Project details

AuthorG.J. Watts- D.C.J. Farrugia- B. Cheong- Z. Husain- M. Zhou I. Gutierrez- D. J. Badiola- J. H. Bianchi- P. Vescovo O. Wiklund- M. Karlberg- M. Schmidtchen- R- Kawalla L. P. Karjalainen- M. C. Somani

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2. 1 Objectives

The objectives as extracted from the Technical Annexe (included in Appendix 8) are, in brief:-

  1. To investigate the constitutive behaviour of steels during complex loading paths

    (a) by laboratory test simulation

    (b) by laboratory hot rolling trials

  2. To identify the mechanisms responsible for the constitutive behaviour.

  3. To formulate constitutive models, including these mechanisms, for predicting flow stress, microstructural evolution, etc.

  4. To incorporate the constitutive models into FE models of rolling and validate using full scale hot rolling.

2. 2 Activities

Outlining in more detail the activities associated with the above objectives, the project investigates the effect of loading path for hot rolling processes of commercial interest to the partners and within a given remit (avoiding processes of very high complexity) viz. the rolling of bar, rod and plate. A wide range of steel qualities of commercial interest to the partners are studied viz. austenitic, ferritic and duplex, with fast and slow recrystallisation kinetics, transforming and non-transforming and in both cast and wrought conditions. It was also planned, however, that all partners should study similar steels viz. CMnNb and stainless steel.

The complex loading paths considered, as stated at the outset are strain reversal and those related to the interpass behaviour i.e. a change in stock orientation in the three principal planes and reverse deformation in tension/compression and torsion. Accordingly standard experimental testing facilities are employed viz. hot torsion and Gleeble machines and also laboratory rolling mills.

The effect of various loading paths on operating parameters and microstructural evolution are assessed experimentally, the microstructural aspects of main interest being grain size, fraction recrystallised and dislocation density. Material characterisation is carried out using both direct and mechanical methods as indicated in Section 2.3 viz. optical metallography, electron microscopy, stress relaxation and double hit techniques.

In order to understand the effect of loading on structural evolution, constitutive models are formulated and validated using experimental data and applied to laboratory and industrial hot rolling processes.

2. 3 Partner resources and interactions

A breakdown of the project activities and the linkage with the technical resources and areas of expertise of the partners is given in Table 1 and shown diagrammatically in the tree diagram (Fig. 1) constructed using 'Mind Map' software 26. From scrutiny of this figure, and using network analysis etc. the commonalities of interests, requirements andPage 16availabilities or otherwise of facilities to meet these requirements can be seen and are the drivers for the partner interactions. This information has been extracted and presented in Table 2. The distribution of these amongst the partners is indicated in a matrix Table 3 and summarised below.

(a) Materials; A range have been used:- Armco Iron and several steel qualities viz. low and medium C, CMnS, CMnNb, CMnNb hiTi, CCrV IFNb. IFNb Ti, stainless steels (Type 316 and duplex). Of these CMnNb, medium C and stainless steel (duplex) are of widespread interest to the partners, in either experimental or theoretical simulations and have been chosen as benchmark materials.

(b) Experimental Testing Facilities: All partners have access to experimental testing facilities, e.g. compression machines at the University of Oulu and Corus, torsion machines at CEIT and TU Freiberg and laboratory rolling mills at TU Freiberg, CSM and Corus.

(c) Pilot/Industrial Rolling Mills accessible/owned by CSM and Corus.

(d) Metallurgical facilities: all partners employ metallographic or optical microscopic techniques for characterisation of structures.

(e) Mathematical Models: All partners have developed or have access to physical, phenomenological or empirical models for describing both forming processes and experimental data. Since they also have a common interest in recrystallisation, either static or dynamic, this phenomenon is covered in all models. Other phenomena are represented in some of the models e.g. recovery, dislocation dynamics,hardening, vacancy generation etc.

(f) Finite Element Software: Most of the partners are using FE packages (e.g. ABAQUS or LS Dyna) for incorporation and implementation of the above models.

Partners have collaborated in providing particular resources where these are needed or in sharing information where there is a common interest.

Discussion has also taken place between the partners on how to present their activities in a common framework. It was agreed that this framework should indicate the experiments or models used for various steel qualities and the range of temperatures, strains and strain- rates employed. It would thus indicate where comparisons may reasonably be made between (a) model predictions/experimental results and (b) steel properties. Equally it would show where further data were required to complete the assessment.

Details have been compiled from communications with partners and from the contents of previous technical reports and are shown in Table 4(a-f).

Key information giving an overall picture of the work carried out by the partners has been extracted from these tables and has been input to a template designed at the University of Oulu. This completed template is included in Appendix 7.

The progress in this period made by each of the six partners towards achieving the above objectives together with plans for further work is summarised in the section below and described in detail in Appendices 1 to 6.

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2. 4 Structure of project

In accordance with the objectives stated in the Technical Annexe and as described therein, the project is structured into tasks or work packages carried out by subsets of the partnership and further divided into subtasks as indicated below:

WP1: Evaluation of Constitutive Models (Corus, MEFOS, CSM; CEIT, the University of Oulu, Freiberg)

WP2: Experimental Investigation of Constitutive Behaviour (the University of Oulu, CEIT; Freiberg)

(i) Strain Rate and Temperature Changes (the University of Oulu)

(ii) Strain Reversal in Tension/Compression (the University of Oulu, Corus, CEIT)

(iii) Strain Reversal in Torsion (CEIT)

(iv) Multi-directional Strain Tests (Corus UK)

(v) Ferritic Tests (the University of Oulu)

(vi) Stock Rotation during Rolling (Corus, Freiberg)

(vii) High Speed Rolling (Freiberg; Corus)

Note: The original list of subheadings has been rationalised by the combination of topics 2.2.6, 2.2.7 in the Technical Annexe as subtask (vi) since they both relate to stock rotation during the interpass and, in practice, involve the same partners.

WP3: Material Characterisation (CEIT, the University of Oulu; Corus)

WP4: Formulation of Constitutive Laws (Freiberg, MEFOS, CSM, Corus; CEIT, the University of Oulu,)

WP5: Incorporation of Constitutive Laws into FE Models of Rolling (MEFOS, CSM; Freiberg, Corus)

WP6: Model Validation (CSM; MEFOS, Corus, TU Freiberg)


[26] Visual Mind 5.01 (demo version), Norcan, copyright 1998-2003.

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