Volume 74, Issue 2

“Quenching and Partitioning” (Q&P) steels have a microstructure consisting of a tempered martensitic matrix with austenite islands, which can be stabilized to room temperature due to the C partitioning from martensite to the remaining austenite. This heat-treatment is a novel approach for producing ultra-high strength and good formable steels. In the present work the impact of the Q&P processing parameters on the phase transformation behavior and mechanical properties of a 4.5 wt.% Mn steel was investigated. Using dilatometry the influence of the quenching temperature (T Q ) on the amount of martensite and the kinetics of the bainitic transformation was thoroughly studied. The microstructure was characterized by means of light optical and scanning electron microscopy. The amount of retained austenite was determined using the saturation magnetization measurement. In order to obtain the mechanical properties hardness measurements according to Vickers were performed. Furthermore, using tensile tests the Q&P concept was compared to the Quenching and Tempering (Q&T) process in terms of strength-ductility performance.

Powder bed-based processes such as laser beam melting (LBM) are becoming increasingly relevant in industrial production environments. A novel approach is to use the LBM process for the targeted addition of alloy elements for the laser deep alloying process. In this two-step process, pre-deposited element layers are remelted and mixed into the base material using a high-power laser and beam modulation. However, the pre-deposition of master alloy by means of LBM may induce pores of varying intensity in the applied layers. The present work deals with the influence of such porosity in pre-deposited layers on the resulting microstructure of deep-alloyed micro-samples and thus on the quality of laser deep alloying. The goal was to investigate the suitability of the LBM process for the addition of alloy elements into the melt pool to maintain high throughput material development. For this purpose, an atomized stainless steel was applied in different layer thicknesses on an unalloyed steel. In addition, a different porosity was set in the layers. On average, only a few pores appeared in the microstructure after laser deep alloying. Instead, cracks occurred unsystematically in the microstructure. The experiments have shown that the porosity of pre-deposited layers has no influence on the formation of pores or cracks in the resulting microstructure after laser deep alloying. Thus, it was established that regarding pores in the layers, the laser deep alloying process is stable against fluctuations in the energy deposition in the LBM process.

However, while low pressure carburizing (LPC) is now well established for smaller components and conventional conditions (up to 980 °C), a number of difficulties are expected when considering high temperature LPC of large components. First, conventional carburizing steels will undergo extensive grain growth during an exposure to 1050 °C for 20 hours; while there are solutions to avoid the problem for shorter durations, there are no materials adapted to such heat-treatment durations. Second, the long exposure at high temperature means that the possibility of significant creep deformation should be considered. And third, the hardenability of the material commonly used for wind turbine gears (18CrNiMo7-6) may not be sufficient when switching from oil to gas quenching. The present work attempts to address these issues. On the basis of theoretical alloy design, numerical modeling and experimental work, two purposely designed steel compositions were industrially cast. They were used to manufacture large wind turbine gears and extensively tested. Experimental results are compared to those obtained with a standard 18CrNiMo7-6. Based on a full analysis of the possible production routes, a cost benefit of 20 % is estimated by switching from the actual to the newly developed manufacturing route.

Researchers of the Collaborative Research Centre CRC 1153 are investigating novel process chains to manufacture function-adapted and lightweight machine components. In each step of the process chain, numerical simulation tools are utilised in the process design to take into account locally specific material behaviour under particular processing conditions. In this paper, solution approaches associated with the modelling of manufacturing processes are presented.

Batch planning is one integral part of all industrial heat treatment processes. Its main goal is the maximization of the number of components in the batch considering the components specifications. During batch planning the temperature distribution in the batch needs to be taken into account at any point and therefore plays the decisive role. So far, the calculation of the load is based on experience. This can lead to loss of quality or reduced productivity. As a result, an interactive batch planning system for plasma nitriding furnaces is being developed in a current research and development project. The planning system contains a radiation model, which calculates the temperature distribution in the batch, and a diffusion model, which allows to predict the nitriding results based on the calculated temperatures. Due to computation time requirements a simplification of the physical model, especially the radiation model, needs to be realized. The permissible simplifications are determined in a study on a complete numerical radiation model. This paper shows the concept of the batch planning system and the development of the complete numerical radiation model.