Investigations on Residual Stresses within Hot-Bulk-Formed Components Using Process Simulation and the Contour Method
Abstract
:1. Introduction
2. Materials and Methods
2.1. Experimental Hot-Forming Process
2.2. FE Simulation of the Hot-Forming Process
2.3. Residual Stress Analysis by Means of the Contour Method
2.4. Light Microscopy and Hardness Measurements According to Vickers
3. Results and Discussion
3.1. Temporal Development of Temperature and Tangential Stresses during Hot Forming
3.2. Spatial Distribution of the Residual Stresses Resulting from the Hot-Forming Process Assessed by FE-Simulation and Contour Method
4. Conclusions
- The FE model applied is a valid tool for mapping the process history of hot-bulk forming, i.e., the local temporal temperature and stress evolution.
- The contour method is well-suited to validate the numerical predictions. In this regard, the distributions predicted by the simulations for the tangential RS on the cut surface of the specimens cooled in water could be qualitatively confirmed by means of the contour method. In particular, the above-mentioned ring-shaped distribution with compressive RS in the core and tensile RS in near-surface areas found in the simulations were well-confirmed by the contour method.
- The simulations quantitatively predicted higher amounts of RS than were obtained with the contour method. This may be due to the fact that continuum-mechanics–based FE simulations are taken into account and micro-mechanical interrelationships are not considered in the model used. On the other hand, removing cutting artefacts from the specimens in order to apply the contour method may lead to a reduction in the overall stress level.
- The different cooling media (water and air) lead to different cooling rates of the specimens. This in turn causes different kinds of microstructural transformations, with rapid cooling in water leading to diffusionless martensitic transformation, and slow cooling in air leading to diffusion-controlled pearlitic phase transformation for AISI 52100, and to bainitic phase transformation for AISI 4140.
- The thermal and transformation-related strains occurring on the specimen surfaces and in the material core with a time delay were found to be the reasons for the high stress gradients during water cooling. A characteristic finding is the ring-shaped distribution of tangential RS on the thick-walled side of the cut surface of the specimens for both materials, with compressive RS in the core and tensile RS in the areas near the surface.
- In the material core, plastic deformation takes place during successive martensitic transformation in the near-surface regions of the specimen, followed by martensitic transformation in the core. After cooling, the material core is expanded contrary to the surface areas as a result. This is favoured by the lower yield strength of the material in the specimen core in contrast to the near-surface area as a consequence of the time-delayed cooling of surface and core. The effect is more pronounced for AISI 4140 than for AISI 52100 due to the higher martensite start temperature.
- Due to the comparatively more homogeneous temperature distribution during cooling in air, no inhomogeneous plastic strain distributions occurred in the specimens. The numerical and experimental results, in agreement, show very low RS of less than <50 MPa in the entire cross-section for the specimens of both materials.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Acknowledgments
Conflicts of Interest
References
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[wt%] | C | Si | Mn | P | S | Cr | Mo | Fe |
---|---|---|---|---|---|---|---|---|
AISI 52100 | 0.98 | 0.28 | 0.31 | 0.012 | 0.006 | 1.42 | 0.010 | Balance |
AISI 4140 | 0.41 | 0.22 | 0.80 | 0.018 | 0.012 | 0.99 | 0.195 | Balance |
- | c1 [MPa s] | c2 [°C−1] | n1 [°C−1] | n2 [-] | l1 [°C−1] | l2 [-] | m1 [°C−1] | m2 [-] |
---|---|---|---|---|---|---|---|---|
AISI 52100 | 3113.02 | −0.0033 | 5.0507 × 10−5 | −0.1090 | −2.0135 × 10−5 | 0.0024 | 6.6491 × 10−4 | −0.5000 |
AISI 4140 | 6054.21 | −0.0039 | −3.0846 × 10−5 | 0.3000 | 1.8926 × 10−5 | −0.03548 | −9.4422 × 10−5 | 0.2484 |
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Behrens, B.-A.; Gibmeier, J.; Brunotte, K.; Wester, H.; Simon, N.; Kock, C. Investigations on Residual Stresses within Hot-Bulk-Formed Components Using Process Simulation and the Contour Method. Metals 2021, 11, 566. https://doi.org/10.3390/met11040566
Behrens B-A, Gibmeier J, Brunotte K, Wester H, Simon N, Kock C. Investigations on Residual Stresses within Hot-Bulk-Formed Components Using Process Simulation and the Contour Method. Metals. 2021; 11(4):566. https://doi.org/10.3390/met11040566
Chicago/Turabian StyleBehrens, Bernd-Arno, Jens Gibmeier, Kai Brunotte, Hendrik Wester, Nicola Simon, and Christoph Kock. 2021. "Investigations on Residual Stresses within Hot-Bulk-Formed Components Using Process Simulation and the Contour Method" Metals 11, no. 4: 566. https://doi.org/10.3390/met11040566