T-TRIP: Investigation of transformation induced plasticity during precipitation formation in quenched and tempered steels and maraging steels

T-TRIP项目旨在更密切地研究迄今为止尚未系统研究的在机械应力下钢的析出形成过程中的相变诱发塑性（TRIP）。为此，从马氏体时效（马氏体时效）钢和回火钢中选择一些钢作为示例材料进行了研究。这些钢等级的选择源于重要的技术应用。热处理钢通常在硬化后回火，从而形成碳化物。由于制造产生的残余应力通常存在于钢构件中，因此沉淀反应是在内部载荷的影响下发生的。这尤其适用于采用电磁感应或激光的现代表面硬化方法。例如，马氏体时效钢用于焊接工艺或增材制造。这些过程导致极高的冷却速率和相关的热诱导残余应力。由于分层处理，已经凝固的区域发生再加热，并在应力和升高的温度的影响下形成沉淀。将从这两类钢中选择析出物体积含量不同的钢成分进行本研究。实验包括在不同的拉伸和压缩应力以及等温和连续温度控制下测量TRIP效应的膨胀测量。此外，还将研究施加应力对材料机械性能的影响。作为这方面的指标，热处理后的屈服强度和硬度要确定。下一步，将检查钢类之间的可转移性，以确定析出类型（回火钢中的碳化物以及马氏体时效钢中的金属间相）对相变诱导塑性的影响。通过x射线和电子显微镜的方法来表征基体的性质以及析出物的形态。力学实验的结果将在微观表征结果的帮助下进行解释和评估，以便更详细地了解马氏体时效和回火过程中的机制。测定的相变诱发塑性的确定依赖关系将用适合这两种钢等级的模型来描述。特别是，对各自钢的析出体积含量的依赖应与TRIP效应的相变塑性常数特征相关联。最后，从结果和建立的模型可以转移到热处理和零件变形领域的技术应用。

The T-TRIP project aims to investigate more closely the so far not systematically studied transformation induced plasticity (TRIP) during the precipitation formation in steels under mechanical stresses. For this purpose, a selection of steels from the class of martensitic aging (maraging) steels and tempering steels are investigated as example materials. The choice of these steel classes results from important technological applications. Heat-treated steels are usually tempered after hardening, resulting in carbide formation. Since residual stresses due to manufacturing are commonly present in steel components, the precipitation reaction occurs under the influence of an internal load. This applies in particular to modern surface hardening methods by means of electro-magnetic induction or lasers. Martensitic aging steels are used, for example, in welding processes or in additive manufacturing. These processes result in extremely high cooling rates and associated thermally induced residual stresses. Due to the layer wise processing, re-heating of already solidified areas occurs and a precipitation formation under the influence of stresses and increased temperatures is initiated. From both classes steel compositions which differ in the volume content of the precipitates will be selected for this investigation. The experiments include dilatometry for the measurement of the TRIP effect at various applied tensile and compressive stresses as well as isothermal and continuous temperature control. In addition, the influence of the applied stress on the resulting mechanical properties of the material is to be investigated. As indicators for this, the yield strength and the hardness after the heat treatment are to be determined. In the next step, the transferability between the steel classes will be examined in order to determine the influence of the precipitation type (carbides in tempered steels as well as intermetallic phases in martensitic aging steels) on the transformation induced plasticity. The properties of the matrix as well as the morphologies of the precipitates will be characterized by means of X-ray and electron microscopic methods.The findings of the mechanical experiments are then to be interpreted and evaluated with the help of the results from the microscopic characterization in order to give a more detailed insight into the mechanisms during martensitic aging and tempering. The determined dependencies of the measured transformation induced plasticity will be described by means of suitable models for both steel classes. In particular, the dependence on the precipitated volume content for the respective steels should be correlated with the transformation plasticity constant characteristic of the TRIP effect. Finally, from the results and created models the transfer to the technological application in the field of heat treatment and component distortion can be made possible.