Temperature dependent cyclic mechanical properties of a hot work steel after time and temperature dependent softening

Jilg, Andreas; Seifert, Thomas

doi:10.1016/j.msea.2018.02.048

Cited by 18 publications

(16 citation statements)

References 13 publications

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“…There are also JMA model based on Johnson–Mehl–Avrami equation and LSW model based on Ostwald ripening mechanism. [ 35,36 ] Some studies have pointed out that, [ 37 ] compared with the JMA model, the LSW model is more suitable for analyzing and predicting the hardness change of steel at low test temperatures ( T ≤ 600 °C). Therefore, considering the heating and holding temperature of this study, the tempering parameter model and LSW model will be used to calculate the softening rate and tempering transition activation energy of the two steels, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…[ 36 ] Its definition is shown in Equation (6) [ 36 ]

\frac{d r}{d t} = \frac{k}{r^{2}}

where dr/dt is the rate of change of the radius of the secondary carbides with time, and k is a coarsening constant, which is related to temperature and is defined by Equation (7) [ 36 ]

k = \frac{4}{9} D Ω c_{\infty} L

where Ω is the atomic volume, c ∞ is the equilibrium concentration, L is the capillary length, and D is the temperature‐dependent diffusion coefficient, as shown in Equation (8) [ 36 ]

D = D_{0} e^{- \frac{Q}{RT}}

where D 0 is an exponential constant that is independent of temperature, Q is the activation energy of tempering transition, R is the ideal gas constant, the value is 8.3143 kJ mol −1 K −1 , T is the tempering temperature (K). The coarsening constant k can also be expressed in engineering form by Equation (9) [ 36 ]

k = k_{normalI} \frac{e^{- \frac{Q}{RT}}}{T}

where k I is the inherent property of the material, independent of temperature. The analytical solution of Equation (6) is shown in Equation (10) [ 36 ]

r^{3} - r_{0}^{3} = 3 kt

where r 0 represents the average radius of the secondary carbides in the tempered state.…”

Section: Discussionmentioning

confidence: 99%

“…The coarsening constant k can also be expressed in engineering form by Equation (9) [ 36 ]

k = k_{normalI} \frac{e^{- \frac{Q}{RT}}}{T}

where k I is the inherent property of the material, independent of temperature. The analytical solution of Equation (6) is shown in Equation (10) [ 36 ]

r^{3} - r_{0}^{3} = 3 kt

where r 0 represents the average radius of the secondary carbides in the tempered state. Based on Equation (10), Equation (11) is used to predict the hardness change of steel during the heat preservation process [ 36 ]

H = H_{normali} + \frac{B_{H}}{\sqrt[3]{3 kt + r_{0}^{3}}}

where H is the hardness in the intermediate heat treatment state, H i is the annealing hardness, and B H is the material property, which is related to the hardening of the particles.…”

Section: Discussionmentioning

confidence: 99%

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Effect of Nitrogen‐Substituted Carbon on Thermal Stability of Cr‐Mo‐V Hot‐Working Die Steel

Zhang

et al. 2020

steel research int.

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To extend service life of Cr‐Mo‐V hot‐working die steel, a method of alloying with nitrogen‐substituted carbon is proposed. The mechanical properties of the test steels in the long‐time heating and holding process are measured. The effect of nitrogen‐substituted carbon on thermal stability is characterized and analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Thermo‐Calc. The results show that the ratio of N in V(C,N) can be increased by nitrogen‐substituted carbon at high temperature, which significantly improves its stability. As a result, it can not only refine the grain but also broaden the austenitizing temperature range and promote the complete solution of alloy elements such as Cr, Mo. In the process of long‐term heating and insulation, nitrogen‐substituted carbon can effectively reduce the precipitation of harmful carbides and the coarsening rate by raising the activation energy of tempering transformation with 20.0 kJ mol−1, and increase the precipitation of the main strengthening phase V(C,N). Nitrogen‐substituted carbon, as an effective alloying method, innovatively improves thermal stability and service life of Cr‐Mo‐V hot‐working die steel.

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Section: Discussionmentioning

confidence: 99%

“…[ 36 ] Its definition is shown in Equation (6) [ 36 ]

\frac{d r}{d t} = \frac{k}{r^{2}}

where dr/dt is the rate of change of the radius of the secondary carbides with time, and k is a coarsening constant, which is related to temperature and is defined by Equation (7) [ 36 ]

k = \frac{4}{9} D Ω c_{\infty} L

where Ω is the atomic volume, c ∞ is the equilibrium concentration, L is the capillary length, and D is the temperature‐dependent diffusion coefficient, as shown in Equation (8) [ 36 ]

D = D_{0} e^{- \frac{Q}{RT}}

k = k_{normalI} \frac{e^{- \frac{Q}{RT}}}{T}

where k I is the inherent property of the material, independent of temperature. The analytical solution of Equation (6) is shown in Equation (10) [ 36 ]

r^{3} - r_{0}^{3} = 3 kt

where r 0 represents the average radius of the secondary carbides in the tempered state.…”

Section: Discussionmentioning

confidence: 99%

“…The coarsening constant k can also be expressed in engineering form by Equation (9) [ 36 ]

k = k_{normalI} \frac{e^{- \frac{Q}{RT}}}{T}

where k I is the inherent property of the material, independent of temperature. The analytical solution of Equation (6) is shown in Equation (10) [ 36 ]

r^{3} - r_{0}^{3} = 3 kt

H = H_{normali} + \frac{B_{H}}{\sqrt[3]{3 kt + r_{0}^{3}}}

where H is the hardness in the intermediate heat treatment state, H i is the annealing hardness, and B H is the material property, which is related to the hardening of the particles.…”

Section: Discussionmentioning

confidence: 99%

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Effect of Nitrogen‐Substituted Carbon on Thermal Stability of Cr‐Mo‐V Hot‐Working Die Steel

Zhang

et al. 2020

steel research int.

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“…Since hot-work tool steels usually operate at elevated temperatures, the high-temperature oxidation behaviour of H11 hot-work tool steel is of great importance. Several authors [3][4][5][6][7][8][9] have studied the effect of elevated temperatures on the mechanical and physical properties of hot-work tool steels. With this consideration, we investigate the oxidation kinetics of AISI H11 in the temperature range between 400 • C and 700 • C.…”

Section: Introductionmentioning

confidence: 99%

High-Temperature Oxidation Behaviour of AISI H11 Tool Steel

Balaško

Vončina

Burja

et al. 2021

Metals

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The high-temperature oxidation of hot-work tool steel AISI H11 was studied. The high-temperature oxidation was investigated in two conditions, the soft annealed condition, and the hardened and tempered condition. First, calculations of the compositions of the oxide layers formed were carried out using the CALPHAD method. The samples were oxidised in a chamber furnace and in a simultaneous thermal analysis instrument, for 100 h in the temperature range between 400 °C and 700 °C. The first samples were used for metallographic (optical microscopy and scanning electron microscopy) and X-ray diffraction analysis of the formed oxide layers, and the second ones for the analysis of the oxidation kinetics by thermogravimetric analysis. Equations describing the high-temperature oxidation kinetics were derived. The kinetics can be described by three mathematical functions, namely: exponential, parabolic, and cubic. However, which function best describes the kinetics depends on the oxidation temperature and the thermal condition of the steel. Hardened and tempered samples have been shown to oxidise less, resulting in a slower oxidation rate. The oxide layers consist of three sublayers, the inner one being spinel-like oxide (Fe, Cr)3O4, the middle one a mixture of magnetite and hematite and the outer one of hematite. At 700 °C there is also some wüstite in the inner oxide sublayer of the soft annealed sample.

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“…Hot-forming is a reliable and relatively economical manufacturing process for metal parts, which relies on high-quality hot-work dies. During hot-forming, regions of the tools may attain high temperatures or pressures, especially regions of the die tool that exhibit a small radii in the die cavities [3]. Because hot-forming dies are exposed to high temperatures and pressures for prolonged periods, the die materials are required to exhibit high strength, hardness, particularly high thermal strength, thermal fatigue, toughness, and wear resistance.…”

Section: Introductionmentioning

confidence: 99%

Microstructural Stability and Softening Resistance of a Novel Hot-Work Die Steel

Liu

et al. 2020

Crystals

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A novel hot-work die steel, named 5Cr5Mo2, was designed to obtain superior thermal stability. The proposed alloy is evaluated in terms of its hardness, microstructure, and tempering kinetics. Compared with the commonly used H13 steel, the softening resistance of the designed steel is superior. Based on SEM and transmission electron microscopy (TEM) observations, a higher abundance of fine molybdenum carbides precipitate in 5Cr5Mo2 steel. Strikingly, the coarseness rate of the carbides is also relatively low during the tempering treatment. Moreover, owing to their pinning effect on dislocation slip, the dislocation density of the 5Cr5Mo2 steel decreases more slowly than that of the H13 steel. Furthermore, a mathematical softening model was successfully deduced and verified by analyzing the tempering kinetics. This model can be used to predict the hardness evolution of the die steels during the service period at high temperature.

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Temperature dependent cyclic mechanical properties of a hot work steel after time and temperature dependent softening

Cited by 18 publications

References 13 publications

Effect of Nitrogen‐Substituted Carbon on Thermal Stability of Cr‐Mo‐V Hot‐Working Die Steel

Effect of Nitrogen‐Substituted Carbon on Thermal Stability of Cr‐Mo‐V Hot‐Working Die Steel

High-Temperature Oxidation Behaviour of AISI H11 Tool Steel

Microstructural Stability and Softening Resistance of a Novel Hot-Work Die Steel

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