Press hardening of alternative materials: conventional high- strength steels

he increase in strength of new high strength steels(HHS) and advanced high strength steels (AHHS) has led toforming issues, such as high springback, low formability, increase of forming forces and tool wear. These problems increase thecosts of manufacturing and maintainingstamping tools in the automotive industry. The aim of this research was to analyse the advantages of applyingthe press-hardening process toconventional HSS and AHSS steel to increase their formability and therefore reduce thenumber of forming steps and productioncosts. With this aimin mind, the press-hardening process was used to manufacturean industrialcomponent using four different automotive steelgrades: dual phase (DP),complex phase (CP), transformation-induced plasticity (TRIP) and martensitic (MS) grade.Springback measurements werecarried out, together with ananalysis of the obtained final mechanical properties and microstructures. The results showed that the formability of all thematerials increased. The mechanical properties of theCP800and TRIP700 materials were maintained or even improved, whereas those of the MS1200 and HCT980Xmaterials were significantly reduced. Weconclude thatpress hardening is a suitable manufacturing processforCP800 and TRIP700components

Effect of Weld Schedule on the Residual Stress Distribution of Boron Steel Spot Welds

Press-hardened boron steel has been utilized in anti-intrusion systems in automobiles, providing high strength and weight-saving potential through gage reduction. Boron steel spot welds exhibit a soft heat-affected zone which is surrounded by a hard nugget and outlying base material. This soft zone reduces the strength of the weld and makes it susceptible to failure. Additionally, different welding regimes lead to significantly different hardness distributions, making failure prediction difficult. Boron steel sheets, welded with fixed and adaptive schedules, were characterized. These are the first experimentally determined residual stress distributions for boron steel resistance spot welds which have been reported. Residual strains were measured using neutron diffraction, and the hardness distributions were measured on the same welds. Additionally, similar measurements were performed on spot welded DP600 steel as a reference material. A correspondence between residual stress and hardness profiles was observed for all welds. A significant difference in material properties was observed between the fixed schedule and adaptively welded boron steel samples, which could potentially lead to a difference in failure loads between the two boron steel welds

Constitutive behavior of magnesium alloy sheet at high strain rates

In an effort to improve the fuel efficiency of automobiles, car designers are investigating new materials to reduce the overall automobile weight. Magnesium alloys are good candidates to achieve that weight reduction due, in part to their low density. As part of a project on the interaction between forming and crashworthiness, constitutive parameters of AZ31B sheets were determined in order to support finite element analysis of the material response throughout the forming process and in crash structures. Stress-strain data was collected at 0.003s−1, 100s−1 and 1000s−1 in both the rolling and transverse directions. The intermediate strain-rate response was collected with an instrumented falling weight impact test for a rate of 100s−1, while 1000s−1 tests were performed with a tensile split Hopkinson bar. The Johnson-Cook model was successfully fit to the experimental data which showed significant strain rate dependence in both directions

High strain rate characterization of ZEK100 magnesium rolled alloy sheet

In this paper, the constitutive behaviour of a rare-earth magnesium alloy ZEK100 sheet is studied at room temperature and over a wide range of strain rates. The tensile data from 1.6 mm thick ZEK100 sheets at quasi-static and high strain rate conditions show strong in-plane anisotropy of tensile properties, such as yield and ultimate strengths, failure strain and work hardening rates. The results also show a decrease in strength and increase in ductility as the orientation changes from the rolling to the transverse direction. The work hardening behaviour is shown to be much stronger in the transverse direction when compared to the rolling and 45∘ directions. The change in stress with respect to strain rate also varied strongly with orientation. The cause of the in-plane anisotropy and strain rate dependence of tensile properties is attributed to the as-rolled crystallographic textures and the active deformation mechanisms

Prediction of Necking in Tubular Hydroforming Using an Extended Stress-Based Forming Limit Curve

NRC publication: Ye