Materials Science Forum Vol. 1184

Abstract: Massively carbon supersaturated (MCSed) tool steel dies were prepared for dry, galling free forging, microtexturing and fine-blanking of titanium and titanium alloy eye-glass frame parts. Titanium temples were forged in dry and galling-free to investigate the role of MCS treatment to reduce surface roughing of temples. They were also micro-textured to discuss the superiority of MCS to product quality. Dry, galling-free fine-blanking was utilized to describe the life-time extension of MCSed tool steel dies. Various eye-glass frame parts were forged in dry to state the statistic evaluation on the galling-free manufacturing features. The intermediate chemical treatments as well as barreling and polishing steps were saved to reduce the amount of wastes from manufacturing factories of titanium and titanium alloy eye-glass frames toward zero emission.

Abstract: The growing demand for lightweight components has highlighted the potential of sheet metal parts made from high-strength aluminum and magnesium alloys. However, the forming of these materials is often limited by complex manufacturing processes that typically require lubricants, raising environmental and economic concerns. This study investigates the feasibility of using thermoplastic polymers as tooling materials for dry forming of aluminum alloy 7075-T6 and magnesium alloy AZ31B at temperatures up to 300 °C. A number of high-performance thermoplastic polymers were selected based on their superior mechanical and thermal properties and evaluated through compression and tensile tests, dilatometry, pin-on-disk and strip drawing tests. In addition, the influence of coatings on the tribological performance of the polymers was systematically investigated. The results showed that thermoplastic tools have the potential for efficient dry forming of AA 7075-T6 and AZ31B parts at temperatures up to 300 °C, achieving good tool stability, wear resistance and part quality. TECAPEEK PVX with original tribological optimization proved to be the most promising candidate and was validated in challenging cross cup forming experiments. This lubricant-free approach offers significant environmental and economic benefits, providing a sustainable solution for prototyping and small-scale production of lightweight metal components.

Abstract: In metal forming, the flattening of asperities on the workpiece surface is important to understand both for the impact it has on the properties of finished parts and the influence that real contact area has on tribological conditions during forming. The current study presents a method for the numerical modeling of asperity flattening of a deep drawing steel under high normal loads and no subsurface strain. At the microscale, a crystal plasticity model is employed to capture the propensity of grains to deform differently depending on their orientation. The continuum scale model is used to provide the boundary conditions to the microscale. The mechanical and microstructural properties of a DC04 deep drawing steel are used to provide the necessary parameters for the continuum and microscale models. The initial surface topography of the experimental material is measured by confocal microscopy and is mimicked in the input to the simulations. Surface topography measurements after flattening the experimental surface are used as validation for the simulated results, with real contact area, mean surface roughness, and autocorrelation length used as the primary figures of merit.

Abstract: Nickel coated steel is used in the industry to produce battery shells. These shells are typically produced in several process steps: drawing, redrawing and several ironing steps at high production rates. The nickel plated steel sheet is subjected to a large range of deformations andpressures. Sometimes scratches in the longitudinal direction of the shell (hairlines) occur, due to the build-up of particles on the tooling (i.e. galling). Cleaning of the tools will be necessary and will bring additional costs. In this paper, analyses are performed on tribological behaviour of nickel plated steel sheet with the focus on tool wear. Adhesive wear has been observed to be the main wear mechanism. The adhesive layer build up consists mainly of compacted particles (often in the shape of flakes) of nickel and iron. The Slider on Sheet Test (SOST) is found to be a relevant set-up to study tribological behaviour of nickel plated steels in battery production.

Abstract: Skin-pass rolling is a finishing process characterized by very small thickness reductions, primarily applied to control surface texture and mechanical properties of rolled steel strips. A key outcome of this process is the transfer of surface roughness from the work roll to the strip, which is governed by local contact conditions at the roll–strip interface. In this study, roughness transfer during skin-pass rolling of DX56 steel sheets is investigated using a combined macro–micro finite element modeling approach supported by pilot-mill experiments. Rolling trials were conducted to measure thickness reduction and resulting surface roughness under different rolling forces and entry tensions. A macro-scale rolling model was first employed to estimate effective friction coefficients by reproducing the experimentally observed thickness reductions for each rolling condition. These calibrated friction coefficients were subsequently applied in a micro-scale finite element model incorporating an electro-discharge textured (EDT) roll surface to analyze local contact pressure, plastic strain accumulation, and roughness transfer mechanisms. The results show that increasing rolling force leads to higher contact pressures, longer roll bites, and enhanced asperity-scale plastic deformation, resulting in increased roughness transfer. Entry tension modifies the stress distribution within the roll bite, which facilitates localized yielding without inducing plastic deformation prior to roll entry. The simulations capture the qualitative trends of surface roughness evolution observed experimentally, demonstrating the capability of the proposed finite element framework to analyze roughness transfer mechanisms in skin-pass rolling.

Abstract: Skin-pass rolling is commonly used to adjust the surface quality of high-strength aluminum alloys. Lubrication plays an important role in this process, as it minimizes material adhesion to the work roll, extends its service life, and also influences the contact conditions and the final surface topography. However, most numerical studies represent lubrication only through an effective friction coefficient. In this work, a finite-element framework that explicitly accounts for lubricant entrapment in engineered surface pockets by using a coupled Eulerian-Lagrangian (CEL) approach is introduced to investigate lubricant-topography interaction. The skin-pass rolling process is approximated by a plane-strain upsetting test to represent the parameters relevant for mapping the interaction between lubricant and mechanical stress, as the rolling process has a large number of influencing factors. The precipitation-hardenable aluminum alloy EN AW-6016 is modeled with rate-dependent plasticity based on experimental flow curves, while the lubricant is represented as a Eulerian material governed by an equation-of-state formulation. The effects of strain rate, friction and different lubricant filling levels in surface pockets are analyzed. The results show that variations in friction mainly affect the global force level, while the presence of lubricant leads to changes in local deformation and stress distributions. Fully filled pockets require higher forming forces due to lubricant compression, whereas partially filled pockets show behavior close to dry conditions. The CEL approach proves suitable for modeling lubricated plane-strain upsetting tests and provides a basis for further investigations of lubricated skin-pass rolling processes.

Abstract: This study investigates the effect of deep cryogenic treatment on the tribological and electrochemical performance of X46Cr13 martensitic stainless steel, with a particular emphasis on the synergistic interaction between wear and corrosion and its microstructural origins. The material was subjected to conventional quenching and tempering and compared with heat treatment routes incorporating cryogenic processing. Hardness measurements, wear tests, and electrochemical characterization by Tafel polarization were combined with quantitative microstructural analysis. Cryogenic treatment induces a pronounced microstructural refinement through the transformation of retained austenite into martensite and the enhanced precipitation of fine chromium-rich carbides, predominantly M₂₃C₆ and M₇C₃. This process results in an increased carbide number density and a reduced average carbide area, leading to a more homogeneous carbide distribution within the martensitic matrix. The refined carbide population contributes to increased hardness and significantly improved wear resistance by effectively hindering plastic deformation and abrasive damage. Simultaneously, the stabilization of the martensitic matrix and the modified carbide–matrix interface promote the formation of a more uniform and stable passive film, improving corrosion resistance. The combined improvement in wear and corrosion behavior reduces the degradation rate under coupled mechanical and electrochemical loading, demonstrating a clear tribocorrosion synergy controlled by carbide characteristics. These findings highlight cryogenic treatment as an effective strategy for tailoring the microstructure of martensitic stainless steels to enhance their performance in aggressive and mechanically demanding environments.

Abstract: Lubrication plays a crucial role in cold forging, influencing key factors such as material flow, surface quality and tool wear. The current state of the art presents conventional mineral-oil-based lubricants as one of a range of effective solutions; however, they generate residues, require cleaning and pose environmental concerns. This work explores CO₂ snow as a potential residue-free, sustainable alternative for cold forming of mild steels. Miniature spike tests were conducted to characterise friction behaviour under varying lubrication and surface conditions. The study demonstrates that CO₂ snow can effectively reduce friction, promote favourable material flow and achieve surface finishes comparable to conventional oils, while eliminating residue and post-processing requirements. These findings suggest that CO₂ snow represents a promising eco-friendly lubrication strategy, offering both technical performance and environmental benefits for sustainable cold forging operations.

Abstract: Experimental determination of the real contact area is essential for the development and validation of advanced friction models in sheet metal forming. However, existing experimental approaches are limited by the need for transparent counterfaces or third agents in the interface, high sensitivity to relocation errors, or unreliable assumptions about the contact shape. This study proposes a novel ex-situ method to determine the real contact area using topographical information from the original and deformed sheet surfaces. The approach identifies a minimum contact area with high confidence and reconstructs from it the full contact area. It provides the real contact area ratio, the contact topography and height distribution. The method is evaluated using results from normal load simulations based on the Pullen and Williamson model as the reference and is compared with other ex-situ methods from literature. Results demonstrate that the proposed method is robust against realistic relocation errors and yields more accurate contact area values than existing approaches. The method offers a reliable experimental tool for tribological analysis and friction modelling in sheet metal forming.