Analysis and modeling of the inherent stresses of high-alloyed cast steel components with regard to the highest dimensional stability requirements
This project aims the development of a model chain and experimental methods to describe the evolution of inherent stresses during the production of a housing component made of austenitic steel.Copyright: © ICMEaix
During the operation of a cast housing component made of austenitic stainless steel, dimensional changes in the bearing area are determined in comparison with the delivery condition. These no longer occur after a stress annealing of the component. Neither from cost, nor from reliability nor from safety aspects is this condition acceptable.
The analysis of the problem yields the following research hypotheses:
- the basic microstructural properties, such as macro- and microsegregation, are adjusted by the casting process.
- In the heat treatment consisting of an austenitizing annealing and a quenching of the component, residual stresses are induced.
- These residual stresses are shifted due to the mechanical processing.
- In operation, local structural characteristics, inherent stresses and operating load lead to a martensitic phase transformation, which involves a volume change and causes distortion.
In addition to the necessary experimental verification of the research hypothesis, the entire process is to be simulated on micro- and macro-level. As a result, not only the current process is better understood, but also new possibilities for application of the material can be developed through more precise predictions of the component properties. For this purpose, the following work was carried out:
- material characterization by metallographic and scanning electron microscopy,
- determination of thermomechanical material parameters,
- measurements of inherent stresses in realistic sample parts,
- thermomechanical simulation of heat treatment,
- simulation of the machining process,
- simulation of the optimized process parameter.
Two pilot components were simulated and tested. One component passed the usual process route and was solution-annealed, quenched and machined. The other component was additionally stress annealed before machining. In general, the simulations of the residual stresses, including machining, showed good agreement with the experimental stress analysis. As expected, large differences were observed with respect to the residual stress levels between the two components. The material characterization shows, on the one hand, that no macrosegregations of technologically relevant magnitude are present. On the other hand, it shows that the elements chromium and molybdenum accumulate between the dendrite arms and nickel is depleted. This can have potential for local mechanically induced martensitic transformations.
RWTH Aachen University
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