Thermo-physical properties of heat-treatable steels in the temperature range relevant for hot-stamping applications
Thermo-physical properties of heat-treatable steels in the temperature range relevant for hot-stamping applications
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DOI：
10.1007/s10853-015-8829-z
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发表时间：
2015-01
影响因子：
4.5
通讯作者：
Jakob Kuepferle;J. Wilzer;S. Weber;W. Theisen
中科院分区：
文献类型：
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作者：
Jakob Kuepferle;J. Wilzer;S. Weber;W. Theisen
在许多工业过程中，所生产的钢部件的机械性能直接受到热物理性能的影响，这对热处理有很大影响。面向应用的模拟的质量在很大程度上取决于输入量，这些输入量通常由回归分析或简单的外推产生。本文的目的是证明热物理性能的影响，这样一个过程模拟参考热冲压。热冲压是汽车工业中生产超高强度零件的既定工艺。用于该应用的典型材料是低合金钢22 MnB 5。根据热冲压过程中随温度变化的显微组织变化，特别是γ向α′的转变，研究了该钢的热导率。采用动态测量方法，测定了22 MnB 5钢不同温度组织的比热容、热膨胀系数、密度和热扩散率。参考测量和外推数据，生成热冲压过程的整个温度范围的热导率。为了解释快速γ-α′相变动力学，应用了一种新的表征和外推方法。与密度的次要影响相比，热容和热扩散率对热导率具有主要影响。将亚稳奥氏体条件（T≥ 900 °C）与马氏体条件（T≤ 400 °C）进行比较。依赖的热导率显著地依赖于晶格的晶体学取向。面心立方晶格（奥氏体）具有相对于体心立方晶格（马氏体）成比例的低导热性。在从奥氏体到马氏体的转变过程中，发展不是线性的，而是基于复杂的相互作用。结果表明，依赖于温度的热导率必须考虑可靠的过程模拟。
In many industrial processes, the resulting mechanical properties of produced steel parts are directly influenced by the thermo-physical properties, which affect the heat treatment significantly. The quality of application-oriented simulations is strongly dependent on the input quantities, which are often generated by regression analysis or simple extrapolations. The aim of this paper is to demonstrate the influence of the thermo-physical properties on such a process simulation referring to the hot stamping. Hot stamping is an established process in the automotive industry to produce ultra-high strength parts. A typical material used for this application is the low-alloyed steel 22MnB5. The thermal conductivity of this steel was investigated referring to the temperature-dependent microstructural changes during the hot-stamping process, particularly the γ to α′ transformation. In terms of the dynamic measuring method, the specific heat capacity, the thermal expansion coefficient, the density and the thermal diffusivity for the different temperature-dependent microstructures of the steel 22MnB5 were determined. The thermal conductivity for the complete temperature range of the hot-stamping process was generated, referring to measured and extrapolated data. To account for the fast γ–α′ transformation kinetics, a novel characterization and extrapolation method was applied. The heat capacity and the thermal diffusivity have a major impact on the thermal conductivity compared to the subordinated influence of the density. The metastable austenitic condition (T≥ 900 °C) was compared to the martensitic condition (T≤ 400 °C). The dependent thermal conductivity is significantly dependent on the crystallographic orientation of the lattice. The face-centred cubic lattice (austenite) has referring to the body-centred cubic lattice (martensite), a proportionally low thermal conductivity. During the transformation from austenite to martensite, the development is not linear but based on complex interactions. The results reveal that the temperature-dependent thermal conductivity has to be considered for reliable process simulations.