopy, suggested that such films possibly contain about 1 mass% carbon.7) It is amazing that the thin films contain such high carbon, though the average carbon content is only 0.3 mass% in the entire sample. To achieve such high carbon content in the austenite film, homogeneously distributed carbon atoms, which are in the austenite state before quenching, must diffuse into the austenite thin films either during quenching or at room temperature (RT) storage after martensitic transformation.Recently, we investigated the development of deformation structures in both low and ultra-low carbon lath martensite steels, i.e. with and without retained austenite films, 8) respectively. The study showed that the martensite laths remain after 50% cold rolling in the Fe-0.2C-2Mn (mass%) steel, although the lath boundaries disappear after 10% cold rolling in the Fe-0.0026C-1.5Mn (mass%) steel. The deformation structure in the Fe-0.2C-2Mn steel contains complex structures such as kinked and irregularly bent laths, and the work-hardening ratio in the Fe-0.2C-2Mn steel is higher than that in the Fe-0.0026C-1.5Mn steel. These results suggest that the presence of carbon-enriched retained austenite films, whose 0.2% offset flow stress increases 77 MPa per atomic percent, 9) play a significant role in the development of the deformation microstructure.Because the movement of dislocations in martensite and/ or austenite is the key factor that affects mechanical properties, the presence of dissolved carbon atoms in retained austenite must play an important role in determining these properties. Ho...

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Carbon Enrichment in Retained Austenite Films in Low Carbon Lath Martensite Steel

et al. 2011

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“…2 (a) (together with a FE mesh). The average grain size was determined by optical microscopy studies of 12% Cr steel (Dong et al, 2013;Yaso et al, 2009). Temperature-dependent physical properties of the material are available in (Wang, 2014).…”

Section: -D Polycrystalline Fe Modelmentioning

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Coupling crystal plasticity and continuum damage mechanics for creep assessment in Cr-based power-plant steel

Zhao

Roy

Wang

et al. 2019

Mechanics of Materials

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To improve the design and safety of power plant components, long-term hightemperature creep behaviour of a power-plant material, such as Cr-based alloy, should be assessed. Prior studies indicate that power-plant components undergo material degradation and premature failure by nucleation, growth and coalescence of microvoids as a result of creep damage. In classical crystal-plasticity-based models, a flow rule and a hardening law do not account for global stiffness degradation of materials due to evolving microvoids, having a significant influence on material behaviour, especially under large deformations. In this study, a crystal-plasticity scheme coupled with an appropriate continuum damage model is developed to capture the anisotropic creep-damage effect on the overall deformation behaviour of Cr-based power-plant steel. Numerical simulations show that the developed approach can characterize creep deformation of the material exposed to a range of stress levels and temperatures under consideration of stiffness degradation under large deformation.

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“…Modified AISI D2 steels have 8 wt% chromium but still contain significant amount of primary carbides. They have been reported to have better mechanical properties . However, lower toughness of these steels are due to alloying element segregation and large primary carbides which increases the risk of chipping, cracking, and breakage of punches and stamping tools .…”

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Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel

Rehan

Medvedeva²,

Högman³

et al. 2016

steel research int.

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The effects of austenitization and tempering temperatures for a 5 wt% Cr cold work tool steel are studied with an aim of understanding the influence on microstructure and mechanical properties. Microstructures are characterized with scanning electron microscopy and light optical microscopy. Retained austenite contents and martensite start temperatures are measured by X-ray diffraction and dilatometry, respectively. Hardness, impact toughness, and compressive yield strength are also determined. When the austenitization temperature is increased from 1020 or 1050 to 1075 8C, followed by tempering at 525 8C, significant hardness is gained while there is no increase in compressive yield strength. Higher austenitization temperatures also produce larger amounts of retained austenite. At the same time, the impact toughness is reduced due to coarsening of the martensitic microstructure. When the steel is tempered at 200 8C, a higher impact toughness and a higher volume fraction of retained austenite are observed. Retained austenite is not found after tempering at temperatures of 525 8C or above. It is concluded that the best combination of mechanical properties is achieved by austenitization at 1020 or 1050 8C followed by tempering at 525 8C.

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Characteristics of Retained Austenite in Quenched High C-High Cr Alloy Steels

Cited by 29 publications

References 13 publications

Carbon Enrichment in Retained Austenite Films in Low Carbon Lath Martensite Steel

Carbon Enrichment in Retained Austenite Films in Low Carbon Lath Martensite Steel

Coupling crystal plasticity and continuum damage mechanics for creep assessment in Cr-based power-plant steel

Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel

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