Micromechanisms and modelling of crack initiation and growth in tool steels: role of primary carbides

Mishnaevsky, Leon; Lippmann, N.; Schmauder, Siegfried

doi:10.1515/ijmr-2003-0117

Cited by 4 publications

(4 citation statements)

References 7 publications

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“…This, in consequence, induces the occurrence of inhomogeneously localized stress within the specific regions where the PCs precipitate. This inhomogeneous stress can easily initiate microcracks near the PCs, which then propagate through the matrix and finally lead to the failure of steels [6][7][8][9]. The morphology and distribution of PCs in the matrix significantly affect the steel performance, i.e., strength, toughness, fatigue life, etc.…”

Section: Introductionmentioning

confidence: 99%

Morphology and Distribution of Primary Carbides in Forged Cr-Ni-Mo-V/Nb Steel

Li,

Xu,

Cao

et al. 2024

Materials

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This study aims to investigate in situ the three-dimensional (3D) morphology and distribution of primary carbides (PCs) in electro-slag remelting (ESR) forged 30Cr3Ni3Mo2V steel. A facile non-aqueous electrolytic etching method was applied to prepare 3D PCs on the matrix. The morphology, composition, and element concentrations of PCs were characterized using a combination of optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and electron back-scattered diffusion (EBSD). The precipitation, type, and composition of PCs in the same steel were also simulated using Thermo-Calc software Version 2015a. The results indicate that PC is rich in Nb, which is a potential heterogeneous nucleating agent. Both the size and number of PCs increase from the edge to the center of the ingot. The large-sized PCs present three dominant types of morphology, which vary in different regions, i.e., a bulky type dominates in the edge region, a lamellar type dominates in the middle region, and a stripy type dominates in the core region. The results of EBSD analysis show that the orientation of PCs with different morphologies is different and that more nanosized V-rich type carbides are precipitated on the matrix. The thermodynamic calculations show that MC precipitates from the liquid phase when the solid phase fraction is greater than 0.985 and that the MC-type carbides are rich in Nb, which agrees well with the experimental results.

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Section: Introductionmentioning

confidence: 99%

Morphology and Distribution of Primary Carbides in Forged Cr-Ni-Mo-V/Nb Steel

Li,

Xu,

Cao

et al. 2024

Materials

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Section: Introductionmentioning

confidence: 99%

“…Mishnaevsky et al have shown that the fracture in tool steels typically starts in or along eutectic carbides. [26] It is, therefore, to be assumed that the morphology of the eutectic carbides must have an influence on the mechanical properties of high-speed steels.High-speed steel alloys typically exhibit a transformation gap in the isothermal time-temperature-transformation (TTT) diagram. The scientific consensus is that no transformation of the metastable austenite takes place in the temperature regime of the transformation gap.…”

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confidence: 99%

Influence of Heat Treatment Parameters on the Carbide Morphology of PM High‐Speed Steel HS 6‐5‐3‐8

Disch

Benito

Röttger

et al. 2023

steel research int.

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Cutting tools are commonly made of high-speed steel to simultaneously fulfill the requirements regarding hardness, strength, and toughness. The microstructure of high-speed steel alloys in as-cast condition is characterized by a microstructure consisting of a metal matrix and eutectic carbides. [1][2][3][4] The further manufacturing route of these materials comprises hot forming to break down the carbide network [1,2] and subsequent heat treatment. The behavior of the carbides during austenitization was examined in several publications. [3][4][5][6][7][8][9] Metastable carbides with the stoichiometry M 2 C (M¼ metal atoms, C ¼ carbon), which are present after casting, are transformed to carbides of the types MC and M 6 C with the transformation path of [3,[10][11][12] Dependent on the austenitization temperature and time and thus on the amount of dissolved carbides, different contents of retained austenite remain after quenching. [9] During typical subsequent tempering at temperatures where a secondary hardening effect occurs, retained austenite decomposes, and the precipitation of finely dispersed tempering carbides occurs. [13][14][15] Besides the conventional production route with casting and hot forming, alternative manufacturing processes like spray forming [16][17][18] or powder metallurgy (PM) with hot isostatic pressing are available. Several studies found that powder metallurgic high-speed steel exhibit higher toughness and better cutting performance compared to cast material. [19][20][21][22][23] In most cases, this is explained by the finer distribution, the isotropic properties, and the more regular shape of the eutectic carbides due to the rapid solidification of the powder particles during powder manufacturing. The carbides are affected in their type, [8] size, [5,24] and distribution [25] by the process variables during primary manufacturing and different heat treatments. Mishnaevsky et al. have shown that the fracture in tool steels typically starts in or along eutectic carbides. [26] It is, therefore, to be assumed that the morphology of the eutectic carbides must have an influence on the mechanical properties of high-speed steels.High-speed steel alloys typically exhibit a transformation gap in the isothermal time-temperature-transformation (TTT) diagram. The scientific consensus is that no transformation of the metastable austenite takes place in the temperature regime of the transformation gap. [27] Kešner et al. found that the size of carbides is affected by hardening in a salt bath under isothermal conditions at temperatures between 300 and 650 °C, which is in the temperature regime of the transformation gap of high-speed steels. [28] However, previous works have paid no attention to the effect of different heat treatment parameters on the shape of eutectic carbides. Our preliminary work shows that isothermal

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“…However, these methods can not easily handle large displacements of the resulting sub-bodies after the fracture, such as the fragments blown up by a detonation. The Element Deletion Method could deal with these large displacements (see [37,38]), but none of these techniques can manage the collision between multiples bodies and the self-collision of boundaries.…”

Section: State Of the Artmentioning

confidence: 99%

Discrete volume method : a variational approach for brittle fracture

Cardoso Nungaray

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This thesis presents a proposal to simulate mechanics and dynamics of brittle fracture. A variational formulation is used to describe Lagrangian mechanics, by minimizing the difference between potential and kinetic energy of the system, obtaining a pair of partial differential equations; the solution of these equations corresponds to the displacement field and damage phase-field respectively. Such an equations are coupled in the sense that the damage field is used in the first equation and the displacement field is used in the second one. In this work we propose a numerical method based on control volumes to solve the differential equations, extending the formulation to support the separation of control volumes, processing these volumes as discrete entities. This treatment results in accurate calculations of stress field and the nucleation of new internal fractures that can be propagated through domain creating multiple bifurcations. To integrate equations inside control volumes we introduce a family of polynomial splines that we refer as homeostatic splines, since its derivatives are null at vertices with a smooth function variation between adjacent volumes. Furthermore, we propose a shape function with trigonometric components for dynamic analysis, allowing bigger time steps that with traditional approaches. Finally, we perform ten numerical experiments to show the effectiveness of the method and to compare our results with those published by other authors. La tesis presenta una propuesta para simular la mecánica y dinámica del fenómeno de fractura frágil. Se plantea una formulación variacional que consiste en minimizar la diferencia entre la energía potencial y la energía cinética del sistema, obteniendo así un par de ecuaciones diferenciales parciales, cuya solución corresponden al campo de desplazamientos y al campo de daño respectivamente. Estas ecuaciones están acopladas en el sentido de que el campo de daño se usa en la primera ecuación y el de desplazamientos en la segunda. En este trabajo se propone un método numérico basado en volúmenes de control para resolver las ecuaciones diferenciales, además el modelo se extiende para soportar la separación de los volúmenes de control, tratándolos posteriormente como entidades discretas, esto permite calcular con precisión el campo de esfuerzos y la aparición de fracturas internas que pueden propagarse a través del dominio y crear múltiples bifurcaciones. Para integrar las ecuaciones dentro de los volúmenes de control se introducen una familia de splines polinomiales, que se les refiere como splines homeostáticos, ya que sus derivadas son nulas en los vértices y el cambio de la función entre dos volúmenes contiguos es suave. Además, se propone una función de forma con componentes trigonométricas para el análisis dinámico, permitiendo pasos de tiempo más grandes que con enfoques tradicionales. Finalmente se realizan diez experimentos numéricos para mostrar la eficacia del método y contrastar los resultados con aquéllos publicados por otros autores.

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Micromechanisms and modelling of crack initiation and growth in tool steels: role of primary carbides

Cited by 4 publications

References 7 publications

Morphology and Distribution of Primary Carbides in Forged Cr-Ni-Mo-V/Nb Steel

Morphology and Distribution of Primary Carbides in Forged Cr-Ni-Mo-V/Nb Steel

Influence of Heat Treatment Parameters on the Carbide Morphology of PM High‐Speed Steel HS 6‐5‐3‐8

Discrete volume method : a variational approach for brittle fracture

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