A novel approach to control the properties of austenitic stainless steels in incremental forming

Katajarinne, T.; Louhenkilpi, Seppo; Kivivuori, Seppo

doi:10.1016/j.msea.2014.03.020

Cited by 12 publications

(4 citation statements)

References 9 publications

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“…They detect a relationship between the parameters of the forming process, the residual stresses, and mechanical characteristics of an incrementally formed part [19]. Katajarinne et al [20] established a progressive method for adjusting material properties, including ductility and strength for the parts produced by incrementally shaping metal sheets. They controlled properties by controlling the martensitic transformation induced by deformation.…”

Section: Introductionmentioning

confidence: 99%

Influence of process parameters on the residual stress state and properties in disc springs made by incremental sheet forming (ISF)

Afzal

Hajavifard

Buhl

et al. 2021

Forsch Ingenieurwes

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Disc springs are machine elements that are used when high forces need to be supplied and in limited installation space. They need to fulfil high demands on the stability of the spring characteristics, reliability and lifetime. In corrosive environments, metastable austenitic stainless steels (MASS) disc springs are often used. Tensile stresses that occur during service limit the lifetime of disc springs. Usually, their durability is enhanced by generating favorable compressive residual stresses using shot peening operations. Such operations lead to extra efforts and additional production costs. In this study, the adaptive and targeted generation of residual stresses via incremental sheet forming (ISF) is investigated as alternative to shot peening focusing on EN 1.4310 and EN 1.4401 stainless steel. Previous work has shown that ISF is capable of controlling the radial and tangential stresses in the springs. However, no analysis of the influence of the residual stress state in the rolled sheet strips and the ISF process parameters was performed. The goal of the current work is to analyze the evolution of residual stress during rolling and subsequent incremental forming of disc springs. In order to examine the role of dissipation and temperature increases in the rolling process, sheet blanks rolled at room and elevated temperature are analyzed. The characteristics of the compressive residual stresses induced by ISF are studied for different process parameters. X‑ray diffraction is used to investigate the buildup of these stresses. Using ISF, the generation of compressive residual stresses can be integrated into the forming process of disc springs, and further post-treatment may be skipped. The results show that the residual stress state in the rolled material is crucial, which requires tight control of the rolling temperature. Another result is that ISF is able to yield high compressive residual stresses and improved spring characteristics when small tool diameters and step-down values are used.

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Section: Introductionmentioning

confidence: 99%

Influence of process parameters on the residual stress state and properties in disc springs made by incremental sheet forming (ISF)

Afzal

Hajavifard

Buhl

et al. 2021

Forsch Ingenieurwes

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“…At the top of the geometry, i.e., Location 4, the effect of the tensile stress superposition is no longer apparent, and other parameters affecting the phase transformation, e.g., temperature, may become dominant since the strain levels at Locations 3 and 4 are comparable for TSSIF (Figure 6a). The decrease in volume percent of α'-martensite observed for TSSIF when comparing Locations 3 and 4 may be caused by the increased temperature in the forming area (see Figure 3b), which is known to inhibit austenite to martensite phase transformation [8,17]. Note that correction factors based on the material thickness are provided by the manufacturer (but not included in these results) and may result in martensitic volume fractions up to 1.15 times those reported in this work [18].…”

Section: Phase Transformationmentioning

confidence: 99%

“…Austenitic stainless steels, which undergo strain-induced transformation into a stronger, more brittle phase, i.e., martensite [5,6], are of interest for many applications, including the automotive, aerospace, and biomedical industries. Several studies have investigated the extent to which the phase transformation from γ-austenite to α'-martensite can be influenced by adjusting the process parameters e.g., in SPIF [7,8] and deep drawing [9]. This also affects the material formability [10] and residual stress development [11].…”

Section: Introductionmentioning

confidence: 99%

Superposing tensile stresses into single point incremental forming to affect martensitic transformation of SS304

Mamros

Maaß

Hahn

et al. 2022

IOP Conf. Ser.: Mater. Sci. Eng.

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Superposing pre-stress on a SS304 sheet metal blank in biaxial tension and performing a single point incremental forming operation on the stretched blank is investigated experimentally. By applying a pre-stress to the sheet metal blank prior to incremental forming, the resulting microstructural change can be affected to obtain functionally graded materials according to the intended application. In austenitic stainless steels, this variation of the stress states alters the phase transformation, specifically the martensitic transformation kinetics, by influencing key process parameters, such as process force, temperature, and equivalent plastic strain. The phase transformation in truncated square pyramids is measured using magnetic induction. These measurements validate the effectiveness of the stress superposition method for achieving the desired mechanical properties based on altering the final microstructure of a simple geometry.

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“…However, no study dealing with a targeted adjustment of the residual stresses and the development of the residual stresses in MASS by ISF has been reported. The only study identified in the literature dealing with ISF and MASS was proposed by Katajarinne et al [24]. They developed a novel approach for regulating the mechanical properties, i.e., strength and ductility during the incremental forming of MASS by controlling the formation of strain-induced martensite.…”

Section: Introductionmentioning

confidence: 99%

Integrated Forming and Surface Engineering of Disc Springs by Inducing Residual Stresses by Incremental Sheet Forming

et al. 2019

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Disc springs are conical annular discs, which are characterized by a high spring force with a small spring travel and good space utilization. In operation, they must meet high demands on the stability of the spring characteristic and the fatigue strength. Under loading, tensile stresses occur which limit the possible applications of disc springs. Compressive stresses can be generated in the stressed areas by means of shot-peening in order to extend the operating limits for a given yield and fatigue strength. Since the spring geometry and characteristics change during shot-peening, the design of the shot-peening treatment is iterative and cumbersome. The present research proposes an incremental forming process for forming and integrated targeted adjustment of residual stresses in disc springs from metastable austenitic stainless steel (MASS), to achieve improved spring properties and high cyclic strength. The main mechanism of residual stress generation is the transformation of metastable austenite into martensite under the action of the forming tool. Different experimental characterization techniques like the hole drilling method, X-ray diffraction, disc compression tests, optical microscopy and cyclic tests are used to correlate the residual stresses and disc spring properties. A numerical model is developed for simulating the martensite transformation in disc springs manufacturing. The results prove that incremental forming enables process-integrated engineering of the desired compressive residual stresses, entailing a higher spring force of metastable austenitic disc springs in comparison to conventional disc springs. Due to martensite formation, the generated residual stresses are stable under cyclic loading, which is not the case for conventionally manufactured springs.

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A novel approach to control the properties of austenitic stainless steels in incremental forming

Cited by 12 publications

References 9 publications

Influence of process parameters on the residual stress state and properties in disc springs made by incremental sheet forming (ISF)

Influence of process parameters on the residual stress state and properties in disc springs made by incremental sheet forming (ISF)

Superposing tensile stresses into single point incremental forming to affect martensitic transformation of SS304

Integrated Forming and Surface Engineering of Disc Springs by Inducing Residual Stresses by Incremental Sheet Forming

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