Quantitative Analysis of Material Behaviour under Profile Grinding of Transformable Steels

Motivation

The functional performance of highly loaded components is influenced by the integrity of their surface and subsurface layers. In addition to geometric accuracy and surface roughness, the microstructure, hardness, and residual stresses within the subsurface zone are also significant factors. The final step to achieve the required surface quality is often grinding process, which takes place after heat treatment. Since grinding usually represents the final stage of the manufacturing process, any defects induced by the process directly impact the surface integrity. Excessive thermal loads during grinding can change the adjusted surface characteristics, such as hardness and residual stress states, which can lead to a shorter component lifetime and reduced reliability. Ensuring the quality of components under these conditions often requires extensive and costly inspection procedures. However, having a fundamental understanding of how grinding affects the surface zone and the subsequent material responses provides significant opportunities for process optimization. This knowledge can be used to improve manufacturing processes, making them more efficient and reducing production costs.

Objectives

• Characterisation of the transformable steels (100Cr6, 60CrNiMo-7-6, 70CrNiMo-7-6, 80CrNiMo-7-6) subjected to extreme thermal and mechanical stresses.
• Quantitative analysis of the microstructure and residual stresses after grinding process, depending on the initial state of the material, thermo-mechanical load and process parameters.
• Development of a simulation model to predict material integrity resulting from the grinding process.

Project Contents

• Dilatometric tests to investigate microstructural changes at high heating and cooling rates, as well as under high strain rates.
• Experimental investigation of the behaviour of materials during tempering under external loads.
• Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to analyse microstructural changes with respect to work hardening, grain refinement, phase transformations, and the dissolution of coarse carbides.
• Transmission electron microscopy (TEM) investigations to characterise fine, tempered carbides.
• Investigation of the changes in hardness of the material in the new hardening and tempering zones.
• Development of a model to simulate microstructural changes induced by the thermo-mechanical loads during grinding.

Project partner

Manufacturing Technology Institute | MTI at RWTH Aachen University

Funding

Funded by German Research Society