Composite materials based on an ethylene-acrylic acid (EAA) copolymer and 20 wt% cellulose fibers were compounded by two runs in a twin-screw extruder. The composite material with cellulose fibers (CF) and a reference of unfilled EAA were injection molded into plaques using three different temperature profiles with end zone temperatures of 170°C, 200°C, and 230°C. The injection molded samples were then characterized in terms of their mechanical properties, thermal properties, appearance (color and gloss), and surface topography. The higher processing temperatures resulted in a clear discoloration of the composites, but there was no deterioration in the mechanical performance. The addition of cellulose typically gave a tensile modulus three times higher than that of the unfilled EAA, but the strength and strain at rupture were reduced when fibers were added. The processing temperature had no significant influence on the mechanical properties of the composites. Gloss measurements revealed negligible differences between the samples molded at the different melt temperatures but the surface smoothness was somewhat higher when the melt temperature was increased. In general, addition of the cellulose to the EAA reduced the gloss level and the surface smoothness.

The automotive industry is continuously developing and finding new ways to respond to the incremental demands of higher safety standards and lower environmental impact. As an answer to weight reduction of vehicles, the combination of boron steel and composite material is being developed along with their joining process, self-pierce riveting. Boron steel is an ultra-high strength material that needs to be locally softened before the joining process. However, the joining process deforms the part. This paper investigates factors affecting the geometrical deformation during the tempering process and lists important phenomena that need to be included when simulating the tempering process.

Induction hardening is a relatively rapid heat treatment method to increase mechanical properties of steel components. However, results from FE-simulation of the induction hardening process show that a tensile stress peak will build up in the transition zone in order to balance the high compressive stresses close to the surface. This tensile stress peak is located in the transition zone between the hardened zone and the core material. The main objective with this investigation has been to non-destructively validate the residual stress state throughout an induction hardened component. Thereby, allowing to experimentally confirming the existence and magnitude of the tensile stress peak arising from rapid heat treatment. For this purpose a cylindrical steel bar of grade C45 was induction hardened and characterised regarding the microstructure, hardness, hardening depth and residual stresses. This investigation shows that a combined measurement with synchrotron/neutron diffraction is well suited to non-destructively measure the strains through the steel bar of a diameter of 20 mm and thereby making it possible to calculate the residual stress profile. The result verified the high compressive stresses at the surface which rapidly changes to tensile stresses in the transition zone resulting in a large tensile stress peak. Measured stresses by conventional lab-XRD showed however that at depths below 1.5 mm the stresses were lower compared to the synchrotron and neutron data. This is believed to be an effect of stress relaxation from the layer removal. The FE-simulation predicts the depth of the tensile stress peak well but exaggerates the magnitude compared to the measured results by synchrotron/neutron measurements. This is an important knowledge when designing the component and the heat treatment process since this tensile stress peak will have great impact on the mechanical properties of the final component.

The microstructure and chemical composition of white layers (WLs) formed during hard turning of AISI 52100 steel were studied using atom probe tomography (APT) and transmission electron microscopy (TEM). APT analyses revealed a major difference in the re-distribution of the carbon (C) atoms between WLs formed above and below the A_c1 temperature, i.e. T-WL and M-WL, respectively. In T-WL, the C-atoms segregate to grain boundaries (GBs) forming interconnected or isolated C-rich clusters, ∼5 nm, with a concentration of 9.8 ± 0.3 at.%C. Apart from the GB segregation, in M-WLs, large C-rich regions were found with 24.8 ± 0.4 at.%C. Owing to the chemical composition (stoichiometry) and element partitioning of such regions, they were assigned as θ-carbides (cementite). The APT results reveal that the original θ-carbides remain un-dissolved in the M-WLs, but might be plastically deformed due to the excessive strain that exists in hard machining process. The obtained results are in good agreement with the temperatures that are reached during formation of M-WLs. The isolated nano-sized C-clusters were assigned as off-stoichiometric carbides whereas the interconnected C-rich clusters were attributed to Cottrell atmospheres, evident by the linear shape of the C-enrichment as observed in the APT reconstructions. The C-contents in the nano-sized martensitic and ferritic grains were estimated to 0.50 ± 0.06 at.%C and ∼0.46 ± 0.02 at.%C, respectively. The C-content in the ferritic grains, beyond the C-solubility limit in ferrite (<0.1 at.%) is governed by the high dislocation density inside the grains, supported by the favorable binding energy between dislocations and C-atoms compared to C-atoms and Fe in carbides. No other evidence of redistribution of the substitutional alloying elements was observed. TEM analyses showed that T-WLs comprises of an equiaxed and nano-sized grains with well-defined cell boundaries, whereas the structure in the M-WLs comprised of elongated sub-grains formed via re-orientation of the original martensite followed by breakage/partitioning into elongated sub-grains.

The performance of powertrain components and rock tools relies on the inherent strength and hardness of ferrous martensite. Currently the industry uses experimental measurements of surface hardness and case depth to qualify their hardening processes. Often there are additional requirements on microstructure constituents, although there are no quantitative methods available to characterize ferrous martensite. Here such methodology is discussed in relation to EBSD measurements on the full practical range of Fe-C alloys. The orientation relationships between austenite and martensite along with the variant pairing tendency of martensite are determined from the EBSD data. These results are related to the well-known morphological transition from lath to plate martensite in Fe-C alloys. Quantitative metallography using EBSD has the potential to complement hardness- and residual-stress measurements when qualifying new steel grades and hardening processes in industry. It may also prove important when investigating the coupling between material properties and fatigue performance.

Press quenching is used to control distortion of large transmission components, e.g. case hardened crown wheels. The unsystematic distortion arises from non-uniformity in the steel properties and processing conditions and is a major concern for gear manufactures. In the present work a methodology is developed to analyze how various properties and parameters influence the distortion during press quenching of crown wheels. To obtain realistic quenching characteristics, to be used for simulation, a number of experiments are carried out on an industrial press quenching machine. In addition, the distortion potential from hardenability is surveyed on a set of non-press quenched crown wheels and quantified by 3D- scanning. Based on the experimentally obtained quenching characteristics the press quenching process is simulated by FEM. Impact of steel properties, quenching characteristics and processing conditions on the distortion is discussed and analyzed in relation to the experiments. From the results it may be concluded that press quenching is a powerful tool that can limit the impact of distortion carriers. However, to exploit the full capability of press quenching and thereby increase process optimization it is necessary to better quantify the distortion carriers in the parts to be hardened. Copyright © 2014 ASM International ® All rights reserved.

To establish the process window for the spray quenching step of the induction hardening process is essential for quality control and optimized use of the quenching capacity supplied by the quenching unit. In general, the process window is established by an empirical approach, where the processing is related to the mechanical properties. On the other hand, there has been a rapid development of computational tools that may facilitate and accelerate process optimization. In the present work it is demonstrated how such tools, e.g., FE-simulation and multivariate analysis, can be applied to couple quenching characteristics to mechanical properties. The methodology is applied to induction hardened steel cylinders that were quenched with different flow rates, temperatures and composition of the quenchant. The results show how mechanical properties can be related to characteristics of the quenching, e.g., heat transfer coefficients and characteristics of the cooling curve. Moreover, the work discusses and exemplifies how the process window can be established and how computational tools allow the user to virtually alter the processing and estimate the impact it may have on the mechanical properties.

Atmospheric case hardening of powertrain components may cause internal oxidation and thus reduce hardenability at the surface zone. This may affect the fatigue strength, which restricts the maximum cyclic load on steel components and hence is a major impediment for powertrain development and design. Here we have investigated the effect of furnace gas atmosphere composition and quenching path on fatigue properties of powertrain components. The results show that the detrimental effect of internal oxidation on fatigue may be compensated for by altering of the furnace atmosphere. Moreover, it is shown that the quenching path below the martensite start temperature also has an impact on the fatigue properties. These experiments were done in a full-scale industrial furnace on steel bars in 16MnCr5 and 20NiMo9-7F.

Atmospheric case hardening of powertrain components may cause internal oxidation and thus reduce hardenability at the surface zone. This may affect the fatigue strength, which restricts the maximum cyclic load on steel components and hence is a major impediment for powertrain development and design. Here we have investigated the effect of furnace gas atmosphere composition and quenching path on fatigue properties of powertrain components. The results show that the detrimental effect of internal oxidation on fatigue may be compensated for by altering of the furnace atmosphere. Moreover, it is shown that the quenching path below the martensite start temperature also has an impact on the fatigue properties. These experiments were done in a full-scale industrial furnace on steel bars in l6MnCr5 and 2ONiMo9-7F. 

Distortion is a major concern for industrial production of case-hardened steel-components. Carriers of distortion have been identified at all stages in the production chain. Often recognized is the effect of steel hardenability, which is defined as “susceptibility to hardening by rapid cooling”. Hardenability is often represented by Jominy- or Grossman numbers, which are determined by experimental testing or calculation. Hardenability is derived from the steel ability to delay diffusion-controlled phase transformations, i.e. being dependent on alloying content and austenite grain-size. Hence, it may be of interest to investigate effects of individual alloying elements on distortion. Here we make an attempt to investigate the effect of hardenability (and alloying content) of case-hardening steel-grade 16NiCrS4 on distortion of ring- and c-shaped steel-components. The steel components are machined from tubes of three 16NiCrS4 heats, being dissimilar in alloying content and hardenability. After stress relief annealing, the steel-components were measured using either 3D-scanner or coordinate measuring machine. Subsequently, they were hardened, without carburization, using oil, gas or salt as quenchant. The components were measured in their hardened state and their distortion determined. The results clearly show the effects of hardenability and quenching on distortion. Moreover, these results are discussed in relation to production follow-up in industrial heat-treatment workshops. It is realized that to effectively handle distortion originating from hardenability; material, processing and component design has to be associated.

Friction is an important parameter in sheet metal forming since it influences the flow of material in the process. Consequently, it is also an important parameter in the design process of new stamping dies when numerical simulations are utilized. Today, the most commonly used friction model in forming simulations is Coulomb’s friction which is a strong simplification of the tribological system conditions and a contributory cause of discrepancy between simulation and physical experiments. There are micromechanical models available but with an inherent complexity that results in limited transparency for users. The objective in this study was to design a phenomenological friction model with a natural level of complexity when Coulomb’s friction is inadequate. The local friction model considers implicit properties of tool and sheet surface topography, lubricant viscosity, sheet metal hardness and strain, and process parameters such as sliding speed and contact pressure. The model was calibrated in a Bending-Under-Tension test (BUT) and the performance was evaluated in a cross shaped geometry (X-die). The results show a significant improvement of the simulation precision and provide the user a transparent tribological system. © Published under licence by IOP Publishing Ltd.