Deakin Research

Institute for Frontier Materials

Steel

Introduction

As in any university situation the nature of the research program reflects a combination of the interests of the staff as well as the availability of students and research funding. The following outlines areas of current activity but these could be easily broadened depending on the industry interests.

Advanced High Strength Steels for the Automotive Industry

This is a very broad research program that considers both the steel industry as well as the automotive industry aspects. Current topics include:

  • Formability of dual phase, TRIP and other steels, including the fracture behaviour, FLD construction, finite element modeling of the forming strains and springback and advanced microstructure-fea models examining strain partitioning.
  • Fatigue behaviour of TRIP and DP steels using our strain controlled 30Hz fatigue tester that can do both tension and compression cycles. This has included examining the effect of prestrain and an understanding of the evolution of the dislocation substructure.
  • Crash Behaviour of AHSS. This work has led to the development of improved models to represent the constitutive behaviour of a wide range of steels under crash conditions. We will be extending this work later this year when the 25m/s tensile frame is commissioned. The objective is to develop a microstructure based constitutive model.
  • Bake Hardening of AHSS. The bake hardening response of these steels is very variable and we have been looking at why this is the case for TRIP and DP steels. By using atom probe tomography (APT) we have been able to link the level of solute C in the ferrite and the nature of the dislocation structure to the bake hardening response.
  • Thermomechanically produced TRIP steels. This is an ongoing project to understand the microstructure evolution and the alloy partitioning and TRIP effect. Again we have recently used APT to examine the details of alloy partitioning.

Some key papers:

Ultrafine Grained and Nanostructured Steels

Our work on the ultrafine grained steels through strain induced transformation is widely known. We still maintain a small program on this, largely in collaboration with NIMS in Japan. Our real focus at present is to understand the fundamentals better and in particular the deformation structure evolution in the austenite prior to or during the transformation. We are considering a range of in-situ techniques for this at present. We have also a program related to the new nanostructured bainities developed by Bhadeshia and co-workers. We have produced a range of structures and are considering their dynamic properties as well as undertaking detailed microstructural characterization including APT. Another project is considering the strength ductility balance of ultrafine structured steels produced by a range of methods. This is linked to a more general program on nanostructured metals.

Some key papers:

Deformation, Precipitation and Recrystallisation during hot working

We have had a number of projects examining the deformation and dynamic and post deformation softening behaviour of steels. This has largely involved advanced use of our EBSD equipment to identify the key features of the microstructure evolution. We have also examined a range of model alloys and recently commenced new work related to strain induced precipitation in Nb microalloyed steels, particularly under multi-pass and strip mill conditions - areas that have not received much attention to date. We are also interested in the potential loss of Nb for latter precipitation strengthening in the production of thick plate.

Some key papers:

Texture Development

Most of this work has previously been related to warm rolling. However, with our new thrust into strip casting this research will consider a much broader range of conditions and microstructures.

Some key papers:

Precipitation Hardening Fundamentals

We have recently commenced a program to re-evaluate precipitation hardening in HSLA steels. This has been driven by the recent work of JFE where they have produced a low C 780MPa grade and appear to also have 980 grade. This is said to be through the control of the precipitate size and spacing and some limited APT work by our group has confirmed much of this although it appears other factors are also involved. In this new study we will more closely consider the interaction between phase transformation and precipitation for different alloy systems.

Key paper:

Phase Transformations

This is largely linked to the TMCP of AHSS and will in the future focus on the potential to develop advanced steels through the strip casting or other near net shaped casting and TMCP routes. We are extending the TMCP TRIP steel work to consider other much higher strength microstructures. Also once we have the ability to make our own melts we will be pursuing other ideas related to standard TRIP compositions. Another thrust for this year will be TWIP steels and in particular designing the compositions for the balance between forming and crash conditions. We would also be interested in pursuing research related to the transformation of more basic TMCP plate and strip steels and using new modeling techniques combined with our excellent experimental capabilities.

Strain Ageing

Besides the work on bake hardening of AHSS we are also continuing work related to strain ageing under wire drawing conditions. This includes developing a kinetic model as a function of the deformation conditions, composition, temperature etc. We will also examine the various stages of ageing using APT.

Roll Forming

This is a new program that is about to commence in late 2008. It will involve developing improved models in conjunction with COPRA a software supplier and a range of industry partners. The steels to be considered range from simple C steels in the soft or recovery annealed condition, through to stainless steels. There is also some interest in considering advanced steels and shapes for the automotive industry

Furnaces, Cooling

Our current focus in this area is in the development of new fluid bed diffusion coatings that permit hard surface layers to be created on the final steel product at low temperatures. The lower the treatment temperature the less frequent are problems associated with distortion. We have developed mathematical and physical models of the process and are using these to support our commercialization effort sin this area.

Computer Modelling

Our group has undertaken a wide range of projects for the automotive and steel industries involving advanced modeling concepts and in particular the incorporation of metallurgical phenomena into these models. These have included:

  • Computational fluid dynamics modeling of fluid bed reactors for heat treatments which are now being extended to model the metallurgical reactions in the parts
  • Finite element modeling of sheet metal forming
  • Cellular automata modeling of dynamic, metadynamic and static recrystallisation
  • Multiscale modeling using cellular automata for shear band initiation and propagation
  • Phase field modeling of phase transformations
  • Atomistic modeling of the deformation of metallic glasses
  • Thermodynamic modeling of various alloy systems
  • Finite element modeling of wear and galling in the sheet metal forming of AHSS
  • Stochastic modeling of stamping for more robust tool designs
  • Modelling of iron castings for porosity elimination
  • Multiscale modeling of ultrafine and nanostructured metals
  • Multiscale modeling of AHSS for improved constitutive modeling

Deakin University acknowledges the traditional land owners of present campus sites.

27th January 2012