The transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are introduced. The metastable austenitic stainless and multiphase TRIP-assisted steels, as well as the more recent third generation AHSS grades, namely the medium-Mn and quenching and partitioning (Q&P) steels, are critically discussed. These steels utilize the TRIP effect and the enhanced work-hardening rate through the transformation of (retained) austenite in their microstructures to martensite during plastic deformation for the improvement of strength-ductility balance, which make them especially suitable for the automotive industry to be used in the lightweight car body for addressing the safety, fuel consumption, and air pollution issues. The kinetics of strain-induced martensitic transformation (SIMT) as well as the effects of chemical composition, grain size, deformation temperature, strain rate, and deformation mode on the austenite stability are reviewed. The effects of holding temperature and time during the isothermal bainitic transformation (IBT) in TRIP-aided steels, during the austenite-reverted-transformation (ART) annealing in medium-Mn steels, and during the quenching and partitioning steps in the Q&P steels are critically discussed towards enhancement of the amount of retained austenite and optimization of strength-ductility trade off. The alternative thermomechanical processing routes as well as the modified grades such as δ-TRIP and quenching-partitioning-tempering steels are also introduced.

Transformation-induced plasticity (TRIP) in advanced steels: A review

A plane stress yield function for anisotropic sheet material by interpolation of biaxial stress states

Deformation mechanisms of Mo alloyed FeCoCrNi high entropy alloy: In situ neutron diffraction

Two new yield functions for orthotropic sheet metals are proposed. The first one, called Yld2011-18p, provides 18 parameters that may be calibrated to experimental data. The second one, called Yld2011-27p, is a straightforward extension and provides 27 parameters. Both yield functions are unconditionally convex. Their formulations are based on the established concept of multiple linear transformations of the stress deviator. Furthermore, they are able to account for planar as well as for three-dimensional stress states. The proposed yield functions are applied to describe complex plastic anisotropies of different alloys. The ability of accurately predicting earing in cup-drawing is demonstrated by means of a non-linear finite element analysis.

New convex yield functions for orthotropic metal plasticity

Numerical analysis of diffuse and localized necking in orthotropic sheet metals

Metastable austenite driven work-hardening behaviour in a TRIP-assisted dual phase steel

The application of simulation models in sheet metal forming in automotive industry has proven to be beneficial to reduce tool costs in the designing stage and for optimising current processes. Moreover, it is a promising tool for a material supplier to optimise material choice and development for both its final application and its forming capacity. The present practice requires a high predictive value of these simulations. The material models in these simulation models need to be developed sufficiently to meet the requirement of the predictions. For the determination of parameters for the material models, mechanical tests at different strain paths are necessary 1. Usually, the material models implemented in the simulation models are not able to describe the plastic material behaviour during monotonic strain paths sufficiently accurate 2. This is true for the strain hardening model, the influence of strain rate and the description of the yield locus in these models. A first stage is to implement the improved material models which describe this single strain path behaviour in a better way. In this work, different yield criteria, a hardening model and their comparison to experiments are described extensively. The improved material model has been validated initially on forming limit curves which are determined experimentally with Nakazima strips. These results will be compared with predictions using Marciniak-Kuczinsky-analysis with both the new material model and the conventional material model. Finally, the validation on real pressed products will be shown by comparing simulation results using different material models with the experimental data. The next challenge is the description of the material after a change of strain path. Experimental evidence given here shows that this behaviour cannot be treated using the classical approach of an equivalent strain as the only history variable.

http://core.ac.uk/download/pdf/11463140.pdf

Characterisation and modelling of the plastic material behaviour and its application in sheet metal forming simulation

Robust processes and robust engineering are enjoying increasing interest throughout industry. Robust engineering is taking into account variations that can occur during manufacturing processes when we analyse or optimise them. Corus is interested in robust engineering, being a supplier of steel not just for its own processes but also for supporting customers. Robust engineering, if properly applied to e.g. the stamping process, ensures that the customer’s forming process is stable and insensitive to material and process variations, thus reducing scrap rates. To analyse a stamping process for robustness input in terms of variation in process and material properties is needed. As a material supplier we focus on the variation in material properties. This paper deals with the effect of the material models used in simulation on the prediction of process variations as well as scrap rate. The effect of models on the variation itself is small, however, the effect on the average (and hence on e.g. scrap rate) is significant. Some examples of the capabilities of commercial software are also added.

Towards robust simulations in sheet metal forming

Finite element analysis of forward/backward extrusion using ALE techniques

In literature the influence of curvature on formability has been reported. This
paper shows results for four materials when an FLC is measured with increasing curvature. It shows the FLC increases for sharper curvature most notably with 20 [mm] tool diameter. The increase is negligible on the left hand side, moderate on the right hand side and large on the plane strain axis. It is thought that contact pressure plays a role here and preliminary simulations indicate that this is quite possible.

E.H. Atzema

Papers

Metastable austenite driven work-hardening behaviour in a TRIP-assisted dual phase steel

Characterisation and modelling of the plastic material behaviour and its application in sheet metal forming simulation

Towards robust simulations in sheet metal forming

Finite element analysis of forward/backward extrusion using ALE techniques

The influence of curvature on FLC’s of mild steel, (A)HSS and aluminium