Projektmenu

Introduction

The prevention of surface damage is an important aspect during the production process of continuous cast slabs, since the deletion of these defects is associated with high costs. An economical production of high quality products therefore requires an optimal production process. This will require better knowledge of mechanisms that lead to crack initiation. In this part of the project, various factors influencing the high temperature ductility behaviour will be tested on different steel samples.

Objectives and Motivation

  • Hot tearing in casting and solidification processes
  • Laboratory investigations and numerical simulation for the influence of process parameters on crack formation

Methodology

Within experimental simulation of surface crack formation in continuous casting the solidification and the thermal history of a sample is adjusted. Surface and subsurface defects and their influence on the ductility will also be considered. Samples will be investigated by light microscopy, electron microscopy and by TEM and atom probe. The experiments will be simulated in calculation tools and finally implemented into level 2 automation.

To learn more about crack formation mechanisms during continuous casting and subsequent hot rolling, the microstructure evolution will be described by optical light microscopy and SEM. Studies related to precipitation size and distribution will be carried out at transmission electron microscopy facilities. For simulations of the thermo-kinetic processes occurring in the material during testing, different software tools will be applied.

Filler materials and weld materials will be characterized by means of DSC measurement and solidification experiments. In parallel, the alloys will be characterized by thermodynamic databases and by tools for phase transformation kinetics. The results will be used to interpret the results from hot cracking experiments and to build up a new time and cost saving “hot cracking tendency” prediction system. This system will finally be used to optimize existing alloying concepts for filler materials and to develop new alloy systems with improved hot cracking performance.

Results and application

The focus of this investigation is laid on the analysis and description of different kinds of precipitates and their cross-correlation to the mechanism and characteristic of the ductility loss in the second ductility minimum. A methodology will be sought for a qualitative prediction of ductility curve based on simulation results. Therefore, chemical composition, heat treatment and microstructure aspects will be taken into account.

Regarding the crack formation mechanisms, the main target of the investigation is to identify the key parameters leading to surface- and surface near cracks during the production processes continuous casting and hot rolling. A methodology will be sought for testing the crack sensitivity by thermo-mechanical treatment of laboratory specimens.

The expected result is a better understanding of the crack formation mechanisms, including the impact of the microstructure and the process parameters.  Furthermore, the industrial processes of continuous casting and hot-rolling are going to be simulated at laboratory scale.

A time saving and cost saving “hot cracking tendency” prediction system/model for adjustment of filler on welding materials will be developed. This system will provide the strategic direction for changes in filler and weld material composition with aim on improved hot cracking Performance.