A Finite Element Approach to Calculate Temperatures Arising During Cryogenic Turning of Metastable Austenitic Steel AISI 347

The application of components often depends to a large extent on the properties of the surface layer. A novel process chain for the production of components with a hardened surface layer from metastable austenitic steel was presented. The investigated metastable austenitic AISI 347 steel was cold-drawn in solution annealed condition at cryogenic temperatures for pre-hardening, followed by post-hardening via cryogenic turning. The increase in hardness in both processes was due to strain hardening and deformation-induced phase transformation from c-austenite to a 0-martensite. Cryogenic turning experiments were carried out with solution annealed AISI 347 steel as well as with solution annealed and subsequently cold-drawn AISI 347 steel. The thermomechanical load of the workpiece surface layer during the turning process as well as the resulting surface morphology was characterized. The forces and temperatures were higher in turning the cold-drawn AISI 347 steel than turning the solution annealed AISI 347 steel. After cryogenic turning of the solution annealed material, deformation-induced phase transformation and a significant increase in hardness were detected in the near-surface layer. In contrast, no additional phase transformation was observed after cryogenic turning of the cold-drawn AISI 347 steel. The maximum hardness in the surface layer was similar, whereas the hardness in the core of the cold-drawn AISI 347 steel was higher compared to that in the solution annealed AISI 347 steel.

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“…Further information for the determination of the temperatures in the cryogenic turning process can be found in Ref. [56].…”

Section: Methodsmentioning

confidence: 99%

Combination of cold drawing and cryogenic turning for modifying surface morphology of metastable austenitic AISI 347 steel

Hotz

Kirsch

Becker

et al. 2019

J. Iron Steel Res. Int.

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“…The temperature in the area of the inaccessible contact zone can hardly be measured. Becker et al (2018) developed a model which allows for the calculation of the temperature distribution inside the workpiece during cryogenic turning. However, numerical errors occur in an area up to approx.…”

Section: Modelling Approachmentioning

confidence: 99%

Impact of the thermomechanical load on subsurface phase transformations during cryogenic turning of metastable austenitic steels

2020

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When machining metastable austenitic stainless steel with cryogenic cooling, a deformation-induced phase transformation from γ-austenite to α′-martensite can be realized in the workpiece subsurface. This leads to a higher microhardness and thus improved fatigue and wear resistance. A parametric and a non-parametric model were developed in order to investigate the correlation between the thermomechanical load in the workpiece subsurface and the resulting α′-martensite content. It was demonstrated that increasing passive forces and cutting forces promoted the deformation-induced phase transformation, while increasing temperatures had an inhibiting effect. The feed force had no significant influence on the α′-martensite content. With the proposed models it is now possible to estimate the α′-martensite content during cryogenic turning by means of in-situ measurement of process forces and temperatures.

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“…In [1,2] a model has been presented to calculate the temperatures arising during dry and cryogenic turning of metastable austenitic steel AISI 347. Pre-calculations were necessary to determine the magnitude of boundary heat fluxes first, which are mainly induced by the tool and the cryogenic cooling.…”

Section: Motivation and Modelmentioning

confidence: 99%

“…

Metastable austenitic steels offer the opportunity of a surface layer hardening integrated in the machining process. [2]. These conditions can be accomplished during cryogenic turning, allowing a phase transformation in the surface layer of the workpiece.

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confidence: 99%

Application of model order reduction to a finite element model of cryogenic turning

Becker

Hotz

Kirsch

et al. 2019

Proc Appl Math and Mech

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Metastable austenitic steels offer the opportunity of a surface layer hardening integrated in the machining process. The hardening effect is achieved by a deformation induced austenite-martensite phase transformation, for which high mechanical loads and low temperatures are necessary, typically below room temperature. These conditions can be accomplished during cryogenic turning, allowing a phase transformation in the surface layer of the workpiece. To study the austenite-martensite transformation behavior, information about the temperatures in the contact zone between tool and workpiece during machining is necessary, which can hardly be measured. Therefore, FE simulations of the process are utilized to calculate the transient process temperatures. In this paper the idea of projection-based model order reduction and its implementation into the finite element program FEAP are described, allowing a solution speed-up while maintaining accuracy of the full-order model. Motivation and ModelIn [1, 2] a model has been presented to calculate the temperatures arising during dry and cryogenic turning of metastable austenitic steel AISI 347. Pre-calculations were necessary to determine the magnitude of boundary heat fluxes first, which are mainly induced by the tool and the cryogenic cooling. This happens in an iterative way in terms of multiple forward solutions in order to correlate measured and simulated temperatures. However, the repeated calculation of such a finite element problem may take a considerable amount of time due to the number of equations to be solved. To counteract this drawback, model order reduction techniques may be considered, which reduce the number of equations and thus solution time, while maintaining accuracy of the solution. In the present case projection-based model order reduction, which is based on the method of snapshots [5], has been implemented into the finite element code of FEAP [6].The underlying equation is the heat equation, which in the present case considers the convective time derivative as well, resulting in an Eulerian representation, c.f. [2]. The finite element system of equations can then be formulated by K T + MṪ = F, which may be referred to as the full-order model (FOM) of size K, M ∈ R m×m and T, F ∈ R m .Model order reduction states the existence of an approximation T ≈ U rT , where the projection matrix U r is calculated from snapshots of FOM solutions. In more detail, n snapshots are gathered in a snapshot matrix ∈ R m×n , which is analyzed using singular value decomposition. The sought projection matrix stems from the left singular vectors U r = U[1 : d], d ∈ [1, n]. Additionally, further projection of the FOM is needed to overcome an over-determined system of equations. In case of Galerkin projection, the projection matrix U r is used for this second projection, like it was utilized in the present approach. In case of Petrov-Galerkin projection, a matrix different from U r performs the second projection. Here the system of equations after Galerkin projection with U r re...

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A Finite Element Approach to Calculate Temperatures Arising During Cryogenic Turning of Metastable Austenitic Steel AISI 347

Cited by 13 publications

References 9 publications

Combination of cold drawing and cryogenic turning for modifying surface morphology of metastable austenitic AISI 347 steel

Combination of cold drawing and cryogenic turning for modifying surface morphology of metastable austenitic AISI 347 steel

Impact of the thermomechanical load on subsurface phase transformations during cryogenic turning of metastable austenitic steels

Application of model order reduction to a finite element model of cryogenic turning

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